A green approach to water purification: amoxicillin adsorption from aqueous solution by a microwave-synthesized graphene-aminated lignin composite

Abstract

This research introduces a new eco-friendly adsorbent, a graphene-aminated lignin (GAL) composite, created through a quick, solvent-free microwave exfoliation method, representing a green and scalable route for advanced adsorbent fabrication. The innovation lies in the integration of defect-minimized graphene with amine-functionalized lignin, enabling enhanced surface functionality, improved dispersion, and abundant active adsorption sites, while polyvinyl alcohol (PVA) was introduced to enhance structural stability and reusability. The composite demonstrated outstanding maximum adsorption capabilities of 96.02 mg g⁻¹, with impressive removal efficiency of 96.02% at an initial concentration of 20 mg L⁻¹ under optimal conditions of pH 6, adsorbent dosage of 0.02 g, and reaching equilibrium within 40–60 minutes. The adsorption kinetics followed the pseudo-second-order model, indicating that the process is primarily governed by chemisorption. Isotherm fitting showed excellent agreement with the Langmuir model, suggesting monolayer adsorption on a homogenous surface, while thermodynamic parameters (ΔG° = −11.59; ΔH° = 27.53 kJ mol⁻¹) indicated the process is spontaneous and endothermic. Furthermore, the GAL composite maintained approximately 86.4% efficiency after five reuse cycles, highlighting its potential for regeneration and scalability in real-world wastewater treatment applications. This study presents a sustainable and high-performance adsorbent platform that combines biopolymer valorization with nanomaterial innovation for the advanced removal of pharmaceutical pollutants.