In situ DRIFTS study of photocatalytic CO_(2) reduction under UV irradiation

Photocatalytic reduction of CO_(2) on TiO_(2) and Cu/TiO_(2) photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)under UV irradiation.The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium(IV)butoxide.Copper precursor was loaded onto TiO_(2) during sol-gel procedure.A large amount of adsorbed H_(2)O and surface OH groups was detected at 25℃on the TiO_(2) photocatalyst after being treated at 500℃under air stream.Carbonate and bicarbonate were formed rapidly due to the reaction of CO_(2) with oxygen-vacancy and OH groups,respectively,on TiO_(2) surface upon CO_(2)adsorption.The IR spectra indicated that,under UV irradiation,gas-phase CO_(2) further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate.The weak signals of reaction intermediates were found on the IR spectra,which were due to the slow photocatalytic CO_(2) reduction on photocatalysts.Photogenerated electrons merge with H^(+)ions to form H atoms,which progressively reduce CO_(2) to form formic acid,dioxymethylene,formaldehyde and methoxy as observed in the IR spectra.The well-dispersed Cu,acting as the active site significantly increases the amount of formaldehyde and dioxymethylene,thus promotes the photoactivity of CO_(2) reduction on Cu/TiO_(2).A possible mechanism of the photocatalytic CO_(2) reduction is proposed based on these intermediates and products on the photocatalysts.