Metal oxide material with combination of oxygen deficiency and Bronsted acid site as well as preparation method and application of metal oxide material

Abstract

The invention relates to a metal oxide material with combination of oxygen deficiency and a Bronsted acid site as well as a preparation method and application of the metal oxide material. A solvothermal method is used for reducing part of metal sites in a metal oxide to construct oxygen defects, and meanwhile, a large number of Bronsted acid sites are formed on the surface of the metal oxide. The preparation method of the material comprises the following steps: dissolving metal salt in a solvent to obtain a metal source solution, and adjusting the pH value condition of the solution; adding a reducing agent into the metal source solution and stirring; and carrying out solvothermal reaction to obtain the metal oxide material with the oxygen deficiency combined with the Bronsted acid site. Wherein the metal oxide material contains, but is not limited to, WO3, TiO2, SnO2, CuO, ZnO and Bi2O3. The metal oxide material provided by the invention can generate hydrogen peroxide only by taking oxygen and water as raw materials under the irradiation of simulated sunlight, so that green and efficient hydrogen peroxide generation at normal temperature and normal pressure is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of green hydrogen peroxide synthesis, and in particular to a metal oxide material combining oxygen defects with Brønsted acid sites, and a preparation method and application thereof. Background Art

[0002] Hydrogen peroxide is an important chemical reagent and industrial product with a wide range of applications in many fields. Hydrogen peroxide is a colorless liquid with strong oxidizing and weak acidity. It is often used as a bleaching agent, chemical raw material, disinfectant and water purifier. In wastewater treatment and pollution control, hydrogen peroxide, as a strong oxidant, can degrade organic pollutants in water bodies, and its only by-product is water. It is a green and environmentally friendly oxidant. The global demand for hydrogen peroxide is growing steadily, mainly concentrated in the application of environmentally friendly technologies, the increase in demand for cleaning and disinfection, and its wide use in industries such as electronics, papermaking and water treatment.

[0003] At present, more than 95% of hydrogen peroxide in the world is produced by the anthraquinone method, which uses anthraquinone molecules as a circulating carrier to generate hydrogen peroxide through catalytic hydrogenation and oxidation reactions. In this process, anthraquinone molecules can be recycled many times and the chemical reaction selectivity is high. The generated hydrogen peroxide has a high purity and is suitable for a variety of industrial applications. However, the anthraquinone method consumes a lot of energy, has high equipment costs and is complex to operate. The hydrogenation and oxidation processes in this method require high temperature and pressure and involve the use of hydrogen. At the same time, the process of this method requires strict control of reaction conditions and has high technical requirements. Against the backdrop of increasing global concern about climate warming and energy shortages, there is an urgent need to develop a green, efficient and sustainable hydrogen peroxide production technology.

[0004] Solar energy is a clean energy source and the main input source of earth energy. Direct development and utilization of renewable solar energy can not only effectively meet energy needs, but also avoid sustainable development challenges and environmental problems caused by excessive use of fossil energy. Photocatalytic hydrogen peroxide generation technology is a green and sustainable hydrogen peroxide generation technology that uses semiconductor photocatalysts as media, oxygen and water as raw materials, and solar energy as an energy source. This technology not only overcomes the limitations of the anthraquinone method such as high energy consumption, high risk and complex operation, but also realizes the in-situ production of hydrogen peroxide, which is convenient for its in-situ utilization. However, the current photocatalytic hydrogen peroxide generation efficiency is low and cannot meet the needs of conventional applications, such as the degradation of organic pollutants. The main reason for limiting the high generation efficiency of this method is that its semiconductor photocatalyst lacks suitable oxygen activation active sites and the suppressed protonation process of hydrogen peroxide intermediates, resulting in a low photocatalytic hydrogen peroxide yield.

