Photocatalytic Reduction of Carbon Dioxide by Using Bare and Copper Oxide Impregnated Nano Titania Catalysts.

Synthesis of nano TiO2 has been done by sol–gel method. Various weight percentages (1%, 3%, 5%, 7% and 10% w/w) of CuO were impregnated over titania. Physicochemical and instrumental characterization of all the catalysts confirmed the crystallinity, structure and morphology of titania and CuO supported titania. The bandgap value of TiO2 decreased from 3.22 eV to 2.82 eV with increase in the impregnation of CuO. Synthesized catalysts and TiO2 (Degussa P25) were evaluated towards the photocatalytic reduction of carbon dioxide under UV irradiation (λ = 254 nm and 6 W). The reduction ability of the most active catalyst was also tested under visible irradiation and compared with that of bare titania. Photocatalytic reduction of carbon dioxide yielded the products such as methanol, formic acid, formaldehyde and among them methanol was found to be the predominant product. Among the catalysts 3%CuO/TiO2 yielded the highest amount of methanol both at 8 hours and 20 hours of UV irradiation (1814 μmol/g cat and 4120 μmol/g cat respectively). Three times recycling the best catalyst (3%CuO/TiO2) yielded 3080 μmol of methanol per gram of the catalyst. The slight loss in catalytic activity is attributed to difficulty in recovering the catalyst. 3%CuO/TiO2 also yielded 408 μmol/g cat of methanol at under visible irradiation. This catalyst on complete reduction and partial oxidation yielded 3%Cu/TiO2 and 3%Cu2O/TiO2. Both reduced and partially oxidized catalysts showed less reduction ability of CO2 than 3%CuO/TiO2.