A molybdenum oxide bismuth vanadate composite photocatalyst, a preparation method and application thereof

Abstract

The application discloses a kind of molybdenum vanadium bismuth oxide composite photocatalyst and its preparation method and application, the method will be dissolved in deionized water with bismuth source and urea, bismuth source is bismuth trichloride or bismuth nitrate pentahydrate, obtain mixed solution, then mixed solution is carried out heat preservation treatment under 160~200 ℃, obtain precipitate, after drying precipitate, calcination treatment in oxygen atmosphere, obtain Bi2O3;Bi2O3 and V2O5 are stirred in nitric acid solution for 50~125h, then the product is collected and dried, to obtain BiVO4;Ammonium paramolybdate and BiVO4 are mixed uniformly in deionized water, to obtain precursor solution, the precursor solution is kept at 160~200 ℃ for 10~16h, then the product is collected and dried, to obtain molybdenum vanadium bismuth oxide composite photocatalyst.The application is simple in operation, raw material is easy to obtain, low in cost, low in energy consumption, good in stability, high in activity, high in efficiency of photoreforming PET hydrolysate.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and environmental governance technology, specifically relating to a bismuth vanadate-molybdenum oxide composite photocatalyst, its preparation method, and its application. Background Technology

[0002] Plastics are widely used due to their good stability, high plasticity, and low price. However, due to improper stockpiling or disposal, they pose a significant threat to natural ecosystems. Currently, there is no environmentally friendly and low-cost way to recycle waste plastics. Most recycled plastics processed through melting and re-extrusion have lower molecular weights than virgin plastics, but their thermal and mechanical properties are reduced.

[0003] The conversion of plastics into alkanes, aromatics, and olefins using photocatalysis and thermocatalysis holds great potential for recycling. While thermocatalysis can convert plastics into value-added chemicals, it requires high temperatures, high pressures, and expensive catalysts, resulting in high costs and hindering its widespread application.

[0004] Photoreforming technology can convert plastics into valuable chemicals and, in addition, generate H2 fuel through water reduction under mild conditions. Polyethylene terephthalate (PET) is one of the most commonly used plastic products in daily life, generally used to produce water bottles and packaging boxes. Therefore, PET photoreforming has high practical value. PET is usually hydrolyzed under alkaline conditions to terephthalate (TPA) and ethylene glycol (EG). Only EG participates in the photoreforming process; TPA can be directly precipitated by adjusting the pH of the solution. For example, Reisner et al. converted EG molecules in PET hydrolysate into formate, glycolate, and acetate, while simultaneously generating hydrogen (H2) from H2O. Compared with photocatalytic water splitting, the potential energy required for photoreforming the alkaline hydrolysis products of PET is almost energy neutral because EG can be considered a sacrificial agent and is preferentially oxidized in the photocatalytic water splitting reaction. Therefore, PET photoreforming should primarily utilize narrow bandgap photocatalysts.

[0005] BiVO4, as a narrow bandgap photocatalyst, possesses advantages such as high visible light response, low cost, and good chemical stability, and is considered one of the most valuable photocatalysts for application. However, its poor carrier transport performance and weak adsorption and activation ability for water limit its photocatalytic performance. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, this invention discloses a bismuth vanadate-molybdenum oxide composite photocatalyst, its preparation method and application. It is simple to operate, the raw materials are readily available, the cost is low, the energy consumption is low, the stability is good, the activity is high, and the efficiency of photo-reforming PET hydrolysate is high.

[0007] This invention is achieved through the following technical solution:

[0008] A method for preparing a bismuth molybdenum oxide-vanadate composite photocatalyst includes the following steps:

[0009] S1, dissolve bismuth source and urea in deionized water. The bismuth source is bismuth trichloride or bismuth nitrate pentahydrate. The mass ratio of bismuth trichloride to urea is 1.6:(0.5-1), and the mass ratio of bismuth nitrate pentahydrate to urea is 2:(0.5-1). A mixture is obtained. The mixture is then kept at 160-200℃ to obtain a precipitate. The precipitate is dried and then calcined in an oxygen atmosphere to obtain Bi2O3.

