Sensitization of TiO2 nanoparticles in micro-emulsion by photo-excited dye molecules: A femtosecond transient absorption study

Photo-induced electron transfer reaction in controlled sized TiO2 particles sensitized by catechol and quinizarin 6-sulfonate (Qz-6S) has been investigated using femtosecond transient absorption spectroscopy. Size-controlled TiO2 nanoparticles were synthesized in reverse micelles using di-octyl sulfosuccinate (Aerosol-OT, AOT) as the surfactant stabilizer. The particle sizes of the nanoparticles were controlled by varying the water-to-surfactant molar ratio, w0 = [H2O]/[AOT]. Optical absorption measurements confirm that only strong coupling between the nanoparticles and the sensitizers can ensure sensitization the nanoparticles in the micro-emulsion media. Electron transfer process has been determined by monitoring electron in the conduction band in nanoparticle at 900 nm and parent cation in the visible region of the sensitizer molecules. Electron injection has been measured from the appearance signal of injected electron at 900 nm and it is found to be pulse-width (<50 fs) in both the systems. We have also carried out electron transfer studies of both the dye-nanoparticle systems in aqueous solutions where the particles have been prepared by sol–gel process and compared the data studied in micro-emulsion to see the effect of micro-environment.