Effects of catalyst characters on the photocatalytic activity and process of NiO nanoparticles in the degradation of methylene blue

By a hydrothermal method combining a subsequent calcination process, series of nano-scale NiO samples with different morphologies and sizes were synthesized and characterized. The effects of synthesis conditions including using different alkali reactants and being calcined at different temperatures on the characters of NiO samples have been investigated. In these characters the integrality of crystal structure and the crystallinity of NiO were found to become the determinative factors which affect the photocatalytic activity and process of NiO catalyst in the degradation of methylene blue (MB). The NiO sample which has a good crystallinity and small particle size (≤100 nm) possesses more shallowly trapped holes to react with chemisorbed oxhydryl OH− or H2O to generate OH radicals, exhibiting a high photocatalytic activity, furthermore, in this UV/NiO suspension the photocatalytic oxidation process of MB occurrs via the attack by OH radicals. The NiO sample which has a higher crystallinity and bigger particle size (>200 nm) possesses more deeply trapped holes (hvb+) to react directly with physisorbed organism, exhibiting a low photocatalytic activity, therefore, in this system the MB is oxidized by direct reacting with holes (hvb+).