Preparation method of graphene oxide / chitosan composite cadmium ion-imprinted hydrogel

Abstract

This invention discloses a method for preparing a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel. First, polycarbonate microspheres are prepared via a self-emulsification method combined with low-temperature quenching. Using the polycarbonate microspheres as templates, orthosilicic acid is loaded onto the template surface, and finally calcined to obtain SiO2 hollow microspheres. In the presence of a cerium ammonium nitrate redox system, acrylic acid is grafted onto graphene oxide to obtain graphene oxide-grafted polyacrylic acid. Acrylic acid is grafted onto chitosan to obtain chitosan-grafted polyacrylic acid. The SiO2 hollow microspheres, chitosan-grafted polyacrylic acid, and graphene oxide-grafted polyacrylic acid are then reacted with Cd... 2+ Chelation, crosslinking with glutaraldehyde and thiourea, and washing with hydrochloric acid yielded a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel.

Description

Technical Field

[0001] This invention relates to a method for preparing a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel, belonging to the field of adsorption materials technology. Background Technology

[0002] Currently Cd 2+ The removal of Cd mainly employs chemical precipitation, ion exchange, microbial methods, electrolysis, and adsorption. While these methods all have some effectiveness, they also have their own limitations. Therefore, there is an urgent need to find a more effective method for removing Cd. 2+ Materials with highly selective adsorption and separation properties.

[0003] Ion imprinting is an important branch of molecular imprinting. Using different metal ions as templates, ion imprinting forms chelated metal-crosslinked polymers through coordination with polymers. After removing the templates, the ion-imprinted polymer is obtained. Compared with other recognition systems, this technique is simple, easy to operate, low-cost, and has good reproducibility. Furthermore, the polymers themselves possess strong mechanical strength, acid and alkali resistance, and long service life. The high selectivity and excellent physicochemical properties of ion-imprinted polymers make them promising for environmental analysis, and they have been the subject of much research in solid-phase extraction, membrane separation, chromatographic analysis, and biosensing. Currently, Ni... 2+ Pb 2+ Cd 2+ Ag + Zn 2 + and Hg + Metal ion-imprinted polymers using various metal ions as templates. For example, Cd... 2+ Using 4-vinylpyridine as the imprinting template and 4-vinylpyridine as the functional monomer, 15 cadmium ion imprinted polymers were prepared through systematic optimization of system conditions. Experimental results show that the prepared cadmium ion imprinted polymers possess good separation and recognition performance and high competitive selectivity, making them suitable for the extraction of Cd ions from complex samples. 2+ Selective removal. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel, so as to solve the above-mentioned problems existing in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel, comprising the following steps:

[0007] S1. Preparation of graphene oxide grafted with polyacrylic acid;

[0008] S2. Preparation of polycarbonate microspheres;

[0009] S3. Ethanol, distilled water, sodium silicate, polyethylene glycol and hexadecyltrimethylammonium bromide are mixed and then added to the polycarbonate microspheres to form a mixture. An aqueous solution of ammonium chloride is added to the mixture and reacted. After filtration, drying and calcination, SiO2 hollow microspheres are obtained.

[0010] S4. Preparation of chitosan-grafted polyacrylic acid;

[0011] S5. Dissolve the chitosan-grafted polyacrylic acid in distilled water, add cadmium nitrate, SiO2 hollow microspheres and graphene oxide-grafted polyacrylic acid, stir to form a mixture, react at 60-70 °C for 5 h, then soak the product in a mixed aqueous solution of glutaraldehyde and thiourea, and carry out a crosslinking reaction at 60-70 °C. Finally, wash to remove the template cadmium ions to obtain a SiO2 microsphere / graphene oxide / chitosan composite cadmium ion imprinted hydrogel.

[0012] As a preferred embodiment, the method for preparing the graphene oxide-grafted polyacrylic acid is as follows:

[0013] Graphene oxide was dissolved in distilled water, acrylic acid monomer was added, and under N2 protection, a nitric acid solution of cerium ammonium nitrate was added. The mixture was refluxed at 80°C, and the product was filtered, washed, and vacuum dried to obtain graphene oxide-grafted polyacrylic acid.

