TIO2-PHOTOCATALYZED OXIDATIVE-DEGRADATION OF CH3CN, CH3OH, C2HCL3, AND CH2CL2 SUPPLIED AS VAPORS AND IN AQUEOUS-SOLUTION UNDER SIMILAR CONDITIONS

Acetonitrile (CH3CN), methanol (CH3OH), trichloroethylene (C2HCl3 TCE) , and methylene chloride (CH2Cl2) were degraded in stirred batch react ors in the presence of O-2 at room temperature over films of pristine P-25 TiO2 under irradiation centered at 360 nm. Molarities of organics , activities of O-2, irradiation flux, deployment of catalyst, and rea ctor configuration were matched for vaporized and aqueous organics. Th e dependence of initial rates and the photoefficiencies of removal on concentrations of rea cta nts and photon flux were measured. ldentitie s and rates of formation and decay of some intermediates were determin ed. Langmuir coefficients were determined for dark adsorption of the o rganic vapors on films of P-25 in the presence of dry and water-satura ted air. Surface concentrations in equilibrium with aqueous solutions in the dark were calculated with the aid of Henry's law constants from the Langmuir coefficients of the water-saturated vapors. Initial rate s of removal of all four compounds from the vapor phase were much high er than from aqueous solution. Initial photoefficiencies of greater th an or equal to 1 molecule removed per incident photon were observed wi th vaporized CH3OH and TCE in dry air. Water vapor strongly inhibited the conversion of CH3OH and CH2Cl2. CH3CN, TCE, and CH2Cl2 vapors appe ared to react with both electrons and holes, and homolytic dissociatio n of the C-C and C-CI bonds of CH3CN and CH2Cl2 appeared to occur.