Covalent organic framework material for selective solid-phase adsorption separation and preparation method and application thereof

Abstract

This invention discloses a covalent organic framework material for selective solid-phase adsorption and separation, its preparation method, and its applications. The material is prepared by polycondensation reaction of electron-deficient triazine rings with short-chain linkers such as hydrazine hydrate, forming a layered structure with a high specific surface area of ​​602 m² / g and a concentrated pore size of 2.0 nm to 3.0 nm. This structure exhibits high adsorption capacity (up to 1.0 mg / g), rapid adsorption kinetics, and excellent selectivity for PAHs in organic solutions through strong π-π interactions and pore confinement effects. The preparation process is simple and the conditions are mild. The material has good thermal stability (>300℃), and its performance retention rate is higher than 92% after 5 cycles. When applied to the solid-phase adsorption of PAHs in petroleum products such as lubricating oil and white oil, it effectively eliminates matrix interference, allowing direct analysis without complex purification steps after adsorption. This overcomes the limitations of traditional materials such as silica gel and activated carbon, which have weak adsorption capacity and require cumbersome post-treatment, providing a new high-performance adsorption material solution for the efficient detection of trace PAHs in petroleum products.

Description

Technical Field

[0001] This invention relates to the intersection of the fields of petrochemical analysis and covalent organic framework materials, specifically to a covalent organic framework material for selective solid-phase adsorption separation, its preparation method, and its applications. Background Technology

[0002] The content of polycyclic aromatic hydrocarbons (PAHs) is a key indicator for evaluating the quality and safety of high-end petroleum products, and its detection is of great concern in the industry. Separating and enriching PAHs (trace PAHs) from petroleum products is a crucial pretreatment step to ensure accurate and reliable detection results, and solid-phase extraction is an important method in this process.

[0003] Solid-phase extraction (SPME) has seen rapid development in the separation and detection of polycyclic aromatic hydrocarbons (PAHs) due to its advantages such as high efficiency, low solvent consumption, and ease of automation. Currently, the solid-phase adsorption materials used for the separation and enrichment of PAHs in petroleum products are mainly traditional adsorbents, such as silica gel and activated carbon. For example, the European Union standard EN 16143 describes the use of silica gel for solid-phase extraction of PAHs from rubber-filled oils. The rubber-filled oil is dissolved in pentane and added to a silica gel solid-phase extraction column for adsorption and separation, followed by desorption with cyclohexane. The separated liquid is then purified using a glucose column, ultimately achieving the separation and enrichment of PAHs from the rubber-filled oil. To overcome the shortcomings of traditional materials, researchers have begun to focus on covalent organic frameworks (COFs) with regular pores and high specific surface areas. However, existing COF materials still face the following challenges when applied to the adsorption of PAHs in petroleum products: Firstly, the important hydrophobic interactions for the adsorption of PAHs in conventional water are no longer applicable; secondly, their structural design is usually not optimized for the planar π-conjugation characteristics of PAHs, resulting in insufficient adsorption forces (such as π-π interactions) between the two, which limits the adsorption capacity and selectivity; thirdly, most COF materials lack sufficient adsorption specificity for PAHs when dealing with complex oil matrices, and may still be affected by a large number of matrix components, affecting the enrichment and purification effect, making it difficult to truly eliminate the need for subsequent purification steps.

[0004] In summary, developing a novel solid-phase adsorption material that combines high adsorption capacity, fast adsorption kinetics, excellent selectivity, and good cycling stability to overcome the shortcomings of traditional materials such as silica gel and activated carbon in adsorbing PAHs in petroleum products, such as weak adsorption force, susceptibility to matrix interference, and the need for complex post-processing, is of great technical significance and application demand. Summary of the Invention

[0005] To address the bottlenecks faced by traditional adsorption materials in the separation and enrichment of polycyclic aromatic hydrocarbons (PAHs) in petroleum products, this invention provides a novel solution: a covalent organic framework material based on electron-deficient triazine units. This material, through its unique chemical and pore structure, can generate strong and specific interactions with PAH molecules, thereby effectively repelling interference from the petroleum matrix while ensuring high adsorption capacity. This invention also includes a simple preparation method for this material and its application as a solid-phase adsorbent, ultimately achieving efficient and selective separation and enrichment of PAHs without the need for complex purification processes.

