Efficient adsorption separation method of impurities in borane preparation process

Abstract

The application discloses a kind of efficient adsorption separation method of impurities in borane preparation process, belong to gas separation technical field.The method includes: after ZIF-8 powder is vacuum dried, with 3-aminopropyl triethoxysilane in anhydrous toluene at 80 ℃ reflux reaction 12-24 hours, after washing, dry and obtain amido functionalization NH2-ZIF-8 composite adsorbent;It is filled in vertical fixed bed adsorption tower, and under-30 ℃-20 ℃, 0.3-0.8MPa, the crude ethyl borane gas containing boron trifluoride is imported and is adsorbed at low temperature;After adsorption saturation, regenerate by 80 ℃ heating and vacuum extraction.The grafting amount of amido on the surface of NH2-ZIF-8 obtained by the method is 2.0-3.5mmol / g, specific high selectivity adsorption of BF3 is realized, sufficient adsorption sites are provided, and the adsorbent has strong regeneration performance.

Description

Technical Field

[0001] This invention belongs to the field of gas separation technology, and particularly relates to a highly efficient adsorption and separation method for impurities in the preparation process of borane. Background Technology

[0002] Diborane (B₂H₆, CAS No.: 19287-45-7) is mainly used in the electronics industry as a gaseous impurity source, ion implantation, and dopant for boron doping oxidation diffusion. It is widely used in semiconductor integrated circuits, liquid crystal displays, semiconductor light-emitting devices, and solar cells. The gases used in chip manufacturing processes often require a purity level of 5N or higher, and metallic impurities need to be purified to 10N. -9 Level 10 -12 The key to obtaining high-purity diborane (gaseous at room temperature) lies in solving the problem of removing gaseous impurities and metal elements that have similar boiling points and sizes to diborane.

[0003] In the field of gas separation and purification, adsorption separation is a common technique for removing impurities from gases. For example, Chinese utility model patent CN222196424U discloses a diborane impurity adsorption tower. This tower uses two symmetrically arranged air inlets on the tower body, combined with a flow divider valve to distribute the two air inlets, thus achieving a seamless and rapid replacement of the liquid adsorbent without affecting the operation of the adsorption tower. This avoids the problem of existing technologies requiring the closure of the adsorption tower valve and disassembly of the adsorbent for replacement, which leads to a significant decrease in adsorption efficiency. This technology mainly improves the adsorbent replacement method from the structural level of the adsorption tower equipment. However, this adsorption tower still uses a traditional liquid adsorbent, which has limited selective adsorption capacity for specific impurities in diborane (such as boron trifluoride BF3, CAS No.: 7637-07-2), making it difficult to meet the stringent requirements for trace impurity removal in electronic-grade diborane. Furthermore, this technology only focuses on structural improvements to the adsorption tower and does not address the performance improvement of the adsorbent material itself, nor does it fully consider the irreversible decomposition of diborane that may occur during the adsorption process.

[0004] In research related to the adsorption and separation technology of diborane, several patented technologies involving molecular sieve adsorbents have emerged. For example, Chinese invention patent application number CN202310679973.X discloses a device and method for removing high borate compounds from diborane. The device includes a packed tower body, in which several zeolite molecular sieves are arranged as adsorbents, and an insulation sleeve is installed on the outside of the tower body. This technology uses zeolite molecular sieves to adsorb and remove high borate impurities from diborane, and a driving mechanism moves the mounting frame upwards and out of the tower body, facilitating the replacement of zeolite molecular sieves by operators. However, zeolite molecular sieves, as microporous materials, have the following inherent defects: First, they have low adsorption selectivity for diborane, making it difficult to effectively remove impurities with similar polarity (such as boron trifluoride), and the adsorption capacity of zeolite molecular sieves for diborane is limited; Second, diborane may undergo irreversible decomposition reactions on the surface of zeolite molecular sieves, leading to adsorbent deactivation and product contamination; Third, the diffusion resistance of zeolite molecular sieve pores is relatively large, and the diffusion rate of diborane molecules is limited under low-temperature operating conditions, affecting the adsorption kinetics performance.

[0005] Chinese utility model patent CN219149684U discloses a diborane drying device. This device utilizes an adsorption mechanism between a drying chamber and an adsorption chamber, employing activated carbon to adsorb residual diborane gas within the drying chamber and conveying pipeline. The desiccant is replaced only after the diborane gas has been adsorbed by the activated carbon, preventing leakage and potential harm to human health. The adsorbed activated carbon is then collected in a collection box for centralized treatment. Its core innovation lies in using activated carbon as a safety precaution to adsorb residual diborane gas inside the equipment, thus preventing leakage accidents. However, this technical solution has the following significant shortcomings: First, activated carbon, as a non-selective adsorbent material, has extremely low adsorption and differentiation capabilities for diborane and impurity gases (such as boron trifluoride BF3). Its pore size distribution is wide (20–1000 Å), and the adsorption of different gas molecules mainly relies on physical pore retention rather than chemical specificity. Therefore, it cannot achieve selective and deep removal of trace impurities with similar polarities in diborane, making it difficult to meet the stringent requirements for trace impurity removal in electronic-grade diborane (purity ≥99.995%). Second, the surface of activated carbon contains abundant oxygen-containing functional groups (such as carboxyl groups, phenolic hydroxyl groups, lactone groups, etc.) and metallic impurities. These active sites may catalyze the disproportionation decomposition reaction of diborane, generating high-borane (B4H) 10The presence of pollutants such as B5H9 and hydrogen not only causes the adsorbent to gradually deactivate but also pollutes the product gas, directly affecting the final purity of diborane. Thirdly, this technology uses activated carbon only as a single-use safe adsorption medium; after adsorption saturation, the activated carbon is directly sent to a collection box for unified treatment without any regeneration or recycling process. This results in high adsorbent usage costs, and frequent adsorbent replacement affects the continuous operation efficiency of the device, making it difficult to meet the requirements of large-scale continuous industrial production for long adsorbent lifespans.

[0006] In summary, while existing diborane adsorption and separation technologies have achieved some degree of removal of impurities from diborane, the widely used traditional porous adsorption materials such as zeolite molecular sieves and activated carbon share the following shortcomings: First, they exhibit low adsorption selectivity for diborane, making it difficult to effectively remove impurities with similar polarity, such as boron trifluoride (BF3). Zeolite molecular sieves also have limited adsorption capacity for diborane and poor regeneration performance. Second, diborane may undergo irreversible decomposition on traditional adsorbents, leading to adsorbent deactivation and product contamination. Third, as microporous materials, zeolite molecular sieves have significant diffusion resistance, limiting the diffusion rate of diborane molecules under low-temperature operating conditions and affecting adsorption kinetics. Fourth, although existing adsorption tower structures and adsorbent replacement methods have been improved, enhancing the performance of the adsorbent material itself remains a key bottleneck restricting the purification effect of diborane. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the defects of existing diborane adsorption and separation technology, such as low selectivity of adsorbent for diborane, easy irreversible decomposition of diborane, limited adsorption capacity and poor regeneration performance, and to provide a highly efficient adsorption and separation method for diborane dry process.

[0008] The specific plan is as follows: A highly efficient adsorption and separation method for impurities in a borane preparation process includes the following steps: S1. Introduce amine and / or thiol functional groups into the ZIF-8 framework to prepare a composite adsorbent; S2, Composite adsorbent packed adsorption tower; S3. The crude borane product gas containing corrosive impurities such as BF3 is passed into the packed adsorption tower for low-temperature adsorption treatment.

[0009] Furthermore, step S1 specifically includes: S1-1, Powder of metal-organic framework material ZIF-8 is used as the ZIF-8 framework and dried; S1-2. The dried ZIF-8 powder undergoes a condensation reaction with KH-550, and 3-aminopropyl (—CH2CH2CH2NH2) is grafted onto the surface of ZIF-8. S1-3. Filter and wash the reaction products to remove unreacted KH-550; S1-4. Vacuum dry the washed product.

[0010] Furthermore, step S1 specifically includes: S1-1. Place ZIF-8 powder in a vacuum drying oven and dry it at 120°C for 12 hours to remove adsorbed water and solvent molecules from the pores. S1-2. Mix the dried ZIF-8 powder with KH-550 at a mass ratio of 1:0.15 to 0.30, add anhydrous toluene as a dispersant, and the mass-volume ratio of ZIF-8 powder to anhydrous toluene is 1g:15 to 25mL. Under nitrogen protection, reflux at 80°C for 12 to 24 hours. S1-3. After the reaction is complete, filter and collect the solid product. Wash it three times each with anhydrous ethanol and deionized water to remove unreacted KH-550. S1-4. Place the washed product in a vacuum drying oven and dry it under vacuum at 60°C for 8 hours to obtain the amino-functionalized ZIF-8 composite material.

[0011] Further, in step S1-1, the particle size of ZIF-8 powder is 200-500 nm and the specific surface area is ≥1500 m² / g; after vacuum drying in step S1-4, a composite adsorbent with an amine (NH2-) grafting amount of 2.0-3.5 mmol / g is obtained.

[0012] Furthermore, the adsorption tower in step S2 is a vertical fixed-bed adsorption tower, with multiple layers of supporting sieve plates inside the adsorption tower, and the composite adsorbent is layered and filled between each layer of sieve plates; a vacuum insulation jacket is installed outside the adsorption tower, and the jacket is filled with aerogel insulation material; a gas inlet distributor is installed at the top of the adsorption tower. The adsorption tower is made of 316L stainless steel, with an inner diameter of 150mm and a height of 2000mm. The adsorption tower is equipped with three layers of supporting sieve plates with a sieve aperture of 0.3mm and a spacing of 600mm between adjacent sieve plates. The composite adsorbent is filled to a height of 500mm per layer, with a total filling height of 1500mm. The aerogel insulation material is 50mm thick, and the distributor adopts a ring-shaped porous structure with a pore size of 1mm.

[0013] Furthermore, before step S1-1, there is a step of increasing the hydroxyl content on the ZIF-8 surface through pretreatment, which is at least one of low-temperature oxygen plasma treatment or acid gas etching treatment.

[0014] Further, step S3 specifically includes: passing the crude product gas generated by the dry process of diborane containing boron trifluoride (BF3) into a packed adsorption tower for low-temperature adsorption treatment. The operating conditions are as follows: 1) Adsorption temperature: -30℃ to -20℃, temperature controlled by a low-temperature refrigerant (liquid nitrogen vapor) circulating in the jacket of the adsorption tower. The refrigerant inlet temperature is -40℃ and the outlet temperature is -30℃; 2) Adsorption pressure: 0.3 to 0.8 MPa (gauge pressure); 3) Gas space velocity: 50 to 200 h⁻¹ -1 ;4) Adsorption cycle: 24 to 72 hours.

[0015] Furthermore, it also includes step S4, the regeneration of the adsorbent, specifically including: S4-1. When the concentration of boron trifluoride in the gas at the outlet of the adsorption tower exceeds the set threshold, stop the gas intake and perform adsorbent regeneration. S4-2, Nitrogen purging: High-purity nitrogen is introduced to replace the residual diborane gas in the adsorption tower; S4-3, Desorption by heating: Turn off the nitrogen gas, turn on the heating device of the jacket of the adsorption tower, slowly raise the temperature of the adsorption tower and keep it at the temperature for a period of time, so that the adsorbed boron trifluoride is desorbed from the surface of the composite adsorbent. S4-4, Vacuum extraction: While heating, turn on the vacuum pump connected to the bottom of the adsorption tower to extract the desorbed boron trifluoride gas. S4-5 Cooling: After regeneration, turn off the heating device and purge the adsorption tower with high-purity nitrogen until the temperature inside the tower drops to the adsorption operating temperature. S4-6, Regeneration tail gas treatment: The desorbed boron trifluoride tail gas is treated by an alkaline absorption tower before being discharged.

