Preparation Of G-C₃N₄-Based Z-Scheme Photocatalysts For Solar-Driven Water Splitting

Graphitic carbon nitride（g-C₃N₄）as a promising visible-light-responsive photocatalyst has received worldwide attention due to its unique electronic structure,included moderate bandgap（≈2.7 eV）and proper electronic band structure,nontoxicity,low cost,good stability,and easy preparation.However,even though the aforementioned advantages for g-C3N4,there is still severe recombination during their long transfer distance,which seriously limits the photochemical conversion.In this paper,three g-C3N4 based Z-scheme photocatalysts have been constructed:g-C₃N₄/Ag/Ag₃PO₄,g-C₃N₄/GDY/Ag₃PO₄ and g-C₃N₄/Ag/WO₃,the detailed works are as follows:（1）The photocatalytic activity were directly influenced by the change of surfa-ceatomic structure.Dodecahedron Ag₃PO₄,tetrahedron Ag₃PO₄,tetrapods Ag₃PO₄ and cubic Ag₃PO₄ were synthesized by precipitation method,X-ray diffraction（XRD）,transmission electron microscopy（TEM）,scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared（FTIR）,UV-Vis diffuse reflectance spectroscopy（UV-Vis DRS）,and surface photovoltage test（SPV）were employed to investigate the phase structure,micromorphology and electron hole separation rate.The correlation between photocatalytic activities and exposed facets were explored by directly split water under visible-light irradiation the results indicated that the exposed{111}facets of g-C₃N₄/Ag/Ag₃PO₄ exhibited the superior photocatalytic activity.Dodecahedron Ag₃PO₄ was chosen to synthesize Z-scheme g-C₃N₄/Ag/Ag₃PO₄photocatalysts by precipitation method.The crystal structure,morphology,optical absorption,and photocatalytic properties were investigated by XRD,TEM,SEM,XPS,FTIR,UV-Vis DRS,and SPV.The enhanced photocatalytic activities are ascribed to a new solid state electronics medium based Z-type photocatalysts g-C₃N₄/Ag/Ag₃PO₄ in which an improved separation efficiency of photogenerated electron-hole pairs.（2）Z-scheme g-C₃N₄/GDY/Ag₃PO₄ photocatalysts were synthesized by precipitation method after g-C3N4 and GDY are combined by ultrasonic method.The GDY serves as conductive electron bridges to collect photo generated electrons and boost the O₂ evolution.The composites were characterized by XRD,UV-Vis,TEM,SEM and so on.The O₂ evolution test indicated that the g-C₃N₄/0.05%GDY/Ag₃PO₄photocatalysts exhibited the highest O₂ evolution rates of 282μmol·g^-1·h^-1,which was11.48 and 1.88 times higher than that of Ag₃PO₄ and g-C₃N₄/Ag₃PO₄,respectively.The significantly enhanced O₂ evolution activity of multi-heterostructured g-C₃N₄/GDY/Ag₃PO₄ composites photocatalysts can be mainly ascribed GDY,which serves as the conductive electron bridges between g-C₃N₄ and Ag₃PO₄ co-catalysts for maximizing the O2 evolution,and improved the catalytic activity.（3）g-C₃N₄/WO₃ composite photocatalytic materials were successfully prepared by solvothermal method,then Z-scheme g-C3N4/Ag/WO3 were prepared on the basis of a silver mirror reaction.The structure,morphology and optical properties of g-C₃N₄/Ag/WO₃ composites were characterized by XRD,UV-Vis,TEM,SEM and so on.The O₂ evolution test indicated that when the usage amount of g-C₃N₄ was 0.01%,the photocatalytic activity of g-C₃N₄/Ag/WO₃ composites was the highest O₂evolution rates of 58.61μmol·g^-1·h^-1,which was 2.44 and 1.95 times higher than that of WO₃ and WO₃/Ag respectively.