Method for preparing photocatalyst based on polysaccharide morphology inducer and method for degrading organic pollutants in wastewater

Abstract

The invention relates to a method for preparing a photocatalyst based on a polysaccharide morphology inducer and a method for degrading organic pollutants in wastewater, and the method comprises the following steps: S1, dispersing algal polysaccharides and chitosan into weakly acidic water according to a mass ratio of 1: (2-4) to obtain a 0.2-0.5 g / mL polysaccharide aqueous dispersion; powder of soluble bismuth salt is added into the dispersion liquid, stirring is conducted for 20-30 min at the rotating speed of 300-500 rpm, and according to the weight of the bismuth element, the final adding concentration of the bismuth salt is 0.1-0.3 g / mL; s2, a chlorine salt aqueous solution is prepared, the molar ratio of chlorine ions contained in chlorine salt to bismuth is 1: 1, the chlorine salt aqueous solution and the reaction system in the S1 are mixed, stirring is conducted for 30-40 min at the rotating speed of 300-500 rpm, the mixture is transferred into a high-pressure reaction kettle, and a heat preservation reaction is conducted for 3-6 h at the temperature of 170-190 DEG C; s3, adding cold water of which the volume is 2-4 times that of the reaction system, stirring for 10-20 minutes at the rotating speed of 10-50 rpm, centrifuging, collecting precipitate, washing the precipitate with distilled water, and drying to obtain the photocatalyst. Compared with BiOCl prepared without a morphology inducer, the photocatalyst shows better degradation efficiency when degradation-resistant organic matters in wastewater are degraded.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of organic photocatalysts, and specifically relates to a method for preparing a photocatalyst based on a polysaccharide morphology inducer and a method for degrading organic pollutants in wastewater. Background Art

[0002] Tetracycline is a broad-spectrum antibiotic widely used in human medicine, veterinary medicine, and agriculture. The presence of tetracycline can reduce the water quality and affect the safety of drinking water sources. In addition, it may interact with other pollutants to form more complex and difficult-to-treat pollution problems. Photocatalytic oxidation technology is a method that uses light energy to activate semiconductor materials to generate electron-hole pairs, thereby degrading organic pollutants and having bactericidal and mildew-proof effects. It only requires light, a catalyst, and air to work. The catalyst can be recycled, the treatment cost is low, and there is no secondary pollution. Therefore, it shows great application potential in wastewater treatment, air purification, and other aspects.

[0003] BiOCl is a promising semiconductor photocatalyst widely used in fields such as photocatalytic hydrogen production, photocatalytic N2 fixation, and photocatalytic water pollution treatment. However, a wide bandgap and less visible light absorption are major drawbacks of the BiOCl photocatalyst. To solve this problem, methods such as constructing heterojunctions, carrier loading, and plasmon sensitization have been adopted in the hope of obtaining a lower bandgap width and stronger photocatalytic effect. However, most of the current methods are relatively complex and rely on the binary relationship between the load and the loaded material. In fact, it will also cause the problem that the separation and transfer rate of photo-generated electron-hole pairs are hindered by the heteromaterial. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] In view of the above-mentioned disadvantages and deficiencies of the prior art, the present invention provides a method for preparing a photocatalyst based on a polysaccharide morphology inducer and a method for degrading organic pollutants in wastewater. The BiOCl photocatalyst prepared by this method has higher photocatalytic efficiency compared with the product prepared without polysaccharide morphology induction, and can be used for the photocatalytic degradation of refractory organic substances such as tetracycline in wastewater.

[0006] (2) Technical Solutions

[0007] In the first aspect, the present invention provides a method for preparing a photocatalyst based on a polysaccharide morphology inducer, which includes:

[0008] S1. Disperse algal polysaccharide and chitosan in weakly acidic water at a mass ratio of 1:2 - 4 to obtain a polysaccharide aqueous dispersion with a concentration of 0.2 - 0.5 g / mL. Add the powder of soluble bismuth salt to this dispersion and stir at a speed of 300 - 500 rpm for 20 - 30 min. Calculated by the weight of bismuth element, the final concentration of the added bismuth salt is 0.1 - 0.3 g / mL.

[0009] S2. Prepare an aqueous solution of chloride salt, where the molar ratio of chloride ions contained in the chloride salt to bismuth element is 1:1. Mix the aqueous solution of chloride salt with the reaction system of S1 at a volume ratio of 1:1. Then stir at a speed of 300 - 500 rpm for 30 - 40 min, transfer it to a high-pressure reactor, and keep the temperature at 170 - 190 °C for 3 - 6 h for reaction.

