Preparation method and application of chitosan-iron-cerium microspheres

Abstract

The present invention discloses a preparation method and application of chitosan-iron-cerium microspheres. The preparation method is as follows: different ferrous salts and cerium salts are selected as the iron source and cerium source, and are respectively dissolved in adipic acid solution together with chitosan powder. The dissolved Fe(II) solution and Ce(III) solution are successively added to the dissolved chitosan solution, and are fully stirred at room temperature to form a chitosan-iron-cerium precursor solution. The precursor solution is dropped into an alkaline solution with a syringe to form microspheres. After aging, the microspheres are washed to neutrality, cross-linked in glutaraldehyde and absolute ethanol, dehydrated and then stored in an ethanol solution, and dried to obtain chitosan-iron-cerium microspheres. The chitosan-iron-cerium microspheres prepared by the present invention can be used to remove heavy metal ions and organic pollutants in water and play a role in catalytic oxidation. The materials used in the preparation process are environmentally friendly and inexpensive, and it is an environmentally friendly and highly efficient catalytic material with low cost and high efficiency.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a water treatment material, chitosan-iron-cerium microspheres, which have both good adsorption enrichment and catalytic oxidation functions and have good development prospects in the field of wastewater treatment. Background Art

[0002] Chitosan is a product of partial (more than 55%) deacetylation of chitin and is a cost-effective material that can be applied to agriculture, medicine, and industrial wastewater treatment. As a water treatment material, chitosan is considered to be one of the promising biopolymers due to its excellent adsorption properties and metal ion stability (MAC, LI F, WANG C, et al. Tuning the adsorption behaviour of beta-structure chitosan by metal binding[J]. Environmental Chemistry, 2018, 15(5): 267-277.). However, pure chitosan adsorbents have insufficient mechanical stability and chemical resistance in water (NEGM NA, HEFNI H H H, ABD-ELAALAAA, et al. Advancement on modification of chitosan biopolymer and its potential applications[J]. International Journal of Biological Macromolecules, 2020, 152: 681-702.), and there is no obvious adsorption selectivity for pollutants, so the actual application range is limited. Preparing chitosan derivatives with chitosan as the carrier through chemical modification reactions can expand the functions and properties of the materials. Chitosan-metal composites can combine the characteristics of chitosan macromolecules and the ability of metal elements themselves to participate in electron transfer and transportation. After modification, chitosan materials can exhibit higher water treatment efficiency and reusability.

[0003] As a common adsorption material, iron oxide is often used in chitosan modification. Huo et al. explored the adsorption performance of the composite adsorbent CTS-Fe(II) crosslinked by chitosans with different molecular weights and ferrous sulfate. The adsorption performance of CTS-Fe(II) for harmful elements such as lead and cadmium contained in the traditional Chinese medicine Ligusticum chuanxiong was tested by atomic absorption spectrometry. The results showed that during the use of the CTS-Fe(II) composite adsorbent, the maximum absorption amount of CTS-Fe(II) for heavy metals was over 90%, and the retention amount of active ingredients was 70%, which was a good adsorbent (Q. Huo, X. Q. Liu, L. Zheng, X. Y. Wang. Study on Crosslinked Chitosan Adsorbent of Heavy Metals in Traditional Chinese Medicine[J]. Asian Journal of Chemistry, 2014, 26(9): 2745-2747.). Although iron oxides also have strong Fenton-like catalytic effects, the adsorption and enrichment of pollutants easily occupy catalytic active sites, thus affecting the catalytic efficiency. Cerium oxide has a high ion mobility due to the presence of oxygen vacancies. In addition to its strong catalytic effect itself, when cerium oxide is combined with other metal oxides, it can also accelerate the flow of oxygen in the crystal phase, providing more active oxygen species for catalytic oxidation, thereby obtaining better activity and thermal stability (Cui Juanni. Preparation and Properties Study of CeO2-MOx (M = Zn / Mn / Cu) Porous Composites[D]. Xi'an University of Technology, 2020.). Compared with chitosan-iron oxide composites with a single metal component, it is expected to obtain a wider range of application scopes and application functions after being combined with cerium.

[0004] When chitosan is combined with metal oxides, especially nano-scale metal oxide particles, maintaining the dispersibility and firmness of metal oxide particles is the key to material preparation. There is an amino group and a hydroxyl group on the sugar residue of chitosan at C-2 and C-3 respectively. The special structure of the equatorial bond makes chitosan have a chelating effect on metal ions with a certain ionic radius and can effectively combine with metal ions under certain pH conditions. When the chitosan-metal complex is used as a precursor, chitosan can provide uniform and dispersed nucleation sites for the formation of metal oxides. At the same time, as a polymer, chitosan can play a confining role in the growth of metal oxide crystals and control the particle size of metal oxides. It shows high adsorption performance for organic and heavy metal pollutants in wastewater, but there are still some limitations, such as the problem of secondary pollution easily generated during the regeneration stage of the adsorbent when eluting with strong acids and alkalis. Therefore, the concept of preparing chitosan-multi-metal materials has been successively proposed. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a chitosan bimetallic microsphere water treatment material with a wider application range and more diverse functions, which can adsorb and enrich and catalytically oxidize and degrade organic pollutants such as antibiotics and heavy metals in wastewater.

