Evaluation of nanocellulose interaction with water pollutants using nanocellulose colloidal probes and molecular dynamic simulations

Atomic Force Microscope (AFM) probes were successfully functionalized with two types of nanocellulose, namely 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO)-mediated oxidized cellulose nanofibers (TOCNF) and cellulose nanocrystals (CNC) and used to study interfacial interactions of nanocellulose with Cu(II) ions and the Victoria blue B dye in liquid medium. TOCNF modified tip showed higher adhesion force due to adsorption of Cu(II) ions and dye molecules compared to CNC ones. Exploring the adsorption properties through classical reactive molecular dynamics simulations (ReaxFF) at the atomic scale confirmed that the Cu(II) ions promptly migrated and adsorbed onto the nanocelluloses through the co-operative chelating action of carboxyl and hydroxyl species. The adsorbed Cu(II) ions showed the tendency to self-organize by forming nano-clusters of variable size, whereas the dye adopted a flat orientation to maximize its adsorption. The satisfactory agreement between the two techniques suggests that functionalized AFM probes can be successfully used to study nanocellulose surface interactions in dry or aqueous environment.