ZnO nanoparticles (NPs) were prepared by an ionothermal precipitation method in a ChCl:DEG deep eutectic solvent using Zn(CH3COO)(2)center dot 2H(2)O as a zinc source. A possible mechanism for the ZnO nucleation is discussed. The as-prepared ZnO samples were thoroughly examined by XRD, TEM, SEM, FTIR and XPS. The thermal and optical properties were further characterized by TGA/DTA, UV-vis and PL spectra, respectively. The results show that wurtzite ZnO mono-crystals with an average size of 30 +/- 1 nm were achieved, and their morphology was expressed as a polyhedron with distorted hexagonal base faces. Furthermore, the DEG molecules were incorporated into the surfaces of the ZnO crystals and could only be removed by thermal annealing; the molecules persisted after washing with ordinary solvents. Dynamic light scattering (DLS) shows that the ZnO NPs modified via DEG molecules are stable in an aqueous suspension without additives. In addition, the inclusion of DEG promotes light absorption at a longer wavelength but reduces the intensity of emissions. XPS reveals that the removal of DEG induced exposed polar surfaces and defects and thus increased the intensity of photoluminescence, especially blue emission. The findings of this work not only provide a facile and environmentally friendly ionothermal method to prepare uniform ZnO NPs protected by DEG but also improve the aqueous suspension stability. Consequently, the photocatalytic performance is enhanced. (C) 2016 Elsevier B.V. All rights reserved.