[0006] Specifically, the first aspect of the present invention provides a covalent organic framework material for selective solid-phase adsorption separation (for selective adsorption of polycyclic aromatic hydrocarbons in petroleum products), which has a repeating unit structure as shown in general formula I:

[0007]

[0008] I In general formula I, Ar is a polyvalent aromatic group containing at least one 1,3,5-triazine ring; more preferably, the Ar group is 2,4,6-tris(substituted phenoxy)-1,3,5-triazine, wherein the three phenoxy groups can be substituted at the para (4-position) and the choice of each substituent is independent of each other; the substituents are hydrogen, C1–C2 alkyl (such as methyl, ethyl), or halogen (such as fluorine, chlorine). For example, the substituent for the phenoxy group at the 2-position can be hydrogen, the 4-position can be methyl, and the 6-position can be fluorine. Such mixed substitution structures can still maintain the C3 symmetry and rigid planar configuration of the molecule, which is beneficial for forming a highly ordered porous structure. In particular, when all substituents are hydrogen, i.e., Ar is 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine, it is the most preferred embodiment of the present invention.

[0009] X is a divalent linker, selected from -NH-NH- or dearoyl group; preferably -NH-NH-.

[0010] Preferably, the covalent organic framework material has electron-deficient triazine units as building blocks; its X-ray powder diffraction pattern shows at least one characteristic diffraction peak in the range of 2θ = 3~7° (e.g., Figure 1 (As shown). The material is a two-dimensional layered crystalline covalent organic framework with a specific surface area ≥500 m². 2 / g, more preferably 500~800 m 2 / g, with a pore size distribution concentrated in the range of 2.0~4.0 nm; more preferably 2.0~3.0 nm.

[0011] The covalent organic framework material described above is prepared by polyaldehyde monomers containing electron-deficient aromatic rings and short-chain linkers through a polycondensation reaction. This material exhibits a higher adsorption capacity for polycyclic aromatic hydrocarbons (PAHs) in a petroleum matrix than traditional silica gel adsorbents; for example, under the same testing conditions, its adsorption capacity for benzo[a]pyrene can reach at least 0.23 mg / g, while the adsorption capacity of commercial silica gel is typically below 0.1 mg / g. After five cycles of use, the performance retention rate of this covalent organic framework material is higher than 92%.

[0012] Preferably, the electron-deficient aromatic ring is a 1,3,5-triazine ring or a derivative thereof.

[0013] More preferably, the short-chain linker is selected from hydrazine or hydrazine hydrate, with hydrazine hydrate being the most preferred.

[0014] More preferably, when the short-chain linker is hydrazine hydrate, the polyaldehyde monomer containing the 1,3,5-triazine ring is tris(4-formylphenoxy)-1,3,5-triazine.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned covalent organic framework material. The method includes the following steps: S1: Mix the polyaldehyde monomer, the short-chain linker, the solvent, and the acid; S2: After degassing and sealing the mixture, carry out a solvothermal reaction at 100℃~150℃; S3: Collect the solid generated by the reaction, wash, purify and dry it to obtain the covalent organic framework material.

[0016] Preferably, in S1, the molar ratio of the polyaldehyde monomer to the short-chain linker is 1:(1~3), and more preferably 1:2; The amount of solvent used can be the amount required to fully dissolve the reactant monomer and form a homogeneous solution or dispersion, for example, 10 mL to 50 mL of solvent per millimole of polyaldehyde monomer.

[0017] Preferably, the solvent in S1 can be any organic solvent capable of dissolving the reactant monomers. The solvent is preferably a mixture of a polar solvent and a non-polar solvent, such as, but not limited to, mixtures of alkane / ether, halogenated hydrocarbon / alcohol, halogenated hydrocarbon / nitrile, halogenated hydrocarbon / alkane, etc. More preferably, mixtures of tricresylbenzene / dioxane, o-dichlorobenzene / n-butanol, o-dichlorobenzene / acetonitrile, or o-dichlorobenzene / petroleum ether in volume ratios can be used. Even more preferably, the volume ratio of the polar solvent to the non-polar solvent in the mixture is 1:5 to 5:1, preferably 1:2 to 2:1.

[0018] Furthermore, in S1, the acid is an organic acid, preferably a weak acid, such as acetic acid, benzoic acid, p-toluenesulfonic acid, etc.

[0019] Furthermore, in S1, the amount of acid used is 8 to 15 times, preferably 10 to 12 times, the molar amount of the polyaldehyde monomer.

[0020] Furthermore, in S1, ultrasonic-assisted mixing may be employed. And / or, in S2, the mixture may be rapidly frozen at a liquid nitrogen temperature (e.g., 77 K) before degassing.

