Method for expanding light absorption range of photocatalytic material to improve photocatalytic hydrogen production performance

Abstract

This invention proposes a method to expand the light absorption range of photocatalytic materials and improve their photocatalytic hydrogen production performance by doping rare earth ions Yb into WO3 rich in oxygen vacancies. 3+ Er 3+ Achieving upconversion luminescence with WO3:Yb 3+ Er 3+ Zn as a sensitizer and photocatalytic semiconductor x Cd 1‑x S, Zn, In2S4, and other compounds form a core-shell structure composite material. Based on the two-photon absorption of WO3 and the upconversion luminescence of rare earth ions, the composite material achieves the simultaneous transfer of high-energy electrons and photons from the sensitizer to the photocatalyst, realizing the goal of photocatalytic reduction of water to produce hydrogen through photo-photo and photo-electro-synergistic sensitization. Through the synergistic effect of the two-photon absorption of WO3 rich in oxygen vacancies and the upconversion luminescence of rare earth ions, and by employing a mild method to combine it with the photocatalytic semiconductor without altering its structure, the composite material can produce hydrogen under ultraviolet-visible-near-infrared light irradiation, significantly improving its solar photocatalytic hydrogen production performance.

Description

TECHNICAL FIELD

[0001] The application relates to a method for expanding the light absorption range of a photocatalytic material and improving the photocatalytic hydrogen production performance, and belongs to the technical field of composite materials. BACKGROUND

[0002] "Energy crisis" and "environmental pollution" are global concerns. Producing clean energy through green and environmentally friendly advanced technology to replace traditional fossil fuels is an effective way to solve energy and environmental problems. In 1972, Fujishima and Honda first reported the groundbreaking discovery of TiO2 photocatalytic decomposition of water to produce H2, revealing the possibility of using sunlight to decompose water to produce hydrogen. Photocatalytic technology can convert solar energy into new energy such as hydrogen energy under mild conditions, convert CO2 into high-value-added products, and also remove organic pollutants and toxic metal ions, bacteria, viruses in the environment, and is therefore widely concerned.

[0003] The solar spectrum is composed of 5% ultraviolet light, 45% visible light and 50% near-infrared light. Only photons with energy greater than or equal to the band gap can cause a photocatalytic reaction. Common semiconductors have a wide band gap and can only absorb the energy of ultraviolet light and short-wave visible light, which cannot fully utilize solar energy and limits the photocatalytic activity. Rare earth ions can convert near-infrared light into ultraviolet light and visible light through upconversion luminescence process. The composite of upconversion luminescence material and semiconductor photocatalyst can realize the light conversion of low-energy near-infrared light to high-energy ultraviolet light and visible light, and then excite the photocatalyst to generate more photo-generated carriers, thereby achieving the purpose of increasing light utilization. At present, most of the upconversion luminescence materials have a too large matrix band gap and do not have photocatalytic activity. Moreover, the composite materials constructed by these substrates and photocatalytic materials often have problems such as mismatched valence band position or inability to form an interface structure conducive to photocatalytic reaction, so they cannot effectively utilize long-wave visible light and near-infrared light. SUMMARY

[0004] The application dopes rare earth ions Yb 3+ ,Er 3+ in WO3 rich in oxygen vacancies to realize upconversion luminescence, and uses WO3:Yb 3+ ,Er 3+ as a sensitizer and a photocatalytic semiconductor Zn x Cd 1-xS, Zn, In2S4, and other compounds form a core-shell structure composite material. Based on the two-photon absorption of WO3 and the upconversion luminescence of rare earth ions, the composite material achieves the simultaneous transfer of high-energy electrons and photons from the sensitizer to the photocatalyst, realizing the goal of photocatalytic reduction of water to produce hydrogen through photo-photo and photo-electro-synergistic sensitization. Using a mild method to composite with the photocatalytic semiconductor without altering its structure, the composite material can produce hydrogen under ultraviolet-visible-near-infrared light irradiation through the synergistic effect of two-photon absorption of oxygen-vacancy-rich WO3 and upconversion luminescence of rare earth ions, significantly improving its solar photocatalytic hydrogen production performance.

