Temperature-sensitive chitosan / PVA / TiO2 composite microsphere as well as preparation method and application thereof

Abstract

The invention discloses a temperature-sensitive chitosan / PVA / TiO2 composite microsphere as well as a preparation method and application thereof, and belongs to the technical field of photocatalytic materials. The method comprises the following steps: S1, dropwise adding a chitosan acetic acid solution into an oil phase solution, uniformly stirring to obtain a water-in-oil emulsion, and washing and drying to obtain a chitosan microcapsule; s2, dissolving the chitosan microcapsule in an organic solvent, adding 2-bromoisobutyryl bromide, a transition metal catalyst and a temperature-sensitive monomer in a protective gas atmosphere, and reacting to obtain temperature-sensitive chitosan; s3, mixing the PVA solution with the temperature-sensitive chitosan solution, and then adding TiO2 to obtain a system I; s4, mixing absolute ethyl alcohol, water and sodium hydroxide to obtain a system II; dropwise adding the system I into the system II to obtain a finished product. The temperature-sensitive chitosan / PVA / TiO2 composite microsphere prepared by the method is used as a photocatalyst for photocatalytic degradation of organic pollutants, has high catalytic degradation rate on methyl orange and rhodamine, and can realize the effect of efficient catalytic degradation of the organic pollutants in wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to a temperature-sensitive chitosan / PVA / TiO 2 composite microsphere and its preparation method and application. Background Technique

[0002] Due to the rapid development of the textile industry, the discharge of printing and dyeing wastewater has increased sharply year by year. Organic dyes are discharged into the environment together with the wastewater. Some dyes are carcinogenic and mutagenic, threatening human health. Therefore, it is necessary to treat the organic dyes in the wastewater. However, due to the inertness of dyes, it is very difficult to remove dyes from water, and most dyes are essentially non-degradable. It is not easy to break the molecular skeleton of dyes, and the decomposition treatment of dyes is full of challenges.

[0003] At present, the methods for treating organic dyes in wastewater mainly include biological treatment, chemical treatment and photocatalysis. Compared with the traditional biological treatment and chemical treatment methods, the photocatalytic oxidation technology has received extensive attention due to its advantages such as simple operation, complete degradation, non-toxic and efficient, no secondary pollution, and the material can be reused. Its principle is: under the illumination condition of a certain wavelength, the electrons on the valence band of the semiconductor photocatalytic material are excited by light energy and jump to the conduction band, leaving holes on the valence band. Subsequently, the photo-generated electrons and holes combine with ions or molecules to generate active free radicals with oxidizing or reducing properties. These active free radicals can mineralize the organic macromolecules in the water unconditionally into water and carbon dioxide, so as to achieve the purpose of degrading organic pollutants. The photocatalytic method has many advantages compared with the traditional sewage treatment methods. First, when photocatalysis is carried out in water, holes are easy to react with water molecules to form extremely oxidizing hydroxyl radicals, which can mineralize all organic substances without selectivity, and are extremely suitable for treating the organic components in sewage. Second, the photocatalytic method uses light energy as the energy source. By seeking catalytic materials that can absorb visible light, solar energy can be effectively utilized, which is economical and environmentally friendly. Finally, during the catalytic reaction process, the photocatalyst itself does not change, so it can be recycled and has a certain practicality. The core problem of the photocatalytic technology lies in the photocatalytic material. Therefore, developing a green, low-cost catalytic material with excellent dye degradation effect is the current research focus. Among various photocatalytic degradation materials, titanium dioxide photocatalytic degradation materials have become the most studied photocatalysts at present due to their excellent physical and chemical properties and photocatalytic effect. However, when single titanium dioxide is used for wastewater treatment, it is easy to agglomerate, resulting in a decrease in the activity of titanium dioxide, and it is difficult to separate and recover. These problems limit its application in degrading organic pollutants.

[0004] Chitosan is a deacetylated polysaccharide synthesized from chitin; amino and hydroxyl groups are the active sites of chitosan, which contribute to the adsorption of organic dyes. Since the amino group is easily protonated in an aqueous medium, it is mainly used for the adsorption of anionic dyes. However, from the perspective of practical applications, chitosan has limitations such as unsatisfactory mechanical properties and deformation after drying. More importantly, chitosan has a high pH sensitivity, it can only dissolve under acidic conditions and is difficult to dissolve in water, with poor hydrophilicity, resulting in a small contact area between chitosan and organic dyes in water and a low degradation rate of organic pollutants.

[0005] Therefore, it is of great significance to provide a photocatalytic material with good degradation effect on organic pollutants and strong self-stability. Summary of the Invention

[0006] Aiming at the above deficiencies of the prior art, one of the purposes of the present invention is to provide a preparation method of thermosensitive chitosan / PVA / TiO 2 composite microspheres. The prepared thermosensitive chitosan / PVA / TiO 2 composite microspheres are used as catalysts for photocatalytic degradation of organic pollutants, with high catalytic degradation rates for methyl orange and rhodamine, and can achieve the effect of efficiently catalytically degrading organic pollutants in wastewater.

