A review of photocatalytic characterization, and environmental cleaning, of metal oxide nanostructured materials

Industrial waste is the primary source of highly toxic organic pollutants and heavy metal contaminants. Treatment of such effluence is necessary to mitigate environmental pollution to provide a clean ecosystem for living species. Various approaches have been effectively utilized for the removal of industrial waste particularly, photocatalysis being an effective, economical, and time-efficient approach to remove toxic ions. Large organic molecules found in pesticides and dyes can be removed with relative ease using nano-photocatalysts with a wide energy band gap, which is one of its major merits. For this purpose, a combination of various metal oxides with relevant materials is generally employed to activate visible regions in photocatalysts. Moreover, modification in physical parameters such as surface area of the catalyst, crystallinity, particle size and morphology, band gap, and microstructure is undertaken, which serves to enhance the photocatalytic activity. Here, advanced techniques that are presently used to synthesize different types of photocatalysts and their potential use in the degradation of the organic dye have been described in detail. The focus of the current review is various metal oxide NPs such as ZnO, TiO2, WO3, SnO2, and CuO with potential applications in photocatalysis, their structural characteristics, classification, and their photocatalytic mechanism. The review covers the influence of dopants on morphological, electrical, optical, and photocatalytic activity of selected nanocomposite systems. Moreover, the current review grasps extensive literature on the role of metal oxides as a photocatalyst that will facilitate researchers by providing guidelines to design more suitable nano-photocatalytic systems.