A narrow bandgap photocatalyst for catalyzing CO2 reduction and conversion, its preparation method and application.

Abstract

This invention provides a narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2, its preparation method, and its application. The preparation method includes the following steps: mixing a photocatalyst precursor and molten salt, followed by calcination to obtain the narrow bandgap photocatalyst; the narrow bandgap photocatalyst is a metal nitride or metal oxide nitride. This invention utilizes a molten salt-assisted method to synthesize a high-quality narrow bandgap photocatalyst. This method reduces lattice defects in the catalyst, and the preparation process is simple and controllable, with low environmental pollution, mild reaction conditions, high yield, and ease of large-scale production, showing good prospects for industrial application. The narrow bandgap photocatalyst prepared by this method can absorb visible light up to 500-750 nm, greatly improving the absorption and utilization rate of sunlight, thereby promoting the separation and transport of photogenerated charges and surface catalytic processes, exhibiting excellent photocatalytic and photothermal synergistic catalytic performance for CO2 conversion, with a methane selectivity of up to 94%.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and application, specifically relating to a narrow bandgap photocatalyst for catalyzing CO2 reduction and conversion, its preparation method, and its application. Background Technology

[0002] Global industrialization and the overexploitation of fossil fuels have led to increasingly serious environmental and energy problems, and human society's demand for and use of clean energy is also increasing.

[0003] The rapid increase in atmospheric CO2 levels is a major cause of global climate change and has recently received increasing attention. Scientists are searching for effective solutions across various fields. Photocatalytic CO2 reduction and conversion, utilizing solar energy conversion technology to recycle CO2 resources and obtain high-value-added carbon-neutral fuels and chemicals, effectively reduces atmospheric CO2 levels while providing green and clean energy—a technology with both environmental and energy benefits. Simultaneously, the introduction of heat energy during light exposure—the photothermal effect—avoids the high-temperature, high-pressure process required for traditional CO2 reduction and conversion. This photothermal synergistic catalysis can further improve CO2 conversion efficiency. However, the catalytic materials for photocatalytic (thermal) CO2 reduction are mainly concentrated on metal oxide semiconductors (TiO2, Ga2O3, SrTiO3, Nb2O5, or NaTaO3, etc.). These wide-bandgap photocatalysts can only absorb ultraviolet light and have poor carrier migration characteristics, resulting in low CO2 reduction reaction efficiency and limited room for improvement, far from meeting industrial needs.

[0004] Therefore, developing high-quality narrow-bandgap photocatalysts to improve the migration characteristics of photogenerated charges and the absorption and utilization rate of sunlight over a wide spectral range is a current research hotspot and challenge. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2, its preparation method, and its applications. This invention utilizes a molten salt-assisted method to synthesize a high-quality narrow bandgap photocatalyst. This preparation method reduces lattice defects in the catalyst during synthesis, and the process is simple, controllable, environmentally friendly, and operates under mild conditions. It also boasts high yield, is easy to mass-produce, and has promising prospects for industrial applications. The narrow bandgap photocatalyst prepared by this method can absorb visible light up to 500-750 nm, significantly improving the absorption and utilization rate of sunlight across a broad spectral range. This promotes the separation and transport of photogenerated charges and surface catalytic processes, exhibiting excellent CO2 conversion performance with a methane selectivity of up to 94%.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2, the preparation method comprising the following steps:

[0008] The narrow bandgap photocatalyst is obtained by mixing the photocatalyst precursor and molten salt and calcining them.

[0009] The narrow bandgap photocatalyst is a metal nitride or a metal nitride oxide.

[0010] This invention synthesizes a high-quality narrow-bandgap photocatalyst using a molten salt-assisted method. This preparation method reduces lattice defects in the catalyst during synthesis, and the process is simple, controllable, environmentally friendly, and operates under mild conditions. It also boasts high yield and is suitable for large-scale production, showing promising prospects for industrial applications. The narrow-bandgap photocatalyst prepared by this method can absorb visible light up to 500-750 nm, significantly improving the absorption and utilization rate of sunlight across a broad spectral range. This promotes the separation and transport of photogenerated charges and surface catalytic processes, exhibiting excellent CO2 conversion performance with a methane selectivity of up to 94%.

[0011] As a preferred embodiment of the present invention, the molten salt comprises any one or a combination of at least two of MCl, M2SO4, MNO3, M2CO3, MOH, SrCl2 or NaNH2, wherein M is an alkali metal element.

[0012] Preferably, the metal nitride includes TaON, Ti3O3N2, Zr3O3N2, ABO2N, LaNbON2, LaTaON2, LaTiO2N, and LaMg. x Ta 1-x O 1+3x N 2-3x Any one or at least two of the following: YTaON2, YTiO2N, Y2Ta2O5N2, GaON, GaN:ZnO, or ZnGeN2:ZnO, wherein A is any one of Ca, Ba, or Sr, and B is Ta or Nb, such as BaTaO2N, BaNbO2N, or SrNbO2N.

