Radiation induced catalytic dechlorination of hexachlorobenzene on oxide surfaces

Radiation induced catalytic dehalogenation of hexachlorobenzene (HCB) adsorbed to alumina (Al₂O₃), silica (SiO₂), titania (TiO₂), zirconia (ZrO₂), and a commercially available zeolite has been studied using Cobalt-60 (⁶⁰Co) as a radiation source. Solid-particulate samples were irradiated over a dose range of 0-58 kGy, and the chemical changes were monitored using Fourier transform infrared diffuse reflectance (FTIR-DR) and gas chromatography with electron capture detection (GC-ECD). The extent of HCB degradation on the metal oxides was found to increase dramatically in samples evacuated under vacuum, pointing to the competitive scavenging of conduction band electrons by surface adsorbed species, primarily oxygen. Coadsorbed water diminished HCB conversion on all oxides but to a greater degree on alumina. HCB degradation on metal oxides was found to be highly dependent upon the conduction band energy of the support material, thus confirming the occurrence of ultra-band-gap excitation and charge separation in irradiated oxides. Higher yields of dechlorination products were witnessed in alumina and silica samples. Zeolite, titania, and zirconia were also found to be inefficient in promoting radiation induced catalysis. The absence of oxidation products in the irradiated HCB/oxide samples suggests the inaccessibility of holes to undergo interfacial charge transfer with the organic substrate.