Nanostructure Regulation Of Vanadate Photocatalytic Materials And Their Research On Photocatalytic Properties

With the rapid development of the global economy and the continuous growth of the population,energy demand and environmental issues have increasingly attracted great concerns from various countries.Photocatalytic technology includes photocatalytic reduction of CO₂ to hydrocarbon fuel,nitrogen fixation to synthesize ammonia,and water splitting into H₂ and O₂,etc.It is one of the effective methods to solve energy shortage and environmental pollution.The photocatalytic reaction needs to meet the requirements of thermodynamics and kinetics.On the one hand,the photocatalytic material must have a small band gap,fully absorb solar energy,and generate electron-hole pairs.On the other hand,the photocatalytic material must have redox capability to ensure the successful progress of photocatalytic reactions.At present,serious photogenerated carriers recombination is the main scientific problem in photocatalysis technology.The starting point of this paper is to improve the separation ability of photogenerated electrons and holes on the basis of ensuring that photocatalytic materials meet thermodynamics and kinetics.Vanadate is an excellent new type of photocatalytic material and has broad application prospects in the field of photocatalysis.Adjust the size,dimension and build composite structure of vanadate photocatalyst,so as to achieve the purpose of improving its photocatalytic efficiency.The main research contents are as follows:(1)Atomically-thin,single-crystalline InVO₄ sheets with the uniform thickness of?1.5 nm were convincingly synthesized,which was identified with strong,low-angle X-ray diffraction peaks.The InVO₄ atomic layer corresponding to 3 unit cells along[110]orientation exhibits highly selective and efficient photocatalytic conversion of CO₂ into CO in the presence of water vapor.Surface potential change measurement and liquid photoluminescence decay spectra confirm that the atomically ultrathin structure can shorten the transfer distance of charge carriers from the interior onto the surface and decrease the recombination in body.It thus allows more electrons to survive and accumulate on the surface,which is beneficial for activation and reduction of CO₂.In addition,exclusively exposed{110}facet of the ultra-thin In VO₄ was found to bind the generating CO weakly,facilitating quick desorption from the catalyst surface to form free CO molecules,which provides an ideal platform to catalytically selective CO product.(2)The unique In VO₄ mesocrystal superstructure particularly with cubical skeleton and hollow interior were successfully fabricated,which may be considered one of the most complex synthetic nano-assemblies.This fascinating superstructure consists of numerous nanocube building blocks,closely stacking by stacking,aligning by aligning,and sharing the same crystallographic orientations.Through meticulously tracing the evolution process and close inspection of the intermediates,the synergy of a reaction-limited aggregation and an Ostwald ripening process is reasonably proposed for the growth of this unique superstructure.The single-particle surface photovoltage spectroscopy measurements demonstrate that the long-range ordered mesocrystal superstructures can significantly retard the recombination of electron-hole pairs through creation of a new pathway for anisotropic electron flow along the inter-nanocubes.This promising charge mobility feature of the superstructure greatly contributes to the pronounced photocatalytic performance of the In VO₄ mesocrystal toward fixation of N₂ into NH₃ with conversion efficiency almost four times that of dispersed nanocube analog and eight times that of the corresponding bulk materials,respectively.In addition,the excellent photocatalytic activity was also derived from existence of the rich mesopores in the mesocrystal skeleton,originating from gaps among the stacking nanocubes.Those mesopores not only provides abundant active catalysis sites,but also shortens the distance of charge carriers charge diffusion onto the surface and decreases the recombination in body,and allows efficient mass transport of reactants and products.The hollow interior also acts as a potential photon trap well to allow the multi-scattering of incidence light to trap more photons to generate more electron-hole pairs for enhancement photo-to-energy conversion.(3)We design a direct Z-scheme photocatalyst nanostructure through assembling ultrathin ZnIn₂S₄ nanosheets onto the surface of BiVO₄ by a hydrothermal treatment.The charge transfer ability of the ZnIn₂S₄/BiVO₄ composite structure was tested by liquid photoluminescence decay curve and photoelectrochemical performance.Compared with the single ZnIn₂S₄ and pure BiVO₄,the ZnIn₂S₄/BiVO₄ photocatalyst has a longer PL life,greater photocurrent intensity,and smaller photoelectrode resistance,which shows that Z-scheme structure can effectively promote the recombination of holes in the valence band of Zn In₂S₄ and electrons in the conduction band of BiVO₄.Therefore,a large number of electrons remain in the conduction band of ZnIn₂S₄,thereby enhancing the photocatalytic CO₂ reduction performance.