Nanocellulose sponges embedding metal oxide nanoparticles for adsorption and photodegradation of microplastics

The pervasive presence and detrimental impact of microplastics (μPs) on the ecosystem necessitates the development of effective remediation strategies. As potential adsorbents for μPs, we present a strategy utilizing metal oxide nanoparticles and cellulose nanomaterials. A nanocellulosic matrix was prepared by processing microfibrillated cellulose (MFC) and (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibers (T-CNF). Magnetic nanocellulose sponges (NCs) embedding Fe₃O₄-TiO₂ nanoparticles into this matrix were prepared using a simple freeze-drying technique. The prepared NCs were modified with hexadecylphosphonic acid (HPA) to utilize its self-assembling behavior with metal oxide nanoparticles in capturing μPs. Surface wettability characteristics revealed the hydrophobic nature of the HPA-modified sponges, with water contact angles exceeding 100°. Polystyrene (PS), a widely used plastic commodity, was chosen as the representative μPs. The adsorption studies on μPs demonstrated a removal efficiency of up to 98 % for PS-NH₂ and 75 % for PS-CO₂H by the optimized sponge. Notably, the NCs exhibited photodegradation of μPs under UV irradiation due to TiO₂ nanoparticles embedded in cellulose matrix. The efficient adsorption capacity combined with remarkable attributes such as easy recovery, recyclability, and biocompatibility of these HPA-functionalized magnetic NCs showcases their potential as a sustainable solution for μPs remediation.