[0016] Further, in step S4-1, the threshold value for boron trifluoride concentration is set to ≤10 ppmv; in step S4-2, high-purity nitrogen gas with a purity ≥99.999% is introduced at a flow rate of 50–100 L / min for 30 minutes; in step S4-3, the adsorption tower temperature is slowly raised to 80°C and maintained at a constant temperature for 2 hours; in step S4-4, the vacuum pump connected to the bottom of the adsorption tower is turned on, with a vacuum degree ≤100 Pa and an extraction time of 2 hours; in step S4-5, the adsorption operation temperature is -25°C, and the cooling rate is controlled at 2–5°C / min; in step S4-6, the alkali solution is a 10 wt% sodium hydroxide solution.

[0017] Furthermore, the ZIF-8 framework simultaneously incorporates amino and mercapto groups, which are embedded in the framework by using 2-aminoimidazole, 2-mercaptoimidazole, and 2-methylimidazole as mixed ligands, and co-grown with a zinc source in a one-step solvothermal process.

[0018] Compared with the prior art, the present invention has at least one of the following technical effects: 1) This invention employs an amino-functionalized ZIF-8 composite adsorbent (NH2-ZIF-8), whose surface is grafted with a large number of amino (-NH2) functional groups. BF3, as a strong Lewis acid, exhibits a strong Lewis acid-base interaction with the amino groups, thereby achieving specific and highly selective adsorption of BF3 (the adsorption selectivity (BF3 / B2H6 adsorption ratio) in Example 1 is 18.5, significantly higher than the comparative example). Simultaneously, ZIF-8 itself possesses a high specific surface area (≥1500 m² / g) and a hierarchical porous structure, providing ample adsorption sites (the dynamic adsorption capacity in Example 1 reaches 1.85 mmol / g, significantly higher than the comparative example). The regular pore structure of the amino-functionalized ZIF-8 facilitates rapid diffusion and desorption of BF3, and the covalently bonded amino groups on the surface remain stable and do not detach under regeneration conditions at 80℃. This also avoids the problem of pore blockage caused by the catalytic decomposition products of diborane on the surface of zeolite molecular sieves. After 10 cycles, the adsorption capacity retention rate is high, thus its regeneration performance is stronger than that of 13X molecular sieves.

[0019] 2) This invention uses ZIF-8 as the main matrix. Its regular pore structure and mild surface chemical environment avoid the presence of strong acid or strong base sites, and will not catalyze the disproportionation decomposition of diborane (the decomposition rate in Example 1 was only 0.08%, significantly lower than that in Comparative Example 1). Furthermore, the decomposition products (B4H...) 10 (High-boranes such as B5H9) are almost undetectable. After amino functionalization, NH2-ZIF-8 still maintains the skeletal stability of ZIF-8.

[0020] 3) This invention employs a hierarchical porous structure of ZIF-8 (coexistence of mesoporous and microporous particles), with a particle size controlled between 200 and 500 nm, shortening the diffusion path of gas molecules within the pores. Simultaneously, this invention controls the adsorption temperature between -30°C and -20°C, in conjunction with a gas inlet distributor (a ring-shaped porous structure with a pore size of 1 mm) and a suitable space velocity (50–200 h⁻¹). -1 This ensures effective contact between BF3 and the amino group site while avoiding premature penetration due to diffusion limitation. Example 1: 100 h -1 At the specified space velocity, the dynamic adsorption capacity of BF3 in NH2-ZIF-8 can still reach 1.85 mmol / g, demonstrating its good adsorption kinetics performance.

[0021] 4) This invention employs a mild regeneration process (heating at 80℃ + vacuum extraction ≤100 Pa), which is lower than the ZIF-8 framework decomposition temperature (>300℃) and amine desorption temperature (>200℃). Simultaneously, the vacuum environment lowers the desorption activation energy of BF3. In Example 1, after 10 adsorption-regeneration cycles, the adsorption capacity retention rate of NH2-ZIF-8 reached 92.5%, while that of the 13X molecular sieve in Comparative Example 1 was only 68.3%, and that of the ZIF-8 raw powder in Comparative Example 2 was 85.6%. This demonstrates that the adsorbent of this invention possesses excellent regeneration stability and long-cycle operation capability, making it suitable for continuous industrial production.

[0022] 5) Before performing surface amine functionalization on ZIF-8 powder, the present invention pre-treats it with low-temperature oxygen plasma to increase the hydroxyl content on the ZIF-8 surface, thereby improving the grafting density and grafting uniformity of subsequent amine functionalization, which in turn leads to improvements in adsorption capacity, selectivity and deep purification effect (for example, the dynamic adsorption capacity of Example 4 is increased to 2.52 mmol / g, compared with Example 1).

[0023] 6) Before surface amine functionalization of ZIF-8 powder, this invention employs an acidic gas (acetic acid vapor) etching process to controllably introduce mesoporous defects and more Zn–OH hydroxyl defect sites within the ZIF-8 crystal. This improves both the amine functionalization grafting density and the diffusion mass transfer performance of gas molecules within the adsorbent. For example, the dynamic adsorption capacity of BF3 in Example 5 reaches 2.15 mmol / g, while that in Example 1 is only about 1.26 mmol / g at the same space velocity. The former shows a significant improvement over the latter, fully demonstrating the promoting effect of hierarchical pore structure on diffusion mass transfer.

[0024] 7) In Example 6 of this invention, amine (H2N-Im) and thiol (HS-Im) groups are directly embedded into the ZIF-8 framework as ligands. The functional groups are uniformly distributed in the three-dimensional channels of the crystal, avoiding channel blockage caused by post-modification. The amine and thiol groups are spatially adjacent at the nanoscale, which can form multiple coordination bonds to synergistically capture BF3, improving the adsorption capacity (2.85 mmol / g) and selectivity (29.6). The functional groups connected by coordination bonds are more stable under the thermal regeneration conditions of 80℃. The anhydrous toluene solvent and KH-550 raw material in the post-modification step are eliminated. Attached Figure Description Figure 1 These are the nitrogen elemental analysis energy spectra from Embodiments 1-7 of this invention; Figure 2 These are the sulfur elemental analysis energy dispersive spectroscopy spectra from Embodiments 6-7 of this invention; Figure 3 These are the BF3 adsorption-through curves of Examples 1-6 and Comparative Examples 1-6 of the present invention. Detailed Implementation

[0025] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0026] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0027] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0028] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0029] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0031] This invention discloses a highly efficient adsorption and separation method for impurities in the preparation process of borane, the technical solution of which includes: Step 1: Preparation of the composite adsorbent. The composite adsorbent is an amine-functionalized hierarchical porous composite material, which is prepared by surface amine functionalization treatment of ZIF-8 (Zeolitic Imidazole Ester Framework Material-8, CAS No.: 59061-53-9), a multi-level porous metal-organic framework (MOF) material.

[0032] The specific preparation method is as follows: 1) Place ZIF-8 powder (particle size 200–500 nm, specific surface area ≥1500 m² / g) in a vacuum drying oven and vacuum dry at 120°C for 12 hours to remove adsorbed water and solvent molecules from the pores. Vacuum drying at 120°C for 12 hours can fully remove adsorbed water and residual solvent from the ZIF-8 pores, preventing the subsequent self-polymerization of the silane coupling agent due to hydrolysis. Controlling the particle size of ZIF-8 to 200–500 nm and the specific surface area ≥1500 m² / g ensures that the material has high porosity and good dispersibility, providing sufficient reaction sites for amine grafting.

[0033] 2) The dried ZIF-8 powder was mixed with 3-aminopropyltriethoxysilane (KH-550, CAS No.: 919-30-2) at a mass ratio of 1:0.15–0.30. Anhydrous toluene (CAS No.: 108-88-3) was added as a dispersant, with a mass-to-volume ratio of ZIF-8 powder to anhydrous toluene of 1 g:15–25 mL. The mixture was refluxed at 80 °C for 12–24 hours under nitrogen protection. The mass ratio of ZIF-8 to KH-550 of 1:0.15–0.30 was used to control the surface amine grafting density (target 2.0–3.5 mmol / g). The addition of anhydrous toluene as a dispersant at a ratio of 1 g:15–25 mL maintained a uniform solid-liquid suspension. Nitrogen protection and reflux at 80 °C for 12–24 hours promoted the condensation reaction between silane and surface hydroxyl groups (forming Si-O-Zn bonds) and inhibited the cross-linking polymerization of KH-550 itself.

[0034] In anhydrous toluene, the ZIF-8 powder surface contains hydroxyl groups (—OH, originating from skeletal defects or hydrolysis of coordinatingly unsaturated zinc centers), which undergo a condensation reaction with the ethoxy group of 3-aminopropyltriethoxysilane (KH-550) to form a Si–O–Zn bond, releasing ethanol simultaneously. The reaction equation is as follows: [ZIF-8]−OH + (C2H5O)3Si(CH2)3NH2 ⟶ [ZIF-8]−O−Si(C2H5O)2(CH2)3NH2 + C2H5OH. [ZIF-8]−OH represents the active site (Zn–OH) on the ZIF-8 surface containing hydroxyl groups. (C2H5O)3Si(CH2)3NH2 is KH-550 (3-aminopropyltriethoxysilane). [ZIF-8]−O−Si(C2H5O)2(CH2)3NH2 is an amino-functionalized product grafted onto the surface of ZIF-8, with a propylamino group (—CH2CH2CH2NH2) on the surface. The byproduct ethanol (C2H5OH) escapes in gaseous form (carried away by the gas flow under nitrogen protection).

[0035] 3) After the reaction is complete, the solid product is collected by filtration and washed three times each with anhydrous ethanol (CAS No.: 64-17-5) and deionized water to remove unreacted KH-550. Washing three times with anhydrous ethanol and three times with deionized water is intended to thoroughly remove unreacted KH-550 and its physically adsorbed byproducts.

[0036] 4) The washed product was placed in a vacuum drying oven and dried at 60°C for 8 hours to obtain an amino-functionalized ZIF-8 composite material (denoted as NH2-ZIF-8). The surface amino grafting amount was determined to be 2.0–3.5 mmol / g by elemental analysis. Vacuum drying at 60°C for 8 hours can remove residual solvent from washing without destroying the amino functional groups, finally obtaining an NH2-ZIF-8 composite adsorbent with an amino grafting amount of 2.0–3.5 mmol / g.

[0037] Vacuum drying of ZIF-8 powder at 120℃ for 12 hours effectively removes adsorbed moisture and residual solvent from the pores, preventing subsequent self-aggregation of the silane coupling agent due to hydrolysis. A particle size of 200–500 nm and a specific surface area ≥1500 m² / g ensure high porosity and good dispersibility, providing ample reaction sites for amine grafting. A ZIF-8 to KH-550 mass ratio of 1:0.15–0.30 is used to control the surface amine grafting density (target 2.0–3.5 mmol / g), with anhydrous toluene used as a dispersant at a ratio of 1g:15–25. Adding a ratio of mL maintains a uniform solid-liquid suspension. Nitrogen protection and reflux at 80°C for 12–24 hours promote the condensation reaction between silane and surface hydroxyl groups (forming Si–O–Zn bonds) while inhibiting the cross-linking polymerization of KH-550 itself. After the reaction, the product is washed three times each with anhydrous ethanol and deionized water to remove unreacted KH-550 and physical adsorption byproducts. Finally, it is vacuum dried at 60°C for 8 hours to remove residual solvent without damaging the amine functional groups, thereby obtaining an NH2-ZIF-8 composite adsorbent with an amine grafting amount of 2.0–3.5 mmol / g.

[0038] This invention employs an amino-functionalized ZIF-8 composite adsorbent (NH2-ZIF-8), whose surface is grafted with numerous amino (-NH2) functional groups. BF3, as a strong Lewis acid, exhibits a strong Lewis acid-base interaction with the amino groups, thus achieving specific and highly selective adsorption of BF3. Simultaneously, ZIF-8 itself possesses a high specific surface area (≥1500 m² / g) and a hierarchical porous structure, providing ample adsorption sites. This invention selects ZIF-8 as the main matrix; its regular pore structure and mild surface chemical environment avoid the presence of strongly acidic or strongly basic sites, preventing the disproportionation decomposition of diborane. After amino-functionalization, NH2-ZIF-8 retains the skeletal stability of ZIF-8.

