Synergistic effect of graphene as a co-catalyst for enhanced daylight-induced photocatalytic activity of Zn0.5Cd0.5S synthesized via an improved one-pot co-precipitation-hydrothermal strategy

Abstract

In this study, a series of reduced graphene oxide (RGO)–Zn_0.5Cd_0.5S nanocomposites was synthesized via an improved one-step co-precipitation-hydrothermal strategy using thiourea as an organic S source. The experimental results demonstrated that thiourea facilitated heterogeneous nucleation of Zn_0.5Cd_0.5S and in situ growth of Zn_0.5Cd_0.5S nanocrystals on the RGO sheets via electrostatic attraction. Moreover, the addition of NaOH as a precipitating agent in the reaction environment was found to reduce the aggregation of Zn_0.5Cd_0.5S on the RGO sheets. Such an intimate interfacial contact between Zn_0.5Cd_0.5S and RGO resulted in well-dispersed nanoparticles decorated on RGO sheets. Photocatalytic performances of the RGO–Zn_0.5Cd_0.5S were evaluated by the degradation of Reactive Black 5 (RB5) under a low-power 15 W energy-saving daylight bulb at ambient conditions. Compared with pristine Zn_0.5Cd_0.5S, 20RGO–Zn_0.5Cd_0.5S (20 wt% of RGO) displayed an enhanced RB5 degradation of 97.4% with a rate constant of 0.0553 min⁻¹ after 60 min of visible light irradiation. 20RGO–Zn_0.5Cd_0.5S exemplified a 1.3-fold enhancement after RGO incorporation relative to that for pristine Zn_0.5Cd_0.5S. The remarkable photocatalytic performance was ascribed to the efficient migration efficiency of the photoinduced electrons from Zn_0.5Cd_0.5S to RGO to inhibit the charge carrier recombination. Additionally, to systematically verify the role of each active species in the degradation of RB5, trapping experiments for radicals and holes were individually explored. It is confirmed that photogenerated ˙O₂⁻, ˙OH and h⁺ were responsible for the degradation of RB5 in the 20RGO–Zn_0.5Cd_0.5S system. Lastly, a postulated visible-light photocatalytic mechanism for the RB5 degradation was discussed.