[0013] Preferably, the value of x is in the range of 1 / 3 ≤ x < 2 / 3, for example, it can be 1 / 3 or 1 / 2, etc.

[0014] Preferably, the metal nitride includes any one or a combination of at least two of Ta3N5, GaN, Ge3N4, ZnGeN2 or Cu3N.

[0015] As a preferred embodiment of the present invention, the calcination atmosphere is a nitrogen-containing atmosphere.

[0016] In this invention, if the calcination atmosphere is a nitrogen-containing atmosphere, the photocatalyst precursor and molten salt can be mixed and calcined under nitriding conditions to obtain the target product. This method allows for one-step nitriding synthesis of the target product, significantly shortening the nitriding time and reducing the nitriding temperature, resulting in a high-quality photocatalyst.

[0017] Preferably, the gas in the nitrogen-containing atmosphere includes ammonia.

[0018] Preferably, the flow rate of the gas in the nitrogen-containing atmosphere is 10-300 mL / min, for example, it can be 10 mL / min, 50 mL / min, 100 mL / min, 150 mL / min, 200 mL / min, 250 mL / min or 300 mL / min, etc.

[0019] Preferably, the calcination temperature is 200-1500℃, for example, it can be 200℃, 500℃, 700℃, 1000℃, 1200℃ or 1500℃, and more preferably 800-1000℃.

[0020] Preferably, the calcination time is 0.5-60h, for example, it can be 0.5h, 1h, 5h, 10h, 20h, 30h, 40h, 50h or 60h, and more preferably 8-15h.

[0021] Preferably, the heating rate of the calcination is 5-10℃ / min, for example, it can be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc.

[0022] As a preferred embodiment of the present invention, the calcination atmosphere is an oxygen atmosphere.

[0023] Preferably, the oxide precursor obtained after calcination is subjected to nitriding treatment to obtain the metal nitride or metal nitride.

[0024] The present invention employs a two-step method to prepare the metal nitride or metal nitride, which allows for morphological and compositional control of the oxide precursor, thereby achieving precise regulation of the catalyst morphology and composition.

[0025] Preferably, the calcination temperature is 600-1500℃, for example, it can be 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃ or 1500℃, and more preferably 900-1200℃.

[0026] In this invention, if the calcination temperature is too low, the reaction will be insufficient and the crystallinity will be low; if the calcination temperature is too high, the molten salt will volatilize severely, resulting in too many product defects.

[0027] Preferably, the calcination time is 5-20 hours, for example, 5 hours, 10 hours, 15 hours or 20 hours.

[0028] Preferably, the nitriding treatment is carried out in a nitrogen-containing atmosphere, wherein the gas in the nitrogen-containing atmosphere includes ammonia.

[0029] Preferably, the nitriding temperature is 200-1500℃, for example, it can be 200℃, 500℃, 700℃, 1000℃, 1200℃ or 1500℃, and more preferably 800-1000℃.

[0030] Preferably, the nitriding treatment time is 0.5-60h, for example, it can be 0.5h, 1h, 5h, 10h, 20h, 30h, 40h, 50h or 60h, etc., and is more preferably 8-15h.

[0031] Preferably, the heating rate of the nitriding treatment is 5-10℃ / min, for example, it can be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc.

[0032] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0033] (1) The photocatalyst precursor and molten salt are mixed and calcined in a nitrogen-containing atmosphere at a flow rate of 10-300 mL / min for 0.5-60 h to obtain the nitrided product. The calcination temperature is 200-1500℃; or,

[0034] The photocatalyst precursor and molten salt were mixed and calcined in an oxygen atmosphere at 600-1500℃ for 5-20h. Then, the mixture was subjected to nitriding treatment in a nitrogen-containing atmosphere at a flow rate of 10-300mL / min for 0.5-60h at a temperature of 200-1500℃ to obtain the nitrided product.

[0035] (2) The nitrided product is cleaned and dried to obtain metal nitride or metal nitride, i.e., narrow bandgap photocatalyst.

[0036] In a second aspect, the present invention provides a narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2, wherein the narrow bandgap photocatalyst is prepared by the preparation method described in the first aspect.

[0037] The narrow bandgap photocatalyst prepared by this invention is a metal nitride or metal nitride that can absorb visible light in the range of 500-750 nm, which enhances the absorption and utilization rate of sunlight, has excellent CO2 reduction and conversion efficiency and selectivity, and has significant economic and social benefits.

[0038] Preferably, the band gap of the narrow band gap photocatalyst is 1.65-2.5 eV, for example, it can be 1.65 eV, 1.7 eV, 1.8 eV, 1.9 eV, 2 eV, 2.1 eV, 2.2 eV, 2.3 eV, 2.4 eV or 2.5 eV.