[0007] The above object of the present invention is achieved by the following technical solutions:

[0008] A preparation method of thermosensitive chitosan / PVA / TiO 2 composite microspheres, comprising the following steps:

[0009] S1. Dissolve chitosan in acetic acid solution to obtain a chitosan acetic acid solution, drop the chitosan acetic acid solution into an oil-phase solution, stir evenly to obtain a water-in-oil emulsion, and obtain chitosan microcapsules after washing and drying;

[0010] S2. Dissolve the chitosan microcapsules obtained in step S1 in organic solvent I, add 2-bromo-2-methylpropionyl bromide and react under a protective gas atmosphere to obtain brominated chitosan; then add brominated chitosan and a thermosensitive monomer into organic solvent II, and react to obtain thermosensitive chitosan after adding a transition metal catalyst;

[0011] S3. Dissolve PVA in water to obtain a PVA solution, dissolve the thermosensitive chitosan obtained in step S2 in acetic acid solution to obtain a thermosensitive chitosan solution, mix the PVA solution and the thermosensitive chitosan solution, and then add TiO 2 , to obtain System I;

[0012] S4. Mix anhydrous ethanol, water and sodium hydroxide evenly to obtain System II; then slowly drop System I into System II to obtain thermosensitive chitosan / PVA / TiO 2Composite microspheres.

[0013] In the present invention, chitosan is first made into chitosan microcapsules, which can form a larger specific surface area and improve the reaction efficiency with 2-bromo-2-methylpropionyl bromide in the subsequent process; then, using chitosan microcapsules and a temperature-sensitive monomer as reaction raw materials, temperature-sensitive chitosan is prepared by atom transfer radical polymerization (ATRP). By performing temperature-sensitive modification on chitosan, on the one hand, the hydrophilicity of chitosan can be improved, enhancing the contact effect of chitosan in water, and thus facilitating the degradation of organic pollutants by the composite microspheres in water. On the other hand, it is beneficial for the dispersion of TiO 2 in chitosan. Under the action of these two aspects, the catalytic degradation effect of the composite microspheres on organic pollutants is improved. In addition, compared with directly mixing a chitosan solution with a temperature-sensitive material, the material prepared by the ATRP method in the present invention is more firm, the material prepared by the chemical bond method is more stable, and the catalytic effect is better. Adding PVA and TiO 2 , PVA enhances chitosan by forming hydrogen bonds with the functional groups NH 2 and NH-R of chitosan. TiO 2 , as a filling particle, can enhance the mechanical properties of the polymer. In summary, the composite microspheres prepared in the present invention are a very useful photocatalytic material with high catalytic activity, greatly improving the degradation effect on organic pollutants; at the same time, this material also has the characteristics of strong stability and low preparation cost.

[0014] Preferably, the preparation method of the oil phase solution in step S1 is: dissolving terephthalaldehyde and polyglycerol ricinoleate in a mixed solvent of benzyl benzoate and cyclohexane to obtain the oil phase solution.

[0015] Preferably, in step S1, the concentration of terephthalaldehyde in the oil phase solution is 0.5 wt% - 2 wt%, and the concentration of polyglycerol ricinoleate is 2 wt% - 6 wt%.

[0016] Preferably, in step S2, the concentration of the chitosan microcapsules in organic solvent I is 0.5 g / (100 - 200) mL.

[0017] Preferably, in step S2, the mass-volume ratio of the chitosan microcapsules to 2-bromo-2-methylpropionyl bromide is 0.5:(1 - 10) g / mL; the mass ratio of the brominated chitosan to the temperature-sensitive monomer is 1:(5 - 20).

[0018] Preferably, in step S2, the transition metal catalyst includes at least one of cuprous chloride, ferrous bromide, cuprous bromide, copper bromide, or ferrous chloride.

[0019] Preferably, in step S2, the temperature-sensitive monomer is N-isopropylacrylamide.

[0020] Preferably, in step S3, the mass ratio of the thermosensitive chitosan to PVA in system one is 1:(0.2~0.8); the mass ratio of the thermosensitive chitosan to TiO 2 is 1:(0.01~0.5).

[0021] Another object of the present invention is to provide a thermosensitive chitosan / PVA / TiO 2 composite microsphere prepared by the preparation method.

[0022] Another object of the present invention is to provide the application of the thermosensitive chitosan / PVA / TiO 2 composite microsphere prepared by the preparation method in the photocatalytic degradation of methyl orange or rhodamine.

[0023] Preferably, the application method of the thermosensitive chitosan / PVA / TiO 2 composite microsphere in the catalytic degradation of methyl orange is as follows: adding the thermosensitive chitosan / PVA / TiO 2 composite microsphere into the methyl orange solution, ultrasonically treating for 5~40 min under dark conditions, and then for 20~30 min under natural light to complete the catalytic degradation.

