Cubic perovskite-type and octahedral pyrochlore-type powders of potassium tantalate (KTaO3) were selectively synthesized by a single-step hydrothermal method under different concentrations of potassium hydroxide (KOH). The obtained photocatalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectra (EDS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and UV-vis absorption spectra (UV-vis). The photocatalytic activities of the KTaO3 samples for reduction of carbon dioxide to methanol under UV light irradiation were investigated. The results showed that the KOH concentration played a significant role in determining the phases of the resultant products. Compared with the cubic crystalline structure, the octahedral crystalline structure exhibited the higher photocatalytic activity. In addition, the photocatalytic activities of KTaO3 were obviously increased when a small amount of nickel oxide (NiO) was loaded as a co-catalyst. The highest rate of methanol formation was 1815 mu mol/g/h when 2 wt% of NiO was loaded. (C) 2017 Elsevier Inc. All rights reserved.