A method for preparing a modified zeolite, a functional concrete and a method for preparing the same

Abstract

The application discloses a preparation method of modified zeolite, functional concrete and a preparation method thereof, and belongs to the technical field of building functional materials. The preparation method comprises the following steps: after sequentially performing activation treatment and hole expansion treatment on a zeolite molecular sieve, a pretreated substrate rich in mesopores is obtained; the pretreated substrate is placed in a reactor, inert carrier gas and steam of a hydrophobic modifier are introduced, gradient vapor deposition treatment is performed, washing, drying are performed, and modified zeolite is obtained; and the hydrophobic modifier is a silane containing a methyl group. The modified zeolite prepared by the preparation method has a core-shell structure of 'external hydrophobicity and internal smoothness', the water contact angle can reach more than 110 DEG, the micropore volume retention rate is more than 80%, the pore blockage problem caused by the traditional modification method is solved, and the CO2 adsorption and mineralization efficiency of the zeolite in a high-humidity environment of concrete can be significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of modified zeolite, functional concrete and a preparation method thereof, in particular to a preparation method of gradient vapor deposition modified zeolite with a core-shell structure of "outer hydrophobicity and inner smoothness", a functional concrete and a preparation method thereof, and belongs to the field of building functional materials and carbon capture, utilization and storage (CCUS) technology. BACKGROUND

[0002] The concrete industry is one of the main sources of global carbon emissions. Carbon dioxide (CO2) mineralization sequestration using concrete is an important path to achieve carbon neutrality. LTA-5A type zeolite molecular sieve is considered as an ideal carbon sequestration additive due to its highly matched pore structure with CO2 molecules and abundant Ca 2+ active sites.

[0003] However, there are three major challenges in directly applying zeolite to concrete:

[0004] (1) Competitive adsorption caused by strong hydrophilicity: LTA-5A type zeolite is prone to water absorption. In the high humidity environment of concrete, water molecules will preferentially occupy the active sites in the pore and form a water film to block the pore opening, preventing CO2 from entering.

[0005] (2) "Hydrophobic-pore" contradiction of traditional modification: In order to be hydrophobic, zeolite is often modified by liquid phase silanization. However, in the liquid phase, silane is prone to hydrolysis and condensation to form amorphous polymers, which can completely plug the zeolite pores like "glue", although hydrophobicity is achieved, but the adsorption function is lost.

[0006] (3) Inhomogeneity of large particle modification: For large particle zeolite aggregate of 3-5mm, traditional constant temperature vapor deposition (CVD) is prone to rapid reaction rate, and the modifier is easy to deposit and block at the outer pore of the particle, resulting in unmodified interior or blocked pores, forming a "skin-core" structure.

[0007] Therefore, developing a precise modification technology that can not only impart excellent hydrophobicity to zeolite, but also maximize the retention of its internal micropore channels, is the key to realizing efficient carbon sequestration of concrete. SUMMARY

[0008] In view of the shortcomings of the prior art, the present application aims to provide a preparation method of modified zeolite with excellent hydrophobicity and high pore retention rate; the second purpose of the present application is to provide a functional concrete and a preparation method thereof.

[0009] In order to solve the above technical problems, the technical scheme of the present application is as follows:

[0010] A preparation method of modified zeolite, comprising the following steps:

[0011] S1. After sequentially activating and expanding the pores of the zeolite molecular sieve, a pretreated matrix rich in mesopores is obtained.

[0012] S2. The pretreated matrix is ​​placed in a reactor, and inert carrier gas and vapor of hydrophobic modifier are introduced. Gradient vapor deposition (GVD) is performed, followed by washing and drying to obtain modified zeolite.

[0013] In the gradient vapor deposition process, the deposition is first carried out at 45-55℃ and a partial pressure of 2-4 kPa for 45-75 min; then at 75-85℃ and a partial pressure of 4-6 kPa for 20-40 min; then at 140-160℃ and a partial pressure of 7-9 kPa for 2.5-3.5 h; and finally at 190-210℃ and a partial pressure of 0 (i.e., no hydrophobic modifier vapor is introduced, only inert carrier gas) for 45-75 min.

[0014] The hydrophobic modifier is a silane containing methyl groups.

