Review on support materials used for immobilization of nano-photocatalysts for water treatment applications

[Display omitted] •Identification of suitable supporting material for photocatalyst immobilization.•Dip-coating is the most commonly adopted immobilization method.•Carbonaceous materials are widely used support materials.•Adherence and regeneration aspects of immobilized photocatalyst.•Factors affecting immobilization and future perspectives. Photocatalysis is a promising treatment technique for the degradation of recalcitrant pollutants in water. Nano-photocatalysts have shown enhanced performance due to larger surface area and better catalytic properties. However, the post-treatment separation of bulk nano-photocatalyst particles is a major challenge. Hence immobilization of the nano-photocatalyst is highly recommended for practical applications. This article reviews the potential and emerging support materials used for the immobilization of nano-photocatalysts. Carbonaceous and polymer-based substrates have gained a lot of attention as these materials could enhance photocatalytic activity. Carbon fiber cloth and carbon nanotubes are found to exhibit larger surface area and high mechanical and thermal stability. Also, deposition of nano-photocatalyst to such support materials is reported to be quite facile. Glass substrates are also being greatly explored due to their chemically inert nature, availability in various forms such as plates, spheres, thin layers and beads, and are very cost-effective. Recently, aerogel, carbon nanotube films, carbon foams, metal wire mesh, metal foam, and polymers are gaining importance as support materials. Various techniques such as sol–gel, electrophoresis, dip-coating, spray pyrolysis, photo-etching, cold plasma, and RF magnetron were successfully employed for the immobilization of nano-photocatalysts. The factors that must be considered for the development of immobilized self-standing recyclable photocatalysts are also discussed in detail. The advancement in the field of photocatalyst immobilization has been majorly attributed to the commercialization of photocatalytic systems.