Book excerpt: In Heterogeneous Nanocomposite-Photocatalysis for Water Purification, the authors introduce various heterogeneous photocatalysts based on novel nanostructures of metal oxide semiconductors and graphene used for water purification, including TiO2, Fe2O3, SnO2, WO3 and g-C3N4, and outlines their advantages and drawbacks. The nanocomposite-photocatalysts ZnO and CdS are compared with reduced graphene oxide (rGO), a rapidly growing materials system. The authors describe how the photocatalytic activity of known nanomaterials can be improved by modifying the structural and optical properties (i.e., phase composition). - Introductory portion of the book includes a brief survey of all different kinds of heterogeneous photocatalysts - Discusses the possible photocatalysis mechanism occurring during the degradation of different toxic pollutants - Provides the photoelectrochemical measurement for synthesized catalysts, supporting the effective transportation of photoelectrons resulting into better catalytic properties