Efficient removal of amine-modified polystyrene nanoplastics utilizing poly(N-isopropylacrylamide)-sodium carboxymethyl cellulose hydrogel beads: Parametric optimization and mechanistic insights

Nanoplastics (NPs), particularly positively charged NPs smaller than 100 nm, are emerging hazardous pollutants that pose a serious threat to aquatic ecosystems because of their non-biodegradable nature, ability to penetrate cell membranes, and tendency to form complexes. Therefore, the development of an effective adsorbent to remove positively charged nanosized NPs from contaminated water is crucial. In this study, interpenetrating polymer double-network (IPN) hydrogel beads composed of poly(N-isopropylacrylamide) (PNIPAM) and sodium carboxymethyl cellulose (NaCMC) were synthesized as adsorbents. The synthesis followed a photoinitiated free-radical mechanism in the presence of poly(ethylene glycol) diacrylate (PEGDA) as a cross-linking agent and 2-hydroxy-2-methylpropiophenone as a photoinitiator, utilizing a gas dynamic virtual nozzle (GDVN). For the first time, an IPN hydrogel synthesized by this approach was used to purify water containing positively charged amine-modified polystyrene (PS) NPs. Parametric optimization confirmed the effectiveness of the hydrogels for NPs elimination, achieving 99.83% removal efficiency (199.64 mg/g). The high efficiencies for the elimination of NPs from real seawater (99.55%) and tap water (98.11%), along with the sufficient adsorption capacity of 94.55% after five successive sorption/regeneration cycles, demonstrate the practical applicability of the synthesized hydrogel. The adsorption process followed a complex mechanism involving chemisorption/electrostatic bonding, as supported by the pseudo-second-order kinetics, Langmuir isotherms, and negative ΔG⁰ values, along with physical adsorption through H-bonding, π–π interactions, and pore filling. Considering its relatively high sorption capability, practical adaptability, and reusability, the synthesized IPN hydrogel is a viable option for treating NP-contaminated water.