Surfactant-directed synthesis of mesoporous films made single-step by a tandem photosol-gel/photocalcination route

Abstract

In view of their technological impact in materials chemistry, a simplified and more efficient synthetic route to mesoporous films is highly sought. We report, herein, a smart UV-mediated approach coupling in a one-stage process sol-gel photopolymerization and photoinduced template decomposition/ablation to making mesoporous silica films. Performed at room temperature with a solvent-free solution of silicate precursor and amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer, the synthesis relies on photoacid generation to induce the fast formation (≈10 min) of mesostructured silica/surfactant domains. Continuation of UV exposure for three additional hours enables subsequent and complete photodegradation of the polyether copolymer, resulting in ordered or disordered mesoporous silica film. One of the most attractive features is that the one-step procedure relies on a continuous illumination provided by the same conventional medium-pressure Hg-Xe arc lamp equipped with a 254 nm reflector to enhance the emission of energetic photons <300 nm. In addition to X-ray diffraction and transmission electron microscopy, time-resolved Fourier transform infrared spectroscopy has proved to be a powerful in situ technique to probe the different chemical transformations accompanying irradiation. Photocalcination strengthens the inorganic network, while allowing to preserve a higher fraction of residual silanol groups compared with thermal calcination. A polyether chain degradation mechanism based on oxygen reactive species-mediated photo-oxidation is proposed.