This thesis presents the synthesis and characterization of copper oxide nano photocatalyst for wastewater purification using visible light. The presented copper oxide nano material can serve as a low-cost and green technology for environmental applications. Uniform cubic, octahedral and rhombic dodecahedral Cu2O nano crystals with a size of 300-600 nm were synthesized using a simple hydrothermal method. The rhombic dodecahedral Cu2O nano crystals are highly active when driven by low-power white LEDs as a light source. In comparison with other reported photocatalysts, the Cu2O nano crystals in this work show a much higher reaction rate and lower electrical energy per order. The reaction rate and photoefficiency are found to be highly correlated with the irradiated photon flux. The surface termination and facet orientation of Cu2O nano particles were accurately tuned by adjusting the amount of hydroxylamine hydrochloride and surfactant. It is found that Cu2O nano particles with Cu-terminated (110) or (111) surfaces show high photocatalytic activity, while other exposed facets show poor reactivity. The density functional theory simulations confirm that the sodium dodecyl sulfate surfactant can lower the surface free energy of Cu-terminated surfaces, increasing the density of exposed Cu atoms at the surfaces, and thus benefiting the photocatalytic activity. It also shows that the poor reactivity of Cu-terminated Cu2O (100) surface is due to the high energy barrier of holes at the surface region. Amorphous CuxO nano flakes with a thickness of 10 to 50 nm were prepared through the dye-assisted transformation of rhombic dodecahedral Cu2O nano crystals under facile hydrothermal condition. The amorphous CuxO nano flake consists of a combination of Cu(I) and Cu(II) with a ratio close to 1:1. It shows enhanced photocatalytic reactivity towards the degradation of methyl orange compared to rhombic dodecahedral Cu2O nano crystals with all active (110):Cu facets. The chemical composition and architecture remain the same after repeating degradation tests. The high surface-to-volume ratio contributes to its better photocatalytic performance while its low surface energy calculated by the density functional theory simulations explains its improved stability. The as-obtained photocatalysts are able to degrade a wide range of aromatic organics including toluene, chlorobenzene and nitrobenzene effectively. We also demonstrate the capability of decontaminating a wide range of aromatic organics in industrial wastewater that comes from an oil company.