文摘
A nominally room temperature photochemical method, simply employing ultraviolet light-(187-254 nm) generated ozone environment, is shown to provide an efficient alternativefor the removal of surfactant templates for a routine production of mesoporous silica thinfilms at low temperatures. The treatment concomitantly strengthens the silicate phase byfostering the condensation of unreacted silanols leading to mesoporous thin films with well-defined mesoscopic morphologies. The surfactant/silicate thin film mesophases were preparedonto a polycrystalline Au surface by dip-coating or spin-casting methods using sub-criticalmicelle concentration (cmc) nonionic ethylene oxide surfactant in an oligomeric silica solmixture. The structures and compositions of the thin film mesophases before and afterexposure to UV/ozone were determined using a combination of reflection-absorption Fouriertransform infrared spectroscopy, transmission electron microscopy, and thin film X-raydiffraction measurements. The pore characteristics of the UV/ozone-treated films weredetermined using nitrogen adsorption/desporption isotherm measurements. Results presentedhere clearly establish that the UV/ozone processing leads to complete removal of thesurfactant template; strengthens the inorganic skeleton by fostering silica condensation;and renders the mesophase thin film surfaces highly hydrophilic. Two of the most attractivefeatures of the method developed here, namely its usefulness in applications for temperatureintolerant substrates (e.g., thin metal films) and in spatially selective removal of thesurfactant templates to create patterns of mesoporous thin films, are also illustrated. Finally,the mechanistic implications of these observations are also discussed.
