Mechanistic investigation of Rhodamine B adsorption onto MWCNT/AgNP nanocomposites under complex aqueous conditions

Abstract

The efficient removal of persistent organic dyes under realistic wastewater conditions remains a major challenge in environmental remediation. Herein, a multi-walled carbon nanotube/silver nanoparticle (MWCNT/AgNP) nanocomposite was developed and systematically evaluated for Rhodamine B (RhB) removal under complex aqueous environments. The material exhibited a high adsorption capacity of 286.5 mg g⁻¹ with rapid equilibrium within 45 min. Adsorption followed the Langmuir model (qₘₐₓ = 279.0 mg g⁻¹) and pseudo-second-order kinetics, while thermodynamic parameters (ΔG° = −5.6 to − 6.9 kJ mol⁻¹, ΔH° = +12.7 kJ mol⁻¹) confirmed a spontaneous and endothermic process. Notably, high adsorption performance was maintained at elevated dye concentration (3000 mg L⁻¹) and under high ionic strength, indicating strong resistance to environmental interference. Mechanistic analysis suggested that RhB adsorption likely involves the synergistic contribution of π–π interactions, hydrophobic effects, electrostatic attraction, and weak Ag-mediated interactions. Unlike conventional adsorption studies under simplified conditions, this work provides a condition-dependent interpretation of adsorption behavior by linking surface chemistry to adsorption performance in complex aqueous media. These findings highlight the robustness of the developed MWCNT/AgNP nanocomposite under the investigated conditions and its promising potential for advanced wastewater treatment applications.