A method for preparing γ-AlOOH / SiO2 composite thin films for Cr(VI) adsorption and their applications

Abstract

The application discloses a preparation method of a gamma-AlOOH / SiO2 composite film for adsorbing toxic Cr(VI) in water and application of the gamma-AlOOH / SiO2 composite film. The method comprises the following steps: adding lactic acid to psephite with a certain solid content to perform peptization; then, adding silica and polyvinyl alcohol in sequence; finally, performing flow casting of the composite sol on a substrate, and naturally drying to obtain the gamma-AlOOH / SiO2 composite film. Most composite films are usually prepared by respectively preparing single sols and then mixing the single sols to prepare a composite sol. The method can prepare the composite sol in one step, uses safer lactic acid to replace commonly used peptizing agents such as nitric acid, glacial acetic acid and hydrochloric acid, and has the advantages of convenient raw material source, non-toxicity and harmlessness, simple preparation process, safe and mild reaction condition and the like. The gamma-AlOOH / SiO2 composite film prepared by the method has a large adsorption capacity and a high adsorption rate for Cr(VI) in water, and has stronger acid resistance and toughness.

Description

Technical Field

[0001] This invention belongs to the technical field of developing adsorbents for treating wastewater containing heavy metal ions, specifically relating to a method for preparing and applying a γ-AlOOH / SiO2 composite film for Cr(VI) adsorption. Background Technology

[0002] Wastewater generated during the electroplating, textile, and metal processing industries often contains large amounts of heavy metal ions such as Cr(VI), Pb(II), and As(V). These ions are widely sourced, highly toxic, persistent, and possess a certain degree of masking and bioaccumulation. Direct discharge into the environment without treatment will cause serious harm to human health and ecosystems. Highly soluble Cr(VI), in particular, has strong mutagenic and carcinogenic effects after absorption through the respiratory tract or skin. Currently, common treatment methods for chromium-containing wastewater include ion exchange, chemical precipitation, membrane separation, and adsorption. Adsorption, which utilizes the high specific surface area and special functional groups of adsorbent materials to remove heavy metal ions from solutions, has advantages such as simple operation, low cost, and high adsorption efficiency, and has therefore attracted much attention. Commonly used powdered adsorbents include activated carbon, zeolite, clay, metal oxides, SiO2, nanomagnetic particles, synthetic polymers, and biomass. However, their use has drawbacks to varying degrees, such as difficulty in separating adsorbed pollutants, easy aggregation, and easy loss leading to secondary pollution of water bodies. In contrast, membrane adsorption materials with an integral structure have attracted attention due to their advantages of easy regeneration and easy separation after adsorption. Considering that industrial wastewater containing Cr(VI) is mostly acidic, it is essential to prepare membrane materials that are stable under acidic conditions.

[0003] Based on the different membrane materials, membranes are mainly classified into four types: inorganic membranes, bio-based membranes, functionalized polymer-based membranes, and mixed matrix membranes. Inorganic membrane materials reported for the adsorption and removal of heavy metal pollutants include NaA-type zeolites, MCM-41, MCM-48, and zeolite molecular sieves. However, in these cases, chromium in most solutions exists as chromate anions, making the aforementioned adsorption membranes clearly unsuitable; highly efficient adsorption membranes should provide abundant binding sites for heavy metal ion adsorption. Compared with membrane material preparation methods such as chemical vapor deposition, spray pyrolysis, thermal evaporation, electron beam evaporation, magnetron sputtering, and anodic oxidation, the sol-gel method has advantages such as low-temperature liquid-phase preparation, simple process, and easy control of product composition and pore structure. Adding a suitable crosslinking agent during sol formation also helps to form membrane materials with high crosslinking degree and good stability.

