| Hydrogen is the most widely distributed element in the universe,which constitutes 75%ofthe mass of the universe.Therefore,hydrogen energy is called the ultimate resource of human beings.Water is a natural reservoir of hydrogen.If using solar energy photocatalytic water splitting to produce hydrogen,it is undoubtedly the most environmentally friendly and ideal way to achieve the development of hydrogen energy,which has attracted great attention.Due to the recombination of photo-generated electron-hole pairs,even for a single semiconductor with good photo-response performance still presents low photocatalytic efficiency.In general,a multi-component photocatalyst composed of high efficiency photocatalyst and suitable cocatalyst is an effective way to achieve high photocatalytic activity.The cocatalyst supported on the photocatalyst can effectively capture the photo-generated carrier,inhibit the charge recombination,provide fine designated sites for surface redox reaction and optimize the kinetics of hydrogen proton reduction.This thesis takes the cocatalyst in the field of photocatalysis as the research object,explores and synthesizes transition metal phosphide non-noble metal cocatalyst with low-dimensional nanostructures,and constructs a series of composite photocatalysts with nano-heterojunction modified by low-dimensional transition metal phosphides.And the composite photocatalysts were used for photocatalytic H2 generation from water splitting under visible light.A series of characterization techniques including XRD,PL,N2adsorption-desorption,SEM,TEM,FT-IR,UV-vis DRS,XPS,and electrochemistry were used to study the effects of preparation conditions on the morphology,crystal structure,optical properties,electrical properties and catalytic performance of the photocatalyst.The methods and means of controlling the morphology and structure of the cocatalyst were explored,and the relationship between the structure and performance of the composite photocatalyst was discussed.The main research results are as follows:（1）0D/2D Ni2P quantum dots（QDs）/red phosphorus（red P）nanosheets composite photocatalyst:Ni2P QDs/red P nanosheets composite photocatalyst was synthesized by one-pot in-situ hydrothermal method.The effect of Ni2P QDs loading content on the photocatalytic H2 evolution activity of the composites was investigated in detail.The results showed that under the irradiation of a 300W Xe lamp with a 420 nm filter,using methanol aqueous solution as a sacrificial reagent,the 0.1Ni2P/red P showed the highest hydrogen production rates(265.43μmol·g-1·h-1),which is 38.58 times higher than pure red P and 3.61times higher than red P loaded with 1 wt%Pt.Research suggested that red P nanosheets with the 2D anisotropy have novel electronic structures and distinctive physicochemical properties,such as high electron mobility,prolonged photogenerated charge lifetime and extremely high percentage of exposed active sites.Ni2P QDs were synthesized and highly dispersed on the surface of red P nanosheets,resulting in the formation of tremendous photocatalytic active sites.During the photocatalytic reaction,driven by the internal electric field of the p-n heterojunction formed by n-type Ni2P QDs and p-type red P nanosheets,the electrons in the CB of Ni2P QDs transferred rapidly to red P nanosheets and then reduced H+into H2.The formation of p-n heterojunction not only effectively reduced the recombination rate of photogenerated electron-hole and improved the photocatalytic activity,but also promoted the migration of photogenerated hole from red P nanosheets to Ni2P QDs,inhibited the photo-corrosion of red P and improved the stability of the composite catalyst.（2）2D-0D layered Fe2P-Cd0.5Zn0.5S（CZS）nanoparticles composite photocatalyst:The Fe2P-CZS composite photocatalyst was constructed via a two-step solvothermal method.The effect of different content of Fe2P on the photocatalytic H2 evolution activity of the composites was investigated.The results showed that under the irradiation of a 300W Xe lamp with a 420 nm filter,using lactic acid aqueous solution as a sacrificial reagent,the 13 wt%Fe2P-CZS displayed the best hydrogen production rate(24.84 mmol·g-1·h-1),which is 37.6times higher than that of CZS.Compared to Fe2P particles,the layered Fe2P with a thickness of 3.1 nm exhibited more excellent conductivity and lower overpotential.The layered Fe2P-modified CZS not only improves its photo-response ability and inhibits the recombination of photogenerated electron-hole pairs,but also improves the redox capacity of photocatalyst;so that the composite photocatalyst exhibited excellent photocatalytic performance.（3）2D-1D ultra-thin Fe2P nanosheets-CdS nanorods composite photocatalyst:the raw material red phosphorus was further purified and then the ultrathin Fe2P nanosheets with a thickness of about 1.41 nm were prepared by solvothermal method.Moreover,the Fe2P nanosheets-CdS nanorods composite photocatalyst was successfully constructed.In the lactic acid aqueous solution system,the effect of Fe2P nanosheets content on the performance of the composite photocatalyst was tested.The results showed that under the irradiation of a 300W Xe lamp with a 420 nm filter,the 11 wt%Fe2P-CdS displayed the best hydrogen production rate(207.82 mmol·h-1·g-1),which is 78.6 times that of CdS.Research suggested that the ultra-thin Fe2P nanosheets-modified CdS photocatalyst provided structural advantages,light absorption advantages,and reduction kinetic advantages for the photocatalytic hydrogen evolution reaction.Among them,1D CdS with length-to-diameter ratio has excellent light absorption ability;Fe2P nanosheets co-catalyst has high electron mobility and percentage of exposed active sites due to its ultra-thin 2D structure;the composite photocatalyst with2D-1D heterojunctions is conducive to photoexcited carrier separation.Moreover,Fe2P-CdS photocatalyst showed a lower hydrogen proton reduction overpotential,which provided better reduction kinetic advantage for hydrogen evolution reaction.（4）2D-0D Co2P nanosheets-Cd0.5Zn0.5S nanoparticles composite photocatalyst:Co2P nanosheets with regular morphology were successfully prepared by simple solvothermal method and the effect of the cobalt-phosphorus ratio on the nanostructure of Co2P products was investigated via adjusting the molar ratio of raw materials cobalt acetate and red phosphorus.2D-0D Co2P nanosheets-Cd0.5Zn0.5S nanoparticles composite photocatalyst was constructed through a two-step solvothermal method.The introduction of Co2P nanosheets promoted the light absorption,optimized the electrical conductivity and reduced the hydrogen evolution potential of the composite photocatalyst.The results showed that the 13wt%Co2P（8）-CZS composites exhibited the highest hydrogen evolution activity(68.02 mmol h-1·g-1),which is 103 times that of CZS.（5）2D-1D Co2P nanosheets-CdS nanorods composite photocatalyst:2D-1D Co2P nanosheets-CdS nanorods composite photocatalyst was prepared by two-step hydrothermal method,and the effect of Co2P content on the performance of the composite catalyst was tested.The results showed that the introduction of 2D Co2P nanosheets improved the light absorption,carrier separation efficiency,light response,electrical conductivity,and hydrogen evolution reduction kinetics of the catalyst.Therefore,the 2D-1D Co2P-CdS nanocomposite photocatalyst exhibited high photocatalytic activity.Especially the 13wt%Co2P-CdS composite exhibited the highest hydrogen production rate(239.14 mmol·h-1·g-1),which is 90.5 times that of CdS. |