[0039] It should be noted that the band gap of SrNbO2N is 1.8-1.94 eV, that of BaNbO2N is 1.65-1.72 eV, and that of BaTaO2N is 1.8-1.9 eV.

[0040] Thirdly, the present invention provides an application of a narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2 as described in the second aspect, wherein the specific steps of using the narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2 include:

[0041] A narrow bandgap photocatalyst, CO2, and an electron donor are mixed to carry out a CO2 reduction and conversion reaction.

[0042] The narrow bandgap photocatalyst provided by this invention is used to catalyze the CO2 reduction and conversion reaction. It can avoid the high temperature and high pressure process required for traditional CO2 reduction and conversion, and does not require the input of additional energy that causes carbon emissions. It has the potential and advantages of significantly improving conversion efficiency and selectivity, as well as the ability to scale up the device.

[0043] The method provided by this invention can achieve high photocatalytic (thermal) CO2 reduction conversion efficiency and selectivity under mild reaction conditions, with methane selectivity reaching 94%, and has good prospects for industrial application.

[0044] As a preferred embodiment of the present invention, the electron donor includes water or H2.

[0045] Preferably, when the electron donor is water, the CO2 reduction and conversion reaction is carried out in a CO2-containing solution.

[0046] Preferably, the flow rate of CO2 is 1-50 mL / min, for example, it can be 1 mL / min, 5 mL / min, 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min or 50 mL / min, etc., and preferably 1-20 mL / min.

[0047] Preferably, when the electron donor is H2, the CO2 reduction and conversion reaction is carried out in a mixed gas containing H2 and CO2.

[0048] Preferably, the volume ratio of H2 to CO2 is (1-6):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1 or 6:1, etc.

[0049] Preferably, based on the volume of the mixed gas, the total volume fraction of H2 and CO2 is 1-50%, for example, it can be 1%, 5%, 10%, 20%, 30%, 40% or 50%, etc., preferably 10-25%.

[0050] It should be noted that, apart from H2 and CO2, the remainder of the mixed gas is an inert gas, including any one of argon, nitrogen or helium.

[0051] Preferably, the temperature of the CO2 reduction and conversion reaction is 10-500℃, for example, it can be 10℃, 50℃, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃ or 500℃, etc., preferably 10-400℃.

[0052] As a preferred embodiment of the present invention, the narrow bandgap photocatalyst undergoes surface modification before being mixed with CO2 and an electron donor.

[0053] This invention modifies the surface of narrow bandgap photocatalysts, enhancing CO2 adsorption on the catalyst surface and altering the reaction pathway, thereby improving the selectivity of reaction products.

[0054] Preferably, the specific steps of the surface modification include:

[0055] A modified narrow bandgap photocatalyst is obtained by mixing a surface modifier and a narrow bandgap photocatalyst.

[0056] Preferably, the surface modifier includes any one of metal oxides, hydroxides, or single-atom co-catalysts.

[0057] As a preferred technical solution of the present invention, based on the mass of the modified narrow bandgap photocatalyst, the mass content of the surface modifier is 0.01-30 wt.%, for example, it can be 0.1 wt.%, 0.3 wt.%, 0.5 wt.%, 1 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%, 25 wt.%, or 30 wt.%, etc.

[0058] Preferably, the metal oxide includes any one or a combination of at least two of alkali metal oxides, alkaline earth metal oxides, lanthanide metal oxides, ZrO2, TiO2, ZnO, WO3, MoO3, Y2O3 or Sc2O3.

[0059] Preferably, the hydroxide includes any one or a combination of at least two of the following: alkali metal hydroxide, alkaline earth metal hydroxide, lanthanide metal hydroxide, Ti hydrated hydroxide, Si hydrated hydroxide, Ta hydrated hydroxide, Y(OH)3, or Sc(OH)3.

[0060] Preferably, the single-atom cocatalyst comprises any one or a combination of at least two of Ag, Cr, Rh, Co, Ir, Pt, Pd, Ru, Fe, Ni, Cu, Au, Mo, or Mn.

[0061] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] (1) This invention uses a molten salt-assisted method to synthesize a high-quality narrow bandgap photocatalyst. This preparation method can reduce lattice defects in the catalyst during the synthesis process. The preparation process is simple and controllable, with little environmental pollution, mild reaction conditions, high yield, and easy large-scale production. It has good prospects for industrial application.

[0064] (2) The narrow bandgap photocatalyst prepared by the method provided in this invention can absorb visible light up to 500-750nm, which greatly improves the absorption and utilization rate of sunlight in a wide spectrum range, thereby promoting the separation and transport of photogenerated charges and surface catalysis, exhibiting excellent CO2 conversion performance and methane selectivity up to 94%.

