CN103990493A - Visible-light catalyst for degrading rhodamine B in water and application of catalyst - Google Patents

Abstract

A visible light catalyst for degrading rhodamine B in water, the chemical formula is [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ][α-SiW ₁₂ O ₄₀ ]·2H ₂ O , is a metal-organic framework based on polyoxometalates and has a three-dimensional framework structure. There are four crystallographically independent Cu ^I ions in the compound, and through its ligand 1,2,4-triazole connected to each other to form a two-dimensional bicyclic cationic framework structure with the coexistence of three-membered rings and ten-membered rings, while [α-SiW ₁₂ O ₄₀ ] ^{4 –anions} are connected to the three copper atoms on the two-dimensional bicyclic ring through their terminal oxygen atoms. The ions are connected to form a three-dimensional framework structure. Advantages of the present invention: the photocatalyst has a simple preparation method, good water stability, and can be recycled after degradation; visible light is used in the degradation of rhodamine B in water by photocatalyst, and solar energy can be fully utilized, with simple process, low cost and high catalytic effect good.

Description

A kind of visible light catalyst for degrading Rhodamine B in water and its application

technical field

The invention belongs to the technical field of photocatalysis, in particular to a visible light catalyst for degrading Rhodamine B in water and its application.

Background technique

In recent years, photocatalysis has become an ideal environmental pollution control technology and clean energy production technology because of its unique properties such as direct use of solar energy as a light source to drive reactions. It has less secondary pollution, mild reaction conditions, easy operation, and energy efficiency. Advantages of low consumption. The key element of the photocatalytic reaction is the photocatalyst. Titanium dioxide as a common photocatalyst has been known as early as the 1950s. Since 1972, Japanese scientist Fujishima Akira published a report on the photolysis of water on a titanium dioxide electrode to produce hydrogen in Nature, which immediately attracted international attention. At the same time, it has also launched a worldwide focus on the photocatalytic oxidation of organic compounds by titanium dioxide. Although TiO ₂ has high stability, high activity, reusability and low cost, etc. advantages, but this kind of research has not been widely used in the end. The main reason is that the band gap of titanium dioxide is relatively large (3.2 eV), which means that only ultraviolet light with a wavelength less than or equal to 387 nm can excite TiO ₂ to generate conduction band electrons and Oxidize and decompose organic matter by valence band holes. However, ultraviolet light with a wavelength of less than 380 nm accounts for less than 4% of the total solar energy received by the earth's surface. If _TiO2 is directly used as a catalyst, more than 95% of the sunlight cannot be effectively utilized. In addition, since the intensity of ultraviolet light that can excite _TiO2 in sunlight is weak, the efficiency of photocatalytic degradation of organic pollutants directly using sunlight as a light source is very low; if artificial light sources are used, energy consumption problems will arise. Therefore, designing and synthesizing highly stable materials with strong photocatalytic activity in the visible light region and utilizing the visible part of sunlight has become the most significant and challenging subject of photocatalysis at present.

Polyoxometalate is a kind of metal oxygen cluster mainly composed of molybdenum and tungsten. It has the properties similar to semiconductor photocatalyst. It is a wide bandgap material (3.1-4.6eV), and its absorption peak is mainly in the ultraviolet region. But its band can extend to the visible region. Under the action of ultraviolet or visible light, the ligand-to-metal charge transfer transition can occur, resulting in an excited state with an oxidation capacity greater than 2.5 V (vs. standard hydrogen electrode), thereby degrading most organic pollutants. As a class of strong oxidizing multi-electron oxidation catalysts, the structure of their anions remains stable after gaining multiple electrons. Therefore, the photocatalytic degradation of polyoxometalates has the advantages of low toxicity, high salinity, mild conditions, stable performance, and high photolysis efficiency. Research in the field of environmental photochemistry has also aroused great interest in recent years. However, polyoxometalates also have their own defects, such as small specific surface area and difficulty in recycling. For this reason, various techniques have been used to modify the catalyst, such as the composite of polyoxometalates and semiconductor compounds (mainly TiO ₂ ). However, the photoresponse range is still limited (mainly in the ultraviolet region), which limits its application.