[0004] Boehmite (γ-AlOOH·nH2O) possesses excellent properties such as high specific surface area, environmental friendliness, high porosity, and abundant hydroxyl groups; amorphous SiO2 is a porous material with high specific surface area, good thermal stability, rich hydroxyl groups on its surface, and good modifiability. Both are adsorbent materials with great potential for industrial wastewater treatment. Tu et al. (Tu WJ, Cai WQ, Jiang YH, et al. Facile synthesis of novel rare earth elements modified SiO2 films for effective Cr(VI) removal from electroplating effluent[J]. Journal of Chemical and Engineering Data, 2019, 64, 2677-2685.) successfully prepared rare earth element modified SiO2 films with smooth and crack-free surfaces using a solvent evaporation-induced self-assembly method. Since the hydroxyl groups on rare earth elements can undergo ion exchange and electrostatic adsorption with Cr(VI) in solution, Cr(VI) can be effectively adsorbed while being reduced to low-toxicity Cr(III) on the film surface. However, rare earth elements are relatively expensive, and their introduction can clog pores, leading to a reduction in the specific surface area and pore volume of the film. Most reported studies currently focus on preparing γ-AlOOH or SiO2 films through doping modification, the introduction of surfactants, hydrothermal treatment, and electrospinning. While this increases the preparation cost, the doped materials may clog pores, reducing the specific surface area and pore volume of the film; or they may introduce new impurity ions, affecting the purity of the sol. Miao et al. (Miao YE, Wang R, Chen D, et al. Electrospun self-standing membrane of hierarchical SiO2@γ-AlOOH(boehmite)core / sheath fibers for water remediation[J].ACS Applied Materials & Interfaces, 2012, 4(10), 5353-5359.) prepared a hierarchical SiO2@γ-AlOOH core / sheath self-supporting membrane by uniformly anchoring γ-AlOOH nanosheets on the surface of SiO2 fibers based on the combination of electrospinning and hydrothermal reaction. This provides a direct contact area between the pseudo-boehmite and the solution, making it easy to handle and recycle. The adsorption capacity for Congo red is 21.3 mg / g. However, hydrothermal treatment will generate certain energy consumption, and the equipment cost of electrospinning is high, the productivity is low, and the preparation process is carried out under high pressure, which has certain dangers.Furthermore, the silicon and aluminum sources used in the research are mostly organic compounds such as tetraethyl orthosilicate, aluminum isopropoxide, and aluminum sec-butoxide, which involve complex hydrolysis processes and numerous influencing factors. When aluminum nitrate or aluminum chloride is used as the aluminum source, it is often necessary to first filter to obtain a precipitate, and then add a certain amount of nitric acid, hydrochloric acid, or acetic acid to prepare a sol, which involves many steps and the added acid is corrosive. CN110064358B discloses a method for preparing a SiO2 / γ-AlOOH composite film for the adsorption of toxic Cr(VI) using aluminum nitrate nonahydrate as the aluminum source and tetraethyl orthosilicate as the silicon source, but it requires the separate preparation of SiO2 sol and γ-AlOOH sol, and then mixing them with acidified PVA solution in a certain proportion, which is relatively cumbersome.

[0005] In summary, developing a silicon-aluminum oxide composite film based on the excellent properties of environmentally friendly γ-AlOOH and SiO2, using a relatively simple preparation process under safe and mild conditions, to synergistically construct a film that is stable in acidic aqueous solutions, exhibits good adsorption performance for toxic Cr(VI), and is easily separated from water, has significant scientific value and application prospects. The successful implementation of this research will provide new ideas for the development of composite oxide membrane materials that are easily separated from solids / liquids and for the treatment of toxic heavy metal ion wastewater. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to synthesize a γ-AlOOH / SiO2 composite film with good adsorption performance for toxic Cr(VI) and easy separation by means of sol-gel method under mild and simple conditions, using boehmite and silicon dioxide as aluminum source and silicon source respectively, and selecting appropriate colloidal solvent and film-forming aid.

[0007] To solve the above-mentioned technical problems, the primary objective of this invention is to provide a method for preparing γ-AlOOH / SiO2 composite films for Cr(VI) adsorption.

[0008] Another object of the present invention is to provide a γ-AlOOH / SiO2 composite film prepared by the above method.

[0009] Another object of the present invention is to provide applications of the above-mentioned γ-AlOOH / SiO2 composite thin film.

