Highly enhanced photocatalytic degradation of methylene blue over the indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions

Abstract

In the present research work, the ternary indirect all-solid-state Z-scheme nanoheterojunctions, graphitic-C3N4/reduced graphene oxide/anatase TiO2 (g-C3N4-RGO-TiO2) with highly enhanced photocatalytic performance were successfully prepared via a simple liquid-precipitation strategy. The photocatalytic activities of indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions were evaluated by the degradation of methylene blue (MB). The results showed that the introduction of RGO as an interfacial mediator into direct Z-scheme g-C3N4-TiO2 nanocomposites can remarkably enhance their photocatalytic activities. The as-obtained indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions, with the optimal loading amount of 10wt% RGO, exhibited the highest rate towards the photocatalytic degradation of MB under simulated solar light irradiation. The degradation kinetics of MB can be described by the apparent first-order kinetics model. The highest degradation rate constant of 0.0137min−1 is about 4.7 and 3.2 times greater than those of the pure g-C3N4 (0.0029min−1) and direct Z-scheme g-C3N4-TiO2 (0.0043min−1), respectively. An indirect all-solid-state Z-scheme charge-separation mechanism was proposed based on the photoluminescence spectra and the trapping experiment procedure of the photo-generated active species. It was believed that the indirect all-solid-state Z-scheme charge separation mechanism in g-C3N4-RGO-TiO2 nanoheterojunctions could lead to the promoted charge separation and transfer, improved oxygen-reduction capacity of electrons in g-C3N4 and the formation of hydroxyl radicals driven by the holes in TiO2, respectively, thus achieving the highly enhanced photocatalytic degradation performance. This work might provide new insights and understanding on the graphene as electron mediators to design highly efficient all-solid-state Z-scheme nanoheterojunctions with enhanced visible-light driven photoactivity for various photocatalytic applications.