Anatase TiO 2 nanosheets with coexposed {101} and {001} facets coupled with ultrathin SnS 2 nanosheets as a face-to-face n-p-n dual heterojunction photocatalyst for enhancing photocatalytic activity

Abstract TiO2 is an n-type conductivity semiconductor because of numerous electron-producing oxygen vacancies forming in its lattice. Whenever TiO2 is coupled with other semiconductors to construct a heterojunction, an n–n heterojunction is always obtained for main semiconductors of n-type conductivity. Moreover, few electrons can transfer between the n–n heterojunction during carrier separation. In this study, anatase TiO2 nanosheets with coexposed {101} and {001} facets were coupled with ultrathin SnS2 nanosheets to construct face-to-face n–p–n dual heterojunctions. This TiO2/SnS2 composite has 47% better photocatalytic activity than pristine TiO2 nanosheets. For comparison, P25 with exposed {101} facets/SnS2 nanosheets with an n–n single heterojunction photocatalyst was obtained and show weaker photocatalytic activity with a ratio of 31%–43% than that of P25. The results confirm that anatase TiO2 nanosheets with coexposed {101} and {001} facets of photocatalysts are critical in constructing heterojunctions. First, the 2D/2D nanosheet shape of TiO2 and SnO2 can form a face-to-face structure heterojunction that can enlarge the contact area between two semiconductors. Second, the {001} facets of SnS2 coupled on the high surface energy {001} facets of TiO2 can form stronger binding compared with {101} facets. Therefore, the photo-induced carriers can easily transfer between the TiO2/SnS2 heterojunctions. Finally, a novel n–p–n dual heterojunction is constructed between anatase TiO2 nanosheets with coexposed {101} and {001} facets and SnS2 nanosheets. In the n–p–n dual heterojunction, photo-induced electrons in CB of {001} facets flowed into the {101} facets of TiO2; therefore, the electrons in CB of SnS2 can flow into the {001} facets of TiO2 to improve the separation efficiency of photo-induced carriers. Most metal sulfides and II–VI compound semiconductors are n-type conductivity; therefore, this work improves upon a new approach to construct heterojunctions with high carrier separation efficiency to enhance photocatalytic activity and other photoelectric properties.