[0024] Preferably, the application method of the thermosensitive chitosan / PVA / TiO 2 composite microsphere in the catalytic degradation of rhodamine is as follows: adding the thermosensitive chitosan / PVA / TiO 2 composite microsphere into the rhodamine solution, mixing, and then adding a PMS solution of 0.1-0.3 mmol / L, and carrying out a catalytic degradation reaction under natural light conditions.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) In the present invention, chitosan is first made into chitosan microcapsules, and then thermosensitive chitosan is prepared by using chitosan microcapsules and a thermosensitive monomer as reaction raw materials. By thermosensitive modification of chitosan, on the one hand, the hydrophilicity of chitosan can be improved, the contact effect of chitosan in water can be enhanced, and thus it is convenient for the composite microsphere to degrade organic pollutants in water. On the other hand, it is beneficial to the dispersion of TiO 2 in chitosan, and the degradation effect of the composite microsphere on organic pollutants is improved under the action of the two aspects.

[0027] (2) Compared with directly mixing the chitosan solution with the thermosensitive material, the material prepared by the ATRP method in the present invention is more firm, the material prepared by the chemical bond method is more stable, and the catalytic effect is better.

[0028] (3) In the present invention, through the functional group NH of PVA and chitosan 2Form hydrogen bonds with NH-R to strengthen chitosan, and through TiO 2 As a filler particle, it enhances the mechanical properties of the polymer, and the obtained material has strong stability.

[0029] (4)The thermosensitive chitosan / PVA / TiO obtained by the present invention 2 The composite microspheres are small and uniform in size, have high catalytic activity, can efficiently and rapidly adsorb and degrade methyl orange and rhodamine in wastewater, and the catalytic degradation process is mild and the components are simple, and can be effectively applied to wastewater treatment. Description of the Drawings

[0030] Figure 1 The physical picture of the thermosensitive chitosan / PVA / TiO obtained in Example 1 2 Composite microspheres;

[0031] Figure 2 The thermosensitive chitosan / PVA / TiO obtained in Example 1 2 Infrared spectrum of the composite microspheres. Detailed Embodiments

[0032] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0033] The embodiment of the present invention provides a preparation method of thermosensitive chitosan / PVA / TiO 2 Composite microspheres, including the following steps:

[0034] S1. Dissolve chitosan in an acetic acid solution to obtain a chitosan acetic acid solution, drop the chitosan acetic acid solution into an oil phase solution, stir evenly to obtain a water-in-oil emulsion, and obtain chitosan microcapsules after washing and drying;

[0035] S2. Dissolve the chitosan microcapsules obtained in step S1 in an organic solvent I, add 2-bromoisobutyryl bromide and react under a protective gas atmosphere to obtain brominated chitosan; then add brominated chitosan and a thermosensitive monomer to an organic solvent II, and add a transition metal catalyst and react to obtain thermosensitive chitosan;

[0036] S3. Dissolve PVA in water to obtain a PVA solution, dissolve the thermosensitive chitosan obtained in step S2 in an acetic acid solution to obtain a thermosensitive chitosan solution, mix the PVA solution and the thermosensitive chitosan solution, and then add TiO 2 , to obtain System I;

[0037] S4. Mix ethanol absolute, water and sodium hydroxide evenly to obtain System Two; then slowly drip System One into System Two to obtain thermosensitive chitosan / PVA / TiO 2 composite microspheres.

[0038] In some embodiments, the preparation method of the oil phase solution in step S1 is: dissolve terephthalaldehyde and polyglycerol ricinoleate in a mixed solvent of benzyl benzoate and cyclohexane to obtain the oil phase solution; the concentration of terephthalaldehyde in the oil phase solution can be 0.5 wt% - 2 wt%, and the concentration of polyglycerol ricinoleate can be 2 wt% - 6 wt%; for example, the concentration of terephthalaldehyde in the oil phase solution is 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, etc., and the concentration of polyglycerol ricinoleate in the oil phase solution can be 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 6 wt%, etc.

[0039] In some embodiments, the organic solvent one is a mixed solvent of triethylamine and dichloromethane, and the organic solvent two is methanol and water. The concentration of the chitosan microcapsules in the organic solvent one is 0.5 g / (100 - 200) mL; for example, the concentration of the chitosan microcapsules in the organic solvent one is 0.5 g / 100 mL, 0.5 g / 160 mL, 0.5 g / 200 mL, etc.

[0040] In some embodiments, in step S2, the mass - volume ratio of the chitosan microcapsules to 2 - bromoisobutyryl bromide is 0.5:(1 - 10) g / mL; the mass ratio of the brominated chitosan to the thermosensitive monomer is 1:(5 - 20).

[0041] In some embodiments, the transition metal catalyst includes at least one of cuprous chloride, ferrous bromide, cuprous bromide, cupric bromide or ferrous chloride.

