Enhanced photocatalytic activity through insertion of plasmonic nanostructures into porous TiO₂/SiO₂ hybrid composite films

Composite TiO₂/SiO₂ porous thin films prepared using the sol–gel process were doped with dispersion of bipyramid-like gold nanoparticles (AuBP). The impact of the presence of the nanoparticles on the photocatalytic activity during degradation of formic acid in aqueous media was fully investigated and an improvement of the efficiency was observed. The films compositions and structures were characterized by means of UV–vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), goniometry, and diffuse reflectance measurements. The photocatalytic activity was evaluated through decomposition of formic acid and correlated with the structure and the spectroscopic characterizations. The best results in terms of photocatalysis were obtained with thin films doped with 1 wt.% of AuBP; more specifically, the initial degradation rate of formic acid was nearly two times higher than with the undoped reference. It was observed that after three cycles the performance of the prepared photocatalyst does not undergo significant changes. No photocatalytic activity was detected for any of the synthesized thin films under visible light irradiation alone. The photocatalytic improvement was correlated with the lowering of the band gap of TiO₂.