Adsorption and photocatalytic and photosensitised bleaching of acid orange 7 on multilayer mesoporous films of TiO2.

A series of mesoporous films of titania of different thicknesses are prepared and their surface areas and porosities determined by physical adsorption using Kr as the adsorbate. The amounts of acid orange 7 (AO7) adsorbed by these films are found to be proportional to their measured surface areas and so the possibility of using this as a method of determining the surface area of thin titania films is discussed. The initial rates of UV-driven photocatalytic- and visible-driven photosensitised-bleaching of AO7 in solution, upon UVA and visible light irradiation, respectively, are also directly dependent upon the measured surface areas of the titania films. The quantum efficiencies for the UV photocatalytic- and visible photosensitised-bleaching of AO7 by the thickest of the AO7 films were estimated to be 0.08 and 0.01%, respectively.