Photon Flux and Wavelength Effects on the Selectivity and Product Yields of the Photocatalytic Air Oxidation of Neat Cyclohexane on TiO 2 Particles

Abstract

Product selectivity and yields of cyclohexanol and cyclohexanone formation in the photocatalytic air oxidation of cyclohexane on TiO2 particles were determined as a function of the irradiation wavelength (254 e λ/nm e 366) and the photon flux (0.3 e I0/neinstein cm-2 s-1 e 5.0). Photonic efficiencies for total monooxygenated products (cyclohexanol + cyclohexanone) ranged from 10 to 25% depending on photon energy and fluency. The cyclohexanol-to-cyclohexanone ratio linearly increases with the incident photon flux at each wavelength and varies more than a magnitude ordersfrom 3 to 32%sat the same incident photon fluencys5 neinstein cm-2 s-1 sby changing the irradiation wavelength from 366 to 303 nm. Experimental evidence indicates that both spectral and intensity effects emerge as a consequence of the change in the frequency of photon absorption per particle. A mechanism is proposed which accounts for the origin of the selectivity changes.