Photocatalytic performance of pristine NiO and NiMnO nanopowders in degradation of Rose Bengal dye.

Effective tuning of bandgap of transition metal oxides is a promising approach in improving their photocatalytic activity towards organic pollutant removal from water. The present paper describes synthesis of nickel oxide and NiMnO nanopowders by simple hydrothermal technique. During the synthesis of nickel oxide by hydrothermal process, addition of Mn source resulted in the formation of NiMnO. X-ray diffraction analysis has confirmed the formation of nickel oxide and NiMnO both having cubic structures. The average crystallite size decreases from 20 to 12 nm on increasing Mn source concentration during the synthesis of nickel oxide. Rectangular, hexagonal, and triangular faceted structures are revealed from the scanning electron microscopic images. HRTEM also indicated formation of cubical shaped structure with average sizes of 32 and 21 nm for pristine NiO and NiMnO nanopowders. In the case of NiMnO nanopowder, inter-connected cubes are seen. Modification in NiMnO nanopowder is found to display multiple optical band gaps at 1.21, 1.82, and 2.65 eV. The formation of NiMnO phase was further confirmed by XPS studies due to the presence of + 4 oxidation state of Mn. The photocatalytic properties of synthesized nickel oxide and NiMnO nanopowders are measured by using Rose Bengal dye under UV illumination. Enhancement in the photocatalytic activity is noticed in the case of NiMnO nanopowder as compared to nickel oxide nanopowder. Nearly 90% dye degradation is observed on utilizing NiMnO nanopowder.