Multifunctional Co2+ and Cr3+ Substituted Ni-Cu Spinel Ferrites for Wastewater Remediation and Supercapacitor Applications

• Co²⁺ and Cr³⁺ substituted ni-cu spinel ferrites (Ni 0.2 Cu 0.8-x Co x Cr y Fe 2₋y O₄) via sol-gel route. • The crystal size of ferrites decreased after Co²⁺ and Cr³⁺ substitution. • 89 % photodegradation of crystal violet dye under sunlight was observed. • Electrochemical measurements of ferrites revealed specific capacitance of 875 F/g. Materials with multiple properties can be employed in applications for wastewater remediation and energy conversion and storage. Co 2+ and Cr 3+ substituted Ni-Cu spinel ferrites (Ni 0.2 Cu 0.8-x Co x Cr y Fe 2-y O 4 ) were synthesized using the sol-gel route. Their structural, optical, and dielectric properties were analyzed via X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV–VIS), and dielectric measurements. The calculated crystallite size was in the range of 8 to 12.9 nm. A decreasing trend of porosity was observed after substitution. Optical studies revealed that the band gap increased after substitution, ranging from 5.280 to 5.58 eV. Dielectric constant and loss were decreased after substitution. Synthesized ferrite showed excellent photocatalytic activity (89 % degradation) for crystal violet dye. The electrochemical properties of the synthesized ferrites were additionally studied by galvanostatic charge/discharge (GCD), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Specific capacitance of 875F/g was observed by ferrites ( x = 0.04, y = 0.2) at 2A/g. These findings suggest that synthesized ferrites possess multifunctional properties making them suitable for wastewater remediation and supercapacitors.