[0014] As a preferred embodiment, the mass ratio of graphene oxide to acrylic acid is (1~2):(40~60).

[0015] As a preferred embodiment, the polycarbonate microspheres are prepared by:

[0016] Polycarbonate was dissolved in tetrahydrofuran, glycerol was added, and homogenization was carried out to obtain an emulsion;

[0017] The emulsion was quenched at -50 to -10°C, then washed and freeze-dried to obtain the polycarbonate microspheres.

[0018] As a preferred embodiment, the polycarbonate, after being dissolved in tetrahydrofuran, has a mass fraction of 2-4%.

[0019] As a preferred embodiment, the mass ratio of sodium silicate to polycarbonate microspheres is (10~30):(5~10); the calcination temperature is 300~500℃.

[0020] As a preferred embodiment, the method for preparing the chitosan-grafted polyacrylic acid is as follows:

[0021] Chitosan was dissolved in an aqueous acetic acid solution, potassium persulfate and acrylic acid were added, and the reaction was carried out at 50-60 °C under N2 protection. Anhydrous ethanol was then added, and the pH was adjusted to 6-7. The mixture was cooled, filtered, washed, and vacuum dried to obtain chitosan-grafted polyacrylic acid.

[0022] As a preferred embodiment, the mass ratio of chitosan to acrylic acid is (1~3):(10~20).

[0023] As a preferred embodiment, the mass ratio of chitosan-grafted polyacrylic acid, cadmium nitrate, SiO2 hollow microspheres and graphene oxide-grafted polyacrylic acid is (3~6):(2~4):(2~4):(3~5), the mass concentration of glutaraldehyde is 3~5%, and the mass concentration of thiourea is 2~4%.

[0024] A graphene oxide / chitosan composite cadmium ion-imprinted hydrogel obtained by the aforementioned preparation method.

[0025] The mechanism of this invention is as follows:

[0026] First, polycarbonate was dissolved in tetrahydrofuran, then mixed with glycerol, and self-emulsified under homogenizing conditions to form an emulsion (quenching solution). Quenching, soaking, and washing yielded PC microspheres. Using the PC microspheres as a template, sodium silicate was reacted with ammonium chloride under surfactant conditions to obtain orthosilicic acid. After removing the template, SiO2 hollow microspheres were obtained. In the presence of a cerium ammonium nitrate redox system, acrylic acid was grafted onto graphene oxide to obtain graphene oxide-grafted polyacrylic acid. Acrylic acid was grafted onto chitosan to obtain chitosan-grafted polyacrylic acid. The SiO2 hollow microspheres, chitosan-grafted polyacrylic acid, and graphene oxide-grafted polyacrylic acid were then reacted with Cd... 2+ Chelation, crosslinking with glutaraldehyde and thiourea, and washing with hydrochloric acid yielded a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel. The large specific surface area and high porosity of SiO2 hollow microspheres and graphene oxide significantly improved the hydrogel's adsorption capacity. Furthermore, grafting amino and carboxyl groups onto polyacrylic acid with chitosan and carboxyl groups onto polyacrylic acid with graphene oxide enhanced the hydrogel's ability to adsorb Cd. 2+ The chelating ability of the hydrogel was improved by introducing thiourea and glutaraldehyde through cross-linking, thereby enhancing the hydrogel's ability to bind Cd. 2+ Adsorption capacity.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. Taking advantage of the high porosity and large specific surface area of ​​SiO2 hollow microspheres and graphene oxide, acrylic acid with heavy metal chelation function is grafted onto graphene oxide and loaded onto SiO2 hollow microspheres. Cadmium ion recognition sites are introduced on the microspheres and graphene using ion imprinting technology. While retaining the advantages of porous microspheres and graphene oxide, they are endowed with the ability to selectively separate cadmium ions.

