Preparation method and application of three-dimensional macroporous chitosan-keratin cryogel adsorbent for selective adsorption of gold

Abstract

The application belongs to the technical field of adsorption separation functional materials, and discloses a preparation method of a three-dimensional macroporous shell chitosan-keratin frozen gel adsorbent for selectively adsorbing gold and application thereof. Chitosan and keratin are used to carry out low-temperature polymerization and modification of vinyl pyrrolidone, and gold (III) in actual electronic waste liquid can be efficiently recovered under ultraviolet irradiation. The adsorbent has macroporous characteristics, and Au (III) reaches adsorption equilibrium within 4 hours. The adsorbent conforms to the Langmuir model, and the adsorption capacity of the adsorbent for Au (III) is as high as 595.63 mg g ‑1 After being continuously used for four cycles, the adsorption efficiency for Au (III) is still maintained. In terms of recovery rate, the adsorbent exhibits the ability of specifically adsorbing gold (III), and the recovery rate reaches 89.2%. The cross-linked biological adsorbent has random pores, and is more conducive to the adsorption of gold (III) than traditional gels. The preparation process is simple, can recover precious metals from electronic waste, is a cost-effective solution, and has wide application prospects in environmental remediation and wastewater treatment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparation of adsorption separation functional materials, and relates to a preparation method of a three-dimensional macroporous shell chitosan-keratin cryogel adsorbent selectively adsorbing gold and application thereof. BACKGROUND

[0002] Precious metals are an important component of contemporary social progress and industrial production, and are often considered as an important indicator of the degree of modernization of a country. Efficient and rapid recovery of precious metals such as platinum (Pt), silver (Ag), palladium (Pd) and gold (Au) is a formidable challenge. This problem has attracted increasing attention in the context of "urban mining". "Urban mining" is recognized for its rich resources, and compared with traditional ore mining, urban mining can usually obtain more of these metals. This is particularly evident on printed circuit boards, as the stockpiles of these metals are increasing with the use of a large number of electronic devices. Gold stands out among all precious metals due to its outstanding physical and chemical properties, including excellent electrical conductivity, strong corrosion resistance and super-strong chemical stability. It is precisely these properties that make it the first choice for high-precision field applications, and thus it also has a relatively rich stockpile in electronic waste. Therefore, the demand for extracting gold from urban mining is imminent, but due to the interference of multiple metal ions, its selective recovery is still a major challenge

[0003] At present, there have been a large number of reports on advanced technologies for gold recovery, including adsorption, ion exchange, electrocoagulation, membrane separation, solvent extraction and chemical precipitation. However, the adsorption method is one of the best ways due to its simple operation, strong adsorption capacity, selective recovery, few harmful by-products and potential for reuse. The efficiency of mature adsorbents is often dependent on cost, especially when used on a large scale. In this regard, many polymeric adsorption materials are more cost-effective compared to other options. Several synthetic adsorbents for gold recovery have been previously documented, which have strong adsorption capacity. However, they still face many limitations and challenges in actual industrial applications. These challenges include high cost, complex synthesis procedure, ecological unfriendliness, particulate morphology and limited product yield. Therefore, a more environmentally friendly and more economically competitive route is necessary for extracting metals therefrom and achieving a sustainable process.

[0004] In recent decades, bio-based materials have attracted great interest as a viable candidate for developing various adsorbents for the removal of various pollutants (including metals, heavy metals, dyes and other organic pollutants) from aquatic environments. Adsorbent materials extracted from biological sources include polysaccharides (such as starch, chitosan, alginate, cellulose and lignin), proteins (such as keratin, soybean, corn protein, gelatin, albumin and silk) and microorganisms (including bacteria and fungi). Among various biopolymers, polysaccharides and proteins are favored due to their natural abundance, biodegradability and significant biosorption capacity. Chitosan (CS) is the second most common polysaccharide, known for its enhanced hydrophilicity and biodegradable properties. The abundance of amine functions in the chitosan (CS) network prompts thousands of scientists to use it for wastewater treatment. Among proteins, keratin (KT) stands out due to its unique and diverse chemical structure, providing exciting opportunities to enhance its advanced biosorption properties. CS and KT have good biocompatibility and have multiple functional groups, including amino, hydroxyl and sulfide connections, which can bind and coordinate various heavy metals and noble metals.

