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.