[0010] S2, Bi2O3 and V2O5 were stirred in nitric acid solution at a mass ratio of 5:2 for 50-125 h, and the product was collected and dried to obtain BiVO4;

[0011] S3, ammonium molybdate tetrahydrate and BiVO4 were mixed evenly in deionized water at a mass ratio of (0.05~0.3):1 to obtain a precursor solution. The precursor solution was kept at 160~200℃ for 10~16h, and then the product was collected and dried to obtain bismuth molybdate vanadate composite photocatalyst.

[0012] Preferably, the ratio of deionized water to urea in S1 is 70 mL: (0.5–1) g.

[0013] Preferably, in step S1, the mixture is kept at 160–200°C for 10–16 hours, and then the resulting reaction solution is stirred and evaporated to dryness to obtain a precipitate.

[0014] Preferably, in step S1, the precipitate is dried at 50–80°C for 6–8 hours and then calcined in an oxygen atmosphere.

[0015] Preferably, the calcination treatment described in S1 is carried out at 450-600°C for 2-6 hours, and the temperature is increased from room temperature at a rate of 5-10°C / min, and then cooled to room temperature to obtain Bi2O3.

[0016] Preferably, the molar concentration of the nitric acid solution in S2 is 0.5 to 2, and the ratio of nitric acid solution to Bi2O3 is 50 mL: 1 g.

[0017] Preferably, the stirring described in S2 is carried out at a rate of 400-600 r / min, and then the product is separated by centrifugation with deionized water and dried at 55-65°C for 6-8 h to obtain BiVO4.

[0018] Preferably, the ratio of ammonium molybdate tetrahydrate to deionized water in S3 is (0.05-0.3) g: 70 mL;

[0019] The product was dried at 55–65°C for 6–8 hours to obtain a bismuth molybdenum vanadate composite photocatalyst.

[0020] A bismuth molybdenum vanadate composite photocatalyst obtained by the preparation method of any one of the above-described methods.

[0021] Application of a bismuth molybdenum oxide-vanadate composite photocatalyst in photo-reforming PET hydrolysate.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] This invention discloses a method for preparing a molybdenum oxide-bismuth vanadate composite photocatalyst. The method involves hydrothermally reacting an aqueous solution of bismuth source and urea, followed by high-temperature calcination to generate Bi₂O₃. Through vigorous and prolonged stirring in a nitric acid solution, Bi₂O₃ reacts with V₂O₅ to form well-crystallized monoclinic bismuth vanadate. Finally, bismuth vanadate and ammonium paramolybdate tetrahydrate are hydrothermally reacted in deionized water to obtain a molybdenum oxide-modified bismuth vanadate-based composite photocatalyst. If the molybdenum oxide content is too low, the bismuth vanadate composite photocatalyst exhibits insufficient photogenerated electron induction ability, resulting in low catalytic efficiency. Conversely, if the molybdenum oxide content is too high, it can cover the active sites of bismuth vanadate, also affecting catalytic efficiency. Modifying bismuth vanadate with molybdenum oxide not only induces the rapid transfer of photogenerated electrons from bismuth vanadate to water molecules via molybdenum oxide, promoting the generation of H radicals and thus H₂ production, but also enhances the polarization effect of EG on bismuth vanadate, promoting surface adsorption of EG and thus facilitating the oxidation of EG molecules. Using molybdenum oxide to modify bismuth vanadate can replace noble metal modification to achieve the desired H₂ and formic acid production, significantly reducing costs. The preparation process of this method is simple, low-cost, and the raw materials are readily available.

[0024] Furthermore, if the drying temperature of the precipitate is too low, a large amount of adsorbed water will remain on the surface; if the drying temperature is too high, it will affect the crystallinity.

[0025] Furthermore, calcination temperature that is too low or calcination time that is too short will affect the purity of the precursor Bi2O3; calcination temperature that is too high or calcination time that is too long will form a large number of vacancies.

[0026] Furthermore, if the molar concentration of the nitric acid solution is too high, the resulting bismuth vanadate particles will be too large; if the molar concentration of the nitric acid solution is too low, the synthesis time of bismuth vanadate will be too long and the purity will be insufficient.

[0027] The bismuth molybdenum vanadate composite photocatalyst prepared by this invention contains BiVO4 as a monoclinic phase crystal, which is non-toxic, resistant to high temperature and acid and alkali corrosion, and is a photocatalytic material with good stability.