[0021] Furthermore, in S2, the solvothermal reaction lasts for 48 h to 96 h; Furthermore, in S3, purification can be carried out by Soxhlet extraction, and the extraction solvent can be selected from one or a mixture of acetone, tetrahydrofuran, methanol, and petroleum ether.

[0022] Thirdly, the present invention provides the application of the above-mentioned covalent organic framework material in the solid-phase extraction and adsorption separation of polycyclic aromatic hydrocarbons in petroleum products. Preferably, the petroleum products include lubricating oil or white oil.

[0023] Furthermore, the application includes: contacting the material as an adsorbent with petroleum products containing polycyclic aromatic hydrocarbons (PAHs), and eluting and analyzing PAHs without purification steps after adsorption, which significantly improves analytical efficiency and accuracy.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) The covalent organic framework material described in this invention uses triazine structure as core group. These structures, as electron-deficient planes, promote π-π interaction with the planar structure of polycyclic aromatic hydrocarbons, thereby laying the foundation for improving adsorption capacity.

[0025] (2) The covalent organic framework material described in this invention uses short chains such as hydrazine hydrate as linking groups. These short-chain linking groups theoretically achieve a more superior specific surface area, promoting the adsorption process and improving adsorption capacity.

[0026] (3) The covalent organic framework material described in this invention is simple to synthesize and has excellent chemical and thermal stability. It can maintain its adsorption performance even after repeated use, and has excellent circular economy.

[0027] (4) The covalent organic framework material of the present invention is prepared by using widely available and abundant light elements to construct the covalent organic framework material, which reduces the dependence on scarce natural resources and conforms to the concept of green chemistry.

[0028] (5) The adsorption process conforms to the pseudo-second-order kinetic model, indicating that it is dominated by chemical adsorption, thus having the characteristic of rapidly reaching adsorption equilibrium and improving separation efficiency.

[0029] (6) The covalent organic framework material described in this invention is applied to the solid-phase adsorption separation of polycyclic aromatic hydrocarbons in petroleum products, which breaks through the limitations of using silica gel and activated carbon materials in the prior art. Through structural design, it realizes the adsorption separation process mainly based on chemical adsorption, which is of great significance for the development of high-performance adsorption materials for polycyclic aromatic hydrocarbons in petroleum products. Attached Figure Description

[0030] Figure 1 This is the XRD pattern of a covalent organic framework material as described in Embodiment 1 of the present invention.

[0031] Figure 2 This is the N2 adsorption-desorption curve of a covalent organic framework material as described in Example 1 of this invention.

[0032] Figure 3 A pore size distribution curve of a covalent organic framework material as described in Embodiment 1 of the present invention.

[0033] Figure 4 Thermogravimetric curve of a covalent organic framework material as described in Example 2 of this invention.

[0034] Figure 5 The adsorption curve of polycyclic aromatic hydrocarbons in a covalent organic framework material as described in Example 1 of this invention.

[0035] Figure 6 The test curve for the repeated use of a covalent organic framework material as described in Example 1 of this invention.

[0036] Figure 7 This is the ultraviolet spectrum of the desorption solution after the material of Example 1 of the present invention adsorbs polycyclic aromatic hydrocarbons. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the technical solution and beneficial effects of the present invention. It should be understood that the following embodiments are only for illustrative purposes and are not intended to limit the scope of protection of the present invention.

[0038] Unless otherwise expressly stated, all reagents, raw materials, and instruments used in this invention are commercially available conventional products, and their use and processing methods follow standard operating procedures in the art or the instructions provided by the supplier. Where specific techniques or conditions are not specified in the embodiments, conventional techniques or conditions in the art can be referred to, or the relevant product instructions can be followed.

[0039] Example 1 Tris(4-formylphenoxy)-1,3,5-triazine (0.05 mmol), hydrazine hydrate (0.1 mmol), mesitylene / dioxane (1.5 mL, V / V = 2 / 1), and acetic acid (0.6 mmol) were added to a high-temperature resistant glass tube. The mixture was sonicated for 10 min. The tube was rapidly frozen at 77 K and degassed by a three-stage thawing cycle using a refrigeration pump, then sealed. The tube was heated to 120 °C and held for 3 days. A pale yellow precipitate was formed, collected by centrifugation, and washed with acetone (4.5 mL). The powder was purified by Soxhlet extraction and dried under vacuum at 120 °C for 12 h to obtain a pale yellow powder (yield 76%).

