M. Sundararajan

Bio: M. Sundararajan is an academic researcher from VIT University. The author has contributed to research in topics: Crystallite & Spinel. The author has an hindex of 10, co-authored 20 publications receiving 556 citations.

Photocatalytic efficiencies of Ni, Mn, Fe and Ag doped ZnO nanostructures synthesized by hydrothermal method: The synergistic/antagonistic effect between ZnO and metals

Abstract: The ZnO and different noble and transition metals (Ni, Mn, Fe and Ag) doped ZnO (M/ZnO) nanostructures were synthesized by hydrothermal method. The ZnO and M/ZnO photocatalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), fourier transform infrared (FTIR) and UV–vis spectrophotometry. The obtained XRD and FESEM results confirmed the well dispersion of Ni and Ag nanoparticles and highly agglomerated Mn and Fe nanoparticles on the surface of ZnO nanostructures. The optical band gap value was calculated as 3.24, 3.15, 3.10, 3.05 and 3.00 eV from UV–vis diffuse reflectance spectra of ZnO, Ag/ZnO, Ni/ZnO, Fe/ZnO and Mn/ZnO photocatalysts, respectively. The results of the photocatalytic degradation of tartrazine in aqueous solutions under the UV-light showed that Ni/ZnO exhibited higher photocatalytic activity than the other ones. Mn/ZnO demonstrated the lowest photocatalytic activity among the synthesized photocatalysts. Thus, Ni and Ag exhibited synergistic effect while Fe and Mn exhibited antagonistic effect on the ZnO photocatalytic activity. The maximum degradation rate of tartrazine was obtained to be 98.2% in the 60 min using Ni/ZnO. The plausible mechanisms were proposed and discussed for the enhanced or decreased photocatalytic activities resulting from different metals doped ZnO.

Synthesis of magnetically recyclable spinel ferrite (MFe2O4, M = Zn, Co, Mn) nanocrystals engineered by sol gel-hydrothermal technology: High catalytic performances for nitroarenes reduction

Abstract: Highly stable and magnetically recoverable MFe 2 O 4 (M = Zn, Co, Mn) spinel ferrite nanoparticles; synthesized using sol gel-hydrothermal technology via utilizing polyvinyl alcohol surfactant, were proposed as heterogeneous catalysts for the reduction of nitroarenes. The morphological characteristics, structural exploration, surface, optical, vibrational and magnetic properties were performed using powder X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray, N 2 sorptiometry, diffused UV–vis reflectance spectroscopy, FTIR, point of zero charge, vibrating sample magnetometer (VSM) and thermokinetic analysis via TGA technique. The results showed that MnFe 2 O 4 exhibited the best performance in the reduction of 4-nitrophenol (4-NP), 2,4,6 tri-nitrophenol (2,4,6-NP) and 4-nitroaniline (4-NA) and revealed 100% conversion into the corresponding amino derivatives in 270 sec with rate constant equal 0.01061 s −1 , 0.01134 s −1 and 0.01355 s −1 , respectively. The superiority of the catalytic reduction of MnFe 2 O 4 was due to increasing the pore radius and pore volume (6.75 nm, 0.227 cm 3 /g) values compared to other nanoferrites. The synthesized nanoferrites indicate independence of the activity on crystallite sizes due to the insignificant margin of change (from 6 to10 nm). Conversely, decreasing the activity of ZnFe 2 O 4 was due to increasing the Zn 2+ ions size that induces an increase in lattice parameter values and thus increases the long-range electron transfer between Fe 2+ –Fe 3+ ions. The MnFe 2 O 4 catalyst that presented the highest saturation magnetization (135 emu/g) indicated the highest reduction potential for 4-NA comparatively in the presence of NaBH 4 and the reduction reaction followed pseudo first-order kinetics. Increasing the reduction performance of 4-NA compared to other nitroaromatics on MnFe 2 O 4 was explained based on the formed intermediates, their reactivities, hydrophobicity and to point of zero charges. It has been explored that the reduction efficacy of 4-NP was enhanced on MnFe 2 O 4 with the addition of ammonium oxalate and benzoquinone where it was inferior following the addition of tertiary-butyl alcohol. More important correlations concerning the effect of octahedral sites, residual organics, heat of activation ( E a ) and activation free energy (Δ G *) values; determined while the removal of citrate/PVA moieties, on nitroarenes reduction rates were well scrutinized and discussed.