[0005] Based on the above background, how to design and develop an efficient semiconductor catalyst with active sites that can efficiently activate oxygen and promote the protonation of hydrogen peroxide intermediates is the key to achieving efficient photocatalytic hydrogen peroxide generation. The design and synthesis method of this catalyst material will have significant energy and environmental significance, and also have great commercial prospects. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a metal oxide material with oxygen defects combined with Brønsted acid sites and a preparation method and application thereof. The present invention uses a reducing agent to induce the detachment of metal oxide lattice oxygen and form a large number of oxygen defects on the surface of the metal oxide material, and at the same time, the solvent thermal reaction conditions modify a large number of Brønsted acid sites on the surface of the metal oxide with oxygen defects.

[0007] The first object of the present invention is to provide a metal oxide material with oxygen defects combined with Brønsted acid sites, including a metal oxide with nanometer size and containing a crystalline structure, wherein a large number of oxygen defects exist on the surface of the metal oxide, a large number of Brønsted acid sites exist on the surface of the crystalline structure of the metal oxide, and oxygen defects and Brønsted acid sites belong to adjacent sites.

[0008] In some embodiments of the present invention, the Brønsted acid sites include crystal water and / or hydroxyl functional groups.

[0009] In some embodiments of the present invention, the metal oxide in the metal oxide material is selected from WO3, TiO2, SnO2, CuO, ZnO and / or Bi2O3.

[0010] The second object of the present invention is to provide a method for preparing the metal oxide material with oxygen defects combined with Brønsted acid sites, comprising the following steps: Providing a metal salt solution and adjusting the pH value of the metal salt solution to 2.0 to 10.0; A reducing agent is added to a metal salt solution, and a solvothermal reaction is performed to obtain a metal oxide material having oxygen defects combined with Brønsted acid sites.

[0011] In some embodiments of the present invention, the concentration of the metal salt solution is 2.0-100.0 mmol / L; To adjust the pH value of the metal salt solution, use an acid solution or an alkaline solution; The acid solution concentration is 0.1 ~ 1.0 mol / L; The concentration of the alkaline solution is 0.1 ~ 1.0 mol / L.

[0012] In some embodiments of the present invention, the metal salt in the metal salt solution is selected from one of Na2WO4, Ti(SO4)2, SnCl4·H2O, Cu(NO3)·3H2O, Zn(CH3COO)2·2H2O, and Bi(NO3)3·5H2O; The solvent of the metal salt solution is selected from one or more of water, ethanol or N,N-dimethylformamide.

[0013] In some embodiments of the present invention, the reducing agent is selected from glucose and / or fructose; the dosage of the reducing agent is 1.0 ~ 20.0 mmol / L.

[0014] In some embodiments of the present invention, the temperature of the solvothermal reaction is 120-200° C., and the reaction time is 16-24 h.

[0015] The third object of the present invention is to provide the use of the metal oxide material combining oxygen defects with Brønsted acid sites in photocatalytic molecular oxygen activation conversion.

[0016] In some embodiments of the present invention, the product of the activation and conversion of molecular oxygen is hydrogen peroxide.

[0017] The above technical solution of the present invention has the following advantages compared with the prior art: (1) The photocatalytic reaction of generating hydrogen peroxide has the advantages of being green, sustainable and low-cost. In the present invention, only sunlight is used as energy input, and oxygen and water are used as raw materials to produce hydrogen peroxide under the catalysis of metal oxide materials with oxygen defects combined with Brønsted acid sites. This process is green and environmentally friendly, and the raw materials are widely available, realizing the preparation of hydrogen peroxide at room temperature and pressure. At the same time, compared with the traditional anthraquinone method, this system does not require large equipment and process investment and strict operating procedures.

[0018] (2) The metal oxide material with oxygen defects combined with Brønsted acid sites described in the present invention has a wider spectrum of light absorption ability and photogenerated carrier separation ability due to its large number of oxygen defects, thereby improving the photocatalytic efficiency. At the same time, the oxygen defects act as molecular oxygen active sites to adsorb and activate molecular oxygen, inducing the efficient activation of molecular oxygen and converting it into superoxide radicals, an intermediate of hydrogen peroxide. At the same time, the metal oxide material with oxygen defects combined with Brønsted acid sites described in the present invention has a large number of Brønsted acid sites. Based on the hydrogen bonding effect of the Brønsted acid sites, it assists in promoting the activation of water molecules to produce a large number of protons, thereby promoting the protonation process of superoxide radicals to produce hydrogen peroxide. The presence of Brønsted acid sites improves the selectivity of hydrogen peroxide generation and also promotes the desorption of generated hydrogen peroxide, inhibits the reduction of hydrogen peroxide, and ultimately increases the yield of hydrogen peroxide.