[0015] Therefore, by first activating and expanding the pores of the zeolite molecular sieve, a pretreated matrix rich in mesopores is obtained, which is ready for subsequent gradient vapor deposition. The mesopores can act as "highways" to significantly reduce the resistance to diffusion of hydrophobic modifiers and CO2 transport in the zeolite molecular sieve. Then, gradient vapor deposition is performed. Specifically, in the low-temperature pre-adsorption stage, a relatively low temperature and partial pressure of the hydrophobic modifier vapor are controlled to allow the hydrophobic modifier molecules to physically adsorb and diffuse onto the surface (inner and outer surfaces) of the zeolite molecular sieve particles, avoiding chemical reactions. In the temperature-increasing adsorption stage, the temperature is increased and the partial pressure of the hydrophobic modifier vapor is raised, allowing more hydrophobic modifier molecules to adsorb and diffuse onto the surface and pores of the zeolite molecular sieve, increasing the adsorption amount. In the intermediate-temperature reaction stage, the temperature and partial pressure of the hydrophobic modifier vapor are further increased to initiate a chemical bonding reaction, where the hydrophobic modifier chemically bonds with surface hydroxyl groups and grafts hydrophobic methyl groups. Due to the uniform spreading in the previous stage, the hydrophobic layer generated at this stage is uniform and close to a monolayer, effectively avoiding pore blockage. In the high-temperature stabilization stage, the temperature is further increased, and the input modifier is stopped, with only an inert carrier gas introduced to promote the rearrangement and densification of the hydrophobic layer, and byproducts (such as HCl) are purged out. Finally, the mixture is washed and dried to obtain the modified zeolite.

[0016] Optionally, in S1, the zeolite molecular sieve is subjected to a step-by-step temperature-increasing activation treatment. The steps of the step-by-step temperature-increasing activation treatment are as follows: first, the zeolite molecular sieve is kept at 110-130℃ for 1-3 hours to remove the physically adsorbed water on the zeolite molecular sieve; then, it is kept at 240-260℃ for 2-4 hours to remove the chemically adsorbed water on the zeolite molecular sieve; then, it is kept at 500-600℃ for 5-7 hours to remove impurities (such as organic impurities) on the zeolite molecular sieve and expose the active sites.

[0017] Optionally, the step-by-step activation treatment can be performed as follows: first, heat to 110-130℃ at a rate of 1-3℃ / min and hold for 1-3 hours; then, heat to 240-260℃ at a rate of 0.5-1.5℃ / min and hold for 2-4 hours; finally, heat to 500-600℃ at a rate of 0.2-0.8℃ / min and hold for 5-7 hours. Controlling the relatively slow heating rate can effectively prevent the zeolite molecular sieve from bursting due to a sudden increase in internal vapor pressure, thus protecting the integrity of the zeolite molecular sieve framework.

[0018] Optionally, in step S1, saturated steam is used to expand the pores of the activated zeolite molecular sieve. Optionally, the pore-expansion treatment is carried out in an autoclave.

[0019] Optionally, the activated zeolite molecular sieve is subjected to pore-expansion treatment for 3-5 hours at 110-130℃ and saturated steam pressure of 0.25-0.35MPa. This process "sculpts" the zeolite molecular sieve by introducing mesopores into its microporous framework.

[0020] Optionally, the activated zeolite molecular sieve is subjected to pore-expansion treatment for 3.5-4.5 hours at 115-125℃ and saturated water vapor pressure of 0.28-0.32MPa.

[0021] Optionally, the zeolite molecular sieve is an LTA type molecular sieve, and more specifically an LTA-5A type molecular sieve; the particle size of the zeolite molecular sieve is 3-5 mm; the pretreated matrix contains mesopores with a pore size of 2-50 nm.

[0022] Optionally, in S2, the hydrophobic modifier is trimethylchlorosilane (TMCS). Optionally, the inert carrier gas is one or more of nitrogen and argon.

[0023] Optionally, in S2, during gradient vapor deposition, deposition is first performed at 48-52℃ with a partial pressure of 2.5-3.5 kPa for 50-70 min; then at 78-82℃ with a partial pressure of 4.5-5.5 kPa for 25-35 min; then at 145-155℃ with a partial pressure of 7.5-8.5 kPa for 2.8-3.2 h; and finally, at 195-205℃ with a partial pressure of 0 kPa for 50-70 min.

[0024] Optionally, in step S2, after washing with an organic solvent, the mixture is filtered and dried by purging with nitrogen at 100-110°C for 3-5 hours. Optionally, the organic solvent is cyclohexane.

[0025] Optionally, in S2, the inert carrier gas is introduced at a rate of 35-65 mL / min, and more specifically, at a rate of 45-55 mL / min.

[0026] Optionally, the modified zeolite has hydrophobic methyl groups grafted onto its surface (inner and outer surfaces) and no polymer clogging of the pores.

[0027] Optionally, the water contact angle of the modified zeolite is ≥110°; further, the micropore volume retention rate of the modified zeolite is ≥80%, and it contains mesoporous mass transfer channels.

