Preparation method and application of oxygen-vacancy-rich germanate long-afterglow photocatalytic material

Abstract

The invention provides a preparation method and application of an oxygen-vacancy-rich germanate long-afterglow photocatalytic material, and belongs to the technical field of catalysis. And after being irradiated by 254 nm ultraviolet light for 10 minutes, Bi < 3 + > obtains long afterglow which exceeds 1 hour in a germanate matrix. A crystal field engineering strategy is used for replacing Y ions with rare earth ions, and the germanate after replacement shows more excellent afterglow luminescence. And hydrogen annealing can increase the concentration of oxygen vacancies, so that the afterglow luminescence intensity of the germanate long afterglow fluorescent powder is further enhanced, and the afterglow luminescence time is prolonged. The afterglow luminescence of the germanate long-afterglow fluorescent powder improved by crystal field engineering and hydrogen annealing is used as a light source to degrade organic pollutants in a dark environment, the degradation efficiency of rhodamine B reaches 30%, and a result shows that the silicon germanate long-afterglow fluorescent powder has relatively strong degradation capability.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic technology, and particularly relates to a preparation method and application of an oxygen-vacancy-rich germanate long-afterglow photocatalytic material. Background Art

[0002] The rapid industrialization process often comes with certain water pollution problems. As a new generation of green treatment technology, photocatalytic technology provides a new solution for the treatment of water pollution due to its high efficiency, environmental protection, sustainability and other characteristics. The use of photocatalytic technology can achieve the harmless degradation of pollutants in water, but this process depends on continuous sunlight or irradiation by a specific light source, which means that the photocatalytic efficiency will be restricted by weather, day and night alternation and light source equipment conditions. Based on long-afterglow materials, photocatalysts are expected to solve this problem. Long-afterglow materials can generate light emission and absorb energy under light excitation, and continue to generate light emission after the light is turned off, so as to maintain the photocatalytic degradation reaction for a certain period of time and reduce the dependence on weather and light source equipment. However, there is a competitive utilization of photo-generated carriers between the long-afterglow-driven photocatalytic reaction and the long-afterglow luminescence process. Both the photocatalytic degradation reaction and the radiative recombination luminescence process will consume photo-generated electrons, which not only reduces the duration of the afterglow, but also causes the accumulation of holes, further leading to the too-fast recombination of photon electrons and holes, and having a negative impact on the photocatalytic reaction efficiency. Improving the carrier utilization rate in the afterglow-driven photocatalytic process is crucial for enhancing the performance of long-afterglow photocatalysts and is conducive to promoting the practical application of long-afterglow photocatalysts. Summary of the Invention

[0003] Aiming at the above deficiencies, the purpose of the present invention is to provide a germanate-based long-afterglow material V O -LiY 0.797 Sc 0.2 GeO 4 :0.003Bi 3+ (Vo-LiYScGeO 4 :Bi 3+ ) that can degrade organic pollutants in water in a dark environment.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A germanate long-afterglow photocatalytic material with a chemical general formula of LiY (1-x-y) Ln x GeO 4 :yBi 3+ , where Ln is a rare earth ion, x is the molar percentage of the rare earth ion in Y, 0 ≤ x ≤ 0.5, and y is the molar percentage of the doped activator Bi 3+ in Y, 0 ≤ y ≤ 0.005.

[0006] Preferably, for the above-mentioned germanate long afterglow photocatalytic material, the oxide of the activator is bismuth oxide.

[0007] Preferably, for the above-mentioned germanate long afterglow photocatalytic material, the oxide of the rare earth ion is one of scandium oxide, lanthanum oxide, lutetium oxide, and gadolinium oxide.

