Construction of carbon nitride and MoS2 quantum dot 2D/0D hybrid photocatalyst: Direct Z-scheme mechanism for improved photocatalytic activity

Graphite-like carbon nitride (g-C3N4)-based compounds have attracted considerable attention because of their excellent photocatalytic performance. In this work, a novel direct Z-scheme system constructed from two-dimensional (2D) g-C3N4 nanoplates and zero-dimensional (OD) MoS2 quantum dots (QDs) was prepared through the combination of a hydrothermal process and microemulsion preparation. The morphologies, structures, and optical properties of the as-prepared photo catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectroscopy. In addition, the photocatalytic performances of the prepared 2D/OD hybrid composites were evaluated based on the photodegradation of rhodamine B under visible-light irradiation. The results demonstrated that the introduction of MoS2 QDs to g-C3N4 greatly enhanced the photocatalytic efficiency. For the optimum 7% MoS2 QD/g-C3N4 photocatalyst, the degradation rate constant was 8.8 times greater than that of pure g-C3N4 under visible-light irradiation. Photocurrent and electrochemical impedance spectroscopy results further demonstrated that the MoS(2)QD/g-C3N4 exhibited higher photocurrent density and lower chargetransfer resistance than those of the pure g-C3N4 or MoS2 QDs. Active species trapping, terephthalic acid photoluminescence, and nitro blue tetrazohum transformation experiments were performed to investigate the evolution of reactive oxygen species, including hydroxyl radicals and superoxide radicals. The possible enhanced photocatalytic mechanism was attributed to a direct Z-scheme system, which not only can increase the separation efficiency of photogenerated electron-hole pairs but also possesses excellent oxidation and reduction ability for high photocatalytic performances. This work provides an effective synthesis approach and insight to help develop other C3N4-based direct Z-scheme photocatalytic systems for environmental purification and energy conversion. (C) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.