In recent years, the rise of metal-organic framework (MOFs) materials has also injected new vitality into photocatalytic technology. It uses the coordination between organic ligands and metal ions to self-assemble to form a supramolecular microporous network structure. A zeolite-like material with unusual pore shape, small specific surface area, and mild synthesis conditions; and because of its structural diversity, unusual photoelectric effect, and many available metal ions, it is rapidly being It has developed into a research hotspot in the interdisciplinary fields of energy, materials and life sciences. In the synthesis technology of MOFs, for organic ligands, the coordination mode and coordination ability of functional groups can be flexibly changed by different Lewis acids and metal ions; for metal nodes, metal ions can form nuclei with ions with large electronegativity. Different metal sub-building blocks with different numbers of connections. Through the advantages of these two aspects, the framework is modified and derived, thus forming a variety of structural types. It is precisely because of its diverse structure, tunability and small specific surface area that it is more conducive to the design and synthesis of materials with adjustable bandgap width, so that it has strong photocatalytic activity in the visible light region and improves the absorption of solar energy. Utilization rate will also have important practical significance for solving energy and environmental pollution problems.

At present, there is an urgent need for a new photocatalytic material with low energy band width and good water stability. If polyoxometalates can be effectively combined with metal-organic framework materials, a new type of photocatalytic material that can expand the photoresponse range and be recyclable can be designed. Catalytic systems to realize efficient catalytic reactions under visible light will have important theoretical significance, and also provide a new idea for the development of efficient, environmentally friendly, and energy-saving organic pollutant treatment technologies.

Contents of the invention

The purpose of the present invention is to address the above existing problems, to provide a visible light catalyst for degrading rhodamine B in water and its application. The preparation method of the photocatalyst is simple, the water stability is good, and it can be recycled after degradation; Visible light is used in the process of degrading Rhodamine B in water by the catalyst, which can make full use of solar light energy, has simple process, low cost and good catalytic effect.

Technical scheme of the present invention:

A visible light catalyst for degrading rhodamine B in water, the chemical formula is [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ][ α -SiW ₁₂ O ₄₀ ]·2H ₂ O , is a metal-organic framework compound based on polyoxometalates and has a three-dimensional framework structure. There are four crystallographically independent Cu ^I ions in the compound, and through its interaction with the ligand 1,2,4-three Triazolium (trz) ^– interconnected to form a two-dimensional bicyclic cationic framework structure with coexistence of three-membered rings and ten-membered rings [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ] ⁴⁺ , while [ α -SiW ₁₂ O ₄₀ ] ^4– anions are connected to Cu1 ^I , Cu2 ^I and Cu3 ^I ions on the two-dimensional double ring through their terminal oxygen atoms (O12, O4 and O6), forming a three-dimensional framework structure .

A method for preparing a visible light catalyst for degrading Rhodamine B in water is prepared by a solvothermal method, and the steps are as follows:

1) Add copper nitrate trihydrate, 1,2,4-triazole and polyoxometalate Na ₁₀ [SiW ₉ O ₃₄ ]·18H ₂ O into a mixed solution of deionized water and absolute ethanol to obtain a mixed solution, The dosage ratio of copper nitrate trihydrate, 1,2,4-triazole, Na ₁₀ [SiW ₉ O ₃₄ ]·18H ₂ O to deionized water and absolute ethanol is 0.05mmol:0.2mmol:0.5mmol:8mL: 2mL;

2) After sealing the above mixed solution in the reaction kettle, place it in an oven at a temperature of 170°C for 72 hours, and then slowly lower it to room temperature at a rate of 4°C/h to obtain orange blocky crystals, which are washed with deionized water After that, it was evaporated to dryness at room temperature, and the visible photocatalyst [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ][ α -SiW ₁₂ O ₄₀ ] · 2H ₂ O.

An application of the prepared visible light catalyst for degrading Rhodamine B in water, for degrading the organic dye Rhodamine B in water, the steps are as follows:

1) Put 100mL rhodamine B solution with a concentration of 15mg/L in a laminated glass beaker, then add 15mg of the prepared visible light catalyst, pour cooling water into the interlayer and stir for 1 hour in the dark to achieve adsorption-desorption equilibrium , to get a mixed system;

2) Move the above mixed system into a simulated solar reactor, and react at room temperature under the irradiation of a simulated solar reactor with a wavelength greater than 420nm. Regularly sample and centrifuge to separate the supernatant and use a UV spectrophotometer (Jasco V-570 , Japan) to test rhodamine B in solution.