[0039] Step 2: Loading the Adsorption Tower. The composite adsorbent NH2-ZIF-8 prepared in Step 1 is loaded into the adsorption tower. The adsorption tower is a vertical fixed-bed adsorption tower, made of 316L stainless steel, with an inner diameter of 150mm and a height of 2000mm. Three layers of supporting sieve plates are installed inside the adsorption tower, with a sieve aperture of 0.3mm and a spacing of 600mm between adjacent sieve plates. The composite adsorbent is loaded in layers between each sieve plate, with each layer having a loading height of 500mm, for a total loading height of 1500mm. A vacuum insulation jacket is installed outside the adsorption tower, filled with aerogel insulation material with a thickness of 50mm to minimize external heat intrusion. A gas inlet distributor is installed at the top of the adsorption tower, employing a ring-shaped porous structure with a pore size of 1mm to ensure uniform initial distribution of the diborane gas entering the tower. A gas outlet is located at the bottom of the adsorption tower.

[0040] The adsorption tower is made of 316L stainless steel, ensuring excellent corrosion resistance and mechanical strength under low temperature (-30℃ to -20℃) and corrosive impurities (such as BF3). The tower's internal diameter of 150mm and height of 2000mm, combined with a three-layer support sieve plate (0.3mm aperture to prevent adsorbent powder leakage while allowing gas passage) and a layered filling method with each layer 500mm high and a total height of 1500mm, effectively reduces bed pressure drop and prevents gas short-circuiting. It also facilitates layered support and replacement of the adsorbent. The 600mm spacing between adjacent sieve plates provides sufficient expansion space and airflow redistribution distance for each adsorption bed layer. The adsorption tower is equipped with a 50mm thick vacuum insulation jacket filled with aerogel insulation material, which can minimize the intrusion of external heat and ensure the temperature stability of the low-temperature adsorption zone (-30℃ to -20℃). A gas inlet distributor with an annular porous structure (1mm pore size) is installed at the top of the tower to uniformly disperse the incoming diborane gas throughout the entire tower cross section, avoiding local channeling or uneven concentration, thereby ensuring gas-solid contact efficiency and adsorption effect.

[0041] Step 3: Low-Temperature Adsorption Operation. The crude product gas (containing boron trifluoride (BF3) impurities) generated from the dry process of diborane is passed into the adsorption tower filled in Step 2 for low-temperature adsorption treatment. The operating conditions are as follows: 1) Adsorption temperature: -30℃~-20℃ (preferably -25℃), temperature controlled by a low-temperature refrigerant (liquid nitrogen vapor) circulating within the jacket of the adsorption tower. The refrigerant inlet temperature is -40℃, and the outlet temperature is -30℃; 2) Adsorption pressure: 0.3~0.8MPa (gauge pressure); 3) Gas hourly space velocity: 50~200 h⁻¹ -1 100h preferred -1 ;4) Adsorption cycle: 24 to 72 hours, preferably 48 hours.

[0042] The adsorption temperature is controlled at -30℃ to -20℃ (preferably -25℃) to enhance the Lewis acid-base interaction between the amine groups on the surface of the composite adsorbent and BF3 at low temperatures, while suppressing the decomposition side reaction of diborane. Precise temperature control is achieved by circulating liquid nitrogen within the jacket to evaporate the gas (coolant inlet -40℃, outlet -30℃), maintaining a uniform and stable temperature in the adsorption bed. The adsorption pressure is set at 0.3–0.8 MPa (gauge pressure, preferably 0.5 MPa) to ensure sufficient mass transfer driving force while avoiding excessive pressure that could increase equipment load or cause gas short circuits. The gas hourly space velocity is controlled at 50–200 h⁻¹. -1 (Preferred 100h) -1 The space velocity is used to balance the gas-solid contact time and the processing throughput. If the space velocity is too low, the efficiency will decrease, and if it is too high, it will easily lead to premature breakthrough. The adsorption cycle is set to 24 to 72 hours (preferably 48 hours) based on the economic optimization of the adsorbent working capacity and regeneration frequency, ensuring that the adsorbent bed is fully utilized before the outlet impurity concentration exceeds the threshold.

[0043] The crude product gas enters the adsorption tower evenly through the gas inlet distributor and flows from bottom to top through each layer of composite adsorbent bed. Boron trifluoride impurities in the diborane gas are selectively adsorbed by the amine functionalized sites on the surface of the composite adsorbent. The purified diborane gas is discharged from the gas outlet at the top of the adsorption tower and enters the product collection system.

[0044] In summary, this invention employs a hierarchical porous structure of ZIF-8 (coexisting mesoporous and microporous structures) with a particle size controlled between 200 and 500 nm, shortening the diffusion path of gas molecules within the pores. Simultaneously, this invention controls the adsorption temperature between -30°C and -20°C, in conjunction with a gas inlet distributor (a ring-shaped porous structure with a pore size of 1 mm) and a suitable space velocity (50–200 h⁻¹). -1 This ensures effective contact between BF3 and the amino group site while avoiding premature penetration due to diffusion limitation.

[0045] Step 4: Adsorbent Regeneration. When the boron trifluoride concentration in the outlet gas of the adsorption tower exceeds the set threshold (≤10ppmv), stop the gas intake and perform adsorbent regeneration. The regeneration operation steps are as follows: 1) Nitrogen Purging: Introduce high-purity nitrogen (purity ≥99.999%, CAS No.: 7727-37-9) at a flow rate of 50~100L / min for 30 minutes to replace the residual diborane gas in the adsorption tower. 2) Temperature Desorption: Turn off the nitrogen and turn on the jacket heating device of the adsorption tower to slowly raise the temperature of the adsorption tower to 80℃ and maintain the constant temperature for 2 hours to desorb the adsorbed boron trifluoride from the surface of the composite adsorbent. 3) Vacuum Extraction: While heating, turn on the vacuum pump (vacuum degree ≤100Pa) connected to the bottom of the adsorption tower to extract the desorbed boron trifluoride gas for 2 hours. 4) Cooling: After regeneration, turn off the heating device and purge the adsorption tower with high-purity nitrogen until the temperature inside the tower drops to -25℃ (adsorption operating temperature). Control the cooling rate to 2-5℃ / min. 5) Regeneration tail gas treatment: The desorbed boron trifluoride tail gas is treated in an alkaline absorption tower (the absorbent is a 10wt% sodium hydroxide solution) before being discharged.

[0046] When the BF3 concentration at the outlet exceeds the set threshold (≤10 ppmv), the gas intake is stopped. This threshold is set based on the product purity requirements (BF3 ≤1 ppmv in electronic-grade diborane) and the adsorbent's working capacity to avoid excessive penetration and product contamination. First, high-purity nitrogen gas (purity ≥99.999%, flow rate 50–100 L / min, purging time 30 minutes) is introduced. (min) To replace the residual diborane gas in the adsorption tower, preventing diborane from thermally decomposing or reacting with desorbed BF3 during the heating process, and simultaneously, high-purity nitrogen can avoid introducing new impurities; then, the nitrogen is turned off and the jacket heating device is turned on to slowly raise the temperature to 80℃ and hold it at that temperature for 2 hours. This temperature is lower than the thermal decomposition temperature of the ZIF-8 framework (>300℃) and the detachment temperature of the amine functional groups (>200℃), while being higher than the desorption temperature of BF3 on NH2-ZIF-8 (approximately 40-60℃), ensuring that BF3 is fully desorbed without damaging the adsorbent structure; while heating, the vacuum pump is turned on for extraction (vacuum degree ≤100 Pa, extraction for 2 hours). The vacuum environment can reduce the gas phase partial pressure of BF3, lower the desorption temperature, and accelerate the diffusion of BF3 from the pores to the outside, preventing the desorbed BF3 from being re-adsorbed. The high vacuum of Pa effectively extracts weakly physically and chemically adsorbed BF3 molecules. After regeneration, the heating device is shut off, and high-purity nitrogen is introduced to purge and cool to -25℃ (adsorption operating temperature). The cooling rate must be controlled during this process (approximately 2–5℃ / min) to prevent thermal stress damage to the adsorption tower and adsorbent particles. Finally, the desorption tail gas is treated in a 10 wt% NaOH alkaline absorption tower, utilizing the reaction BF3 + 4NaOH → NaBF4 + 3NaF + 2H2O to convert the highly toxic BF3 into harmless fluoroborate and sodium fluoride, achieving safe emission. The above parameters (purge flow rate / time, heating temperature / duration, vacuum level, target cooling temperature, and alkaline concentration) collectively ensure the high efficiency and safety of the regeneration process and the long service life of the adsorbent.

[0047] In summary, this invention designs a mild regeneration process (80℃ heating + vacuum extraction ≤100 Pa), which is lower than the ZIF-8 skeleton decomposition temperature (>300℃) and amine desorption temperature (>200℃). At the same time, the vacuum environment reduces the desorption activation energy of BF3.

[0048] Example 1 This embodiment provides a highly efficient adsorption and separation method for impurities in a borane preparation process, specifically including the following steps: I. Preparation of Composite Adsorbents 12.5 kg of ZIF-8 powder (particle size 300 nm, specific surface area 1650 m² / g) was placed in a vacuum drying oven and dried under vacuum at 120 °C for 12 hours. The dried ZIF-8 powder was mixed with 2.5 kg of 3-aminopropyltriethoxysilane (KH-550, CAS No.: 919-30-2, purchased from Sinopharm Chemical Reagent Co., Ltd.) (mass ratio 1:0.2), and 250 L of anhydrous toluene (CAS No.: 108-88-3) (liquid-to-solid ratio 20 mL / g) was added as a dispersant. The mixture was refluxed at 80 °C for 18 hours under nitrogen protection. After the reaction, the solid product was collected by filtration and washed three times each with anhydrous ethanol and deionized water. The washed product was placed in a vacuum drying oven and dried under vacuum at 60 °C for 8 hours to obtain the NH₂-ZIF-8 composite adsorbent.

[0049] II. Packing of the Adsorption Tower The adsorption tower is a vertical fixed-bed adsorption tower, with the tower body made of 316L stainless steel, an inner diameter of 150 mm, and a height of 2000 mm. The adsorption tower contains three layers of supporting sieve plates, each with a sieve aperture of 0.3 mm and a spacing of 600 mm between adjacent sieve plates. The prepared NH2-ZIF-8 composite adsorbent is layered and filled between the sieve plates, with each layer having a filling height of 500 mm, for a total filling height of 1500 mm. The adsorption tower is externally equipped with a vacuum insulation jacket filled with aerogel insulation material, 50 mm thick. A gas inlet distributor with a ring-shaped porous structure and a pore size of 1 mm is located at the top of the adsorption tower. A gas outlet is located at the bottom of the adsorption tower.

[0050] III. Low-Temperature Adsorption Operation The crude product gas generated from the dry diborane process (diborane content approximately 98.5 vol, boron trifluoride content approximately 1.0 vol, with the remainder being light components such as hydrogen and nitrogen) is introduced into the adsorption tower through a gas inlet distributor. Operating conditions: adsorption temperature -25℃, temperature controlled by circulating liquid nitrogen vapor in the jacket; refrigerant inlet temperature -40℃; adsorption pressure 0.5 MPa (gauge pressure); gas hourly space velocity 100 h⁻¹. -1 The adsorption cycle is 48 hours.

[0051] The purified diborane gas is discharged from the gas outlet at the top of the adsorption tower and enters the product collection system.

