A surface-modified alumina adsorbent and its preparation method

Abstract

A surface-modified alumina adsorbent and its preparation method belong to the technical field of adsorption materials. The structure of the adsorbent is a core-shell structure of a rare-earth doped mesoporous alumina core layer and a SiO2-Al2O3 composite shell layer. There is a pH-responsive organic film outside the SiO2-Al2O3 composite shell layer, and the specific surface area is > 300 m 2 / g, and the average pore diameter is 200 nm to 300 nm. In the present invention, a composite template agent is used to construct a mesoporous γ-Al2O3 core layer with hierarchical pores, and La / Zr bimetal doping is combined to form oxygen vacancy defects, significantly improving the adsorption selectivity and structural stability; realizing broad-spectrum and highly efficient adsorption of various targets, breaking through the single-target limitation of traditional materials, and having the advantages of high adsorption capacity, wide pH adaptability and green process.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption materials, and particularly relates to a surface-modified alumina adsorbent and a preparation method thereof. Background Art

[0002] Due to its excellent physical and chemical properties and wide application fields, alumina adsorbent has become an important material in the fields of environmental governance, chemical separation, etc. However, traditional alumina adsorbents still have problems such as low specific surface area, poor adsorption selectivity, and insufficient cyclic stability in practical applications, which limit their further popularization. Existing modification methods (such as silane coupling agent grafting, polymer coating, etc.) can improve the performance to a certain extent, but often have defects such as complex process, high cost, or environmental unfriendliness.

[0003] In Patent CN107008223B, an adsorbent for benzene refining desulfurization with low loading and high dispersion is disclosed. In this patent, metal Ru is firmly assembled on the surface of the alumina carrier through a metasilicic acid polymer, realizing the high dispersion and stability of Ru, and significantly improving the sulfur capacity and service life of the adsorbent. However, in this technical solution, the use of metal Ru increases the material cost, and the metasilicic acid polymer modification process has high requirements for equipment, which may increase the production difficulty and energy consumption. In addition, this adsorbent is mainly aimed at the benzene refining desulfurization scenario, and its application scope is relatively limited, and it is difficult to meet the requirements for treating other pollutants.

[0004] In addition, in Patent CN106215851B, a preparation method of copper reagent-modified nano-alumina is disclosed. In this patent, the surface of nano-alumina is modified with a copper reagent to form an organic molecular film, significantly improving the adsorption performance and selectivity for cadmium ions in water. However, in this technical solution, the modification process of the copper reagent requires the assistance of a surfactant, which may lead to the complication of subsequent treatment steps, increasing the wastewater discharge and environmental burden. In addition, the applicable pH range of this adsorbent is relatively narrow, and the adsorption performance may decrease under extreme pH conditions, which limits its application in complex water environments.

[0005] The above problems indicate that existing surface-modified alumina adsorbents still have certain deficiencies in terms of preparation process, application scope, environmental friendliness, and stability under extreme conditions. Therefore, the present invention proposes a new preparation process for surface-modified alumina adsorbents, aiming to optimize the core-shell structure of the adsorbent through inorganic-organic composite modification and rare earth doping technology, improve its adsorption capacity, wide pH applicability, and regeneration efficiency, so as to meet the requirements of modern industry for efficient and environmentally friendly adsorption materials. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a preparation method of a surface-modified alumina adsorbent with high adsorption capacity, wide pH applicability and regeneration efficiency.

[0007] The technical solution adopted by the present invention to solve its technical problems is: a surface-modified alumina adsorbent, characterized in that its structure is a core-shell structure of a rare-earth doped mesoporous alumina core layer and a SiO2-Al2O3 composite shell layer, and a pH-responsive organic film is provided outside the SiO2-Al2O3 composite shell layer, and the specific surface area is > 300 m 2 / g, and the average pore diameter is 200 nm to 300 nm.

[0008] Through the synergistic design of the rare-earth doped mesoporous core layer and the SiO2-Al2O3 composite shell layer of the surface-modified alumina adsorbent of the present invention, combined with the outer layer pH-responsive organic film, the triple advantages of ultra-high adsorption performance, wide pH adaptability and long-term recyclability are realized. Rare-earth doping optimizes the mesoporous structure and preferentially adsorbs organic pollutants with a molecular weight < 1000 (such as benzene series and phenols). The core-shell structure enhances the chemical stability. Combining with the pH-responsive characteristics of the organic film, the adsorbent can maintain an adsorption efficiency of more than 90% in the pH range of 3-10. This dynamic response characteristic makes it suitable for wastewater treatment in complex pH environments.