The simulated sunlight reactor consists of a 85-1A magnetic stirrer, 300W PLS-SXE300C xenon lamp, UVcut420 cut-off filter, black cloth hood, circulating water bath pump and convection ventilation system, wherein the xenon lamp light source and mixing The distance between the liquid surface of the system is 10cm.

The advantages of the present invention are: 1) The photocatalyst has a simple preparation method, good water stability, and can be recycled after degradation; 2) Visible light is used in the process of using photocatalyst to degrade rhodamine B in water, which can make full use of sunlight energy , and the process is simple, the cost is low, and the catalytic effect is good.

Description of drawings

Figure 1 is the ball-and-stick model of the structural unit of the visible light catalyst.

Figure 2 is the three-dimensional structure diagram of the visible light catalyst.

Figure 3 shows the degradation of 15 mg/L rhodamine B by the visible light catalyst by visible light with a wavelength greater than 420nm.

Figure 4 shows the recyclability of the visible light catalyst to degrade 15mg/L rhodamine B by visible light irradiation with a wavelength greater than 420nm.

Detailed ways

Example 1:

A visible light catalyst for degrading rhodamine B in water, the chemical formula is [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ][ α -SiW ₁₂ O ₄₀ ]·2H ₂ O , is a metal-organic framework compound based on polyoxometalates and has a three-dimensional framework structure. There are four crystallographically independent Cu ^I ions in the compound, and through its interaction with the ligand 1,2,4-three Triazolium (trz) ^– interconnected to form a two-dimensional bicyclic cationic framework structure with coexistence of three-membered rings and ten-membered rings [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ] ⁴⁺ , while [ α -SiW ₁₂ O ₄₀ ] ^4– anions are connected to Cu1 ^I , Cu2 ^I and Cu3 ^I ions on the two-dimensional double ring through their terminal oxygen atoms (O12, O4 and O6), forming a three-dimensional framework structure .

The preparation method of the visible light catalyst for degrading rhodamine B in water is prepared by solvothermal method, and the steps are as follows:

1) Add 0.048g (0.05mmol) copper nitrate trihydrate, 0.035g (0.2mmol) 1,2,4-triazole and 0.123g (0.5mmol) polyoxometalate Na ₁₀ [SiW ₉ O ₃₄ ]· 18H ₂ O was added to a 23mL polytetrafluoroethylene autoclave, and then a mixed solution of 8mL deionized water and 2mL absolute ethanol was added to obtain a mixed solution;

2) After sealing the above mixed solution in the reaction kettle, place it in an oven at a temperature of 170°C for 72 hours, and then slowly lower it to room temperature at a rate of 4°C/h to obtain orange blocky crystals, which are washed with deionized water After that, it was evaporated to dryness at room temperature, and the visible photocatalyst [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ][ α -SiW ₁₂ O ₄₀ ] · 2H ₂ O.

Figure 1 is the ball-and-stick model of the structural unit of the visible light catalyst, which shows that there are four crystallographically independent Cu ^I ions in the compound, which form a three-membered ring and a ten-membered ring coexisting through interconnection with the ligand trz ^– Two-dimensional bicyclic cationic framework [Cu ^I ₁₂ (trz) ₈ (H ₂ O) ₂ ] ⁴⁺ . And the [ α -SiW ₁₂ O ₄₀ ] ^4– anion is connected to the Cu1 ^I , Cu2 ^I and Cu3 ^I ions on the two-dimensional bicyclic ring through its terminal oxygen atoms (O12, O4 and O6), respectively, forming a structure as shown in Figure 2 3D frame structure.

The prepared visible light catalyst for degrading Rhodamine B in water is used to degrade the organic dye Rhodamine B in water, and the steps are as follows:

1) Put 100mL rhodamine B solution with a concentration of 15mg/L in a laminated glass beaker, then add 15mg of the prepared visible light catalyst, pour cooling water into the interlayer and stir for 1 hour in the dark to achieve adsorption-desorption equilibrium , to get a mixed system;

2) Move the above mixed system into a simulated sunlight reactor, and react at room temperature under the irradiation of a simulated sunlight reactor with a wavelength greater than 420nm. The simulated sunlight reactor consists of a 85-1A magnetic stirrer, 300W PLS -SXE300C xenon lamp, UVcut420 cut-off filter, black cloth hood, circulating water bath pump and convection ventilation system. The distance between the xenon lamp light source and the liquid surface of the mixed system is 10cm. Visible light of 420nm, centrifugation and separation of samples at regular intervals to obtain the supernatant, and use a UV spectrophotometer (Jasco V-570, Japan) to test the Rhodamine B in the solution.