[0029] 2. Modification and crosslinking with glutaraldehyde and thiourea introduces thiol groups into the molecular chain, which is beneficial for the control of Cd. 2+ The chelation adsorption greatly improves the adsorption performance of the adsorbent. Attached Figure Description

[0030] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0031] Figure 1 This is a flowchart illustrating the preparation of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel in Example 1 of this invention.

[0032] Figure 2 This is a scanning electron microscope image of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel prepared in Example 1 of this invention. Detailed Implementation

[0033] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0034] Definitions:

[0035] Imprinting factor: The ratio of the maximum adsorption capacity of the imprinted sample to that of the non-imprinted sample.

[0036] Cd 2+ / Cu 2+ Selectivity factor: The selectivity factor is the ratio of the number of samples to the number of Cd samples. 2+ Maximum adsorption capacity and Cu 2+ The ratio of maximum adsorption capacity.

[0037] Example 1

[0038] (1) Preparation of SiO2 hollow microspheres

[0039] 3 g of polycarbonate (PC) was added to 100 g of tetrahydrofuran solvent and magnetically stirred at 60 °C for 2 h until completely dissolved. 300 g of glycerol at 40 °C was added to the prepared mixture, and the mixture was homogenized at 50 °C for 20 min to form an emulsion. The emulsion was transferred to a 2 L beaker and placed in a pre-cooled -20 °C freezer for 5 h. After quenching, 1 L of an ice-water mixture was quickly added to the beaker, with the water changed every 8 h for 2 days. Finally, the sample was freeze-dried for 24 h to obtain PC microspheres.

[0040] 10 g ethanol, 30 g distilled water, 1.6 g sodium silicate, 0.1 g polyethylene glycol, and 0.01 g hexadecyltrimethylammonium bromide were added to a three-necked flask and dissolved by magnetic stirring. After dissolution, 0.6 g PC microspheres were added and the mixture was stirred magnetically to form a solution. 1 g ammonium chloride was dissolved in 5 mL distilled water to form an ammonium chloride solution. This solution was added dropwise to the three-necked flask and stirred magnetically. The mixture was reacted at 40 °C for 0.5 h. After the reaction, the mixture was washed, filtered, and dried. Finally, the sample was calcined at 450 °C for 2 h to obtain SiO2 hollow microspheres.

[0041] (2) Graphene oxide grafted with polyacrylic acid

[0042] 0.05 g of graphene oxide was dissolved in 90 mL of distilled water, and then 2 g of acrylic acid monomer was added. Under N2 protection, 0.02 g of cerium ammonium nitrate was dissolved in 20 mL of 1 mol / L nitric acid. The two solutions were mixed and refluxed at 80 °C for 24 h. The product was filtered, washed, and vacuum dried to obtain graphene oxide-grafted polyacrylic acid.

[0043] (3) Preparation of chitosan grafted with polyacrylic acid

[0044] 1.5 g of chitosan was dissolved in 200 mL of 1% acetic acid aqueous solution and magnetically stirred until dissolved. Then, 0.1 g of potassium persulfate and 15 g of acrylic acid were added. The mixture was reacted at 60 °C for 12 h under nitrogen protection. After the reaction was completed, anhydrous ethanol was added, and the pH was adjusted to 7 with sodium hydroxide solution. The mixture was cooled, filtered, washed, and vacuum dried to obtain chitosan-grafted polyacrylic acid.

[0045] (4) Preparation of oxidized graphene / chitosan composite cadmium ion-imprinted hydrogel

