Photocatalysis vs adsorption by metal oxide nanoparticles

Metal oxide (MO) nanomaterials and related nanocomposites have been extensively studied for their potential use in water treatment. Because of their controlled morphologies, texture qualities, variable surface chemistry, distinct crystalline nature, high stability, and tunable band edges, MO nanostructured materials are highly selective towards deleting organic contaminants and heavy metal ions via adsorption and semiconductor photocatalysis. Metal-enhanced photocatalysis has recently received increasing interest, mainly due to the ability of the metal to directly or indirectly degrade pollutants. A diverse selection of MOs, with titanium dioxide (TiO2), zinc oxide (ZnO), iron oxides (IO), and tungsten (W), as well as graphene-MOs nanocomposites with variable structure, crystalline, and morphological properties, offers a powerful platform for the growth of effective catalysts. The current work discusses novel advancements and potential for the removal of adsorptive and photocatalytic degradation of organic compounds (phenolic, pesticide molecules, dyes, and so on) as well as heavy metal ions using semiconductor materials. A photocatalyst based on a MO-scheme heterostructure can manage the appropriate conduction band (CB) and valence band (VB) locations, securing considerable redox aptitude. This review should be of interest to the broad readership dealing with applied and fundamental aspects of water treatments and material sciences. Various strategies including surface modification, plasmonic enhancement, and metal cocatalysts have been introduced to enhance photocatalytic performance. The current article discussed the significantly utilized synthesis strategies and mechanism of heterojunction photocatalysts using a Z-scheme. Furthermore, adsorption sections guarantee that mercury, chromium, cadmium, arsenic, and lead-based ions are successfully removed from polluted water via the adsorption route. Numerous characteristics, such as concentration, coexisting ions, pH, and kind of chemical have converged to comprehend the adsorption procedure. The technological challenges and future approaches are discussed to maximize the photocatalytic and adsorption efficacy and the reusability of MO-based nanomaterials for water security.