[0006] A preparation method of chitosan-iron-cerium microspheres, which selects different ferrous salts and cerium salts and dissolves them in adipic acid, fully stirs and mixes them with a chitosan solution also dissolved in adipic acid to form a precursor solution, and then drops the precursor solution into an alkaline solution with a syringe to form spherical substances. After aging, cross-linking is carried out in a glutaraldehyde ethanol solution, and dehydration is gradually carried out and stored in absolute ethanol, and chitosan-iron-cerium microspheres are obtained by drying.

[0007] Preferably, the concentration of the ferrous salt solution in the present invention is 0.35-2.0 mol / L; the ferrous salt is at least one of ferrous chloride and ferrous nitrate.

[0008] Preferably, the concentration of the cerium salt solution in the present invention is 0.03-1.00 mol / L; the cerium salt is at least one of cerium nitrate and cerium carbonate.

[0009] Preferably, the molar ratio of the cerium salt to the ferrous salt in the present invention is 1:(1-5).

[0010] Preferably, the concentration of adipic acid in the present invention is 0.10 mol / L-0.20 mol / L.

[0011] Preferably, the dosage of chitosan in the present invention is 10.0-30.0 g / L.

[0012] Preferably, the concentration of the alkaline solution in the present invention is 1-3 mol / L.

[0013] Preferably, the ratio of glutaraldehyde to absolute ethanol in the present invention is 1:(3-5).

[0014] Preferably, the stirring time at room temperature in the present invention is 0.5-3 h; the aging time is 6-24 hours, and the cross-linking time is 8-14 hours; the drying method is vacuum drying, and the drying temperature is 45-55 °C.

[0015] An application of a chitosan-iron-cerium microsphere material prepared by the preparation method of the present invention.

[0016] When preparing chitosan-iron-cerium microspheres, the present invention comprises the following steps: dissolving chitosan, ferrous salt and cerium salt in an adipic acid solution respectively; sequentially adding a dissolved Fe(II) solution and a Ce(III) solution into the dissolved chitosan solution; fully stirring at room temperature to form a chitosan-iron-cerium precursor solution; dripping the solution into an alkaline solution with a syringe to form microspheres; aging the solution and washing the solution to neutrality; cross-linking the solution in glutaraldehyde and anhydrous ethanol; dehydrating the solution and storing the solution in an ethanol solution; and drying the solution to obtain the chitosan-iron-cerium microspheres.

[0017] Considering that chitosan is almost insoluble in solutions with a pH greater than 6.5, 0.12 mol / L adipic acid solution is used for dissolution. At the same time, the dissolved chitosan-iron-cerium precursor solution is dropped into an alkaline solution with a concentration greater than 1 mol / L, and spherical particles can be prepared by the action of surface tension.

[0018] To promote the complexation of chitosan with the two metal ions, Fe(III) and Ce(III), ferrous and ceric salts coordinate in a specific ratio. Therefore, the concentration of the ferrous salt solution is selected to be 1.5-2.0 mol / L, and the concentration of the ceric salt solution is selected to be 0.07-0.35 mol / L. Ceric salts accelerate electron transfer on the surface of the complex material through surface oxygen vacancies, promoting the Fe(III) / Fe(II) cycle in the Fenton-like reaction, thereby continuously oxidizing and degrading pollutants. However, when the ceric salt concentration is too low, the Fenton-like cycle will not proceed smoothly. A high or low molar ratio of ferrous salt to ceric salt will affect the coordination of chitosan with the two metal ions, affecting the complex material's spherical formation and pollutant removal ability. Furthermore, because chitosan has abundant amino and hydroxyl groups in its structure, they not only provide sites for crystal formation but also prevent aggregation during growth.

[0019] The chitosan-iron-cerium microspheres prepared by the above method not only adsorb and remove pollutants, but the addition of cerium salts also enables them to catalyze pollutants. The complex can be directly added to wastewater for reaction, promoting the Fe(III) / Fe(II) cycle in a Fenton-like reaction, thereby continuously oxidizing and degrading heavy metal ions.

[0020] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0021] (1) The chitosan-iron-cerium microspheres prepared by the method of the present invention are simple to prepare and inexpensive. The reagents and drugs involved in the preparation process are non-toxic and harmless and will not cause secondary pollution. In addition, the use of the complex material is very simple.

[0022] (2) Compared with the single-metal chitosan complex, the chitosan-iron-cerium microspheres prepared by the method of the present invention have cerium oxide and goethite in the complex material due to the addition of ferrous chloride and cerium nitrate. On the one hand, the presence of iron oxides can effectively increase the specific surface area of the complex, thereby enhancing the adsorption performance of the material and increasing the reaction sites. On the other hand, the presence of cerium oxide can accelerate the electron transfer on the material surface through the oxygen vacancies on the surface, promoting the Fe(Ⅲ) / Fe(Ⅱ) cycle in the Fenton-like reaction and continuously catalyzing the oxidation of heavy metal ions.

