Surface modified aluminum oxide adsorbent and preparation method thereof

Abstract

The invention discloses a surface-modified aluminum oxide adsorbent and a preparation method thereof, and belongs 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, a pH responsive organic film is arranged outside the SiO2-Al2O3 composite shell layer, the specific surface area is greater than 300m < 2 > / g, and the average pore size is 200nm-300nm. The mesoporous gamma-Al2O3 nuclear layer with hierarchical pore channels is constructed through the composite template agent, oxygen vacancy defects are formed by combining La / Zr bimetal doping, and the adsorption selectivity and the structural stability are remarkably improved; broad-spectrum efficient adsorption on multiple targets is achieved, the limitation of single targeting of a traditional material is broken through, and the composite material has 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. Although existing modification methods (such as grafting with silane coupling agents, polymer coating, etc.) can improve the performance to a certain extent, they are often accompanied by defects such as complex processes, high costs, 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 needs of other pollutant treatment.

[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 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, limiting 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 preparation process for a new type of surface-modified alumina adsorbent, 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 needs of modern industry for high-efficiency 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 SiO 2 -Al 2 O 3 composite shell layer, and a pH-responsive organic film is provided outside the SiO 2 -Al 2 O 3 composite shell layer, with a specific surface area > 300 m 2 / g and an average pore diameter of 200 nm to 300 nm.

[0008] The surface-modified alumina adsorbent of the present invention realizes triple advantages of ultra-high adsorption performance, wide pH adaptability and long-term recyclability through the collaborative design of a rare-earth doped mesoporous core layer and a SiO 2 -Al 2 O 3 composite shell layer, combined with the outer layer of pH-responsive organic film. 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 chemical stability. Combined with the pH-responsive characteristics of the organic film, the adsorbent can maintain an adsorption efficiency of more than 90% within 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 Y 2 O 3 ) also strengthen the grain boundary bonding force, so that after 10 regenerations of the present 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 a comprehensive improvement in adsorption performance through multi-scale structural design and functional collaborative innovation: a preparation method of the above-mentioned surface-modified alumina adsorbent, characterized in that it includes the following steps: (1) Mix pseudo-boehmite and a template agent in a mass ratio of 1:0.05 - 0.1, add deionized water and ultrasonically disperse for 25 - 35 minutes, carry out hydrothermal reaction at 180°C - 220°C for 22 - 26 hours, filter and dry, and then calcine to obtain mesoporous γ-Al 2 O 3 ; In step (1), the hydrothermal method is adopted in combination with the template agent to regulate mesoporous γ-Al 2 O 3The pore structure enables its specific surface area to exceed 300 m 2 / g. At the same time, the average pore diameter of 250 nm can accommodate the diffusion and adsorption of both small molecule pollutants (such as phenol) and some macromolecular organic substances (such as dyes). This structural advantage stems from the layered precursor characteristics of pseudo-boehmite, and a highly ordered mesoporous network is formed through the induction of a template agent. Compared with alumina prepared by the traditional precipitation method, the adsorption capacity is increased by 5 to 8 times.

[0011] (2) Immerse the mesoporous γ-Al 2 O 3 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-Al 2 O 3 composite oxide; in step (2), the La-Zr bimetal doping strengthens the alumina lattice through the ion replacement effect, forming stable oxygen vacancy defect sites in the mesoporous framework. This structure not only preferentially captures organic pollutants with a molecular weight < 1000 (such as benzene series and phenols), but also inhibits the γ→α phase transformation during the high-temperature regeneration process, enabling the structural integrity retention rate of the adsorbent to reach 92% after 10 cycles. Experiments show that the synergistic effect of La 3+ and Zr 4+ can increase the distribution coefficient of the adsorbent for phenol to more than 3 times that of traditional materials.

[0012] (3) Dissolve aluminum isopropoxide and perfluorosilane in toluene according to 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 according to 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 SiO 2 -Al 2 O 3 inorganic composite shell on the composite oxide to obtain an inorganic-coated mesoporous Al 2 O 3 ; the SiO 2 -Al 2 O 3 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 a strong acid / strong base environment (pH = 3 - 10) to prevent the dissolution of the framework. At the same time, the introduction of SiO 2 adjusts the isoelectric point of the surface from 9.1 to 6.8, broadening the applicability of the adsorbent in a 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.