[0065] (3) The narrow bandgap photocatalyst provided by the present invention is used to catalyze the CO2 reduction and conversion reaction. It can avoid the high temperature and high pressure process required for the traditional CO2 reduction and conversion, and does not require the input of additional energy that causes carbon emissions. It has the potential and advantages of significantly improving conversion efficiency and selectivity and scaling up the device. Attached Figure Description

[0066] Figure 1 This is an electron microscope image of the narrow bandgap photocatalyst prepared in Example 1 of the present invention.

[0067] Figure 2 The image shows the XRD phase diagram of the narrow bandgap photocatalyst prepared in Example 1 of this invention.

[0068] Figure 3 The image shows the UV-Vis absorption spectrum of the narrow bandgap photocatalyst prepared in Example 1 of this invention.

[0069] Figure 4 The image shows the XRD phase diagram of the narrow bandgap photocatalyst prepared in Example 2 of this invention.

[0070] Figure 5 The image shows the UV-Vis absorption spectrum of the narrow bandgap photocatalyst prepared in Example 2 of this invention.

[0071] Figure 6This is an electron microscope image of the narrow bandgap photocatalyst prepared in Example 4 of the present invention.

[0072] Figure 7 The image shows the XRD phase diagram of the narrow bandgap photocatalyst prepared in Example 4 of this invention.

[0073] Figure 8 The image shows the UV-Vis absorption spectrum of the narrow bandgap photocatalyst prepared in Example 4 of this invention.

[0074] Figure 9 Electron microscopy morphology of the narrow bandgap photocatalyst prepared in Example 5 of this invention.

[0075] Figure 10 XRD phase diagram of the narrow bandgap photocatalyst prepared in Example 5 of this invention.

[0076] Figure 11 The UV-Vis absorption spectrum of the narrow bandgap photocatalyst prepared in Example 5 of this invention.

[0077] Figure 12 Electron microscopy morphology of the narrow bandgap photocatalyst prepared in Comparative Example 1 of this invention.

[0078] Figure 13 XRD phase diagram of the narrow bandgap photocatalyst prepared in Comparative Example 1 of this invention. Detailed Implementation

[0079] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0080] Example 1

[0081] This embodiment provides a method for preparing a narrow bandgap photocatalyst, the method comprising the following steps:

[0082] (1) SrCO3, Nb2O5 and RbCl were mixed in a molar ratio of 2:1:10, ground evenly and placed in a box furnace. The mixture was calcined in an oxygen atmosphere at 1150℃ for 5h to obtain Sr2Nb2O7 oxide precursor. The Sr2Nb2O7 oxide precursor was then placed in a horizontal tube furnace and nitrided in an ammonia atmosphere at a flow rate of 200mL / min for 10h. The nitriding temperature was 900℃ and the heating rate was 10℃ / min to obtain the nitrided product.

[0083] (2) The nitrided product is washed with hot water and dried to obtain SrNbO2N powder, which is the narrow bandgap photocatalyst with a bandgap of 1.85 eV.

[0084] This embodiment also provides a process for using the above-mentioned narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction, the process including the following steps:

[0085] (a) A modified narrow bandgap photocatalyst was obtained by loading 0.3 wt.% Ru co-catalyst onto the surface of the narrow bandgap photocatalyst by impregnation method;

[0086] (b) Disperse 0.2 g of the modified narrow bandgap photocatalyst onto a glass slide and place it at the bottom of the reactor. Use Ar to purge the air from the reactor, and then introduce a mixture of CO2 and H2, wherein the volume ratio of H2, CO2, and Ar is 1:1:18.

[0087] (c) CO2 hydrogenation reaction was carried out under visible light source (300W xenon lamp equipped with a 420nm short-wavelength cutoff filter) with circulating condensate to control the reaction temperature at 15℃. The reaction products were analyzed online by gas chromatography, and qualitative and quantitative analyses were performed using TCD and FID detectors, respectively. The specific reaction performance is listed in Table 1.

[0088] Figure 1 The electron microscope image of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the narrow bandgap photocatalyst prepared in this embodiment has a porous surface structure.

[0089] Figure 2 The XRD phase diagram of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the XRD diffraction peaks of the prepared narrow bandgap photocatalyst all belong to SrNbO2N, and no other impurity peaks appear, indicating that the nitridation product is single crystal SrNbO2N.

[0090] Figure 3 The UV-Vis absorption spectrum of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the absorption edge of the obtained narrow bandgap photocatalyst is located at 670 nm, corresponding to a bandgap of 1.85 eV.

[0091] Example 2

[0092] This embodiment provides a method for preparing a narrow bandgap photocatalyst, the method comprising the following steps:

[0093] (1) SrCO3, Nb2O5 and RbCl were mixed in a molar ratio of 2:1:10, ground evenly and placed in a box furnace. The mixture was calcined for 10 h in an ammonia atmosphere with a flow rate of 200 mL / min to obtain the nitrided product. The calcination temperature was 900℃ and the calcination heating rate was 10℃ / min.

