Origin of the Improved Photoelectrochemical and Photocatalytic Activity in a ZnO-TiO2 Nanohybrid Revealed by Experimental and Density Functional Theory Studies

Heterojunctions of metal oxides have attracted a great deal of attention as photo (electro) catalysts owing to their excellent photoactivity. While multiple fundamental studies have been dedicated to heteroaggregation, self-assembly of oppositely charged particles to obtain heterojunctions for energy applications has been underexplored. Herein, we report the synthesis of ZnO-TiO2 heterojunctions using the electrostatic self-assembly approach. The synthesized ZnO-TiO2 heterojunctions were characterized by using multiple experimental techniques. Density functional theory calculations were conducted to establish the heterojunction formation mechanism and electronic properties. The ZnO-TiO2 nanohybrid was tested for the photodegradation of rhodamine B dye and water splitting applications. The photocatalytic performance of the ZnO-TiO2 nanohybrid is 3.5 times higher than that of bare ZnO. In addition, the heterostructure exhibited an excellent photocurrent density of 2.4 mA cm–2 at a low onset potential during photoelectrochemical oxygen evolution. The performance improvements are attributed to the formation of the type II heterojunction between ZnO and TiO2, which suppresses carrier recombination and enhances carrier transport, boosting the catalytic activity.