Figure 3 shows the degradation of 15 mg/L rhodamine B by the visible light catalyst by visible light with a wavelength greater than 420nm. The figure shows that after 6 hours of irradiation with visible light with a wavelength greater than 420nm, the degradation rate of the photocatalyst to the dye Rhodamine B in water reaches 88%.

Figure 4 shows the recyclability of the visible light catalyst to degrade 15mg/L rhodamine B by visible light irradiation with a wavelength greater than 420nm. The figure shows that after the photocatalyst degrades rhodamine B for four rounds, the degradation ability is still not significantly weakened.

Claims (4)

1. A visible light catalyst for degrading rhodamine B in water, characterized in that: the chemical formula is [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ][ α -SiW ₁₂ O ₄₀ ]·2H ₂ O is a metal-organic framework compound based on polyoxometalates and has a three-dimensional framework structure. There are four crystallographically independent Cu ^I ions in the compound, which can be combined with ligand 1 ,2,4-triazole (trz) ^– interconnected to form a two-dimensional bicyclic cationic framework structure with coexistence of three-membered and ten-membered rings [Cu ^I ₁₂ (1,2,4-triazole) ₈ ( H ₂ O) ₂ ] ⁴⁺ , while [ α -SiW ₁₂ O ₄₀ ] ^4– anion interacts with Cu1 ^I , Cu2 ^I and Cu3 ^I ions on the two-dimensional bicyclic ring through its terminal oxygen atoms (O12, O4 and O6), respectively Connected to form a three-dimensional frame structure. 2. a kind of preparation method that is used for the visible light catalyst of rhodamine B in degradation water as claimed in claim 1, is characterized in that adopting solvothermal method to prepare, and step is as follows: 1) Add copper nitrate trihydrate, 1,2,4-triazole and polyoxometalate Na ₁₀ [SiW ₉ O ₃₄ ]·18H ₂ O into a mixed solution of deionized water and absolute ethanol to obtain a mixed solution, The dosage ratio of copper nitrate trihydrate, 1,2,4-triazole, Na ₁₀ [SiW ₉ O ₃₄ ]·18H ₂ O to deionized water and absolute ethanol is 0.05mmol:0.2mmol:0.5mmol:8mL: 2mL; 2) After sealing the above mixed solution in the reaction kettle, place it in an oven at a temperature of 170°C for 72 hours, and then slowly lower it to room temperature at a rate of 4°C/h to obtain orange blocky crystals, which are washed with deionized water After that, it was evaporated to dryness at room temperature, and the visible photocatalyst [Cu ^I ₁₂ (1,2,4-triazole) ₈ (H ₂ O) ₂ ][ α -SiW ₁₂ O ₄₀ ] · 2H ₂ O. 3. an application of a visible light catalyst for degrading rhodamine B in water as claimed in claim 1, characterized in that it is used to degrade organic dye rhodamine B in water, and the steps are as follows: 1) Put 100mL rhodamine B solution with a concentration of 15mg/L in a laminated glass beaker, then add 15mg of the prepared visible light catalyst, pour cooling water into the interlayer and stir for 1 hour in the dark to achieve adsorption-desorption equilibrium , to get a mixed system; 2) Move the above mixed system into a simulated solar reactor, and react at room temperature under the irradiation of a simulated solar reactor with a wavelength greater than 420nm. Regularly sample and centrifuge to separate the supernatant and use a UV spectrophotometer (Jasco V-570 , Japan) to test rhodamine B in solution. 4. The application of the visible light catalyst for degrading rhodamine B in water according to claim 3 is characterized in that: the simulated sunlight reactor consists of a 85-1A type magnetic stirrer, 300W PLS-SXE300C xenon lamp, UVcut420 It consists of a cut-off filter, a black cloth hood, a circulating water bath pump and a convection ventilation system, and the distance between the xenon lamp light source and the liquid surface of the mixed system is 10cm.