[0094] (2) The nitrided product is washed with hot water and dried to obtain SrNbO2N powder, which is the narrow bandgap photocatalyst with a bandgap of 1.85 eV.

[0095] This embodiment also provides a process for using the above-mentioned narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction, the process including the following steps:

[0096] (a) A modified narrow bandgap photocatalyst was obtained by loading 0.3 wt.% Ru co-catalyst onto the surface of the narrow bandgap photocatalyst by impregnation method;

[0097] (b) Disperse 0.2g of the modified narrow bandgap photocatalyst onto a glass slide and place it at the bottom of the reactor. Use Ar to purge the air from the reactor and then introduce a mixture of CO2 and H2, wherein the volume ratio of H2, CO2 and Ar is 1:1:18.

[0098] (c) CO2 hydrogenation reaction was carried out under visible light source (300W xenon lamp equipped with a 420nm short-wavelength cutoff filter) with circulating condensate to control the reaction temperature at 15℃. The reaction products were analyzed online by gas chromatography, and qualitative and quantitative analyses were performed using TCD and FID detectors, respectively. The specific reaction performance is listed in Table 1.

[0099] Figure 4 The XRD phase diagram of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the XRD diffraction peaks of the prepared narrow bandgap photocatalyst all belong to SrNbO2N, and no other impurity peaks appear, indicating that the nitridation product is single crystal SrNbO2N.

[0100] Figure 5 The UV-Vis absorption spectrum of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the absorption edge of the obtained narrow bandgap photocatalyst is located at 670 nm, corresponding to a bandgap of 1.85 eV.

[0101] Example 3

[0102] The difference between this embodiment and Embodiment 1 is that the reaction temperature in step (c) is 198°C.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Example 4

[0105] This embodiment provides a method for preparing a narrow bandgap photocatalyst, the method comprising the following steps:

[0106] (1) BaCO3, Nb2O5 and NaCl were mixed in a molar ratio of 2:1:18, ground evenly, and then placed in a box furnace and calcined in an oxygen atmosphere at 900℃ for 5 hours to obtain Ba5Nb4O 15 Oxide precursor, then Ba5Nb4O 15The oxide precursor was placed in a horizontal tube furnace and subjected to nitriding treatment in an ammonia atmosphere at a flow rate of 200 mL / min for 15 h. The nitriding treatment temperature was 930 °C and the heating rate was 10 °C / min, to obtain the nitrided product.

[0107] (2) The nitrided product is washed with hot water and dried to obtain BaNbO2N powder, which is the narrow bandgap photocatalyst.

[0108] This embodiment also provides a process for using the above-mentioned narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction, the process including the following steps:

[0109] (a) A modified narrow bandgap photocatalyst was obtained by loading 0.3 wt.% Ru co-catalyst onto the surface of the narrow bandgap photocatalyst by impregnation method;

[0110] (b) Disperse 0.2g of the modified narrow bandgap photocatalyst onto a glass slide and place it at the bottom of the reactor. Use Ar to purge the air from the reactor and then introduce a mixture of CO2 and H2, wherein the volume ratio of H2, CO2 and Ar is 1:1:18.

[0111] (c) CO2 hydrogenation reaction was carried out under visible light source (300W xenon lamp equipped with a 420nm short-wavelength cutoff filter) with circulating condensate to control the reaction temperature at 15℃. The reaction products were analyzed online by gas chromatography, and qualitative and quantitative analyses were performed using TCD and FID detectors, respectively. The specific reaction performance is listed in Table 1.

[0112] Figure 6 The electron microscope image of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the narrow bandgap photocatalyst particles are of different sizes, indicating that they have a rough and non-uniform morphology.

[0113] Figure 7 The XRD phase diagram of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the XRD diffraction peaks of the obtained narrow bandgap photocatalyst all belong to BaNbO2N, and no other impurity peaks appear, indicating that the nitriding product is single-crystal BaNbO2N.

[0114] Figure 8 The UV-Vis absorption spectrum of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the absorption edge of the obtained narrow bandgap photocatalyst is located at 700 nm, corresponding to a bandgap of 1.77 eV.

[0115] Example 5

[0116] This embodiment provides a method for preparing a narrow bandgap photocatalyst, the method comprising the following steps:

[0117] (1) La2O3, Ta2O5 and KCl were mixed in a molar ratio of 1:1:18, ground evenly and placed in a box furnace. The mixture was calcined for 15 h in an ammonia atmosphere with a flow rate of 200 mL / min to obtain the nitrided product. The calcination temperature was 950 °C and the calcination heating rate was 10 °C / min.

[0118] (2) The nitrided product is washed with hot water and dried to obtain LaTaON2 powder, which is the narrow bandgap photocatalyst with a bandgap of 2.0 eV.

