Preparation Of Rod-like G-C₃N₄ Composite And Its Photocatalytic Hydrogen Production Properties

Among developed energy conversion strategies for hydrogen production,photocatalytic water splitting has been considered as an ideal pathway due to its low cost and abundance.Photocatalytic hydrogen production converts solar energy into hydrogen energy,has a higher energy density and is easier to store and transport.In the process of hydrogen production by catalytic reaction,it can fully meet the requirements of green,clean and pollution-free new energy conversion.Therefore,photocatalysis technology has become a research hotspot in the field of new energy.The choice of catalysts in photocatalytic hydrogen production is the most important factor affecting the yield.Graphite carbon nitride（g-C₃N₄）is a metal-free,non-polluting materials with low production cost,suitable band gap（2.7 e V）,which can be used to produce hydrogen and oxygen.However,the g-C₃N₄ prepared by the conventional method limits its high practicability due to problems such as less exposed active sites,low visible light absorption efficiency,and high recombination rate of photogenerated carriers.In this work,the intermediate melem was prepared by calcination of melamine by thermal condensation method,then the melem of hexagonal rod structure was prepared by ultrasonic assisted hydrothermal method,and g-C₃N₄ nanorods were prepared by calcining melem nanorods in air.g-C₃N₄ is controlled by microscopic morphology to obtain nanorod structure,and ammonium fluoride（NH₄F）and nickel sulfide（NiS）are respectively modified to g-C₃N₄ nanorods to obtain fluorine-doped g-C₃N₄ with higher photocatalytic hydrogen production activity.The composite photocatalysts were used to systematically study the preparation process,photoelectric properties and hydrogen production rate.The results show that the hydrogen generation performance of the samples doped with halogen elements has been improved.Compared with other halogen elements,the samples doped with fluorine have the highest photocatalytic hydrogen evolution activity.The specific surface area of fluorine-doped g-C₃N₄ can reach 149.40 m²/g,which is 8.2 times that of the bulk g-C₃N₄.The increase in specific surface area exposes more active sites and accelerates the efficiency of carrier separation and transfer.Fluorine doping reduces the band gap of g-C₃N₄,changes the band gap structure,and increases the light response range.The maximum hydrogen production rate of the modified composite was 2600μmol·g^-1·h^-1,and the quantum efficiency under the light of 420 nm reached 13.98%.NiS as a co-catalyst,replaces precious metal platinum,and is closely combined with rod-shaped g-C₃N₄ to form a heterostructure,which increases the visible light response range.The photo-generated electrons generated on g-C₃N₄ are quickly transferred to NiS,which suppresses the recombination of carriers and accelerates the charge transfer ability.The rod-like structure increases the specific surface area of the material,exposes more active reaction sites,and improves the hydrogen evolution efficiency of the composite photocatalyst.There is an optimal value for NiS loading.When the NiS loading is 3.5%,the highest hydrogen production activity is 325μmol·g^-1·h^-1.