[0040] Example 2 Tris(4-formylphenoxy)-1,3,5-triazine (0.05 mmol), hydrazine hydrate (0.1 mmol), o-dichlorobenzene / butanol (1.5 mL, V / V = 2 / 1), and benzoic acid (0.6 mmol) were added to a high-temperature resistant glass tube. The mixture was sonicated for 10 min. The tube was rapidly frozen at 77 K and degassed by a three-stage thawing cycle using a refrigeration pump, then sealed. The tube was heated to 120 °C and held for 3 days. A pale yellow precipitate was formed, collected by centrifugation, and washed with acetone. The powder was purified by Soxhlet extraction and then dried under vacuum at 120 °C for 12 h to obtain a pale yellow powder (yield 68%).

[0041] Example 3 In Example 1, the powder sample was tested using XRD. The X-ray powder diffraction pattern was measured at 298 K, with a scanning range of 2°–40° and a scanning speed of 5° per minute. The results are as follows: Figure 1 As shown, the strongest diffraction peak appears at 3.24°, while a relatively weaker diffraction peak appears at 5.88°. These sharp diffraction peaks indicate the successful synthesis of a highly crystalline, structurally ordered covalent organic framework material.

[0042] Example 4 The sample in Example 1 was tested using an ASAP 2460 physical adsorption analyzer from McMurray Technology, Inc. After degassing at 120°C for 24 hours, the sample was tested at -196°C. o Isothermal adsorption-desorption experiments of N2 were conducted using C. Specific surface area, pore volume, and average pore size were calculated according to the BET equation, and pore analysis was performed using a DFT model. Results are as follows: Figure 2 , Figure 3 As shown. The specific surface area of ​​Example 1 is 602 m². 2 / g, with pores concentrated in the range of 2.0nm~3.0nm, is conducive to achieving size-selective adsorption, thereby synergistically achieving high adsorption capacity and high selectivity.

[0043] Example 5 The powder sample from Example 2 was tested using a NETZSCH 5 thermogravimetric analyzer under a nitrogen atmosphere. The test temperature ranged from room temperature to 700°C, with a heating rate of 10°C / min. The results are as follows: Figure 4 As shown, the sample exhibits no significant weight loss below 300℃, demonstrating good thermal stability. This provides crucial assurance for its reliability, reusability (such as thermal desorption regeneration), and long-term service performance in practical applications.

[0044] Example 6 Two mg of the material from Example 1 was added to 1 mL of a petroleum product containing benzo[a]pyrene (initial concentration 3.53 mg / L), and adsorption was performed at ambient temperature with shaking at 1200 rpm. The adsorption capacity at different adsorption times was tested as follows: Figure 5 As shown in the figure, the maximum adsorption capacity was 1 mg / g, and the adsorption equilibrium time was 60 min. The equilibrium adsorption capacity was significantly higher than that of traditional materials (see Comparative Example 2), demonstrating its advantage of high adsorption capacity.

[0045] Example 7 The adsorbed material from Example 1 was subjected to Soxhlet extraction for 2 hours, vacuum dried at 120°C for 6 hours, and the process was repeated 5 times. The amount of benzo[a]pyrene adsorbed on the petroleum product was then tested, and the results are as follows: Figure 6 As shown, the data indicates that the adsorption retention rate is higher than 92.6% during repeated testing, effectively demonstrating the material's excellent reusability. The excellent cycle stability (performance retention rate >92% after 5 cycles) directly proves that the material of this invention possesses a robust chemical structure and physical stability. It exhibits outstanding circular economy, aligning with the concept of green and sustainable applications.

[0046] Comparative Example 1 After activation, the activated carbon adsorbent material, under the same experimental conditions as in Example 7, showed a color change in the test solution after repeated use, and its absorbance was observed to be enhanced by ultraviolet-visible spectroscopy.

[0047] Example 8 The adsorption kinetic data from Example 6 were fitted using pseudo-first-order and pseudo-second-order kinetic models, respectively, and the results are shown in Table 1. The correlation coefficient of the pseudo-second-order kinetic model was much higher than that of the pseudo-first-order model, and its calculated equilibrium adsorption capacity (0.99 mg / g) was in high agreement with the experimentally measured value (1.00 mg / g). This indicates that the adsorption process is more consistent with the pseudo-second-order kinetic model, and its rate-controlling step is not physical diffusion, but is dominated by the chemical interaction between the active sites on the adsorbent surface and the adsorbate. This result is consistent with the structural design of the material of this invention: the strong π-framework electron interaction generated between the electron-deficient triazine plane and the electron-rich plane of the polycyclic aromatic hydrocarbon in the COF framework is the key chemical force that dominates this rapid and efficient adsorption process.

