Monitoring molecular adsorption on high-area titanium dioxide via modulated diffraction of visible light

Patterned thin films of titanium dioxide (TiO2), with micrometer-sized feat ures, were prepared on transparent, conductive indium-tin oxide glass platf orms via microtransfer molding and electrochemical deposition. The grating pattern produces optical diffraction, where the efficiency of diffraction ( g) depends on the degree of contrast in refractive index between the patter ned material and the surrounding medium. The refractive index of a represen tative micropatterned TiO2 film (anatase) was estimated, via solvent index matching experiments, to be 2.72-a value sufficiently large to achieve good contrast with air or water. A new method, based on the measurement of chan ges in diffraction efficiency, is described for the detection and evaluatio n of organic chemical adsorption on various titanium dioxide surfaces. The strategy is illustrated for the vapor-phase adsorption of chloroform on hig h-area amorphous, anatase, and rutile forms of titanium dioxide. The uptake of 2,4,5-trichlorophenol from aqueous solutions by amorphous TiO2 was also examined by the modulated optical-diffraction-grating technique.