Ti(iv) nanoclusters as a promoter on semiconductor photocatalysts for the oxidation of organic compounds

Abstract

The surface modification of semiconductors is a potential approach for the development of visible-light-sensitive photocatalysts. Here, we report that amorphous Ti(IV) nanoclusters grafted onto metal oxide photocatalysts function as efficient promoters for the oxidation of organic contaminants, including acetaldehyde and 2-propanol. Ti(IV) nanoclusters were facilely grafted onto metal oxides like titanium dioxide (TiO₂) and tungsten trioxide (WO₃) by using a simple impregnation method. The photocatalytic activity of Ti(IV) nanocluster-grafted TiO₂ under UV-light irradiation was much higher than that of bare TiO₂, even though the surface area and photon absorption of these two materials were identical. The improved photocatalytic activity was attributable to hole trapping by the Ti(IV) nanoclusters, which form a unique electronic structure, resulting in efficient charge separation. Kelvin probe force microscopy analysis revealed that the highest occupied molecular orbital (HOMO) of the Ti(IV) nanoclusters has a more negative potential than the valence band of bulk rutile TiO₂, which allows hole transfer from bulk TiO₂ to the Ti(IV) nanoclusters. The grafting of Ti(IV) nanoclusters was also shown to increase the photocatalytic activity of WO₃. WO₃ also requires reduction reaction promoters, such as Cu(II) nanoclusters, because of the low energy of its conduction band (CB). The grafting of both Ti(IV) and Cu(II) nanoclusters onto WO₃ resulted in the highest reaction rate reported to date for the decomposition of gaseous 2-propanol under visible-light irradiation.