[0028] Optionally, the modified zeolite exhibits synergistic carbon fixation characteristics of physical and chemical adsorption: 1) Physical adsorption characteristics: Under conditions of 25℃ and 0-1 bar, the CO2 adsorption isotherm conforms to the characteristics of a type I isotherm, and the CO2 adsorption kinetics conforms to a pseudo-second-order kinetic model (R0). 2 >0.98), indicating that the adsorption rate is controlled by the chemisorption mechanism and is not limited by diffusion. 2) Chemisorption characteristics: In the CO2 temperature-programmed desorption (CO2-TPD) spectrum, it exhibits a dual desorption peak feature, including a main peak at around 300℃ corresponding to the original active site, and a high-temperature shoulder peak at around 500℃ corresponding to the synergistic adsorption site introduced by modification.

[0029] Optionally, the modified zeolite possesses the mineralization function of adsorbing carbon dioxide and catalytically generating calcium carbonate at room temperature and pressure.

[0030] Based on the same inventive concept, the present invention also provides: a functional concrete containing modified zeolite prepared by the preparation method described above.

[0031] Modified zeolite can act as a functional aggregate in functional concrete, giving it good carbon sequestration properties.

[0032] Based on the same inventive concept, the present invention also provides: a method for preparing concrete as described above, wherein, by weight, 160-250 parts of water, 400-450 parts of cement, 100-110 parts of fly ash, 400-420 parts of aggregate, 5-10 parts of foaming agent, 5-10 parts of water-reducing agent, and 50-100 parts of modified zeolite are taken and mixed evenly to obtain the concrete.

[0033] Optionally, the cement is silicate cement.

[0034] Optionally, the aggregate is lightweight aggregate. Optionally, the lightweight aggregate is one or more of ceramsite, pumice, and volcanic slag.

[0035] Optionally, the foaming agent is a protein-based foaming agent; the water-reducing agent is an aminosulfonate high-efficiency water-reducing agent or a melamine-based water-reducing agent, which can be selected according to the specific needs.

[0036] This invention helps to achieve a perfect balance between the functionalization and structural preservation of zeolite molecular sieves by precisely controlling the pretreatment structure and surface reaction kinetics of zeolite molecular sieves.

[0037] The modified zeolite prepared by the method of the present invention has a core-shell structure that is hydrophobic on the outside and unobstructed on the inside, with a water contact angle of over 110° and a micropore volume retention rate of over 80%. This solves the problem of pore blockage caused by traditional modification methods such as liquid-phase silanization, and helps to significantly improve the CO2 adsorption and mineralization efficiency of zeolite in the high humidity environment of concrete.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) The modified zeolite of the present invention has an extremely high pore retention rate: BET test shows that the micropore volume retention rate of the modified zeolite prepared by the present invention is as high as 83.6%, while that of the traditional liquid phase method is only 26.2% and that of the isothermal vapor phase method is 44.3%. This is due to the precise control of reaction kinetics by the pretreatment and gradient vapor phase deposition process of the present invention, which avoids polymer pore blockage.

[0040] (2) The modified zeolite of the present invention has excellent hydrophobic and water-resistant properties. The water contact angle of the modified zeolite is increased to about 114°, which can effectively repel liquid water and prevent it from competing for adsorption.

[0041] (3) Dual enhancement of physical and chemical adsorption: 1) Physical level (channel protection): The mesopores (2-50nm) introduced by the step-by-step pretreatment in this invention act as rapid transport channels for CO2 molecules. Combined with the monolayer hydrophobic membrane constructed by the GVD process, it effectively avoids the competitive occupation of the channels by water molecules, which significantly reduces the physical diffusion resistance of CO2 and makes the adsorption kinetics close to the level of the original zeolite. 2) Chemical level (site synergy): GVD modification not only retains the original Ca in the framework of zeolite molecular sieves, but also2+ Strong Lewis acid sites (corresponding to the 300℃ desorption peak) also induce new high-energy chemisorption sites (corresponding to the 500℃ desorption peak) through the interaction between organic functional groups and the framework. This synergistic effect enables the material to not only "adsorb quickly" but also "lock in firmly," ultimately promoting the chemical mineralization transformation of CO2 into carbonates.

[0042] (4) The modified zeolite of the present invention has a high efficiency in carbon fixation and mineralization. In-situ DRIFTS spectroscopy confirmed that the modified zeolite can be rapidly converted into bicarbonate after adsorbing CO2 and finally mineralized into calcium carbonate. The amount of mineralization products generated is significantly higher than that of the comparative sample. Attached Figure Description

[0043] Figure 1 The XRD patterns are of LTA-5A molecular sieve and the modified zeolites obtained in Example 1 and Comparative Examples 1-2.

[0044] Figure 2 This is a SEM image of LTA-5A molecular sieve.

[0045] Figure 3 This is a SEM image of TMCS@LTA5A-L.

[0046] Figure 4 SEM image of TMCS@LTA5A-V.