[0010] The technical problem to be solved by the present invention is achieved through the following technical solution:

[0011] A method for preparing a γ-AlOOH / SiO2 composite film for the adsorption of toxic Cr(VI) in water: First, boehmite powder is dispersed in water at room temperature, and lactic acid is added for degellation to obtain a suspension; then, nano-silica powder is uniformly dispersed in the above suspension, and polyvinyl alcohol, a film-forming aid, is added. After stirring evenly at room temperature, a composite sol is obtained; finally, the composite sol is uniformly coated on a substrate, cast into shape, and dried at room temperature to obtain a γ-AlOOH / SiO2 composite film.

[0012] The ratio of the pseudoboehmite powder to lactic acid is based on a mass ratio of m(lactic acid) / m(pseudoboehmite) = 0.15 to 0.75, with the preferred ratio being m(lactic acid) / m(pseudoboehmite) = 0.45 to 0.75.

[0013] The mass ratio of the pseudoboehmite powder to the silica powder is (2-6):1.

[0014] The mass fraction of boehmite in the suspension is 2–8 wt%.

[0015] The amount of polyvinyl alcohol added is (0.1-0.8g) polyvinyl alcohol / 10mL composite sol.

[0016] The preparation method specifically includes the following steps:

[0017] (1) Disperse 0.8 to 3.2 parts by weight of pseudoboehmite powder in deionized water at room temperature, and then quickly add 0.12 to 2.4 parts by weight of lactic acid to degelatinate;

[0018] (2) Add 0.133 to 1.600 parts by mass of nano-silica powder to the solution obtained in step (1) and stir at room temperature for a certain time to obtain a composite sol;

[0019] (3) Take the composite sol from step (2), add polyvinyl alcohol, stir for 2 hours, and finally coat the γ-AlOOH / SiO2 composite sol onto the substrate for casting. After drying at room temperature and in static air for 48 hours, peel off the film, which is the γ-AlOOH / SiO2 composite film.

[0020] In step (1), the mass of aluminum sol is kept at 40g, that is, the sum of the mass parts of boehmite powder, lactic acid and deionized water is 40 parts.

[0021] The stirring time in step (2) is 8 hours.

[0022] The γ-AlOOH / SiO2 composite film prepared by the above method can be used to adsorb Cr(VI) in water.

[0023] When the γ-AlOOH / SiO2 composite film was used to adsorb a Cr(VI) solution with pH=2 and a concentration of 50 mg / L, its adsorption capacity for Cr(VI) was the highest, reaching 23.91 mg / g. In comparison, the adsorption capacities of the single γ-AlOOH film and the SiO2 film for Cr(VI) were 19.42 mg / g and 20.37 mg / g, respectively.

[0024] Furthermore, the γ-AlOOH / SiO2 composite film obtained by the above preparation method exhibits strong toughness and elasticity under acidic conditions. After immersing the composite film in an aqueous solution at pH=1 for 5 hours, it was found that the γ-AlOOH film lost 28.16% of its mass; although the SiO2 film only lost 3.85% of its mass, it was extremely brittle; while the γ-AlOOH / SiO2 composite film did not crack after being stretched and could rebound, retaining not only the toughness of the γ-AlOOH film but also only losing 12.75% of its mass, demonstrating significantly enhanced acid resistance.

[0025] The principle underlying this invention is as follows: both γ-AlOOH and SiO2 surfaces are rich in hydroxyl groups. After lactic acid sol-gel treatment, they react with the film-forming agent polyvinyl alcohol (PVA) through hydrogen and covalent bonds. During the subsequent drying process, PVA undergoes a cross-linking reaction with silica and boehmite to form a uniform composite film. PVA provides the composite film with excellent mechanical properties, making it easy to separate Cr(VI) after adsorption. Silica and boehmite, as the active components of the adsorbent, provide numerous adsorption sites for Cr(VI) ions.

[0026] Compared with other Cr(VI) adsorbents, the γ-AlOOH / SiO2 composite film prepared in this invention has the following advantages:

[0027] (1) Use cheap and non-toxic commercial pseudoboehmite powder as the aluminum source to replace toxic and expensive aluminum alkoxide.

