Molecular Metal Oxide Cluster-Surface Modified Titanium(IV) Dioxide Photocatalysts

Abstract

The surface modification of TiO 2 with molecular sized metal oxide clusters has recently been shown to be a promising approach for providing TiO 2 with visible-light activity and/or improved UV activity. This short review summarizes the effects of the surface modification of TiO 2 with the oxides of iron and tin selected from d-and p-blocks, respectively, on the photocatalytic activity. Fe(acac) 3 and [Sn(acac) 2 ]Cl 2 chemisorption on the TiO 2 surface occurs by ligand-exchange and ion-exchange, respectively. Taking advantage of the strong adsorption, we formed extremely small metal oxide clusters on TiO 2 by the chemisorption-calcination cycle (CCC) technique with their loading amount strictly controlled. The iron oxide surface modification of P-25 (anatase/rutile ¼ 4 : 1, w/w, Degussa) gives rise to a high level of visible-light activity and a concomitant increase in the UV-light activity for the degradation of model organic pollutants. On the other hand, only the UV-light activity is increased by the tin oxide surface modification of ST-01 (anatase, Ishihara Sangyo). This striking difference can be rationalized on the basis of the material characterization and DFT calculations, which show that FeO x surface modification of rutile leads to visible-light activity, while SnO 2 -modified anatase enhances only the UV-light activity. We propose the mechanisms behind the FeO x and SnO 2 surface modification, where the surface-to-bulk and bulk-to-surface interfacial electron transfer are taken into account in the former and the latter, respectively.

Tin-grafted TiO2 with enhanced activity for photocatalytic hydrogen generation from aqueous methanol solutions

“…No obvious change in the light absorbance of TiO 2 is observed after the surface modification with tin species. This is in accordance with theoretical calculation results of molecularsized SnO 2 clusters adsorbed on anatase surfaces [37], indicating tin oxide derived states do not appear inside the TiO 2 energy gap and thus lead to no shift of light absorption. However, it cannot be excluded that the tin-related electronic states may be close to the CB of TiO 2 and thus do not exert a large influence on the optical absorption of TiO 2 [21], which is in line with the low tin content.…”

Loading Effect in Copper(II) Oxide Cluster-Surface-Modified Titanium(IV) Oxide on Visible- and UV-Light Activities

“…Similar shifts in the VB edge for other metal oxide-nanocluster modified TiO 2 are explained on the basis of the formation of new VB states coming from the oxide nanocluster. [17][18][19][20][21] This interfacial electron transfer causes efficient charge carrier separation contributing to the increases in the photocatalytic activities and the reduction in the TiO 2 Figure 12. Atomic structure, adsorption energy in eV and Ti 3d and Cu 3d projected electronic density of states (PEDOS) for anatase TiO2 modified with CuO, Cu2O2 and Cu4O4 clusters Figure 11.…”

“…We have recently reported that FeO x and NiO cluster-surface modified TiO 2 prepared by the chemisorption-calcination cycle (CCC) technique shows high photocatalytic activities under illumination of visible-and UV-light. [17][18][19][20][21] In both the systems, strong dependence of the photocatalytic activity on the loading amount of the clusters is observed, [17][18][19][20][21] but the reason has not been fully understood.…”

“…Recently, visible-light activation of TiO 2 has been achieved by metal halide-and metal ion-grafting [11][12][13][14][15][16] and the surface modification with metal oxide clusters. [17][18][19][20][21][22][23][24] Among them, Cu 2+ ion and CuO have attracted much interest as a promising surface modifier. [25][26][27][28][29][30][31][32] Interestingly, Irie et al have shown that Cu 2+ -grafted TiO 2 (Cu 2+ /TiO 2 ) prepared by the impregnation method has oxidation ability sufficient for completely decomposing 2-propanol under visible-light irradiation.…”

Towards Global Artificial Photosynthesis (Global Solar Fuels): Energy, Nanochemistry, and Governance

“…The former, for example, displays a narrowed band gap, giving visible light absorption compared with pure TiO 2 . [24] The paper by Beniamino Iandolo and Michael Zäch from Chalmers University of Technology ('Enhanced Water Splitting on Thin-Film Hematite Photoanodes Functionalized with Lithographically Fabricated Au Nanoparticles') highlights why hematite or iron oxide (a-Fe 2 O 3 ) is arguably preferable to Co and Mn as a catalyst in the race for development of a commercially viable device for water splitting-based solar fuels because of its low cost, high stability, abundance, and potentially high solar-to-hydrogen conversion efficiency. [25] A focus on the practical commercial realities of water splitting technologies also characterises the paper from Alex Izgorodin, Orawan Winther-Jensen, and Douglas MacFarlane of Monash University ('On the Stability of Water Oxidation Catalysts: Challenges and Prospects').…”