Reduction of dissolved carbon dioxide in aqueous solution by UV-LED/TiO2 process under periodic illumination

Abstract

The application of controlled periodic illumination (CPI) using ultraviolet light-emitting diodes (UV-LED) for the photocatalytic reduction of CO2 in the aqueous phase was investigated in this study. The experiments were conducted with P-25 TiO2 as photocatalyst under the UV light intensity of 160 mW/cm2 with 60 min of total illumination time and pH 2. The target product of the photocatalytic reduction of CO2 by UV-LED process was methanol with the highest selectivity of 28.31 %. The reduction efficiency of CO2 and the reaction rate reached the highest value of 86.31 % and 15.76 × 10−5 M min−1, respectively, for experiment conducted with the smallest duty cycle of 0.09. The photonic efficiency was enhanced from 0.47 % to 2.7 % with decreasing duty cycle from 1.00 to 0.09. The electric energy saving increased significantly from 13.11%–93.34%, including with a decrease of electric energy per order from 139.68 to 10.71 kW h m-3 order-1 for experiments conducted with decreasing γ from 0.91 to 0.09. The photocatalytic reduction of CO2 in the aqueous phase was well modeled by the Langmuir-Hinshewood kinetic equation. Furthermore, the proposed mechanism for photocatalytic CO2 reduction in aqueous phase under CPI was introduced.