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) (ZrFe(2)O(5) NPs), was synthesized through coprecipitation and calcination processes at 300 °C and 500 °C using iron rust. The ZrFe(2)O(5) 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.