[0019] (3) The metal oxide materials with oxygen defects combined with Brønsted acid sites described in the present invention include but are not limited to WO3, TiO2, SnO2, CuO, ZnO and / or Bi2O3, and thus have a certain degree of universality. The cheap and readily available metal oxides can be regulated to become catalysts for the photocatalytic generation of hydrogen peroxide. At the same time, the system is not limited to the site and can be generated and utilized in situ at the desired hydrogen peroxide production site. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein: Figure 1 HAADF-STEM images of the metal oxide material with oxygen defects combined with Brønsted acid sites prepared in Example 1 and the metal oxide material without oxygen defects but containing Brønsted acid sites in Comparative Example 1; wherein a is the metal oxide material with oxygen defects combined with Brønsted acid sites prepared in Example 1, and b is the metal oxide material without oxygen defects but containing Brønsted acid sites in Comparative Example 1; Figure 2 XRD patterns of the metal oxide material with oxygen defects and Brønsted acid sites prepared in Example 1 and the metal oxide material without oxygen defects but with Brønsted acid sites in Comparative Example 1; Figure 3 XPS graphs of the metal oxide material with oxygen defects and Brønsted acid sites prepared in Example 1 and the metal oxide material without oxygen defects but with Brønsted acid sites in Comparative Example 1; Figure 4 The performance of photocatalytic molecular oxygen activation and conversion to generate hydrogen peroxide by different catalyst materials in the present invention; Figure 5 The performance of the catalyst materials in Example 1, Comparative Example 1 and Comparative Example 4 in photocatalytic activation and conversion of molecular oxygen to generate superoxide radicals as the intermediate of hydrogen peroxide; Figure 6 The present invention obtains the charge distribution of the metal oxide material with oxygen defects combined with Brønsted acid sites during the molecular oxygen activation and conversion process through first principle calculation (DFT); wherein, the molecular oxygen structure obtains electrons from the material catalyst, indicating that the material catalyst can efficiently activate molecular oxygen; at the same time, the OH bond length in the water molecules adsorbed on the surface of the material catalyst is significantly longer than the OH bond of ordinary water molecules, indicating that the material catalyst can effectively activate water molecules to promote the formation of protons, thereby facilitating the protonation process of the hydrogen peroxide intermediate superoxide free radical, and finally generating hydrogen peroxide. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0022] Example 1

[0023] This embodiment provides a preparation method and application of a metal oxide material having oxygen defects combined with Brønsted acid sites.

[0024] (I) A method for preparing a metal oxide material with oxygen defects combined with Brønsted acid sites, as follows: (1) Dissolve 2.0 mmol Na2WO4 in 60 mL water to produce a transparent solution, and adjust the pH of the solution to 4.0 using 1 mol / L hydrochloric acid solution; (2) adding 10.0 mmol of glucose to the solution in step (1) to obtain a transparent solution; (3) The transparent solution obtained in step (2) was transferred to a high-pressure reactor lined with polytetrafluoroethylene. The reaction conditions were: reaction temperature of 120°C and reaction time of 24 h. The WO3·H2O metal oxide material with oxygen defects combined with Brønsted acid sites was obtained. The structure of the material was characterized. Figure 1 , Figure 2 and Figure 3 .

[0025] The HAADF-STEM image of the metal oxide material with oxygen defects and Brønsted acid sites obtained in this example is as follows: Figure 1 The XRD characterization results of the obtained materials are shown in Figure 2 The XPS characterization results of the obtained materials are shown in Figure 3 As shown, it indicates that oxygen defects and Brønsted acid sites are successfully modified on the surface of metal oxides and have no significant effect on the crystal structure of metal oxides.

