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.