[0009] In addition, rare-earth elements (such as Y2O3) also strengthen the grain boundary bonding force, so that after 10 regenerations of this adsorbent, the adsorption capacity attenuation is less than 8%, and the regeneration process only requires soaking in dilute alkali or dilute acid without high-temperature treatment.

[0010] The preparation method of the surface-modified alumina adsorbent provided by the present invention realizes the comprehensive improvement of the adsorption performance through multi-scale structure design and functional synergistic innovation: a preparation method of the above-mentioned surface-modified alumina adsorbent, characterized by including the following steps:

[0011] (1) Mix pseudoboehmite and a template agent in a mass ratio of 1:0.05 to 0.1, add deionized water and ultrasonically disperse for 25 to 35 minutes, perform hydrothermal reaction at 180 °C to 220 °C for 22 to 26 hours, filter and dry, and then calcine to obtain mesoporous γ-Al2O3; Step (1) adopts the hydrothermal method combined with a template agent to regulate the pore structure of mesoporous γ-Al2O3, so that its specific surface area breaks through 300 m 2 / g, and at the same time, the average pore diameter of 250 nm can accommodate the diffusion adsorption of small molecule pollutants (such as phenol) and some macromolecular organic matters (such as dyes). This structural advantage stems from the layered precursor characteristics of pseudoboehmite, and a highly ordered mesoporous network is induced by the template agent. Compared with alumina prepared by the traditional precipitation method, the adsorption capacity is increased by 5 to 8 times.

[0012] (2) Immerse the mesoporous γ-Al2O3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate, stir magnetically for 6 hours, and after vacuum degassing, calcine to obtain La-Zr-Al2O3 composite oxide; in step (2), the La-Zr bimetallic doping strengthens the alumina lattice through the ion exchange effect, forming stable oxygen vacancy defect sites in the mesoporous framework. This structure not only preferentially captures organic pollutants with molecular weight <1000 (such as benzene series and phenols), but also inhibits the γ→α phase transition during the high-temperature regeneration process, so that the structural integrity retention rate of the adsorbent reaches 92% after 10 cycles. Experiments show that La 3+ and Zr 4+ 's synergistic effect can increase the distribution coefficient of the adsorbent for phenol to more than 3 times that of traditional materials.

[0013] (3) Dissolve aluminum isopropoxide and perfluorosilane in toluene at a mass ratio of 10:0.15~0.25 to form an oil phase; disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 4~5 and add an anionic surfactant to form an aqueous phase. Mix at an oil phase / water phase volume ratio of 1:2.8~3.3 and stir at 75~85°C for 10~15 hours to form a SiO2-Al2O3 inorganic composite shell on the composite oxide to obtain inorganic-coated mesoporous Al2O3; the SiO2-Al2O3 composite shell constructed in step (3) forms a dense interface through Al-O-Si bonding, forming a physical barrier to the alumina core layer in strong acid / strong base environments (pH 3~10) to prevent the framework from dissolving. At the same time, the introduction of SiO2 adjusts the surface isoelectric point from 9.1 to 6.8, broadening the applicability of the adsorbent in the near-neutral environment. The test data shows that this structure enables the adsorbent to still maintain 85% of the initial adsorption capacity at pH = 2, which is better than the 30% attenuation rate of single alumina materials.

[0014] (4) Immerse the inorganic-coated mesoporous Al2O3 in a polyacrylic acid solution with a pH of 3~4, and form a PAA layer through electrostatic adsorption; then transfer it to an acetic acid solution with a pH of 5~6 of chitosan and let it stand for adsorption to form a CS layer. Repeat the alternate deposition 3~5 times to form a crude adsorbent with a stable composite film; the SiO2-Al2O3 composite shell constructed in step (3) forms a dense interface through Al-O-Si bonding, forming a physical barrier to the alumina core layer in strong acid / strong base environments (pH 3-10) to prevent the framework from dissolving. At the same time, the introduction of SiO2 adjusts the surface isoelectric point from 9.1 to 6.8, broadening the applicability of the adsorbent in the near-neutral environment. The test data shows that this structure enables the adsorbent to still maintain 85% of the initial adsorption capacity at pH = 2, which is better than the 30% attenuation rate of single alumina materials.

[0015] (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 - 6 and react for 30 - 60 minutes; then obtain the product after filtration, washing, and drying. In step (5), the glutaraldehyde cross-linking process only requires room temperature reaction and can solidify the organic film in a short time. Compared with the high-temperature calcination method, the energy consumption is reduced by 70%.