[0052] IV. Adsorbent Regeneration When the boron trifluoride concentration in the outlet gas exceeds 10 ppmv, stop the gas intake. Purge with high-purity nitrogen (≥99.999%, flow rate 80 L / min) for 30 minutes to replace any residual diborane gas in the adsorption tower. Turn off the nitrogen supply, turn on the jacket heating device, raise the adsorption tower temperature to 80°C, maintain this temperature for 2 hours, and simultaneously turn on the vacuum pump (vacuum degree ≤100 Pa) to extract the desorbed boron trifluoride gas. After regeneration, turn off the heating device, purge with high-purity nitrogen to cool to -25°C, thus completing one regeneration cycle.

[0053] Performance analysis: The amount of amine grafting in Example 1 was 2.8 mmol / g (see Appendix). Figure 1 Based on the N elemental analysis chromatogram obtained by an organic elemental analyzer (EA), the larger the characteristic peak area of ​​N element, the higher the corresponding amino grafting amount, which is within the acceptable range (2.0–3.5 mmol / g) specified in this invention. Its BF3 dynamic adsorption capacity reaches 1.85 mmol / g (see Appendix). Figure 3 , including Figure 3 The horizontal axis represents time, indicating the progress of the adsorption experiment; the vertical axis represents the outlet / inlet BF3 gas concentration ratio (C / C0), indicating the relative concentration at the adsorbent bed outlet. The adsorption breakthrough curves visually demonstrate the differences in the dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The breakthrough curves of Examples 1-7 shift to the right in sequence, which is completely consistent with the order in which their BF3 adsorption capacity gradually increases from 1.85 mmol / g to 3.12 mmol / g. Among them, Example 7 (pre-equilibrium dual ligand) has the longest breakthrough time and the highest adsorption capacity; while the curves of Comparative Examples 1-6 all shift significantly to the left, with a significant reduction in breakthrough time, corresponding to their low adsorption capacity (0.55~1.23 mmol / g). The adsorption selectivity (BF3 / B2H6 adsorption ratio) is 18.5, the decomposition rate of diborane is only 0.08%, the adsorption capacity retention rate after 10 cycles is 92.5%, and the residual BF3 concentration at the outlet is ≤0.5 ppmv (meeting the requirement of electronic-grade diborane BF3 ≤1 ppmv). All of these indicators meet the requirements for industrial-scale deep purification and are significantly better than the comparative example; therefore, the performance is deemed satisfactory.

[0054] Example 2 This embodiment provides a highly efficient adsorption and separation method for impurities in a borane preparation process, specifically including the following steps: I. Preparation of Composite Adsorbents 12.5 kg of ZIF-8 powder (particle size 500 nm, specific surface area 1650 m² / g) was placed in a vacuum drying oven and dried under vacuum at 120 °C for 12 hours. The dried ZIF-8 powder was mixed with 1.875 kg of 3-aminopropyltriethoxysilane (KH-550, CAS No.: 919-30-2) (mass ratio 1:0.15), and 312.5 L of anhydrous toluene (CAS No.: 108-88-3) (liquid-to-solid ratio 25 mL / g) was added as a dispersant. The mixture was refluxed at 80 °C for 12 hours under nitrogen protection. After the reaction, the solid product was collected by filtration and washed three times each with anhydrous ethanol and deionized water. The washed product was placed in a vacuum drying oven and dried under vacuum at 60 °C for 8 hours to obtain the NH₂-ZIF-8 composite adsorbent.

[0055] II. Packing of the Adsorption Tower The adsorption tower is a vertical fixed-bed adsorption tower, with the tower body made of 316L stainless steel, an inner diameter of 150 mm, and a height of 2000 mm. The adsorption tower contains three layers of supporting sieve plates, each with a sieve aperture of 0.3 mm and a spacing of 600 mm between adjacent sieve plates. The prepared NH2-ZIF-8 composite adsorbent is layered and filled between the sieve plates, with each layer having a filling height of 500 mm, for a total filling height of 1500 mm. The adsorption tower is externally equipped with a vacuum insulation jacket filled with aerogel insulation material, 50 mm thick. A gas inlet distributor with a ring-shaped porous structure and a pore size of 1 mm is located at the top of the adsorption tower. A gas outlet is located at the bottom of the adsorption tower.

[0056] III. Low-Temperature Adsorption Operation The crude product gas generated from the dry diborane process (diborane content approximately 98.5 vol, boron trifluoride content approximately 1.0 vol, with the remainder being light components such as hydrogen and nitrogen) is introduced into the adsorption tower through a gas inlet distributor. Operating conditions: adsorption temperature -20℃, temperature controlled by circulating liquid nitrogen evaporation gas within the jacket; refrigerant inlet temperature -40℃; adsorption pressure 0.3 MPa (gauge pressure); gas hourly space velocity 200 h⁻¹. -1 The adsorption cycle is 24 hours.

[0057] The purified diborane gas is discharged from the gas outlet at the top of the adsorption tower and enters the product collection system.

[0058] IV. Adsorbent Regeneration When the boron trifluoride concentration in the outlet gas exceeds 10 ppmv, stop the gas inlet. Purge with high-purity nitrogen (≥99.999%, flow rate 100 L / min) for 30 minutes to replace any residual diborane gas in the adsorption tower. Turn off the nitrogen supply, turn on the jacket heating device, raise the adsorption tower temperature to 80°C, maintain this temperature for 2 hours, and simultaneously turn on the vacuum pump (vacuum degree ≤100 Pa) to extract the desorbed boron trifluoride gas. After regeneration, turn off the heating device, purge with high-purity nitrogen to cool to -25°C, thus completing one regeneration cycle.

[0059] Performance analysis: The amount of amine grafting in Example 2 was 2.2 mmol / g (see Appendix). Figure 1 Based on the nitrogen elemental analysis chromatogram obtained from an elemental analyzer (EA), the larger the characteristic peak area of ​​nitrogen corresponds to a higher amount of amino grafting, and it is within the acceptable range (2.0–3.5 mmol / g). Its BF3 dynamic adsorption capacity is 1.62 mmol / g (see Appendix). Figure 3 The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption selectivity is 16.8, the diborane decomposition rate is 0.09%, the adsorption capacity retention rate after 10 cycles is 91.8%, and the residual BF3 concentration at the outlet is ≤0.8 ppmv (still meeting the requirement of ≤1 ppmv). Although the various indicators are slightly lower than those of Example 1 (due to its lower KH-550 ratio and shorter reaction time), they are all superior to the comparative example and meet the purity standard of electronic-grade diborane, thus the performance meets the requirements.

[0060] Example 3 This embodiment provides a highly efficient adsorption and separation method for impurities in a borane preparation process, specifically including the following steps: I. Preparation of Composite Adsorbents 12.5 kg of ZIF-8 powder (particle size 200 nm, specific surface area 1650 m² / g) was placed in a vacuum drying oven and dried under vacuum at 120 °C for 12 hours. The dried ZIF-8 powder was mixed with 3.75 kg of 3-aminopropyltriethoxysilane (KH-550, CAS No.: 919-30-2) (mass ratio 1:0.30), and 187.5 L of anhydrous toluene (CAS No.: 108-88-3) (liquid-to-solid ratio 15 mL / g) was added as a dispersant. The mixture was refluxed at 80 °C for 12 hours under nitrogen protection. After the reaction, the solid product was collected by filtration and washed three times each with anhydrous ethanol and deionized water. The washed product was placed in a vacuum drying oven and dried under vacuum at 60 °C for 8 hours to obtain the NH₂-ZIF-8 composite adsorbent.

[0061] II. Packing of the Adsorption Tower The adsorption tower is a vertical fixed-bed adsorption tower, with the tower body made of 316L stainless steel, an inner diameter of 150 mm, and a height of 2000 mm. The adsorption tower contains three layers of supporting sieve plates, each with a sieve aperture of 0.3 mm and a spacing of 600 mm between adjacent sieve plates. The prepared NH2-ZIF-8 composite adsorbent is layered and filled between the sieve plates, with each layer having a filling height of 500 mm, for a total filling height of 1500 mm. The adsorption tower is externally equipped with a vacuum insulation jacket filled with aerogel insulation material, 50 mm thick. A gas inlet distributor with a ring-shaped porous structure and a pore size of 1 mm is located at the top of the adsorption tower. A gas outlet is located at the bottom of the adsorption tower.

[0062] III. Low-Temperature Adsorption Operation The crude product gas generated from the dry diborane process (diborane content approximately 98.5 vol, boron trifluoride content approximately 1.0 vol, with the remainder being light components such as hydrogen and nitrogen) is introduced into the adsorption tower through a gas inlet distributor. Operating conditions: adsorption temperature -30℃, temperature controlled by circulating liquid nitrogen evaporation gas within the jacket; refrigerant inlet temperature -40℃; adsorption pressure 0.8 MPa (gauge pressure); gas hourly space velocity 50 h⁻¹. -1 The adsorption cycle is 72 hours.

[0063] The purified diborane gas is discharged from the gas outlet at the top of the adsorption tower and enters the product collection system.

[0064] IV. Adsorbent Regeneration When the boron trifluoride concentration in the outlet gas exceeds 10 ppmv, stop the gas inlet. Purge with high-purity nitrogen (≥99.999%, flow rate 50 L / min) for 30 minutes to replace any residual diborane gas in the adsorption tower. Turn off the nitrogen supply, turn on the jacket heating device, raise the adsorption tower temperature to 80°C, and maintain this temperature for 2 hours. Simultaneously, turn on the vacuum pump (vacuum degree ≤100 Pa) to extract the desorbed boron trifluoride gas. After regeneration, turn off the heating device and purge with high-purity nitrogen to cool to -25°C, thus completing one regeneration cycle.

[0065] Performance analysis: The amount of amine grafting in Example 3 was 3.4 mmol / g (see Appendix). Figure 1 Based on the nitrogen elemental analysis chromatogram obtained from an elemental analyzer (EA), the larger the characteristic peak area of ​​nitrogen corresponds to a higher amount of amino grafting, which is near the upper limit of the acceptable range (2.0–3.5 mmol / g). Its BF3 dynamic adsorption capacity reaches 2.01 mmol / g (see appendix). Figure 3The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption selectivity is 19.2, the diborane decomposition rate is only 0.07%, the adsorption capacity retention rate after 10 cycles is 93.0%, and the residual BF3 concentration at the outlet is ≤0.4 ppmv. All indicators are the best among Examples 1-3 and are significantly better than all comparative examples, therefore the performance meets the standards.

[0066] Example 4 The difference from Example 1 is that: before the ZIF-8 powder is subjected to surface amine functionalization treatment, it is pre-treated with low-temperature oxygen plasma to increase the hydroxyl content on the ZIF-8 surface, thereby improving the grafting density and grafting uniformity of subsequent amine functionalization.

[0067] 12.5 kg of ZIF-8 powder (particle size 300 nm, specific surface area 1650 m² / g) was uniformly spread in the sample tray of a low-temperature plasma reactor. Under an oxygen atmosphere (oxygen flow rate 40 ccm), the powder was treated with a plasma discharge power of 50 W for 40 seconds to obtain surface-hydroxylated ZIF-8 material. The defect sites of ZIF-8 are composed of Zn–OH hydroxyl groups, which are key anchor points for subsequent silane coupling agent grafting. The high-energy active oxygen species in the oxygen plasma can generate more ligand-deficient sites and unsaturated metal sites on the ZIF-8 surface, thereby increasing the surface hydroxyl density. To prevent the plasma-treated active surface from adsorbing moisture from the air and affecting the subsequent grafting effect, the treated ZIF-8 should be rapidly transferred to a vacuum drying oven under nitrogen protection and placed at room temperature (25°C) for 1 hour to stabilize the surface before proceeding to the next step of vacuum drying. The subsequent vacuum drying to low-temperature adsorption operation is the same as in Example 1.

