“…have been widely explored for this purpose. − However, practical applications of such materials are limited by their low photocatalytic activity in solar light, , as these oxides are wide band gap materials. The common strategies for developing visible photocatalysts are doping and the sensitization of wide band gap materials by low band gap ones. , It may be noted that the semiconducting catalysts can be used not only for the degradation of dyes but also for other organic pollutants such as erythrosine, Eosin Y., phenol, yellow auramine dye, benzene–toluene–xylene (BTX), etc. , Organic contaminants either degrade into colorless form or dissociate and evaporate in the form of CO 2 by the photocatalysts that generate reactive oxygen species (ROS) including the superoxide radical (O 2 – ), hydroxyl radical ( • OH), and peroxide (H 2 O 2 ). − Though the decontamination of water is achieved through the latter process, the colorless form of some dyes has various applications. The leuco-methylene blue (LMB) and leuco-malachite green (LMG) are the colorless forms of methylene blue and malachite green, respectively, which can be used in data storage, holographic industries, colorimetric oxygen indicators in food and pharmaceutical industries, etc …”