Improved Methane Production by Photocatalytic CO(2) Conversion over Ag/In(2)O(3)/TiO(2) Heterojunctions

In this work, the role of In(2)O(3) in a heterojunction with TiO(2) is studied as a way of increasing the photocatalytic activity for gas-phase CO(2) reduction using water as the electron donor and UV irradiation. Depending on the nature of the employed In(2)O(3), different behaviors appear. Thus, with the high crystallite sizes of commercial In(2)O(3), the activity is improved with respect to TiO(2), with modest improvements in the selectivity to methane. On the other hand, when In(2)O(3) obtained in the laboratory, with low crystallite size, is employed, there is a further change in selectivity toward CH(4), even if the total conversion is lower than that obtained with TiO(2). The selectivity improvement in the heterojunctions is attributed to an enhancement in the charge transfer and separation with the presence of In(2)O(3), more pronounced when smaller particles are used as in the case of laboratory-made In(2)O(3), as confirmed by time-resolved fluorescence measurements. Ternary systems formed by these heterojunctions with silver nanoparticles reflect a drastic change in selectivity toward methane, confirming the role of silver as an electron collector that favors the charge transfer to the reaction medium.