N-doped ZnO micropolyhedrons were fabricated by calcining the mixture of commercial ZnO (analytical grade) and NH4NO3 at 600 degrees C for 1.5 h, in which NH4NO3 was utilized as the nitrogen source. The structure, composition, BET specific surface area and optical properties of N-doped ZnO sample were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, wavelength dispersive X-ray fluorescence spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, N-2 adsorption-desorption isotherms, and UV-vis diffuse reflectance spectroscopy. The photocatalytic results demonstrated that the as-synthesized N-doped ZnO microcrystals possessed much higher photocatalytic activity than N-doped TiO2 (which was synthesized by calcining the mixture of P25 TiO2 and NH4NO3 at 600 degrees C for 1.5 h) and commercial pure ZnO in the decomposition of formaldehyde under visible-light (lambda > 420 nm) irradiation. The present work suggests that NH4NO3 is a promising nitrogen source for one-step calcination synthesis of microcrystalline N-doped ZnO, which can be applied as a visible-light-activated photocatalyst in efficient utilization of solar energy for treating formaldehyde wastewater. (C) 2014 Elsevier B.V. All rights reserved.