[0008] The preparation method of the above-mentioned germanate long afterglow photocatalytic material includes the following steps:

[0009] 1) Put the powders of lithium-containing compound, yttrium oxide, germanium oxide, bismuth oxide, and rare earth ion oxide into an agate mortar and grind them to mix evenly to obtain a mixture;

[0010] 2) Place the mixture obtained in step 1) in a corundum crucible and then put it into a muffle furnace for high-temperature sintering once, cool to room temperature, and then perform high-temperature sintering again and cool to room temperature;

[0011] 3) Grind the solid sample obtained in step 2) in an agate mortar to obtain the target product.

[0012] Preferably, in the above preparation method, in step 1), the lithium-containing compound is lithium carbonate or lithium oxide.

[0013] Preferably, in the above preparation method, in step 1), the grinding time is 30 - 60 min.

[0014] Preferably, in the above preparation method, in step 2), the atmosphere for high-temperature sintering is air atmosphere, the temperature for the first high-temperature sintering is 800 °C, the heating rate is 3 - 5 °C / min, the sintering time is 2 h, the temperature for the second high-temperature sintering is 1250 °C, the heating rate is 3 - 5 °C / min, and the sintering time is 5 h.

[0015] Preferably, in the above preparation method, in step 3), the grinding time is 5 - 10 min.

[0016] A germanate long afterglow photocatalytic material with rich oxygen vacancies, and its preparation method includes the following steps:

[0017] 1) Put the germanate long afterglow photocatalytic material described in any one of the above into a tubular furnace, anneal it in hydrogen, and then cool to room temperature;

[0018] 2) Grind the solid sample obtained in step 1) in an agate mortar for 5 - 10 min to obtain the target product, which is a germanate long afterglow photocatalytic material with rich oxygen vacancies.

[0019] Preferably, for the preparation method of the above germanate long afterglow photocatalytic material with rich oxygen vacancies, the tubular furnace is heated to 500 - 700 °C at a rate of 3 - 5 °C / min, and the annealing time is 2 - 5 h.

[0020] Use of the germanate long afterglow photocatalytic material according to any one of the above in degrading pollutants in a dark environment.

[0021] Use of the oxygen-rich vacancy germanate long afterglow photocatalytic material according to any one of the above in degrading pollutants in a dark environment.

[0022] Preferably, in the above application, the pollutant is Rhodamine B.

[0023] The beneficial effects of the present invention are as follows: The present invention uses germanate as the matrix material. This material has stable physical and chemical properties, optical transparency, simple preparation process, high temperature resistance, and environmental friendliness. When doped with Bi ions, it can produce ultraviolet afterglow. After hydrogen annealing, the increased oxygen vacancy concentration and the increased trap concentration after equivalent substitution by crystal field engineering can improve the afterglow luminescence intensity and extend the afterglow luminescence time of this material. And this material can be used as a light source of a long afterglow photocatalyst to degrade pollutants in water in a dark environment. Description of the Drawings

[0024] Figure 1 XRD pattern of the oxygen-rich vacancy germanate long afterglow photocatalytic material prepared in Example 1.

[0025] Figure 2 SEM image (a) and elemental mapping image (b) of the oxygen-rich vacancy germanate long afterglow photocatalytic material prepared in Example 1.

[0026] Figure 3 Afterglow decay curve of the oxygen-rich vacancy germanate long afterglow photocatalytic material when substituted by different concentrations of Sc in Example 1.

[0027] Figure 4 Afterglow decay curve of the oxygen-rich vacancy germanate long afterglow photocatalytic material in Example 1.

[0028] Figure 5 Degradation curve of RhB by the oxygen-rich vacancy germanate long afterglow photocatalytic material in Example 1. Detailed Description of the Invention

