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

Abstract

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. TiO 2 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-TiO 2 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-TiO 2 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-TiO 2 and graphene-ZnO nanocomposites have also found application in wastewater treatment.

Biophotocatalytic Reduction of CO2 in Anaerobic Biogas Produced from Wastewater Treatment Using an Integrated System

“…Obviously, the hydroxyl ions and Fe 2+/ Fe 3+ species might have influenced the acid/base equilibrium of the wastewater [27]. This affirms other reported studies suggesting that the oxidative occurrence and reaction mechanism with organic substrates can occur in three phases [26,27]. This includes (a) hydrogen abstraction from aliphatic carbon atoms (1), (b) electrophilic addition to double bonds or aromatic rings ( 2) and (c) electron transfer reactions with a constant rate close to the circulation-controlled limit (3).…”

“…Furthermore, when monitoring the recovered Fe-TiO 2 by the Ms, it was observed that at the onset of the process, there were no black precipitates on the Ms walls. However, at the end, there were black precipitates on the Ms walls, which suggests the iron (Fe 2+/ Fe 3+ ) of Fe-TiO 2 might have precipitated other contaminants [26][27][28]. Likewise, the decomposition of TiO 2 (Fe-TiO 2 ) might have resulted in the formation of OH• radicals, which increased photocatalytic activity [28].…”

Macroporous TiO2 and Graphite-like Carbon Hybrid Hierarchical Interfaces for Improved Photocatalytic Activity Derived from Particle-Stabilized Emulsions

“…In order to further improve the photocatalytic performance of materials, people have explored numerous composites composed of TiO 2 and carbonaceous materials, such as carbon nanotubes (CNTs), activated carbons (ACs), and graphene (Gr). − Compared with pure TiO 2 photocatalysts, Gr or graphite-like carbon has unique electronic properties, good transparency, flexibility, large theoretical specific surface areas, etc. − …”

Sonochemical preparation and characterization of Sm‐doped GO/KSrPO4 nanocomposite photocatalyst for degradation of methylene blue dye

“…But it can be overcome by introducing other materials to associate with TiO 2 and help prevent the electron-hole pair recombination (Kale et al, 2020;Potle et al, 2020). Carbon-based materials, especially graphene-based nanomaterials, are suitable materials that can form nanocomposites with other materials (Barai et al, 2020;Thakre et al, 2021). When graphene-based material is introduced to TiO 2 , it synergistically enhances the photocatalytic performance of TiO 2 by preventing electronhole pair recombination by imparting high electron mobility (Bhanvase et al, 2017).…”