Preparation of porous TEMPO-oxidized cellulose nanofiber (TOCNF) composites via Pickering-emulsion template for adsorption of aromatic pollutants

Abstract

TEMPO-oxidized cellulose nanofiber (TOCNF) based materials have garnered significant attention as functional adsorbents but high hydrophilicity restricts their application. In this study, three different synthetic polymers, polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA) and polystyrene (PS) were incorporated into the TOCNF network via Pickering emulsion templates to create porous composite materials for adsorption of typical aromatic pollutants (nitrobenzene, chlorobenzene and naphthalene). The effects of oil phase types, TOCNF concentration and oil/water ratios on emulsion stability, physicochemical properties and adsorption performance of the resultant composites were thoroughly investigated. The composites exhibited a macroporous structure with high porosity exceeding 80% and densities ranging from 0.084 to 0.226 g/cm³. Compared to pure TOCNF aerogel, the composites demonstrated significantly improved hydrophobicity, with the PS composite achieving the highest contact angle of 108.9°. Additionally, their mechanical strength and adsorption capacity for aromatic pollutants were markedly enhanced. Kinetic modeling results indicated that the PDMS composites showed the fastest adsorption rate. Freundlich isothermal modeling results indicated that the PS composite had the highest adsorption capacity, likely due to π-π interactions, which increased further at lower TOCNF concentration and lower oil/water ratio. All adsorption processes were spontaneous and exothermic physical processes. The adsorbents could be recycled for at least five cycles using ethanol as desorbing agent. This study highlights the potential of Pickering emulsion in developing novel functional adsorbents from natural biomass resources.