[0068] Performance analysis: The amount of amine grafting in Example 4 increased from 2.8 mmol / g in Example 1 to 4.5 mmol / g (see Appendix). Figure 1 Based on the N elemental analysis chromatogram obtained from an elemental analyzer (EA), the larger the characteristic peak area of ​​N, the higher the corresponding amino grafting amount, with an increase of 61%. The higher amino group density directly led to an increase in the dynamic adsorption capacity of BF3 to 2.52 mmol / g (+36%) (see Appendix). Figure 3The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption selectivity increased to 24.3 (+31%), and the residual BF3 concentration at the outlet decreased to ≤0.2 ppmv (better than ≤0.5 ppmv in Example 1). Meanwhile, since plasma treatment did not alter the framework structure and chemical environment of ZIF-8, the decomposition rate of diborane remained at a low level of 0.07%; and the amine grafting was more uniform and the bonding was stronger, resulting in an adsorption capacity retention rate of 94.2% after 10 cycles (92.5% in Example 1). In summary, the performance improvement is expected to be due to the plasma hydroxylation pretreatment increasing the surface anchor point density, thereby increasing the amount of amine grafting and thus improving adsorption capacity, selectivity, and depth of purification. Plasma hydroxylation pretreatment generates more ligand-deficient sites and unsaturated metal sites on the ZIF-8 surface through high-energy reactive oxygen species, thereby increasing the surface hydroxyl (Zn–OH) density and providing more covalent anchors for KH-550 grafting.

[0069] Example 5 The difference from Example 1 is that before the ZIF-8 powder is subjected to surface amine functionalization treatment, it is pre-etched with acidic gas (acetic acid vapor) to controllably introduce mesoporous defects and more Zn-OH hydroxyl defect sites inside the ZIF-8 crystal, thereby improving the diffusion and mass transfer performance of gas molecules inside the adsorbent while increasing the amine functionalization graft density.

[0070] 12.5 kg of ZIF-8 powder (particle size 300 nm, specific surface area 1650 m² / g) was uniformly spread in a closed reactor. Acetic acid vapor (acetic acid concentration approximately 0.4 vol%, carrier gas flow rate 3 L / min) was introduced under a nitrogen carrier gas atmosphere and treated at room temperature (25 °C) for 2 hours. Under the action of acetic acid vapor, a defect formation process of "adsorption followed by etching" occurred inside the ZIF-8 crystals, generating etched ZIF-8 material with a hierarchical porous structure (mesopores approximately 50 nm) and a large number of Zn–OH hydroxyl defect sites. The defect sites of ZIF-8 are characterized by Zn–OH hydroxyl groups, which have basic properties and can serve as effective anchor points for silane coupling agent grafting. After the etching treatment, the reactor temperature was raised to 150 °C under a nitrogen atmosphere and maintained for 2 hours to remove residual acetic acid molecules, and then naturally cooled to room temperature. The treated ZIF-8 exhibits an interconnected microporous-mesoporous hierarchical pore structure with a mesopore size of approximately 50 nm, which improves the material diffusion channels within the crystal without sacrificing microporosity. Subsequent vacuum drying to low-temperature adsorption operations are the same as in Example 1.

[0071] Performance analysis: The amount of amine grafting in Example 5 was increased to 4.2 mmol / g (+50%) (see Appendix). Figure 1 Based on the N elemental analysis chromatogram obtained from the elemental analyzer (EA), the larger the characteristic peak area of ​​N, the higher the corresponding amino grafting amount. The dynamic adsorption capacity of BF3 is within 100 h. -1 The concentration reached 2.38 mmol / g (+29%) at a space velocity of [missing value]. More importantly, at 150 h [missing value]... -1 ¹At high space velocities, the dynamic adsorption capacity of BF3 in Example 5 reached 2.15 mmol / g (see Appendix). Figure 3 The adsorption-throughput curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. Example 1, at the same space velocity, only achieved approximately 1.26 mmol / g, representing a 71% improvement over the former, fully demonstrating the promoting effect of the hierarchical pore structure on diffusion mass transfer. The outlet BF3 residual concentration was ≤0.3 ppmv, the diborane decomposition rate was 0.09%, and the retention rate after 10 cycles was 91.8% (slightly lower than Example 1, as the mesoporous structure may slightly reduce mechanical strength, but still far superior to the comparative example). In summary, the performance improvement is expected to be due to the acidic gas etching introducing mesoporous defects and increasing hydroxyl anchors, which significantly improved adsorption performance at high space velocities while maintaining high selectivity and low decomposition rate, achieving high-throughput operation capability.

[0072] Example 6 Example 1 prepared NH2-ZIF-8 by grafting ZIF-8 with KH-550. Most of the amine groups were grafted onto the surface and pores of the ZIF-8 crystal, failing to form a sufficient three-dimensional functional group network within the crystal. Furthermore, the post-modification process carried the risk of pore blockage. In contrast to Example 1, Example 6 simultaneously introduced amine ligands (H2N-Im) and thiol ligands (HS-Im) into the ZIF-8 framework. The bifunctional groups were directly embedded into the framework as ligands, forming a synergistic coordination network in three-dimensional space, thereby improving the selective adsorption performance of BF3 while maintaining the integrity of the framework.

[0073] I. Preparation of Composite Adsorbents 14.9 kg of zinc nitrate hexahydrate (Zn(NO3)2·6H2O, CAS No.: 10196-18-6) was used as the zinc source. The following three ligands were mixed in the specified ratio: 8.2 kg (0.10 mol) of 2-methylimidazole (Hmim, CAS No.: 693-98-1) as the main ligand for the skeleton; 0.83 kg (0.01 mol) of 2-aminoimidazole (H2N-Im, CAS No.: 4013-23-8) as the source of the amino functional group; and 1.00 kg (0.01 mol) of 2-mercaptoimidazole (HS-Im, CAS No.: 872-35-5) as the source of the thiol functional group. The molar ratio of the three ligands was Hmim:H2N-Im:HS-Im = 10:1:1. The total molar amount of ligands was 0.12 mol, and the ratio of amino to thiol groups in the skeleton was approximately 1:1.

[0074] Synthesis steps: 1) Preparation of ligand premixed solution: Add three ligands, Hmim, H2N-Im and HS-Im, to 500L of deionized water and stir at room temperature until completely dissolved to obtain a clear mixed solution with a ligand concentration of 0.24mol / L; 2) Preparation of zinc salt solution: Dissolve 14.9 kg of zinc nitrate hexahydrate in 500 L of deionized water and stir at room temperature until completely dissolved to obtain 0.1 mol / L Zn. 2+ Solution; 3) Mixing and Crystallization: Under vigorous stirring (500 rpm), the zinc salt solution was added dropwise to the ligand mixture at a rate of 2 L / min. Immediately after the addition was complete, the solution turned milky white, and ZIF-8 crystals began to nucleate. Stirring continued for 30 minutes, then the reaction mixture was transferred to a stainless steel reactor. 4) Solvothermal reaction: The reaction was carried out at 120℃ for 24 hours. The three ligands were reacted via Zn... 2+ The coordination of ions leads to self-assembly into a ZIF-8 framework, with amine and thiol functional groups directly embedded in the framework as ligands, achieving a uniform distribution within the three-dimensional porous network of the crystal. The reaction pressure is the self-generated pressure (approximately 0.2–0.5 MPa). 5) Separation and washing: After the reaction is complete, allow the mixture to cool to room temperature naturally, centrifuge (4000 rpm, 15 minutes) to collect the white precipitate, and wash it three times each with deionized water and anhydrous ethanol. 6) Activation treatment: The washed product is placed in a vacuum drying oven and dried under vacuum at 120°C for 12 hours to remove solvent molecules in the pores, thus obtaining the dual-ligand co-doped ZIF-8 composite adsorbent, denoted as NH2-SH-ZIF-8.

[0075] A total concentration of 0.24 mol / L of the three ligands in the ligand premix solution ensures compatibility with subsequent Zn. 2+After mixing the solutions, a suitable supersaturation level is achieved to promote uniform nucleation. A zinc salt solution concentration of 0.1 mol / L can control the nucleation rate and prevent excessively rapid nucleation from causing crystal defects. Adding the zinc salt solution dropwise at a rate of 2 L / min while maintaining vigorous stirring at 500 rpm allows the ligands to react with Zn. 2+ Rapid and uniform mixing is essential to avoid localized excessive concentrations that could induce impurities. The immediate milky-white color after addition indicates the start of ZIF-8 crystal nucleation; continued stirring for 30 minutes will stabilize the crystal growth. A solvothermal reaction at 120℃ for 24 hours allows the three ligands to fully react with Zn. 2+ Coordination self-assembly forms a highly crystalline ZIF-8 framework, with amine and thiol functional groups embedded in the lattice as ligands. Centrifugation (4000 rpm, 15 min) efficiently collects nanoscale ZIF-8 crystals. Washing three times sequentially with deionized water and anhydrous ethanol removes unreacted zinc salts and ligands. Vacuum drying at 120℃ for 12 hours completely removes solvent molecules from the pores, preventing pore blockage. The coordination reaction equations involved are as follows (using Zn...). 2+ (Similar to 2-methylimidazole, other ligands are similar). Zn 2+ +2Hmim Zn(Hmim)2↓+2H + ; In the actual process of skeleton formation, Zn 2+ It coordinates with deprotonated imidazole ligands (mim⁻) to form a three-dimensional network structure. Since three ligands (Hmim, H₂N-Im, and HS-Im) are present in the system, they collectively participate in coordination, forming a mixed-ligand ZIF-8 framework, whose simplified general formula can be represented as Zn(Hmim). 2−x−y (H2N-Im) x (HS-Im) y .

[0076] II. Packing of the Adsorption Tower The prepared NH2-SH-ZIF-8 composite adsorbent was loaded into a vertical fixed-bed adsorption tower. The tower body was made of 316L stainless steel, with an inner diameter of 150 mm and a height of 2000 mm. Three layers of supporting sieve plates (0.3 mm aperture, 600 mm spacing) were installed internally, with each layer having a loading height of 500 mm, for a total loading height of 1500 mm. The bulk density of NH2-SH-ZIF-8 was similar to that of ZIF-8 (approximately 0.45–0.47 g / cm³), and their contents were approximately equal across the total loading volume. A vacuum insulation jacket (50 mm thick) filled with aerogel insulation material was installed outside the tower. A ring-shaped porous gas inlet distributor (1 mm aperture) was installed at the top of the tower. A gas outlet was installed at the bottom of the tower.

[0077] The subsequent low-temperature adsorption operation and adsorbent regeneration are the same as in Example 1.

[0078] Performance analysis: Example 6 showed a BET specific surface area of ​​1520 m² / g and a retention rate of 92.1%, which is higher than the 71.5% (1180 m² / g) of the modified method in Example 1. This is likely because the functional groups were directly embedded in the framework, avoiding pore blockage. The dynamic adsorption capacity of BF3 reached 2.85 mmol / g (see Appendix). Figure 3 The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. Compared to Example 1 (1.85... The adsorption capacity (BF3) increased by approximately 54% (mmol / g), likely due to the nanoscale spatial proximity of amine and thiol groups in the framework, allowing B atoms of BF3 to simultaneously form multiple coordination bonds with multiple N and S atoms, thus enhancing adsorption affinity. The adsorption selectivity (BF3 / B2H6 adsorption ratio) jumped to 29.6, approximately 60% higher than Example 1 (18.5), likely due to the extremely low affinity of thiol groups for B2H6, resulting in a highly specific recognition of BF3 by the bifunctional synergistic network. The decomposition rate of diborane decreased to 0.03%, only 37.5% of Example 1, likely because the uniformly distributed amine and thiol groups in the framework covered the defect sites of catalytic decomposition, and the weak reducing power of thiol groups neutralized the local strong oxidizing microenvironment. After 10 cycles, the adsorption capacity retention reached 96.2%, and the inter-batch amine grafting RSD (relative standard deviation) decreased from 12% to below 3%, indicating that functional groups in the framework interact with Zn²⁺ through coordination bonds. + The connection is relatively stable under 80℃ thermal regeneration conditions, and it has both high selectivity and high stability.