[0005] As a rare resource, the supply of noble metals is very limited. By recycling and reusing noble metals in electronic waste, the service life of noble metals can be effectively extended, and the mining of mineral resources can be reduced. There are still some difficulties in realizing the precise recycling of noble metals. First, in the recycling process, there are other interfering ions such as Ni(II), Cr(III), Co(II), Zn(II), Al(II), Cu(II), etc., so it is crucial to invent a monomer that selectively adsorbs gold. Second, most of the existing materials have a dense powder structure, and the material structure is unstable, the recycling is complex and not suitable for large-scale application. While the synthesis method of some materials with porous and sponge-like structure is very complex and consumes a lot of energy in the synthesis process.

[0006] Considering the above limitations, the present application turns to a freezing method (carried out below freezing temperature) and uses ultraviolet irradiation to rapidly graft low-temperature polymerization, successfully preparing high-porosity, biodegradable chitosan-keratin biosorbents. These adsorbent materials can effectively adsorb gold (III) in electronic waste solution. SUMMARY

[0007] In order to solve the problems of complex preparation process, high energy consumption and poor stability of adsorbent materials in the prior art, the present application proposes a low-temperature ultraviolet-induced polymerization of a three-dimensional macroporous chitosan-keratin freezing gel adsorbent for selective adsorption of gold, a method for quickly and highly selectively extracting gold, and is used for the rapid and selective recovery of gold in electronic waste liquid. It also has certain prospects in environmental remediation and wastewater treatment.

[0008] To achieve the above technical purpose, the technical scheme adopted by the present application is:

[0009] A preparation method of a three-dimensional macroporous chitosan-keratin cryogel adsorbent selectively adsorbing gold, comprising the following steps:

[0010] (1) Solution pre-polymerization

[0011] The vinyl pyrrolidone monomer, chitosan biopolymer, and keratin biopolymer, and N,N'-methylene bisacrylamide are dispersed and dissolved in deionized water to obtain solution A;

[0012] Then, a proper amount of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropenone photoinitiator is dissolved in deionized water to obtain solution B;

[0013] After mixing solution A and solution B, ultrasonic treatment is performed until all components are dissolved, and acetic acid is added for complete dissolution, and the CS and KT solutions are transparent.

[0014] (2) Low-temperature polymerization

[0015] The completely dissolved solution of step (1) is poured into a culture dish and frozen in a low-temperature thermostat. After freezing is completed, the frozen solution is controlled at the same temperature and irradiated with a UV lamp to ensure low-temperature induced polymerization.

[0016] (3) Thawing

[0017] After the low-temperature induced polymerization is completed, the sample is thawed at room temperature to dissolve the remaining ice crystals in the sample. In order to remove the unreacted monomers, biopolymers and cross-linking agents, the sample is washed with a mixture of deionized water and methanol. Then, freeze-drying is performed to obtain the product VP-CS-KT composite macroporous biopolymer adsorbent, which is stored in a desiccator.

[0018] In solution A of step (1), the amount ratio of vinyl pyrrolidone monomer, chitosan biopolymer, keratin biopolymer, N,N'-methylene bisacrylamide and deionized water is 450-550uL:175-225mg, 50-200mg:70-280mg:20-80mL;

[0019] In solution B of step (1), the amount ratio of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropenone and deionized water is 40-60mg:20mL;

[0020] In step (1), the volume ratio of solution A and solution B is 20-80mL:20mL; and the ultrasonic treatment time is 15-30min.

[0021] In step (2), the freezing temperature is -15 to -20℃, and the freezing time is 1-2h.

[0022] In step (2), the UV lamp output power is 15-20W, the wavelength λmax=365nm, and the irradiation time is 1-2h.

[0023] In step (3), the thawing time after low-temperature induced polymerization is 24-48h, and the time for freeze-drying of the pure sample is 24-48h.