[0010] S3. After the reaction is completed, add cold water with a volume 2 - 4 times that of the reaction system, stir at a speed of 10 - 50 rpm for 10 - 20 min, centrifuge to collect the precipitate, wash the precipitate with distilled water 2 - 4 times, and dry it to obtain the photocatalyst.

[0011] According to a preferred embodiment of the present invention, in S1, the weakly acidic water is acetic acid water with a pH of 4 - 5.

[0012] According to a preferred embodiment of the present invention, in S1, the molecular weight of algal polysaccharide is 50 - 200 KDa, and the molecular weight of chitosan is 5 - 20 KDa.

[0013] According to a preferred embodiment of the present invention, in S1, the bismuth salt is bismuth nitrate, bismuth acetate, hydrate of bismuth nitrate or hydrate of bismuth acetate.

[0014] According to a preferred embodiment of the present invention, in S1, the chloride salt is potassium chloride or sodium chloride.

[0015] According to a preferred embodiment of the present invention, in S2, keep the temperature at 180 °C for 4 h for reaction.

[0016] In the second aspect, the present invention provides a photocatalyst prepared by the method of any one of the above embodiments.

[0017] In the third aspect, the present invention provides a method for degrading organic pollutants in wastewater, which includes: putting the photocatalyst prepared in the above embodiment into water, with a dosage of 0.5 - 1 g / L. After stirring in the dark environment for 30 min, then carry out a photocatalytic reaction for 0.5 - 1 h; the light is artificial light source or sunlight.

[0018] (III) Beneficial effects

[0019] The present invention utilizes the unique cross-linking characteristics of chitosan and sodium alginate. When used in combination, they can provide a more robust template by forming a double network structure, which helps to obtain BiOCl products with specific morphologies and enables precise control of the microstructure such as the particle size and porosity of the photocatalyst. As an anionic polysaccharide, sodium alginate has electrostatic interactions with cationic chitosan, which can help better disperse bismuth salts and chloride salts, thereby improving the reaction efficiency and reducing the possibility of non-uniform precipitation, resulting in products with high uniformity in performance.

[0020] Experiments have proven that the BiOCl photocatalyst prepared by the method of the present invention has a higher degradation rate for tetracycline in water under the same time and the same light conditions. Description of the Drawings

[0021] Figure 1 SEM image of the photocatalyst prepared in Example 1 of the present invention at a scale of 1.00 μm.

[0022] Figure 2 XRD pattern of the photocatalyst BiOCl prepared in Example 1 tested by X-ray diffraction.

[0023] Figure 3 Degradation curves of the photocatalysts of Examples 1-3 and Comparative Example 1 for tetracycline in water. Detailed Embodiments

[0024] To better explain the present invention for easy understanding, the present invention will be described in detail below with reference to the drawings through specific embodiments.

[0025] Example 1

[0026] This example provides a method for preparing a photocatalyst based on a polysaccharide morphology inducer, and the steps are as follows:

[0027] (1) Weigh an appropriate amount of seaweed polysaccharide with a molecular weight of 50KDa - 200KDa and chitosan with a molecular weight of 5KDa - 20KDa. Disperse the seaweed polysaccharide and chitosan in acetic acid water with a pH of 4.5 according to a mass ratio of 1:3 to obtain a polysaccharide aqueous dispersion with a concentration of 0.3 g / mL. Add the powder of Bi(NO3)3·5H2O2 to the dispersion, stir at a speed of 400 rpm for 25 min. Calculated by the weight of bismuth element, the final concentration of the added bismuth salt is 0.15 g / mL.

[0028] (2) Weigh potassium chloride in an equimolar amount to Bi(NO3)3·5H2O2, prepare an aqueous solution of potassium chloride with the same volume as the dispersion system in step (1), mix the potassium chloride aqueous solution with the dispersion system in step (1), stir at a speed of 400 rpm for 30 min, transfer it to a high-pressure reaction kettle, and keep the reaction at 180 °C for 4 h.

[0029] (3) After the reaction is completed, add cold water with a volume three times that of the reaction system, stir at a speed of 20 rpm for 20 min, centrifuge to collect the precipitate, wash the precipitate 4 times with distilled water, and dry it at 60 °C for 12 h to obtain the photocatalyst.