[0026] 2. Photocatalytic molecular oxygen activation and conversion reaction experiment The photocatalytic molecular oxygen activation and conversion performance of the WO3·H2O metal oxide material catalyst with oxygen defects combined with Brønsted acid sites obtained in this example was evaluated on a CEL-HXF300 photocatalytic device (Beijing Zhongjiao Jinyuan Scientific Instrument Co., Ltd., China), which was equipped with a xenon lamp with a wavelength of 320 nm to 2500 nm, and conducted a photocatalytic molecular oxygen activation and conversion experiment under simulated sunlight conditions. The evaluation results were taken as the average of 3 tests.

[0027] 0.5 g / L of the WO3·H2O metal oxide material with oxygen defects and Brønsted acid sites obtained in this example was added to 30.0 mL of deionized water, and stirred for reaction under the illumination of the photocatalytic device for 1.0 h. Subsequently, 2.0 mL of the reaction suspension was taken out from the reaction container and filtered with a 0.22 μm water filter membrane. The resulting solution was measured for hydrogen peroxide concentration by DPD-POD colorimetric method. The experimental results are shown in Figure 4 As shown, it indicates that oxygen defects cooperate with Brønsted acid sites to activate molecular oxygen and convert it into hydrogen peroxide.

[0028] Example 2

[0029] The preparation method is the same as that of Example 1, except that in step (1): 6 mmol Ti(SO4)2 is dissolved in 60 mL water to produce a transparent solution, and 1 mol / L sodium hydroxide solution is used to adjust the pH of the solution to 3.0; step (3) reaction conditions: reaction temperature is 175°C, and reaction time is 18 h.

[0030] 2. Photocatalytic molecular oxygen activation and conversion reaction experiment The method for evaluating the photocatalytic molecular oxygen activation and conversion performance of the TiO2 metal oxide material catalyst with oxygen defects combined with Brønsted acid sites obtained in this example is the same as that in Example 1. The efficiency of the molecular oxygen activation and conversion of the metal oxide material with oxygen defects combined with Brønsted acid sites to generate hydrogen peroxide is shown in FIG. Figure 4 shown.

[0031] Example 3

[0032] The preparation method is the same as that of Example 1, except that in step (1): 2 mmol SnCl4·H2O is dissolved in 65 mL water to produce a transparent solution, and 0.1 mol / L sodium hydroxide solution is used to adjust the pH of the solution to 8.5; step (3) reaction conditions: reaction temperature is 200°C, and reaction time is 20 h.

[0033] 2. Photocatalytic molecular oxygen activation and conversion reaction experiment The method for evaluating the photocatalytic molecular oxygen activation and conversion performance of the SnO2 metal oxide material catalyst with oxygen defects combined with Brønsted acid sites obtained in this example is the same as that in Example 1. The efficiency of the catalyst for the activation and conversion of molecular oxygen to hydrogen peroxide is shown in FIG. Figure 4 shown.

[0034] Comparative Example 1 This comparative example uses a metal oxide material that does not contain oxygen defects but contains Brønsted acid sites as a control.

[0035] (I) A method for preparing a metal oxide material that does not contain oxygen defects but contains Brønsted acid sites, the specific steps are as follows: (1) Dissolve 2.0 mmol Na2WO4 in 60 mL water to produce a transparent solution, and adjust the pH of the solution to 4.0 using 1 mol / L hydrochloric acid solution; (2) The solution obtained in step (1) was transferred to a high-pressure reactor lined with polytetrafluoroethylene. The reaction conditions were: reaction temperature of 120°C and reaction time of 24 h. A WO3·H2O metal oxide material containing no oxygen defects but Brønsted acid sites was obtained. The structure of the material was characterized. The results are shown in Figure 1 , Figure 2 and Figure 3 .

[0036] The HAADF-STEM image of the metal oxide material without oxygen defects and Brønsted acid sites obtained in this comparative example is as follows Figure 1 The XRD characterization results of the obtained materials are shown in Figure 2 The XPS characterization results of the obtained materials are shown in Figure 3 As shown, it is shown that oxygen vacancies and Brønsted acid sites are successfully modified on the surface of the metal oxide and have no significant effect on the crystal structure of the metal oxide. In addition, this comparative example produces a WO3·H2O metal oxide material that does not contain oxygen defects but contains Brønsted acid sites.