[0119] This embodiment also provides a process for using the above-mentioned narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction, the process including the following steps:

[0120] (a) A modified narrow bandgap photocatalyst was obtained by loading 0.3 wt.% Ru co-catalyst onto the surface of the narrow bandgap photocatalyst by impregnation method;

[0121] (b) Disperse 0.2g of the modified narrow bandgap photocatalyst onto a glass slide and place it at the bottom of the reactor. Use Ar to purge the air from the reactor and then introduce a mixture of CO2 and H2, wherein the volume ratio of H2, CO2 and Ar is 1:1:18.

[0122] (c) CO2 hydrogenation reaction was carried out under visible light source (300W xenon lamp equipped with a 420nm short-wavelength cutoff filter) with circulating condensate to control the reaction temperature at 15℃. The reaction products were analyzed online by gas chromatography, and qualitative and quantitative analyses were performed using TCD and FID detectors, respectively. The specific reaction performance is listed in Table 1.

[0123] Figure 9 The electron microscope image of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the narrow bandgap photocatalyst prepared in this embodiment is a cuboid particle with a smooth surface.

[0124] Figure 10 The XRD phase diagram of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the XRD diffraction peaks of the obtained narrow bandgap photocatalyst all belong to LaTaO2N, and no other impurity peaks appear, indicating that the nitridation product is single-crystal LaTaO2N.

[0125] Figure 11 The UV-Vis absorption spectrum of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the absorption edge of the obtained narrow bandgap photocatalyst is located at 620 nm, corresponding to a bandgap of 2 eV.

[0126] Example 6

[0127] This embodiment provides a method for preparing a narrow bandgap photocatalyst, the method comprising the following steps:

[0128] (1) SrCO3, Nb2O5 and RbCl were mixed in a molar ratio of 2:1:10, ground evenly and placed in a box furnace. The mixture was calcined in an oxygen atmosphere at 1500℃ for 5h to obtain Sr2Nb2O7 oxide precursor. The Sr2Nb2O7 oxide precursor was then placed in a horizontal tube furnace and nitrided in an ammonia atmosphere at a flow rate of 200mL / min for 60h. The nitriding temperature was 900℃ and the heating rate was 5℃ / min to obtain the nitrided product.

[0129] (2) The nitrided product is washed with dilute hydrochloric acid and dried to obtain SrNbO2N powder, which is the narrow bandgap photocatalyst with a bandgap of 1.85 eV.

[0130] This embodiment also provides a process for using the above-mentioned narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction, the process including the following steps:

[0131] (a) A modified narrow bandgap photocatalyst was obtained by loading 0.3 wt.% Ru co-catalyst onto the surface of the narrow bandgap photocatalyst by impregnation method;

[0132] (b) 0.2 g of the modified narrow bandgap photocatalyst was dispersed in a CO2-containing solution at a CO2 flow rate of 25 mL / min. The CO2 hydrogenation reaction was carried out under visible light irradiation (a 300 W xenon lamp equipped with a 420 nm short-wavelength cutoff filter) with circulating condensate to maintain the reaction temperature at 50 °C. The reaction products were analyzed online by gas chromatography, using TCD and FID detectors for qualitative and quantitative analysis, respectively. Specific reaction performance is listed in Table 1.

[0133] Example 7

[0134] This embodiment provides a method for preparing a narrow bandgap photocatalyst, the method comprising the following steps:

[0135] (1) SrCO3, Nb2O5 and RbCl were mixed in a molar ratio of 2:1:10, ground evenly and placed in a box furnace. The mixture was calcined for 60 h in an ammonia atmosphere with a flow rate of 200 mL / min to obtain the nitrided product. The calcination temperature was 900℃ and the calcination heating rate was 5℃ / min.

[0136] (2) The nitrided product is washed with hot water and dried to obtain SrNbO2N powder, which is the narrow bandgap photocatalyst with a bandgap of 1.85 eV.

[0137] This embodiment also provides a process for using the above-mentioned narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction, the process including the following steps:

[0138] (a) A modified narrow bandgap photocatalyst was obtained by loading 0.3 wt.% Ru co-catalyst onto the surface of the narrow bandgap photocatalyst by impregnation method;

[0139] (b) 0.2 g of the modified narrow bandgap photocatalyst was dispersed in a CO2-containing solution at a flow rate of 30 mL / min. The CO2 hydrogenation reaction was carried out under irradiation with a visible light source (300 W xenon lamp equipped with a 420 nm short-wave cutoff filter) and the reaction temperature was controlled at 100 °C using circulating condensate. The reaction products were analyzed online by gas chromatography, and qualitative and quantitative analyses were performed using TCD and FID detectors, respectively. Specific reaction performance is listed in Table 1.

[0140] Example 8

[0141] The difference between this embodiment and embodiment 1 is that the calcination temperature in step (1) is 500°C.

[0142] The remaining preparation methods and parameters are consistent with those in Example 1.