[0024] The present application has the following beneficial effects:

[0025] (1) The present application grafts n-vinyl pyrrolidone (VP) vinyl monomer onto the chains of chitosan (CS) and keratin (KT) and other biopolymers under the action of a low-temperature condition, a photoinitiator (HHMP) and a UV lamp. Under the irradiation of a UV lamp, the photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl-propenone (HHMP) decomposes to generate benzoyl and hydroxyl alkyl radicals. These radicals then combine with the vinyl bonds of VP and MBA to generate additional radicals. At the same time, the crosslinking agent (MBA) interacts with the reactive polymer chains of CS and KT, which helps to form a complex 3D crosslinked macroporous biosorbent.

[0026] (2) The biosorbent can not only recover precious metals from electronic waste, but also has a promising prospect in environmental remediation and wastewater treatment. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Figure 1 is a schematic diagram of the preparation process of the three-dimensional macroporous chitosan-keratin frozen gel biosorbent in Example 1.

[0028] Figure 2 Figures (a) and (b) are SEM images of the three-dimensional macroporous chitosan-keratin frozen gel biosorbent in Example 1 and Example 4, respectively.

[0029] Figure 3 Figures are TGA analysis graphs of the three-dimensional macroporous chitosan-keratin frozen gel biosorbent in Example 1 and Example 4.

[0030] Figure 4 Figure is a comparison of the infrared spectra of the three-dimensional macroporous chitosan-keratin frozen gel biosorbent VP-CS-KT-200 and its synthetic monomers VP, CS and KT.

[0031] Figure 5 Figure is an adsorption data graph of different ratios of KT concentration (50mg, 100mg, 150mg and 200mg corresponding to Examples 1, 2, 3 and 4, respectively).

[0032] Figure 6This is a display of the pH results for Example 5, showing the adsorption data of the three-dimensional macroporous chitosan-keratin cryogel adsorbent VP-CS-KT-200 prepared in Example 4 at different pH values.

[0033] Figure 7 This is a demonstration of the adsorption kinetics experiment results of Example 6, in which the three-dimensional macroporous chitosan-keratin cryogel adsorbent VP-CS-KT-200 prepared in Example 4 was subjected to kinetic adsorption experiments.

[0034] Figure 8 This is an example of the adsorption isotherm experiment results from Example 7. The adsorption experiment was conducted on the three-dimensional macroporous chitosan-keratin cryogel adsorbent VP-CS-KT-200 prepared in Example 4 using Freundlich and Langmuir isotherm models.

[0035] Figure 9 This is a demonstration of the test results for the stability of the adsorbent in Example 8.

[0036] Figure 10 This demonstrates the competitive adsorption performance of the three-dimensional macroporous chitosan-keratin cryogel adsorbent for gold ions in the presence of multiple ions in Example 9. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0038] Figure 1 This is a schematic diagram of the preparation process of the three-dimensional macroporous chitosan-keratin cryogel adsorbent of the present invention.

[0039] Example 1:

[0040] (1) Solution prepolymerization

[0041] 500 μL of vinylpyrrolidone monomer, 200 mg of chitosan biopolymer, 50 mg of keratin biopolymer, and 70 mg of N,N'-methylenebisacrylamide were dispersed and dissolved in 20 mL of water. 50 mg of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropenone was dissolved in 20 mL of deionized water. The two solutions were mixed and sonicated for 15 minutes to ensure complete dissolution of all components. Then, 500 μL of acetic acid was added to ensure complete dissolution. The CS and KT solutions were then clear.

[0042] (2) Low-temperature polymerization

[0043] The completely dissolved solution was poured into a petri dish and frozen in a cryostat at -18°C for 1 hour. After the freezing was completed, the frozen solution was irradiated at room temperature for 1 hour using an ultraviolet lamp (LED-0016) with an output power of 30 W and a λmax = 365 nm to ensure cryopolymerization.

[0044] (3) Thawing

[0045] After the completion of the cryopolymerization, the sample was thawed at room temperature for 24 hours to dissolve the remaining ice crystals in the cryogel. To remove the unreacted monomers, biopolymers, and crosslinking agents, the sample was washed using a mixed solution of 20 mL of deionized water and 20 mL of methanol. Thereafter, it was freeze-dried for 24 hours to obtain the product VP-CS-KT-50, which was stored in a desiccator.