[0028] When the composite photocatalyst of the present invention is applied in photo-reforming PET hydrolysate, the molybdenum oxide-modified bismuth vanadate composite photocatalyst of the present invention exhibits significantly improved activity compared to unmodified bismuth vanadate material, with H2 and formate yields increasing by 6.1 and 5.9 times, respectively. Attached Figure Description

[0029] Figure 1 The image shows the XRD pattern of the bismuth molybdenum vanadate composite photocatalyst prepared in this invention. The black vertical thin lines in the image correspond to the PDF card of the monoclinic phase BiVO4.

[0030] Figure 2 This is a comparison diagram of the catalytic activity of the bismuth molybdenum vanadate composite photocatalysts prepared in Examples 1-4 of this invention with gallium oxide;

[0031] Figure 3 This is a steady-state surface photovoltage diagram of the bismuth molybdenum vanadate composite photocatalyst prepared in Example 1 of the present invention.

[0032] Figure 4 This is a diagram showing the H radical capture of the bismuth molybdenum oxide-vanadate composite photocatalyst prepared in Example 1 of the present invention. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. These descriptions are intended to explain the invention and not to limit it.

[0034] This invention discloses a method for preparing a bismuth molybdenum vanadate composite photocatalyst, comprising the following steps:

[0035] Step 1: Prepare a 70 mL solution of bismuth source (1.60 g bismuth trichloride or 2 g bismuth nitrate pentahydrate);

[0036] Step 2: Add 0.5-1g of urea to the bismuth source solution obtained in Step 1. Alternatively, bismuth trichloride or bismuth nitrate pentahydrate can be dissolved together with urea in deionized water. Stir well and react at 160-200℃ for 10-16h. Take out the suspended reaction solution, stir and evaporate to dryness to obtain the precipitate.

[0037] Step 3: Dry the precipitate obtained in Step 2 at 50-80℃ for 6-8 hours, and then heat it from room temperature in an oxygen atmosphere at a rate of 5-10℃ / min. After that, calcine it at a high temperature of 450-600℃ for 2-6 hours and then cool it to room temperature to obtain Bi2O3.

[0038] Step 4: Add 0.4g V2O5 and 1g Bi2O3 obtained in Step 3 to 50.0mL of nitric acid aqueous solution with a molar concentration of 0.5-2, stir vigorously at room temperature (400-600r / min) for 50-125h, then centrifuge with 30-50.0mL of deionized water 3-5 times (in subsequent examples, centrifuge 4 times with 40.0mL each time), and dry the precipitate at 55-65℃ for 6-8h to obtain pure BiVO4.

[0039] Step 5: Add 1g of pure BiVO4 to 70mL of molybdenum source (0.05-0.3g ammonium molybdate tetrahydrate) solution, stir evenly, and react at 160-200℃ for 10-16h. After naturally cooling to room temperature, centrifuge to separate the lower precipitate (the specific operation is the same as in Step 4). Dry at 55-65℃ for 6-8h to obtain the molybdenum oxide bismuth vanadate composite photocatalyst. The mass ratio of molybdenum oxide to bismuth vanadate is (1.2-6.7):100. Bismuth vanadate is a monoclinic phase crystal BiVO4.

[0040] The bismuth molybdenum vanadate composite photocatalyst obtained by this invention can be used in photo-reforming PET hydrolysate.

[0041] Example 1

[0042] This invention discloses a method for preparing a bismuth molybdenum vanadate composite photocatalyst, comprising the following steps:

[0043] Weigh 2g of bismuth nitrate pentahydrate and 1g of urea and dissolve them in 70mL of deionized water. Stir well to obtain a mixed solution. Place the solution in a 100mL polytetrafluoroethylene liner and hydrothermally heat it at 180℃ for 10h. Stir the reaction solution and evaporate it to dryness to obtain a white precipitate.

[0044] The white precipitate was placed in a 60℃ oven and dried for 6 hours. The precipitate was then calcined in oxygen at 500℃ for 3 hours with a heating rate of 5℃ / min, and then cooled to room temperature to obtain the Bi2O3 precursor.

