Impact of Gd3+ doping on structural, electronic, magnetic, and photocatalytic properties of MnFe2O4 nanoferrites and application in dye-polluted wastewater remediation.

The present work focuses on developing Gd-doped Mn spinel nanoferrites and their potential application in the photodegradation of water pollutants. The impact of Gd3+ ion substitution on structural, electronic, and magnetic characteristics of manganese ferrites has been studied. Nanocrystalline samples of MnGdxFe2-xO4 (x = 0.0 to 0.10, in step size of 0.02) ferrites were prepared via sol-gel self-ignition route. The Rietveld, XPS, HRTEM, and SAED characterization methods confirmed the formation of phase pure ferrite nanoparticles (~ 8-22 nm) in the cubic spinel structure. The Gd3+ content in these nanoferrites responded to a systematic reduction in the size of nanocrystallites and an upsurge in the density of nanoferrites. The XPS study revealed fine assimilation of constituent elements in the fcc lattice and ruled out impurities in the nanoferrites. The Fe and the Gd ions were found to be in Fe3+ and Gd3+ states, respectively. While a major fraction of the Mn ions were found to be in the Mn2+ state, a small fraction of Mn4+ ions was observed on the surface of nanoparticles. The nanoferrites were found to exhibit a soft ferromagnetic state from 300 to 20 K limits. The highest saturation magnetization was observed for x = 0.02 (MS = 66.6 emu/g at 20 K). The observed magnetic properties can be understood with the competing (Fe3+ and Mn2+)A-O2--[Fe3+, Mn2+, and Gd3+]B superexchange interactions and magnetocrystalline anisotropy. Due to the small band gap energy of Gd-doped Mn ferrites than that of the pure Mn ferrite, they have demonstrated excellent photocatalytic activity for the degradation of methylene blue (MB) dye under visible light illumination. As much as 96.35% of the MB dye was found to get degraded in 70 min of light illumination over synthesized nanoparticles and the photodegradation reaction followed pseudo-first-order kinetics. The increased optical absorbance due to lower band gap, suppressed recombination rate of charge carriers, and enhanced charge mobility make them effective visible light active photocatalysts. This study revealed that the electronic, optical, and magnetic properties of MnFe2O4 nanoferrites could be easily tuned by varying the Gd3+ content and the prepared Gd-doped MnFe2O4 nanomaterials have boundless potential to be utilized in the future making promising active photocatalysts and degradation of harmful industrial dyes for enhanced protection in the fields of environment and health care.

Electronic Structure and Room Temperature Ferromagnetism in Gd-doped Cerium Oxide Nanoparticles for Hydrogen Generation via Photocatalytic Water Splitting.

Enhanced visible light photocatalytic activity of Gd-doped CeO2 nanoparticles (NPs) is experimentally demonstrated, whereas there are very few reports on this mechanism with rare earth doping. All-pure and Gd-doped CeO2 NPs are synthesized using a coprecipitation method and characterized using X-ray diffraction (XRD), absorption spectroscopy, surface-enhanced Raman Spectroscopy (SERS), X-ray photoelectron spectroscopy (XPS), and superconducting quantum interference device (SQUID). The effect of Gd-doping on properties of CeO2 is discussed along with defects and oxygen vacancies generation. The XRD confirms the incorporation of Gd3+ at the Ce3+/Ce4+ site by keeping the crystal structure same. The average particle size from transmission electron microscopy (TEM) images is in the range of 5-7 nm. The XPS spectra of Ce 3d, O 1s, and Gd 4d exhibits the formation of oxygen vacancies to maintain the charge neutrality when Ce4+ changes to Ce3+. The gradual increase in hydrogen production is observed with increasing Gd concentration. The observed results are in good correlation with the characterization results and a mechanism of water splitting is proposed on the basis of analyses. The absorption spectra reveal optical band gap (2.5-2.7 eV) of samples, showing band gap narrowing leads to desired optical absorbance and photoactivity of NPs.

Kinetics of sonophotocatalytic degradation of an anionic dye nigrosine with doped and undoped zinc oxide.

The current research focuses on the photocatalytic, sonocatalytic and sonophotocatalytic degradation of nigrosine dye with nitrogen-doped and undoped zinc oxide powders. The sonophotocatalytic degradation of dye was found to occur at a higher rate than during photo- or sonocatalytic processes. Nitrogen-doped and undoped zinc oxide powders were synthesized by a wet chemical method. Further, scanning electron microscopy (FESEM), electron dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-VIS spectroscopy (UV-VIS) and transmission electron microscopy (TEM) were used for the characterization of N-doped ZnO. The kinetics of nigrosine degradation were also studied and the results indicated that the degradation kinetics of nigrosine followed the first-order kinetics. The rate constant and the percentage of degradation were found to be highest, 7.33 × 10-4 (s-1) and 92% respectively, for sonophotocatalytic process after 90 min of reaction. Due to an increase in the available surface area or active sites of the catalyst, a higher rate constant and degradation efficiency was observed in the sonophotocatalytic system than in the photocatalysis system.