Semiconductor−Metal Composite Nanostructures. To What Extent Do Metal Nanoparticles Improve the Photocatalytic Activity of TiO₂ Films?

TLDR

The study examines how semiconductor–metal composite films can accelerate the photocatalytic degradation of an azo dye. Noble metal (Au, Pt, Ir) nanoparticles were deposited onto nanostructured TiO₂ films by electrophoretic deposition and characterized using UV‑absorption spectroscopy and atomic force microscopy. TOAB‑capped metal nanoparticles on TiO₂ films enhanced photocurrent, shifted the flat‑band and quasi‑Fermi levels to more negative potentials, reduced oxygen‑mediated electron scavenging, but long‑term irradiation caused photocurrent loss due to interface chemical changes.

Abstract

Noble metal particles of Au, Pt, and Ir were deposited on nanostructured TiO2 film using an electrophoretic approach. The nanocomposite films were characterized by UV-absorption and atomic force microscopy (AFM). The deposition of tetraoctylammonium bromide (TOAB)-capped metal nanoparticles on TiO2 films improved the photocurrent generation and induced a shift in the apparent flat band potential. The TiO2 films modified with TOAB-capped metal nanoparticles were less prone to the electron scavenging by the oxygen in solution. Improved photoelectrochemical performance of semiconductor−metal composite film is attributed to the shift in quasi-Fermi level of the composite to more negative potentials. Continuous irradiation of the composite films over a long period causes photocurrent to decrease as the semiconductor−metal interface undergoes chemical changes. The role of semiconductor−metal composite films in improving the rate of photocatalytic degradation of an azo dye is also discussed.