Microscopic Structure of Separately Accommodated Porphyrins and Viologens in Mesoporous Silica and Titania Nanosheet Hybrid Films

Abstract

The microscopic structures of two nano-structured inorganic films, one based on titania nanosheets (TNS) and the other on mesoporous silica (MPS), were investigated. The clear stacking structure of the TNS and MPS films were observed by the XRD, SEM, and TEM analyses. The selective adsorption of the porphyrin derivatives into the MPS nano-cavities and viologens into the TNS nano-Iayers was also investigated by absorption and energy-dispersive spectroscopy (EDS).

Photoinduced Electron Transfer between the Anionic Porphyrins and Viologens in Titania Nanosheets and Monodisperse Mesoporous Silica Hybrid Films

“…27,28 Upon UV-light illumination of the photocatalytic TNS, 43,47 the (MV 2þ -TNS)/(H 2 TMPyP 4þ -MMSS), MV 2þ radical ions (MV þ• ) were formed at the expense of the oxidative consumption of H 2 TMPyP 4þ , resulting in electron transfer through the interface between the TNS and mesoporous silica, thus leading to charge separation at the interface between the two nanostructured inorganic hosts. 27,28,48 The charge separated states obtained in these materials were highly stabilized and lasted for several hours even in the ambient atmosphere. 49 However, this photoinduced electron transfer through the interface of the TNS and the cubic-MPS films or the MMSS microsized particles was only observed for the cationic MTMPyP 4þ adsorbed in the mesoporous silica nanocavities.…”

“…The hybridization of nanostructured inorganic hosts with organic photofunctional molecules has been widely and extensively studied. − The photofunctional organic functional molecules hybridized with nanosized inorganic hosts have been observed to have unique redox properties in photochemical and photophysical processes. ,− In our previous studies, − consecutively stacked hybrid thin films of mesoporous silica films ( cubic -MPS) − or monodisperse mesoporous silica spheres (MMSS) − and layered titania nanosheets (TNS) ,,− were shown to exhibit unique photoinduced electron transfer between the cationic porphyrins (MTMPyP 4+ ; M = H 2 , Zn, and Co) and methyl viologen (MV 2+ ), which were separated and were present in different inorganic hosts. , Upon UV-light illumination of the photocatalytic TNS, , the (MV 2+ -TNS)/(H 2 TMPyP 4+ -MMSS), MV 2+ radical ions (MV +• ) were formed at the expense of the oxidative consumption of H 2 TMPyP 4+ , resulting in electron transfer through the interface between the TNS and mesoporous silica, thus leading to charge separation at the interface between the two nanostructured inorganic hosts. ,, The charge separated states obtained in these materials were highly stabilized and lasted for several hours even in the ambient atmosphere …”