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 alpha-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. An iron oxides/carbon composite with well-defined heterophase grain boundaries is synthesized and explored as dye removal for both the anionic Congo red and cationic crystal violet, which are found to be advantageous over homophase iron oxide/carbon composite counterparts. This fact is attributed to the charged defects and higher number of active sites available from heterophase grain boundaries.image (c) 2023 WILEY-VCH GmbH