Tailored surface modification of cellulose nanofibers enables enhanced co-adsorption of nanoplastics and mercury ions

Abstract

Addressing the challenge of simultaneous removal of disparate pollutants like nanoplastics (NPs) and heavy metal ions (Hg²⁺), we developed a bifunctional cellulose nanofibrous membrane via electrospinning followed by targeted surface modification. Material characterization confirmed the intended structural and chemical features. Adsorption kinetics fit the pseudo-second-order model, while equilibrium data aligned with the Langmuir model, yielding maximum capacities of 47.6 mg g⁻¹ for NPs and 65.2 mg g⁻¹ for Hg²⁺. Thermodynamic analysis indicated spontaneous and endothermic chemisorption processes. XPS and DFT calculations provided detailed mechanistic insights, identifying quaternary ammonium sites as crucial for NP binding (electrostatic interaction, H-bonding) and C–S–C, –NH₂, and –COOH groups, particularly the engineered C–S–C linkage, as key chelating sites for Hg²⁺. Significantly, a unique synergistic bridging mechanism was discovered during simultaneous adsorption: Hg²⁺ reduced NP surface charge, enabling layered stacking, while NPs facilitated Hg²⁺ uptake via platform bridging, enhancing removal efficiency beyond single-pollutant scenarios. These findings highlight complex interactions in multi-component adsorption systems and offer avenues for designing efficient multifunctional materials.