[0143] Example 9

[0144] The difference between this embodiment and Embodiment 1 is that the calcination temperature in step (1) is 1600℃.

[0145] The remaining preparation methods and parameters are consistent with those in Example 1.

[0146] Comparative Example 1

[0147] This comparative example provides a method for solid-state synthesis of narrow bandgap photocatalysts, the method comprising the following steps:

[0148] (1) BaCO3 and Ta2O5 were mixed in a molar ratio of 2:1, ground evenly, and then placed in a box furnace and calcined in an oxygen atmosphere at 1000℃ for 10 h to obtain Ba5Ta4O 15 Oxide precursor, then Ba5Ta4O 15 The oxide precursor was placed in a horizontal tube furnace and nitrided for 30 h in an ammonia atmosphere at a flow rate of 200 mL / min. The nitriding temperature was 950 °C and the heating rate was 10 °C / min, to obtain the nitrided product.

[0149] (2) The nitrided product is washed with hot water and dried to obtain BaTaO2N powder, which is the narrow bandgap photocatalyst with a bandgap of 1.9 eV.

[0150] This embodiment also provides a process for using the above-mentioned narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction, the process including the following steps:

[0151] (a) A modified narrow bandgap photocatalyst was obtained by loading 0.3 wt.% Ru co-catalyst onto the surface of the narrow bandgap photocatalyst by impregnation method;

[0152] (b) Disperse 0.2g of the modified narrow bandgap photocatalyst onto a glass slide and place it at the bottom of the reactor. Use Ar to purge the air from the reactor and then introduce a mixture of CO2 and H2, wherein the volume ratio of H2, CO2 and Ar is 1:1:18.

[0153] (c) CO2 hydrogenation reaction was carried out under visible light source (300W xenon lamp equipped with a 420nm short-wavelength cutoff filter) with circulating condensate to control the reaction temperature at 15℃. The reaction products were analyzed online by gas chromatography, and qualitative and quantitative analyses were performed using TCD and FID detectors, respectively. The specific reaction performance is listed in Table 1.

[0154] Figure 12 The electron microscope image of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the obtained sample particles are severely aggregated, with varying particle sizes and no obvious morphology.

[0155] Figure 13 The XRD phase diagram of the narrow bandgap photocatalyst prepared in this embodiment is shown. As can be seen from the figure, the XRD diffraction peaks of the obtained sample all belong to BaTaO2N, and no other impurity peaks appear, indicating that the nitridation product is single-crystal BaTaO2N.

[0156] Performance testing

[0157] After the narrow bandgap photocatalysts prepared in the above examples and comparative examples were used to catalyze the CO2 reduction and conversion reaction, the resulting reaction products were qualitatively and quantitatively analyzed using TCD and FID detectors, respectively. The specific reaction performance is listed in Table 1.

[0158] Table 1

[0159]

[0160]

[0161] analyze:

[0162] As shown in the table above, the narrow bandgap photocatalyst prepared based on the method provided by this invention can absorb visible light up to 500-700 nm, which greatly improves the absorption and utilization rate of sunlight over a wide spectral range. This promotes the separation and transport of photogenerated charges and the surface catalytic process, exhibiting excellent CO2 conversion performance and a methane selectivity of up to 94%.

[0163] The data from Examples 1 and 2 show that calcination in an ammonia atmosphere reduces the crystallinity and specific surface area of ​​nitrides (oxides), thus affecting surface modification and reducing activity.

[0164] As can be seen from the data results of Example 4, expanding the light absorption range can improve the utilization rate of solar energy. At the same time, the driving force of electron-hole reduction oxidation in the intrinsic band of semiconductor photocatalyst will decrease. However, through the modification of surface active sites and functional sites, the photocatalytic CO2 reduction reaction is promoted, and based on this, a methane selectivity of up to 94% is obtained.

[0165] The data from Examples 1 and 8-9 show that if the calcination temperature is too low, the crystallinity of nitrogen oxides will be reduced, resulting in a decrease in photocatalytic CO2 reduction activity; if the calcination temperature is too high, the molten salt will evaporate too quickly, resulting in too many product defects, and at the same time, the specific surface area of ​​nitrogen oxides will be reduced, thereby affecting surface modification and causing a decrease in photocatalytic CO2 reduction activity.

[0166] The data from Example 1 and Comparative Example 1 show that if a narrow bandgap photocatalyst is synthesized using a solid-state method, the nitrogen oxides will contain a mixed phase, and the morphology and size of the powder particles will be uncontrollable, resulting in decreased crystallinity, increased crystal defects, and affecting the modification of surface active sites and catalytic activity.

