Preparation And Photocatalytic Performance Of G-C₃N₄/Co₃O₄ Composites

With the exhaustion of fossil energy and the increasingly prominent environmental problems,it is urgent to find a renewable and clean energy to alleviate the current energy situation.Photocatalytic water splitting to produce hydrogen can transform solar energy through a series of reactions in a certain medium,which iis the lowest energy consumption of hydrogen production technology at present.Therefore,the development of photocatalysts that can effectively convert solar energy into hydrogen energy is the focus of current research.Co₃O₄,as a common material of photocatalyst,is rarely used in the study of photocatalytic hydrogen production due to the mismatch of energy level structure.In this study,based on Co₃O₄,g-C₃N₄/Co₃O₄composite photocatalysts with p-n heterojunction were synthesized and optimized by an improved preparation process and applied it to the study of photocatalytic hydrogen production.Sheets Co₃O₄nanomaterials were prepared by hydrothermal synthesis using Co(NO₃)₂as cobalt source,H₂O₂as oxidant and Co(CH₂)₂as precipitator.The optimal Co₃O₄nanosheets preparation process was selected by comparing Co₃O₄synthesized at different temperatures(80?,100?,120?)and different times(8 h,10 h,12 h).It was found that the hydrothermal time and hydrothermal temperature had great influence on the performance of Co₃O₄nanosheets for hydrogen production by photocatalytic splitting of water.The photocatalytic performance of Co₃O₄nanosheets hydrothermally prepared at 120?for 12h was the best,and the hydrogen production rate was 29.5?mol?g^-1?h^-1.In order to further improve the photocatalytic performance of Co₃O₄catalyst,p-n heterojunctions were constructed on the basis of Co₃O₄to improve its catalytic performance.g-C₃N₄/Co₃O₄p-n heterojunctions photocatalysts were prepared by ultrasonic self-assembly combined with calcination based on Co₃O₄nanosheets prepared by hydrothermal method.The energy level structure of Co₃O₄nanosheets was adjusted by loading g-C₃N₄nanoparticles to meet the requirements of photocatalytic hydrogen production,and the g-C₃N₄/Co₃O₄composite photocatalyst with p-n heterojunction was synthesized,and the effect of its photocatalytic performance was studied.The results show that the tight p-n heterojunctions structure between Co₃O₄and g-C₃N₄can significantly promoting the photocatalytic activity of g-C₃N₄/Co₃O₄photocatalyst.The photocatalytic activity of g-C₃N₄/Co₃O₄photocatalyst was the best when the loading mass of g-C₃N₄was 20%,and the hydrogen production rate was 134.6?mol?g^-1?h^-1.The energy level structure and photoelectrical properties of g-C₃N₄/Co₃O₄photocatalyst with 20%load mass of g-C₃N₄were studied,and the mechanism of photocatalytic hydrogen production was proposed.The results showed that the energy level structure of Co₃O₄nanosheet was adjusted by loading g-C₃N₄nanoparticles to meet the requirements of photocatalytic hydrogen production.Moreover g-C₃N₄/Co₃O₄photocatalyst has better photocurrent intensity.In addition,g-C₃N₄/Co₃O₄showed better photocatalytic activity due to the construction of p-n heterojunction.