Study On The Photocatalytic Hydrogen Production Of Morphology-modified Nano-g-C₃N₄ And The Heterojunction With MoS₂

Photocatalysis,which can convert solar energy into other forms of energy and decompose pollutants under light,can be used as a potential solution to the energy crisis and environmental pollution problems.g-C₃N₄ is a promising photocatalyst,however,there are some disadvantages hindering its further practical application,such as the high recombination rate of charge carriers and the necessity of Pt as the co-catalyst.Therefore,the modification of g-C₃N₄ itself and the fabrication of g-C₃N₄/MoS₂heterostructure are significant in improving the photocatalytic hydrogen production performance and reducing the cost as well.In this paper,the bulk g-C₃N₄ can be etched into g-C₃N₄ nanosheets after being re-calcinated in the air at high temperatures?500⁵20^oC?.The influence of calcination time on the optical absorption,the carrier separation rate and the photocatalytic activity of g-C₃N₄ were investigated.With increasing calcination time,the absorption of g-C₃N₄nanosheets was slightly blue-shifted;whereas the separation efficiency of electron-hole pairs was improved.By adjusting the experimental parameters and testing the photocatalytic hydrogen production performance,the optimal calcination time of g-C₃N₄ nanosheets was determined to be 3 hours.Moreover,g-C₃N₄/MoS₂ heterostructure can be fabricated by thermal drying of MoS₂ nanosheets and g-C₃N₄ nanosheets.The relevant properties of the heterostructure were characterized by UV-Vis absorption,fluorescence spectroscopy and hydrogen production tests,which indicating that MoS₂can effectively improve the performance of g-C3N4 nanosheets and partially replace nobel metal catalyst Pt.In order to optimize the photocatalytic hydrogen production performance of g-C₃N₄,three-dimensional?3D?g-C₃N₄ decorated with cyano groups was prepared by the salt template freeze-drying process.The effects of the raw material ratio on the microstructure of g-C₃N₄ network,the utilization of photo-generated carriers,photocurrent and hydrogen evolution were studied.It showed that with decreasing thiourea concentration in the precursor,the thickness of g-C3N4 in 3D network became smaller and the photocatalytic hydrogen production performance was improved gradually.The optimal experimental parameters were determined as the mass ratio of thiourea to sodium chloride was 1:20.Furthermore,the heterostructures were formed by thermal drying of MoS₂ nanosheets and 3D g-C₃N₄ decorated with cyano groups.The variation of hydrogen production indicated that the dosage of MoS₂ was involved with the specific surface area of g-C₃N₄.In this paper,the self modification of g-C₃N₄ was realized by constructing g-C₃N₄ nanosheets and 3D g-C₃N₄.The g-C₃N₄/MoS₂ heterostructure prepared by thermal dry methodcan further enhance the photocatalytic hydrogen production performance,partially replace Pt catalyst and reduce the cost of practical applications.