Water pollution caused by hazardous substances has become a global concern. Textile and dyestuff industries produce large amounts of wastewater containing various dye pollutants. Most azo dyes are nonbiodegradable, and their release into the environment poses a major threat to the surrounding ecosystems. Remediation of organic aquatic pollutants by photocatalytic oxidation has proven to be an attractive and promising technology among the advanced oxidation processes. Semiconductor photocatalysis is a topic of current interest, mainly in view of its potential application in the mineralization of pollutants. Synthesizing heterostructured nanomaterials of specific morphologies and the development of highly efficient solar/UV active photocatalysts with higher surface area is an urgent and important issue for energy and environmental problems. We had developed more than 200 photocatalysts by (i) doping/codoping semiconductor oxides with metals and nonmetals, (ii) coupling of semiconductor oxides, (iii) supporting semiconductor oxides with surface-active agents, (iv) loading rare earth oxides, (v) incorporating single metal atom oxides in photocatalytic nanocomposites. Most of these modified catalysts were solar-active nanocomposites with significant efficiency in the degradation of toxic chemicals. Application of photocatalysts in the degradation of toxic chemicals and treatment of different industrial wastewater, both in bench and pilot scales, will be discussed, along with a brief outline on photocatalytic decontamination of air.