[0047] Figure 5 SEM image of TMCS@LTA5A-G.

[0048] Figure 6 Here is an EDS surface scan analysis plot of element C, where, Figure 6 a is the EDS surface scan analysis image of TMCS@LTA5A-L. Figure 6 b is the EDS surface scan analysis plot of TMCS@LTA5A-V. Figure 6 c is the EDS surface scan analysis image of TMCS@LTA5A-G.

[0049] Figure 7 This is the elemental percentage spectrum for Raw-LTA.

[0050] Figure 8 for Figure 6 The elemental percentage spectrum of TMCS@LTA5A-L in region a is shown.

[0051] Figure 9 for Figure 6 The elemental percentage spectrum of TMCS@LTA5A-V in region b.

[0052] Figure 10 for Figure 6The elemental percentage spectrum of TMCS@LTA5A-G in region c.

[0053] Figure 11 Nitrogen adsorption-desorption isotherms for Raw-LTA, LTA-Pretreated, TMCS@LTA5A-G, TMCS@LTA5A-L, and TMCS@LTA5A-V.

[0054] Figure 12 Diagram showing the pore distribution of Raw-LTA, LTA-Pretreated, TMCS@LTA5A-G, and TMCS@LTA5A-V.

[0055] Figure 13 The diagram shows the water droplet morphology and water contact angle on the TMCS@LTA5A-V surface.

[0056] Figure 14 The diagram shows the water droplet morphology and water contact angle on the TMCS@LTA5A-L surface.

[0057] Figure 15 The diagram shows the water droplet morphology and water contact angle on the TMCS@LTA5A-G surface.

[0058] Figure 16 Bar charts showing the left and right water contact angles for Raw-LTA, TMCS@LTA5A-G, TMCS@LTA5A-L, and TMCS@LTA5A-V.

[0059] Figure 17 The in-situ DRIFTS 3D waterfall plot of the carbon fixation process of TMCS@LTA5A-G.

[0060] Figure 18 The final spectra of Raw-LTA, TMCS@LTA5A-G, TMCS@LTA5A-L, and TMCS@LTA5A-V after 6 hours of carbon fixation.

[0061] Figure 19 The graphs show the physical adsorption curves of Raw-LTA, TMCS@LTA5A-G, TMCS@LTA5A-L, and TMCS@LTA5A-V.

[0062] Figure 20 The CO2-TPD spectra are for Raw-LTA, TMCS@LTA5A-G, TMCS@LTA5A-L, and TMCS@LTA5A-V.

[0063] Figure 21 The figure shows the fitted curve of CO2 adsorption kinetics for Raw-LTA.

[0064] Figure 22 The figure shows the fitted curve of CO2 adsorption kinetics for TMCS@LTA5A-V.

[0065] Figure 23 The figure shows the fitted curve of CO2 adsorption kinetics for TMCS@LTA5A-L.

[0066] Figure 24 The figure shows the fitted curve of CO2 adsorption kinetics for TMCS@LTA5A-G. Detailed Implementation

[0067] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0068] Example 1

[0069] The preparation method of the modified zeolite in this embodiment includes the following steps:

[0070] (1) Pretreatment: Take 100g of LTA-5A molecular sieve (Raw-LTA) and place it in a muffle furnace for activation by heating. Specifically, first heat the sieve to 120℃ at a rate of 2℃ / min and hold it at that temperature for 2h; then heat the sieve to 250℃ at a rate of 1℃ / min and hold it at that temperature for 3h; then heat the sieve to 550℃ at a rate of 0.5℃ / min and hold it at that temperature for 6h, and then cool it. Then place it in an autoclave and introduce saturated steam at 120℃ and 0.3MPa for pore expansion treatment for 4h to obtain activated and expanded LTA-5A molecular sieve (LTA-Pretreated).

[0071] The LTA-5A molecular sieve (Raw-LTA) has a particle size of 3-5 mm and a BET specific surface area of ​​152.6 m². 2 / g, with a single-point specific surface area of ​​155.9929 m². 2 / g, total pore volume is 0.127cm³ 3 / g, t-Plot microwell volume is 0.06cm³. 3 / g, the cumulative pore volume of BJH adsorption (1.7-300 nm) is 0.067944 cm⁻¹. 3 / g, micropores (pore size <2nm) contribute more than 80% of the specific surface area and nearly 50% of the pore volume, and are the core adsorption sites; mesopores (pore size 2-50nm) account for about 20%-30%.

