Chitosan-Silver PolyHIPE Nanocomposites as Sustainable Bactericidal Filters

Pickering high internal phase emulsions (HIPEs) were employed as templates to fabricate chitosan (CS)-silver macroporous nanocomposites (polyHIPE NCs) with a three-dimensional interconnected structure and accessible bactericidal surfaces. Silver nanoparticles (AgNPs) were synthesized in situ within the CS continuous phase via chemical reduction and acted as functional stabilizing agents in combination with the nonionic surfactant Pluronic F127. Subsequent cross-linking of the CS continuous phase with glutaraldehyde solidified the emulsion structure, preserving the emulsion-derived porosity and enabling the localization of AgNPs on the porous surface. The resulting polyHIPE NCs exhibited high cross-linking degrees (>86%) and controlled swelling behavior in water (gravimetric water uptake = 138.3 ± 2.3% and volumetric = 36.9 ± 1.2% at equilibrium). The influence of AgNPs loading and surfactant concentration (2, 5, and 7 wt %) on pore architecture and bactericidal performance was systematically investigated. Reducing the surfactant concentration from 7 to 5 wt % was only feasible at the highest AgNPs loading due to the synergistic stabilization effect between nanoparticles and surfactant, yielding monoliths with an average pore diameter of 16.8 ± 0.3 μm, an average pore window of 4.31 ± 0.4 μm, a degree of openness of 16%, and silver content of 2.01 mg kg^-1. When evaluated as bactericidal filters against Escherichia coli (ATCC 25922), the optimized monolith achieved removal efficiencies up to ∼99.2% (∼2.1 log reduction) with negligible silver leaching in the treated water (3.0 × 10^-4 mg L^-1). Bacteria were not only retained within the porous network but also exhibited visible membrane damage, suggesting inactivation upon contact with the bactericidal polyHIPE NCs surface. These findings demonstrate that CS-silver polyHIPE NCs can provide an effective and sustainable bactericidal filtration platform, integrating hierarchical porosity, accessible bactericidal surfaces, and negligible AgNPs release. Their chitosan-based matrix suggests potential biodegradability, supporting their use in environmentally compatible water treatment applications.