Photocatalytic properties of plasma-synthesized zinc oxide and tin-doped zinc oxide (TZO) nanopowders and their applications as transparent conducting films

Transparent conducting zinc oxide and tin-doped zinc oxide (TZO) nanopowders were synthesized for the first time using a novel plasma-assisted chemical vapor synthesis route. The injected precursors were volatized completely and rapidly followed by chemical reactions and subsequent quenching to yield fine nanopowder. The amount of tin nitrate was varied to obtain 3 and 5 at.% Sn designated as TZO1 and TZO2 respectively. XRD diffraction peaks of TZO1 nanoparticles indicated the presence of wurtzite structure without any tin oxide peaks except in TZO2 sample and SEM micrographs revealed spherical particles. The nanosized powders would make an excellent material for use as photocatalyst due to high surface to volume ratio. Optical examinations indicated that the band gap in TZO1 was redshifted to 3.16 eV from 3.22 eV in undoped ZnO nanoparticles. The photocatalytic properties of ZnO and TZO nanopowders were investigated using the methylene blue dye degradation under UV light irradiation and kinetic analyses indicated that the photodegradation of methylene blue followed pseudo-first order kinetic model using Langmuir–Hinshelwood mechanism. Furthermore, the TZO1 nanoparticles exhibited superior photocatalytic activity compared with ZnO and the improvement was ascribed to increase in specific surface area and enhanced oxygen vacancies as revealed from the XPS O 1s and PL spectra. Deposited films showed a hexagonal wurtzite structure and exhibited a c-axis preferred orientation perpendicular to the substrate. A minimum resistivity of 1.4 × 10^− 3 Ωcm was obtained at lower doping amount of 3 at.% Sn as in TZO1 film and all the films exhibited an average transmission of 80% indicating their suitability as a promising material in optoelectronic applications. Optical constants of the films were determined, which varied with doping amount. The photo-current properties of ZnO and TZO films were investigated and only TZO1 film showed photo response property when irradiated with UV lamp.