SYNTHESIS AND CHARACTERIZATION OF PALLADIUM BASED CATALYSTS FOR PHOTODEGRADATION OF AZO DYES IN AQUEOUS SOLUTIONS

Abstract

Mixed oxide PdO/NiO and bimetallic Pd/Ni nanoparticles were successfully prepared by facile chemical co-precipitation and co-reduction methods and were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDX), UV-Vis diffuse reflectance spectrophotometry (UV-DRS), Brunauer-Emmett-Teller (BET) Nitrogen adsorption method and thermal analysis (TGA) techniques. Mixed oxide PdO/NiO nanoparticles have an average crystallite size of 20. 7 nm, 2.95 eV band gap energy and surface area of 15.931 m 2 /g, while bimetallic Pd/Ni has an average crystallite size of 64.6 nm, 3.02 eV band gap energy and surface area of 13.401 m 2 /g. The photocatalytic activities of the nanoparticles were dtermined using congo red, methyl red, methyl orange and eriochrome black dyes in aqueous solutions and the degradation efficiencies of the system were evaluated with respect to catalyst load, irradiation time, pH, initial concentration, co- occurring anions, irradiation source and oxidants. Optimum pH was observed under acidic region for all dyes with mixed oxide catalyst and optimum pH was observed under the mild alkaline condition for all dyes with the bimetallic catalyst. The optimum mixed oxide catalyst load for congo red, methyl red, methyl orange and eriochrome black were 0.1, 0.2, 0.15 and 0.15 g respectively while for the bimetallic catalyst, it was 0.05, 0.2, 0.05 and 0.05 g respectively. Both UV and solar light degradation for both catalysts gave superior photocatalytic efficiencies towards all the dye solutions as compared in the dark. The pseudo-first-order equation was revealed to be in good agreement with the experimental data with high R 2 values and the COD results obtained showed a good mineralization rate for the azo dyes in solution. The results reveal that the mixed oxide PdO/NiO and bimetallic Pd/Ni nanoparticles have a high photocatalytic performance of 93 – 99 % toward most of the azo dyes degradation and show good photostability and can be reused over 12 cycles before the loss of activities.