[0016] Preferably, in the preparation method of the above surface-modified alumina adsorbent, the template agent in step (1) is cetyltrimethylammonium bromide (CTAB) or / and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (PEO-PPO-PEO). As a cationic surfactant, CTAB can form a highly ordered mesoporous network through micelle self-assembly, improving the specific surface area and pore size uniformity of alumina; the PEO-PPO-PEO block copolymer can construct a hierarchical pore structure through the dynamic self-assembly of hydrophilic and hydrophobic segments, enhancing the pollutant diffusion efficiency.

[0017] More preferably, the template agent is a composite template agent of cetyltrimethylammonium bromide and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer with a mass ratio of 10:4 - 7. After the two are compounded in a specific ratio, the pore channel rigidity and dynamic tunability can be balanced, reducing pore collapse during high-temperature calcination, while broadening the pH adaptability and achieving high adsorption capacity and cycle stability.

[0018] Preferably, in the preparation method of the above surface-modified alumina adsorbent, the solid-liquid ratio in the system after adding deionized water in step (1) is 1:8 - 12. The preferred solid-liquid ratio ensures a moderate viscosity of the system, maintaining sufficient contact between the template agent and the aluminum source during the high-temperature and high-pressure reaction, while avoiding pore channel collapse caused by excessive swelling and ensuring that the average pore size is stable at the required size.

[0019] Preferably, in the preparation method of the above surface-modified alumina adsorbent, the calcination temperature in step (1) is 380°C - 450°C, and the calcination time is 3.5 - 4.5 hours. The preferred low-temperature calcination conditions can effectively remove the template agent and retain the mesoporous structure: this temperature range is lower than the critical temperature of alumina phase transformation (usually >500°C), avoiding pore channel collapse caused by the transformation of γ-Al2O3 to the α phase and maintaining the pore size; at the same time, avoiding grain coarsening caused by long-term high temperature and ensuring the substrate stability for subsequent rare earth doping and composite shell coating.

[0020] Preferably, in the preparation method of the above surface-modified alumina adsorbent, the total concentration of the mixed solution of lanthanum nitrate and zirconium nitrate in step (2) is 0.08 mol / L - 0.12 mol / L, and the La / Zr molar ratio is 1:0.8 - 1.2. This concentration range can ensure the uniform doping of bimetallic ions on the surface of alumina, forming stable oxygen vacancy defects (La 3+ Inhibiting the phase transformation of γ-Al2O3, Zr4+ (Enhanced oxygen storage capacity), improving the density of adsorption active sites; the doping ratio of La / Zr balances the dispersion of lanthanum and the pore channel regulation effect of zirconium, avoiding pore channel blockage or lattice distortion, and maintaining the average pore diameter and specific surface area; the synergistic effect of the two optimizes the surface acidity and oxygen migration ability of the adsorbent, enabling the adsorbent to maintain an efficiency of over 90% in the pH range of 3 to 10 and enhancing the thermal stability.

[0021] Preferably, in the preparation method of the above-mentioned surface-modified alumina adsorbent, the pressure of the vacuum degassing in step (2) is -0.093 MPa to -0.098 MPa, the temperature is 140 °C to 160 °C, the temperature of the calcination is 530 °C to 580 °C, and the calcination time is 100 min to 150 min. These vacuum degassing process conditions and calcination process conditions have synergistic advantages: Vacuum degassing deeply removes the residual moisture and organic templates in the pores, avoiding the collapse of the pore walls due to the rapid escape of volatiles during subsequent high-temperature calcination, and maintaining a high specific surface area; precisely controlling the temperature can not only achieve the full pyrolysis of the templates but also prevent the premature sintering and deactivation of the active components (such as La / Zr); the calcination process can promote the uniform loading of transition metal oxides on the surface of alumina, enhance the oxygen vacancy density, and improve the activity of the adsorption sites.

[0022] Preferably, in the preparation method of the above-mentioned surface-modified alumina adsorbent, the total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase in step (3) is 8% to 15%. This concentration range ensures that aluminum isopropoxide is fully hydrolyzed to form a mesoporous alumina framework, and at the same time, perfluorosilane is molecularly dispersed through toluene solvent, forming stable Si-O-Al bonds with the hydroxyl groups on the alumina surface, and the fluorination coverage rate > 95%; at this concentration, it can not only avoid pore channel blockage caused by excessive perfluorosilane but also prevent rapid hydrolysis of aluminum isopropoxide from causing particle aggregation.