[0030] Example 2

[0031] This example provides a method for preparing a photocatalyst based on a polysaccharide morphology inducer, and the steps are as follows:

[0032] (1) Weigh an appropriate amount of alginate with a molecular weight of 50 KDa - 100 KDa and chitosan with a molecular weight of 5 KDa - 10 KDa. Disperse the alginate and chitosan in acetic acid water with a pH of 5 according to a mass ratio of 1:2 to obtain a polysaccharide aqueous dispersion with a concentration of 0.25 g / mL. Add the powder of Bi(NO3)3·5H2O2 to the dispersion, stir at a speed of 400 rpm for 20 min. According to the weight of bismuth element, the final concentration of the bismuth salt added is 0.1 g / mL.

[0033] (2) Weigh potassium chloride in an equimolar amount of Bi(NO3)3·5H2O2, prepare an aqueous solution of potassium chloride with the same volume as the dispersion system in step (1), mix the aqueous solution of potassium chloride with the dispersion system in step (1), stir at a speed of 400 rpm for 30 min, transfer it to a high-pressure reactor, and keep the temperature at 190 °C for 3 h.

[0034] (3) After the reaction is completed, add cold water with a volume three times that of the reaction system, stir at a speed of 30 rpm for 20 min, centrifuge to collect the precipitate, wash the precipitate 3 times with distilled water, and dry it at 70 °C for 10 h to obtain the photocatalyst.

[0035] Example 3

[0036] This example provides a method for preparing a photocatalyst based on a polysaccharide morphology inducer, and the steps are as follows:

[0037] (1) Weigh an appropriate amount of alginate with a molecular weight of 50 KDa - 100 KDa and chitosan with a molecular weight of 5 KDa - 10 KDa. Disperse the alginate and chitosan in acetic acid water with a pH of 4.3 according to a mass ratio of 1:4 to obtain a polysaccharide aqueous dispersion with a concentration of 0.4 g / mL. Add the powder of bismuth citrate to the dispersion, stir at a speed of 500 rpm for 30 min. According to the weight of bismuth element, the final concentration of the bismuth salt added is 0.25 g / mL.

[0038] (2) Weigh potassium chloride in an equimolar amount of bismuth citrate, prepare an aqueous solution of potassium chloride with the same volume as the dispersion system in step (1), mix the potassium chloride aqueous solution with the dispersion system in step (1), stir at a speed of 500 rpm for 30 min, transfer it to a high-pressure reactor, and keep the temperature at 170 °C for 6 h for reaction.

[0039] (3) After the reaction is completed, add cold water with a volume 4 times that of the reaction system, stir at a speed of 30 rpm for 20 min, centrifuge to collect the precipitate, wash the precipitate 3 times with distilled water, and dry it at 80 °C for 8 h to obtain the photocatalyst.

[0040] As Figure 1 shown, it is the SEM image of the photocatalyst in Example 1 at a scale of 1.00 μm.

[0041] Furthermore, the photocatalysts prepared in Examples 1 - 3 were tested by X-ray diffraction, and the obtained XRD patterns are as Figure 2 shown. It can be seen from the figure that the positions of the diffraction peaks are completely consistent with the standard card (JCPDS: 85 - 0861), indicating that the synthesized sample is a pure phase of BiOCl; upon careful observation, it is found that the diffraction peak shapes are sharp and the intensities are relatively large, indicating that the synthesized samples have good crystallinity.

[0042] Comparative Example 1

[0043] In the preparation of the photocatalyst in this comparative example, seaweed polysaccharide and chitosan were not used, and other operation steps and conditions were the same as those in Example 1. Specifically, the preparation method of the photocatalyst in Comparative Example 1 was as follows: Take acetic acid water with a pH of 4.5, add the powder of Bi(NO3)3·5H2O2, stir at a speed of 400 rpm for 25 min, and according to the weight of bismuth element, the final concentration of the added bismuth salt was 0.15 g / mL. Weigh potassium chloride in an equimolar amount of Bi(NO3)3·5H2O2, prepare an aqueous solution of potassium chloride with the same volume as the dispersion system in step (1), mix the potassium chloride aqueous solution with the dispersion system in step (1), stir at a speed of 400 rpm for 30 min, transfer it to a high-pressure reactor, and keep the temperature at 180 °C for 4 h for reaction. After the reaction is completed, add cold water with a volume 3 times that of the reaction system, stir at a speed of 20 rpm for 20 min, centrifuge to collect the precipitate, wash the precipitate 4 times with distilled water, and dry it at 60 °C for 12 h to obtain the photocatalyst.

