TiO_2 nanometer particles were prepared by the sol-gel process and characterized by X-ray diffraction (XRD). Photocatalytic decomposition of acid black dyes was investigated in a cylinder type photoreactor made of quartz glass using a middle-pressure Hg lamp as the light source. The effects of the calcination temperature, flow rate of air, pH of solution and illumination time on the photodegradation rate of acid black dyes were discussed. The results showed that the calcination temperature greatly enhanced ...