[0023] (3) The chitosan-iron-cerium microsphere material prepared by the method of the present invention broadens the application scope of iron-based and cerium-based materials in the removal of organic pollutants such as antibiotics and heavy metal pollutants in wastewater by constructing an "adsorption enrichment-catalytic oxidation degradation" system in advanced oxidation technology.

[0024] In summary, the present invention uses a chitosan-iron-cerium complex as a precursor to prepare a microsphere material with uniformly dispersed iron and cerium oxide particles. Its simultaneous adsorption enrichment and catalytic oxidation functions can effectively adsorb organic pollutants and metal pollutants in wastewater. Combined with the addition of oxidants such as hydrogen peroxide, it can simultaneously catalytically oxidize and degrade organic pollutants or convert metal pollutants into less harmful forms. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the XRD pattern of the chitosan-iron-cerium microsphere material of the present invention. According to the comparison results of the database, the main components of the material are goethite (FeOOH) and cerium oxide (CeO2).

[0026] Figure 2a It is the XPS spectrum of the total ion map of the chitosan-iron-cerium microsphere material of the present invention before and after the reaction.

[0027] Figure 2b It is the XPS spectrum of O1s of the chitosan-iron-cerium microsphere material of the present invention before and after the reaction.

[0028] Figure 2c It is the XPS spectrum of Fe2p of the chitosan-iron-cerium microsphere material of the present invention before and after the reaction.

[0029] Figure 2d It is the XPS spectrum of Ce3d of the chitosan-iron-cerium microsphere material of the present invention before and after the reaction.

[0030] It can be seen by comparison that the proportion of defective oxygen decreases before and after the reaction. In the catalytic reaction, electron transfer occurs at the oxygen vacancies. At the same time, Fe(Ⅱ), Fe(Ⅲ), Ce(Ⅲ) and Ce(Ⅳ) exist in the crystal structure of the complex material, which is beneficial to the electron transfer on the oxygen vacancies, thereby promoting the decomposition of hydrogen peroxide in the Fenton-like reaction process.

[0031] Figure 3a This is the SEM image of the chitosan-iron-cerium microsphere material of the present invention.

[0032] Figure 3b This is the TEM image of the chitosan-iron-cerium microsphere material of the present invention.

[0033] Figure 3c This is the HR-TEM image of the chitosan-iron-cerium microsphere material of the present invention with a lattice fringe spacing of 0.31 nm.

[0034] Figure 3d This is the HR-TEM image of the chitosan-iron-cerium microsphere material of the present invention with a lattice fringe spacing of 0.25 nm.

[0035] It can be intuitively found from the EDS image that Fe and Ce elements can be evenly distributed in the material. Combining with the TEM image, it can be found that goethite (FeOOH) is in the form of thin flakes, and some are curled. Cerium oxide (CeO2) mainly exists in the form of particles. HR-TEM shows that the lattice fringe spacings of 0.31 nm and 0.25 nm correspond to the (111) crystal plane reflection of CeO2 and the (100) crystal plane reflection of FeOOH respectively. Detailed implementation mode

[0036] To make the present invention more obvious and understandable, preferred embodiments are hereby described in detail in conjunction with the accompanying drawings as follows.

[0037] Example 1

[0038] Weigh 0.07 mol / L cerium nitrate and 1.75 mol / L ferrous chloride, and dissolve them in 50 ml and 10 ml of 0.12 mol / L adipic acid solution respectively. Weigh 2.0 g of chitosan and dissolve it in 0.12 mol / L adipic acid solution, and stir at room temperature for 1 h to obtain the chitosan-iron-cerium precursor solution. Drop the chitosan-iron-cerium precursor solution into 2 mol / L NaOH solution with an aging time of 12 h. Wash it with deionized water until neutral, then transfer it to 5% glutaraldehyde ethanol solution and let it stand for 12 h. Subsequently, dehydrate it step by step with 25%, 50%, and 100% ethanol solutions, and finally store it in absolute ethanol and seal it to isolate oxygen. Then dry it in an oven at 55 °C for use.

[0039] Example 2

[0040] Weigh 0.07 mol / L cerium carbonate and 1.75 mol / L ferrous chloride, and dissolve them in 50 ml and 10 ml of 0.12 mol / L adipic acid solution respectively. Weigh 2.0 g of chitosan and dissolve it in 0.12 mol / L adipic acid solution, and stir for 1 h at room temperature to obtain a chitosan-iron-cerium precursor solution. Drop the chitosan-iron-cerium precursor solution into 2 mol / L NaOH solution with an aging time of 12 h. Wash it with deionized water until neutral, then transfer it into 5% glutaraldehyde ethanol solution and let it stand for 12 h. Subsequently, dehydrate it step by step with 25%, 50%, and 100% ethanol solutions, and finally store it in absolute ethanol, sealed off from oxygen. Then dry it in an oven at 55 °C for use.

