A photocatalyst with two-dimensional intercalated bismuth molybdate microspheres as a carrier for loading cadmium sulfide, and a preparation method and application thereof

Abstract

The present invention discloses a photocatalyst with cadmium sulfide loaded on a two-dimensional intercalated bismuth molybdate microsphere as a carrier, and its preparation method and application. The supported photocatalyst is prepared by in-situ growth method to load CdS on a two-dimensional intercalated Bi2MoO6 microsphere semiconductor carrier with light absorption. The good two-dimensional sheet structure exposes a large specific surface area, enabling the loading amount of cadmium sulfide to reach 50% without obvious agglomeration. The preparation method of the obtained CdS / Bi2MoO6 photocatalyst in the present invention is simple, with outstanding morphology. It can effectively catalyze the reduction of carbon dioxide into CO, which is the raw material of hydrocarbon products, under room temperature xenon lamp illumination, and has good stability and repeatability. Compared with the Bi2MoO6 carrier, the performance of photocatalytic carbon dioxide reduction has been significantly improved, and it has good application prospects in the field of photocatalytic carbon dioxide conversion.

Description

Technical Field

[0001] The present invention belongs to the field of energy utilization and environmental protection, and specifically relates to a photocatalyst using two-dimensional intercalated Bi2MoO6 microspheres as carriers to load CdS, and a preparation method and application thereof. The preparation method of the loaded catalyst is simple and easy, and can realize efficient photocatalytic conversion of carbon dioxide into carbon monoxide at room temperature by ultraviolet visible light irradiation, and has good activity, providing a new idea for the study of photocatalytic carbon dioxide reduction and the reaction mechanism of CO2 and H2O on the catalyst surface. Background Art

[0002] In the past few decades of development, the demand for coal and oil in people's production and life has been increasing. However, since these two fossil fuels are limited and non-renewable, and the use of these fossil fuels has brought us air and water pollution, it has also led to an explosive growth in carbon dioxide emissions, which in turn has led to serious global climate change. Therefore, it is urgent to develop effective methods to reduce carbon dioxide emissions and explore green and sustainable energy. According to conservative estimates, the energy that the sun irradiates the earth exceeds 120,000 terawatts per year, while human energy consumption does not exceed 30 terawatts per year, so solar energy can be considered an ideal renewable energy source to replace traditional fossil fuels. Photocatalytic reduction is a so-called artificial photosynthetic process that aims to use sunlight as the only energy input. It is of great significance to use photocatalytic carbon dioxide reduction to obtain and store solar energy in the form of chemical fuels, which is abundant in carbon dioxide and water in the atmosphere.

[0003] Although photocatalytic technology has shown its unique advantages in carbon dioxide reduction, the low utilization rate of solar energy and energy conversion rate in the reaction process, as well as the serious recombination of photogenerated carriers and holes in the materials, have hindered the industrialization of photocatalytic technology. Therefore, improving the activity and product selectivity of photocatalytic CO2 reduction reaction and deepening the research on the reaction mechanism of CO2 and H2O on the catalyst surface are of great significance for the conversion of CO2 into high value-added products.

[0004] Bismuth molybdate (Bi2MoO6) as an n-type semiconductor has a small band gap (2.59 eV) and can capture visible light. From the unique structure of Bi2MoO6, it can be found that [Bi2O2 2+ ] layer and [MoO4 2-The inner field directly formed by the layer can promote carrier separation. Unfortunately, Bi2MoO6 also has some disadvantages, such as: the conduction band position is relatively positive, restricting the reduction ability of photo-generated electrons; the recombination of photo-generated carriers is serious. CdS is a semiconductor metal sulfide with visible light absorption, and photo-corrosion is likely to occur in its valence band. Constructing a Z-scheme heterojunction can solve the deficiencies of Bi2MoO6 and CdS themselves. Although there are reports on CdS-loaded Bi2MoO6 catalysts at present, the CdS loading amounts are all relatively low. Due to the weak interfacial interaction between the two, they are prone to agglomeration, thus reducing the catalytic activity. Therefore, the present invention attempts to use the in-situ growth method to load CdS on two-dimensional sheet-like Bi2MoO6. The Bi2MoO6 with a two-dimensional ultrathin morphology can expose more unsaturated atoms, providing a large number of reaction sites for improving the CO2 reduction activity. Moreover, the CdS / Bi2MoO6 photocatalyst compounded by the in-situ growth method has closer contact, which is conducive to the rapid transfer of photo-generated carriers and holes in the Z-scheme heterojunction. The strong reduction ability at the CdS end can ensure the adsorption and activation of CO2, realizing a high loading amount while effectively inhibiting the separation of photo-generated carriers, and using the supported catalyst for photocatalytic CO2 reduction. Summary of the Invention

