Photocatalysis of 2,2′,3,4,4′,5′-hexachlorobiphenyl and its intermediates using various catalytical preparing methods

Four etching solutions used on support materials and two coating methods of TiO2 were conducted to investigate the effects of catalytical preparing methods on the photocatalysis of 2,2',3,4,4',5'-hexachlorobiphenyl (PCB congener 138). The results of XRD analyses confirmed that various etching solutions used on support substrates did not influence the characteristics of titanium(IV) oxide. The XRD patterns of crystallization for the catalysts before and after purification remained unchanged. Hydrofluoric acid used as an etching solution for the support substrates provided the best adhesion stability for the catalysts that demonstrated the highest photocatalytic efficiency for congener 138. Xenon and ultraviolet lamps were used to compare the irradiation effect on photocatalysis. The shortest half-lives of congener 138 were 7.4 and 12.2 h using xenon and UV reactors, respectively. Lower chlorinated biphenyls (lower congener numbers) were identified through the continuous dechlorination of congener 138. PCB congeners 99, 87, 66, 49, 28, 17, 9, and 7 were detected as a result of dechlorination from higher chlorinated congeners to lower chlorinated congeners along with the extension of exposure times. The concentrations of chloride ion were increased with increasing exposure time through dechlorination, while the concentrations of organic chlorine of congener 138 were decreased. Meta-dechlorination was the most commonly found mechanism for the photocatalysis of PCB 138. The activation energy of the photocatalysis of congener 138 was 70.8 kJ mol(-1). (c) 2006 Elsevier B.V. All rights reserved.