[0023] Preferably, in the preparation method of the above-mentioned surface-modified alumina adsorbent, the anionic surfactant in step (3) is sodium dodecyl sulfate (SDS), and the concentration of sodium dodecyl sulfate in the aqueous phase is 45 mg / mL to 50 mg / mL. This concentration range enables SDS molecules to form stable micelles in the aqueous phase, adsorb on the surface of alumina through the hydrophobic chain and arrange directionally, forming a dense monolayer, optimizing the exposure density of the hydrophobic groups (C12 chains), and improving the adsorption selectivity for oils and fats; this concentration range can not only ensure that the hydroxyl groups on the alumina surface are fully combined with the sulfate groups of SDS to form a uniform modification layer but also avoid the increase in the viscosity of the aqueous phase caused by excessive free SDS and inhibit particle aggregation.

[0024] Preferably, in the preparation method of the above surface-modified alumina adsorbent, the thickness of the SiO2-Al2O3 composite shell layer formed in step (3) is 10 nm to 20 nm. This thickness range can maintain the integrity of the shell layer structure and avoid pore blockage caused by excessive thickness by regulating the interfacial bonding strength between SiO2 and Al2O3. This thickness can not only ensure the uniform coating of SiO2 on the surface hydroxyl groups of Al2O3 to form a dense passivation layer, inhibit the high-temperature phase change of γ-Al2O3, and enhance surface hydrophobicity, but also optimize the stress distribution of the shell layer, improve the mechanical strength of the core-shell structure, and cooperate with the mesoporous framework to form hierarchical pores (micropore-mesopore synergistic adsorption) to ensure the adsorption capacity of the adsorbent.

[0025] In step (4) of this preparation method, the inorganic-coated mesoporous Al2O3 is immersed in a polyacrylic acid (PAA) solution (when the pH is 3 to 4, it is negatively charged), and a PAA layer is formed by electrostatic adsorption; then it is transferred to an acetic acid solution of chitosan (CS) (when the pH is 5 to 6, it is positively charged), and allowed to stand for adsorption to form a CS layer. The alternate deposition is repeated 3 to 5 times, and a stable composite film is formed by the electrostatic interaction between amino groups and carboxyl groups. The deposited material is immersed in a 0.5% to 1.0% glutaraldehyde solution (pH 5 to 6) for cross-linking for 30 to 60 minutes, which can enhance the mechanical stability of the film layer. Subsequently, after vacuum drying at about 60 °C, the unreacted monomers are removed by rinsing with deionized water, and finally a pH-responsive PAA / CS-coated SiO2-Al2O3 composite adsorbent is obtained. In acidic conditions (pH < 5), the protonation of the CS amino group enhances the adsorption of cationic pollutants, and in alkaline conditions (pH > 7), the deprotonation of the PAA carboxyl group preferentially adsorbs anionic pollutants.

[0026] Compared with the prior art, the beneficial effects of a surface-modified alumina adsorbent and its preparation method of the present invention are as follows: The present invention constructs a mesoporous γ-Al2O3 core layer with hierarchical pores through a composite template agent (CTAB / PEO-PPO-PEO), combines La / Zr bimetal doping to form oxygen vacancy defects, and significantly improves adsorption selectivity and structural stability; the surface isoelectric point is regulated to 6.8 through the SiO2-Al2O3 composite shell layer, and a pH-responsive film with alternating deposition of PAA / CS is introduced, so that the adsorbent maintains an efficiency of > 90% in the pH range of 3 - 10; the energy consumption is reduced by using the vacuum degassing and short-time low-temperature calcination process; finally, the broad-spectrum and high-efficiency adsorption of multiple targets is realized, breaking through the single-target limitation of traditional materials, and having the advantages of high adsorption capacity, wide pH adaptability and green process. Specific Embodiments

[0027] The following further illustrates the present invention with specific embodiments, and Embodiment 1 is the best embodiment. Embodiment 1

[0028] (1) Mix pseudoboehmite with a templating agent at a mass ratio of 1:0.08. The templating agent is a composite templating agent of CTAB and PEO-PPO-PEO at a mass ratio of 10:5.5. Add deionized water until the solid-liquid ratio in the system is 1:10, then perform ultrasonic dispersion for 30 minutes. After hydrothermal reaction at 200 °C for 24 hours, filter and dry, and then calcine at 400 °C for 4 hours to obtain mesoporous γ-Al2O3.

[0029] (2) Immerse the mesoporous γ-Al2O3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate. The total concentration of the mixed solution is 0.1 mol / L, and the La / Zr molar ratio is 1:1. Stir magnetically for 6 hours, perform vacuum degassing at -0.095 MPa and 150 °C for 45 min, and then calcine at 550 °C for 120 min to obtain La-Zr-Al2O3 composite oxide.

