Preparation Of Nitride Heterostructure And Its Photocatalytic Performance

With the development of the times,environmental and energy problems have become increasingly serious.Therefore,we urgently need to find a renewable way to obtain green and safe energy sources to alleviate the current severe situation.Photocatalytic technology is a solution to obtain renewable energy by solving the energy crisis by using renewable light energy,that is,solar energy.At this time,two-dimensional nitrides in many photocatalytic materials have gradually attracted researchers' interest because of their excellent performance in photoelectric conversion.Based on the unique morphology of its two-dimensional lamellae,it has a larger specific surface area and a thinner thickness than the bulk material.In this way,on the one hand,the transmission distance of photo-generated carriers is reduced,and on the other hand,more catalytic reaction active sites are provided,which greatly improves the performance of the photocatalytic reaction.In addition,compared with the traditional oxide photocatalyst,the nitride photocatalyst has a larger light absorption range.A larger light absorption range means more available sunlight,which greatly improves the utilization of solar energy.At the same time,recent studies on heterojunctions have found that the key control step in photocatalytic reactions can greatly improve the separation and migration rate of photogenerated carriers.Generally speaking,by forming a heterogeneous structure,the photo-generated carriers generated by one of the materials are transferred to the surface of the other material to occur the redox reaction.Since the lifetime of photo-generated carriers excited by light is extended,the serious recombination problem of photo-generated carriers is reduced.In addition,the heterostructure can also use a narrow band gap and wide band gap photocatalyst to make a narrow band gap photocatalytic material as a light absorbing material,widen the light absorption range of the catalyst and ultimately improve the photocatalytic performance.Based on the modification of nitride materials,a new type of broadspectrum photocatalyst was synthesized by low-dimensionalization,heterostructure construction,and doping with other elements,which is used to realize photocatalytic synthesis of green energy.It mainly includes the following aspects:The first photocatalyst is based on the preparation of black phosphorustungsten nitride heterostructure and its photocatalytic performance.In this section,a ball-milled 2D black phosphorus?BP?and tungsten nitride nanosheet?WN?heterostructure are constructed by ball milling for photocatalytic broadspectrum hydrogen evolution.Traditional photocatalysts are difficult to achieve water decomposition in the near-infrared spectrum,and we can overcome this difficulty by introducing a continuous photonic structure of the conductor photocatalyst WN.Without any precious metal cocatalyst and sacrificial agent,the precipitation rate of hydrogen?H₂?of BP-BM/WN under light radiation of ?> 700 nm is 10.77 ?molg^-1h^-1,which is nearly 8 times of WN 5 times of BP-BM.In addition,the existence of heterojunctions was proved by HRTEM and photoelectrochemical experiments.It is also proved that the formation of heterojunctions improves the separation and transfer of photogenerated carriers and broadens the absorption range of photocatalytic materials.It provides new research ideas for the synthesis of noble metal-free photocatalysts with nearinfrared light response.The second photocatalyst is the research of formic acid modified carbon nitride for photocatalytic carbon dioxide?CO₂?reduction.In this section,formic acid is used to introduce carbon element into the carbon nitride precursor through the oil bath method,and the final catalyst material is fired in the last step to reduce CO₂ by visible light.Compared with pure carbon nitride samples,the obtained formic acid modified carbon nitride samples greatly broadened the photo-absorption range and significantly enhanced the photocatalytic reduction of CO₂.Under visible light irradiation,the CO₂ reduction rate of formic acidmodified carbon nitride produces CO at a rate of 1.266 ?molg^-1h^-1,which is about four times that of ordinary carbon nitride.Through photoelectrochemical experiments and fluorescence spectroscopy,it was found that the photoelectric conversion ability of carbon nitride was enhanced after formic acid modification.And it can also proved that the lifetime of photo-generated carriers was extended.