The decoloration mechanism of Methylene Blue in a CuO/TiO_2-H_2O_2 photocatalytic system

A CuO/TiO2 photocatalyst is prepared using the hydrolysis method.It exhibites excellent photocatalytic activity under both UV and Vis light.After investigating the quantity of hydroxyl radicals and the decoloration rate under different pH situations irradiated by UV or Vis light,a new methylene(MB) blue photocatalytic decoloration mechanism is proposed.Under UV light irradiation,methylene blue is decolored by mass hydroxyl radicals which diffuse into the liquid phase in acidic conditions.A few hydroxyl radicals are generated in alkaline conditions,and these radicals affect the MB which is absorbed on the photocatalyst surface.There is a synergistic effect of the above in neutral conditions.The removal rate under strongly acidic,strongly alkaline or neutral conditions is much higher than in weak acid or alkaline conditions.Under Vis light irradiation,fewer hydroxyl radicals exist in this system for an electron-transfer formation loop,and the hydroxyl radicals must diffuse into liquid to react with MB,so the decoloration rates are extremely low under acidic and neutral conditions.A high decoloration rate is achieved under strongly alkaline conditions because MB is absorbed on the surface of the photocatalyst which increases the hydroxyl radical utilization efficiency.Photosensitization also accelerates the decoloration.