Photocatalytic degradation of chloroform in the gas phase on the porous TiO2 pellets: effect of Cl accumulated on the catalyst surface

The photocatalytic degradation of chloroform was studied in a tubular photoreactor packed with TiO2 pellets prepared by sol–gel method. Concentrations of chloroform and CO2 in the gas stream and Cl− ion which was dissolved from the pellets into water after the photodegradation experiments were detected quantitatively. Chloroform was completely mineralized to CO2 and HCl but the conversion decreased drastically with an increase in the irradiation time. Such a decrease in the catalytic activity was attributable to the accumulation of Cl− on the TiO2 surface and was recovered by washing the pellets with water. The presence of Cu and Ca(OH)2 increased the concentration of Cl− accumulated on the surface. The deterioration of the catalytic activity was suppressed with Ca(OH)2 whereas no appreciable effect was observed with Cu. The TiO2 prepared by sol–gel method exhibited a higher catalytic activity than commercially available Degussa P-25.