Using the ionic liquid (IL), 1-butyl-3-methyl-imidazole tetrafluoroborate, and the precursor Cu 7 Cl 4 (OH) 10 ⋅H 2 O, series of phase-manipulable Cu-based nanomaterials were synthesized by hydrothermal and microwave assisted routes, respectively. The structural characters of the as-prepared CuO, CuO/Cu 2 O composites and pure Cu nanoparticles were investigated by XRD, SEM, TEM and HRTEM, and their surface photovoltaic properties were studied by surface photovoltage spectra. Via hydrothermal route Cu 2+ ions were found to be reduced gradually into Cu + and subsequently Cu 0 with increasing the IL, and various phase ratio of CuO, Cu 2 O and Cu composite nanosheets and pure Cu nanoparticles were obtained. This implies that the IL could function as both a reductant in the oxygen-starved condition and a template for the nanosheet products. The 1 H-NMR result of the IL supports it being a reductant. In microwave assisted route, however, only monoclinic single crystalline CuO nanosheets were obtained, which indicates the IL being a template only in oxygen-rich condition. Therefore, the crystal phase, composition and morphology of the Cu-based products could be controlled by simply adjusting the quantity of the IL and oxygen in solution routes. The molecular structure of the IL after oxidation reactions was investigated by 1 H-NMR and a possible reaction mechanism was proposed.