[0005] This invention discloses a method for expanding the light absorption range of photocatalytic materials and improving photocatalytic hydrogen production performance. First, 5 mL of nitric acid solution is added to 20-25 mL of deionized water and stirred for 10-30 min. Then, 2-4 g of Na₂WO₄·2H₂O is dispersed in 5 mL of deionized water to obtain a Na₂WO₄ solution. Next, the Na₂WO₄ solution is slowly added to an HNO₃ solution and stirred at room temperature for 10-30 min. Then, ytterbium nitrate pentahydrate and erbium nitrate hexahydrate are added to the above solution and stirred further for 0.5-1 hour. The total rare earth ion concentration is 1-3 mmol, and the ratio of Yb to Er is 1:1-10:1. Subsequently, the mixture is transferred to a 50 mL stainless steel reactor lined with polytetrafluoroethylene and kept at 180-200°C for 3 hours. After cooling to room temperature (30°C), the yellow product is centrifuged and washed three times with deionized water and ethanol. Then, it is vacuum dried at 60-80°C for 6-12 hours, removed, and ground to obtain WO₃:Yb. 3+ Er 3+ Powder. Finally, the obtained WO3:Yb 3+ Er 3+ The powder was placed in a muffle furnace and annealed in air at 300-350℃. WO3:Yb 3+ Er 3+ The composite material with photocatalytic semiconductors is prepared by in-situ growth method, and Zn is prepared accordingly. 0.5 Cd 0.5 The precursors required for the three photocatalytic semiconductors S, CdS and ZnI n2S4 and WO3:Yb 3+ Er 3+ The mixture was added to a beaker containing 30-50 mL of deionized water at a ratio of 1%-15 wt%, and stirred at room temperature for 1-2 hours. Then it was washed three times with water and ethanol, and dried in a vacuum oven at 60°C for 6-12 hours to obtain the composite material.

[0006] The beneficial effects of this invention compared to the prior art are as follows:

[0007] The rare earth is doped in WO3 rich in oxygen vacancies to obtain two-photon absorption and upconversion luminescence. The in-situ growth method is used to form a core-shell structure composite material with a photo-catalytic semiconductor as a photosensitizer. On one hand, the light response range is expanded to the visible and near-infrared regions. On the other hand, the heterostructure helps to improve the utilization rate of photo-generated charges, thereby enhancing the photocatalytic hydrogen production performance. The prepared composite photocatalytic material has an absorption spectrum covering the ultraviolet-visible-near-infrared light region and has excellent photocatalytic hydrogen evolution performance. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 Zn 0.5 Cd 0.5 S, WO3 / Zn 0.5 Cd 0.5 S and WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S XRD pattern.

[0009] Figure 2 WO3:Yb 3+ ,Er 3+ SEM image.

[0010] Figure 3 WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S SEM image.

[0011] Figure 4 Zn 0.5 Cd 0.5 S, WO3 / Zn 0.5 Cd 0.5 S and WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S absorption spectrum.

[0012] Figure 5 Zn 0.5 Cd 0.5 S, WO3 / Zn 0.5 Cd 0.5 S and WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S photocatalytic hydrogen production performance. DETAILED DESCRIPTION

[0013] Example 1. First, 5 mL of nitric acid solution was added to 25 mL of deionized water and stirred for 10 minutes. 3.2 g of Na₂WO₄·2H₂O was dispersed in 5 mL of deionized water to obtain a Na₂WO₄ solution. Then, the Na₂WO₄ solution was slowly added to an HNO₃ solution and stirred at room temperature. Next, ytterbium nitrate pentahydrate and erbium nitrate hexahydrate were added to the above solution and stirred further for 1 hour, resulting in a total rare earth ion concentration of 2 mmol. Subsequently, the mixture was transferred to a 50 mL PTFE-lined stainless steel reactor and kept at 180 °C for 3 hours. After cooling to room temperature, the yellow product was centrifuged and washed three times with deionized water and ethanol. Afterward, it was vacuum dried at 60 °C for 6 hours, then removed and ground to obtain WO₃:Yb. 3+ Er 3+ Powder. Finally, the obtained WO3:Yb 3+ Er 3+ The powder was placed in a muffle furnace and annealed at 350°C in air. WO3:Yb 3+ Er 3+ / Zn 0.5 Cd 0.5 S was prepared by in-situ growth method, using 0.128g CdCl2·2.5H2O, 0.076g ZnCl2, 1.32g Na2S·9H2O and 10mg WO3:Yb 3+ Er 3+ The solution was placed in a beaker containing 30 mL of deionized water and stirred at room temperature for 1 hour. Then it was washed three times with water and ethanol, and dried in a vacuum oven at 60 °C for 12 hours. This yielded WO3:Yb. 3+ Er 3+ / Zn 0.5 Cd 0.5 S composite material.