[0028] (2) Innovative use of organic acid lactic acid as a glue solvent to replace conventional corrosive strong acids, which is non-toxic and safe to operate;

[0029] (3) The sol-gel method used has low requirements for equipment, mild preparation conditions, and simple operation;

[0030] (4) The prepared γ-AlOOH / SiO2 composite film has a certain adsorption capacity for Cr(VI). When the initial concentration of Cr(VI) is 50 mg / L, the adsorption capacity of Cr(VI) is the highest at 23.91 mg / g, and the adsorption removal rate is as high as 94.67%.

[0031] (5) The prepared γ-AlOOH / SiO2 composite film has good toughness in acidic environment and is not easy to crack;

[0032] (6) The γ-AlOOH / SiO2 composite film prepared is easy to separate after adsorbing pollutants, and will not cause secondary pollution. Attached Figure Description

[0033] Figure 1 The adsorption kinetics curves of Cr(VI) on the γ-AlOOH / SiO2 composite films prepared in Examples 1-7 are shown.

[0034] Figure 2 Adsorption kinetic curves of the γ-AlOOH / SiO2 composite thin film (BSPM) prepared in Example 1, the γ-AlOOH thin film (BPM) prepared in Example 8, and the SiO2 thin film (SPM) prepared in Example 9;

[0035] Figure 3 XRD patterns of the γ-AlOOH / SiO2 composite thin film (BSPM) prepared in Example 1, the γ-AlOOH thin film (BPM) prepared in Example 8, and the SiO2 thin film (SPM) prepared in Example 9.

[0036] Figure 4 SEM images of the γ-AlOOH / SiO2 composite film (BSPM) prepared in Example 1, the γ-AlOOH film (BPM) prepared in Example 8, and the SiO2 film (SPM) prepared in Example 9;

[0037] Figure 5 A photograph of the γ-AlOOH / SiO2 composite film prepared in Example 1;

[0038] Figure 6 A toughness photograph of the γ-AlOOH / SiO2 composite film prepared in Example 3 after adsorption of Cr(VI);

[0039] Figure 7 The image shows a comparison of the γ-AlOOH / SiO2 composite film prepared in Example 1 before and after adsorption of Cr(VI). Detailed Implementation

[0040] The present invention will now be described in further detail with reference to embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto. For process parameters not specifically specified, conventional techniques can be referred to.

[0041] Example 1:

[0042] (1) At room temperature, 3.2g of pseudoboehmite powder was dispersed in 34.4g of water, and 2.4g of lactic acid was slowly added dropwise to degelatinate and prepare a suspension. Then, 1.6g of nano silica powder was uniformly dispersed in the above suspension and stirred for 8h to obtain γ-AlOOH / SiO2 composite sol.

[0043] (2) Take 10 mL of the composite sol in step (1), add 8 g of 10 wt% polyvinyl alcohol, stir for 2 h, and finally coat the γ-AlOOH / SiO2 composite sol onto a 2 cm × 6 cm polytetrafluoroethylene plate to cast it into shape. After drying at room temperature and static air for 48 h, peel off the film to obtain the γ-AlOOH / SiO2 composite film.

[0044] (3) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of γ-AlOOH / SiO2 composite film. The parameters of the constant temperature shaking oven were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the γ-AlOOH / SiO2 composite film is shown in [Figure number missing]. Figure 1 Its adsorption removal rate for Cr(VI) was 94.67%, and the adsorption capacity was 23.91 mg / g.

[0045] Example 2:

[0046] (1) At room temperature, 2g of pseudoboehmite powder was dispersed in 37.1g of water, and 0.9g of lactic acid was slowly added dropwise to degelatinate and prepare a suspension. Then, 1g of nano silica powder was uniformly dispersed in the above suspension and stirred for 8h to obtain γ-AlOOH / SiO2 composite sol.