[0045] 1 g of Bi₂O₃ precursor and 0.4 g of V₂O₅ were weighed and placed in 50.0 mL of 1 M nitric acid aqueous solution. The mixture was stirred at 600 r / min and 25 °C for 100 h, and then centrifuged to obtain a bright yellow precipitate. The precipitate was then dried in an oven at 60 °C for 6 h to obtain bismuth vanadate solid powder.

[0046] Weigh 0.1 g of ammonium molybdate tetrahydrate and dissolve it in 70 mL of deionized water. Then add 1 g of bismuth vanadate solid powder and stir well. Place the solution in a 100 mL polytetrafluoroethylene liner and hydrothermally heat at 180 °C for 16 h. After the reaction is complete, allow it to cool naturally to room temperature, then centrifuge to separate the lower precipitate. Dry the precipitate in a 60 °C oven for 6 hours to obtain a molybdenum oxide to bismuth vanadate composite material with a molybdenum oxide to bismuth vanadate mass ratio of 2.3:100.

[0047] Example 2

[0048] This invention discloses a method for preparing a bismuth molybdenum vanadate composite photocatalyst, comprising the following steps:

[0049] Weigh 2g of bismuth nitrate pentahydrate and 0.5g of urea and dissolve them in 70mL of deionized water. Stir well to obtain a mixed solution. Place the solution in a 100mL polytetrafluoroethylene liner and hydrothermally heat it at 160℃ for 12h. Stir the reaction solution and evaporate it to dryness to obtain a white precipitate.

[0050] The white precipitate was placed in a 50°C oven and dried for 8 hours. The precipitate was then calcined in oxygen at 500°C for 4 hours at a heating rate of 10°C / min, and then cooled to room temperature to obtain the Bi₂O₃ precursor.

[0051] 1 g of Bi₂O₃ precursor and 0.4 g of V₂O₅ were weighed and placed in 50.0 mL of 0.5 M nitric acid aqueous solution. The mixture was stirred at 400 r / min and 25 °C for 50 h, and then centrifuged to obtain a bright yellow precipitate. The precipitate was then dried in an oven at 60 °C for 8 h to obtain bismuth vanadate solid powder.

[0052] Weigh 0.15 g of ammonium molybdate tetrahydrate and dissolve it in 70 mL of deionized water. Then add 1 g of bismuth vanadate solid powder and stir well. Place the solution in a 100 mL polytetrafluoroethylene liner and hydrothermally heat at 160 °C for 12 h. After the reaction is complete, allow it to cool naturally to room temperature, then centrifuge to separate the lower precipitate. Dry the precipitate in a 60 °C oven for 6 hours to obtain a molybdenum oxide to bismuth vanadate composite material with a molybdenum oxide to bismuth vanadate mass ratio of 3.3:100.

[0053] Example 3

[0054] This invention discloses a method for preparing a bismuth molybdenum vanadate composite photocatalyst, comprising the following steps:

[0055] Weigh 2g of bismuth nitrate pentahydrate and 1g of urea and dissolve them in 70mL of deionized water. Stir well to obtain a mixed solution. Place the solution in a 100mL polytetrafluoroethylene liner and hydrothermally heat it at 140℃ for 10h. Stir the reaction solution and evaporate it to dryness to obtain a white precipitate.

[0056] The white precipitate was placed in a 60℃ oven and dried for 6 hours. The precipitate was then calcined in oxygen at 400℃ for 3 hours with a heating rate of 7℃ / min, and then cooled to room temperature to obtain the Bi2O3 precursor.

[0057] 1 g of Bi₂O₃ precursor and 0.4 g of V₂O₅ were weighed and placed in 50.0 mL of 2 M nitric acid aqueous solution. The mixture was stirred at 600 r / min and 25 °C for 75 h, and then centrifuged to obtain a bright yellow precipitate. The precipitate was then dried in an oven at 60 °C for 6 h to obtain bismuth vanadate solid powder.

[0058] Weigh 0.05 g of ammonium molybdate tetrahydrate and dissolve it in 70 mL of deionized water. Then add 1 g of bismuth vanadate solid powder and stir well. Place the solution in a 100 mL polytetrafluoroethylene liner and hydrothermally heat at 200 °C for 10 h. After the reaction is complete, allow it to cool naturally to room temperature, then centrifuge to separate the lower precipitate. Dry the precipitate in a 60 °C oven for 6 hours to obtain a molybdenum oxide to bismuth vanadate composite material with a molybdenum oxide to bismuth vanadate mass ratio of 1.2:100.