[0037] 2. Photocatalytic molecular oxygen activation and conversion reaction experiment The method for evaluating the photocatalytic molecular oxygen activation conversion performance of the metal oxide material having no oxygen defects but containing Brønsted acid sites obtained in this comparative example is the same as that in Example 1. The efficiency of the catalyst for the activation and conversion of molecular oxygen to hydrogen peroxide is as follows: Figure 4 shown.

[0038] Comparative Example 2 This comparative example uses a metal oxide material that does not contain oxygen defects but contains Brønsted acid sites as a control.

[0039] 1. Preparation method of metal oxide materials without oxygen defects but containing Brønsted acid sites This comparative example uses a metal oxide material that does not contain oxygen defects but contains Brønsted acid sites as a control.

[0040] (1) 6 mmol Ti(SO4)2 was dissolved in 60 mL water to produce a transparent solution; and the pH of the solution was adjusted to 3.0 using 1 mol / L sodium hydroxide solution; (2) The transparent solution obtained in step (1) is transferred to a high-pressure reactor lined with polytetrafluoroethylene, and the reaction conditions are: reaction temperature is 175°C, and reaction time is 18 h. A TiO2 metal oxide material containing no oxygen defects but Brønsted acid sites is obtained.

[0041] 2. Photocatalytic molecular oxygen activation and conversion reaction experiment The method for evaluating the photocatalytic molecular oxygen activation and conversion performance of the metal oxide material obtained in this comparative example is the same as that in Example 1. The efficiency of the catalyst for the activation and conversion of molecular oxygen to hydrogen peroxide is as follows: Figure 4 shown.

[0042] Comparative Example 3 This comparative example uses a metal oxide material that does not contain oxygen defects but contains Brønsted acid sites as a control.

[0043] (I) A method for preparing a metal oxide material that does not contain oxygen defect bonding but contains Brønsted acid sites is as follows: (1) Dissolve 2 mmol SnCl4·H2O in 65 mL water to produce a transparent solution, and adjust the pH of the solution to 8.5 using 0.1 mol / L sodium hydroxide solution; (2) The transparent solution obtained in step (1) is transferred to a high-pressure reactor lined with polytetrafluoroethylene, and the reaction conditions are: reaction temperature is 200°C, and reaction time is 20 h. A SnO2 metal oxide material containing no oxygen defect but containing Brønsted acid sites is obtained.

[0044] 2. Photocatalytic molecular oxygen activation and conversion reaction experiment The method for evaluating the photocatalytic molecular oxygen activation and conversion performance of the material in this embodiment is the same as that in Example 1. The efficiency of the catalyst in activating molecular oxygen to generate hydrogen peroxide is as follows: Figure 4 shown.

[0045] Comparative Example 4 This comparative example uses a WO3 metal oxide material without Brønsted acid sites but containing oxygen defects as a control.

[0046] 1. Preparation method of metal oxide materials without Brønsted acid sites but containing oxygen defects (1) Dissolve 2.0 mmol Na2WO4 in 60 mL water to produce a transparent solution, and adjust the pH of the solution to 4.0 using 1 mol / L hydrochloric acid solution; (2) adding 10.0 mmol of glucose to the solution in step (1) to obtain a transparent solution; (3) The transparent solution obtained in step (2) was transferred to a high-pressure reactor lined with polytetrafluoroethylene. The reaction conditions were: reaction temperature of 120°C and reaction time of 12 h.

[0047] (4) The yellow solid powder obtained in step (3) was transferred to a porcelain boat, heated to 400°C at a rate of 10°C / min in a tube furnace, and reacted for 4.0 hours under Ar atmosphere to obtain a WO3 metal oxide material containing no Brønsted acid sites but containing oxygen defects. In this comparative example, the crystal water in WO3·H2O was removed by heating and calcining, and the crystal water was lost as a Brønsted acid site.

