Charge transfer in SnS₂/Na_0.9Mg_0.45Ti_3.55O₈ heterojunction in photocatalytic process

SnS₂/Na_0.9Mg_0.45Ti_3.55O₈ (SNMTO) composite photocatalyst was synthesized by a hydrothermal method. The chemical combination in lattice scale between SnS₂ and Na_0.9Mg_0.45Ti_3.55O₈ (NMTO) was observed by high-resolution transmission electron microscopy, indicating that heterojunctions were obtained between SnS₂ and NMTO. The photocatalytic activity of SNMTO heterojunctions was improved in comparison with that of pure NMTO and SnS₂ for the photocatalytic degradation of methylene blue and Rhodamine B. Electrons were excited in n-type semiconductors NMTO and SnS₂ under light illumination, and a part of them moved to the interface, determined with the surface potential reduction observed directly by Kelvin probe force microscopy. The charge redistribution in the composite illustrates a high density of interface states between SnS₂ and NMTO, which attract lots of photoelectrons, as a result enhancing the photocatalytic performance. This finding is very different from the speculation that the photogenerated electrons and holes migrate from one part to another because it is difficult for charge carriers to travel through the interface with high energy.