[0048] Table 1. Dynamic model parameters of a covalent organic framework material according to an embodiment of the present invention.

[0049] Example 9 Two mg of the material from Example 1 was added to 1 mL of a petroleum product containing benzo[a]pyrene (initial content was 1.38 mg / L). The adsorption was carried out at 1200 rpm under ambient temperature for 60 min, and the adsorption amount was measured to be 0.23 mg / g.

[0050] Example 10 The adsorbent material used in Example 9 was added to 3 mL of cyclohexane and adsorbed by shaking at 1200 rpm at ambient temperature. The desorption time was 120 min. After desorption, the mixture was centrifuged and filtered through a 0.22 μm organic filter membrane to obtain the filtrate. The absorption spectrum of the filtrate was measured by ultraviolet spectrophotometer. It was found that the maximum absorption peak was at 381 nm, which matched the absorption peak of benzo[a]pyrene. The results are as follows. Figure 7 As shown, this invention demonstrates that the material exhibits excellent selective adsorption capacity for polycyclic aromatic hydrocarbons (PAHs), effectively rejecting interference from matrices such as saturated hydrocarbons and monocyclic aromatic hydrocarbons present in large quantities in petroleum products. This achieves the core advantage of allowing direct instrumental analysis after adsorption without the need for complex purification steps.

[0051] Comparative Example 2 2mg of commercial silica gel material (particle size 200-300 mesh, specific surface area not less than 400m²) was used. 2 The benzo[a]pyrene (g) was added to 1 mL of petroleum product containing benzo[a]pyrene (initial content was 1.38 mg / L). The adsorption was carried out at 1200 rpm under ambient temperature for 60 min. The adsorption amount was measured to be 0.07 mg / g.

[0052] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A covalent organic framework material for selective solid-phase adsorption and separation, characterized in that, It has a repeating unit structure as shown in the following general formula I: I In the formula, Ar contains at least one polyvalent aromatic group of a 1,3,5-triazine ring; X is a divalent linker, selected from -NH-NH- or aromaticyl groups.

2. The material according to claim 1, characterized in that, It is prepared by polycondensation reaction of a polyaldehyde monomer containing an electron-deficient aromatic ring and a short-chain linker, wherein the electron-deficient aromatic ring is a 1,3,5-triazine ring or a derivative thereof; and the short-chain linker is selected from hydrazine or hydrazine hydrate.

3. The material according to claim 1, characterized in that, The polyaldehyde monomer containing an electron-deficient aromatic ring is tris(4-formylphenoxy)-1,3,5-triazine.

4. The covalent organic framework material according to any one of claims 1 to 3, characterized in that, The specific surface area is ≥500m² / g, and the pore size is 2~4 nm.

5. The material according to any one of claims 1 to 4, characterized in that, The X-ray diffraction pattern shows at least one characteristic diffraction peak in the range of 2θ = 3 to 7°.

6. A method for preparing the covalent organic framework material according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Mix the polyaldehyde monomer containing an electron-deficient aromatic ring, the short-chain linker, a solvent, and an acid; S2: After degassing and sealing the mixture obtained in step S1, carry out a solvothermal reaction at 100~150℃; S3: Collect the solid generated in step S2, and obtain the final product after washing, purification and drying.

7. The method according to claim 6, characterized in that, The acid in step S1 is an organic acid, and a weak acid; the solvent used in the purification process in step S3 is selected from one or a mixture of acetone, tetrahydrofuran, methanol, and petroleum ether.

8. The method according to claim 6, characterized in that, The solvent in step S1 is a mixture of polar and non-polar solvents, and the volume ratio of the non-polar solvent to the polar solvent is 1:5 to 5:1; the mixture is selected from one of the following: mesitylene / dioxane, o-dichlorobenzene / butanol, o-dichlorobenzene / acetonitrile, or o-dichlorobenzene / petroleum ether.

9. The application of the covalent organic framework material according to any one of claims 1 to 5 in the solid-phase extraction and adsorption separation of polycyclic aromatic hydrocarbons in petroleum products.

10. The application according to claim 9, characterized in that, The petroleum product is lubricating oil or white oil.

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