[0041] Example 3

[0042] Weigh 0.07 mol / L cerium nitrate and 1.75 mol / L ferrous nitrate, and dissolve them in 50 ml and 10 ml of 0.12 mol / L adipic acid solution respectively. Weigh 2.0 g of chitosan and dissolve it in 0.12 mol / L adipic acid solution, and stir for 1 h at room temperature to obtain a chitosan-iron-cerium precursor solution. Drop the chitosan-iron-cerium precursor solution into 2 mol / L NaOH solution with an aging time of 12 h. Wash it with deionized water until neutral, then transfer it into 5% glutaraldehyde ethanol solution and let it stand for 12 h. Subsequently, dehydrate it step by step with 25%, 50%, and 100% ethanol solutions, and finally store it in absolute ethanol, sealed off from oxygen. Then dry it in an oven at 55 °C for use.

[0043] Comparative Example 1

[0044] Change the cerium nitrate added in Example 1 to cerium sulfate, and keep the rest the same as in Example 1 to prepare a chitosan-iron microsphere material.

[0045] Comparative Example 2

[0046] Change the cerium nitrate added in Example 1 to cerium oxalate, and keep the rest the same as in Example 1 to prepare a chitosan-iron microsphere material.

[0047] Comparative Example 3

[0048] Change the ferrous chloride added in Example 1 to ferrous sulfate, and keep the rest the same as in Example 1 to prepare a chitosan-iron microsphere material.

[0049] Comparative Example 4

[0050] Change the ferrous chloride added in Example 1 to ferrous oxalate, and keep the rest the same as in Example 1 to prepare a chitosan-iron microsphere material.

[0051] Experiment 1: Weigh 0.20 g of the microsphere materials prepared by the methods of Examples 1 to 3 and Comparative Examples 1 to 4 respectively, and put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L, 50 mL of potassium pyroantimonate solution with a concentration of 50 mg / L, 50 mL of dye reactive black 5 with a concentration of 50 mg / L, and 50 mL of antibiotic oxytetracycline solution with a concentration of 50 mg / L. Stir at 400 r / min for 3 h at room temperature. Use ICP to measure the content of Sb(III / V) in the solution before and after the reaction, use an ultraviolet spectrophotometer to measure the content of reactive black 5 in the solution before and after the reaction, and use HPLC to measure the content of antibiotic oxytetracycline before and after the reaction.

[0052] Table 1

[0053]

[0054] As shown in Table 1, when preparing the chitosan-iron-cerium precursor solution, the selection of cerium salt and iron salt will affect the removal effect of the prepared chitosan-iron-cerium microspheres on pollutants. Especially when cerium sulfate and ferrous sulfate are selected, since sulfate can directly complex with chitosan, only a small part of metals Fe and Ce can be fixed on the chitosan molecule during the microsphere preparation process, and after dropping into the alkaline solution, the surface tension is insufficient to form spheres and can only be dispersed in the alkaline solution. The solubility of cerium oxalate and ferrous oxalate is relatively low, and the content that can be dissolved during the preparation process is extremely small. As a result, the content of metal cerium and iron in the prepared microsphere materials is the lowest. In Comparative Examples 1 to 4, due to the differences in the properties of the cerium salt and iron salt added during the preparation process, the material preparation effect is poor, and the removal effect on pollutants is also poor. In Examples 1 to 3, the combination of cerium nitrate and ferrous chloride has the best removal effect on the four pollutants.

[0055] Comparative Example 5

[0056] Change the dosage of cerium nitrate in Example 1 to 0 mol / L, and the rest are the same as in Example 1 to prepare the chitosan-iron microsphere material.

[0057] Comparative Example 6

[0058] Change the dosage of ferrous chloride in Example 1 to 0 mol / L, and the rest are the same as in Example 1 to prepare the chitosan-cerium microsphere material.

[0059] Experiment 2: Weigh 0.20 g of the microsphere materials prepared by the methods of Example 1 and Comparative Examples 5-6 respectively, and put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L, 50 mL of potassium pyroantimonate solution with a concentration of 50 mg / L, 50 mL of dye reactive black 5 with a concentration of 50 mg / L, and 50 mL of antibiotic oxytetracycline solution with a concentration of 50 mg / L respectively. Stir at 400 r / min for 3 h at room temperature. Use ICP to measure the content of Sb(III / V) in the solution before and after the reaction, use a UV spectrophotometer to measure the content of reactive black 5 in the solution before and after the reaction, and use HPLC to measure the content of antibiotic oxytetracycline before and after the reaction.

[0060] Table 2

[0061]

[0062] As shown in Table 2, the chitosan-iron-cerium microsphere materials prepared by using iron and cerium bimetals have obvious differences in the performance of removing heavy metal antimony compared with the chitosan-iron microsphere materials and chitosan-cerium microsphere materials of single metals. The bimetallic complex materials have much better removal performance for the four pollutants than the monometallic complex materials.