[0005] The photocatalyst of the present invention is prepared by loading CdS on two-dimensional intercalated Bi2MoO6 microspheres by the in-situ growth method. The supported catalyst is used for photocatalytic CO2 reduction. The preparation method is simple, and it can improve the photocatalytic reduction performance of the Bi2MoO6 catalyst under ultraviolet-visible light. Its purpose is to overcome the deficiencies of the photocatalytic CO2 reduction performance of Bi2MoO6, improve the activity of the catalyst under ultraviolet-visible light, solve the problem that the conduction band position of Bi2MoO6 is not enough in photocatalytic reduction resulting in low activity, and the close contact interface accelerates the charge transfer rate, providing an idea for subsequent catalyst design and having good application prospects.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A photocatalyst with two-dimensional intercalated Bi2MoO6 microspheres as the carrier and CdS loaded thereon, which is a supported photocatalyst with Bi2MoO6 as the carrier and CdS as the main component. The content of the main component cadmium sulfide accounts for 50% of the total molar amount of the catalyst.

[0008] Due to the structural advantages of bismuth molybdate in the photocatalyst, the content of CdS reaches 50% of the total molar amount of the catalyst without obvious agglomeration, which can enhance the photocatalytic activity and reduce the electron-hole recombination. CdS grows closely on the Bi2MoO6 lamellae by the in-situ growth method, which is more conducive to charge transfer.

[0009] As described above, the Z-scheme heterojunction constructed by CdS-modified Bi2MoO6 can effectively improve the photocatalytic CO2 reduction yield under ultraviolet and visible light.

[0010] The preparation method of the photocatalyst with two-dimensional intercalated Bi2MoO6 microspheres as the carrier and CdS loaded thereon is as described above. BiCl3 and (NH4)6Mo7O 24 ·4H2O are used to synthesize the Bi2MoO6 catalyst by a solvothermal method, and then CdS is loaded on Bi2MoO6 by an in-situ growth method. The specific preparation steps are as follows:

[0011] (1) First, 0.97 g of BiCl3 and 0.242 g of (NH4)6Mo7O 24 ·4H2O are respectively dissolved in ethylene glycol, stirred for 30 min, and then the BiCl3 solution and the (NH4)6Mo7O 24 ·4H2O solution are dropped into ethanol, stirred for 30 min, loaded into a 100 ml hydrothermal autoclave, maintained at 160 °C for 12 h, cooled to room temperature, centrifuged, washed three times with absolute ethanol and deionized water respectively, and vacuum dried at 60 °C for 8 h to obtain the Bi2MoO6 carrier;

[0012] (2) Deionized water is added to the Bi2MoO6 carrier obtained in step (1) and ultrasonicated for 30 min. Subsequently, 0.0374 g of CdCl2 is dispersed in this solution, and an aqueous solution of Na2S·9H2O is slowly dropped in with stirring. After stirring for 1 h, the precipitate is washed many times with deionized water and dried in a vacuum oven at 60 °C for 6 h to prepare a photocatalyst with two-dimensional intercalated bismuth molybdate microspheres as the carrier and cadmium sulfide loaded thereon.

[0013] Among them, the concentration of the aqueous solution of Na2S·9H2O is 0.0164 mol / L, and the dosage is 10 ml; the dosage of ethylene glycol is 10 ml, the dosage of absolute ethanol is 40 ml, and the dosage of deionized water is 30 ml.

[0014] The supported CdS / Bi2MoO6 catalyst is used for CO2 conversion in the atmospheric environment. The obtained CdS / Bi2MoO6 catalyst has a simple, convenient and feasible preparation method under room temperature ultraviolet and visible light irradiation, providing a new idea for the research on photocatalytic carbon dioxide reduction.