[0030] (3) Dissolve aluminum isopropoxide and perfluorosilane at a mass ratio of 10:0.2 in toluene to form an oil phase. The total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase is 10%. Disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 4 and add SDS to form an aqueous phase. The concentration of SDS in the aqueous phase is 48 mg / mL. Mix at an oil phase / water phase volume ratio of 1:3 and stir at 80 °C for 12 hours to form a 15-nm-thick SiO2-Al2O3 inorganic composite shell on the composite oxide to obtain inorganic-coated mesoporous Al2O3.

[0031] (4) Immerse the inorganic-coated mesoporous Al2O3 in a polyacrylic acid solution with a pH of 3 to form a PAA layer by electrostatic adsorption. Subsequently, transfer it to an acetic acid solution of chitosan with a pH of 5 and let it stand for adsorption to form a CS layer. Repeat the alternate deposition 4 times to obtain a crude adsorbent with a stable composite membrane.

[0032] (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 and react for 40 minutes. After filtration, washing, and drying, it is obtained. Example 2

[0033] (1) Mix pseudoboehmite with CTAB at a mass ratio of 1:0.08. Add deionized water until the solid-liquid ratio in the system is 1:10, then perform ultrasonic dispersion for 30 minutes. After hydrothermal reaction at 200 °C for 24 hours, filter and dry, and then calcine at 400 °C for 4 hours to obtain mesoporous γ-Al2O3.

[0034] (2) Immerse the mesoporous γ-Al2O3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate. The total concentration of the mixed solution is 0.1 mol / L, and the La / Zr molar ratio is 1:1. Stir magnetically for 6 hours, perform vacuum degassing at -0.095 MPa and 150 °C for 45 min, and then calcine at 550 °C for 120 min to obtain La-Zr-Al2O3 composite oxide.

[0035] (3) Dissolve aluminum isopropoxide and perfluorosilane in toluene at a mass ratio of 10:0.2 to form an oil phase, and the total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase is 10%; disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 4 and add SDS to form an aqueous phase, and the concentration of SDS in the aqueous phase is 48 mg / mL; mix at an oil phase / aqueous phase volume ratio of 1:3 and stir at 80 °C for 12 hours to form a 15-nm-thick SiO2-Al2O3 inorganic composite shell on the composite oxide to obtain inorganic-coated mesoporous Al2O3;

[0036] (4) Immerse the inorganic-coated mesoporous Al2O3 in a polyacrylic acid solution with a pH of 3 to form a PAA layer by electrostatic adsorption; then transfer it to an acetic acid solution of chitosan with a pH of 5 and let it stand for adsorption to form a CS layer, and repeat the alternate deposition 4 times to obtain a crude adsorbent with a stable composite film;

[0037] (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 and react for 40 minutes; obtain the product after filtration, washing, and drying. Example 3

[0038] (1) Mix pseudoboehmite and a template agent at a mass ratio of 1:0.08. The template agent is a composite template agent of CTAB and PEO-PPO-PEO at a mass ratio of 10:5.5; add deionized water until the solid-liquid ratio in the system is 1:10, then perform ultrasonic dispersion for 30 minutes, carry out hydrothermal reaction at 200 °C for 24 hours, filter and dry, and then calcine at 400 °C for 4 hours to obtain mesoporous γ-Al2O3;

[0039] (2) Immerse the mesoporous γ-Al2O3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate. The total concentration of the mixed solution is 0.1 mol / L, and the La / Zr molar ratio is 1:0.5; stir magnetically for 6 hours, perform vacuum degassing at -0.095 MPa and 150 °C for 45 min, and then calcine at 550 °C for 120 min to obtain La-Zr-Al2O3 composite oxide;

[0040] (3) Dissolve aluminum isopropoxide and perfluorosilane in toluene at a mass ratio of 10:0.2 to form an oil phase, and the total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase is 10%; disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 4 and add SDS to form an aqueous phase, and the concentration of SDS in the aqueous phase is 48 mg / mL; mix at an oil phase / aqueous phase volume ratio of 1:3 and stir at 80 °C for 12 hours to form a 15-nm-thick SiO2-Al2O3 inorganic composite shell on the composite oxide to obtain inorganic-coated mesoporous Al2O3;

[0041] (4) Immerse the inorganic-coated mesoporous Al2O3 in a polyacrylic acid solution with a pH of 3 to form a PAA layer through electrostatic adsorption; then transfer it to an acetic acid solution of chitosan with a pH of 5 and let it stand for adsorption to form a CS layer. Repeat the alternate deposition 4 times to obtain a crude adsorbent with a stable composite film;

[0042] (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 and react for 40 minutes; obtain the product after filtration, washing, and drying. Example 4

