Photocatalytic electron flow through the interface of titania nanosheets and mesoporous silica hybrid films

Abstract

UV-light induced redox reactions between cationic porphyrins (H 2TMPyP) and methyl viologen (MV 2+) separately incorporated in titania nanosheets (TNS) and cubic-mesoporous silica (MPS) integrated films, respectively, were investigated. In this system, the following two modified hybrids, i.e., the normally stacked (MV 2+–TNS)/(H 2TMPyP–MPS) on a FTO electrode and the inversely stacked (H 2TMPyP–MPS)/(TNS) films on a FTO electrode were examined. In accordance with the expected electron flow from H 2TMPyP to MV 2+, cathodic photocurrents were observed for the normally stacked film in acetonitrile (CH 3CN) under a negative bias voltage of −0.4 V. However, under the influence of a positive bias voltage of +0.3 V, anodic photocurrents were observed even in CH 3CN. On the other hand, anodic photocurrents were also observed in water for the normally stacked films at both bias voltages of +0.3 and −0.4 V due to photoreduction followed by proton abstraction of the H 2TMPyP molecules from H 2O within the MPS nano-cavities. In addition, ca. 0.98 mC of the photocurrents were determined in water for the inversely stacked (H 2TMPyP–MPS)/(TNS) films without MV 2+, of which ca. 50% resulted in the oxidative consumption of H 2TMPyP in the MPS cavities.