Constructing of GQDs/ZnO S-scheme heterojunction as efficient piezocatalyst for environmental remediation and understanding the charge transfer mechanism

Highly efficient catalysts are challenging in the fields of environmental remediation. In this work, for the first time, we combined graphene quantum dots (GQDs) and piezocatalytic materials (ZnO) to construct a novel Sscheme GQDs/ZnO heterojunction via facile method. The obtained GQDs/ZnO heterojunction presented excellent piezocatalytic activity such as higher reaction kinetic rate constant (0.051 min-1) and degradation efficiency (96.1 % within 60 min) as well as superior stability toward methyl orange (MO) dye degradation, far exceeding those of pure ZnO and most reported other typical piezocatalysts. This superior piezocatalytic performance of GQDs/ZnO could be ascribed to S-scheme heterojunction facilitating charge carrier transfer and separation, and enhancing the redox ability as well as the formation atomic-level interfacial bridge of Zn-C-O bond at GQDs/ ZnO interface. Furthermore, density functional theory (DFT) calculations demonstrated the charge transfer path of GQDs/ZnO S-scheme heterojunction and provided a novel understanding for S-scheme heterojunction mechanism in piezocatalytic field, which supports the experimental evidences of S-scheme heterojunction. This research provides an effective strategy to modulate charge transfer from the atomic level, highlighting an innovative insight for the practical application of highly efficient piezocatalysts in environmental remediation.