[0013] (4) The inorganic-coated mesoporous Al2 O 3 Immerse it 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 of chitosan with a pH of 5 - 6, 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 SiO 2 -Al 2 O 3 The composite shell layer forms a dense interface through Al - O - Si bonding, forming a physical barrier to the alumina core layer in a strong acid / strong base environment (pH = 3 - 10) to prevent the dissolution of the framework. At the same time, the introduction of SiO 2 adjusts the surface isoelectric point from 9.1 to 6.8, broadening the applicability of the adsorbent in a 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 superior to the 30% attenuation rate of a single alumina material.

[0014] (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 - 6 and react for 30 - 60 minutes; then obtain it after filtration, washing, and drying. The glutaraldehyde cross - linking process in step (5) only needs to react at room temperature and can cure the organic film in a short time, reducing the energy consumption by 70% compared with the high - temperature calcination method.

[0015] Preferably, for the preparation method of the above - mentioned 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.

[0016] 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 composite can balance the pore rigidity and dynamic tunability, reducing pore collapse during high - temperature calcination of the material, while broadening the pH adaptability and achieving high adsorption capacity and cycle stability.

[0017] Preferably, for the preparation method of the above - mentioned 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 that the viscosity of the system is moderate, maintaining sufficient contact between the template agent and the aluminum source during the high - temperature and high - pressure reaction, and avoiding pore collapse caused by excessive swelling, ensuring that the average pore diameter is stable at the required size.

[0018] Preferably, in the preparation method of the above-mentioned surface-modified alumina adsorbent, the calcination temperature in step (1) is 380°C to 450°C, and the calcination time is 3.5 to 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 the pore collapse caused by the transformation of γ-Al 2 O 3 to α phase, maintaining the pore diameter; at the same time, avoiding the grain coarsening caused by long-term high temperature, ensuring the substrate stability for subsequent rare earth doping and composite shell coating.

[0019] Preferably, in the preparation method of the above-mentioned 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 to 0.12 mol / L, and the La / Zr molar ratio is 1:0.8 to 1.2. This concentration range can ensure the uniform doping of bimetallic ions on the alumina surface, forming stable oxygen vacancy defects (La 3+ inhibiting the γ-Al 2 O 3 phase transformation, Zr 4+ enhancing the 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 blockage or lattice distortion, 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 more than 90% in the pH range of 3 to 10 and enhancing the thermal stability.

[0020] 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 calcination temperature 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 template agent in the pores, avoiding the collapse of the pore wall caused by the rapid escape of volatiles during subsequent high-temperature calcination, maintaining a high specific surface area; precise temperature control can not only achieve the full pyrolysis of the template agent but also prevent the premature sintering inactivation of active components (such as La / Zr); the calcination process can promote the uniform loading of transition metal oxides on the alumina surface, enhance the oxygen vacancy density, and improve the activity of adsorption sites.

[0021] Preferably, in the preparation method of the above surface-modified alumina adsorbent, the total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase in step (3) is 8% - 15%. This concentration range ensures that aluminum isopropoxide is fully hydrolyzed to form a mesoporous alumina skeleton, while perfluorosilane is molecularly dispersed through toluene solvent and forms stable Si-O-Al bonds with the hydroxyl groups on the alumina surface, with a fluorination coverage rate > 95%; at this concentration, it can avoid pore blockage caused by excessive perfluorosilane and prevent rapid hydrolysis of aluminum isopropoxide from causing particle agglomeration.

[0022] Preferably, in the preparation method of the above 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 - 50 mg / mL. This concentration range enables SDS molecules to form stable micelles in the aqueous phase, adsorb on the alumina surface through hydrophobic chains and arrange directionally to form a dense monolayer, optimizing the exposure density of hydrophobic groups (C12 chains) and enhancing the adsorption selectivity for oils and fats; this concentration range can not only ensure that the hydroxyl groups on the alumina surface fully combine 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 agglomeration.

