Synthesis and Characterization of Z-Scheme Heterojunction ${\mathrm{CoWO}}_4/\mathrm{RGO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ as a Visible Light-Driven Photocatalyst for Novel Removal of Organic Pollutant

In this study, novel Z-scheme heterojunction photocatalyst ${\mathrm{CoWO}}_4/\mathrm{RGO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ was successfully fabricated by a facial hydrothermal. Obtained morphology and topography studies indicated that deposition of reduced graphene oxide (RGO) and ${\mathrm{CoWO}}_4$ nanoparticles did not affect the structure of $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ sheets. However, optical results showed that visible light absorption of the material was significantly improved. The synthesized heterojunction photocatalyst exhibited improved photocatalytic performance in the novel degradation of rhodamine B, even upon visible irradiation. The improved photocatalytic performance was ascribed to interfacial contact between $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ and ${\mathrm{CoWO}}_4$ in a Z-scheme heterojunction in which RGO served as electron mediator accelerating its transfer between $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ and ${\mathrm{CoWO}}_4$ to minimize recombination of photogenerated electron-hole pairs. Therefore, rhodamine B degradation by ${\mathrm{CoWO}}_4/\mathrm{RGO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ was 1.87 times higher than pristine $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$. The synthesized heterojunction was relatively stable with no distinct reduction in photocatalytic activity after three recycling runs. The fabrication of heterojunction ${\mathrm{CoWO}}_4/\mathrm{RGO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ is an efficient strategy to develop high-performance photocatalysts for various photocatalytic applications.

The process of rapid industrialization and modernization has led to a global population explosion and resulting severe environmental pollution of soil, water, and air. In the process of treating environmental pollutants, humans leave wastewater with a large amount of hazardous pollutants such as heavy metals, carcinogenic metals, pesticides, insecticides, herbicides, and dyes, which are discharged directly into ecosystem and the natural environment. There are many different methods and materials to remove these pollutants. Among the most optimal approaches to remove pollutants are photocatalysis and carbon nitride ($\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$)-based nanomaterials ($\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ is a nonmetallic semiconductor material with high thermal, chemical stability, low bandgap energy, and a layered structure similar to graphite). It is useful in reducing operating costs and the scale of the equipment system and increasing recovery of contaminants after reaction. Due to its advantage in specific surface area, which is a very important property for pollutant removal, $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ materials are currently being used as advanced materials. It has the potential for future removal of pollutants compared with previous traditional materials. This study summarizes the potential use of this nanomaterial to remove contaminants in solution, and future directions for developing countries such as Vietnam.