[0042] In some embodiments, the thermosensitive monomer is N - isopropylacrylamide.

[0043] In some embodiments, the mass ratio of the thermosensitive chitosan to PVA in System One can be 1:(0.2 - 0.8), for example, the mass ratio of the thermosensitive chitosan to PVA is 1:0.2, 1:0.5, 1:0.8, etc.; the mass ratio of the thermosensitive chitosan to TiO 2 can be 1:(0.01 - 0.5), for example, the mass ratio of the thermosensitive chitosan to TiO 2 can be 1:0.01, 1:0.1, 1:0.5, etc.

[0044] In the following examples and comparative examples, the degree of deacetylation of chitosan ≥ 95%, the viscosity is 100 - 200 mpa.s; the volume concentration of the acetic acid solution is 1% - 5%.

[0045] Example 1

[0046] This example provides a method for preparing thermosensitive chitosan / PVA / TiO 2 composite microspheres, comprising the following steps:

[0047] S1. Dissolve chitosan in an acetic acid solution with a volume concentration of 2% to obtain a chitosan acetic acid solution with a chitosan concentration of 2 wt%. Dissolve terephthalaldehyde and polyglycerol ricinoleate in a mixed solvent of benzyl benzoate and cyclohexane (the volume ratio of benzyl benzoate to cyclohexane is 1:1) to obtain a mixed oil phase solution. The concentration of terephthalaldehyde in the mixed oil phase solution is 1 wt%, and the concentration of polyglycerol ricinoleate is 4 wt%. Then, drop 10 mL of the chitosan acetic acid solution into 100 mL of the mixed oil phase solution, and stir at 700 rpm simultaneously to form a uniform water-in-oil emulsion. Wash away the unreacted reagents and dry to obtain chitosan microcapsules;

[0048] S2. Mix 0.5 g of chitosan microcapsules, 97 mL of dichloromethane and 3 mL of triethylamine in a reactor, and gently stir in an ice-water bath at 2°C. Then, slowly drop 2 mL of 2-bromoisobutyryl bromide into the solution under nitrogen. After 8 h, wash the reacted chitosan microcapsules with ethanol and dry at 50°C to obtain brominated chitosan. Add 0.1 g of brominated chitosan and 0.5 g of N-isopropylacrylamide to a mixed solvent of 20 mL of methanol and 30 mL of water, and then add 0.03 g of CuBr and 0.1 g of CuBr 2 as a catalyst and 0.1 mL of pentamethyldiethylenetriamine, and react for 24 h under nitrogen to obtain thermosensitive chitosan;

[0049] S3. Add 0.5 g of PVA to 20 mL of distilled water, add a magnetic stirrer, and heat in an oil bath at 90°C for 3.5 h to obtain a PVA solution. Add 1 g of thermosensitive chitosan to 40 g of an acetic acid solution with a volume concentration of 1%, add a magnetic stirrer, and stir for 5 h to obtain a thermosensitive chitosan solution. Then mix the PVA solution and the thermosensitive chitosan solution, and then add 0.1 g of TiO 2 , and stir until TiO 2 is evenly distributed to obtain System 1;

[0050] S4. Take 60 mL of absolute ethanol, 40 mL of distilled water and 12 g of sodium hydroxide and add them to a 250 mL beaker, add a magnetic stirrer, and stir for 2.5 h until it is colorless and transparent to obtain System 2. Then use a 5 mL syringe to drop the solution in System 1 into System 2 at a rate of 2 mL / min. Wash the product three times with ethanol and distilled water in sequence, and dry at 50°C for 3 h to obtain thermosensitive chitosan / PVA / TiO2 Composite microspheres.

[0051] The physical picture of the composite material prepared in Example 1 is as Figure 1 shown. It can be seen from the figure that the morphology of the prepared material is uniform and can well form regular spherical materials. Moreover, the specific surface area of the material is relatively large, and it can effectively adsorb dyes during the degradation process. The infrared spectrum of the composite material prepared in Example 1 is as Figure 2 shown. It can be seen from the figure that the prepared material contains the characteristic functional groups of chitosan and thermosensitive materials. Around 3400 cm -1 is attributed to the characteristics of chitosan, and the characteristic peak near 1650 cm -1 is attributed to the amide bond of the thermosensitive material, proving the successful preparation of the material.

