Unraveling the dual-site adsorption mechanisms and environmental sustainability of poly(N-vinylpyrrolidone)-graphene oxide composite for heavy metal removal: A combined experimental, DFT, and LCA study

The PNVP-GO composite was fabricated for efficient heavy metal removal. • The composite exhibited a high adsorption capacity of 86.96 mg·g −1 for Pb 2+ . • Topological analyses unveiled a synergistic dual-site specific adsorption mechanism. • Flexible PNVP chains overcome Pb 2+ lone pair hindrance via V-shaped cavity formation. A poly( N -vinylpyrrolidone)-graphene oxide (PNVP-GO) composite synthesized via optimized suspension polymerization demonstrated exceptional performance in removing Cu 2+ , Ni 2+ , and Pb 2+ . Adsorption of Cu 2+ and Ni 2+ followed the Langmuir isotherm, Pb 2+ recognition exhibited pronounced surface energetic heterogeneity accurately described by the three-parameter Sips and Toth models. Mechanistically, all uptake processes were rate-governed by spontaneous, endothermic chemisorption, consistent with the pseudo-second-order (PSO) kinetics, achieving maximum capacities of 73.96, 77.76, and 86.96 mg·g −1 for Cu 2+ , Ni 2+ , and Pb 2+ , respectively. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) confirmed chemisorption, while density functional theory (DFT) coupled with wavefunction topological analyses (ELF and IGMH) unveiled distinct dual-site specific adsorption mechanisms. Rigid GO carboxyl domains efficiently coordinate Cu 2+ and Ni 2+ but experience steric repulsion against the stereochemically active 6s 2 lone pair of Pb 2+ . Crucially, flexible PNVP chains overcome this barrier via conformational torsion (forming a V-shaped cavity) to accommodate the massive lone pair. A life cycle assessment (LCA) evaluated environmental sustainability and identified grid electricity for vacuum freeze-drying as the primary driver of Global Warming Potential (GWP, 75%). In comparison, ethanol washing was identified as the major contributor to Marine Eutrophication Potential (MEP, 29%). This study provides a universal theoretical paradigm for designing heavy metal adsorbents and highlights eco-design pathways to mitigate their life-cycle environmental footprints. Download: Download high-res image (288KB) Download: Download full-size image