Heterojunctions Comprised of Graphitic Carbon Nitride Nanosheets and SnO₂ Nanoparticles with Exposed {221} Crystal Facets for Photocatalytic Hydrogen Evolution

The construction of graphitic carbon nitride (g-C3N4 or CN)-based heterojunctions for an enhanced photocatalytic performance has aroused extensive attention. However, junctions with specific crystal-facets-exposed metal oxides, which show unique properties, such as ledges, high-density atom steps, and dangling bonds, are rarely investigated. Herein, thermal exfoliated CN and octahedral stannic oxide (O-SnO2) nanoparticles are prepared by two-step calcination and one-step hydrothermal methods, respectively. Then the nanocomposite photocatalyst is obtained by a facile mixing approach. The SnO2 nanocrystals with well-designed morphology are uniformly dispersed on the surface of the CN nanosheets with a large specific surface area, which affords a sufficient interface to tailor the photoelectric and physicochemical features of the final composites. The combination of CN nanosheets and SnO2 nanoparticles exposed with {221} crystal facets is beneficial for the formation of a typical Z-type junction, thereby facilitating charge-carrier separation and transport and suppressing recombination of the photogenerated electron-hole pairs. As a consequence, photocatalytic hydrogen production of the CN/O-SnO2 heterojunction is enhanced compared with that of exfoliated CN nanosheets under visible-light irradiation (lambda > 420 nm). This work provides insight into boosting charge-carrier generation and transport in heterojunction photocatalysts by using metal oxides exposed to specific crystal facets.