[0072] (2) GVD modification: The activated and expanded LTA-5A molecular sieve (LTA-Pretreated) was placed in a quartz tube reactor and purged with N2 (inert carrier gas) at a rate of 50 mL / min to obtain the sample after GVD modification. The GVD modification procedure is as follows: First, deposition was carried out at 50℃, purged with N2, and the partial pressure of TMCS vapor was 3 kPa for 60 min; then deposition was carried out at 80℃, purged with N2, and the partial pressure of TMCS vapor was 5 kPa for 30 min; then deposition was carried out at 150℃, purged with N2, and the partial pressure of TMCS vapor was 8 kPa for 3 h; finally, TMCS was stopped, and only N2 was introduced to purge at 200℃ for 60 min.

[0073] (3) Post-processing: After cooling the GVD modified sample, wash it with cyclohexane at 40°C for 2 hours, filter it, and dry it with nitrogen at 105°C to obtain the modified zeolite (TMCS@LTA5A-G).

[0074] Comparative Example 1: Liquid Phase Method

[0075] Repeat Example 1, except that step (2) of this comparative example is as follows: LTA-5A molecular sieve (LTA-Pretreated) is immersed in a 10% (v / v) hexane solution of TMCS and refluxed at 69°C for 6 hours. The resulting modified zeolite is denoted as TMCS@LTA5A-L.

[0076] Comparative Example 2: Isothermal Gas Phase Method

[0077] Repeat Example 1, except that step (2) of this comparative example is as follows: Under constant temperature of 150°C, saturated TMCS vapor is directly introduced into a reactor containing LTA-5A molecular sieve (LTA-Pretreated) and reacted for 4 hours. The resulting modified zeolite is denoted as TMCS@LTA5A-V.

[0078] Performance testing and analysis:

[0079] (1) Crystal structure characterization: XRD-6000 X-ray diffractometer (Shimadzu, Japan), Cu target, tube voltage 40kV, tube current 30mA, scanning range 10-80°, step size 0.02°.

[0080] See Figure 1 A comparison of the XRD patterns of zeolite before and after modification shows that the crystal structure of the zeolite molecular sieve remains undamaged before and after modification.

[0081] (2) Microscopic morphology and composition characterization: S-4800 type SEM / EDS (Hitachi, Japan), accelerating voltage 15kV, magnification 20-10000 times, elemental surface scan coverage C, Si, O, Al, Ca.

[0082] See Figure 2 and Figure 5 SEM images of the modified zeolite from Example 1 show that its surface is clean and retains a clear cubic crystal outline. See also... Figure 6 c, its EDS surface scan shows that the carbon element is distributed very uniformly and diffusely.

[0083] See Figure 3 SEM images of the modified zeolite in Comparative Example 1 show that its surface is encapsulated by a layer of amorphous polymer "capsules," indicating severe grain agglomeration. (See also...) Figure 6 a. Its EDS surface scan shows that the carbon elements are in a non-uniform aggregated state.

[0084] See Figure 4 The SEM image of the modified zeolite in Comparative Example 2 showed obvious deposition spots at its pore openings, indicating the presence of localized overreaction.

[0085] (3) Pore structure characterization: A BSD-PS2 surface area analyzer (Beijing Bestech) was used. Nitrogen adsorption was performed at 77K, and degassing conditions were 300℃ / 3h. The specific surface area was calculated using the BET method, micropore parameters were analyzed using the t-plot method, and the pore size distribution was fitted using the NLDFT model. Specific results are as follows: Figure 11 , Figure 12 As shown in Table 1.

[0086] Table 1. Texture properties of different zeolite molecular sieves

[0087]

[0088] Among them, S BET S represents the total specific surface area; micro S represents the specific surface area of ​​micropores. ext V represents the external specific surface area; total V represents the total pore volume; micro This indicates the volume of the micropores.

[0089] As shown in Table 1, the specific surface area of ​​LTA-5A molecular sieve (LTA-Pretreated) reaches 142.3 m². 2 / g, with a micropore volume of 0.061cm³. 3 / g. The modified zeolite (TMCS@LTA5A-G) obtained in Example 1 has a specific surface area of ​​127.6 m². 2 / g, with a micropore volume of 0.051cm³. 3 / g. The micropore volume retention rate reached 83.6% (0.051 / 0.061×100%), indicating that the vast majority of the pores were not blocked.

[0090] The specific surface area of ​​TMCS@LTA5A-L obtained in Comparative Example 1 was only 24.3 m². 2 / g, micropore volume is 0.016cm³ 3 / g. The micropore volume retention rate was only 26.2%, indicating that the pores were basically blocked. The specific surface area of ​​TMCS@LTA5A-V obtained in Comparative Example 2 was only 72.1 m². 2 / g, micropore volume is 0.027cm³ 3 / g. The micropore volume retention rate is only 44.2%, which is significantly lower than the micropore volume retention rate of the modified zeolite prepared by the preparation method of this invention.

