Molecular-Scale Transition Metal Oxide Nanocluster Surface-Modified Titanium Dioxide as Solar-Activated Environmental Catalysts

Abstract

The development of environmental catalysts is an urgent subject to be tackled by scientists and engineers all over the world due to the borderless nature of environmental pollution. We named the catalyst enabling the decomposition of the pollutants by effectively utilizing the solar energy from ultraviolet to infrared as “solar environmental catalysts”. This Feature Article reviews the recent studies on a novel class of solar environmental catalysts consisting of TiO2 and molecular scale oxides of 3d metals and for comparison d10 (Sn) on the surface (MOs/TiO2). The TiO2 surface modification with MO clusters by the chemisorption–calcination cycle (CCC) technique presents novel band engineering for finely tuning the top of the valence band, while the unique physicochemical and electronic properties of MOs/TiO2 give rise to the outstanding photo- and thermocatalytic activities for the decomposition of organic pollutants. In the first part following the Introduction, the CCC technique for forming extremely small MO clusters on TiO2, the structures, physicochemical properties, and electronic structures of MOs/TiO2 are described. The second part deals with their thermo- and photocatalytic activities for the degradation of model organic pollutants and the essential action mechanisms of the MO clusters. The combination of experiments and first-principles density functional theory simulations shows that Co2O3/TiO2 can be a prototype of the solar environmental catalyst with high levels of photo­(UV and visible)- and thermocatalytic activities.

Design of Novel Visible Light Active Photocatalyst Materials: Surface Modified TiO2

“…A particularly interesting insight is that the oxidation state of Sn or Pb can be used to control both the appearance of a shift in the absorption edge and the mechanism underlying this shift. The experimental work indicates that these nanoclustermodified TiO2 composite materials can be prepared using standard techniques, such as CVD [102] , ALD [93] and Chemisorption-Calcination [73] , using non-critical materials. In addition, the materials appear to be stable over time and under illumination, which is a significant advantage over, e.g.…”

“…Modification of TiO2 with metal species, [17][18][19][20][21] or with nanoclusters of other metal oxides [73] provides an exciting route to meeting this aim.…”

“…Our experimental collaborators in the group of Prof. Tada have developed the chemisorptioncalcination cycle (CCC) technique, where metal complexes are adsorbed via chemical bonds and the organic part is oxidized by post-heating, to prepare extremely small nanoclusters of oxides supported on TiO2 [73,76] . In this regard, Figure 4 presents some key spectroscopic results from this experimental work [77,78] , showing the effect of CuO modification on the electronic structure of TiO2.…”

“…In experimental work from a number of groups [73,77,78,[89][90][91][92][93][94]102,103,[112][113][114][115][116][117] doped TiO2 system, we consider N-F co-doped TiO2 [118] which shows visible light absorption, but no photocurrent. The surface modification approach has the potential to alleviate some of these issues with doped TiO2.…”

Multi‐Electron Oxygen Reduction by a Hybrid Visible‐Light‐Photocatalyst Consisting of Metal‐Oxide Semiconductor and Self‐Assembled Biomimetic Complex

“…A fascinating approach is the hybridization of metal oxide semiconductors exhibiting a strong absorption in the wide spectral range and molecular metal complexes with highly efficient and selective electrocatalytic activity. [6,7] Although this type of hybrid photocatalysts has recently attracted much interest for H 2 generation, [8] CO 2 reduction, [9,10] and environmental purification, [11] …”