Creation of an internal electric field in SnO2@ZnS-ZnSn(OH)6 dual-type-II heterojunctions for efficient NO photo-oxidation

Abstract

Well-designed heterojunction photocatalysts are promising high-performance materials, effective in inducing charge transfer to achieve a particular migration path and long-lasting carriers. However, the traditional binary heterojunction photocatalysts still show low-efficiency charge separation. Herein, we report a direct dual-type-II SnO2@ZnS-ZHS (ZHS = ZnSn(OH)6) ternary heterojunction, obtained by a facile in-situ face-to-face growth approach. Experimental results and density functional theory calculations reveal that the carrier dynamics of SnO2@ZnS-ZHS, with dual-type-II mechanisms, enables the photogenerated holes (h+) of SnO2 to migrate to the valence bands of ZHS and ZnS. This ensures that SnO2@ZnS-ZHS has twice as much oxidizing potential to produce enough hydroxyl radicals (·OH) to participate in NO oxidation reactions. With a unique dual-type-II ternary structure, SnO2@ZnS-ZHS shows the highest NO removal rate (44.5%) after 30 min, which is 23.5, 29.7 and 15.9 times higher than the values shown by the single components ZHS, SnO2 and ZnS, respectively. A reaction mechanism is proposed. The improved photocatalytic activity shows the advantages of the SnO2@ZnS-ZHS heterostructure as a promising candidate for ternary heterojunction design. [Figure not available: see fulltext.].