[0091] (4) Hydrophobicity test equipment and process: JC2000D2W contact angle measuring instrument (Shanghai Zhongchen), using 2μL deionized water droplets, tested at room temperature, 5 different sites were measured for each group of samples, and the average value was taken.

[0092] See Figures 13-16 Water contact angle tests showed that the original zeolite (Raw-LTA) had extremely strong hydrophilicity (contact angle ≈ 0°). The water contact angle of TMCS@LTA5A-L obtained in Comparative Example 1 increased to 118°, effectively improving the hydrophobicity of the zeolite molecular sieve, but at the same time sacrificing the pore openness of the zeolite molecular sieve. The water contact angle of TMCS@LTA5A-V obtained in Comparative Example 2 increased to 109°, but a significant portion of the pores were also blocked. The modified zeolite (TMCS@LTA5A-G) obtained in Example 1 increased the water contact angle to 114°, achieving highly efficient hydrophobicity without sacrificing the pore openness of the zeolite molecular sieve.

[0093] (5) In-situ DRIFTS testing: Nicoleti S50 Fourier transform infrared spectrometer (Thermo Fisher Scientific). Specifically, using the ATR mode of the Nicoleti S50 Fourier transform infrared spectrometer, at 25°C and 30%RH, the sample (e.g., TMCS@LTA5A-G) was placed on the ATR crystal surface, and the spectral range was set to 4000-600 cm⁻¹. -1 Resolution is 4 cm -1 A 5% CO2 / N2 mixed gas was introduced (flow rate 50 mL / min), and spectra were collected every 30 min for at least 6 h. HCO3 was monitored. - (~1674 cm -1 ) and CaCO3 (~1378 cm) -1The changes in the peak were observed, and the carbon fixation efficiency was evaluated by comparing the CaCO3 peak area in the 6-hour spectrum, to demonstrate that the modified zeolite can efficiently mineralize adsorbed CO2 into stable carbonates.

[0094] Mineralization process: See Figure 17 and Figure 18 After CO2 was introduced, bicarbonate (HCO3-) rapidly appeared in the spectrum of the modified zeolite (TMCS@LTA5A-G) obtained in Example 1. - ~1674cm -1 The intermediate peak, over time, reaches ~1378 cm⁻¹. -1 The intensity of the characteristic peak of calcium carbonate (CaCO3) at the reaction site continuously increased. Regarding carbon fixation efficiency, comparing the spectra after 6 hours of reaction, it can be seen that the modified zeolite (TMCS@LTA5A-G) obtained in Example 1 produced the largest calcium carbonate peak area, far exceeding that of Comparative Examples 1 and 2. This directly proves that the modified zeolite obtained in this invention, as a "microreactor," can efficiently convert physically adsorbed CO2 into chemically stable carbonate minerals.

[0095] (6) CO2 adsorption performance test: The physical adsorption isotherm and kinetic curve were tested using an ASAP2460 gas adsorption instrument (American Mack) at 25℃ and 0-1 bar; CO2-TPD test was conducted using an AutoChemII2920 chemical adsorption instrument (adsorption temperature 25℃, heating rate 10℃ / min, termination temperature 700℃).

[0096] Physical adsorption performance analysis (pore accessibility and kinetics):

[0097] 1) Adsorption capacity: CO2 adsorption isotherm tests were conducted under dry conditions at 25℃. See [link to relevant documentation]. Figure 19 The saturated adsorption capacity of Example 1 (TMCS@LTA5A-G) remained at a high level, significantly better than that of Comparative Example 1 (TMCS@LTA5A-L). TMCS@LTA5A-L experienced a precipitous drop in adsorption capacity due to severe pore blockage by the polymer, falling to less than 25% of the original zeolite (Raw-LTA).

[0098] 2) Adsorption kinetics: A pseudo-second-order kinetic model was used to fit the adsorption rate. See [link / reference] Figures 21-24 The results showed that the fitting correlation coefficient R of the modified zeolite in Example 1 was [missing information]. 2The adsorption rate constant is greater than 0.99, and is very close to that of the original zeolite (Raw-LTA). This indicates that the pretreatment of this invention introduces mesoporous fast channels, and the hydrophobic layer formed by GVD modification does not hinder gas diffusion, thus achieving rapid physical transport of CO2 molecules. In contrast, the TMCS@LTA5A-V obtained in Comparative Example 2 exhibits a significantly slower adsorption rate due to increased diffusion resistance caused by pore size contraction.

[0099] Chemisorption performance analysis (active sites and mineralization capacity):

[0100] 1) CO2-TPD (temperature programmed desorption) test: Site retention: see Figure 20 In the TPD spectrum of Example 1 (TMCS@LTA5A-G), a distinct desorption peak appears at approximately 300°C, with an area comparable to that of the original zeolite (Raw-LTA), demonstrating that this invention preserves the original Ca of the zeolite to the maximum extent. 2+ The active site is ineffective if it is not covered by the modifier.