[0046] Example 2:

[0047] (1) Solution prepolymerization

[0048] 500 μL of vinylpyrrone monomer, 200 mg of chitosan biopolymer, 100 mg of keratin biopolymer, and 140 mg of N,N'-methylenebisacrylamide were dissolved in 40 mL of water, and 50 mg of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropenone was dissolved in 20 mL of deionized water. Both solutions were sonicated for 20 minutes to ensure complete dissolution of all components. 600 μL of acetic acid was further added to completely dissolve the CS and KT solutions, which became transparent quickly.

[0049] (2) Cryopolymerization

[0050] The completely dissolved solution was poured into a petri dish and frozen in a cryostat at -18°C for 1 hour. Thereafter, the frozen solution was exposed to an ultraviolet lamp (LED-0016) with an output power of 30 W and a λmax = 365 nm at the same temperature for an additional 1 hour to ensure cryopolymerization.

[0051] (3) Thawing

[0052] After the completion of the cryopolymerization, the sample was thawed at room temperature for 24 hours to dissolve the remaining ice crystals in the cryogel. To remove the unreacted monomers, biopolymers, and crosslinking agents, the sample was washed using a mixed solution of 30 mL of deionized water and 30 mL of methanol. Thereafter, it was freeze-dried for 24 hours to obtain the product VP-CS-KT-100, which was stored in a desiccator.

[0053] Example 3:

[0054] (1) Solution prepolymerization

[0055] A solution of 500 μL of vinylpyrrone monomer, 200 mg of chitosan biopolymer, 150 mg of keratin biopolymer, 210 mg of N,N'-methylene bisacrylamide crosslinking agent was dispersed and dissolved in 60 mL of deionized water, and 50 mg of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropenone photoinitiator was dissolved in 20 mL of deionized water. The two solutions were mixed and ultrasonically treated for 25 minutes to ensure complete dissolution of all components. 700 μL of acetic acid was added to ensure complete dissolution, and the CS and KT solutions were transparent.

[0056] (2) Cryopolymerization

[0057] The completely dissolved solution was poured into a petri dish and frozen in a cryostat at -18°C for 1 hour. Subsequently, the frozen solution was irradiated at room temperature for 1 hour using a UV lamp (LED-0016) with an output power of 30 W and λmax = 365 nm to ensure cryopolymerization.

[0058] (3) Thawing

[0059] After the completion of cryopolymerization, the sample was thawed at room temperature for 24 hours to dissolve the remaining ice crystals in the cryogel. To remove unreacted monomers, biopolymers, and crosslinking agents, the sample was washed using a mixture of 40 mL of deionized water and 40 mL of methanol. Subsequently, it was freeze-dried for 24 hours to obtain the product VP-CS-KT-150, which was stored in a desiccator.

[0060] Example 4:

[0061] (1) Solution prepolymerization

[0062] A solution of 500 μL of vinylpyrrone monomer, 200 mg of chitosan biopolymer, 200 mg of keratin biopolymer, 280 mg of N,N'-methylene bisacrylamide was dispersed and dissolved in 80 mL of deionized water, and 50 mg of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropenone was dissolved in 20 mL of deionized water. The solution was ultrasonically treated for 30 minutes to ensure complete dissolution of all components. 800 μL of acetic acid was added to ensure complete dissolution, and the CS and KT solutions were quickly transparent.

[0063] (2) Cryopolymerization

[0064] The completely dissolved solution was poured into a petri dish and frozen in a cryostat at -18°C for 1 hour. Subsequently, the frozen solution was irradiated at the same temperature for an additional 1 hour using a UV lamp (LED-0016) with an output power of 30 W and λmax = 365 nm to ensure cryopolymerization.

[0065] (3) Thawing

[0066] After the completion of the low temperature polymerization, the sample was thawed at room temperature for 24 h to dissolve the remaining ice crystals in the low temperature gel formed. To remove the unreacted monomers, biopolymers and crosslinking agent, the sample was washed with a mixture of 50 mL of deionized water and 50 mL of methanol. After that, the product VP-CS-KT-200 was obtained by freeze-drying for 24 h and stored in a desiccator.

