Supported catalysts for heterogeneous electro-Fenton processes: Recent trends and future directions

Extremely low pH requirement and additional sludge management for the homogeneous electro-Fenton (EF) process necessitated the development of heterogeneous electro-Fenton (HEF) reactions that utilize solid catalysts that can be recovered and reused. In the recent decades, supported catalysts have immensely attracted researchers owing to the outstanding physical, chemical, and electronic properties of the supports that benefit the EF process by enhancing the removal efficiency, reducing reaction time, and extending the operational pH range. This review enlightens the readers about various materials that have been used for supporting the catalysts, their importance, method of impregnation, and optimum conditions required to attain maximum pollutant removal. From the wide array of catalysts reviewed, porous supports with a high surface area such as activated carbon, biochar and fibres adsorbs the pollutants near their surface facilitating enhanced Fenton reactions and degradation of pollutants. Alginate-based catalysts can be prepared by a simple procedure and exhibit good degradation efficiency when used in batch and continuous EF reactors. Zeolite-based catalysts are structurally stable and display promising results for successive cycles. The flexible and conductive nature of fibre-based supports performs the dual role as a catalyst and cathode. The highly stable and conductive properties of graphene and carbon nanotubes promote electron transfer, much required for continuous EF reactions.