[0046] 0.6 g of chitosan-grafted polyacrylic acid was dissolved in 100 mL of distilled water. 0.3 g of cadmium nitrate was added, and the mixture was thoroughly mixed. Then, 0.3 g of SiO2 hollow microspheres and 0.5 g of graphene oxide-grafted polyacrylic acid were added, and the mixture was magnetically stirred to form a solution. The reaction was carried out at 60 °C for 5 h. The product was then immersed in 50 mL of a mixed aqueous solution of 4% glutaraldehyde and 2% thiourea, and reacted at 70 °C for 8 h. After immersion, the product was removed and repeatedly washed with 1 mol / L hydrochloric acid to remove cadmium ions from the template. Finally, it was washed with a large amount of distilled water to remove residual hydrochloric acid and vacuum dried to constant weight to obtain the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel. The preparation flow chart of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel is shown below. Figure 1 As shown in the image. Scanning electron microscopy (SEM) of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel. Figure 1 As shown in the figure, the hydrogel exhibits a loose, porous structure. The porosity and specific surface area of ​​the composite cadmium ion-imprinted hydrogel are 92.1% and 18.1 m², respectively. 2 The composite cadmium ion-imprinted hydrogel has a maximum adsorption capacity of 77.8 mg / g and an imprinting factor of 2.33 for Cd. 2+ / Cu 2+ The selectivity factor is 2.55.

[0047] Example 2

[0048] (1) Preparation of SiO2 hollow microspheres

[0049] 2 g of polycarbonate (PC) was added to 100 g of tetrahydrofuran solvent and magnetically stirred at 60 °C for 2 h to ensure complete dissolution. 300 g of glycerol at 40 °C was added to the prepared mixture, and the mixture was homogenized at 50 °C for 30 min to form an emulsion. The emulsion was poured into a 2 L beaker and placed in a pre-cooled -30 °C freezer for 5 h. After quenching, 1 L of an ice-water mixture was quickly added to the beaker, with the water changed every 8 h for 2 days. Finally, the sample was freeze-dried for 24 h to obtain PC microspheres.

[0050] 10 g ethanol, 30 g distilled water, 1.8 g sodium silicate, 0.1 g polyethylene glycol, and 0.01 g hexadecyltrimethylammonium bromide were added to a three-necked flask and dissolved by magnetic stirring. After dissolution, 0.8 g PC microspheres were added and the mixture was stirred magnetically to form a solution. 1 g ammonium chloride was dissolved in 5 mL distilled water to form an ammonium chloride solution. This solution was added dropwise to the three-necked flask, and the mixture was stirred magnetically and reacted at 40 °C for 0.5 h. After the reaction, the mixture was washed, filtered, and dried. Finally, the sample was calcined at 400 °C for 2 h to obtain SiO2 hollow microspheres.

[0051] (2) Graphene oxide grafted with polyacrylic acid

[0052] 0.07 g of graphene oxide was dissolved in 90 mL of distilled water, and then 2.5 g of acrylic acid monomer was added. Under N2 protection, 0.02 g of cerium ammonium nitrate was dissolved in 20 mL of 1 mol / L nitric acid. The two solutions were mixed and refluxed at 80 °C for 24 h. The product was filtered, washed, and vacuum dried to obtain graphene oxide-grafted polyacrylic acid.

[0053] (3) Preparation of chitosan grafted with polyacrylic acid

[0054] 1.5 g of chitosan was dissolved in 200 mL of 1% acetic acid aqueous solution and magnetically stirred until dissolved. Then, 0.1 g of potassium persulfate and 14 g of acrylic acid were added. The mixture was reacted at 60 °C for 12 h under nitrogen protection. After the reaction was completed, anhydrous ethanol was added, and the pH was adjusted to 7 with sodium hydroxide solution. The mixture was cooled, filtered, washed, and vacuum dried to obtain chitosan-grafted polyacrylic acid.