[0014] Example 2. First, 5 mL of nitric acid solution was added to 25 mL of deionized water and stirred for 10 minutes. 2 g of Na₂WO₄·2H₂O was dispersed in 5 mL of deionized water to obtain a Na₂WO₄ solution. Then, the Na₂WO₄ solution was slowly added to an HNO₃ solution and stirred at room temperature. Next, ytterbium nitrate pentahydrate and erbium nitrate hexahydrate were added to the above solution and stirred further for 0.5 hours, resulting in a total rare earth ion concentration of 2 mmol. Subsequently, the mixture was transferred to a 50 mL PTFE-lined stainless steel reactor and kept at 180 °C for 10 hours. After cooling to room temperature, the yellow product was centrifuged and washed three times with deionized water and ethanol. Afterward, it was vacuum dried at 60 °C for 6 hours, then removed and ground to obtain WO₃:Yb. 3+ Er 3+ Powder. Finally, the obtained WO3:Yb 3+ Er 3+The powder was annealed in a muffle furnace at 350 °C in air atmosphere. WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S composite was prepared by in-situ growth method. 0.128 g of CdCl2-2.5H2O, 0.076 g of ZnCl2, 1.32 g of Na2S-9H2O and 20 mg of WO3:Yb 3+ ,Er 3+ were put into a beaker containing 30 mL of deionized water and stirred at room temperature for 1 hour. Then washed with water and ethanol three times and dried in a vacuum oven at 60 °C for 12 hours. WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S composite was obtained.

[0015] Example 3. First, 5 mL of nitric acid solution was added to 25 mL of deionized water and stirred for 10 minutes, and 3.2 g of Na2WO4-2H2O was dispersed in 5 mL of deionized water to obtain a Na2WO4solution. Then the Na2WO4solution was slowly added to the HNO3solution and stirred at room temperature, then ytterbium nitrate pentahydrate and erbium nitrate hexahydrate were added to the above solution and further stirred for 1 hour, and the rare earth ions were 2 mmol. Subsequently, the mixture was transferred to a 50 mL polytetrafluoroethylene lined stainless steel reaction kettle, and kept at 200 °C for 3 hours, after cooling to room temperature, the yellow product was centrifuged and washed with deionized water and ethanol three times, then dried in a vacuum oven at 60 °C for 6 hours, then taken out and ground, to obtain WO3:Yb 3+ ,Er 3+ powder. Finally, the obtained WO3:Yb 3+ ,Er 3+ powder was annealed in a muffle furnace at 350 °C in air atmosphere. WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S composite was prepared by in-situ growth method. 0.128 g of CdCl2-2.5H2O, 0.076 g of ZnCl2, 1.32 g of Na2S-9H2O and 5 mg of WO3:Yb 3+ ,Er 3+ were put into a beaker containing 30 mL of deionized water and stirred at room temperature for 1 hour. Then washed with water and ethanol three times and dried in a vacuum oven at 60 °C for 12 hours. WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S composite was obtained.

[0016] Example 4. First, 5 mL of nitric acid solution was added to 20 mL of deionized water and stirred for 10 minutes, 3.2 g of Na2WO4-2H2O was dispersed in 5 mL of deionized water to obtain a Na2WO4solution. Then the Na2WO4solution was slowly added to the HNO3solution and stirred at room temperature, then ytterbium nitrate pentahydrate and erbium nitrate hexahydrate were added to the above solution and further stirred for 1 hour, and the rare earth ions were 2 mmol. Subsequently, the mixture was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel reaction kettle, and kept at 200°C for 3 hours, after cooling to room temperature, the yellow product was centrifuged and washed with deionized water and ethanol three times, then taken out and ground after vacuum drying at 60°C for 6 hours, to obtain WO3:Yb 3+ ,Er 3+ powder. Finally, the obtained WO3:Yb 3+ ,Er 3+ powder was placed in a muffle furnace and annealed at 350°C in an air atmosphere. WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S composite material was prepared by in-situ growth method, 0.128 g of CdCl2-2.5H2O, 0.076 g of ZnCl2, 1.32 g of Na2S-9H2O and 15 mg of WO3:Yb 3+ ,Er 3+ were placed in a beaker containing 30 mL of deionized water, stirred at room temperature for 1 hour. Then washed with water and ethanol three times, and dried in a vacuum oven at 60°C for 12 hours. WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S composite material was prepared by in-situ growth method, 0.128 g of CdCl2-2.5H2O, 0.076 g of ZnCl2, 1.32 g of Na2S-9H2O and 15 mg of WO3:Yb

