The Surface Grafting of Doped and Undoped Titanium Dioxide with Transition Metal Ion Nanoclusters to Develop Efficient Visible Light Photocatalyst

by Aigerim

ABSTRACT

Titanium dioxide (TiO2) is an excellent semiconductor for photocatalysis, widely used for renewable energy and environmental purification, on account of its non-toxic, photochemically stable, and resource-abundant properties. However, the photoactivity of TiO2 is limited by a wide band gap energy and a rapid electron-hole recombination rate, and hence TiO2 photocatalyst has a poor absorption of visible light irradiation. The doping of TiO2 with transition metal cations and anions can be implemented to extend the light absorption to the visible light region, but dopants can also impair its photocatalytic activity by introducing impurity levels in the band gap that serve as recombination centers. Herein, the efficient visible-light-sensitive photocatalyst can be developed by grafting amorphous nanoclusters of transition-metal-ions (Cu(II), Fe(III), Ti(IV)) on the surface of TiO2 via a facile impregnation method. In the photocatalytic systems of metal-ion nanocluster grafted metal-ion-doped TiO2 nanocomposites, surface-grafted and bulk-doped metal ions function as cocatalysts and as visible-light absorbers, respectively. Upon visible light irradiation, the efficient interfacial charge transfer (IFCT) from the valence band (VB) of TiO2 to surface nanoclusters is induced. The photogenerated holes in the valence band (VB) of TiO2 enable the efficient oxidative decomposition of organic compounds, while excited electrons accumulated in the nanoclusters mediate a multielectron reduction of oxygen molecules. The surface modification of TiO2 with two ubiquitous nanoclusters is another novel approach with the same concept, in which one group of metal-ion nanoclusters act as hole-trapping centers and the other as cocatalysts. The coupling of amorphous nanoclusters on the surface of TiO2 exhibits the highest quantum efficiency (QE = 92.2%) and photocatalytic reaction rate (0.69 μmol/h) among the stated photocatalytic systems. The efficiency of the photocatalysts is evaluated by the decomposition of gaseous 2-propanol under visible-light irradiation (420-530 nm). Additionally, the advantageous properties of nanocluster grafted TiO2 photocatalysts such as high stability under visible light and ubiquitous elements composition signify their great potential for large-scale practical uses