Engineering Z-system hybrids of 0D/2D F-TiO2 quantum dots/g-C3N4 heterostructures through chemical bonds with enhanced visible-light photocatalytic performance

Abstract

Constructing a direct Z-scheme system for photocatalysts is a promising strategy to enhance photocatalytic redox performance owing to its effective charge transfer; however, building a reasonable interfacial charge transfer bridge for charge selective recombination is still a challenge. Herein, a F-doped TiO₂ quantum dot/g-C₃N₄ nanosheet Z-scheme photocatalyst is synthesized via a facile method of fluorine-containing solvothermal treatment. In this Z-scheme structure, F-TiO₂ quantum dots (QDs, 3–7 nm) are bridged with g-C₃N₄ nanosheets through C–O covalent bonds. Thus, the oxidizability and reducibility of the composite photocatalyst and the interfacial charge transfer ability are greatly improved. Meanwhile, the TiO₂ quantum dots provide more active sites and enhance the light harvesting, which are both beneficial for the photocatalytic reaction process. In this designed catalyst, the C–O covalent bond, as a chemical group bridge, provides an effective pathway for charge transfer and selective recombination, which greatly enhances the utilization of photogenerated electrons and holes. As a result, the FT/CNS-1-2 photocatalyst shows the highest photocatalytic activity for photocatalytic rhodamine B (RhB) decomposition, Cr(VI) reduction and phenol decomposition under visible light irradiation, which are about 17.1/4, 16/5.3 and 23.5/4.4 times higher than those of pure F-TiO₂/g-C₃N₄, respectively. The excellent photocatalytic activity is mainly ascribed to the Z-scheme charge transfer model, which greatly enhanced the separation and transfer of charge carriers. In addition, the trapping experiments found that ˙O₂⁻ and ˙OH are the dominant active species in the photocatalytic process. This study of the chemically bonded Z-scheme F-TiO₂/g-C₃N₄ photocatalyst provides ideas for the fabrication of such TiO₂ QD based materials and a Z-scheme system for effective change transfer in photocatalysis processes.