WIT Press


Conversion Of CO2 To Methanol In Aqueous Medium On Visible Light Active BiVO4, Cu2BiVO6 Photocatalysts And In CM-n-TiO2 - Cu PEC By Simultaneous Electron And Proton Transfer Reactions

Price

Free (open access)

Paper DOI

10.2495/EQ160201

Volume

205

Pages

12

Page Range

213 - 224

Published

2016

Size

1,072 kb

Author(s)

V. Palanichamy, M. Frites, S. U. M. Khan

Abstract

Photocatalytic conversions of CO2 to methanol were carried out in aqueous medium on visible light active bismuth vanadium oxide (BiVO4) and on copper bismuth vanadium oxide (Cu2BiVO6) photocatalysts under illumination of light intensity of 1 sun (0.1 W cm−2). The percent solar to methanol conversion efficiency (% STME) was found to be 2.78% on of BiVO4 compared to 2.50% on Cu2BiVO6 photocatalyst under same illumination condition for 80 min reaction time. Such small difference in the photoconversion efficiencies can be attributed to similar band gap energies, absorption coefficient of light and particle sizes for both samples. At more than 80 min reaction time, the amount of methanol formation reduced drastically due to rapid uncontrollable back reaction on the same photocatalyst surface. Much higher solar to methanol photoconversion efficiency (% STME) of 5.83% was observed when CO2 was reduced to methanol on Cu cathode and water was oxidized to O2 on visible light active carbon modified titanium oxide (CM-n-TiO2) photoanode in a photoelectrochemical cell (PEC) under minimal external bias of 0.3 V for the reaction time of 10 min. Methanol formation was found to be dependent on the way the CO2 solution was prepared under pressure in deionized water and followed by addition of NaOH solution so that the most of the dissolved CO2 remained intact in its molecular form. A mechanism of the photoelectrochemical reduction of adsorbed CO2 (aq) to methanol was given in terms of multi electron and proton transfer reactions under illumination followed by removal of a water molecule from the intermediate.

Keywords

carbon dioxide, methanol, photocatalysts, photoelectrode, PEC