[0043] (1) Mix pseudo-boehmite and a template agent at a mass ratio of 1:0.08. The template agent is a composite template agent of CTAB and PEO-PPO-PEO at a mass ratio of 10:5.5; add deionized water until the solid-liquid ratio in the system is 1:10, then perform ultrasonic dispersion for 30 minutes, carry out hydrothermal reaction at 200 °C for 24 hours, filter, dry, and calcine at 400 °C for 4 hours to obtain mesoporous γ-Al2O3;

[0044] (2) Immerse the mesoporous γ-Al2O3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate. The total concentration of the mixed solution is 0.1 mol / L, and the La / Zr molar ratio is 1:1; stir magnetically for 6 hours, perform vacuum degassing at -0.095 MPa and 150 °C for 45 min, and then calcine at 550 °C for 120 min to obtain La-Zr-Al2O3 composite oxide;

[0045] (3) Dissolve aluminum isopropoxide and perfluorosilane at a mass ratio of 10:0.2 in toluene to form an oil phase, and the total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase is 10%; disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 4 and add SDS to form an aqueous phase, and the concentration of SDS in the aqueous phase is 48 mg / mL; mix according to the volume ratio of oil phase / aqueous phase of 1:1 and stir at 80 °C for 12 hours to form a 15-nm-thick SiO2-Al2O3 inorganic composite shell on the composite oxide to obtain inorganic-coated mesoporous Al2O3;

[0046] (4) Immerse the inorganic-coated mesoporous Al2O3 in a polyacrylic acid solution with a pH of 3 to form a PAA layer through electrostatic adsorption; then transfer it to an acetic acid solution of chitosan with a pH of 5 and let it stand for adsorption to form a CS layer. Repeat the alternate deposition 4 times to obtain a crude adsorbent with a stable composite film;

[0047] (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 and react for 40 minutes; obtain the product after filtration, washing, and drying. Example 5

[0048] (1) Mix pseudoboehmite with a templating agent at a mass ratio of 1:0.05. The templating agent is a composite templating agent of CTAB and PEO-PPO-PEO at a mass ratio of 10:4. Add deionized water until the solid-liquid ratio in the system is 1:8, then perform ultrasonic dispersion for 25 minutes, carry out hydrothermal reaction at 180 °C for 26 hours, filter, dry, and calcine at 380 °C for 4.5 hours to obtain mesoporous γ-Al2O3;

[0049] (2) Immerse the mesoporous γ-Al2O3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate. The total concentration of the mixed solution is 0.08 mol / L, and the La / Zr molar ratio is 1:0.8. Stir magnetically for 6 hours, perform vacuum degassing at -0.093 MPa and 140 °C for 50 min, and then calcine at 530 °C for 150 min to obtain La-Zr-Al2O3 composite oxide;

[0050] (3) Dissolve aluminum isopropoxide and perfluorosilane at a mass ratio of 10:0.15 in toluene to form an oil phase. The total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase is 8%. Disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 4 and add SDS to form an aqueous phase. The concentration of SDS in the aqueous phase is 45 mg / mL. Mix at an oil phase / aqueous phase volume ratio of 1:2.8 and stir at 75 °C for 10 hours to form a 10-nm-thick SiO2-Al2O3 inorganic composite shell on the composite oxide to obtain inorganic-coated mesoporous Al2O3;

[0051] (4) Immerse the inorganic-coated mesoporous Al2O3 in a polyacrylic acid solution with a pH of 3 to form a PAA layer by electrostatic adsorption. Subsequently, transfer it to an acetic acid solution of chitosan with a pH of 5 and let it stand for adsorption to form a CS layer. Repeat the alternate deposition 3 times to form a crude adsorbent with a stable composite film;

[0052] (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 and react for 30 minutes. Obtain the product after filtration, washing, and drying. Example 6

[0053] (1) Mix pseudoboehmite with a templating agent at a mass ratio of 1:0.1. The templating agent is a composite templating agent of CTAB and PEO-PPO-PEO at a mass ratio of 10:7. Add deionized water until the solid-liquid ratio in the system is 1:12, then perform ultrasonic dispersion for 35 minutes, carry out hydrothermal reaction at 220 °C for 22 hours, filter, dry, and calcine at 450 °C for 3.5 hours to obtain mesoporous γ-Al2O3;

[0054] (2) The mesoporous γ-Al2O3 obtained in step (1) was impregnated in a mixed solution of lanthanum nitrate and zirconium nitrate. The total concentration of the mixed solution was 0.12 mol / L, and the La / Zr molar ratio was 1:1.2. It was magnetically stirred for 6 hours, degassed under vacuum at -0.098 MPa and 160 °C for 30 min, and then calcined at 580 °C for 100 min to obtain La-Zr-Al2O3 composite oxide;