[0015] The remarkable advantages of the present invention are as follows:

[0016] (1) A photocatalyst with two-dimensional intercalated Bi2MoO6 microspheres as the carrier and CdS loaded thereon. It is prepared by combining a solvothermal method and an in-situ growth method, has a simple preparation method, and has a microwave flaky two-dimensional morphology;

[0017] (2) The obtained Bi2MoO6 is a photocatalyst with CdS loaded on the carrier, which can construct a Z-scheme heterojunction, and the in-situ growth method makes their contact closer, facilitating the rapid transfer of photo-generated carriers and holes; the Z-scheme heterojunction composite system can solve the problem of insufficient conduction band position of Bi2MoO6 and the photo-corrosion of CdS, and a rich electron region is formed at the CdS end, which is beneficial to the adsorption and activation of CO2. It provides a new idea for the CO2 reduction reaction mechanism;

[0018] (3) Using a two-dimensional intercalation structure as the carrier and loading cadmium sulfide in this in-situ growth way can extremely improve the loading amount of cadmium sulfide, form a strong interfacial interaction force while avoiding agglomeration, which helps to further enhance the separation of photo-generated electron-hole pairs and thus improve the catalytic activity. Description of the Drawings

[0019] Figure 1 XRD patterns of Bi2MoO6, CdS / Bi2MoO6, and CdS obtained in Example 1;

[0020] Figure 2 UV-vis diffuse reflectance spectra of Bi2MoO6, CdS / Bi2MoO6, and CdS obtained in Example 1;

[0021] Figure 3 SEM images of Bi2MoO6 and CdS / Bi2MoO6 obtained in Example 1;

[0022] Figure 4 Photocatalytic CO2 reduction performance diagrams of Bi2MoO6, CdS / Bi2MoO6, and CdS obtained in Example 1; Detailed Embodiments

[0023] To make the above features and advantages of the present invention more obvious and understandable, specific examples are given below and described in detail in conjunction with the drawings, but the present invention is not limited thereto.

[0024] Example 1

[0025] Preparation of 50% CdS / Bi2MoO6 Catalyst

[0026] (1) First, 0.97 g of BiCl3 and 0.242 g of (NH4)6Mo7O 24 ·4H2O were respectively dissolved in 10 ml of ethylene glycol, stirred for 30 min, and then the BiCl3 solution and (NH4)6Mo7O 24The ·4H2O solution was dropped into 40 ml of ethanol, stirred thoroughly for 30 min, loaded into a 100 ml polytetrafluoroethylene autoclave, maintained at 160 °C for 12 h, cooled to room temperature, centrifuged, washed three times with absolute ethanol and deionized water respectively, and dried in vacuum at 60 °C for 8 h to obtain the Bi2MoO6 support;

[0027] (2)30 ml of deionized water was added to the Bi2MoO6 support obtained in step (1) and ultrasonicated for 30 min. Subsequently, 0.0374 g of CdCl2 was dispersed in this solution. While stirring, 10 ml of an aqueous solution of Na2S·9H2O with a concentration of 0.0164 mol / L was slowly dropped in. After stirring for 1 h, the precipitate was washed repeatedly with deionized water and dried in a vacuum oven at 60 °C for 6 h to prepare a photocatalyst with cadmium sulfide supported on a two-dimensional intercalated bismuth molybdate microsphere as the support.

[0028] Example 2 Photocatalytic CO2 reduction performance test.

[0029] The performance evaluation of the catalyst was carried out in a batch reactor with a volume of 175 mL. The upper part was made of quartz glass, and light could penetrate through it to irradiate the surface of the catalyst. Before the reaction, 20 mg of the catalyst was loaded into the upper part of the reactor. The device was evacuated through a vacuum pump, and the other end was connected to high-purity carbon dioxide (99.999%). After evacuating multiple times, the reaction gas CO2 was filled. Then, 0.5 mL of deionized water was injected into the reactor and continuously stirred on a magnetic stirrer. The light source was a 300 W xenon lamp. Every 1 h, 1 mL of gas was extracted from the reactor through a gas sampling needle and injected into a gas chromatograph to detect the products. A high-sensitivity thermal conductivity detector (TCD) and a flame ionization detector (FID) were used to detect the content of the photocatalytic products.

