Magnetic Nitrogen and Sulfur Doped Reduced Graphene Oxide for Congo Red Removal; Mechanism for the Synthesis of Adsorbent

Nitrogen‐ and sulfur‐doped reduced graphene oxide (NSrGO) was synthesized using a hydrothermal technique with thiourea and graphene oxide as precursors, and then magnetized via the co‐precipitation method. The synthesized magnetic NSrGO was then characterized using field emission scanning electron microscopy (FESEM), energy dispersive X‐ray (EDX) analysis, Fourier transform infrared spectrophotometry (FT‐IR), X‐ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). The magnetic NSrGO was then applied for the removal of the anionic dye Congo red (CR) from water samples. Optimization of key parameters—pH, adsorbent dosage, and removal time—revealed that a pH of 4, 15 mg of adsorbent, and a 20‐min removal time achieved over 90% removal efficiency. Adsorption isotherm analysis showed that CR adsorption onto magnetic NSrGO follows a multilayer process (the Freundlich isotherm model), with a maximum adsorption capacity of 135.1 mg/g. Additionally, the pseudo‐first‐order kinetic model best described the adsorption behavior of CR over time. The reusability assessment confirmed that magnetic NSrGO could be effectively employed over six consecutive adsorption/desorption cycles, consistently maintaining a removal efficiency above 80%. Overall, the results highlight the potential of magnetic NSrGO as an efficient and reusable adsorbent for the effective removal of CR from contaminated water.