[0052] Example 2

[0053] This example provides a preparation method of thermosensitive chitosan / PVA / TiO 2 composite microspheres, including the following steps:

[0054] S1. Dissolve chitosan in acetic acid solution with a volume concentration of 2% to obtain a chitosan acetic acid solution with a chitosan concentration of 2 wt%. Dissolve terephthalaldehyde and polyglycerol ricinoleate in a mixed solvent of benzyl benzoate and cyclohexane (the volume ratio of benzyl benzoate to cyclohexane is 1:1) to obtain a mixed oil phase solution. The concentration of terephthalaldehyde in the mixed oil phase solution is 0.5 wt%, and the concentration of polyglycerol ricinoleate is 4.5 wt%. Then, drop 10 mL of the chitosan acetic acid solution into 100 mL of the mixed oil phase solution, and stir at 700 rpm simultaneously to form a uniform water-in-oil emulsion. Wash away the unreacted reagents and dry to obtain chitosan microcapsules;

[0055] S2. Mix 0.5 g of chitosan microcapsules, 97 mL of dichloromethane and 3 mL of triethylamine in a reactor, and gently stir in an ice-water bath at 2°C. Then, slowly drop 1 mL of 2-bromo-2-methylpropionyl bromide into the solution under nitrogen. After 8 h, wash the reacted chitosan microcapsules with ethanol and dry at 50°C to obtain brominated chitosan. Add 0.1 g of brominated chitosan and 1 g of N-isopropylacrylamide to a mixed solvent of 20 mL of methanol and 30 mL of water, and then add 0.03 g of CuBr and 0.1 g of CuBr 2 as a catalyst, 0.1 mL of pentamethyldiethylenetriamine, and react for 24 h under nitrogen to obtain thermosensitive chitosan;

[0056] S3. Add 0.4 g of PVA into 29.6 mL of distilled water, add a magnetic stir bar, and heat in an 80 °C oil bath for 4 h to obtain a PVA solution. Add 1 g of thermosensitive chitosan into 100 g of acetic acid solution with a volume concentration of 1%, add a magnetic stir bar, and stir for 5 h to obtain a thermosensitive chitosan solution. Then mix the PVA solution and the thermosensitive chitosan solution, and then add 0.05 g of TiO 2 , and stir until TiO 2 is evenly distributed to obtain System 1;

[0057] S4. Take 60 mL of absolute ethanol, 40 mL of distilled water and 12 g of sodium hydroxide and add them into a 250 mL beaker, add a magnetic stir bar, and stir for 2.5 h until it is colorless and transparent to obtain System 2. Then use a 5 mL syringe to drop the solution in System 1 into System 2 at a rate of 1 mL / min. The product is washed three times with ethanol and distilled water respectively, and dried at 50 °C for 2 h to obtain thermosensitive chitosan / PVA / TiO 2 composite microspheres.

[0058] Example 3

[0059] This example provides a method for preparing thermosensitive chitosan / PVA / TiO 2 composite microspheres, which includes the following steps:

[0060] S1. Dissolve chitosan in acetic acid solution with a volume concentration of 2% to obtain a chitosan acetic acid solution with a chitosan concentration of 2 wt%. Dissolve terephthalaldehyde and polyglycerol ricinoleate in a mixed solvent of benzyl benzoate and cyclohexane (the volume ratio of benzyl benzoate to cyclohexane is 1:1) to obtain a mixed oil phase solution. The concentration of terephthalaldehyde in the mixed oil phase solution is 2 wt%, and the concentration of polyglycerol ricinoleate is 3 wt%. Then drop 10 mL of the chitosan acetic acid solution into 100 mL of the mixed oil phase solution, and stir at 700 rpm simultaneously to form a uniform water-in-oil emulsion. Wash away the unreacted reagents and dry to obtain chitosan microcapsules;

[0061] S2. Mix 0.5 g of chitosan microcapsules, 97 mL of dichloromethane and 3 mL of triethylamine in a reactor, and gently stir in an ice-water bath at 2 °C. Then, slowly drop 10 mL of 2-bromo-2-methylpropionyl bromide into the solution under nitrogen. After 8 h, wash the reacted chitosan microcapsules with ethanol and dry at 50 °C to obtain brominated chitosan. Add 0.1 g of brominated chitosan and 2 g of N-isopropylacrylamide into a mixed solvent of 20 mL of methanol and 30 mL of water, and then add 0.03 g of CuBr and 0.1 g of CuBr 2 as catalysts, and 0.1 mL of pentamethyldiethylenetriamine, and react for 24 h under nitrogen to obtain thermosensitive chitosan;

[0062] S3. Add 0.5 g of PVA into 20 mL of distilled water, add a magnetic stir bar, and heat in an oil bath at 95 °C for 2 h to obtain a PVA solution. Add 1 g of temperature-sensitive chitosan into 40 g of acetic acid solution with a volume concentration of 1%, add a magnetic stir bar, and stir for 5 h to obtain a temperature-sensitive chitosan solution. Then mix the PVA solution and the temperature-sensitive chitosan solution, and then add 0.5 g of TiO 2 , and stir until TiO 2 is evenly distributed to obtain System 1;

[0063] S4. Take 60 mL of absolute ethanol, 40 mL of distilled water and 12 g of sodium hydroxide and add them into a 250 mL beaker, add a magnetic stir bar, and stir for 2.5 h until it is colorless and transparent to obtain System 2. Then use a 5 mL syringe to drop the solution in System 1 into System 2 at a speed of 3 mL / min. The product is washed three times with ethanol and distilled water respectively, and dried at 50 °C for 3 h to obtain temperature-sensitive chitosan / PVA / TiO 2 composite microspheres.

