This book highlights the promising photocatalytic methods for synthesizing organic chemicals by simultaneously degrading the toxicity of raw substances used for organic synthesis. It presents various semiconducting materials with high catalytic activities in hydrogen evolution reactions (HERs) and hydrogenation reactions, as well as the material characterizations for identifying semiconductor photocatalysts. The focus is on understanding the hydrogen dissociation and activation of substances in the process of hydrogenation and the fabrication of nanostructured catalysts with desired activity and selectivity. Recent works show photocatalytic hydrogenation reactions with in situ generated H+ on catalyst surfaces utilizing initial chemicals such as nitrophenol, nitrobenzene, azobenzene, and benzene for valorization. In addition, the photocatalytic valorization of waste glycerol is also discussed. Besides the hydrogenation reactions, the reduction of oxygen to form H2O2 can be done with aphotocatalytic method in atmospheric conditions. Some related perspectives and outlooks are also discussed for possible future development.