Recently, it is demonstrated that semi-conducting materials, which are capable of mediating photocatalytic oxidation of organic compounds, can be alternatives to conventional methods for the removal of organic pollutants from water. Photocatalytic degradation of organic pollutants by nanostructured semiconductors offers great potentials for the complete elimination of toxic chemicals and environmental pollutions. Scientists are investigating many semiconductors that can utilize visible light to degrade a high number of recalcitrant materials in aqueous system. The monograph therefore focuses on the sonochemical synthesis method, pointing out advantages where appropriate. Strategies for generating different nanostructures, such as coralline-like, hollow prisms, nanosheet-based microspheres with hierarchical structures, and nanoflower are also discussed. Applications of nano photocatalysts for the degradation of organic dyes are reviewed, as well.