[0064] Comparative Example 1

[0065] The preparation method of the temperature-sensitive chitosan / PVA / TiO 2 composite microspheres in this comparative example is basically the same as that in Example 1, and the difference is only that Step S4 is as follows: directly dry and grind System 1 to obtain a composite material with a powdery morphology.

[0066] Comparative Example 2

[0067] The preparation method of the temperature-sensitive chitosan / PVA / TiO 2 composite microspheres includes the following steps:

[0068] S1. Mix 0.5 g of chitosan, 97 mL of dichloromethane and 3 mL of triethylamine in a reactor, and gently stir in an ice-water bath at 2 °C. Then, slowly drop 2 mL of 2-bromo-2-methylpropionyl bromide into the solution under nitrogen. After 8 h, wash the reacted chitosan with ethanol and dry it at 50 °C to obtain brominated chitosan. Add 0.1 g of brominated chitosan and 0.5 g of N-isopropylacrylamide into a mixed solvent of 20 mL of methanol and 30 mL of water, and then add 0.03 g of CuBr and 0.1 g of CuBr 2 as a catalyst and 0.1 mL of pentamethyldiethylenetriamine, and react for 24 h under nitrogen conditions to obtain temperature-sensitive chitosan;

[0069] S2. Add 0.5 g of PVA into 20 mL of distilled water, add a magnetic stir bar, and heat in an oil bath at 90 °C for 3.5 h to obtain a PVA solution. Add 1 g of temperature-sensitive chitosan into 40 g of acetic acid solution with a volume concentration of 1%, add a magnetic stir bar, and stir for 5 h to obtain a temperature-sensitive chitosan solution; then mix the PVA solution and the temperature-sensitive chitosan solution, and then add 0.1 g of TiO 2 , and stir until TiO 2 is evenly distributed to obtain System 1;

[0070] S3. Take 60 mL of absolute ethanol, 40 mL of distilled water and 12 g of sodium hydroxide and add them into a 250 mL beaker, add a magnetic stir bar, and stir for 2.5 h until it is colorless and transparent to obtain System 2; then use a 5 mL syringe to drip the solution in System 1 into System 2 at a rate of 2 mL / min. The product is washed three times with ethanol and distilled water respectively, and dried at 50 °C for 3 h to obtain temperature-sensitive chitosan / PVA / TiO 2 composite microspheres;

[0071] That is, compared with Example 1, this comparative example omits the step of making chitosan into microcapsules.

[0072] Comparative Example 3

[0073] The preparation method of the temperature-sensitive chitosan / PVA / TiO 2 composite microspheres in this comparative example is basically the same as that in Example 1, except that step S2 is as follows:

[0074] Dissolve 0.5 g of chitosan microcapsules in 50 mL of acetic acid solution with a volume concentration of 1%, stir evenly, and then add a solution of the temperature-sensitive material poly(N-isopropylacrylamide) (0.1 g of the temperature-sensitive material is dissolved in 10 mL of distilled water), and stir evenly to obtain temperature-sensitive chitosan;

[0075] That is, compared with Example 1, this comparative example omits the ATRP polymerization step and directly mixes chitosan and the temperature-sensitive material.

[0076] Comparative Example 4

[0077] The preparation method of the chitosan / PVA / TiO 2 composite microspheres in this comparative example includes the following steps:

[0078] S1. Add 0.5 g of PVA into 20 mL of distilled water, add a magnetic stir bar, and heat in an oil bath at 90 °C for 3.5 h to obtain a PVA solution. Add 1 g of chitosan into 40 g of acetic acid solution with a volume concentration of 1%, add a magnetic stir bar, and stir for 5 h to obtain a chitosan solution; then mix the PVA solution and the chitosan solution, and then add 0.1 g of TiO 2, stir until TiO 2 is evenly distributed to obtain System 1;

[0079] S2. Add 60 mL of absolute ethanol, 40 mL of distilled water, and 12 g of sodium hydroxide into a 250 mL beaker, add a magnetic stir bar, and stir for 2.5 h until it becomes colorless and transparent to obtain System 2; then use a 5 mL syringe to drip the solution in System 1 into System 2 at a rate of 2 mL / min. The product is washed three times with ethanol and distilled water successively, and dried at 50 °C for 3 h to obtain thermosensitive chitosan / PVA / TiO 2 composite microspheres;

[0080] That is, compared with Example 1, this comparative example omits the step of making chitosan into microcapsules, and does not perform thermosensitive modification on chitosan either. Instead, chitosan is directly made into microspheres with PVA and TiO 2 .