[0023] Preferably, in the preparation method of the above surface-modified alumina adsorbent, the SiO 2 -Al 2 O 3 The thickness of the composite shell layer formed in step (3) is 10 nm - 20 nm. This thickness range controls the interfacial bonding strength between SiO 2 and Al 2 O 3 to maintain the integrity of the shell structure while avoiding pore blockage caused by excessive thickness. This thickness can ensure that SiO 2 uniformly coats the hydroxyl groups on the surface of Al 2 O 3 to form a dense passivation layer, inhibit the high-temperature phase transformation of γ-Al 2 O 3 and enhance surface hydrophobicity; it can also optimize the stress distribution of the shell layer, improve the mechanical strength of the core-shell structure, and cooperate with the mesoporous skeleton to form hierarchical pores (micropore-mesopore synergistic adsorption) to ensure the adsorption capacity of this adsorbent.

[0024] In step (4) of this preparation method, the inorganic-coated mesoporous Al 2 O 3Immerse it in a polyacrylic acid (PAA) solution (when the pH is 3 - 4, it makes the solution negatively charged), and form a PAA layer through electrostatic adsorption; then transfer it to an acetic acid solution of chitosan (CS) (when the pH is 5 - 6, it makes the solution positively charged), and let it stand for adsorption to form a CS layer. Repeat the alternate deposition 3 - 5 times, and use the electrostatic interaction between amino groups and carboxyl groups to form a stable composite membrane. Immerse the deposited material in a 0.5% - 1.0% glutaraldehyde solution (pH is 5 - 6) for crosslinking for 30 - 60 minutes, which can enhance the mechanical stability of the membrane layer. Then, after vacuum drying at about 60 °C, rinse it with deionized water to remove unreacted monomers, and finally obtain a pH-responsive PAA / CS-coated SiO 2 -Al 2 O 3 composite adsorbent. Under acidic conditions (pH < 5), the protonation of CS amino groups enhances the adsorption of cationic pollutants, and under alkaline conditions (pH > 7), the deprotonation of PAA carboxyl groups preferentially adsorbs anionic pollutants.

[0025] 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-Al with hierarchical pores through a composite template agent (CTAB / PEO-PPO-PEO) 2 O 3 core layer, combines La / Zr bimetal doping to form oxygen vacancy defects, and significantly improves the adsorption selectivity and structural stability; through SiO 2 -Al 2 O 3 composite shell to regulate the surface isoelectric point to 6.8, and introduce a pH-responsive membrane with alternating deposition of PAA / CS, so that the adsorbent maintains an efficiency of > 90% in the pH range of 3 - 10; the energy consumption is reduced by using vacuum degassing and short-time low-temperature calcination processes; finally, broad-spectrum and high-efficiency adsorption of multiple targets is achieved, breaking through the single-target limitation of traditional materials, and having the advantages of high adsorption capacity, wide pH adaptability and green process. Detailed implementation manners

[0026] The following further illustrates the present invention with specific embodiments, and Embodiment 1 is the best embodiment. Embodiment 1

[0027] (1) Mix pseudoboehmite and the 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-Al 2 O 3 ; (2) The mesoporous γ-Al obtained in step (1)2 O 3 Impregnated 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; magnetic stirring for 6 hours, vacuum degassing at -0.095 MPa and 150 °C for 45 min, and then calcined at 550 °C for 120 min to obtain La-Zr-Al 2 O 3 composite oxide; (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 according to the volume ratio of oil phase / aqueous phase of 1:3, and stir at 80 °C for 12 hours to form a 15-nm-thick SiO 2 -Al 2 O 3 inorganic composite shell to obtain inorganic-coated mesoporous Al 2 O 3 ; (4) Immerse the inorganic-coated mesoporous Al 2 O 3 in a polyacrylic acid solution with a pH of 3, and 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. Repeat the alternate deposition 4 times to obtain a crude adsorbent with a stable composite film; (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 5 and react for 40 minutes; obtain it after filtration, washing, and drying. Example 2

[0028] (1) Mix pseudo-boehmite and 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, 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-Al 2 O 3 ; (2) Immerse the mesoporous γ-Al 2 O 3 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; magnetic stirring for 6 hours, vacuum degassing at -0.095 MPa and 150 °C for 45 min, and then calcined at 550 °C for 120 min to obtain La-Zr-Al 2 O 3 composite oxide; (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 according to the volume ratio of oil phase / aqueous phase of 1:3 and stir at 80 °C for 12 hours to form a SiO with a thickness of 15 nm on the composite oxide 2 -Al 2 O 3 inorganic composite shell to obtain inorganic-coated mesoporous Al 2 O 3 ; (4) Immerse the inorganic-coated mesoporous Al 2 O 3 into a polyacrylic acid solution with a pH of 3, and 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, and repeat the alternate deposition 4 times to obtain a crude adsorbent with a stable composite film; (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 3

