Simultaneous Growth of the SnO2 Nanostructure and Phase Transformation of the Carbon Nitride Matrix by a Hydrothermal Process for Efficient Solar Hydrogen Evolution

To construct the heterojunction photocatalyst, SnO2 nanostructures are deposited on carbon nitrides using a hydrothermal method in this work. Structural alternation of melon carbon nitride after the process is inspected when studying the charge transfer mechanism through the examination of the locations of photoreduced Pt cocatalysts at the heterostructures. Co-existence of melon and poly(heptazine imide) (PHI) structures in the carbon nitride matrix of the SnO2–carbon nitride heterojunction is further resolved by X-ray diffraction and solid-state nuclear magnetic resonance. It is indicated that the pristine melon carbon nitride is partially converted to PHI during the hydrothermal process in the absence of molten salt. Accordingly, the growth of a SnO2 nanostructure and phase transformation of the carbon nitride matrix are simultaneously driven under the hydrothermal condition. The produced SnO2–carbon nitride heterostructure, which possesses both SnO2-PHI and melon-PHI heterojunctions, demonstrates superior photocatalytic activity for H2 evolution to the pristine melon carbon nitride.