Industrial & Engineering Chemistry Research, Vol.50, No.13, 7977-7984, 2011
Dimethyl Sulfide Photocatalytic Degradation in a Light-Emitting-Diode Continuous Reactor: Kinetic and Mechanistic Study
This study investigated the feasibility, kinetics, and reaction pathways of the photocatalytic degradation of dimethyl sulfide (DMS) in a light-emitting-diode- (LED-) based continuous reactor. Four types of LEDs, with peak wavelengths at 365, 375, 385, and 402 nm, were used for comparison. The data were fitted with the Langmuir-Hinshelwood kinetic model, in which the rate constants for 365- and 375-nm LEDs were significantly larger than those for the 385- and 402-nm LEDs. The effect of wavelength on the reaction rate followed the TiO2 absorption spectrum. The effect of radiation intensity agreed with a nonlinear power law and was attributed to the TiO2 absorption of photon energy. For the 365- and 375-nm LEDs, the transition of the exponent values from first-order to one-half-order was estimated to occur at 0.5-1.0 mW.cm(-2), whereas the 385- and 402-nm LEDs did not show a transition at this intensity. Dimethyl sulfoxide (DMSO), dimethyl sulfone (DMSO2), dimethyl disulfide (DMDS), methanethiol (MT), methanesulfonic acid (MSA), and sulfate were identified as the reaction products by gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and ion chromatography (IC). A plausible reaction mechanism is proposed for DMS photocatalytic degradation based on the reaction products detected and possible intermediates formed.