[0167] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2, characterized in that, The preparation method includes the following steps: The narrow bandgap photocatalyst is obtained by mixing the photocatalyst precursor and molten salt and calcining them. The narrow bandgap photocatalyst is a metal nitrogen oxide; The metal nitride is SrNbO2N or BaNbO2N; The calcination temperature is 600-1500℃; The specific steps for using the narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction include: A narrow bandgap photocatalyst, CO2, and an electron donor are mixed to carry out a CO2 reduction and conversion reaction; The electron donor is H2; the CO2 reduction and conversion reaction is carried out in a mixed gas containing H2 and CO2; the volume ratio of H2 to CO2 is (1-6):

1.

2. The preparation method according to claim 1, characterized in that, The molten salt is SrCO3 or BaCO3.

3. The preparation method according to claim 1, characterized in that, The calcination atmosphere is a nitrogen-containing atmosphere.

4. The preparation method according to claim 3, characterized in that, The gas in the nitrogen-containing atmosphere includes ammonia.

5. The preparation method according to claim 3, characterized in that, The flow rate of the gas in the nitrogen-containing atmosphere is 10-300 mL / min.

6. The preparation method according to claim 1, characterized in that, The calcination temperature is 800-1000℃.

7. The preparation method according to claim 1, characterized in that, The calcination time is 0.5-60 hours.

8. The preparation method according to claim 7, characterized in that, The calcination time is 8-15 hours.

9. The preparation method according to claim 1, characterized in that, The heating rate for calcination is 5-10℃ / min.

10. The preparation method according to claim 1, characterized in that, The calcination atmosphere is an oxygen atmosphere. The oxide precursor obtained after calcination is subjected to nitriding treatment to obtain the metal nitride.

11. The preparation method according to claim 10, characterized in that, The calcination temperature is 600-1500℃.

12. The preparation method according to claim 11, characterized in that, The calcination temperature is 900-1200℃.

13. The preparation method according to claim 10, characterized in that, The calcination time is 5-20 hours.

14. The preparation method according to claim 10, characterized in that, The nitriding treatment is carried out in a nitrogen-containing atmosphere, the gas in which ammonia is present.

15. The preparation method according to claim 10, characterized in that, The nitriding treatment temperature is 200-1500℃.

16. The preparation method according to claim 15, characterized in that, The nitriding treatment temperature is 800-1000℃.

17. The preparation method according to claim 10, characterized in that, The nitriding treatment time is 0.5-60 hours.

18. The preparation method according to claim 17, characterized in that, The nitriding treatment time is 8-15 hours.

19. The preparation method according to claim 10, characterized in that, The heating rate for the nitriding treatment is 5-10 °C / min.

20. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) The photocatalyst precursor and molten salt are mixed and calcined in a nitrogen-containing atmosphere at a flow rate of 10-300 mL / min for 0.5-60 h to obtain the nitrided product. The calcination temperature is 600-1500 °C; or, The photocatalyst precursor and molten salt were mixed and calcined in an oxygen atmosphere at 600-1500℃ for 5-20h. Then, the mixture was subjected to nitriding treatment in a nitrogen-containing atmosphere at a flow rate of 10-300mL / min for 0.5-60h at a temperature of 200-1500℃ to obtain the nitrided product. (2) The nitrided product is cleaned and dried to obtain metal nitride, i.e., narrow bandgap photocatalyst.

21. A narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2, characterized in that, The narrow bandgap photocatalyst is prepared using the preparation method described in any one of claims 1-20.

22. The narrow bandgap photocatalyst according to claim 21, characterized in that, The narrow bandgap photocatalyst has a bandgap of 1.65-2.5 eV.

23. The application of a narrow bandgap photocatalyst for catalyzing the reduction and conversion of CO2 as described in claim 21 or 22, characterized in that, The specific steps for using the narrow bandgap photocatalyst to catalyze the CO2 reduction and conversion reaction include: A narrow bandgap photocatalyst, CO2, and an electron donor are mixed to carry out a CO2 reduction and conversion reaction.

24. The application according to claim 23, characterized in that, The total volume fraction of the electron donors H2 and CO2 is 1-50%.

25. The application according to claim 24, characterized in that, The total volume fraction of the electron donors H2 and CO2 is 10-25%.

26. The application according to claim 23, characterized in that, The temperature of the CO2 reduction and conversion reaction is 10-500℃.

27. The application according to claim 26, characterized in that, The temperature of the CO2 reduction and conversion reaction is 10-400℃.

28. The application according to claim 23, characterized in that, The narrow bandgap photocatalyst is surface modified before being mixed with CO2 and electron donors.

29. The application according to claim 28, characterized in that, The specific steps of the surface modification include: A modified narrow bandgap photocatalyst is obtained by mixing a surface modifier and a narrow bandgap photocatalyst.

30. The application according to claim 29, characterized in that, The surface modifier is a single-atom cocatalyst.

31. The application according to claim 29, characterized in that, Based on the mass of the modified narrow bandgap photocatalyst, the mass content of the surface modifier is 0.01-30 wt.%.

32. The application according to claim 30, characterized in that, The single-atom cocatalyst is Ru.

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