ABSTRACT
The overall photocatalytic principle and mechanism achieved as a result of generation of electron-hole pairs with hydroxyl radical formation is detailed. This chapter highlights the efficiency of various catalysts for the photocatalytic treatment of oily wastewater discharge from multiple sources. The process of photocatalysis takes place under the influential power of illuminators like, ultraviolet, visible light and solar light However, there are various catalysts, based upon the nature of oily wastage and spillage (free-floating or emulsified), the source of illumination and catalyst types including titanium dioxide (TiO2) and zinc oxide (ZnO) with their suitable mechanism are opted. The catalyst chosen should be highly dependent upon the band gap and suitable crystalline structures, where the catalyst with specified crystalline structures (like TiO2-anatase, rutile, and brookite; ZnO-hexagonal wurtzite and cubic zinc blende) are adopted according to the effectiveness and prominence of process. Other than these, the morphological properties and shape of the catalyst plays a pivotal role in determining the supremacy of the catalytic property. Exclusively, other pollutants like pharmaceuticals, radioactive wastes, pesticides, and dyes waste treatment are also accentuated. TiO2 has been reported to be superior to the ZnO catalyst in terms of efficiency. Though both the metal oxides are highly stable ZnO is a better UV absorber than the TiO2 for a wider range of wavelengths. Also, in terms of toxicity, ZnO is highly preferred as titanium is a toxic heavy metal, whereas zinc is a healthy metal nutrient.