[0055] (4) Preparation of oxidized graphene / chitosan composite cadmium ion-imprinted hydrogel

[0056] 0.4 g of chitosan-grafted polyacrylic acid was dissolved in 100 mL of distilled water. 0.4 g of cadmium nitrate was added, and the mixture was thoroughly mixed. Then, 0.4 g of SiO2 hollow microspheres and 0.4 g of graphene oxide-grafted polyacrylic acid were added, and the mixture was magnetically stirred to form a solution. The reaction was carried out at 60 °C for 5 h. The product was then immersed in 50 mL of a mixed aqueous solution of 3% glutaraldehyde and 3% thiourea, and reacted at 70 °C for 8 h. After immersion, the product was removed and repeatedly washed with 1 mol / L hydrochloric acid to remove cadmium ions from the template. Finally, it was washed with a large amount of distilled water to remove residual hydrochloric acid and vacuum dried to constant weight to obtain a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel. The porosity and specific surface area of ​​the composite cadmium ion-imprinted hydrogel were 93.1% and 20.9 m², respectively. 2 The composite cadmium ion-imprinted hydrogel has a maximum adsorption capacity of 86.9 mg / g and an imprinting factor of 2.87 for Cd. 2+ / Cu 2+ The selectivity factor is 2.69.

[0057] Example 3

[0058] (1) Preparation of SiO2 hollow microspheres

[0059] 2.5 g of polycarbonate (PC) was added to 100 g of tetrahydrofuran solvent and magnetically stirred at 60 °C for 2 h to ensure complete dissolution. 300 g of glycerol at 40 °C was added to the prepared mixture, and the mixture was homogenized at 50 °C for 25 min to form an emulsion. The emulsion was transferred to a 2 L beaker and placed in a pre-cooled -10 °C freezer for quenching for 5 h. After quenching, 1 L of an ice-water mixture was quickly added to the beaker, with the water changed every 8 h for 2 days. Finally, the sample was freeze-dried for 24 h to obtain PC microspheres.

[0060] 10 g ethanol, 30 g distilled water, 2 g sodium silicate, 0.1 g polyethylene glycol, and 0.01 g hexadecyltrimethylammonium bromide were added to a three-necked flask and dissolved by magnetic stirring. After dissolution, 0.7 g PC microspheres were added and the mixture was stirred magnetically to form a solution. 1 g ammonium chloride was dissolved in 5 mL distilled water to form an ammonium chloride solution. This solution was added dropwise to the three-necked flask, and the mixture was stirred magnetically and reacted at 40 °C for 0.5 h. After the reaction, the mixture was washed, filtered, and dried. Finally, the sample was calcined at 380 °C for 2 h to obtain SiO2 hollow microspheres.

[0061] (2) Graphene oxide grafted with polyacrylic acid

[0062] 0.06 g of graphene oxide was dissolved in 90 mL of distilled water, and then 2.3 g of acrylic acid monomer was added. Under N2 protection, 0.03 g of cerium ammonium nitrate was dissolved in 20 mL of 1 mol / L nitric acid. The two solutions were mixed and refluxed at 80 °C for 24 h. The product was filtered, washed, and vacuum dried to obtain graphene oxide-grafted polyacrylic acid.

[0063] (3) Preparation of chitosan grafted with polyacrylic acid

[0064] 1.2 g of chitosan was dissolved in 200 mL of 1% acetic acid aqueous solution and magnetically stirred until dissolved. Then, 0.1 g of potassium persulfate and 16 g of acrylic acid were added. The mixture was reacted at 60 °C for 12 h under nitrogen protection. After the reaction was completed, anhydrous ethanol was added, and the pH was adjusted to 7 with sodium hydroxide solution. The mixture was cooled, filtered, washed, and vacuum dried to obtain chitosan-grafted polyacrylic acid.

[0065] (4) Preparation of oxidized graphene / chitosan composite cadmium ion-imprinted hydrogel

[0066] 0.5 g of chitosan-grafted polyacrylic acid was dissolved in 100 mL of distilled water. 0.4 g of cadmium nitrate was added, and the mixture was thoroughly mixed. Then, 0.3 g of SiO2 hollow microspheres and 0.5 g of graphene oxide-grafted polyacrylic acid were added, and the mixture was magnetically stirred to form a solution. The reaction was carried out at 60 °C for 5 h. The product was then immersed in 50 mL of a mixed aqueous solution of 3% glutaraldehyde and 4% thiourea, and reacted at 70 °C for 8 h. After immersion, the product was removed and repeatedly washed with 1 mol / L hydrochloric acid to remove cadmium ions from the template. Finally, it was washed with a large amount of distilled water to remove residual hydrochloric acid and vacuum dried to constant weight to obtain a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel. The porosity and specific surface area of ​​the composite cadmium ion-imprinted hydrogel were 90.9% and 22.1 m², respectively. 2 The composite cadmium ion-imprinted hydrogel has a maximum adsorption capacity of 80.6 mg / g and an imprinting factor of 2.65 for Cd. 2+ / Cu 2+ The selectivity factor is 2.78.