[0055] (3) Aluminum isopropoxide and perfluorosilane were dissolved in toluene according to a mass ratio of 10:0.25 to form an oil phase, and the total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase was 15%. The composite oxide obtained in step (2) was dispersed in a sodium acetate buffer solution with a pH of 5 and SDS was added to form an aqueous phase. The concentration of SDS in the aqueous phase was 50 mg / mL. They were mixed according to an oil phase / aqueous phase volume ratio of 1:3.3 and stirred at 85 °C for 15 hours to form a 20-nm-thick SiO2-Al2O3 inorganic composite shell on the composite oxide to obtain inorganic-coated mesoporous Al2O3;

[0056] (4) The inorganic-coated mesoporous Al2O3 was immersed in a polyacrylic acid solution with a pH of 4, and a PAA layer was formed by electrostatic adsorption; then it was transferred to an acetic acid solution of chitosan with a pH of 6 and allowed to stand for adsorption to form a CS layer. The alternate deposition was repeated 3 - 5 times to form a crude adsorbent with a stable composite film;

[0057] (5) The crude adsorbent was immersed in a glutaraldehyde solution with a pH of 6 and reacted for 60 minutes; it was obtained after filtration, washing, and drying.

[0058] The performance of the surface-modified alumina adsorbents prepared in each example was tested, and the test results are shown in Table 1.

[0059] Table 1 Performance test results

[0060] 。

[0061] It can be seen from Table 1 that the surface-modified alumina adsorbents prepared in the examples of the present invention have a large adsorption capacity, a wide pH adaptation range, and a long service life.

[0062] Comparative Example 1

[0063] Only doped with La (0.1 mol / L lanthanum nitrate solution), Zr doping was omitted, and La-Zr synergistic oxygen vacancy defects were not formed; other processes and steps were the same as in Example 1.

[0064] Performance comparison: The adsorption selectivity for pollutants with a molecular weight < 1000 decreased by 35%, and the phenol distribution coefficient was only 60% of that in Example 1 of the present invention. After regeneration, the pore volume attenuation was 15% (in the present invention < 8%), because single La doping could not effectively inhibit grain boundary migration.

[0065] Comparative Example 2

[0066] Omit the SiO2 - Al2O3 composite shell coating in step (3), directly deposit the PAA / CS film, and use the uncoated La - Zr - Al2O3 core layer; other processes and steps are the same as in Example 1.

[0067] Performance comparison: When pH = 2, the adsorption capacity drops sharply to 50% (greater than 85% in the present invention), because the core layer directly contacts the acidic medium, resulting in the dissolution of Al 3+ dissolution. After regeneration at high temperature (400 °C), the specific surface area decreases by 28% (only 5% under the protection of the composite shell).

[0068] Comparative Example 3

[0069] In step (3), only SDS (45 mg / mL) is used, perfluorosilane and aluminum isopropoxide hydrolysis are not introduced, and the surface modification layer is a single - layer SDS monolayer; other processes and steps are the same as in Example 1.

[0070] Performance comparison: Poor hydrophobicity (contact angle 110° vs greater than 147° in the present invention), the oil adsorption efficiency is only 65% (the present invention > 95%). The shedding rate of the SDS modification layer is > 30% when pH > 8, resulting in poor cycle stability.

[0071] Comparative Example 4

[0072] In step (5), high - temperature calcination at 300 °C is used to cure the organic film, replacing glutaraldehyde room - temperature cross - linking; other processes and steps are the same as in Example 1.

[0073] Performance comparison: The energy consumption increases by 70%, and high temperature causes carbonization of the PAA / CS film, resulting in the failure of pH response (the adsorption efficiency in alkaline conditions drops to 60%). The mechanical strength of the film layer decreases by 50%, and the film rupture rate is > 40% after cyclic use.

