Microsphere assembly of TiO2 mesoporous nanosheets with highly exposed (101) facets and application in a light-trapping quasi-solid-state dye-sensitized solar cell

The morphology of nano-titania has a significant effect on the photoelectric properties of dye-sensitized solar cells. In this study, microsphere assembly of a TiO2 mesoporous nanosheet constructed by nanocuboids was conducted via a simple hydrothermal process. The XRD pattern indicated that the hierarchical mesoporous microspheres are anatase phase with decreased (004) peaks. Raman spectrum shows enhanced Eg peaks at 143 and 638 cm(-1) caused by the symmetric stretching vibration of O-Ti-O of the (101) crystalline facet in anatase TiO2. FESEM and TEM images show that well monodispersed TiO2 microspheres with a diameter of 2 μm are assembled by TiO2 mesoporous nanosheets with exposed (101) facets. The oriented attachment of TiO2 nanocuboids along the (101) direction leads to the formation of mesoporous titania nanosheets. The UV-Vis spectrum shows that the mesoporous TiO2 nanosheets have high scattering ability and light absorption by dye. Quasi-solid-state dye-sensitized solar cells that incorporate these microspheres into the top scattering layers exhibit a prominent improvement in the power conversion efficiency of 7.51%, which shows a 45.8% increase in the overall conversion efficiency when compared with the spine hierarchical TiO2 microspheres (5.15%). There is the potential application for microsphere assembly of mesoporous TiO2 nanosheets in quasi-solid-state dye-sensitized solar cells with excellent stability.

Effect of ceria on the organization and bio-ability of anatase fullerene-like crystals

The presence of Ce atoms induce the formation of fullerene-like structures and increase the oxygen storage capacity of the anatase. It was demonstrated that such special effects can be exploited to modulate fibroblast proliferation.

Unraveling the photocatalytic mechanisms on TiO2 surfaces using the oxygen-18 isotopic label technique

During the last several decades TiO₂ photocatalytic oxidation using the molecular oxygen in air has emerged as a promising method for the degradation of recalcitrant organic pollutants and selective transformations of valuable organic chemicals. Despite extensive studies, the mechanisms of these photocatalytic reactions are still poorly understood due to their complexity. In this review, we will highlight how the oxygen-18 isotope labeling technique can be a powerful tool to elucidate complicated photocatalytic mechanisms taking place on the TiO₂ surface. To this end, the application of the oxygen-18 isotopic-labeling method to three representative photocatalytic reactions is discussed: (1) the photocatalytic hydroxylation of aromatics; (2) oxidative cleavage of aryl rings on the TiO₂ surface; and (3) photocatalytic decarboxylation of saturated carboxylic acids. The results show that the oxygen atoms of molecular oxygen can incorporate into the corresponding products in aqueous solution in all three of these reactions, but the detailed incorporation pathways are completely different in each case. For the hydroxylation process, the O atom in O₂ is shown to be incorporated through activation of O₂ by conduction band electrons. In the cleavage of aryl rings, O atoms are inserted into the aryl ring through the site-dependent coordination of reactants on the TiO₂ surface. A new pathway for the decarboxylation of saturated carboxylic acids with pyruvic acid as an intermediate is identified, and the O₂ is incorporated into the products through the further oxidation of pyruvic acid by active species from the activation of O₂ by conduction band electrons.

Green synthesis of anatase TiO(2) nanocrystals with diverse shapes and their exposed facets-dependent photoredox activity

The exposed facets of a crystal are known to be one of the key factors to its physical, chemical and electronic properties. Herein, we demonstrate the role of amines on the controlled synthesis of TiO2 nanocrystals (NCs) with diverse shapes and different exposed facets. The chemical, physical and electronic properties of the as-synthesized TiO2 NCs were evaluated and their photoredox activity was tested. It was found that the intrinsic photoredox activity of TiO2 NCs can be enhanced by controlling the chemical environment of the surface, i.e.; through morphology evolution. In particular, the rod shape TiO2 NCs with ∼25% of {101} and ∼75% of {100}/{010} exposed facets show 3.7 and 3.1 times higher photocatalytic activity than that of commercial Degussa P25 TiO2 toward the degradation of methyl orange and methylene blue, respectively. The higher activity of the rod shape TiO2 NCs is ascribed to the facetsphilic nature of the photogenerated carriers within the NCs. The photocatalytic activity of TiO2 NCs are found to be in the order of {101}+{100}/{010} (nanorods) > {101}+{001}+{100}/{010} (nanocuboids and nanocapsules) > {101} (nanoellipsoids) > {001} (nanosheets) providing the direct evidence of exposed facets-depended photocatalytic activity.

Catalytic role of TiO(2) terminal oxygen atoms in liquid-phase photocatalytic reactions: oxidation of aromatic compounds in anhydrous acetonitrile

On the basis of experiments carried out with controlled amounts of residual oxygen and water, or by using oxygen-isotope-labeled Ti(18) O2 as the photocatalyst, we demonstrate that (18) Os atoms behave as real catalytic species in the photo-oxidation of acetonitrile-dissolved aromatic compounds such as benzene, phenol, and benzaldehyde with TiO2 . The experimental evidence allows a terminal-oxygen indirect electron-transfer (TOIET) mechanism to be proposed, which is a new pathway that involves the trapping of free photogenerated valence-band holes at Os species and their incorporation into the reaction products, with simultaneous generation of oxygen vacancies at the TiO2 surface and their subsequent healing with oxygen atoms from either O2 or H2 O molecules that are dissolved in the liquid phase. According to the TOIET mechanism, the TiO2 surface is not considered to remain stable, but is continuously changing in the course of the photocatalytic reaction, challenging earlier interpretations of TiO2 photocatalytic phenomena.

Influence of sol counter-ions on the visible light induced photocatalytic behaviour of TiO2 nanoparticles

Titanium dioxide (TiO₂) nanoparticles are attracting increasing interest because of their superior photocatalytic and antibacterial properties.