[0048] 2. Photocatalytic molecular oxygen activation and conversion reaction experiment The method for evaluating the photocatalytic molecular oxygen activation and conversion performance of the metal oxide material having no Brønsted acid sites but containing oxygen defects obtained in this comparative example is the same as that in Example 1. The efficiency of the catalyst for the activation and conversion of molecular oxygen to generate hydrogen peroxide is as follows: Figure 4 shown.

[0049] from Figure 3 It can be seen that, compared with the comparative example, the catalyst material in Example 1 contains both oxygen defects and Brønsted acid sites, while the catalyst material in Comparative Example 1 does not contain oxygen defects but contains Brønsted acid sites.

[0050] from Figure 4 It can be seen that, compared with the comparative examples, the metal oxide materials with oxygen defects combined with Brønsted acid sites prepared by different methods in Examples 1-3 all exhibited the activity of molecular oxygen activation and conversion into hydrogen peroxide, while Comparative Examples 1-4 all exhibited lower activity of molecular oxygen activation and conversion into hydrogen peroxide, indicating that the oxygen defects and Brønsted acid sites in the catalyst material jointly determine the generation of hydrogen peroxide, and both are indispensable.

[0051] from Figure 5 It can be seen that the different catalyst materials in Example 1 and Comparative Example 4 all show the activity of activating molecular oxygen into superoxide radicals as an intermediate of hydrogen peroxide, while the metal oxide material in Comparative Example 1 that does not contain oxygen defects but contains Brønsted acid sites does not show the activity of activating molecular oxygen into superoxide radicals as an intermediate of hydrogen peroxide, indicating that oxygen defects are the main active sites for activating molecular oxygen to form superoxide radicals, and Brønsted acid sites are the main active sites for promoting the protonation of superoxide radical intermediates to generate hydrogen peroxide, and the two synergistically promote the activation of molecular oxygen into hydrogen peroxide.

[0052] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A metal oxide material having oxygen defects combined with Brønsted acid sites, characterized in that: The invention comprises a metal oxide having a nanometer size and a crystal structure, oxygen defects are present on the surface of the metal oxide, and Brønsted acid sites are present on the surface of the crystal structure of the metal oxide.

2. The metal oxide material with oxygen defects combined with Brønsted acid sites according to claim 1, characterized in that: The Brønsted acid sites include crystal water and / or hydroxyl functional groups.

3. The metal oxide material with oxygen defects combined with Brønsted acid sites according to claim 1, characterized in that: The metal oxide in the metal oxide material is selected from WO3, TiO2, SnO2, CuO, ZnO and / or Bi2O3.

4. A method for preparing the metal oxide material with oxygen defects combined with Brønsted acid sites as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: Providing a metal salt solution and adjusting the pH value of the metal salt solution to 2.0 to 10.0; A reducing agent is added to a metal salt solution, and a solvothermal reaction is performed to obtain a metal oxide material having oxygen defects combined with Brønsted acid sites.

5. The preparation method according to claim 4, characterized in that: The concentration of the metal salt solution is 2.0-100.0 mmol / L; To adjust the pH value of the metal salt solution, use an acid solution or an alkaline solution; The acid solution concentration is 0.1 ~ 1.0 mol / L; The concentration of the alkaline solution is 0.1 ~ 1.0 mol / L.

6. The preparation method according to claim 4, characterized in that: The metal salt in the metal salt solution is selected from one of Na2WO4, Ti(SO4)2, SnCl4·H2O, Cu(NO3)·3H2O, Zn(CH3COO)2·2H2O, and Bi(NO3)3·5H2O; The solvent of the metal salt solution is selected from one or more of water, ethanol or N,N-dimethylformamide.

7. The preparation method according to claim 4, characterized in that: The reducing agent is selected from glucose and / or fructose; the dosage of the reducing agent is 1.0 ~ 20.0 mmol / L.

8. The preparation method according to claim 4, characterized in that: The temperature of the solvothermal reaction is 120 ~ 200 °C, and the reaction time is 16 ~ 24 h.

9. Use of the metal oxide material with oxygen defects combined with Brønsted acid sites according to any one of claims 1 to 3 in photocatalytic activation and conversion of molecular oxygen.

10. The use according to claim 9, characterized in that: The product of the molecular oxygen activation conversion is hydrogen peroxide.

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