Performance Regulation And Mechanism Exploration Of 2D Nb₂CT_x Modified W₁₈O₄₉ In CO₂ Photocatalytic Reduction

According to the artificial photosynthesis,the photocatalytic technology by solar-driven is the conversion of carbon dioxide（CO₂）into high value-added hydrocarbon fuels by using efficient semiconductors,which is expected to provide the technical support for the major national strategy of"carbon peaking and carbon neutrality".The solar-driven photocatalytic reduction of CO₂ possesses limitations including complex reaction pathways,low catalytic activity,and scarcity of high-value products.The efficient and stable photocatalysts are crucial for determining the reaction pathways,catalytic efficiency,and reduction products.At present,there are relatively few photocatalysts that directly and efficiently convert CO₂ into liquid fuels with high energy density such as methanol（CH₃OH）through a multi-electron reaction pathway.Therefore,the accurate design and controllable construction of photocatalysts have important scientific significance and potential application value,and it is also the key to improving the photocatalytic CO₂ conversion efficiency to generate CH₃OH.Oxygen-rich W₁₈O₄₉ semiconductor is considered to be a candidate in the field of photocatalytic CO₂ reduction due to its local surface plasmon resonance effect and broad-spectrum solar energy absorption and utilization ability.However,the bulk phase recombination of photogenerated carriers is prone to occur during the CO₂ photocatalytic reaction,resulting in a decrease in the number of photogenerated charges,which makes it difficult to drive the multi-electron-proton coupling transfer reaction.So,it makes the reduction products more complex,including Carbon monoxide（CO）,Hydrogen（H₂）,methane（CH₄）and so on.In this paper,the nanocomposite photocatalyst of W₁₈O₄₉/Nb₂CT_x was constructed through the controlled assembly of W₁₈O₄₉ and two-dimensional niobium carbide（Nb₂CT_x）,and CH₃OH was produced by highly selective and highly active CO₂ reduction.Based on accelerating the separation and transport of photogenerated carriers by regulating the proton-electron coupling transfer process in the CO₂ reduction reaction.The main research contents of the paper are as follows:（1）Two-dimensional Nb₂CT_x were successfully prepared by improved chemical etching and intercalation.Subsequently,one-dimensional W₁₈O₄₉/two-dimensional Nb₂CT_x nanocomposite photocatalyst was successfully prepared by a solvothermal method using tungsten hexachloride as tungsten source,and one-dimensional W₁₈O₄₉ nanorods in-situ grew on the surface of two-dimensional Nb₂CT_x nanosheets by solvothermal method.Under simulated sunlight,the rate of reducing CO₂ to CH₃OH was 1744μmol·g^-1·h^-1,which was about 8 times higher than that of single-phase W₁₈O₄₉(225μmol·g^-1·h^-1).The ¹³C isotope tracing method confirmed that the carbon source in CH₃OH originated from CO₂.The EPR results showed that the introduction of Nb₂CT_x increased the electron concentration near the oxygen defect.XPS spectroscopy under illumination revealed that Nb₂CT_x acts as a photogenerated electron transport medium,accelerating charge separation transport between interfaces.In situ testing techniques（Near-Ambient Pressure-X-ray Photoelectron Spectroscopy,Diffuse reflectance infrared Fouier transform spectroscopy,Raman spectroscopy）confirmed the intermediates and reaction pathways of the reduction reaction.Theoretical calculation results further elucidate the mechanism of CH₃OH produced by the highly selective reduction of CO₂ reaction of the composite photocatalyst.（2）Using the synergistic strategy of transition metal doping and composite construction,the transition metal doped W₁₈O₄₉/Nb₂CT_x nanocomposite photocatalytic materials were constructed controllably,and further investigated the effects of different transition metal doped in the photocatalytic reduction.Different transition metals（Mn,Co,Ni）doped W₁₈O₄₉ were in situ grown on the surface of two-dimensional Nb₂CT_x nanosheets by the solvothermal method using transition metal chloride as the metal source and tungsten hexachloride as the tungsten source.Among them,Co-doped W₁₈O₄₉/Nb₂CTx showed the best photocatalytic activity.When the doping amount was 5%,the rate of CH₃OH in the CO₂ photoreduction reaction was 2965μmol·g^-1·h^-1.It was about twice higher than that of W₁₈O₄₉/Nb₂CTx and 13 times higher than that of single-phase W₁₈O₄₉.The results of transmission electron microscopy and elemental analysis confirmed the successful doping of transition metals.The photoelectrochemical test results show that transition metal doped accelerates the photogenerated charges separating and transporting.The transition metals doped induced the formation of impurity levels in W₁₈O₄₉,thereby optimizing its band structure and accelerating the CO₂ photoreduction reaction from the perspective of catalytic kinetics.