Preparation Of Bimetallic Oxide/g-C₃N₄ Photocatalytic Materials And Study On Their Photocatalytic Performance

Hydrogen energy,which is defined by the International Energy Agency as"advanced"energy,is an ideal high-quality clean energy source.At present,hydrogen is mainly derived from the steam reforming process of fossil energy.However,over-reliance on fossil fuels has caused a series of environmental problems,such as greenhouse effect,acid rain,water pollution and so on.Therefore,it is very urgent to develop a green hydrogen production technology to solve energy shortage and environmental problems.Currently,photocatalytic technology is considered to be an ideal way to obtain hydrogen from water using solar energy.Traditional photocatalysts,such as Ti O₂,can only absorb ultraviolet light due to its wide bandgap;Cd S is prone to photocorrosion and contains heavy metal elements,which is not conducive to practical applications.Graphite-phase carbon nitride（g-C₃N₄）with a two-dimensional layered structure has attracted the interest of researchers due to its high physical and chemical stability,suitable band structure,and and visible light response.However,the shortcomings of its visible light absorption capacity（λ<470 nm）,small specific surface area,poor conductivity,and high photo-generated carrier recombination rate limit its photocatalytic hydrogen production performance.Moreover,photocatalytic reaction is a complex heterogeneous catalytic process,and it is extremely difficult to achieve high hydrogen production efficiency with single-component materials.Generally,the photocatalytic performance of g-C₃N₄ is improved by combining with other semiconductors to build a heterojunction.In recent years,transition bimetallic oxides have attracted extensive attention because of their excellent photoelectric properties and potential applications.Bimetal oxides have higher electrical conductivity and lower hydrogen-producing overpotential than single metals,and a variety of different valence cations can provide rich surface redox sites.Based on the above analysis,MCo₂O₄（M:Ni,Cu）/g-C₃N₄ heterojunction was constructed for photocatalytic decomposition of water to produce hydrogen.The main research contents and results are as follows:（1）Ni Co₂O₄ nanoparticles were supported on g-C₃N₄ nanosheets by in-situ calcination.The photocatalytic hydrogen production experiment results show that the 17.5wt%-Ni Co₂O₄/g-C₃N₄ sample shows excellent photocatalytic performance and its hydrogen production rate within 5 hours is 5480μmol?g^-1?h^-1,which is better than that of Co₃O₄/g-C₃N₄,Ni O/g-C₃N₄ and Pt/g-C₃N₄ composite samples.Ni Co₂O₄/g-C₃N₄ remained high activity after 20 hours of light exposure.Under 400（±7.5）nm light irradiation,the quantum efficiency of 17.5 wt%-Ni Co₂O₄/g-C₃N₄ can reach 4.5%.The results show that the electron-hole transfer path of Ni Co₂O₄/g-C₃N₄ composite sample follows the Z-scheme. recombine in space charge region,at the meantime,the e^-in conduction band of Ni Co₂O₄and h⁺in valence band of g-C₃N₄ will be preserved for water reduction and for oxidation of triethanolamine（TEOA）,respectively,which can effectively inhibit the photogenic carrier recombination.Moreover,the coexistence of nickel ions and cobalt ions gives those richer active sites and better carrier transport performance,which greatly improves the photocatalytic performance of composite samples.（2）A method for in-situ deposition of Cu Co₂O₄ nanoparticles on a two-dimensional g-C₃N₄surface has prepared a g-C₃N₄ heterojunction photocatalyst supported by highly dispersed Cu Co₂O₄ nanoparticles.The optimal composite hydrogen production rate of Cu Co₂O₄/g-C₃N₄ can reach 4187.6μmol?g^-1?h^-1,which is significantly higher than that of Co₃O₄ and Cu O modified g-C₃N₄ in the TEOA sacrificial agent.Based on photoelectrochemical characterization and NH₃-TPD analysis,it was found that Cu Co₂O₄/g-C₃N₄ has faster surface reaction kinetics and more surface acid sites on the surface,which is beneficial to the rapid precipitation of H₂ from the catalyst surface and and the chemical adsorption of TEOA on the catalyst surface.In addition,the transfer pathways of charge carriers at the interface between Cu Co₂O₄ and g-C₃N₄ were also studied.It was verified by photodegradation of Rh B and photodeposition of Pt nanoparticles,proving that the transfer path of charge carriers of Cu Co₂O₄/g-C₃N₄photocatalysts all conform to the Z-scheme transfer mechanism.