[0047] (2) Take 10 mL of the composite sol in step (1), add 5 g of 10 wt% polyvinyl alcohol, stir for 2 h, and finally coat the γ-AlOOH / SiO2 composite sol onto a 2 cm × 6 cm polytetrafluoroethylene plate to cast it into shape. After drying at room temperature and static air for 48 h, peel off the film to obtain the γ-AlOOH / SiO2 composite film.

[0048] (3) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of the γ-AlOOH / SiO2 composite film sample. The parameters of the isothermal shaking oven were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the γ-AlOOH / SiO2 composite film is shown in [Figure number missing]. Figure 1 Its adsorption removal rate for Cr(VI) was 91.75%, and the adsorption capacity was 23.41 mg / g.

[0049] Example 3:

[0050] (1) At room temperature, 0.8g of pseudoboehmite powder was dispersed in 38.84g of water, and 0.36g of lactic acid was slowly added dropwise to degelatinate and prepare a suspension. Then, 0.13g of nano silica powder was uniformly dispersed in the above suspension and stirred for 8h to obtain γ-AlOOH / SiO2 composite sol.

[0051] (2) Take 10 mL of the composite sol in step (1), add 8 g of 10 wt% polyvinyl alcohol, stir for 2 h, and finally coat the γ-AlOOH / SiO2 composite sol onto a 2 cm × 6 cm polytetrafluoroethylene plate to cast it into shape. After drying at room temperature and static air for 48 h, peel off the film to obtain the γ-AlOOH / SiO2 composite film.

[0052] (3) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of γ-AlOOH / SiO2 composite film. The parameters of the constant temperature shaking oven were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the γ-AlOOH / SiO2 composite film is shown in [Figure number missing]. Figure 1 Its adsorption removal rate for Cr(VI) was 85.57%, and the adsorption capacity was 22.05 mg / g.

[0053] Example 4:

[0054] (1) At room temperature, 0.8 g of pseudoboehmite powder was dispersed in 38.6 g of water, and 0.6 g of lactic acid was slowly added dropwise to degelatinate and prepare a suspension. Then, 0.2 g of nano silica powder was uniformly dispersed in the above suspension and stirred for 8 h to obtain γ-AlOOH / SiO2 composite sol.

[0055] (2) Take 10 mL of the composite sol in step (1), add 5 g of 10 wt% polyvinyl alcohol, stir for 2 h, then coat the γ-AlOOH / SiO2 composite sol onto a 2 cm × 6 cm polytetrafluoroethylene plate, cast it into shape, and dry it at room temperature and static air for 48 h before peeling off the film to obtain the γ-AlOOH / SiO2 composite film.

[0056] (3) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of the γ-AlOOH / SiO2 composite film sample. The parameters of the isothermal shaking oven were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the γ-AlOOH / SiO2 composite film is shown in [Figure number missing]. Figure 1Its adsorption removal rate for Cr(VI) was 87.63%, and the adsorption capacity was 21.91 mg / g.

[0057] Example 5:

[0058] (1) At room temperature, 2g of pseudoboehmite powder was dispersed in 37.7g of water, and 0.3g of lactic acid was slowly added dropwise to degelatinate and prepare a suspension. Then, 0.5g of nano silica powder was uniformly dispersed in the above suspension and stirred for 8h to obtain γ-AlOOH / SiO2 composite sol.

[0059] (2) Take 10 mL of the composite sol in step (1), add 8 g of 10 wt% polyvinyl alcohol, stir for 2 h, and finally coat the γ-AlOOH / SiO2 composite sol onto a 2 cm × 6 cm polytetrafluoroethylene plate to cast it into shape. After drying at room temperature and static air for 48 h, peel off the film to obtain the γ-AlOOH / SiO2 composite film.

[0060] (3) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of the γ-AlOOH / SiO2 composite film sample. The parameters of the isothermal shaking oven were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the γ-AlOOH / SiO2 composite film is shown in [Figure number missing]. Figure 1 Its adsorption removal rate for Cr(VI) was 90.21%, and the adsorption capacity was 22.55 mg / g.

