Synthesis of High Surface Area and Different Properties of N-Doped Porous Carbon/Iron Oxide Materials via a One-Step Solvent-Free Self-Assembly Method; Effective Anionic and Cationic Dye Adsorption

This study presents the development of N-doped porous carbon/iron oxide composites with high surface areas, designed for the effective removal of organic contaminants from aqueous solutions. Using an environmentally friendly, one-step, solvent-free self-assembly method, the materials were synthesized at temperatures ranging from 500°C to 900°C, using dimethylglyoxime (DMG) as the carbon/nitrogen source and FeCl 3 as both a complexing and activating agent. Characterization via XRD, SEM-EDS, FTIR, VSM, XPS, and BET analyses showed that increasing the carbonization temperature significantly altered and improved the composites' textural properties. FeDMG800 and FeDMG900 demonstrated optimal hierarchical porous structures, high surface areas (829 and 978 m 2 /g, respectively), and superior pore volumes. Furthermore, adsorption kinetics followed the pseudo-second-order model optimally for both methylene blue and methyl orange, demonstrating that chemical adsorption is the rate-limiting step. Isotherm data fit both the Langmuir and the Freundlich models, suggesting a complex mechanism of monolayer and multilayer adsorption on heterogeneous surfaces. FeDMG800 and FeDMG900 achieved exceptional maximum capacities of 1099.66 mg/g for MB and 591.72 mg/g for MO. Thermodynamic analysis of FeDMG700 revealed spontaneous, endothermic adsorption with increasing entropy for both dyes, confirming physiosorption. These properties position FeDMG composites as versatile, highly efficient adsorbents for dye removal in wastewater treatment. • Environmentally friendly, single-step, solvent-free self-assembly method was used to develop N-doped porous carbon/iron oxide composites. • A high BET surface area of 978 m 2 /g was obtained for FeDMG900 with a well-developed porous structure. • FeDMG900 showed superior maximum adsorption capacities of 1099.66 mg/g for MB and 591.72 mg/g for MO. • Adsorption follows a so-called second-order model and is endothermic, spontaneous, and thermodynamically favorable.