Development of a β-cyclodextrin-chitosan polymer as active coating for cellulosic surfaces and capturing of microcystin-LR

Abstract

In the search for more environmentally friendly adsorbent materials, the use of polysaccharides results attractive. Especially, as they can be used as coatings to add functionality to common materials as a new avenue to explore. Their inherent tendency to adsorb into each other is valuable as it adds a variety of functional groups on the outmost surface layer. Our project focuses on the pre-modification of the bio-polymer chitosan (Ch) with a 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) oxidized β-cyclodextrin (Ch-TOCD), which was then adsorbed onto the cellulose nanofibrils (CNF) surface. Furthermore, the mechanism driving the adsorption of the modified chitosan onto the cellulose backbone was studied by using three different Ch-TOCD conjugates possessing different degrees of substitutions. This was conducted to evaluate whether the adsorption was guided by the change of the available electrostatic interactions between the amino (Ch) and the residual carboxyl groups of cellulose or if the adsorption was driven by the dispersive forces of the hydroxyl groups from both polysaccharides. Finally, to assess the viability of the added hydrophobic cavities (Ch-TOCD conjugate), the capture of an amphipathic toxin categorized as a monitored pollutant (microcystin-LR) was followed by Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) on a surface level and by High-performance liquid chromatography (HPLC) when the Ch-TOCD coating was applied in CNF beads. Results showed that the adsorption of Ch-TOCD was accomplished at similar levels independent of the degree of substitution. The highest adsorbed amounts of microcystin-LR were 20.5 mg/g on the model coated CNF surface, and 2.36 mg/g on the CNF coated beads. The successful coating of two nanocellulose systems and the positive adsorption of the microcystin suggest a broad-scale application of this bio-based, low energy input coating in high-end fields such as drug delivery, textile, and water restoration.