Publications

Bulk processing of porous silicon nanoparticles (nSi) of 50–300 nm size and surface area of 25–230 m²/g has been developed using a combustion synthesis method. nSi exhibits consistent photoresponse to AM 1.5 simulated solar excitation. In confirmation of photoactivity, the films of nSi exhibit prompt bleaching following femtosecond laser pulse excitation resulting from the photoinduced charge separation. Photocurrent generation observed upon AM 1.5 excitation of these films in a photoelectrochemical cell shows strong dependence on the thickness of the intrinsic silica shell that encompasses the nanoparticles and hinders interparticle electron transfer.

Iridium oxide, a water oxidation cocatalyst, plays an important role in mediating the hole transfer process of a UV-irradiated TiO₂ system. Spectroscopic identification of trapped holes has enabled their characterization in colloidal TiO₂ suspension and monitoring of the transfer of trapped holes to IrO₂. Titration of trapped holes with potassium iodide yields an estimate of three holes per particle during 7 min of UV irradiation of TiO₂ suspension in ethanol containing 5% acetic acid. The hole transfer to IrO₂ occurs with a rate constant of 6 × 10⁵ s^–1. Interestingly, IrO₂ also catalyzes the recombination of trapped holes with reduced oxygen species. The results discussed here provide a mechanistic and kinetic insight into the catalytic role of IrO₂ in the photogenerated hole transfer process.