[0081] Application Example 1

[0082] Add the composite materials prepared in each example and comparative example as photocatalytic materials into a methyl orange solution with a concentration of 0.025 g / L (the solid-liquid ratio of the photocatalytic material to the methyl orange solution is 0.1 g / L), ultrasonically treat for 5 min, then place it in a photoreaction test tube, without any treatment, directly stir at room temperature and under sunlight for 20 min, and then perform centrifugation to take the supernatant; use a UV-visible spectrophotometer to perform a full-band scan of 0.025 g / L methyl orange from 300 nm to 600 nm, select the best detection wavelength (about 464 nm), measure the absorbance of the above-mentioned supernatant at the best detection wavelength, and calculate the degradation rate. The degradation rate calculation formula is as follows:

[0083] Degradation rate = (A 降解前 - A 降解后 ) / A 降解前 × 100%

[0084] Among them, A 降解前 represents the absorbance corresponding to the peak at 464 nm measured before mixing the methyl orange solution with the material; A 降解后 represents the absorbance corresponding to the peak at 464 nm measured after mixing the methyl orange solution with the material and irradiating and stirring;

[0085] The degradation rate results are shown in Table 1.

[0086] Table 1 Catalytic degradation effect of photocatalytic materials on methyl orange

[0087]

[0088] As can be seen from the results in Table 1, the thermosensitive chitosan / PVA / TiO of the present invention 2The degradation rate of the composite microspheres for the organic dye methyl orange is as high as 98%, and the catalytic effect is good. Compared with Example 1, in Comparative Example 1, the material was not made into microspheres, but directly dried to obtain a powder material, and the degradation rate of methyl orange decreased to 59%. This is mainly because the morphology of the microsphere material can significantly increase the contact area between the material and the organic dye methyl orange, thereby significantly improving the catalytic effect. Compared with Example 1, in Comparative Example 2, the step of making chitosan into microcapsules was omitted, and the degradation rate of methyl orange decreased to 75%. This is mainly because making chitosan into microcapsules can enhance the effect of thermosensitive modification. In Comparative Example 3, the ATRP polymerization step was omitted, and chitosan and the thermosensitive material were directly mixed, and the degradation rate of methyl orange decreased to 63%. This shows that compared with directly mixing the chitosan solution with the thermosensitive material, using the ATRP method to perform thermosensitive modification on chitosan can improve the catalytic effect of the composite material. In Comparative Example 4, the step of making chitosan into microcapsules was omitted, and chitosan was not thermosensitively modified either. Chitosan was directly mixed with PVA and TiO 2 to make microspheres, and the degradation rate of methyl orange decreased to 31%. This shows that using the method of the present invention to perform thermosensitive modification on chitosan can improve the degradation effect of the composite material on methyl orange.

[0089] Application Example 2

[0090] The application method of this application example is different from that of Application Example 1. The catalytic degradation object of this application example is rhodamine, and the application process is as follows: Prepare a 5 mg / L RhB solution, and measure 50 mL of the RhB solution into a 100 ml conical flask. Weigh about 5 mg of the photocatalytic material and add it to the conical flask and mix. Add a 0.2 mmol / L PMS solution, shake well, and stir magnetically. Under natural light conditions, take out 1 mL of the sample at regular intervals. Filter the reaction with a 0.22 µL membrane, and add 100 µL of absolute ethanol to terminate the reaction. Then use a UV spectrophotometer to measure the remaining RhB content in the solution to determine the degradation rate at each time point.

[0091] The degradation rates of the catalytic materials in each example and comparative example in this application example for rhodamine at 20 min are shown in Table 2 below.

[0092] Table 2 Catalytic degradation effect of the photocatalytic material on rhodamine

[0093]

[0094] As can be seen from the results in Table 2, the thermosensitive chitosan / PVA / TiO of the present invention 2The degradation rate of the composite microspheres for the organic dye rhodamine was as high as 96% at 20 min, indicating good catalytic performance. Compared with Example 1, in Comparative Example 1, the material was not made into microspheres but directly dried to obtain a powder material, and the degradation rate of methyl orange decreased to 64%, showing a worse catalytic effect, indicating that the microsphere morphology has a better degradation effect on rhodamine; compared with Example 1, in Comparative Example 2, the step of making chitosan into microcapsules was omitted, and the degradation rate of rhodamine decreased to 69%, mainly because making chitosan into microcapsules can enhance the effect of thermosensitive modification; in Comparative Example 3, the ATRP polymerization step was omitted, and chitosan and the thermosensitive material were directly mixed, and the degradation rate of rhodamine decreased to 58%, indicating that compared with directly mixing the chitosan solution with the thermosensitive material, using the ATRP method to perform thermosensitive modification on chitosan can improve the catalytic effect of the composite material; in Comparative Example 4, the step of making chitosan into microcapsules was omitted, and chitosan was not thermosensitively modified either, and chitosan was directly mixed with PVA and TiO 2 into microspheres, and the degradation rate of rhodamine decreased to 26%, indicating that using the method of the present invention to perform thermosensitive modification on chitosan can improve the degradation effect of the composite material on rhodamine.