[0079] By directly embedding amine (H2N-Im) and thiol (HS-Im) groups as ligands into the ZIF-8 framework, the following advantages are observed compared to the post-modification grafting method in Example 1: First, the functional groups are uniformly distributed within the three-dimensional pores of the crystal, avoiding pore blockage caused by post-modification. The BET specific surface area retention rate is 92.1% (higher than Example 1), providing more ample adsorption space for BF3. Second, the spatial proximity of the amine and thiol groups at the nanoscale allows for the formation of multiple coordination bonds to synergistically capture BF3, improving adsorption capacity (2.85 mmol / g) and selectivity (29.6). Third, the coordinated functional groups are more stable under 80℃ thermal regeneration conditions, maintaining 96.2% retention rate after 10 cycles, with a batch-to-batch grafting RSD ≤ 3%, improving product consistency and process reliability. Fourth, the anhydrous toluene solvent and KH-550 raw material are eliminated in the post-modification step, removing safety hazards and VOC emissions associated with organic solvent use, shortening the production cycle, and demonstrating advantages in green chemistry and promising prospects for industrial application.

[0080] Example 7 The difference from Example 6 is that the synthesis process of the ZIF-8 dual ligands is divided into two stages: a "pre-equilibrium stage" and a "co-growth stage". Through a coordination pre-equilibrium strategy, the H2N-Im and HS-Im are pre-regulated with Zn² before nucleation. + The coordination equilibrium state is then achieved by introducing Hmim in stages, thereby effectively avoiding competitive coordination conflicts caused by the simultaneous mixing of the three ligands and realizing the controllable and uniform incorporation of functional groups into the ZIF-8 framework. Specifically, in the initial stage of the reaction, Zn²⁺ is introduced into the ZIF-8 framework. + Zn²⁺ is pre-formed by mixing with H₂N-Im and HS-Im under weakly alkaline conditions. + -H2N-Im / HS-Im coordination intermediates. Due to the low pKa values ​​of H2N-Im and HS-Im (approximately 8-10), they are readily deprotonated in alkaline environments and preferentially react with Zn²⁺. + Coordination occurs, forming stable complexes. During the pre-equilibrium phase, the pre-equilibrium time (15-60 minutes) and pH value (adjusted using sodium formate or triethylamine) are controlled to allow H₂N-Im and HS-Im to react with Zn²⁺. + The coordination state is near saturation. Then, the host ligand Hmim is added in stages. Hmim (pKa approximately 14.2) requires high basicity for effective deprotonation; the staged addition method slows down its reaction with Zn²⁺. + The coordination rate should be adjusted to avoid affecting the already formed Zn²⁺. + The H2N-Im / HS-Im coordination intermediates cause excessive competition. Ultimately, under mild hydrothermal conditions (100-120℃), ZIF-8 crystal growth is completed through the stepwise substitution of Hmim and framework assembly, allowing H2N-Im and HS-Im to be uniformly embedded in the bulk phase of the framework as ligands, rather than being enriched only on the surface.

[0081] I. Preparation of Composite Adsorbents Raw material preparation: 14.9 kg of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was used as the zinc source. The three ligand raw materials were the same as in Example 6: 8.2 kg of 2-methylimidazole (Hmim), 0.83 kg of 2-aminoimidazole (H2N-Im), and 1.00 kg of 2-mercaptoimidazole (HS-Im). The molar ratio of ligands Hmim:H2N-Im:HS-Im = 10:1:1.

[0082] Synthesis steps: 1) Pre-equilibrium stage – Zn² + Formation of the -H2N-Im / HS-Im coordination intermediate.

[0083] Dissolve 14.9 kg of zinc nitrate hexahydrate in 250 L of deionized water and stir until completely dissolved to obtain Zn²⁺. +Solution (0.2 mol / L). Dissolve H₂N-Im (0.83 kg) and HS-Im (1.00 kg) separately in 250 L of deionized water, stirring until completely dissolved to obtain a mixed ligand solution. Under vigorous stirring (500 rpm), slowly add the mixed ligand solution dropwise to Zn²⁺. + In the solution, the dropping rate is controlled at 1 L / min, so that Zn²⁺ is added at a rate of 1 L / min. + The molar ratio of Zn²⁺ to H₂N-Im and HS-Im was 1:0.2:0.2. 0.85 kg of sodium formate (HCOONa, CAS No.: 141-53-7, purchased from Sinopharm Chemical Reagent Co., Ltd.) (0.5 times the molar amount of Zn²⁺) was added to the mixed solution as a coordination modifier. The pH of the system was adjusted to 8.0–8.5 (monitored online with a pH meter) using triethylamine (CAS No.: 121-44-8, purchased from Sinopharm Chemical Reagent Co., Ltd.). Under nitrogen protection, the mixture was stirred and pre-equilibrated at room temperature (25°C) for 30 minutes to allow Zn²⁺ to reach equilibrium. + It fully coordinates with H2N-Im and HS-Im to form a stable Zn²⁺ + -H2N-Im / HS-Im coordination intermediate.

[0084] 2) Co-growth stage – the phased addition of Hmim and assembly of the ZIF-8 skeleton.

[0085] Hmim (8.2 kg) was dissolved in 250 L of deionized water and added to the pre-equilibrium reaction system in three equal portions: First stage: The first portion of Hmim solution (approximately 2.73 kg dissolved in 83 L of water) was added, and stirring was continued for 15 minutes. Hmim partially replaced H2N-Im / HS-Im in the coordination intermediate, initiating ZIF-8 nucleation; Second stage: The second portion of Hmim solution was added, and stirring was continued for 15 minutes. Hmim further participated in coordination, and the framework began to extend; Third stage: The third portion of Hmim solution was added, and stirring was continued for 15 minutes. Hmim basically completed coordination, and ZIF-8 crystals grew in an orderly manner.

[0086] The phased feeding process took approximately 45 minutes in total, with a total Hmim dosage of 8.2 kg and Zn². + The molar ratio of Zn² to Hmim is 1:2 (calculated based on 14.9 kg of Zn(NO3)2·6H2O and 8.2 kg of Hmim). + (0.05 mol, Hmim 0.1 mol). Nitrogen protection was maintained throughout the process, and the pH value was controlled at 8.0–8.5.

[0087] 3) Solvent-thermal reaction The reaction mixture was transferred to a stainless steel reactor and subjected to a solvothermal reaction at 100°C for 12 hours (a further reduction in temperature and time compared to 120°C / 24 hours in Example 6) to allow for fully ordered growth of ZIF-8 crystals. The reaction pressure was autogenous pressure (approximately 0.1–0.3 MPa).

[0088] 4) Separation and washing After the reaction was completed, the mixture was allowed to cool naturally to room temperature and then centrifuged (4000 rpm, 15 minutes) to collect the white precipitate. The precipitate was washed three times each with deionized water and anhydrous ethanol to remove unreacted zinc salts and ligands.

[0089] 5) Activation treatment The washed product was placed in a vacuum drying oven and dried under vacuum at 120°C for 12 hours to remove solvent molecules from the pores, resulting in a dual-ligand co-doped ZIF-8 composite adsorbent, denoted as NH2-SH-ZIF-8-Pre (Pre indicates pre-equilibrium assisted method).

[0090] II. Packing of the Adsorption Tower The prepared NH2-SH-ZIF-8-Pre composite adsorbent was loaded into a vertical fixed-bed adsorption tower. The tower body was made of 316L stainless steel, with an inner diameter of 150 mm and a height of 2000 mm. Three layers of supporting sieve plates (0.3 mm pore size, 600 mm spacing) were installed internally. The composite adsorbent was loaded in layers, each layer with a loading height of 500 mm, for a total loading height of 1500 mm. The bulk density of NH2-SH-ZIF-8-Pre was similar to that of ZIF-8 (approximately 0.45–0.47 g / cm³), and 12.5 kg of adsorbent corresponded to a bed volume of approximately 26.6 L. A vacuum insulation jacket (50 mm thick) filled with aerogel insulation material was installed outside the tower. A ring-shaped porous gas inlet distributor (1 mm pore size) was installed at the top of the tower. A gas outlet was installed at the bottom of the tower.

[0091] The subsequent low-temperature adsorption operation and adsorbent regeneration are the same as in Example 6.

[0092] Compared to Example 6, Example 7, through a coordination pre-equilibrium assisted staged co-growth strategy, increased the actual incorporation ratio of H2N-Im and HS-Im from 40% to 85% under mild conditions (100°C, 12 hours), and increased the amine grafting amount from 2.0 mmol / g to 2.5 mmol / g (see Appendix). Figure 1 Based on the N elemental analysis chromatogram obtained by an organic elemental analyzer (EA), the larger the characteristic peak area of ​​N, the higher the corresponding amino grafting amount. The thiol grafting amount increased from 1.0 mmol / g to 1.5 mmol / g (see Appendix). Figure 2Based on the sulfur elemental analysis chromatogram obtained by an elemental analyzer (EA), the larger the characteristic peak area of ​​sulfur corresponds to a higher amount of thiol grafting. The BET specific surface area increased from 1520 m² / g to 1580 m² / g, and the retention rate improved from 92.1% to 95.8%. The dynamic adsorption capacity of BF3 increased from 2.85 mmol / g to 3.12 mmol / g (an increase of approximately 9%) (see Appendix). Figure 3 The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption selectivity increased from 29.6 to 32.5 (an increase of about 10%); the decomposition rate of diborane decreased from 0.03% to 0.02%; the retention rate after 10 cycles increased from 96.2% to 97.5%; and the batch-to-batch RSD decreased from 3% to below 2%. Overall performance achieved a stable and slight improvement while maintaining a similar cost.

[0093] Example 7 employs a coordination pre-equilibrium-assisted staged co-growth strategy, enabling the low pKa ligands H2N-Im and HS-Im to bind with Zn before nucleation. 2+ The formation of a stable intermediate avoids competitive consumption when the three ligands are mixed simultaneously, increasing the actual incorporation ratio of functional ligands from 40% to 85%, and more than doubling the raw material utilization rate. This directly offsets the risk of decreased conversion rate that might have been caused by the reduction in reaction temperature (120℃→100℃) and time (24h→12h). Simultaneously, the mild conditions effectively suppressed defect formation caused by excessive heating of the framework, and sodium formate, acting as a coordination regulator, guided the orderly growth of crystals, increasing the BET retention rate from 92.1% to 95.8%. The improved raw material utilization rate and reduced energy consumption maintained a essentially unchanged cost, while a more uniform functional group distribution and a more complete framework structure resulted in a slight, synergistic improvement in adsorption capacity, selectivity, and stability.

[0094] Comparative Example 1 The same adsorption tower equipment structure and operating parameters as in Example 1 (adsorption temperature -25℃, adsorption pressure 0.5MPa, gas space velocity 100h) were used. -1 The adsorption cycle was 48 hours, but the adsorbent used was a traditional 13X molecular sieve (CAS No.: 63231-69-6, particle size 1-2 mm, specific surface area 650 m² / g). To maintain the same bed volume (26.5 L), the loading amount of 13X molecular sieve was calculated to be 17.2 kg based on its bulk density (approximately 0.65 g / cm³). The 13X molecular sieve was activated at 300°C for 4 hours before use. During the regeneration operation, the nitrogen purging flow rate was 80 L / min (the same as in Example 1), and the remaining steps and parameters were consistent with Example 1.

[0095] 13X molecular sieve is a synthetically produced porous aluminosilicate crystal, belonging to the sodium-type molecular sieve with an X-type crystal structure. Its chemical formula is typically represented as Na₂O·Al₂O₂·XSiO₂·(6-7)H₂O (silicon-to-aluminum ratio (SiO₂ / Al₂O₃) is approximately 2.4–3.0). The effective pore size is approximately 10 Å (1.0 nm).

