Structure Design And Photocatalytic Oxidation Of NO Properties Of Novel Mxenes-based Catalysts

The traditional industrial nitrogen fixation method,the Haber-Bosch method,accounts for about 1%to 2%of global power consumption and greenhouse gas emissions,and emits a large amount of polluting gases in the process of production and transportation.At present,there are some shortcomings in the technology for the treatment of nitrogen oxide?NO_x?,such as high price of reducing agent NH₃,high operating cost,secondary pollution caused by NH₃ leakage and strict temperature requirements of the catalyst.The development of industrial nitrogen fixation technology at room temperature and pressure is very important for human beings to achieve sustainable development.Although some progress has been made in photocatalytic nitrogen fixation in the past,there is still a big gap between photocatalytic nitrogen fixation and practice,which needs further research.In this paper,a new two-dimensional carbide crystal?MXene?was selected as the main material to study the photocatalytic oxidation of NO performance.MXene is recombined with semiconductors with different bandgap widths to produce new semiconductor materials.The valence band,conduction band and band gap of semiconductors overlap due to the inconsistency of valence band,conduction band and band gap energy,so as to improve the separation rate of photogenerated electrons and holes,and then improve the photoelectric nitrogen fixation performance of the materials.In this paper,three kinds of MXene-based heterojunction catalysts were prepared and used in photocatalytic oxidation of NO,and the photocatalytic mechanism of each system was also discussed,which provides a reference for the application of MXene-based catalysts in the field of photocatalytic nitrogen fixation.The main results are as follows:?1?Study on the photocatalytic activity of Bi₂O₃/V₂C MXene under visible light.Flower-like Bi₂O₃ and two-dimensional multilayer V₂C were compounded by hydrothermal method.Compared with the single sample,the specific surface area of Bi₂O₃/V₂C MXene-2 is increased,which is favorable to improve the photocatalytic efficiency,but it is not the key factor to improve the photocatalytic performance of the system.The analysis of UV-vis absorption spectrum and band gap energy estimation shows that the construction of heterojunction broadens the light response range,improves the light absorption capacity,and obtains a narrower band gap than a single component,which is beneficial to the utilization of light.PL,TPC and EIS analysis revealed that Bi₂O₃/V₂C MXene had a strong carrier mobility,which further confirmed that the photocatalytic oxidation performance of the system was dominant in the photocatalytic oxidation of NO reaction.?2?Study on the performance of MIL-100?Fe?/Ti₃C₂ MXene photocatalytic oxidation of NO.The octahedral MIL-100?Fe?has a large specific surface area of 1965.0 m²g^-1.With the addition of MIL-100?Fe?,M/T-x catalyst has large specific surface area and high adsorption performance.The increase of adsorption capacity is helpful to improve the photooxidation efficiency of NO.Ti³⁺in MIL-100?Fe?/Ti₃C₂ MXene can also be used as the adsorption site of NO and photoelectron capture site.Comparative analysis of the XPS,of composite catalysts before and after photocatalytic reaction showed that the relative contents of C=O and-COO functional groups of MIL-100?Fe?/Ti₃C₂ MXene were increased after photocatalytic reaction,and these functional groups could promote the photocatalytic oxidation of NO.The UV-vis absorption spectrum shows that the light trapping ability of the composite catalyst is enhanced and the band gap becomes narrower.The phototrapping ability and photothermal effect are important causes of the synergistic effect of M/T-x catalysts,and these enhanced abilities are attributed to the blackbody effect of Ti₃C₂ MXene components.Schottky heterojunction provides an effective channel for rapid charge transfer in photochemical reaction.The charge transfer caused by different Fermi levels of MIL-100?Fe?and Ti₃C₂ MXene produces a depletion layer,which can be used as an energy barrier to prevent electrons from returning to MIL-100?Fe?,thus reducing the carrier recombination rate.Due to the synergistic effect of adsorption and photocatalysis,MIL-100?Fe?/Ti₃C₂ MXene showed outstanding photocatalytic oxidation of NO performance.?3?Study on the performance and mechanism of Ti₃C₂ MXene QDs/SiC photocatalytic oxidation of NO.Ti₃C₂ MXene QDs/SiC is used in the field of photocatalytic nitrogen fixation,and a high oxidation of NO efficiency of 74.6%is achieved at room temperature without adding auxiliaries.According to XPS and FTIR,there are terminal Ti atoms in Ti₃C₂ QDs/SiC heterostructures,which can give Ti₃C₂ MXene QDs stronger redox ability than other quantum dots.From anode photocurrent obtained by TPC test and the Mott-Schottky diagram,we know that Ti₃C₂ MXene QDs,SiC and Ti₃C₂ MXene QDs/SiC are all n-type semiconductors,so their E_FB is equal to E_F.The distance between the maximum value of VB and E_F is obtained through the valence band XPS,and the VB and CB are calculated according to the formula.The energy band structure shows that the CB energy level of Ti₃C₂ MXene QDs/SiC-20 is more negative than E?O₂/·O₂^–?,so it can produce·O₂^–.The valence band potential is higher than E?NO/NO₃^-?,so the valence band h⁺can directly oxidize NO to NO₃^-.