[0029] (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 and dry, and then calcine at 400 °C for 4 hours to obtain mesoporous γ-Al 2 O 3 ; (2) Immerse the mesoporous γ-Al 2 O 3 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-Al 2 O 3 composite oxide; (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 according to the volume ratio of oil phase / aqueous phase of 1:3 and stir at 80 °C for 12 hours to form a SiO with a thickness of 15 nm on the composite oxide2 -Al 2 O 3 An inorganic composite shell yields an inorganic-coated mesoporous Al 2 O 3 ; (4) Immerse the inorganic-coated mesoporous Al 2 O 3 into a polyacrylic acid solution with a pH of 3, and form a PAA layer through 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 film; (5) Immerse the crude adsorbent into a glutaraldehyde solution with a pH of 5 and react for 40 minutes; obtain the product after filtration, washing, and drying. Example 4

[0030] (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-Al 2 O 3 ; (2) Immerse the mesoporous γ-Al 2 O 3 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-Al 2 O 3 composite oxide; (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 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 SiO 2 -Al 2 O 3 inorganic composite shell to obtain an inorganic-coated mesoporous Al 2 O 3 ; (4) Immerse the inorganic-coated mesoporous Al 2 O 3Immerse it 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; (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

[0031] (1) Mix boehmite and a template agent at a mass ratio of 1:0.05. The template agent is a composite template 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 and dry, and then calcine at 380 °C for 4.5 hours to obtain mesoporous γ-Al 2 O 3 ; (2) Immerse the mesoporous γ-Al 2 O 3 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-Al 2 O 3 composite oxide; (3) Dissolve aluminum isopropoxide and perfluorosilane in toluene at a mass ratio of 10:0.15 to form an oil phase, and 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, and the concentration of SDS in the aqueous phase is 45 mg / mL; mix at an oil phase / water phase volume ratio of 1:2.8 and stir at 75 °C for 10 hours to form a 10-nm-thick SiO 2 -Al 2 O 3 inorganic composite shell on the composite oxide to obtain an inorganic-coated mesoporous Al 2 O 3 ; (4) Immerse the inorganic-coated mesoporous Al 2 O 3 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 3 times to obtain a crude adsorbent with a stable composite film; (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

[0032] (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 then calcine at 450 °C for 3.5 hours to obtain mesoporous γ-Al 2 O 3 ; (2) Immerse the mesoporous γ-Al 2 O 3 obtained in step (1) in a mixed solution of lanthanum nitrate and zirconium nitrate. The total concentration of the mixed solution is 0.12 mol / L, and the La / Zr molar ratio is 1:1.2. Stir magnetically for 6 hours, perform vacuum degassing at -0.098 MPa and 160 °C for 30 min, and then calcine at 580 °C for 100 min to obtain La-Zr-Al 2 O 3 composite oxide; (3) Dissolve aluminum isopropoxide and perfluorosilane in toluene at a mass ratio of 10:0.25 to form an oil phase. The total mass concentration of aluminum isopropoxide and perfluorosilane in the oil phase is 15%. Disperse the composite oxide obtained in step (2) in a sodium acetate buffer solution with a pH of 5 and add SDS to form an aqueous phase. The concentration of SDS in the aqueous phase is 50 mg / mL. Mix at an oil phase / water phase volume ratio of 1:3.3 and stir at 85 °C for 15 hours to form a 20-nm-thick SiO 2 -Al 2 O 3 inorganic composite shell on the composite oxide to obtain an inorganic-coated mesoporous Al 2 O 3 ; (4) Immerse the inorganic-coated mesoporous Al 2 O 3 in a polyacrylic acid solution with a pH of 4 to form a PAA layer by electrostatic adsorption; then transfer it to an acetic acid solution of chitosan with a pH of 6 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; (5) Immerse the crude adsorbent in a glutaraldehyde solution with a pH of 6 and react for 60 minutes; after filtration, washing, and drying, it is obtained.

[0033] Perform performance tests on the surface-modified alumina adsorbents prepared in each example. The test results are shown in Table 1.

[0034] Table 1 Performance test results .