[0017] Example 5. First, 5 mL of nitric acid solution was added to 25 mL of deionized water and stirred for 10 minutes, 3.2 g of Na2WO4-2H2O was dispersed in 5 mL of deionized water to obtain a Na2WO4solution. Then the Na2WO4solution was slowly added to the HNO3solution and stirred at room temperature, then the Na2WO4solution was slowly added to the HNO3solution and stirred at room temperature. Subsequently, the mixture was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel reaction kettle, and kept at 180°C for 3 hours, after cooling to room temperature, the yellow product was centrifuged and washed with deionized water and ethanol three times, then taken out and ground after vacuum drying at 60°C for 6 hours, to obtain WO3 powder. Finally, the obtained WO3 powder was placed in a muffle furnace and annealed at 350°C in an air atmosphere. WO3 / Zn 0.5 Cd 0.5S composite was prepared by in-situ growth method. 0.128 g CdCl2.2.5H2O, 0.076 g ZnCl2, 1.32 g Na2S.9H2O and 10 mg WO3 were put into a beaker containing 30 mL deionized water, stirred at room temperature for 1 hour. Then washed with water and ethanol for three times, dried in a vacuum oven at 60 °C for 12 hours. WO3 / Zn 0.5 Cd 0.5 S composite.

[0018] Example 6. First, 5 mL nitric acid solution was added into 25 mL deionized water and stirred for 10 minutes, 3.2 g Na2WO4.2H2O was dispersed in 5 mL deionized water to obtain a Na2WO4solution. Then the Na2WO4solution was slowly added into the HNO3 solution, stirred at room temperature, then ytterbium nitrate pentahydrate and erbium nitrate hexahydrate were added into the above solution and further stirred for 1 hour, the rare earth ions were 2 mmol. Subsequently, the mixture was transferred into a 50 mL polytetrafluoroethylene lined stainless steel reaction kettle, and kept at 180 °C for 3 hours, after cooling to room temperature, the yellow product was centrifuged and washed with deionized water and ethanol for three times, then taken out and ground after vacuum drying at 60 °C for 6 hours, to obtain WO3:Yb 3+ ,Er 3+ powder. Finally, the obtained WO3:Yb 3+ ,Er 3+ powder was put into a muffle furnace and annealed at 350 °C in air atmosphere. WO3:Yb 3+ ,Er 3+ / CdS composite was prepared by in-situ growth method. 0.256 g CdCl2.2.5H2O, 1.32 g Na2S.9H2O and 10 mg WO3:Yb 3+ ,Er 3+ were put into a beaker containing 30 mL deionized water, stirred at room temperature for 1 hour. Then washed with water and ethanol for three times, dried in a vacuum oven at 60 °C for 12 hours. WO3:Yb 3+ ,Er 3+ / CdS composite.

[0019] Example 7. First, 5 mL of nitric acid solution was added to 25 mL of deionized water and stirred for 10 minutes, 3.2 g of Na2WO4·2H2O was dispersed in 5 mL of deionized water to obtain a Na2WO4 solution. Then the Na2WO4 solution was slowly added to the HNO3 solution and stirred at room temperature, then ytterbium nitrate pentahydrate and erbium nitrate hexahydrate were added to the above solution and further stirred for 1 hour, and the rare earth ions were 2 mmol. Subsequently, the mixture was transferred to a 50 mL polytetrafluoroethylene lined stainless steel reaction kettle, and kept at 180℃ for 3 hours, after cooling to room temperature, the yellow product was centrifuged and washed with deionized water and ethanol three times, then vacuum dried at 60℃ for 6 hours, taken out and ground after vacuum drying at 60℃ for 6 hours, to obtain WO3:Yb 3+ ,Er 3+ powder. Finally, the obtained WO3:Yb 3+ ,Er 3+ powder was placed in a muffle furnace and annealed at 350℃ in an air atmosphere. WO3:Yb 3+ ,Er 3+ / Zn In2S4 was prepared by an in-situ growth method, 0.11 g of ZnCl2, 0.35 g of InCl3, 1.32 g of Na2S·9H2O and 10 mg of WO3:Yb 3+ ,Er 3+ were placed in a beaker containing 30 mL of deionized water and stirred at room temperature for 1 hour. Then washed with water and ethanol three times, and dried in a vacuum oven at 60℃ for 12 hours. WO3:Yb 3+ ,Er 3+ / Zn In2S4 composite material was obtained.