[0044] Photocatalytic performance test

[0045] The photocatalysts BiOCl of Examples 1-3 and Comparative Example 1 were used in the tetracycline degradation experiment. 100 mL of a tetracycline (TC) solution with an initial concentration of 10 mg / L was measured and placed in a beaker. 0.05 g of each catalyst sample was weighed and added to the beaker. The water temperature was maintained at 20 °C, and the mixture was stirred in the dark for 30 min. After reaching the adsorption-desorption equilibrium, a sample was taken as a blank control. Then, the light source (300 W xenon lamp) was turned on, and samples were taken every 10 min. After filtering twice with a 0.22 μm aqueous filter membrane, the absorbance of TC was measured with a UV-visible spectrophotometer, and the degradation rate was calculated.

[0046] Degradation rate = (1 - C / C0) × 100%; C represents the remaining concentration, and C0 represents the initial concentration.

[0047] As Figure 3 shown, the photocatalysts of different groups had better degradation effects on tetracycline under visible light irradiation than Comparative Example 1. Among them, the photocatalyst of Example 1 achieved a degradation rate of 80.6% for tetracycline in 60 minutes, the photocatalyst of Example 2 achieved a degradation rate of 78.8% for tetracycline in 60 minutes, and the photocatalyst of Example 3 achieved a degradation rate of 76.5% for tetracycline in 60 minutes. The product of Comparative Example 1 achieved a degradation rate of 43.6% for tetracycline in 60 minutes. Thus, it can be seen that the photocatalyst prepared based on the polysaccharide morphology inducer of the present invention has good application prospects in the degradation of refractory organic pollutants in wastewater.

[0048] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing examples, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements, or in the case where the technical features in the above examples do not conflict with each other, can be combined in the manner described in the examples, and these modifications, replacements or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various examples of the present invention.

Claims

1. A method for preparing a photocatalyst based on a polysaccharide morphology inducer, characterized in that: The steps include: S1. Dispersing seaweed polysaccharide and chitosan in weakly acidic water at a mass ratio of 1:2-4 to obtain a 0.2-0.5 g / mL polysaccharide aqueous dispersion; adding soluble bismuth salt powder to the dispersion, stirring at a speed of 300-500 rpm for 20-30 min, and the final concentration of the bismuth salt added is 0.1-0.3 g / mL based on the weight of the bismuth element; S2, prepare a chloride salt aqueous solution, the molar ratio of chloride ions to bismuth elements in the chloride salt is 1:1, mix the chloride salt aqueous solution with the S1 reaction system at a volume ratio of 1:1, then stir at a speed of 300-500 rpm for 30-40 minutes, transfer to a high-pressure reactor, and keep the reaction at 170-190°C for 3-6 hours; S3. After the reaction is completed, add 2-4 times the volume of cold water of the reaction system, stir at a speed of 10-50 rpm for 10-20 min, collect the precipitate by centrifugation, wash the precipitate with distilled water 2-4 times, and dry to obtain a photocatalyst.

2. The method for preparing a photocatalyst according to claim 1, characterized in that: In S1, the weakly acidic water is acetic acid water with a pH of 4-5.

3. The method for preparing a photocatalyst according to claim 1, characterized in that: In S1, the molecular weight of seaweed polysaccharide is 50-200KDa, and the molecular weight of chitosan is 5-20KDa.

4. The method for preparing a photocatalyst according to claim 1, characterized in that: In S1, the bismuth salt is bismuth nitrate, bismuth acetate, a hydrate of bismuth nitrate or a hydrate of bismuth acetate.

5. The method for preparing a photocatalyst according to claim 1, characterized in that: In S1, the chloride salt is potassium chloride or sodium chloride.

6. The method for preparing a photocatalyst according to claim 1, characterized in that: In S2, the reaction was kept at 180°C for 4 hours.

7. A photocatalyst, characterized in that: The method is prepared by the method according to any one of claims 1 to 6.

8. A method for degrading organic pollutants in wastewater, characterized in that: include: The photocatalyst according to claim 7 is added into water at a dosage of 0.5-1 g / L, stirred in a dark environment for 30 minutes, and then subjected to light irradiation reaction for 0.5-1 hour; the light is an artificial light source or sunlight.

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