[0067] Comparative Example 1

[0068] Unlike Example 1, in step 3), the amount of graphene oxide grafted with polyacrylic acid added was 0, ultimately yielding a chitosan-cadmium ion-imprinted hydrogel. This hydrogel had a porosity of 80.1% and a specific surface area of ​​10.1 m². 2 The composite cadmium ion-imprinted hydrogel has a maximum adsorption capacity of 55.1 mg / g and an imprinting factor of 2.59 for Cd. 2+ / Cu 2+ The selectivity factor was 2.59. Compared with Comparative Example 1, the porosity and specific surface area of ​​the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel prepared in Example 1 were increased, and the maximum adsorption capacity also increased from 55.1 mg / g to 77.8 mg / g. This was mainly because the addition of graphene greatly improved the porosity and specific surface area of ​​the hydrogel, thus increasing the adsorption capacity.

[0069] Comparative Example 2

[0070] Unlike Example 1, in step 3), "graphene oxide grafted with polyacrylic acid" was replaced with "graphene oxide," ultimately yielding a graphene oxide / chitosan cadmium ion-imprinted hydrogel. This hydrogel has a porosity of 90.1% and a specific surface area of ​​17.8 m². 2 The composite cadmium ion-imprinted hydrogel has a maximum adsorption capacity of 65.1 mg / g and an imprinting factor of 2.49 for Cd. 2+ / Cu 2+The selectivity factor was 2.61. Compared with Comparative Example 2, the maximum adsorption capacity of the oxidized graphene / chitosan composite cadmium ion imprinted hydrogel prepared in Example 1 also increased from 65.1 mg / g to 77.8 mg / g. This is mainly because after grafting polyacrylic acid onto graphene oxide, carboxyl groups are introduced into the molecular chain. Carboxyl groups have a strong chelating function for cadmium ions, thus increasing the adsorption capacity of the hydrogel.

[0071] Comparative Example 3

[0072] Unlike Example 1, in step 3), the amount of SiO2 hollow microspheres added was 0, ultimately yielding an oxidized graphene oxide / chitosan cadmium ion-imprinted hydrogel. The porosity and specific surface area of ​​this hydrogel were 78.1% and 10.9 m², respectively. 2 The composite cadmium ion-imprinted hydrogel has a maximum adsorption capacity of 60.8 mg / g and an imprinting factor of 2.77 for Cd. 2+ / Cu 2+ The selectivity factor was 2.67. Compared with Comparative Example 3, the porosity and specific surface area of ​​the oxidized graphene / chitosan composite cadmium ion-imprinted hydrogel prepared in Example 1 were significantly improved, and the maximum adsorption capacity of the hydrogel also increased from 62.1 mg / g to 77.8 mg / g. This was mainly because the addition of SiO2 hollow microspheres to the system greatly increased the porosity and specific surface area of ​​the hydrogel, thus increasing the adsorption capacity of the hydrogel.

[0073] Comparative Example 4

[0074] Unlike Example 1, in step 3), "chitosan" was used instead of "chitosan-grafted polyacrylic acid," ultimately yielding an oxidized graphene oxide / chitosan cadmium ion-imprinted hydrogel. This hydrogel has a porosity of 90.9% and a specific surface area of ​​20.8 m². 2 The composite cadmium ion-imprinted hydrogel has a maximum adsorption capacity of 62.1 mg / g and an imprinting factor of 2.23 for Cd. 2+ / Cu 2+ The selectivity factor was 2.73. Compared with Comparative Example 4, the maximum adsorption capacity of the oxidized graphene / chitosan composite cadmium ion imprinted hydrogel prepared in Example 1 also increased from 62.1 mg / g to 77.8 mg / g. This is mainly because after chitosan is grafted with polyacrylic acid, carboxyl groups are introduced into the molecular chain. Carboxyl groups have a strong chelating function for cadmium ions, thus increasing the adsorption capacity of the hydrogel.

