Nanoparticles of various compositions, including titania, ferrites, semiconductor quantum dots and high entropy solids, exhibit good performance in photocatalytic reaction. With proper designs on composition and surface modification, nanoparticles can be used to harvest light energy and catalyzed the various reactions in organic syntheses. Nanoparticle catalysts combine high reactivity of homogeneous catalysts and high recovery and reusability of heterogeneous catalysts. Moreover, the nanoparticle catalysts can be readily applied in aqueous-based reaction for green synthesis of organic compounds.