Zirconium ferrite nanoparticles as smart materials for energy and environmental applications: fractional-order supercapacitors, reservoirs of F− ions, and efficient electrocatalysts for water splitting

A novel electrocatalyst, zirconium ferrite nanoparticles (NPs) (ZrFe₂O₅ NPs), was synthesized through coprecipitation and calcination processes at 300 °C and 500 °C using iron rust. The ZrFe₂O₅ NPs were used as catalysts for the hydrogen evolution reaction. Furthermore, these NPs in an alkaline medium exhibited superior properties of a fractional order supercapacitor, based on which a prototype device was fabricated to demonstrate its energy storage applications. The capacitance and phase graphs of the fractional-order supercapacitor exhibit a peak value of 1.5 F s^−1−α in the mid-frequency range, followed by a decrease at increased frequencies. Furthermore, these NPs were found to be the most effective agents for removing fluoride ions. In a modified one-pot synthetic approach, the hydrogel (Hy) was synthesized using PVA and glycerine in an aqueous medium at 100 °C. The composite Hy membranes were prepared by mixing Hy with these NPs, which were applied to remove fluoride ions efficiently within the pH range of 1–10 from the aqueous medium through adsorption, yielding defluorinated water. The adsorption process of fluoride ions was correlated with the Freundlich and Langmuir isotherms, with pseudo-second-order kinetics as the preferred approach. The zirconium ferrite NPs and the composite Hy membranes were characterized through various characterization techniques, i.e., XRD, XPS, FTIR, solid UV-visible spectroscopy, STA, FESEM, HRTEM, and BET surface area analysis.