[0035] As can be seen from Table 1, the surface-modified alumina adsorbent prepared in the embodiment of the present invention has a large adsorption capacity, a wide pH adaptation range, and a long service life.

[0036] Comparative Example 1 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 those in Example 1.

[0037] 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 decreased by 15% (less than 8% in the present invention), because single La doping could not effectively inhibit grain boundary migration.

[0038] Comparative Example 2 Omitted the SiO 2 -Al 2 O 3 composite shell coating, directly carried out PAA / CS membrane deposition, and used the uncoated La-Zr-Al 2 O 3 core layer; other processes and steps were the same as those in Example 1.

[0039] Performance comparison: When pH = 2, the adsorption capacity dropped suddenly to 50% (more than 85% in the present invention), because the core layer directly contacted the acidic medium, resulting in the dissolution of Al 3+ dissolution. After regeneration at high temperature (400 °C), the specific surface area decreased by 28% (only decreased by 5% under the protection of the composite shell).

[0040] Comparative Example 3 In step (3), only SDS (45 mg / mL) was used, perfluorosilane and isopropanol aluminum hydrolysis were not introduced, and the surface modification layer was a single SDS monolayer film; other processes and steps were the same as those in Example 1.

[0041] Performance comparison: Poor hydrophobicity (contact angle 110° vs more than 147° in the present invention), and the oil adsorption efficiency was only 65% (more than 95% in the present invention). The shedding rate of the SDS modification layer was > 30% when pH > 8, resulting in poor cycle stability.

[0042] Comparative Example 4 In step (5), high-temperature calcination at 300 °C was used to cure the organic membrane, replacing glutaraldehyde room-temperature crosslinking; other processes and steps were the same as those in Example 1.

[0043] Performance comparison: The energy consumption increased by 70%, and high temperature caused carbonization of the PAA / CS membrane, resulting in the failure of pH response (the adsorption efficiency decreased to 60% under alkaline conditions). The mechanical strength of the membrane layer decreased by 50%, and the membrane rupture rate was > 40% after repeated use.

[0044] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in any other form. Any person skilled in the relevant art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above 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: Its structure is a core-shell structure of rare earth doped mesoporous alumina core layer and SiO2-Al2O3 composite shell layer, and the SiO2-Al2O3 composite shell layer has a pH responsive organic film outside, with a specific surface area of ​​300m 2 / g, and the average pore size is 200nm~300nm.

2. A method for preparing the surface-modified alumina adsorbent according to claim 1, characterized in that: The following steps are involved: (1) Pseudo-boehmite and template agent are mixed in a mass ratio of 1:0.05-0.1, deionized water is added for ultrasonic dispersion for 25-35 minutes, hydrothermally reacted at 180°C-220°C for 22-26 hours, filtered, dried and then calcined to obtain mesoporous γ-Al2O3; (2) impregnating the mesoporous γ-Al2O3 obtained in step (1) into a mixed solution of lanthanum nitrate and zirconium nitrate, stirring magnetically for 6 hours, vacuum degassing and calcining to obtain La-Zr-Al2O3 composite oxide; (3) dissolving aluminum isopropoxide and perfluorosilane in toluene at a mass ratio of 10:0.15-0.25 to form an oil phase; dispersing the composite oxide obtained in step (2) in a sodium acetate buffer having a pH of 4-5 and adding an anionic surfactant to form an aqueous phase, mixing at an oil phase / aqueous phase volume ratio of 1:2.8-3.3, stirring at 75-85° C. for 10-15 hours to form a SiO2-Al2O3 composite shell on the composite oxide to obtain an inorganic coated mesoporous Al2O3; (4) The inorganic coated mesoporous Al2O3 is immersed in a polyacrylic acid solution with a pH of 3-4 to form a PAA layer by electrostatic adsorption; then it is transferred to an acetic acid solution of chitosan with a pH of 5-6 and allowed to stand for adsorption to form a CS layer. The alternating deposition is repeated 3-5 times to form a crude adsorbent with a stable composite film; (5) The crude adsorbent is immersed in a glutaraldehyde solution with a pH of 5 to 6 and reacted for 30 to 60 minutes; the adsorbent is filtered, washed, and dried to obtain the product.

3. The method for preparing a surface-modified alumina adsorbent according to claim 2, characterized in that: The template agent in step (1) is hexadecyltrimethylammonium bromide and / or a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

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

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

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

2.

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

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