Abstract: By employing different spin trapping agents: POBN (α-(4-pyridyl-N-oxide)-N-tert-butyl nitrone), MV2+ (methylviologen), TCNQ (7, 7, 8, 8-tetracyano-p-qui-nodimethane) and NB (nitrosobenzene), EPR spectroscopy was used to probe the photocatalytic dehydrogenation pathway of aqueous ethanol solution suspended by Pt/CdS powder under the irradiation of visible light (λ≥450nm). The results indicated that the amount of hydrogen produced from the system of Pt/CdS-CH₃CH₂OH/H₂O was relatively high (0.0136 mmol) upon irradiation for 3 hours. However adding in POBN to this system resulted in the decreasing of the amount of hydrogen to 2/3 of the value, suggesting that the CH₃CHOH was trapped and it was easier to produce hydrogen via H⁺ decomposed from CH₃CHOH than from water. For the system adding TCNQ or NB, no hydrogen has been detected, probably due to the trapping of electron or H radical, and indicating that the dehydrogenation mechanism of aqueous ethanol solution catalyst upon irradiation was vis: H⁺+e^-→Ñ→1/2H₂.

Key words: Visible light, photocatalytic dehydrogenation, spin trapping, Pt/CdS, EPR