A review of graphene‐TiO2 and graphene‐ZnO nanocomposite photocatalysts for wastewater treatment

Technologies for wastewater remediation have been growing ever since the environmental and health concern is realized. Development of nanomaterials has enabled mankind to have different methods to treat the various kinds of inorganic and organic pollutants present in wastewater from many resources. Among the many materials, semiconductor materials have found many environmental applications due to their outstanding photocatalytic activities. TiO2 and ZnO are more effectively used as photocatalyst or adsorbents in the withdrawal of inorganic as well as organic wastes from the wastewater. On the other hand, graphene is tremendously being investigated for applications in environmental remediation in view of the superior physical, optical, thermal, and electronic properties of graphene nanocomposites. In this work, graphene‐TiO2 and graphene‐ZnO nanocomposites have been reviewed for photocatalytic wastewater treatment. The various preparation techniques of these nanocomposites have been discussed. Also, different design strategies for graphene‐based photocatalyst have been revealed. These nanocomposites exhibit promising applications in most of the water purification processes which are reviewed in this work. Along with this, the development of these nanocomposites using biomass‐derived graphene has also been introduced. Practitioner Points Graphene‐TiO2 and graphene‐ZnO nanocomposites are effective for wastewater treatment through photocatalysis. These nanocomposite photocatalysts have been used in the form of membrane as well as antibacterial agents. Synthetic strategies and design considerations of graphene‐based photocatalyst play a major role. Biomass‐derived graphene‐TiO2 and graphene‐ZnO nanocomposites have also found application in wastewater treatment. Attachment of TiO2 or ZnO nanoparticles to the graphene nanosheet enables improvement in their photocatalytic activity towards degradation of pollutants from wastewater. Adoption of novel strategies for synthesis of graphene‐based nanostructures can aid in environmental remediation.