[0101] 2) Enhanced Synergy: More importantly, see [link to relevant documentation] Figure 20 Example 1 (TMCS@LTA5A-G) exhibited a novel high-temperature shoulder peak at approximately 500°C, a feature not present in Comparative Examples 1 and 2. This peak corresponds to a novel composite adsorption site with stronger binding energy, indicating a synergistic chemisorption effect between the gradient deposition layer (hydrophobic layer) and the zeolite framework, enhancing the binding capacity for CO2.

[0102] 3) Comparison results: The TPD signal of TMCS@LTA5A-L obtained in Comparative Example 1 is weak, indicating that its chemical active sites have been largely lost.

[0103] In summary, the modified zeolite prepared by this invention repels water molecules through its "external hydrophobic" properties, ensuring unobstructed physical adsorption channels. Simultaneously, its "internal unobstructed" structure and surface synergistic sites enhance the chemical adsorption and mineralization reactions. This relay mechanism of physical adsorption enrichment and chemical adsorption mineralization enables it to achieve highly efficient carbon fixation in concrete.

[0104] Comparative Example 3

[0105] Example 1 was repeated, except that the GVD modification procedure was as follows: first, deposition was carried out at 80°C, with N2 purging and a TMCS vapor partial pressure of 5 kPa for 90 min; then deposition was carried out at 150°C, with N2 purging and a TMCS vapor partial pressure of 8 kPa for 3 h; finally, TMCS was stopped, and only N2 was introduced, and purging was carried out at 200°C for 60 min.

[0106] The results showed that the micropore volume retention rate decreased to approximately 60% (far lower than the 83.6% in Example 1), the water contact angle was uneven (averaging approximately 95°, with large local variations), the CO2 adsorption capacity decreased by 15%-20%, and the kinetic fit (quasi-secondary model R) was poor. 2 The value <0.95 indicates increased diffusion resistance, and the mineralization efficiency (CaCO3 peak area in the DRIFTS spectrum) is only 70% of that of the complete GVD, resulting in a significant deterioration in carbon fixation performance. A possible reason is that omitting the low-temperature pre-adsorption step prevents TMCS molecules from being fully physically adsorbed and uniformly diffused into the zeolite's internal pores. Instead, a rapid reaction preferentially occurs at the outer pore openings, leading to localized polymer accumulation.

[0107] Comparative Example 4

[0108] Example 1 was repeated, except that the GVD modification procedure was as follows: first, deposition was carried out at 50°C, with N2 purging and a TMCS vapor partial pressure of 3 kPa for 90 min; then, deposition was carried out at 150°C, with N2 purging and a TMCS vapor partial pressure of 8 kPa for 3 h; finally, TMCS was stopped, and only N2 was introduced, and purging was carried out at 200°C for 60 min.

[0109] The results showed that the micropore volume retention rate decreased to about 65%; the water contact angle was about 100°, but it was prone to failure in high humidity environments; the CO2-TPD spectrum showed that the high-temperature shoulder peak (synergistic site at about 500℃) was weakened, and the chemisorption performance was reduced by 20%. The possible reason is that the temperature-raising adsorption stage was omitted, resulting in insufficient TMCS adsorption, incomplete chemical bonding reaction, and incomplete hydrophobic layer coverage.

[0110] Comparative Example 5

[0111] Example 1 was repeated, except that the GVD modification procedure was as follows: first, deposition was carried out at 50°C, with N2 purging and a TMCS vapor partial pressure of 3 kPa for 60 min; then, deposition was carried out at 80°C, with N2 purging and a TMCS vapor partial pressure of 5 kPa for 30 min; and finally, deposition was carried out at 150°C, with N2 purging and a TMCS vapor partial pressure of 8 kPa for 3 h.

[0112] The results showed that the micropore volume retention rate decreased to approximately 55%; the water contact angle was approximately 105°, but the stability was poor (decreasing by 10° after long-term exposure); DRIFTS testing showed a weakened calcium carbonate peak intensity, and the mineralization conversion rate was significantly lower than in Example 1; CO2 adsorption kinetics slowed down, and the synergistic enhancement mechanism (physicochemical adsorption relay) was hindered. A possible reason is that the high-temperature stabilization step was omitted, resulting in insufficient rearrangement and densification of the hydrophobic layer, and residual byproducts (such as HCl) interfering with site activity.

[0113] Comparative Example 6

[0114] Repeat Example 1, except that the heating activation step in step (1) is omitted.

