Synthesis, structural and electrical conduction of some dual doped semiconductor oxides nanoparticles for photocatalytic degradation of Victoria blue-B and Brilliant yellow under solar light irradiation

In this study, the nanoparticles of undoped and dual (codoped) doped semiconductor oxides such as Bi2O3, Bi1.9Sm0.038Cu0.062O3; Co3O4, Co2.902Mn0.049Dy0.049O4; V2O5, V1.91Ni0.043Gd0.047O5; Cu2O, Cu1.927Mn0.036Yb0.037O; CeO2, and Ce0.938Ni0.028Zn0.034O2 were synthesized by tartarate and hydroxide coprecipitation method. The composition, structure, morphology, surface and optical properties of undoped and dual doped semiconductor oxides have been investigated by X-ray fluorescence spectroscopy (XRF), Energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), Scanning electron micrographs (SEM), X-ray photoelectron spectroscopy (XPS), BET surface area analyzer and UV–Vis diffuse reflectance absorption spectra (UV–vis DRS). The XRD and SEM studies showcase monodispersion of undoped and dual (co-doped) doped semiconductor oxides in the average grain size range of 36–65 nm with a monoclinic structure for Bi2O3 and its doped oxide, cubic structure for Co3O4, Cu2O, CeO2 and their respective doped oxides and orthorhombic structure for V2O5 and its doped oxide. Rietveld refinements of XRD pattern and XPS results confirmed that the dual dopants exist in + 2 or + 3 states and successfully incorporated into the semiconductor oxide matrix. BET surface areas for these oxides were found in the range of 25.3–65.4 m2g−1. The band gap energy (Eg) of undoped and doped semiconductor had a direct transition to fall between 2.10 and 3.12 eV as estimated from the optical absorption data (UV–vis DRS) and found absorption band edge (λg) in the visible-light range. The d.c. electrical conductivity and thermo-electric power measurements for all compounds showed n-type semiconductor except undoped and doped Cu2O and Co3O4 compounds showed p-type semiconductivity. The photo catalytic activity of undoped and dual doped semiconductor oxides in the Victoria blue-B (VB) and Brilliant yellow (BY) solutions were studied in sunlight irradiation. A set of optimized conditions such as the amount of these oxides, initial dye concentration, pH, contact time and dopants on the photodegradation of these dyes were investigated in detail. The dual doped semiconductor oxides showed a noteworthy enhancement in the degradation of VB and BY dyes under exposure to sunlight. The enhanced photocatalytic activity can be attributed to the incorporation of multivalent dopants in semiconductor oxide matrix promoted the separation of photogenerated charges, inhibited the recombination of photogenerated carriers, and thus prolonged the charges lifetime to participate in the photocatalytic reaction. The kinetic measurements indicate the dominance of pseudo-first order rate constant for Victoria blue-B (VB) were higher than that of Brilliant yellow (BY) in all cases, indicating that the photocatalytic degradation of VB was easier and more rapid than BY dye during the adsorption and also ascribed to different molecular structure to these dyes. A tentative reaction mechanism has also been proposed for this photocatalytic reaction.