Preparation Of Ni₂P/g-C₃N₄ Catalyst And Its Photocatalytic Performance For Hydrogen Production

Converting solar energy into hydrogen?H₂?via water splitting over semiconductor photocatalysts is a promising pathway to mitigate the dependence on fossil fuels,while simultaneously resolving the environmental contamination issue.As a visible-light-responsive polymeric semiconductor material,graphitic carbon nitride?g-C₃N₄?has received extensive notice in virtue of its rich earth's surface content,convenient preparation methods,excellent chemical stability,appropriate band position,and environmental friendliness.However,pristine g-C₃N₄ normally suffers from the intrinsic bottlenecks such as small specific surface area,low photocatalytic activity,fast recombination rate of photo-generated electron-hole pairs,poor charge-carriers mobility and narrow visible light response caused by larger bandgap,which inevitably hampers its solar-to-hydrogen?STH?conversion efficiency.An important approach for overcoming these obstacles is incorporating suitable hydrogen evolution reaction?HER?co-catalysts on g-C₃N₄ surface.It is widely acknowledged that platinum co-catalysts is not suitable for large-scale commercial use.Transition metal phosphides?TMPs?eapecially Ni₂P is an alternative kind of HER co-catalysts for replacing platinum-based catalysts owing to its excellent electrical conductivity,and remarkable catalytic activity.Ni₂P is selected in this subject to study its promotion of hydrogen production of g-C₃N₄ material.Aiming at solving the above defects of pristine g-C₃N₄ material,a thermal oxidation etching process and physical self-assembly method was adopted in this paper.a kind of nanostructured semiconductor material with a larger specific surface area is prepared to provide more active sites for the photocatalytic reaction.In this paper,the thermal oxidation etching of bulk g-C₃N₄ material prepared by thermal polycondensation of melamine was studied,and two-dimensional porous g-C₃N₄ nanosheets material with larger specific surface area was prepared.And it is combined with Ni₂P nanocrystals with size of 8-10 nm prepared by one-step hot solvent method through simple physical self-assembly method.The introduction of Ni₂P nanocrystals provides more active sites for hydrogen evolution reaction,and accelerates the separation and migration of photogenerated electrons and holes inside the composite to a certain extent,thereby improving the performance of photocatalytic hydrogen productionAiming at solving the problem of the irregular uniformity of Ni₂P nanocrystal distribution and the tightness of connection with g-C₃N₄ nanosheets in the composite material prepared by self-assembly method,we developed a facile and convenient route to in-situ incorporate Ni₂P nanocrystals?NCs?co-catalysts on the surface of g-C₃N₄ nanosheets?NSs?via a co-heating reaction.Well-crystallized Ni₂P NCs with sizes of 8-10 nm were uniformly and tightly anchored on porous g-C₃N₄ NSs.Compared with the Ni₂P/g-C₃N₄ hybrid photocatalyst obtained by the physical self-assembly method,Ni₂P/g-C₃N₄ hybrid photocatalyst obtained by the in-situ loading method forms a strong chemical coupling bond Ni??+?-N??-?between the Ni₂P NCs and the g-C₃N₄ NSs.This chemical coupling is more conductive to extract the charge-carriers from semiconductor photocatalysts to co-catalysts for the rapid separation of the photo-generated electron-hole pairs,and Ni₂P NCs are not easily shedding from g-C₃N₄ NSs.Therefore,compared with the Ni₂P/g-C₃N₄ hybrid photocatalyst obtained by the physical self-assembly method,Ni₂P/g-C₃N₄ hybrid photocatalyst obtained by the in-situ loading method displays a superior photocatalytic H2 evolution activity and excellent durability.