N. Chronopoulou, M. Panagopoulou, D.S. Tsoukleris, S. Spanou, E.A. Pavlatou
7th International Conference on Materials Science and Condensed Matter Physics (2014), 16-19 September, Chisinau, Moldova (poster)
For a considerable number of practical applications, TiO2 and related semiconducting materials have been widely used as photocatalysts in order to decompose liquid industrial pollutants. The photocatalyst, usually is immobilized in the form of a thin film on an inert substrate1. In this framework, this work describes the synthesis of efficient Ni-P titania photocatalysts which have a high stability, an excellent corrosion resistance and a photocatalytic action against liquid pollutants. Nano-structured composite coatings were obtained by electrochemical codeposition of TiO2 nano-particles (mean diameter 21 nm, Degussa P25) with NiP matrix, from an additive-free Watts type bath, under both direct and pulse current conditions. The impact of pulse plating parameters, such as frequency of applied current pulses over a wide range of values, as well as the load of the particles in the electrolyte, on the composition, microstructure, morphology and microhardness of the Ni–P TiO2 composite coatings were examined. The aim of the study was to correlate the observed structural characteristics of the coatings with the resulting mechanical (microhardness), wear and photocalaytic behavior. The surface morphology and the structure of composites were investigated, along with the distribution and the percentage of the embedded nano-particles in nickel based matrices. The data revealed that enhanced codeposition percentages of titania nanoparticles in the alloy matrix were obtained under high pulse frequencies and relatively high load of particles in the bath. Moreover, thermal treatment of the coatings was found to be beneficial for enhancing microhardness values, and improving wear and photo-induced properties. The wear behavior of the coatings was investigated by using a Ball-on-Disc tribometer under dry uni-directional sliding conditions, and the results showed that the presence of the reinforcing TiO2 nanoparticles increased the wear resistance of the composite coatings compared to the pure NiP ones. For the majority of the composites, the sliding wear took place by abrasive and adhesive mechanisms. The photo-induced properties of the Ni–P TiO2 composite coatings were investigated by means of photocatalytic degradation of methyl-orange under UV irradiation (350 nm) as well as by contact angle measurements. The best photo-induced properties were observed for composites thermally treated and exhibiting the highest TiO2 codeposition percentage in the alloy.