[0061] Example 6:

[0062] (1) At room temperature, 0.8 g of pseudoboehmite powder was dispersed in 39.08 g of water, and 0.12 g of lactic acid was slowly added dropwise to degelatinate and prepare a suspension. Then, 0.4 g of nano silica was uniformly dispersed in the above suspension and stirred for 8 h to obtain γ-AlOOH / SiO2 composite sol.

[0063] (2) Take 10 mL of the composite sol in step (1), add 1 g of 10 wt% polyvinyl alcohol, stir for 2 h, and finally coat the γ-AlOOH / SiO2 composite sol onto a 2 cm × 6 cm polytetrafluoroethylene plate to cast it into shape. After drying at room temperature and static air for 48 h, peel off the film to obtain the γ-AlOOH / SiO2 composite film.

[0064] (3) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of the γ-AlOOH / SiO2 composite film sample. The parameters of the isothermal shaking oven were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the γ-AlOOH / SiO2 composite film is shown in [Figure number missing]. Figure 1 Its adsorption removal rate for Cr(VI) was 76.63%, and the adsorption capacity was 18.97 mg / g.

[0065] Example 7:

[0066] (1) At room temperature, 3.2g of pseudoboehmite powder was dispersed in 36.32g of water, and 0.48g of lactic acid was slowly added dropwise to degelatinate and prepare a suspension. Then, 0.53g of nano silica powder was uniformly dispersed in the above suspension and stirred for 8h to obtain γ-AlOOH / SiO2 composite sol.

[0067] (2) Take 10 mL of the composite sol in step (1), add 5 g of 10 wt% polyvinyl alcohol, stir for 2 h, and finally coat the γ-AlOOH / SiO2 composite sol onto a 2 cm × 6 cm polytetrafluoroethylene plate to cast it into shape. After drying at room temperature and static air for 48 h, peel off the film to obtain the γ-AlOOH / SiO2 composite film.

[0068] (3) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of the γ-AlOOH / SiO2 composite film sample. The parameters of the isothermal shaking oven were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the γ-AlOOH / SiO2 composite film is shown in [Figure number missing]. Figure 1 Its adsorption removal rate for Cr(VI) was 64.95%, and the adsorption capacity was 16.40 mg / g.

[0069] Example 8:

[0070] To compare the adsorption performance of γ-AlOOH / SiO2 composite films and γ-AlOOH films, γ-AlOOH films were also prepared. The relevant steps and adsorption performance testing process are as follows:

[0071] (1) At room temperature, 3.2g of pseudoboehmite powder was dispersed in 34.4g of water, and 2.4g of lactic acid was slowly added dropwise to degelatinate the mixture. After stirring for 8h, 10mL of γ-AlOOH sol was taken and 8g of 10wt% polyvinyl alcohol was added. The mixture was stirred for 2h. Finally, the γ-AlOOH sol was coated on a 2cm×6cm polytetrafluoroethylene plate to cast the mixture. After drying at room temperature and in static air for 48h, the film was peeled off.

[0072] (2) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of γ-AlOOH film sample. The parameters of the isothermal shaking incubator were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the γ-AlOOH film is shown in [Figure number missing]. Figure 2 Its adsorption removal rate for Cr(VI) was 77.66%, and the adsorption capacity was 19.97 mg / g.

[0073] Example 9:

[0074] To compare the adsorption performance of γ-AlOOH / SiO2 composite films and SiO2 films, SiO2 films were also prepared. The relevant steps and adsorption performance testing process are as follows:

[0075] (1) At room temperature, 1.6 g of nano silica powder was uniformly dispersed in 40 g of water and stirred for 8 h to obtain SiO2 sol. Then, 10 mL of SiO2 sol was mixed with 8 g of 10 wt% polyvinyl alcohol and stirred for 2 h. Finally, it was coated onto a 2 cm × 6 cm polytetrafluoroethylene plate for casting and drying at room temperature and static air for 48 h before the film was peeled off.

