光催化乙醇水溶液脱氢的EPR研究

本文报道,在含有Pt/CdS的乙醇水溶液中分别加入不同俘获剂: POBN (α-(4-pyridyl N-oxide)-N-tert-butyl nitrone), MV²⁺(methylviologen), NB(nitrosobenzene)或 TCNQ(7,7,8,8-tetracyano-p-quinodimethane),在可见光(λ≥450nm)照射下,光催化产氢及其光催化脱氢机理的EPR(电子顺磁共振)研究。结果表明,在Pt/CdS-CH₃CH₂OH/H₂O体系中进行可见光反应3小时,其产氢量相当高(0.0136 mmol);在加入POBN的体系中,由于其俘获了CH₃HOH自由基而使产氢量降低了三分之二,这说明由CH₃HOH经H⁺产氢比水分解经H⁺产氢更容易。在加入TCNQ或NB的体系中,由于其俘获了电子(e^-)或自由基,因而都未检测到氢气;这说明在可见光照射下,Pt/CdS催化乙醇水溶液脱氢的机理是经由: H⁺+e^-→Ñ→1/2H₂.

EPR STUDIES OF THE PHOTOCATALYTIC DEHYDROGE-NATION FOR AQUEOUS ETHANOL SOLUTIONS

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.