[0059] Example 4

[0060] This invention discloses a method for preparing a bismuth molybdenum vanadate composite photocatalyst, comprising the following steps:

[0061] Weigh 2g of bismuth nitrate pentahydrate and 1g of urea and dissolve them in 70mL of deionized water. Stir well to obtain a mixed solution. Place the solution in a 100mL polytetrafluoroethylene liner and hydrothermally heat it at 200℃ for 16h. Stir the reaction solution and evaporate it to dryness to obtain a white precipitate.

[0062] The white precipitate was placed in a 60℃ oven and dried for 6 hours. The precipitate was then calcined in oxygen at 500℃ for 5 hours at a heating rate of 10℃ / min, and then cooled to room temperature to obtain the Bi2O3 precursor.

[0063] 1 g of Bi₂O₃ precursor and 0.4 g of V₂O₅ were weighed and placed in 50.0 mL of 1 M nitric acid aqueous solution. The mixture was stirred at 600 r / min and 25 °C for 125 h, and then centrifuged to obtain a bright yellow precipitate. The precipitate was then dried in an oven at 60 °C for 6 h to obtain bismuth vanadate solid powder.

[0064] Weigh 0.3 g of ammonium molybdate tetrahydrate and dissolve it in 70 mL of deionized water. Then add 1 g of bismuth vanadate solid powder and stir well. Place the solution in a 100 mL polytetrafluoroethylene liner and hydrothermally heat at 160 °C for 12 h. After the reaction is complete, allow it to cool naturally to room temperature, then centrifuge to separate the lower precipitate. Dry the precipitate in a 60 °C oven for 6 hours to obtain a molybdenum oxide to bismuth vanadate composite material with a molybdenum oxide to bismuth vanadate mass ratio of 6.7:100.

[0065] Take 300 mg of the samples prepared in Examples 1-4, and perform X-ray diffraction to obtain the following results. Figure 1 The XRD diffraction pattern shown. Figure 1 The mid-peak shape is sharp, typical of bismuth vanadate crystals. Figure 1 A comparison of the mid-peak position with the standard card (PDF#14-0688) shows that only one phase exists, namely the monoclinic bismuth vanadate phase.

[0066] Preparation of PET hydrolysate:

[0067] After 1.5g of commercial PET granules were chopped, they were placed in 40mL of 1M KOH solution and stirred at 50℃ for 48h. The supernatant was then used as the photo-reforming reactant.

[0068] Activity testing process:

[0069] 50 mg of samples from Examples 1-4 and 50 mg of bismuth vanadate were weighed out respectively. Five experiments were set up, and the five samples were dispersed in a photocatalytic reactor containing 40 mL of PET hydrolysate. Argon gas was introduced to purge the air. The samples were then irradiated with a 300 W xenon lamp for 5 hours. The concentration of the product in the photocatalytic reactor was detected by gas chromatography and liquid chromatography every hour to obtain the following results. Figure 2 The bar chart shown. From Figure 2 It can be seen that, compared with unmodified bismuth vanadate, the samples of Examples 1 to 4 significantly improved the efficiency of photo-reforming PET hydrolysate, and significantly increased the yield of H2 and formate esters. Example 1 was the best, with increases of 6.1 and 5.9 times, respectively.

[0070] Take 20 mg of the sample prepared in Example 1 and an equal amount of bismuth vanadate, and compare them by surface photovoltage measurement and electron paramagnetic resonance to obtain... Figure 3 , Figure 4 .from Figure 3 The results show that the separation efficiency of photogenerated carriers in the composite material is significantly improved. This semiconductor photocatalytic material has a band gap; under illumination, valence band electrons transition to the conduction band, but simultaneously, electrons return to the ground state and recombine with holes. The improved photoelectric separation efficiency also means that more electrons and holes will undergo redox reactions on the material surface, reducing H2O to H2 and oxidizing EG to formate. Furthermore, as... Figure 4 As shown, molybdenum oxide modification facilitates the rapid transfer of photogenerated electrons from bismuth vanadate, thereby generating H radicals and promoting H2 production. Therefore, improving the photoelectric separation efficiency of the material can increase the yield of H2 and formic acid. However, excessive molybdenum oxide content is detrimental to yield improvement because the active sites of bismuth vanadate are covered. The activity is optimal when the mass ratio of molybdenum oxide to bismuth vanadate is 2.3:100.

