Heterophase Grain Boundary-Rich Superparamagnetic Iron Oxides/Carbon Composite for Cationic Crystal Violet and Anionic Congo Red Dye Removal

Iron oxide-based nanostructures receive significant attention as efficient adsorbents for organic dye removal applications. Herein, iron oxide/carbon composite with well-defined heterophase grain boundaries is synthesized by a simple precipitation method and followed by calcination. The local structure, spin dynamics, and magnetic properties of heterophase iron oxides/carbon composite are thoroughly investigated to explore its cationic and anionic dye removal capability. To validate the effectivity of the presence of heterogeneous grain boundaries, iron oxide/carbon nanocomposite with homogeneous grain boundaries is also examined. For an initial dye concentration of 50 mg L⁻¹, pH 7, and adsorbent dose of 0.2 g L⁻¹, the hetero-IOCC exhibits a removal capacity of 71.63 and 140.19 mg g⁻¹ for the cationic crystal violet and the anionic Congo red dyes, respectively. These values are significantly greater than those exhibited by as-synthesized imidazole-capped superparamagnetic α-Fe₂O₃, 48.15 and 53.19 mg g⁻¹; and homophase iron oxide/carbon nanocomposite, 12.51 and 17.95 mg g⁻¹, respectively. Adsorption isotherms and kinetic studies indicate that the Langmuir isotherm model is found to be an appropriate model following the Elovich kinetic model. A detailed dye adsorption investigation on the pH effect, thermodynamic parameters, coexisting ionic effect, and reusability is also carried out.