Efficient adsorptive removal of nortriptyline pharmaceutical residue from wastewater using a new 3D sulfur-doped graphene composite

• A new 3D sulphur-doped graphene (3DSG) composite for notriptyline removal. • Langmuir model fits best with a maximum adsorption capacity of 472.9 mg/g. • Adsorption kinetics best represented by the pseudo-second-order model. • Nortriptyline removal was successfully optimized by central composite design. • Optimized removal: 80.74 % at 12.5 mg 3DSG, 100 ppm solution, 30 °C and 35 min. Nortriptyline, a widely prescribed tricyclic antidepressant, has been increasingly detected in natural water bodies due to the limited removal efficiency of conventional wastewater treatment systems, thus posing ecological risks to aquatic life. This study reports the development of a new three-dimensional sulfur-doped graphene oxide (3DSG) composite for the removal of nortriptyline from aqueous environments. The 3DSG integrates graphene oxide with sulfur doping, resulting in a porous structure enriched with hydroxyl and sulfonic functional groups, as confirmed through characterization studies, and these enhance its adsorption performance. The adsorption equilibrium was best described by the Langmuir isotherm model (R 2 : 0.947–0.973; RMSE: 27.81–38.41; χ 2 : 30.10–49.95), with a maximum adsorption capacity of 472.9 mg/g. The adsorption kinetics followed the pseudo-second-order model (R 2 : 0.993–0.998; RMSE: 3.088–9.361; χ 2 : 0.379–2.329). Thermodynamic analysis indicated that the process is endothermic (ΔH: 2.368 to 28.20 kJ/mol) and spontaneous (ΔG: −27.21 to −19.60 kJ/mol). The adsorption mechanism involves multiple interactions including hydrogen bonding, hydrophobic, π-π and electrostatic interactions. The reusability of the 3DSG composite was confirmed over four runs, using 0.1 mol/L hydrochloric acid as the regeneration medium. Optimization via response surface methodology resulted in a high removal efficiency of 80.74 %, achieved with 12.5 mg of 3DSG at 100 ppm nortriptyline concentration, within 35 min at 30 °C. Overall, the findings highlight the potential of 3DSG as a highly effective and reusable nanomaterial for the remediation of nortriptyline contaminated water, offering a sustainable solution for wastewater treatment.