[0029] Example 1

[0030] The chemical formula composition of the germanate long afterglow photocatalytic material in this example is LiY 0.797 Sc 0.2 GeO 4 :0.003Bi 3+ (LiYScGeO 4 :Bi 3+), the preparation method is as follows: Weigh 0.3658 g of lithium carbonate, 1.799 g of yttrium oxide, 0.1046 g of germanium oxide, 0.0275 g of scandium oxide, and 0.0013 g of bismuth oxide respectively; put the weighed powders into an agate mortar and grind them clockwise for 30 min to mix them evenly, then transfer them to a corundum crucible, place the crucible in a high-temperature muffle furnace, with a heating rate of 3 °C / min, heat up to 800 °C and calcine for 2 h, then cool down to room temperature with the furnace; put it back into the muffle furnace again, with a heating rate of 3 °C / min, heat up to 1250 °C and calcine for 5 h, and grind the obtained solid sample in an agate mortar for 5 min to obtain LiY 0.797 Sc 0.2 GeO 4 :0.003Bi 3+ (LiYScGeO 4 :Bi 3+ )。

[0031] In the above preparation process, without adding the raw material scandium oxide, changing 1.799 g of yttrium oxide to 2.2251 g of yttrium oxide, and keeping the other raw materials unchanged, LiY 0.997 GeO 4 :0.003Bi 3+ (LiYGeO 4 :Bi 3+ ) sample.

[0032] Put the obtained germanate long afterglow photocatalytic material LiYScGeO 4 :Bi 3+ into a tube furnace and heat it to 550 °C at a rate of 3 - 5 °C / min, anneal it in hydrogen for 2 h, and after cooling to room temperature, the obtained sample is an oxygen vacancy-rich germanate long afterglow photocatalytic material (Vo-LiYScGeO 4 :Bi 3+ )。

[0033] Then perform a phase analysis on the sample, and the obtained XRD pattern is as Figure 1 shown. Compared with the standard PDF card (JPCDS#98 - 000 - 0226), the main peak positions of LiYGeO 4 :Bi 3+ and LiYScGeO 4 :Bi 3+ and Vo-LiYScGeO 4 :Bi 3+ match well, indicating that the doping and substitution of rare earth ions hardly change the lattice structure, and hydrogen annealing cannot cause serious lattice distortion of the matrix. However, for LiYScGeO 4 :Bi 3+ and Vo-LiYScGeO 4 :Bi3+ There are impurity peaks at 2θ = 32° and 2θ = 58° for the phosphor, and the impurity peaks at these two positions are derived from the YSc impurity phase. Figure 2 For Vo-LiYScGeO 4 :Bi 3+ SEM images and elemental mapping spectra. When Sc is substituted for Y at different concentrations and the substitution concentration of Sc is 0.2, Vo-LiYScGeO 4 :Bi 3+ has the best afterglow luminescence intensity and time ( Figure 3 ). After irradiating LiYScGeO 4 :Bi 3+ and Vo-LiYScGeO 4 :Bi 3+ under a 254 nm ultraviolet lamp for 10 min and then quickly moving them into an ultraviolet fluorescence photometer, the afterglow luminescence spectra are measured at regular intervals, and the obtained afterglow luminescence intensities are fitted. As Figure 4 shown, the afterglow luminescence intensity and time of Vo-LiYScGeO 4 :Bi 3+ are better than those of LiYScGeO 4 :Bi 3+ .

[0034] After irradiating LiYScGeO 4 :Bi 3+ and Vo-LiYScGeO 4 :Bi 3+ under a 254 nm ultraviolet lamp for 10 min, they are used to degrade rhodamine B (RhB) in a dark environment. Put the RhB solution (50 mL, 10 mg / L) and the photocatalytic material (10 mg) in a 100 mL beaker. Take 2 mL of the RhB solution at regular intervals. Measure the absorbance of RhB with an ultraviolet-visible spectrophotometer to evaluate the photocatalytic activity of LiYScGeO 4 :Bi 3+ and Vo-LiYScGeO 4 :Bi 3+ . The degradation curves of RhB by LiYScGeO 4 :Bi 3+ and Vo-LiYScGeO 4 :Bi 3+ are as shown in Figure 5 . The maximum degradation efficiencies of RhB by LiYScGeO 4 :Bi 3+ and Vo-LiYScGeO 4 :Bi 3+ are 18% and 30% respectively in 1 hour.

