Removal of copper (II) by spinel ferrite oxides and rGO composite electrodes in capacitive deionization

Heavy metals such as copper are among the hazardous components found in wastewater, which can be removed by capacitive deionization (CDI). The nanoscale spinel ferrite oxide crystals demonstrate lattice-driven pseudocapacitive electrosorption. A two-step hydrothermal method was employed to fabricate nanocomposite electrodes comprising NiFe₂O₄/rGO (NFO/rGO) and CoFe₂O₄/rGO (CFO/rGO). The hybrid pseudocapacitive nanocomposites NFO/rGO and CFO/rGO exhibited electrochemical capacitances of 123. 16 F g⁻¹ and 186.08 F g⁻¹, respectively at 10 mVs⁻¹. The CDI experiments confirmed that the nanocomposites NFO/rGO and CFO/rGO exhibited high capacities for removing Cu²⁺, with values of 49.08 mg g⁻¹ and 51.89 mg g⁻¹, respectively, greater than those of conventional carbon-based materials. An in-depth quantitative electrochemical analysis showed that the pseudocapacitive contributions on electrosorption were about 43–67 % for NFO/rGO and 57–79 % for CFO/rGO as scan rates decreased from 70 mV s⁻¹ to 10 mV s⁻¹. Both nanocomposites NFO/rGO and CFO/rGO demonstrated superior adsorption performance compared to rGO and similar materials reported in the literature. This improvement was attributed to its enhanced crystallinity, reduced particle size, and increased surface area, which collectively facilitated more efficient ionic diffusion kinetics. Both nanocomposite electrodes were fully regenerative and maintained consistent performance over multiple cycles. This study underscores the significance of using high-performance pseudocapacitive spinel ferrite oxide electrodes for the removal of heavy metals from wastewater.