[0020] The effect of the present application was verified by the following experiments:

[0021] The WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S material prepared by the present application was respectively characterized by XRD ( Figure 1 ), scanning electron microscopy ( Figure 2 , Figure 3 ), DRS characterization ( Figure 4 ) and photocatalytic hydrogen production performance test ( Figure 5 ). The XRD characteristic peak position of the WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S material is consistent with the XRD standard card of WO3 and Zn 0.5 Cd 0.5 S material. Figure 2 and Figure 3WO3:Yb 3+ ,Er 3+ and WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S. It is obvious that uniform sheet WO3:Yb 3+ ,Er 3+ and WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S core-shell structure is formed. Figure 4 It is shown that the light absorption of the composite photocatalytic material covers the ultraviolet-visible-near infrared region. Figure 5 It is shown that compared with Zn 0.5 Cd 0.5 S and WO3 / Zn 0.5 Cd 0.5 S, WO3:Yb 3+ ,Er 3+ / Zn 0.5 Cd 0.5 S has higher photocatalytic hydrogen production performance under simulated sunlight irradiation.

Claims

1. A method for expanding the light absorption range of a photocatalytic material to improve the photocatalytic hydrogen production performance, characterized in that: Firstly, nitric acid solution is added to deionized water and stirred, Na2WO4·2H2O is dispersed in deionized water to obtain a Na2WO4 solution; then the Na2WO4 solution is slowly added to the HNO3 solution, stirred at room temperature, then ytterbium nitrate pentahydrate and erbium nitrate hexahydrate are added to the above solution and further stirred; then, the mixture is transferred to a polytetrafluoroethylene-lined stainless steel reactor for heat preservation, then cooled to room temperature, the yellow product is centrifuged and washed with deionized water and ethanol three times, then dried and ground to obtain a WO3:Yb 3+ ,Er 3+ powder; finally, the obtained WO3:Yb 3+ ,Er 3+ powder is placed in a muffle furnace for annealing treatment; WO3:Yb 3+ ,Er 3+ is compounded with a photocatalytic semiconductor by an in-situ growth method, and the precursors required for preparing three kinds of photocatalytic semiconductors Zn 0.5 Cd 0.5 S, CdS and ZnIn2S4 and WO3:Yb 3+ ,Er 3+ are placed in a beaker containing 30-50 mL of deionized water in an appropriate proportion, stirred at room temperature for 1-2 hours; then washed with water and ethanol three times, and dried in a vacuum oven at 60°C for 6-12 hours to obtain a composite material.

2. The method of claim 1, wherein the method is characterized by: 5 mL nitric acid solution was added to 20-25 mL deionized water and stirred for 10-30 minutes.

3. The method of claim 1, wherein the method is characterized by: 2-4 g Na2WO4·2H2O was dispersed in 5 mL deionized water to obtain a Na2WO4 solution.

4. The method of claim 1, wherein the method is characterized by: The stirring time was 0.5-1 hour.

5. The method of claim 1, wherein the method is characterized by: The rare earth ions were 1-3 mmol in total, and the ratio of Yb to Er was 1:1-10:

1.

6. The method of claim 1, wherein the method is characterized by: The volume of the reaction kettle was 50-100 mL, and the mixture was kept at 180-200 ℃ in the reaction kettle for 3 hours.

7. The method of claim 1, wherein the method is characterized by: After vacuum drying at 60-80 ℃ for 6-12 hours, it was taken out and ground. 8.The method of extending the light absorption range of a photocatalyst and improving the hydrogen production performance of the photocatalyst according to claim 1, characterized in that: Annealing treatment was carried out at 300-350 ℃ in an air atmosphere.

9. The method of claim 1, wherein the method is characterized by: The photocatalytic semiconductor can be Zn 0.5 Cd 0.5 S, CdS, ZnIn2S4or other semiconductors that can form a suitable heterostructure with WO3:Yb 3+ ,Er 3+ semiconductor.

10. The method of claim 1, wherein the method is characterized by: WO3:Yb 3+ ,Er 3+ with Zn 0.5 Cd 0.5 The proportion of S, CdS, ZnIn2S4semiconductors is 1-15 wt%.

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