[0063] Experiment 3: Weigh 0.20 g of the microsphere materials prepared by the methods of Example 1 and Comparative Examples 5-6 respectively, and put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L, 50 mL of potassium pyroantimonate solution with a concentration of 50 mg / L, 50 mL of dye reactive black 5 with a concentration of 50 mg / L, and 50 mL of antibiotic oxytetracycline solution with a concentration of 50 mg / L respectively. Add 0.15 mL of H2O2 solution (concentration: 30 wt%) dropwise, stir at 400 r / min for 3 h at room temperature. Use ICP to measure the content of Sb(III / V) in the solution before and after the reaction, use a UV spectrophotometer to measure the content of reactive black 5 in the solution before and after the reaction, and use HPLC to measure the content of antibiotic oxytetracycline before and after the reaction.

[0064] Table 3

[0065]

[0066]

[0067] As shown in Table 3, on the basis of Experiment 2, when adding H2O2 during the addition of microsphere materials to remove pollutants, it can be clearly found that the chitosan-iron-cerium microsphere materials have an obvious catalytic effect. For the single-metal material, chitosan-iron microspheres, under the action of H2O2, the catalytic effect is not particularly obvious. There are oxygen vacancies on the surface of the microsphere materials, which can accelerate the electron transfer on the material surface, promote the redox reaction between Fe(III) / Fe(II), and then accelerate the activation and decomposition of H2O2 into ·OH free radicals, significantly improving the generation efficiency of ·OH. It continuously oxidizes and degrades dyes and OTC. During the degradation of OTC, ·OH plays a dominant role, attacking the aromatic ring structure of OTC through hydrogen extraction and hydroxyl addition reactions, and gradually decomposing it into small molecule compounds and organic acids, and finally mineralizing it into water and carbon dioxide.

[0068] Experiment 4: Weigh 0.20 g of the microsphere materials prepared by the methods of Example 1 and Comparative Examples 5-6 respectively, and put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L. Then add 0.15 mL of H2O2 solution (with a concentration of 30 wt%), stir at 400 r / min at room temperature for 3 h, and use AFS to measure the total antimony and Sb(III) contents in the solution before and after the reaction.

[0069] Table 4

[0070]

[0071] As shown in Table 4, on the basis of Experiment 3, when adding H2O2 during the addition of microsphere materials to remove heavy metal antimony, it can be clearly found that the chitosan-iron-cerium microsphere materials have an obvious oxidation effect. During the removal of Sb(III), it can oxidize and degrade highly toxic Sb(III) into low-toxic Sb(V). In the single-metal chitosan-iron microsphere material, there is no cerium, so it cannot smoothly promote the Fe(Ⅲ) / Fe(Ⅱ) cycle in the Fenton-like reaction, and thus cannot effectively play a catalytic role.

[0072] Comparative Example 7

[0073] Change the 0.12 mol / L adipic acid solution in Example 1 to 1% (v / v) acetic acid solution, and the rest are the same as in Example 1 to prepare chitosan-iron microsphere materials.

[0074] Comparative Example 8

[0075] Change the 0.12 mol / L adipic acid solution in Example 1 to 1% (v / v) hydrochloric acid solution, and the rest are the same as in Example 1 to prepare chitosan-cerium microsphere materials.

[0076] Experiment 5: Weigh 0.20 g of the microsphere materials prepared by the methods of Example 1 and Comparative Examples 7-8 respectively, and put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L, 50 mL of potassium pyroantimonate solution with a concentration of 50 mg / L, 50 mL of dye reactive black 5 with a concentration of 50 mg / L, and 50 mL of antibiotic oxytetracycline solution with a concentration of 50 mg / L respectively. Stir at 400 r / min for 3 h at room temperature. Use ICP to measure the content of Sb(III / V) in the solution before and after the reaction, use a UV spectrophotometer to measure the content of reactive black 5 in the solution before and after the reaction, and use HPLC to measure the content of antibiotic oxytetracycline before and after the reaction.

[0077] Table 5

[0078]

[0079] As shown in Table 5, when changing the solvents for dissolving chitosan, iron salt and cerium salt during the preparation of the chitosan-iron-cerium precursor solution, it will affect the pollutant removal performance of the prepared microsphere materials. The 1% acetic acid solution and 1% hydrochloric acid solution used in the comparative examples play a weaker role than adipic acid during the complexation of chitosan and metal.

[0080] Comparative Example 9

[0081] Change the mass of chitosan in Example 1 from 2.0 g to 0.5 g, and the rest are the same as in Example 1 to prepare the chitosan-iron-cerium microsphere material.

[0082] Comparative Example 10

[0083] Change the mass of chitosan in Example 1 from 2.0 g to 4.0 g, and the rest are the same as in Example 1 to prepare the chitosan-iron-cerium microsphere material.

[0084] Experiment 6: Weigh 0.20 g of the microsphere materials prepared by the methods of Example 1 and Comparative Examples 9-10 respectively, and put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L, 50 mL of potassium pyroantimonate solution with a concentration of 50 mg / L, 50 mL of dye reactive black 5 with a concentration of 50 mg / L, and 50 mL of antibiotic oxytetracycline solution with a concentration of 50 mg / L respectively. Stir at 400 r / min for 3 h at room temperature. Use ICP to measure the content of Sb(III / V) in the solution before and after the reaction, use a UV spectrophotometer to measure the content of reactive black 5 in the solution before and after the reaction, and use HPLC to measure the content of antibiotic oxytetracycline before and after the reaction.