[0076] (2) Adsorption of 50 mL, 50 mg / L Cr(VI) solution: The pH was adjusted to 2 with 0.1 mol / L HCl solution, followed by the addition of 0.1 g of SiO2 film. The parameters of the constant temperature shaking oven were set to 25 °C and 150 r / min. The adsorption kinetics curve of Cr(VI) on the SiO2 composite film is shown in [Figure number missing]. Figure 2 Its adsorption removal rate for Cr(VI) was 82.30%, and the adsorption capacity was 20.37 mg / g.

[0077] Example 10:

[0078] To test the acid resistance of the γ-AlOOH / SiO2 composite film, 0.1 g of the film samples from "Example 1", "Example 8" and "Example 9" were taken and added to a solution with pH adjusted to 1 by 50 mL of HCl solution. The parameters of the constant temperature shaking chamber were set to 25℃, 150 r / min and shaking time for 5 h.

[0079] The results showed that the γ-AlOOH film had certain toughness, but lost 28.16% of its mass; the SiO2 film lost only 3.85% of its mass, but it was very brittle; while the γ-AlOOH / SiO2 composite film did not crack after being stretched and could rebound, and the γ-AlOOH film retained good toughness while losing only 12.75% of its mass, and its acid resistance was significantly enhanced.

[0080] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a γ-AlOOH / SiO2 composite thin film for Cr(VI) adsorption, characterized in that... Includes the following steps: First, the pseudoboehmite powder was dispersed in water at room temperature, and lactic acid was added to degelatinate it, thus obtaining a suspension. Subsequently, nano-silica powder was uniformly dispersed in the above suspension, and film-forming aid polyvinyl alcohol was added. After stirring evenly at room temperature, a composite sol was obtained. Finally, the composite sol was uniformly coated on the substrate, cast and shaped, and dried at room temperature to obtain a γ-AlOOH / SiO2 composite film.

2. The method for preparing a γ-AlOOH / SiO2 composite thin film for Cr(VI) adsorption according to claim 1, characterized in that, The mass ratio of lactic acid to pseudoboehmite powder is 0.15 to 0.75:

1.

3. The method for preparing a γ-AlOOH / SiO2 composite thin film for Cr(VI) adsorption according to claim 1, characterized in that, The mass ratio of lactic acid to pseudoboehmite powder is 0.45 to 0.75:

1.

4. The method for preparing a γ-AlOOH / SiO2 composite thin film for Cr(VI) adsorption according to claim 1, characterized in that, The mass ratio of the pseudoboehmite powder to the nano silica powder is (2-6):1; the mass fraction of pseudoboehmite in the suspension is 2-8 wt%.

5. The method for preparing a γ-AlOOH / SiO2 composite thin film for Cr(VI) adsorption according to claim 1, characterized in that, The amount of polyvinyl alcohol added is (0.1-0.8g) polyvinyl alcohol / 10mL composite sol.

6. The method for preparing a γ-AlOOH / SiO2 composite thin film for Cr(VI) adsorption according to claim 1, characterized in that, The preparation method specifically includes the following steps: (1) Disperse 0.8 to 3.2 parts by weight of pseudoboehmite powder in deionized water at room temperature, and then quickly add 0.12 to 2.4 parts by weight of lactic acid to degelatinate; (2) Add 0.133 to 1.6 parts by mass of silica powder to the solution obtained in step (1) and stir at room temperature for a certain time to obtain a composite sol; (3) Take the composite sol from step (2), add polyvinyl alcohol at a ratio of (0.1~0.8g) polyvinyl alcohol / 10mL composite sol, stir for 2h, and finally coat the γ-AlOOH / SiO2 composite sol onto the substrate for casting. After drying at room temperature and in static air for 48h, peel off the film, which is the γ-AlOOH / SiO2 composite film.

7. The method for preparing a γ-AlOOH / SiO2 composite thin film for Cr(VI) adsorption according to claim 1, characterized in that, The stirring time in step (2) is 8 hours.

8. A γ-AlOOH / SiO2 composite film prepared by the method according to any one of claims 1-7.

9. The application of the γ-AlOOH / SiO2 composite film according to claim 8 in Cr(VI) adsorption.

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