[0075] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a graphene oxide / chitosan composite cadmium ion-imprinted hydrogel, characterized in that, Includes the following steps: S1. Preparation of graphene oxide grafted with polyacrylic acid; S2. Preparation of polycarbonate microspheres; S3. Ethanol, distilled water, sodium silicate, polyethylene glycol and hexadecyltrimethylammonium bromide are mixed and then added to the polycarbonate microspheres to form a mixture. An aqueous solution of ammonium chloride is added to the mixture and reacted. After filtration, drying and calcination, SiO2 hollow microspheres are obtained. S4. Preparation of chitosan-grafted polyacrylic acid; S5. Dissolve the chitosan-grafted polyacrylic acid in distilled water, add cadmium nitrate, SiO2 hollow microspheres and graphene oxide-grafted polyacrylic acid, stir to form a mixture, react at 60-70℃ for 5 h, then soak the product in a mixed aqueous solution of glutaraldehyde and thiourea, and carry out a cross-linking reaction at 60-70℃. Finally, wash to remove template cadmium ions to obtain SiO2 microsphere / graphene oxide / chitosan composite cadmium ion imprinted hydrogel. The preparation method of the graphene oxide grafted polyacrylic acid is as follows: Graphene oxide was dissolved in distilled water, acrylic acid monomer was added, N2 was passed through for protection, nitric acid solution of cerium ammonium nitrate was added, and the reaction was refluxed at 80°C. The product was filtered, washed, and vacuum dried to obtain graphene oxide grafted polyacrylic acid. The polycarbonate microspheres are prepared by: Polycarbonate was dissolved in tetrahydrofuran, glycerol was added, and homogenization was carried out to obtain an emulsion; The emulsion was quenched at -50 to -10°C, then washed and freeze-dried to obtain the polycarbonate microspheres.

2. The preparation method of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel as described in claim 1, characterized in that, The mass ratio of graphene oxide to acrylic acid is (1~2):(40~60).

3. The preparation method of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel as described in claim 1, characterized in that, The polycarbonate, after being dissolved in tetrahydrofuran, has a mass fraction of 2-4%.

4. The preparation method of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel as described in claim 1, characterized in that, The mass ratio of sodium silicate to polycarbonate microspheres is (10~30):(5~10); the calcination temperature is 300~500℃.

5. The preparation method of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel as described in claim 1, characterized in that, The preparation method of the chitosan-grafted polyacrylic acid is as follows: Chitosan was dissolved in an aqueous acetic acid solution, potassium persulfate and acrylic acid were added, and the reaction was carried out at 50-60°C under N2 protection. Anhydrous ethanol was then added, and the pH was adjusted to 6-7. The mixture was cooled, filtered, washed, and vacuum dried to obtain chitosan-grafted polyacrylic acid.

6. The preparation method of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel as described in claim 5, characterized in that, The mass ratio of chitosan to acrylic acid is (1~3):(10~20).

7. The preparation method of the graphene oxide / chitosan composite cadmium ion-imprinted hydrogel as described in claim 1, characterized in that, The mass ratio of chitosan-grafted polyacrylic acid, cadmium nitrate, SiO2 hollow microspheres, and graphene oxide-grafted polyacrylic acid is (3~6):(2~4):(2~4):(3~5), the mass concentration of glutaraldehyde is 3~5%, and the mass concentration of thiourea is 2~4%.

8. A graphene oxide / chitosan composite cadmium ion-imprinted hydrogel obtained by the preparation method according to any one of claims 1 to 7.

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