[0071] Modifying bismuth vanadate with molybdenum oxide not only accelerates the rapid migration and transfer of photogenerated electrons from bismuth vanadate to molybdenum oxide, but also induces an enhanced polarization effect of EG on bismuth vanadate, promoting surface adsorption of EG and improving the photoelectric separation efficiency of the material. This facilitates the reduction of water and the oxidation of EG. Therefore, bismuth vanadate modified with molybdenum oxide can replace precious metals to improve the photo-reformed PET hydrolysate.

Claims

1. The application of a bismuth molybdenum oxide-vanadate composite photocatalyst in photo-reforming PET hydrolysate, characterized in that, The preparation method of the composite photocatalyst includes the following steps: S1, dissolve bismuth source and urea in deionized water. The bismuth source is bismuth trichloride or bismuth nitrate pentahydrate. The mass ratio of bismuth trichloride to urea is 1.6:(0.5~1), and the mass ratio of bismuth nitrate pentahydrate to urea is 2:(0.5~1) to obtain a mixed solution. Then, the mixed solution is kept at 160~200℃ to obtain a precipitate. After drying the precipitate, it is calcined in an oxygen atmosphere to obtain Bi2O3. S2, Bi2O3 and V2O5 were stirred in nitric acid solution at a mass ratio of 5:2 for 50-125 h, and the product was collected and dried to obtain BiVO4; S3, ammonium molybdate tetrahydrate and BiVO4 were mixed evenly in deionized water at a mass ratio of (0.05~0.3):1 to obtain a precursor solution. The precursor solution was kept at 160~200℃ for 10~16h, and then the product was collected and dried to obtain bismuth molybdate vanadate composite photocatalyst.

2. The application of the bismuth vanadate-molybdenum oxide composite photocatalyst according to claim 1 in photo-reforming PET hydrolysate, characterized in that, The ratio of deionized water to urea in S1 is 70 mL: (0.5~1) g.

3. The application of the bismuth vanadate-molybdenum oxide composite photocatalyst according to claim 1 in photo-reforming PET hydrolysate, characterized in that, S1 The mixture is kept at 160~200℃ for 10~16h, and then the resulting reaction solution is stirred and evaporated to dryness to obtain a precipitate.

4. The application of the bismuth vanadate-molybdenum oxide composite photocatalyst according to claim 1 in photo-reforming PET hydrolysate, characterized in that, S1 The precipitate is dried at 50~80℃ for 6~8h, and then calcined in an oxygen atmosphere.

5. The application of the bismuth vanadate-molybdenum oxide composite photocatalyst according to claim 1 in photo-reforming PET hydrolysate, characterized in that, The calcination treatment described in S1 is carried out at 450~600℃ for 2~6 hours, and the temperature is increased from room temperature at a rate of 5~10℃ / min, and then cooled to room temperature to obtain Bi2O3.

6. The application of the bismuth vanadate-molybdenum oxide composite photocatalyst according to claim 1 in photo-reforming PET hydrolysate, characterized in that, The molar concentration of the nitric acid solution in S2 is 0.5~2 M, and the ratio of nitric acid solution to Bi2O3 is 50 mL: 1 g.

7. The application of the bismuth molybdenum oxide-vanadate composite photocatalyst according to claim 1 in photo-reforming PET hydrolysate, characterized in that, The stirring described in S2 is carried out at a rate of 400~600 r / min. After centrifugation with deionized water, the product is dried at 55~65 ℃ for 6~8 h to obtain BiVO4.

8. The application of the bismuth vanadate-molybdenum oxide composite photocatalyst according to claim 1 in photo-reforming PET hydrolysate, characterized in that, The ratio of ammonium molybdate tetrahydrate to deionized water in S3 is (0.05~0.3) g: 70 mL; The product was dried at 55-65 °C for 6-8 h to obtain a bismuth molybdenum vanadate composite photocatalyst.

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