[0035] Example 2

[0036] Replace 0.0275 g of scandium oxide in Example 1 with 0.0651 g of lanthanum oxide, and keep the remaining steps unchanged. The obtained long afterglow catalyst is LiLaGeO 4 :Bi 3+ 、LiLaScGeO 4 :Bi 3+ and Vo-LiLaScGeO 4 :Bi 3+ 。

[0037] Example 3

[0038] Replace 0.0275 g of scandium oxide in Example 1 with 0.0795 g of lutetium oxide, and keep the remaining steps unchanged. The obtained long afterglow catalyst is LiLuGeO 4 :Bi 3+ 、LiLuScGeO 4 :Bi 3+ and Vo-LiLuScGeO 4 :Bi 3+ 。

[0039] Example 4

[0040] Replace 0.0275 g of scandium oxide in Example 1 with 0.0724 g of gadolinium oxide, and keep the remaining steps unchanged. The obtained long afterglow catalyst is LiGdGeO 4 :Bi 3+ 、LiGdScGeO 4 :Bi 3+ and Vo-LiGdScGeO 4 :Bi 3+ 。

Claims

1. A germanate long afterglow photocatalytic material, characterized in that: Its chemical formula is LiY (1-x-y) Ln x GeO4:yBi 3+ , where Ln is a rare earth ion, x is the molar percentage of rare earth ions in Y, 0≤x≤0.5, and y is the doping activator Bi 3+ The molar percentage of Y is 0≤y≤0.

005.

2. The germanate long afterglow photocatalytic material according to claim 1, characterized in that: The oxide of the activator is bismuth oxide.

3. The germanate long afterglow photocatalytic material according to claim 2, characterized in that: The oxide of the rare earth ion is one of scandium oxide, lanthanum oxide, lutetium oxide and gadolinium oxide.

4. The method for preparing a germanate long afterglow photocatalytic material according to claim 3, characterized in that: The steps include: 1) putting oxide powders containing a lithium compound, yttrium oxide, germanium oxide, bismuth oxide and rare earth ions into an agate mortar, grinding and mixing them uniformly to obtain a mixture; 2) placing the mixture obtained in step 1) in a corundum crucible and then placing it in a muffle furnace, sintering at high temperature once, cooling to room temperature, sintering at high temperature again, and cooling to room temperature; 3) Grinding the solid sample obtained in step 2) in an agate mortar to obtain the target product.

5. The preparation method according to claim 4, characterized in that: In step 1), the lithium-containing compound is lithium carbonate or lithium oxide.

6. The preparation method according to claim 4, characterized in that: In step 1), the grinding time is 30 to 60 minutes.

7. The preparation method according to claim 4, characterized in that: In step 2), the high-temperature sintering atmosphere is an air atmosphere, the temperature of the first high-temperature sintering is 800°C, the heating rate is 3-5°C / min, and the sintering time is 2h, and the temperature of the second high-temperature sintering is 1250°C, the heating rate is 3-5°C / min, and the sintering time is 5h.

8. The preparation method according to claim 4, characterized in that: In step 3), the grinding time is 5 to 10 minutes.

9. An oxygen-rich vacancy germanate long afterglow photocatalytic material, characterized in that: The preparation method thereof comprises the following steps: 1) placing the germanate long afterglow photocatalytic material according to any one of claims 1 to 3 into a tube furnace, heating the tube furnace to 500-700° C. at 3-5° C. / min, annealing in hydrogen for 2-5 hours, and then cooling to room temperature; 2) Grinding the solid sample obtained in step 1) in an agate mortar for 5 to 10 minutes to obtain the target product, which is an oxygen vacancy-rich germanate long afterglow photocatalytic material.

10. Use of the germanate long afterglow photocatalytic material according to any one of claims 1 to 3 or the oxygen vacancy rich germanate long afterglow photocatalytic material according to claim 9 in degrading pollutants in a dark environment.

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