[0085] Table 6

[0086]

[0087] As shown in Table 6, when the content ratio of cerium salt and iron salt in the precursor solution is appropriate, the dosage of chitosan will affect the removal effects of chitosan-iron-cerium microspheres on heavy metal antimony, dye reactive black 5 and antibiotic oxytetracycline. Especially when the dosage of chitosan is too high, the distribution of Fe and Ce in the prepared microsphere material is too small, which not only greatly reduces the active adsorption sites, but also weakens the catalytic effect of Ce. When the dosage of chitosan is too low, the sites provided by chitosan molecules for crystal nucleation growth will be reduced, thereby weakening the pollutant removal performance.

[0088] Example 4

[0089] Weigh 0.035 mol / L cerium nitrate and 1.75 mol / L ferrous chloride, and dissolve them in 50 ml and 10 ml of 0.12 mol / L adipic acid solution respectively. Weigh 2.0 g of chitosan and dissolve it in 0.12 mol / L adipic acid solution, and stir at room temperature for 1 h to obtain the chitosan-iron-cerium precursor solution. Drop the chitosan-iron-cerium precursor solution into 2 mol / L NaOH solution with a syringe, and the aging time is 12 h. Wash it with deionized water until neutral, then transfer it to 5% glutaraldehyde ethanol solution and let it stand for 12 h. Subsequently, dehydrate it step by step with 25%, 50%, and 100% ethanol solutions, and finally store it in absolute ethanol and seal it to isolate oxygen. Then dry it in an oven at 55 °C for use.

[0090] Example 5

[0091] Weigh 0.07 mol / L cerium nitrate and 0.35 mol / L ferrous chloride, and dissolve them in 50 ml and 10 ml of 0.12 mol / L adipic acid solution respectively. Weigh 2.0 g of chitosan and dissolve it in 0.12 mol / L adipic acid solution, and stir at room temperature for 1 h to obtain the chitosan-iron-cerium precursor solution. Drop the chitosan-iron-cerium precursor solution into 2 mol / L NaOH solution with a syringe, and the aging time is 12 h. Wash it with deionized water until neutral, then transfer it to 5% glutaraldehyde ethanol solution and let it stand for 12 h. Subsequently, dehydrate it step by step with 25%, 50%, and 100% ethanol solutions, and finally store it in absolute ethanol and seal it to isolate oxygen. Then dry it in an oven at 55 °C for use.

[0092] Comparative Example 11

[0093] Change the dosage of cerium nitrate in Example 1 from 0.07 mol / L to 0.02 mol / L, and keep the others the same as in Example 1 to prepare the chitosan-iron-cerium microsphere material.

[0094] Comparative Example 12

[0095] Change the dosage of ferrous chloride in Example 1 from 1.75 mol / L to 0.10 mol / L, and keep the rest the same as in Example 1 to prepare the chitosan-iron-cerium microsphere material.

[0096] Experiment 7: Weigh 0.20 g of the complex materials prepared by the methods of Example 1, Examples 4-5, and Comparative Examples 10-11 respectively, and put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L, 50 mL of potassium pyroantimonate solution with a concentration of 50 mg / L, 50 mL of dye reactive black 5 with a concentration of 50 mg / L, and 50 mL of antibiotic oxytetracycline solution with a concentration of 50 mg / L. Then add 0.15 mL of H2O2 solution (with a concentration of 30 wt%), stir at 400 r / min at room temperature for 3 h, use ICP to measure the content of Sb(III / V) in the solution before and after the reaction, use an ultraviolet spectrophotometer to measure the content of reactive black 5 in the solution before and after the reaction, and use HPLC to measure the content of antibiotic oxytetracycline before and after the reaction.

[0097] Table 7

[0098]

[0099] As shown in Table 7, selecting an appropriate dosing ratio of cerium salt and iron salt will also affect the performance of the microsphere material in removing pollutants. Among them, when the molar ratio of iron to cerium is 1:5, the antimony removal performance of the complex is the best. Although there are slight differences in the pollutant removal rate and catalytic degradation effect of the microsphere materials prepared within the appropriate cerium-iron molar ratio range, the influence is small. When the content of ferrous chloride in the precursor solution is too low, the surface active sites of the microsphere catalyst will be greatly reduced, thus reducing the pollutant removal efficiency; when the content of cerium nitrate in the precursor solution is too low, it cannot smoothly promote the Fe(Ⅲ) / Fe(Ⅱ) cycle in the Fenton-like reaction, and thus cannot effectively play a catalytic degradation role.

[0100] Experiment 8: On the basis of Experiment 7, weigh 0.20 g of the complex materials prepared by the methods of Example 1, Examples 4-5, and Comparative Examples 11-12, put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L, add 0.15 mL of H2O2 solution (with a concentration of 30 wt%), stir at 400 r / min at room temperature for 3 h, and use AFS to measure the content of Sb(III) and total antimony in the solution.