[0067] Figure 2 SEM images of the three-dimensional macroporous chitosan-keratin cryogel adsorbents in Example 1 and Example 4 were analyzed by SEM to investigate the surface morphology and porosity of the prepared flexible macroporous bio-adsorbents, as shown in Figs. 2a and 2b. The SEM images at low KT concentration (Fig. 2a) and high KT concentration (Fig. 2b) show macroporous structures with pore sizes between 20-150 μm. When the KT concentration is low, the pores are large and the walls are thin, while at high KT concentration, the higher crosslinking density results in smaller and thicker walls. Figure 2 Figure 2 Figure 2 The SEM images at low KT concentration (Fig. 2a) and high KT concentration (Fig. 2b) show macroporous structures with pore sizes between 20-150 μm. When the KT concentration is low, the pores are large and the walls are thin, while at high KT concentration, the higher crosslinking density results in smaller and thicker walls.

[0068] Figure 3 TGA analysis of the three-dimensional macroporous chitosan-keratin cryogel adsorbents in Example 1 and Example 4, it can be seen that the stability of the VP-CS-KT-50 composite macroporous bio-adsorbent is lower than that of the VP-CS-KT-200 composite macroporous bio-adsorbent. When exposed to 800°C, the VP-based adsorbent is completely degraded, while the composite adsorbent exhibits superior stability, retaining 20-40% of its initial weight.

[0069] Figure 4 The infrared spectra of the three-dimensional macroporous chitosan-keratin cryogel adsorbent VP-CS-KT-200 and its synthetic monomers VP, CS, KT are compared, and through the modification of functional groups and the change of infrared spectrum, it can be seen that the final product is successfully synthesized.

[0070] Figure 5 Experiments were carried out at different ratios of KT concentration (50 mg, 100 mg, 150 mg and 200 mg corresponding to Examples 1, 2, 3, 4, respectively), while keeping the CS and VP concentrations constant. The adsorption results show that as the KT concentration increases, the recovery efficiency also increases, confirming that the -s-s- bond plays a key role in Au(III) adsorption.

[0071] Example 5: Effect of solution pH on gold ion adsorption capacity

[0072] Accurately weigh 6 portions of 3 mg of the low temperature gel bio-adsorbent VP-CS-KT-200 prepared under the conditions described in Example 4, and add them to 3 mL of solution with pH values of 1, 2, 3, 4, 5, 6, respectively, all with a concentration of 500 mg L -1 ​​In a gold ion solution, the solution was placed in a shaker at room temperature for 12 hours for adsorption. The solution was collected, filtered through a membrane, and the concentration of the remaining gold ions was detected by inductively coupled plasma atomic emission spectrometry (ICP). Three sets of parallel experiments were performed.

[0073] Figure 6 This is an example of pH results from Example 5. The three-dimensional macroporous chitosan-keratin cryogel adsorbent VP-CS-KT-200 prepared in Example 4 was adsorbed at different pH values. As the pH value increased from 1 to 3, the adsorption efficiency of Au(III) increased. When the pH value was higher than 3 (between 4 and 6), the adsorption efficiency of AuCl increased. 4- Hydrolysis and deprotonation reduce the ability of macroporous biosorbents to capture Au(III).

[0074] Example 6: Effect of adsorption time on the amount of gold ions adsorbed

[0075] Accurately weigh 7 portions of 3 mg of the low-temperature gel biosorbent VP-CS-KT-200 prepared under the conditions described in Example 4, and add them to 5 mL of a 500 mg / L solution. -1 In a gold ion solution with a pH of 3, the solution was placed in a shaker at room temperature for adsorption at 0, 15, 30, 60, 120, 240, and 360 min, respectively, and then centrifuged. The collected solution was filtered through a membrane and the concentration of the remaining gold ions was detected by inductively coupled plasma atomic emission spectrometry (ICP). Three parallel experiments were performed.

[0076] Figure 7 This section presents the adsorption kinetics results of Example 6. The three-dimensional macroporous chitosan-keratin cryogel adsorbent VP-CS-KT-200 prepared in Example 4 was subjected to kinetic adsorption experiments. The results show the adsorption of Au(III) within 0-360 minutes at pH 3. The maximum adsorption was observed to occur within the first 60 minutes, with Au(III) adsorption equilibrium reached in approximately 240 minutes. This is mainly attributed to the macroporous nature of the biosorbent, highlighting the rapid mass transfer effect of macroporous biosorbents.