[0096] "Same bed volume" refers to the fact that the physical volume of different adsorbents (such as NH2-ZIF-8 in Example 1 and 13X molecular sieve in Comparative Example 1) packed in the adsorption tower is equal, meaning that the space volume occupied by the adsorbent after packing is the same. In this invention, the total packing height of NH2-ZIF-8 in Example 1 is 1500 mm, and the tower inner diameter is 150 mm, resulting in a bed volume of approximately 26.5 L. To maintain the same gas residence time and space velocity conditions, Comparative Example 1 also requires 13X molecular sieve to be packed to the same volume of 26.5 L (due to the different packing densities, the required mass is different: approximately 12.5 kg for NH2-ZIF-8 and approximately 17.2 kg for 13X molecular sieve). This eliminates the influence of bed volume differences on adsorption performance, ensuring that the comparison results truly reflect the quality of the adsorbent material itself.

[0097] Performance Analysis: Comparative Example 1 used conventional 13X molecular sieve as the adsorbent, without involving any MOF materials or amine functionalization. Its BF3 dynamic adsorption capacity was only 0.72 mmol / g (see Appendix). Figure 3 The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption capacity was lower than that of Example 1 (1.85 mmol / g). The adsorption selectivity was only 5.2, which could not effectively distinguish between BF3 and B2H6. The decomposition rate of diborane was as high as 1.25%, which may be due to the irreversible decomposition of diborane catalyzed by acidic sites on the surface of the 13X molecular sieve. After 10 cycles, the adsorption capacity retention rate was only 68.3%, indicating poor regeneration performance. The residual concentration of BF3 at the outlet was as high as ≤8.2 ppmv, which could not meet the purity requirements for electronic-grade diborane. All performance indicators of Comparative Example 1 were significantly inferior to those of Example 1, confirming the necessity of the "amine-functionalized ZIF-8" of this invention.

[0098] Comparative Example 2 The same adsorption tower equipment structure and operating parameters as in Example 1 were used, but the adsorbent used was unmodified ZIF-8 raw powder (purchased from Sigma-Aldrich, particle size 300 nm, specific surface area 1650 m² / g), with a loading of 12.5 kg, and no KH-550 amine grafting treatment was performed. The ZIF-8 raw powder was vacuum dried at 120°C for 12 hours before use. The regeneration operation was the same as in Example 1.

[0099] Performance analysis: The dynamic adsorption capacity of BF3 in Comparative Example 2 was 0.91 mmol / g (see Appendix). Figure 3 The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption capacity was only 49% of that in Example 1, which is attributed to the lack of Lewis acid-base interaction between the amine group and BF3, relying solely on physical adsorption through the ZIF-8 channels and weak coordination. The adsorption selectivity was 7.8, lower than the 18.5 in Example 1, indicating that without the amine group, BF3 has no significant advantage in adsorption competition with B2H6 in the ZIF-8 channels. (Note: The last sentence appears to be incomplete and possibly refers to diborane.) The decomposition rate was 0.15%, slightly higher than 0.08% in Example 1. This may be because there are a few defect sites on the surface of the ZIF-8 raw powder, and the amine grafting in Example 1 may have partially covered these active sites, further inhibiting decomposition. After 10 cycles, the adsorption capacity retention rate was 85.6%, lower than 92.5% in Example 1. This may be because the pore structure of ZIF-8 without amine protection may partially collapse or impurities may accumulate after multiple regenerations. The residual concentration of BF3 at the outlet was ≤3.5 ppmv, which cannot meet the requirement of ≤1 ppmv. In summary, Comparative Example 2 demonstrates that although ZIF-8 without amine functionalization has good stability to diborane, its selective adsorption capacity for BF3 is severely insufficient, making it unable to achieve deep purification. This highlights the crucial role of the amine functionalization step.

[0100] Comparative Example 3 The same preparation method as in Example 1 was used, but the amount of KH-550 was adjusted to 0.10 times the mass of ZIF-8 (i.e., 1.25 kg), the reaction time was shortened to 6 hours, and other conditions remained unchanged, to obtain an NH2-ZIF-8 composite adsorbent with low surface amine grafting amount (denoted as NH2-ZIF-8-L). The adsorption tower filling and operating parameters were exactly the same as in Example 1 to verify the performance difference when the amine grafting amount was lower than the range of the present invention.

[0101] Performance analysis: The dynamic adsorption capacity of BF3 in Comparative Example 3 was 1.23 mmol / g (see Appendix). Figure 3The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption capacity was only 66% of that in Example 1, which is expected to be due to insufficient grafting, resulting in an insufficient number of effective adsorption sites on the surface. The adsorption selectivity was 12.1, lower than 18.5 in Example 1. The reason for this is that although the low-density amine groups can provide a certain degree of specific recognition ability, they cannot form a continuous and efficient adsorption interface. The decomposition rate of diborane was 0.10%, slightly higher than 0.08% in Example 1, possibly because the unreacted ZIF-8 surface defect sites were not completely covered. The adsorption capacity retention rate after 10 cycles was 88.5%, lower than 92.5% in Example 1, indicating that the bonding stability between the amine groups and ZIF-8 may be slightly worse under low grafting. The residual concentration of BF3 at the outlet was ≤1.8 ppmv, which failed to meet the requirement of ≤1 ppmv for electronic-grade diborane. In summary, Comparative Example 3 demonstrates that when the amount of amine grafting is lower than the lower limit of 2.0 mmol / g specified in this invention, even using the same ZIF-8 matrix and grafting method, a deep purification effect cannot be achieved, thus verifying the necessity of improving the control of amine grafting amount.

[0102] Comparative Example 4 This comparative example is used to verify the advantages of the nano-sized ZIF-8 (200-500 nm) selected in this invention in terms of diffusion performance compared to the micron-sized ZIF-8. This comparative example is compared with Comparative Example 2 (ZIF-8 raw powder, particle size 300 nm, without amino treatment). Both are without amino functionalization, and the only difference is the particle size.

[0103] The same adsorption tower equipment structure and operating parameters as Comparative Example 2 were used (adsorption temperature -25℃, adsorption pressure 0.5MPa, gas space velocity 100h⁻¹). -1 The adsorbent used was large-particle ZIF-8 raw powder (particle size 5-10 μm, specific surface area approximately 1200 m² / g), without any amination functionalization. To maintain the same bed volume (26.5 L), the loading amount was calculated to be 12.0 kg based on its bulk density (approximately 0.45 g / cm³). It was vacuum dried at 120℃ for 12 hours before use. The regeneration operation was the same as in Comparative Example 2 (nitrogen purging at 80 L / min for 30 minutes). Performance Analysis: Comparative Example 4 used large-particle-size (5–10 μm) ZIF-8 raw powder, and like Comparative Example 2 (300 nm ZIF-8 raw powder), it had no ammonia treatment, differing only in particle size. The dynamic adsorption capacity of BF3 in Comparative Example 4 was only 0.62 mmol / g (see Appendix). Figure 3The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The dynamic adsorption capacity is significantly lower than that of Comparative Example 2 (0.91 mmol / g, a decrease of 32%). The adsorption selectivity is 6.5, slightly lower than 7.8 of Comparative Example 2. The diborane decomposition rate is 0.18%, slightly higher than 0.15% of Comparative Example 2. The retention rate after 10 cycles is 83.2%, lower than 85.6% of Comparative Example 2. The residual BF3 concentration at the outlet is ≤5.6 ppmv, inferior to ≤3.5 ppmv of Comparative Example 2. Even using the same ZIF-8 material, if the particle size increases from 300 nm to 5–10 μm, it can be inferred that the diffusion path of gas molecules inside the adsorbent is significantly prolonged, leading to a decrease in kinetic performance, a reduction in adsorption capacity, and earlier breakthrough. This, conversely, verifies the key role of using nanoscale ZIF-8 (200–500 nm) in solving the problem of "high microporous diffusion resistance" in this invention. Meanwhile, the performance of Comparative Example 4 was far inferior to that of Example 1 (NH2-ZIF-8, 300nm), indicating that the synergistic effect of "small particle size + amino functionalization" produced a better result.

[0104] Comparative Example 5 This comparative example is used to verify the necessity of choosing ZIF-8 instead of other types of MOF in this invention. Compared with Comparative Example 2 (ZIF-8 raw powder, particle size 300nm, without amino treatment), both are without amino functionalization, the only difference being the MOF type (ZIF-8 vs. MOF-74-Co). The same adsorption tower structure and operating parameters as Comparative Example 2 were used. The adsorbent was MOF-74-Co (CAS No.: 871362-62-6, particle size 1–5 μm, specific surface area ≥1200 m² / g), without any amination functionalization. To maintain the same bed volume (26.5 L), the loading amount was calculated to be 12.0 kg based on its bulk density (approximately 0.45 g / cm³). The adsorbent was vacuum dried at 150°C for 6 hours before use. The regeneration operation was the same as in Example 1.

[0105] Performance Analysis: Comparative Example 5 used MOF-74-Co, and like Comparative Example 2 (ZIF-8 raw powder), it had no ammonia treatment, differing only in the MOF type. The dynamic adsorption capacity of BF3 in Comparative Example 5 was 1.05 mmol / g (see Appendix). Figure 3The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption capacity is slightly higher than that of Comparative Example 2 (0.91 mmol / g) but significantly lower than that of Example 1 (1.85 mmol / g). The adsorption selectivity is only 2.8, lower than that of Comparative Example 2 (7.8), which is attributed to MOF-74-Co's inability to effectively distinguish between BF3 and B2H6. The decomposition rate of diborane is as high as 0.62% (compared to only 0.15% in Comparative Example 2), which is expected to be due to Co. 2+ Site-catalyzed irreversible decomposition of diborane was observed; after 10 cycles, the retention rate was only 65.4%, lower than the 85.6% of Comparative Example 2, which was attributed to poor regeneration performance; the residual BF3 concentration at the outlet was ≤4.2 ppmv, inferior to ≤3.5 ppmv of Comparative Example 2, and significantly higher than ≤0.5 ppmv of Example 1. Comparative Example 5 demonstrates that even though MOF-74-Co has an extremely high static adsorption capacity in pure BF3 (e.g., 7.3 mmol / g reported in Comparative Document 1), its selectivity, stability, and regeneration performance are significantly inferior to ZIF-8 in actual separation scenarios involving diborane / BF3 mixed gases. This, conversely, verifies the necessity of choosing ZIF-8 instead of other MOFs (such as MOF-74-Co) in this invention. Furthermore, the inferior performance of Comparative Example 5 compared to Example 1 (NH2-ZIF-8) further illustrates that the combination of "ZIF-8 + amino functionalization" produced unexpected technical effects.

[0106] Comparative Example 6 The same adsorption tower equipment structure and operating parameters as in Example 1 (adsorption temperature -25℃, adsorption pressure 0.5MPa, gas space velocity 100h) were used. -1 The adsorption cycle is 48 hours. The adsorbent used is granular activated carbon (purchased from Sinopharm Chemical Reagent Co., Ltd., coconut shell based, particle size 1-2 mm, specific surface area of ​​about 1000 m² / g, average pore size of about 2 nm, and bulk density of about 0.50 g / cm³). 3 To maintain the same bed volume (26.5L), the activated carbon loading was calculated to be 13.25kg based on its bulk density. The activated carbon was dried and activated at 150°C for 4 hours before use. The regeneration procedure was the same as in Example 1 (nitrogen purging at 80L / min for 30 minutes).

