title: Photoinduced charge separation in a colloidal system of exfoliated layered semiconductor controlled by coexisting aluminosilicate clay.
abstract: We investigated photoinduced charge separation occurring in a multicomponent colloidal system composed of oxide nanosheets of photocatalytically active niobate and photochemically inert clay and electron accepting methylviologen dications (MV2+). The inorganic nanosheets were obtained by exfoliation of layered hexaniobate and hectorite clay. The niobate and clay nanosheets were spatially separated in the colloidally dispersed state, and the MV2+ molecules were selectively adsorbed on the clay platelets. UV irradiation of the colloids led to electron transfer from the niobate nanosheets to the MV2+ molecules adsorbed on clay. The photoinduced electron transfer produced methylviologen radical cations (MV*+), which was characterized by high yield and long lifetime. The yield and stability of the MV*+ species were found to depend strongly on the clay content of the colloid: from a few mol % to approximately 70 mol % of the yield and several tens of minutes to more than 40 h of the lifetime. The contents of the niobate nanosheets and MV2+ molecules and the aging of the colloid also affected the photoinduced charge separation. In the absence of MV2+ molecules in the colloid, UV irradiation induced electron accumulation in the niobate nanosheets. The stability of the electron-accumulated state also depended on the clay content. The variation in the photochemical behavior is discussed in relation to the viscosity of the colloid.
authors.affiliation: Division of Bio-Applications and Systems Engineering (BASE), Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei-shi, Tokyo 184-8588, Japan. tnakat@cc.tuat.ac.jp
authors.forename: Teruyuki
authors.initials: T
authors.lastname: Nakato
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Yamada
authors.forename: Nobuyoshi
authors.initials: N
authors.lastname: Miyamoto
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D000077215:Clay; D003102:Colloids / Q000737:chemistry; D004573:Electrolytes; D008958:Models, Molecular; D015394:Molecular Structure; D055668:Photochemical Processes; D012666:Semiconductors; D013053:Spectrophotometry; D014783:Viscosity
chemical_list: D000538:Aluminum Silicates; D003102:Colloids; D004573:Electrolytes; D000077215:Clay