Processing of bio-based photocatalytic sponge-like structures containing C,N-TiO2 colloidally dispersed onto cellulose nanofibers for microplastic remediation

This study presents an innovative approach for immobilizing a highly efficient photocatalyst on a bio-based matrix derived from biorefinery processing of agricultural biomass. This strategy adds significant value to the lignocellulosic fraction, while reducing the number of unit operations typically required for photocatalyst recovery (e.g., filtration, centrifugation, or sedimentation) in the photocatalysis of microplastics (MPs) for water pollution control. The removal of polyethylene (PE) MPs was investigated using a green photocatalytic C,N-TiO₂ powder immobilized on a cellulose nanofiber (CNF) support. The resulting sponge-like structures (aerogels) combined the photocatalytic activity of C,N-TiO₂ with the physical collection capabilities of CNF to enhance the removal of MPs. At low pH and MPs concentrations, CNF-C,N-TiO₂ achieved 18.46 % MPs removal after 6 h of irradiation at 254 nm, primarily via photocatalytic degradation driven by reactive oxygen species (ROS) rather than physical collection. Photocatalysis was confirmed by MPs surface roughness reduction, formation of C=O bond-containing compounds, and OH^● scavenger tests. Additionally, smaller PE fragments were detected in the CNF-C,N-TiO₂ aerogel. Comparative analysis of the pure CNF and CNF-P25 TiO₂ structures showed limited MP removal. This was attributed to photolysis for CNF, and to photocatalysis and physical collection for CNF-P25 TiO₂. Overall, this study highlights the potential of CNF-C,N-TiO₂ sponge-like structures for MPs removal through a combined photocatalytic and physical approach, while also emphasizing the need to optimize the reaction conditions for maximum efficiency.