Green approaches to nanocomposite synthesis: Plant based metal oxide, magnetic, carbon and polymer based nanocomposites for efficient dye photodegradation

Rapid population growth, industrialization, agricultural practices, and anthropogenic activities have significantly increased the discharge of harmful pollutants, such as synthetic dyes, into freshwater resources. The discharge of synthetic dyes from different industries into the aquatic system, cause harm to aquatic life and environment. Traditional dye degradation methods like adsorption, coagulation/flocculation, membrane filtration, chemical oxidation are expensive, use chemicals to trap dye molecules, high maintenance cost, clogging of filters and difficulty in regeneration. Moreover, they produce toxic sludge whose disposal causes secondary pollution. Therefore, these conventional methods often fail to completely eliminate these dyes from wastewater. Green-synthesized nanocomposites, owing to their physicochemical surface properties, have emerged as efficient photo materials for the organic dye degradation in polluted water. Utilizing plant extracts, biopolymers as eco-friendly reducing and stabilizing agents, these materials eliminate the need for toxic chemicals during synthesis. The synergistic combination of components, such as metal oxides and carbon-based materials, enhances light absorption by extending it from UV to the visible region, improving charge separation, and generating reactive species. As a result, these nanocomposites exhibit good photocatalytic activity under visible light illumination for the various dyes removal. Their low cost, environmental compatibility, and reusability make them promising candidates for advanced wastewater treatment applications. Available literatures confirm the photodegradation of dyes at lab scale conditions however, direct comparison remains restricted by inconsistent operating parameters, incomplete data about surface area and kinetic parameters. Furthermore, strategies to improve photocatalytic performance such as doping, different types of heterojunctions have been discussed. Different green synthesized nanocomposites used to treat real wastewater have also been discussed here. Moreover, catalyst reusability as well as catalyst recovery, limitations of green synthesized nanocomposites in photocatalytic dye degradation related to reproducibility, scale up is demonstrated in this review.