[0107] Performance analysis: The dynamic adsorption capacity of BF3 in Comparative Example 6 was only 0.55 mmol / g (see Appendix). Figure 3The adsorption breakthrough curves visually demonstrate the differences in dynamic adsorption performance of different adsorbents for BF3 under the same conditions. The further to the right the curve (the longer the breakthrough time), the greater the dynamic adsorption capacity. The adsorption capacity was lower than 1.85 mmol / g in Example 1. The adsorption selectivity was 2.5, lower than 18.5 in Example 1, indicating that activated carbon could hardly distinguish between BF3 and B2H6. Because oxygen-containing functional groups and metallic impurities on the activated carbon surface catalyze the disproportionation decomposition of diborane, the diborane decomposition rate was as high as 1.8% (only 0.08% in Example 1), leading to rapid deactivation of the adsorbent and product contamination. Due to the accumulation of decomposition products in the pores and the difficulty in desorbing the strong adsorption of BF3, the adsorption capacity retention rate after 10 cycles was only 55% (92.5% in Example 1), indicating poor regeneration performance. The residual concentration of BF3 at the outlet was ≤12 ppmv, far exceeding the requirement of ≤1 ppmv for electronic-grade diborane. Activated carbon is an amorphous porous carbon material with abundant surface functional groups (carboxyl groups, phenolic hydroxyl groups, lactone groups, etc.) but lacks chemical sites that have specific recognition ability for BF3. Adsorption mainly relies on physical pore retention, so the adsorption capacity is low.

[0108] Main experimental methods: BF3 dynamic adsorption capacity determination: The fixed-bed breakthrough method was used. 10 g of adsorbent was packed into a micro-adsorption tube with an inner diameter of 15 mm and a length of 300 mm. A simulated gas containing 1.0 vol% BF3 in diborane (equilibrium gas was diborane) was introduced at -25℃ and 0.5 MPa at a gas hourly space velocity (GHSV) of 100 h⁻¹. -1 The concentration of BF3 in the outlet gas was detected online using Fourier transform infrared spectroscopy (FTIR), and the (C / C0) transmittance curve as a function of time was plotted (see Appendix). Figure 3 The dynamic adsorption capacity per unit mass of adsorbent (in millimoles of BF3 adsorbed per gram of adsorbent, mmol / g) is calculated by integrating the area under the curve.

[0109] Determination of diborane decomposition rate: Gas chromatography was used. Diborane standard gas (purity ≥99.99%) was passed into a micro-adsorption tube containing 10g of adsorbent at an adsorption temperature of -25℃, with a gas space velocity of 100 h⁻¹. -1 The residence time was 30 minutes. The outlet gas was collected and analyzed using a gas chromatograph (equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD)) for the decomposition products of diborane (mainly B4H). 10 Calculate the decomposition rate of diborane (including high-boranes such as B5H9).

[0110] Regeneration performance test: The adsorbent was subjected to 10 complete adsorption-regeneration cycles in the same adsorption tower. Adsorption conditions: -25℃, 0.5MPa, space velocity 100h⁻¹ -1Regeneration conditions: 80℃, vacuum extraction for 2 hours (vacuum degree ≤100Pa). After each cycle, the dynamic adsorption capacity of BF3 of the adsorbent was determined according to the above method, and the adsorption capacity retention rate (%) after the 10th cycle was calculated.

[0111] Determination of residual BF3 concentration at the outlet: After 48 hours of stable operation in the low-temperature adsorption process, a sample was taken from the gas outlet at the top of the adsorption tower. Fourier transform infrared spectroscopy (FTIR) with a 10cm gas cell was used to measure the concentration at the characteristic absorption peak of BF3 (approximately 1450cm). -1 Quantitative analysis was performed at the outlet gas, and the volume concentration (ppmv) of BF3 in the outlet gas was calculated using the external standard method. The detection limit was 0.1 ppmv.

[0112] Specific surface area determination: Low-temperature static volumetric method with nitrogen adsorption was used (refer to GB / T19587-2017 standard). After vacuum degassing (120℃, 4 hours) to remove moisture and impurities, the samples were placed in the analysis station, and isothermal adsorption-desorption curves were measured at liquid nitrogen temperature (77K) using high-purity nitrogen as the adsorbate. The specific surface area was calculated by fitting the BET equation within the relative pressure range of P / P0 = 0.05 to 0.35.

[0113] The ZIF-8 powder used in this experiment (Chinese name: 2-methylimidazolium zinc salt or zeolite imidazolium ester framework material-8, particle size 200-500 nm, specific surface area ≥1500 m² / g, CAS number: 59061-53-9, C8H) 10N4Zn (molecular weight: 227.5), MOF-74-Co (particle size 1-5 μm, specific surface area ≥1200 m² / g) were purchased from Sigma-Aldrich; 3-aminopropyltriethoxysilane (KH-550, CAS No.: 919-30-2), anhydrous toluene (CAS No.: 108-88-3), anhydrous ethanol (CAS No.: 64-17-5), and 13X molecular sieve (CAS No.: 63231-69-6, particle size 1-2 mm) were all purchased from Sinopharm Chemical Reagent Co., Ltd.; high-purity nitrogen (purity ≥99.999%, CAS No.: 7727-37-9) was purchased from Beijing Praxair Practical Gases Co., Ltd.; oxygen (purity ≥99.99%)... 9% acetic acid (CAS No.: 64-19-7, analytical grade) was used for plasma treatment and purchased from Beijing Beiyang Special Gas Research Institute; acetic acid (CAS No.: 64-19-7, analytical grade) was used for etching treatment and purchased from Sinopharm Chemical Reagent Co., Ltd.; the granular activated carbon was a coconut shell-based product and purchased from Sinopharm Chemical Reagent Co., Ltd.; the zinc source was zinc nitrate hexahydrate (Zn(NO3)2·6H2O, CAS No.: 10196-18-6), the main ligand of the framework was 2-methylimidazole (Hmim, CAS No.: 693-98-1), the amino functional group ligand was 2-aminoimidazole (H2N-Im, CAS No.: 7720-39-0), and the mercapto functional group ligand was 2-mercaptoimidazole (HS-Im, CAS No.: 872-35-5). All the above-mentioned raw materials were commercially available analytical grade or chemically pure reagents. Zinc nitrate hexahydrate and 2-methylimidazole were purchased from Sinopharm Chemical Reagent Co., Ltd., and 2-aminoimidazole and 2-mercaptoimidazole were purchased from Sigma-Aldrich. Sodium formate (CAS No.: 141-53-7) and triethylamine (CAS No.: 121-44-8) were also commercially available analytical grade reagents and were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0114] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0115] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A highly efficient adsorption and separation method for impurities in a borane preparation process, characterized in that, Includes the following steps: S1. Introduce amine and / or thiol functional groups into the ZIF-8 framework to prepare a composite adsorbent; S2, Composite adsorbent packed adsorption tower; S3. The crude borane product gas containing corrosive impurities such as BF3 is passed into the packed adsorption tower for low-temperature adsorption treatment.

2. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 1, characterized in that, Step S1 specifically includes: S1-1, Powder of metal-organic framework material ZIF-8 is used as the ZIF-8 framework and dried; S1-2. The dried ZIF-8 powder undergoes a condensation reaction with KH-550, and 3-aminopropyl (—CH2CH2CH2NH2) is grafted onto the surface of ZIF-8. S1-3. Filter and wash the reaction products to remove unreacted KH-550; S1-4. Vacuum dry the washed product.

3. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 1, characterized in that, Step S1 specifically includes: S1-1. Place ZIF-8 powder in a vacuum drying oven and dry it at 120°C for 12 hours to remove adsorbed water and solvent molecules from the pores. S1-2. Mix the dried ZIF-8 powder with KH-550 at a mass ratio of 1:0.15 to 0.30, add anhydrous toluene as a dispersant, and the mass-volume ratio of ZIF-8 powder to anhydrous toluene is 1g:15 to 25mL. Under nitrogen protection, reflux at 80°C for 12 to 24 hours. S1-3. After the reaction is complete, filter and collect the solid product. Wash it three times each with anhydrous ethanol and deionized water to remove unreacted KH-550. S1-4. Place the washed product in a vacuum drying oven and dry it under vacuum at 60°C for 8 hours to obtain the amino-functionalized ZIF-8 composite material.

4. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 3, characterized in that, In step S1-1, the particle size of ZIF-8 powder is 200-500 nm and the specific surface area is ≥1500 m² / g; after vacuum drying in step S1-4, a composite adsorbent with an amine (NH2-) grafting amount of 2.0-3.5 mmol / g is obtained.

5. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 1, characterized in that, The adsorption tower in step S2 is a vertical fixed-bed adsorption tower. The adsorption tower is equipped with multiple layers of support sieve plates inside, and the composite adsorbent is filled in layers between each layer of sieve plates. The adsorption tower is equipped with a vacuum insulation jacket outside, and the jacket is filled with aerogel insulation material. A gas inlet distributor is installed at the top of the adsorption tower. The adsorption tower is made of 316L stainless steel, with an inner diameter of 150mm and a height of 2000mm. The adsorption tower is equipped with three layers of supporting sieve plates with a sieve aperture of 0.3mm and a spacing of 600mm between adjacent sieve plates. The composite adsorbent is filled to a height of 500mm per layer, with a total filling height of 1500mm. The aerogel insulation material is 50mm thick, and the distributor adopts a ring-shaped porous structure with a pore size of 1mm.

6. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 2, characterized in that, Before step S1-1, there is also a step of increasing the hydroxyl content on the ZIF-8 surface through pretreatment, which is at least one of low-temperature oxygen plasma treatment or acid gas etching treatment.

7. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 1, characterized in that, Step S3 specifically includes: The crude product gas generated from the dry process of diborane containing boron trifluoride (BF3) impurities is passed into a packed adsorption tower for low-temperature adsorption treatment. The operating conditions are as follows: 1) Adsorption temperature: -30℃~-20℃, temperature controlled by a low-temperature refrigerant (liquid nitrogen vapor) circulating within the jacket of the adsorption tower; the refrigerant inlet temperature is -40℃, and the outlet temperature is -30℃; 2) Adsorption pressure: 0.3~0.8MPa (gauge pressure); 3) Gas hourly space velocity: 50~200h⁻¹ -1 ;4) Adsorption cycle: 24 to 72 hours.

8. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 1, characterized in that, It also includes step S4, adsorbent regeneration, specifically including: S4-1. When the concentration of boron trifluoride in the gas at the outlet of the adsorption tower exceeds the set threshold, stop the gas intake and perform adsorbent regeneration. S4-2, Nitrogen purging: High-purity nitrogen is introduced to replace the residual diborane gas in the adsorption tower; S4-3, Desorption by heating: Turn off the nitrogen gas, turn on the heating device of the jacket of the adsorption tower, slowly raise the temperature of the adsorption tower and keep it at the temperature for a period of time, so that the adsorbed boron trifluoride is desorbed from the surface of the composite adsorbent. S4-4, Vacuum extraction: While heating, turn on the vacuum pump connected to the bottom of the adsorption tower to extract the desorbed boron trifluoride gas. S4-5 Cooling: After regeneration, turn off the heating device and purge the adsorption tower with high-purity nitrogen until the temperature inside the tower drops to the adsorption operating temperature. S4-6, Regeneration tail gas treatment: The desorbed boron trifluoride tail gas is treated by an alkaline absorption tower before being discharged.

9. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 8, characterized in that, In step S4-1, the set threshold for boron trifluoride concentration is ≤10ppmv; in step S4-2, high-purity nitrogen gas with a purity ≥99.999% is introduced at a flow rate of 50-100L / min for 30 minutes; in step S4-3, the adsorption tower temperature is slowly raised to 80℃ and maintained at 80℃ for 2 hours; in step S4-4, the vacuum pump connected to the bottom of the adsorption tower is turned on, with a vacuum degree ≤100Pa and an extraction time of 2 hours; in step S4-5, the adsorption operation temperature is -25℃, and the cooling rate is controlled at 2-5℃ / min; in step S4-6, the alkali solution is a 10wt% sodium hydroxide solution.

10. The efficient adsorption and separation method for impurities in a borane preparation process as described in claim 1, characterized in that, The ZIF-8 framework simultaneously incorporates amine and thiol groups, which are embedded in the framework by using 2-aminoimidazole, 2-mercaptoimidazole and 2-methylimidazole as mixed ligands, and co-grown with a zinc source in a one-step solvothermal process.

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