[0115] The results showed that the micropore volume retention rate decreased to about 50%; the water contact angle was about 90°, indicating weak hydrophobicity; the area of ​​the CO2-TPD main peak (300℃) shrank by 15%, and new synergistic sites were missing. A possible reason is that omitting the step-by-step heating activation step resulted in residual physically / chemically adsorbed water and organic impurities on the zeolite surface, failing to expose sufficient active sites, reducing the efficiency of subsequent pore-expanding treatment, and causing insufficient introduction of mesopores (uneven pore size distribution).

[0116] Comparative Example 7

[0117] Repeat Example 1, except that the hole enlargement step in step (1) is omitted.

[0118] The results showed that the micropore volume retention rate decreased to approximately 70%; the water contact angle was approximately 110°, but the internal channels were easily blocked; and the adsorption kinetics fitting indicated diffusion limitation (R0). 2 <0.96); the area of ​​the DRIFTS mineralization peak decreased by 20%; the possible reason is that after omitting the pore-expansion treatment step, the zeolite lacks mesoporous mass transfer channels (2-50nm), which is not conducive to the subsequent GVD modification process, and the CO2 diffusion resistance increases.

[0119] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method for preparing modified zeolite, characterized in that, Includes the following steps: S1. After sequentially activating and expanding the pores of the zeolite molecular sieve, a pretreated matrix rich in mesopores is obtained. S2. The pretreated matrix is ​​placed in a reactor, and inert carrier gas and vapor of hydrophobic modifier are introduced. After gradient vapor deposition, the matrix is ​​washed and dried to obtain modified zeolite. In the gradient vapor deposition process, deposition is first carried out at 45-55℃ and a partial pressure of 2-4 kPa for hydrophobic modifier vapor for 45-75 min; then at 75-85℃ and a partial pressure of 4-6 kPa for 20-40 min; then at 140-160℃ and a partial pressure of 7-9 kPa for 2.5-3.5 h; and finally at 190-210℃ and a partial pressure of 0 for 45-75 min. The hydrophobic modifier is a silane containing methyl groups.

2. The method for preparing modified zeolite according to claim 1, characterized in that, In S1, the zeolite molecular sieve is subjected to a step-by-step temperature-increasing activation treatment. The steps for the step-by-step temperature-increasing activation treatment are as follows: first, the zeolite molecular sieve is kept at 110-130℃ for 1-3 hours, then at 240-260℃ for 2-4 hours, and then at 500-600℃ for 5-7 hours.

3. The method for preparing modified zeolite according to claim 2, characterized in that, The steps for the stepwise temperature-increasing activation treatment are as follows: First, increase the temperature to 110-130℃ at a rate of 1-3℃ / min and hold for 1-3 hours; then increase the temperature to 240-260℃ at a rate of 0.5-1.5℃ / min and hold for 2-4 hours; then increase the temperature to 500-600℃ at a rate of 0.2-0.8℃ / min and hold for 5-7 hours.

4. The method for preparing modified zeolite according to claim 1, characterized in that, In S1, saturated steam is used to expand the pores of the activated zeolite molecular sieve.

5. The method for preparing modified zeolite according to claim 4, characterized in that, The activated zeolite molecular sieve was subjected to pore-expansion treatment for 3-5 hours at 110-130℃ and saturated steam pressure of 0.25-0.35MPa.

6. The method for preparing modified zeolite according to any one of claims 1-5, characterized in that, The zeolite molecular sieve is an LTA type molecular sieve; the particle size of the zeolite molecular sieve is 3-5 mm; the pretreated matrix contains mesopores with a pore size of 2-50 nm.

7. The method for preparing modified zeolite according to any one of claims 1-5, characterized in that, In S2, the hydrophobic modifier is trimethylchlorosilane; and / or, during gradient vapor deposition, deposition is first performed at 48-52°C and a partial pressure of 2.5-3.5 kPa for 50-70 min; then at 78-82°C and a partial pressure of 4.5-5.5 kPa for 25-35 min; then at 145-155°C and a partial pressure of 7.5-8.5 kPa for 2.8-3.2 h; and finally, at 195-205°C and a partial pressure of 0 kPa for 50-70 min.

8. The method for preparing modified zeolite according to any one of claims 1-5, characterized in that, In S2, after washing with an organic solvent, the mixture is filtered and then purged with nitrogen at 100-110℃ for 3-5 hours to dry.

9. A type of functional concrete, characterized in that, The modified zeolite is prepared by the preparation method according to any one of claims 1-8.

10. The method for preparing functional concrete as described in claim 9, characterized in that, By weight, take 160-250 parts water, 400-450 parts cement, 100-110 parts fly ash, 400-420 parts aggregate, 5-10 parts foaming agent, 5-10 parts water-reducing agent, and 50-100 parts modified zeolite, mix them evenly, and you will get the product.

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