[0077] Example 7: Effect of initial gold ion concentration on adsorption capacity

[0078] Accurately weigh 6 portions of 3 mg of low temperature gel biosorbent VP-CS-KT-200 prepared under the conditions described in Example 4, and add to 3 mL of gold ion solution with concentrations of 50, 100, 200, 300, 400, and 500 mg / L (pH = 3) respectively. Place the solution in a shaking bed at room temperature for 12 h of adsorption, and then separate by centrifugation to collect the adsorption solution. Repeat the operation at 35°C and 45°C. After passing through a membrane, detect the concentration of the remaining gold ions by inductively coupled plasma emission spectrometer (ICP), and perform three sets of parallel experiments.

[0079] Figure 8 is the result of the adsorption isotherm experiment of Example 7, which shows that the three-dimensional macroporous chitosan-keratin cold freeze gel adsorbent VP-CS-KT-200 prepared in Example 4 is subjected to adsorption experiments using Freundlich and Langmuir isotherm models. The adsorption amount of Au(III) increases with increasing temperature, and the experimental results are consistent with the Freundlich isotherm model. R 2 is 0.972, 0.987, and 0.984 at 298 K, 303 K, and 308 K, respectively. Therefore, the adsorption of Au(III) by the VP-CS-KT-200 macroporous biosorbent is mainly a multilayer adsorption on the heterogeneous surface of the low temperature gel.

[0080] Example 8: Effect of adsorbent stability on gold ion adsorption amount

[0081] (1) Regeneration stability

[0082] Accurately weigh 3 mg of low temperature gel biosorbent VP-CS-KT-200 prepared under the conditions described in Example 4, and add to 3 mL of gold ion solution with a concentration of 500 mg / L -1 and a pH of 3. After placing the solution in a shaking bed at room temperature for 12 h of adsorption and separating by centrifugation, remove the solution and wash with deionized water, then add 1 mL of eluent of 1 mol / L -1 thiourea in 0.1 mol / L -1 hydrochloric acid, continue dynamic adsorption on the shaking bed, and then separate by magnet, remove the solution and wash with deionized water. This is one cycle, and a total of four cycles are performed. After passing through a membrane, detect the adsorption and desorption solutions by inductively coupled plasma emission spectrometer (ICP), and perform three sets of parallel experiments.

[0083] (2) Storage stability

[0084] Accurately weigh 3 mg of low temperature gel biosorbent VP-CS-KT-200 prepared under the conditions described in Example 4, and store in a desiccator for 6 months. Then add 3 mL of gold ion solution with a concentration of 500 mg / L -1A gold ion solution with a pH of 3 was prepared and adsorbed on a shaker at room temperature for 12 hours. The adsorbate was then collected by centrifugation. After membrane filtration, the concentration of remaining gold ions was detected by inductively coupled plasma atomic emission spectrometry (ICP). Three parallel experiments were performed.

[0085] (3) Thermal stability

[0086] Accurately weigh 3 mg of the cryogenic gel biosorbent VP-CS-KT-200 prepared under the conditions described in Example 4, expose it to a temperature up to 100°C for 4 hours, and then add 3 mL of a 500 mg L solution. -1 A gold ion solution with a pH of 3 was prepared and adsorbed on a shaker at room temperature for 12 hours. The adsorbate was then collected by centrifugation. After membrane filtration, the concentration of remaining gold ions was detected by inductively coupled plasma atomic emission spectrometry (ICP). Three parallel experiments were performed.

[0087] Figure 9 This is a demonstration of the test results for the stability of the adsorbent in Example 8. The three-dimensional macroporous chitosan-keratin cryogel adsorbent VP-CS-KT-200 prepared in Example 4 was used as the test sample. As shown in (1), VP-CS-KT-200 can be used for multiple cycles. After four consecutive cycles, the loss of adsorbed Au(III) is limited to 1% to 2%, which shows good reproducibility and practicality. As shown in (2), the adsorption capacity of Au(III) was not affected after the adsorbent was stored in a desiccator for 6 months. This observation confirms that the adsorbent material has a stable shelf life, which is a very advantageous characteristic for industrial applications. As shown in (3), the adsorbent structure can still remain intact when exposed to temperatures up to 100°C. The test results for the adsorption performance of Au(III) also show that the macroporous bioadsorbent has thermal stability.