[0030] The yield of CO can be calculated by the following formula:

[0031]

[0032] where Y is the yield of CO, k is the CO standard curve coefficient measured by the external standard method, S a is the area of the CO content determined by gas chromatography, V is the volume of the reactor, m cat is the mass of the catalyst, and t is the reaction time.

[0033] The sample prepared according to Example 1 was scanned by an X-ray diffractometer, and the results are shown in Figure 1 . From Figure 1 it can be determined that when cadmium sulfide is supported on bismuth molybdate, its crystal structure does not change.

[0034] Figure 2The UV-diffuse reflection spectra of Bi2MoO6, CdS / Bi2MoO6, and CdS are shown. It can be seen that there is an obvious red shift for CdS / Bi2MoO6 compared to the Bi2MoO6 support, enhancing the light absorption.

[0035] Bi2MoO6 and CdS / Bi2MoO6 were prepared according to Example 1 and observed by field emission scanning electron microscopy. The results are shown in Figure 3 , and from Figure 3 (a), it can be intuitively seen that Bi2MoO6 has a two-dimensional intercalated microsphere sheet-like morphology. After loading CdS ( Figure 3 b), it can be observed that CdS is inserted into its sheets without much change in its morphology.

[0036] Figure 4 The photocatalytic CO2 reduction performance diagrams of the obtained Bi2MoO6, CdS / Bi2MoO6, and CdS are shown. It can be seen that the photocatalytic performance of Bi2MoO6 after loading CdS has been significantly improved compared to Bi2MoO6 and CdS.

[0037] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. Application of a photocatalyst with two-dimensional intercalated bismuth molybdate microspheres as a carrier loaded with cadmium sulfide, characterized in that: Use of the photocatalyst with cadmium sulfide loaded on two-dimensional intercalated bismuth molybdate microspheres as a carrier in photocatalytic reduction of carbon dioxide to carbon monoxide at room temperature and under ultraviolet and visible light; The photocatalyst is a Z-scheme heterojunction system constructed with two-dimensional intercalated Bi2MoO6 microspheres as the carrier and CdS as the supported catalyst; In the photocatalyst, due to the structural advantages of bismuth molybdate, the content of CdS reaches 50% of the total molar amount of the catalyst without obvious agglomeration, enhancing the photocatalytic activity and reducing electron-hole recombination. CdS grows tightly on the Bi2MoO6 lamellae by in-situ growth, which is more conducive to charge transfer; Preparation method of the photocatalyst with cadmium sulfide loaded on two-dimensional intercalated bismuth molybdate microspheres as a carrier, specifically including the following steps: (1) First, dissolve BiCl3 and (NH4)6Mo7O 24 ·4H2O in ethylene glycol respectively, stir for 30 min, and then drop the BiCl3 solution and (NH4)6Mo7O 24 ·4H2O solution into ethanol, stir for 30 min, load it into a 100 ml polytetrafluoroethylene reaction kettle, keep it at 160 °C for 12 h, after cooling to room temperature, centrifuge, wash it three times with absolute ethanol and deionized water respectively, and dry it under vacuum at 60 °C for 8 h to obtain the Bi2MoO6 support; (2) Add deionized water to the Bi2MoO6 carrier obtained in step (1) and ultrasonicate for 30 min. Then disperse CdCl2 in this solution, slowly dropwise add an aqueous solution of Na2S·9H2O under stirring. After stirring for 1 h, wash the precipitate with deionized water multiple times and dry it in a vacuum oven at 60 °C for 6 h to obtain the photocatalyst with cadmium sulfide loaded on two-dimensional intercalated bismuth molybdate microspheres as a carrier; In step (1), the dosages of BiCl3 and (NH4)6Mo7O 24 ·4H2O are 0.97 g and 0.242 g respectively; In step (2), the dosage of CdCl2 is 0.0374 g, the concentration of the aqueous solution of Na2S·9H2O is 0.0164 mol / L, and 10 ml is dropped in.

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