[0101] Table 8

[0102]

[0103] As shown in Table 8, by measuring the changes in total antimony and Sb(III) during the removal of Sb(III) by chitosan-iron-cerium microspheres, it can be more clearly found that different cerium-iron molar ratios during the preparation of the precursor solution will affect the removal ability and catalytic oxidation ability of the microsphere material for pollutants. When the Fe content in the precursor solution is too low, the removal ability of the microspheres for antimony is greatly reduced; when the Ce content in the precursor solution is too low, the oxidation ability of the microspheres for Sb(III) is greatly weakened.

[0104] Comparative Example 13

[0105] Weigh 0.07 mol / L cerium nitrate and 1.75 mol / L ferrous chloride, dissolve them in 50 ml and 10 ml of 0.12 mol / L adipic acid solution respectively, weigh 2.0 g of chitosan and dissolve it in 0.12 mol / L adipic acid solution, and stir at room temperature for 1 h to obtain a chitosan-iron-cerium precursor solution. Drop the chitosan-iron-cerium precursor solution into 3 mol / L NH3·H2O solution with a syringe, with an aging time of 12 h. After washing with deionized water until neutral, transfer it to a 5% glutaraldehyde ethanol solution and let it stand for 12 h. Then dehydrate it step by step with 25%, 50%, and 100% ethanol solutions, and finally store it in absolute ethanol under oxygen isolation and seal it. Then dry it in an oven at 55 °C for use.

[0106] Experiment 9: Weigh 0.20 g of the complex materials prepared by the methods of Example 1 and Comparative Example 12, and separately put them into 50 mL of potassium antimonyl tartrate solution with a concentration of 50 mg / L, 50 mL of potassium pyroantimonate solution with a concentration of 50 mg / L, 50 mL of dye reactive black 5 with a concentration of 50 mg / L, and 50 mL of antibiotic oxytetracycline solution with a concentration of 50 mg / L. Add 0.15 mL of H2O2 solution (with a concentration of 30 wt%), stir at 400 r / min at room temperature for 3 h, use ICP to measure the content of Sb(III / V) in the solution before and after the reaction, use a UV spectrophotometer to measure the content of reactive black 5 in the solution before and after the reaction, and use HPLC to measure the content of antibiotic oxytetracycline before and after the reaction.

[0107] Table 9

[0108]

[0109] As shown in Table 9, when changing the incubation conditions of the chitosan-iron-cerium microspheres, the impact on the removal of pollutants is not obvious.

[0110] Figure 1 This is the XRD pattern of the chitosan-iron-cerium microsphere material of the present invention. According to the database comparison results, the main components of the material are goethite (FeOOH) and cerium oxide (CeO2). Figure 1The 2Theta (degree) is the XRD diffraction angle / °, and the vertical coordinate Intensity (a.u.) is the peak intensity.

[0111] Figure 2a This is the XPS spectrum of the total ion map of the chitosan-iron-cerium microsphere material of the present invention before and after the reaction. Figure 2b This is the XPS spectrum of O1s of the chitosan-iron-cerium microsphere material of the present invention before and after the reaction. Figure 2c This is the XPS spectrum of Fe2p of the chitosan-iron-cerium microsphere material of the present invention before and after the reaction. Figure 2d This is the XPS spectrum of Ce3d of the chitosan-iron-cerium microsphere material of the present invention before and after the reaction. In the figure, the abscissa Binding energy (eV) is the binding energy, and the vertical coordinate Intensity (a.u.) is the peak intensity. Figure 2b Among them, the characteristic peak at the binding energy of 529.08 eV corresponds to OⅠ (lattice oxygen), the binding energy of 530.76 eV corresponds to the characteristic peak of OⅡ (defect oxygen), and the characteristic peak of 532.49 eV is similar to the binding energy of surface adsorbed oxygen. The proportions of the three are 17.82%, 36.98%, and 45.20% respectively. The higher the ratio of OⅡ, the more oxygen vacancies. After the reaction, the binding energy of O1s shifts to a higher energy, corresponding to 529.22 eV, 530.78 eV, and 532.64 eV respectively, and the proportion of defect oxygen decreases to 24.62%, indicating that electron transfer occurs at the oxygen vacancies during the catalytic reaction. Figure 2c This is the Fe2p energy spectrum. The photoelectron peaks with binding energies of 710.16 eV and 723.55 eV prove the existence of Fe 2+ The peaks with binding energies of 712.38 eV and 725.72 eV indicate the existence of Fe 3+ The existence, and the remaining four belong to Fe 2+ and Fe 3+ Satellite peaks. The proportions of Fe 2+ and Fe 3+ Change before and after the reaction. Combining the analysis of the O1s and Ce3d spectra, it can prove the progress of the Fenton-like reaction during the reaction process. Figure 2d This depicts the energy spectrum of Ce 3d. Among them, 885.33 eV, 881.52 eV, 888.72 eV, and 897.51 eV correspond to Ce 3d5 / 2, and 900.01 eV, 903.5 eV, 906.07 eV, and 915.89 eV belong to Ce 3d3 / 2. The peaks centered at 885.33 eV and 903.5 eV are the characteristic peaks of Ce 3+ The characteristic peaks, and the others all belong to Ce 4 + Characteristic peaks, and Ce 3+Its existence may be due to the reaction of CeO2 with surrounding atoms. It can be seen from the XPS comparison before the reaction that the proportion of defective oxygen decreases before and after the reaction. In the catalytic reaction, electron transfer occurs at the oxygen vacancies. At the same time, Fe(II), Fe(III), Ce(III) and Ce(IV) exist in the crystal structure of the complex material, which is conducive to the electron transfer at the oxygen vacancies, thereby promoting the decomposition of hydrogen peroxide during the Fenton-like reaction process. In the present invention, by doping two metals, Fe and Ce, into chitosan, the redox reaction between Ce(IV) / Ce(III) can be utilized to promote the Fe(III) / Fe(II) cycle during the reaction, and it is also conducive to the generation of oxygen vacancies and the electron transfer at the oxygen vacancies.

