Plasma synthesis of photocatalytic TiOxthin films

The development of efficient photocatalytic materials is promising technology for sustainable and green energy production, fabrication of self-cleaning, bactericidal, and super hydrophilic surfaces, CO2 photoreduction, and decomposition of toxic pollutants in air and water. Semiconductors with good photocatalytic activity have been known for four decades and they are regarded as promising candidates for these new technologies. Low-pressure discharge plasma is one of the most versatile technologies being used for the deposition of photocatalytic semiconductor thin films. This article reviews the main results obtained by the author in using low-pressure plasma for synthesis of TiOx thin films with applications in photocatalysis. Titanium dioxide thin films were obtained by radio frequency magnetron sputtering deposition, plasma enhanced chemical vapour deposition, and high power impulse magnetron sputtering deposition. The effects of the plasma deposition method, plasma parameters, film thickness and substrate on the film structure, chemical composition and photocatalytic activity are investigated. The photocatalytic activity of plasma synthesised TiOx thin films was estimated by UV light induced hydrophilicity. Measurements of photocurrent decay in TiOx thin films in vacuum and air showed that the photocatalytic activity is closely connected to the production, recombination and availability for surface reactions of photo-generated charge carriers. The photocatalytic activity of TiOx thin films was investigated at nanoscale by atomic force microscopy. Microscopic regions of different hydrophilicity on UV light irradiated films are discriminated by AFM atomic force microscopy measurements of adhesion and friction force.