[0074] The above - mentioned are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the relevant art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change, and modification made to the above - mentioned embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A surface-modified alumina adsorbent, characterized in that, It has a core-shell structure with a rare-earth-doped mesoporous alumina core layer and a SiO2-Al2O3 composite shell layer. There is a pH-responsive organic film outside the SiO2-Al2O3 composite shell layer. The specific surface area is >300 m² / g, and the average pore diameter is 200 nm to 300 nm; The preparation steps include: (1) Mix pseudoboehmite and a template agent in a mass ratio of 1:0.05 to 0.1, add deionized water and ultrasonically disperse for 25 to 35 minutes, carry out hydrothermal reaction at 180°C to 220°C for 22 to 26 hours, filter, dry, and then calcine to obtain mesoporous γ-Al2O3; (2) Immerse the mesoporous γ-Al2O3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate, magnetically stir for 6 hours, carry out vacuum degassing, and then calcine to obtain a La-Zr-Al2O3 composite oxide; (3) Dissolve aluminum isopropoxide and perfluorosilane in toluene in a mass ratio of 10:0.15 to 0.25 to form an oil phase; disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 4 to 5 and add an anionic surfactant to form an aqueous phase. Mix according to an oil phase / aqueous phase volume ratio of 1:2.8 to 3.3, and stir at 75°C to 85°C for 10 to 15 hours to form a SiO2-Al2O3 composite shell layer on the composite oxide to obtain an inorganic-coated mesoporous Al2O3; (4) Immerse the inorganic-coated mesoporous Al2O3 in a polyacrylic acid solution with a pH of 3 to 4, and form a PAA layer through electrostatic adsorption; then transfer it to an acetic acid solution of chitosan with a pH of 5 to 6, and statically adsorb to form a CS layer. Repeat the alternate deposition 3 to 5 times to form a crude adsorbent with a stable composite film; (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 to 6 and react for 30 to 60 minutes; after filtering, washing, and drying, it is obtained.

2. The preparation method of the surface-modified alumina adsorbent according to claim 1, characterized in that, It includes the following steps: (1) Mix pseudoboehmite and a template agent in a mass ratio of 1:0.05 to 0.1, add deionized water and ultrasonically disperse for 25 to 35 minutes, carry out hydrothermal reaction at 180°C to 220°C for 22 to 26 hours, filter, dry, and then calcine to obtain mesoporous γ-Al2O3; (2) Immerse the mesoporous γ-Al2O3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate, magnetically stir for 6 hours, carry out vacuum degassing, and then calcine to obtain a La-Zr-Al2O3 composite oxide; (3) Dissolve aluminum isopropoxide and perfluorosilane in toluene in a mass ratio of 10:0.15 to 0.25 to form an oil phase; disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 4 to 5 and add an anionic surfactant to form an aqueous phase. Mix according to an oil phase / aqueous phase volume ratio of 1:2.8 to 3.3, and stir at 75°C to 85°C for 10 to 15 hours to form a SiO2-Al2O3 composite shell layer on the composite oxide to obtain an inorganic-coated mesoporous Al2O3; (4) Immerse the inorganic-coated mesoporous Al2O3 in a polyacrylic acid solution with a pH of 3 to 4, and form a PAA layer through electrostatic adsorption; then transfer it to an acetic acid solution of chitosan with a pH of 5 to 6, and statically adsorb to form a CS layer. Repeat the alternate deposition 3 to 5 times to form a crude adsorbent with a stable composite film; (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 to 6 and react for 30 to 60 minutes; obtain the product after filtration, washing, and drying.

3. The preparation method of a surface-modified alumina adsorbent according to claim 2, characterized in that: The template agent described in step (1) is cetyltrimethylammonium bromide or / and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer.

4. The preparation method of a surface-modified alumina adsorbent according to claim 2, characterized in that: After adding deionized water in step (1), the solid-liquid ratio in the system is 1:8 to 12.

5. The preparation method of a surface-modified alumina adsorbent according to claim 2, wherein: The calcination temperature described in step (1) is 380 °C to 450 °C, and the calcination time is 3.5 to 4.5 hours.

6. The preparation method of a surface-modified alumina adsorbent according to claim 2, characterized in that: In step (2), the total concentration of the mixed solution of lanthanum nitrate and zirconium nitrate is 0.08 mol / L to 0.12 mol / L, and the La / Zr molar ratio is 1:0.8 to 1.

2.

7. The preparation method of a surface-modified alumina adsorbent according to claim 2, characterized in that: In step (2), the pressure of the vacuum degassing is -0.093 MPa to -0.098 MPa, the temperature is 140 °C to 160 °C, the calcination temperature is 530 °C to 580 °C, and the calcination time is 100 min to 150 min.

8. The preparation method of a surface-modified alumina adsorbent according to claim 2, characterized in that: In step (3), the total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase is 8% to 15%.

9. The preparation method of a surface-modified alumina adsorbent according to claim 2, wherein: The anionic surfactant described in step (3) is sodium dodecyl sulfate, and the concentration of sodium dodecyl sulfate in the aqueous phase is 45 mg / mL to 50 mg / mL.

10. The preparation method of a surface-modified alumina adsorbent according to claim 2, characterized in that: The thickness of the SiO2-Al2O3 composite shell formed in step (3) is 10 nm to 20 nm.