[0088] Example 9: Effect of multiple ion coexistence conditions on adsorbed gold ions

[0089] Accurately weigh 3 mg of the low-temperature gel biosorbent VP-CS-KT-200 prepared under the conditions described in Example 4, add 3 mL of simulated electronic waste liquid containing metal ions such as Au(III), Al(III), Co(II), Cr(III), Cu(II), Mn(II), Na(I), Ni(II), and Zn(II) (pH=3), place it on a magnetic stirrer at 25°C, and dynamically adsorb on a shaker for 12 h. After centrifugation, collect the adsorbent liquid, filter it through a membrane, and detect the concentration of the remaining ions by inductively coupled plasma atomic emission spectrometry (ICP). Perform three parallel experiments.

[0090] Figure 10The competitive adsorption performance of the three-dimensional macroporous shell chitosan-keratin cryogel adsorbent in Example 9 on gold ions in the presence of various ions was demonstrated, and the three-dimensional macroporous shell chitosan-keratin cryogel adsorbent VP-CS-KT-200 prepared in Example 4 was used as an adsorption sample. The results show that the removal rate of gold ions by VP-CS-KT-200 is significantly higher than that of other ions, indicating that VP-CS-KT-200 has high selectivity for gold ions.

[0091] The above examples are preferred embodiments of the present application, but the present application is not limited to the above embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art without departing from the essential content of the present application shall fall within the protection scope of the present application.

Claims

1. A process for the preparation of a three-dimensional macroporous chitosan-keratin cryogel adsorbent selective for gold, characterized by, It comprises the following steps: (1) Solution prepolymerization The vinyl pyrrolidone monomer, chitosan biopolymer CS, and keratin biopolymer KT, crosslinking agent N, N'-methylene bisacrylamide are dispersed and dissolved in deionized water to obtain solution A; Then 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl propenone photoinitiator is dissolved in deionized water to obtain solution B; After mixing solution A and solution B, ultrasonic treatment is performed until all components are dissolved, and acetic acid is added to completely dissolve the solution, and the CS and KT solutions are transparent; In solution A of step (1), the amount ratio of vinyl pyrrolidone monomer, chitosan biopolymer, keratin biopolymer, N, N'-methylene bisacrylamide and deionized water is 450-550 μL: 175-225 mg: 50-200 mg: 70-280 mg: 20-80 mL; (2) Low temperature polymerization The completely dissolved solution of step (1) is poured into a culture dish and frozen in a low temperature thermostat, after freezing, the frozen solution is controlled at the same temperature and irradiated with a UV lamp to ensure low temperature induced polymerization; The freezing temperature is -15 ~ -20℃, and the freezing time is 1-2 h; The output power of the ultraviolet lamp is 15-20 W, the wavelength λmax=365 nm, and the irradiation time is 1-2 h; (3) Thawing After low temperature induced polymerization is completed, the sample is thawed at room temperature to dissolve the remaining ice crystals in the sample, in order to remove unreacted monomers, biopolymers and crosslinking agents, the sample is washed with a mixture of deionized water and methanol, and then freeze-dried to obtain the product three-dimensional macroporous chitosan-keratin freeze gel adsorbent, which is stored in a desiccator.

2. The production method according to claim 1, wherein In solution B of step (1), the amount ratio of 2-hydroxy-4 '-(2-hydroxyethoxy)-2-methyl propenone and deionized water is 40-60 mg: 20 mL.

3. The production method according to claim 1, wherein In step (1), the volume ratio of solution A and solution B is 20-80 mL: 20 mL; the ultrasonic treatment time is 15-30 min.

4. The production method according to claim 1, wherein In step (3), the thawing time after low temperature induced polymerization is 24-48 h.

5. The production method according to claim 1, wherein In step (3), the freeze-drying time of the pure sample is 24-48 h.

6. A three-dimensional macroporous chitosan-keratin cryogel adsorbent selective for gold, characterized in that, It is prepared by the preparation method of any one of claims 1-5.

7. Use of the three-dimensional macroporous chitosan-keratin freeze gel adsorbent of claim 6 for selective adsorption of gold ions.

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