Rare Earth Ions (La3+ And Eu3+) Doped Nickel Zinc Ferrite Nanomaterials and Their Composites with Reduced Graphene Oxide for Photocatalytic and Electrochemical Sensor Applications

Abstract

The regulation of colorants used in food products and industrial wastes is crucial, as they negatively affect human health and the environment. In this study magnetically separable rare earth metal ions (RE=La3+ and Eu3+) doped nickel-zinc (NZF) spinel ferrite (Ni0.75Zn0.25RExFe2-xO4) nanoparticles and their composite with reduced graphene oxide (Ni0.75Zn0.25RE0.06Fe1.94O4@rGO) were successfully synthesized by sol-gel auto-combustion and ultra-sonication methods respectively. The synthesized nanomaterials and nanocomposites were characterized by using different advanced instruments. The X-ray diffraction (XRD) analysis confirmed the formation of Face-centered cubic (FCC) ferrites with a crystal size range of 21.41 and 44.94 nm. The formation of the desired nanocomposite, with uniformly distributed spherical-shaped polycrystalline nanoparticles on nanosheets of reduced graphene oxide, was verified by scanning electron microscopy (SEM) equipped with energy dispersive x-ray (EDAX) and high resolution –transmitted electron microscope equipped with small angle electron diffraction (HR-TEM/SAED). The elements' surface composition and valance states in Ni0.75Zn0.25RE0.06Fe1.94O4@rGO nanocomposite were identified using X-ray photon electron spectroscopy (XPS). The specific surface area and pore size distribution of La3+and Eu3+ doped Ni0.75Zn0.25Fe2O4 nanomaterials and their composite with rGO were obtained by Brunauer-Emmett-Teller (BET) analysis. From UV-diffractive spectroscopy (UV-DRS) analysis, the band gap energies were found to be 1.691 eV, 1.797 eV, and 1.624 eV for NZLF@rGO, NZEF@rGO, and NZL EF@rGO nanocomposite respectively. The synthesized nanocomposite materils (NZLF@rGO, NZEF@rGO, and NZL-EF@rGO) were applied for the photocatalytic decolorization of selected binary dyes (methylene blue (MB) and methyl orange (MO)) under irradiation of visible light and modification of carbon paste electrode for selective detection of common food colorants (sunset yellow (SY) and tartrazine (TZ)). Results showed that as compared to La3+and Eu3+ doped NZF ferrite nanoparticles, Ni0.75Zn0.25RE0.06Fe1.94O4@rGO nanocomposite had exhibited potential photocatalytic efficiency for simultaneous degradation of MB and MO and electrochemical detection of SY and TZ. Their degradation efficiency was exhibited up to 92-97 % for MB and 96-99 % for MO within 40 min under the optimized conditions of pH = 9, initial concentration of dyes (5mg/L), and catalyst dosage of (50 mg), irradiation time (40 min). Compared to other reactive species, hydroxyl radical (•OH) plays a vital role in the simultaneous degradation of binary dyes. The synergetic effect of Ni0.75Zn0.25Fe2O4, RE ion, and rGO in Ni0.75Zn0.25RE0.06Fe1.94O4@rGO nanocomposite also efficiently improved the electrochemical response of carbon paste electrode on the simultaneous detection of SY and TZ. The detection limits were in the range of 0.0043-0.0067 μM for SY and 0.0034-0.0048 µΜ for TZ under the optimized pH=6, analyte concentration 10 mg, and scan rate (50 mV/s). The high sensitivity, selectivity, reproducibility, straightforward fabrication process, good electrode stability, and capacity to regenerate the electrode surface under the optimized conditions make the fabricated electrode ideal for the simultaneous detection of SY and TZ in real samples.