[0095] Application Example 3

[0096] Based on the test results of the above Application Example 1, this application example investigated the reusability of the composite material prepared in Example 1. The material was reused after centrifugation, washing, and drying. The specific steps are as follows:

[0097] Weigh the recovered photocatalytic material and add it to a methyl orange solution with a concentration of 0.025 g / L (the solid-liquid ratio of the photocatalytic material to the methyl orange solution is 0.1 g / L). Sonicate for 5 min, then place it in a photoreaction test tube, without any treatment, directly stir at room temperature and under sunlight for 20 min, then perform centrifugation, take the supernatant, measure the absorbance of the above supernatant at the optimal detection wavelength, calculate the degradation rate, and the degradation results of the recovered catalytic material are shown in Table 3 below.

[0098] Table 3 Catalytic degradation effect of the recovered catalytic material on methyl orange

[0099]

[0100] As can be seen from the results in Table 3, the recovered catalytic material still maintains good catalytic performance. After being reused 5 times, the degradation rate of methyl orange still remains at 91%.

[0101] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing thermosensitive chitosan / PVA / TiO2 composite microspheres, characterized in that: The following steps are involved: S1, dissolving chitosan in an acetic acid solution to obtain a chitosan acetic acid solution, adding the chitosan acetic acid solution dropwise to an oil phase solution, stirring to obtain a water-in-oil emulsion, and washing and drying to obtain chitosan microcapsules; S2, dissolving the chitosan microcapsules obtained in step S1 in an organic solvent 1, adding 2-bromoisobutyryl bromide to react in a protective gas atmosphere to obtain brominated chitosan; then adding the brominated chitosan and a thermosensitive monomer to an organic solvent 2, adding a transition metal catalyst to react to obtain thermosensitive chitosan; S3, dissolving PVA in water to obtain a PVA solution, dissolving the temperature-sensitive chitosan obtained in step S2 in an acetic acid solution to obtain a temperature-sensitive chitosan solution, mixing the PVA solution and the temperature-sensitive chitosan solution, and then adding TiO2 to obtain system 1; S4. Evenly mix anhydrous ethanol, water and sodium hydroxide to obtain system 2; then slowly drip system 1 into system 2 to obtain thermosensitive chitosan / PVA / TiO2 composite microspheres.

2. The method for preparing a thermosensitive chitosan / PVA / TiO2 composite microsphere according to claim 1, characterized in that: The preparation method of the oil phase solution in step S1 is: dissolving terephthalaldehyde and polyglycerol polyricinoleate in a mixed solvent of benzyl benzoate and cyclohexane to obtain the oil phase solution.

3. The method for preparing a thermosensitive chitosan / PVA / TiO2 composite microsphere according to claim 1, characterized in that: In step S2, the mass volume ratio of the chitosan microcapsules to 2-bromoisobutyryl bromide is 0.5:(1-10) g / mL; the mass ratio of the brominated chitosan to the thermosensitive monomer is 1:(5-20).

4. The method for preparing a thermosensitive chitosan / PVA / TiO2 composite microsphere according to claim 1, characterized in that: In step S2, the transition metal catalyst includes at least one of cuprous chloride, ferrous bromide, cuprous bromide, cupric bromide or ferrous chloride.

5. The method for preparing a thermosensitive chitosan / PVA / TiO2 composite microsphere according to claim 1, characterized in that: The temperature-sensitive monomer is N-isopropylacrylamide.

6. The method for preparing a thermosensitive chitosan / PVA / TiO2 composite microsphere according to claim 1, characterized in that: In step S3, the mass ratio of the thermosensitive chitosan to PVA in system 1 is 1:(0.2-0.8); the mass ratio of the thermosensitive chitosan to TiO2 is 1:(0.01-0.5).

7. Thermosensitive chitosan / PVA / TiO2 composite microspheres prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the thermosensitive chitosan / PVA / TiO2 composite microspheres prepared by the preparation method according to any one of claims 1 to 6 in catalytic degradation of methyl orange or rhodamine.

9. The use according to claim 8, characterized in that: The application method of the thermosensitive chitosan / PVA / TiO2 composite microspheres in the catalytic degradation of methyl orange has the following steps: adding the thermosensitive chitosan / PVA / TiO2 composite microspheres to a methyl orange solution, ultrasonically treating for 5 to 40 minutes under light-proof conditions, and then subjecting the solution to catalytic degradation for 20 to 30 minutes under natural light.

10. The use according to claim 8, characterized in that: The application method of the thermosensitive chitosan / PVA / TiO2 composite microspheres in the photocatalytic degradation of rhodamine has the following steps: adding the thermosensitive chitosan / PVA / TiO2 composite microspheres to a rhodamine solution, mixing, then adding 0.1-0.3 mmol / L of a PMS solution, and performing a catalytic degradation reaction under natural light conditions.

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