[0112] Figure 3a This is the SEM image of the chitosan-iron-cerium microsphere material of the present invention. Figure 3b This is the TEM image of the chitosan-iron-cerium microsphere material of the present invention. Figure 3c This is the HR-TEM image of the chitosan-iron-cerium microsphere material of the present invention with a lattice fringe spacing of 0.31 nm. Figure 3d This is the HR-TEM image of the chitosan-iron-cerium microsphere material of the present invention with a lattice fringe spacing of 0.25 nm. In the chitosan-iron-cerium microsphere material of the present invention, FeOOH is in the form of thin flakes, and cerium dioxide mainly exists in the form of particles with a particle diameter between 10 and 50 nm.

[0113] In the present invention, a chitosan-iron-cerium complex is used as a precursor to prepare a microsphere material with uniformly dispersed iron and cerium oxide particles. Its simultaneously possessed adsorption enrichment and catalytic oxidation functions can effectively adsorb organic pollutants and metal pollutants in wastewater. Combined with the addition of oxidants such as hydrogen peroxide, it can simultaneously catalytically oxidize and degrade organic pollutants or convert metal pollutants into less harmful forms.

Claims

1. A preparation method of chitosan-iron-cerium microspheres with adsorption enrichment-catalytic oxidation dual functions, characterized in that, Different ferrous salts and cerium salts are selected and dissolved in adipic acid. The solution is fully stirred and mixed with a chitosan solution also dissolved in adipic acid to form a precursor solution. Then, it is dropped into an alkaline solution with a syringe to form spherical substances. After aging, crosslinking is carried out in a glutaraldehyde ethanol solution, and dehydration is gradually carried out and stored in absolute ethanol. Chitosan-iron-cerium microspheres are obtained by drying. Among them, the concentration of the ferrous salt solution is 1.5 - 2.0 mol / L, and the concentration of the cerium salt solution is 0.07 - 0.35 mol / L; the molar ratio of the cerium salt to the ferrous salt is 1:(1 - 5); iron exists in the form of goethite, and cerium exists in the form of cerium oxide.

2. The preparation method of the chitosan-iron-cerium microspheres with adsorption enrichment-catalytic oxidation bifunction according to claim 1, characterized in that, The ferrous salt is at least one of ferrous chloride and ferrous nitrate.

3. The preparation method of the chitosan-iron-cerium microspheres with adsorption enrichment-catalytic oxidation bifunction according to claim 1, wherein, The cerium salt is at least one of cerium nitrate and cerium carbonate.

4. The preparation method of the chitosan-iron-cerium microspheres with adsorption enrichment-catalytic oxidation bifunction according to claim 1, characterized in that, The concentration of the adipic acid is 0.10 mol / L - 0.20 mol / L.

5. The preparation method of the chitosan-iron-cerium microsphere with adsorption enrichment-catalytic oxidation bifunction according to claim 1, characterized in that, The dosage of the chitosan is 10.0 - 30.0 g / L.

6. The preparation method of the chitosan-iron-cerium microspheres with adsorption enrichment-catalytic oxidation bifunction according to claim 1, characterized in that, The concentration of the alkaline solution is 1 - 3 mol / L.

7. The preparation method of the chitosan-iron-cerium microspheres with adsorption enrichment-catalytic oxidation bifunction according to claim 1, characterized in that, The ratio of glutaraldehyde to absolute ethanol is 1:(3 - 5).

8. The preparation method of the chitosan-iron-cerium microsphere with adsorption enrichment-catalytic oxidation bifunction according to claim 1, wherein, The stirring time is 0.5 - 3 h; the aging time is 6 - 24 hours, and the crosslinking time is 8 - 14 hours; the drying temperature is 45 - 55 °C.

9. Application of a chitosan-iron-cerium microsphere material with adsorption enrichment-catalytic oxidation bifunction prepared by the preparation method according to any one of claims 1 - 8.

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