Self-Assembled and Cross-Linked Animal and Plant-Based Polysaccharides: Chitosan-Cellulose Composites and Their Anion...

Self-assembled and cross-linked chitosan/cellulose glutaraldehyde composite materials (CGC) were prepared with enhanced surface area and variable morphology. FTIR, CHN, and ¹³C solid state NMR studies provided support for the cross-linking reaction between the amine groups of chitosan and glutaraldehyde; whereas, XRD and TGA studies provided evidence of cellulose-chitosan interactions for the composites. SEM, equilibrium swelling, and nitrogen adsorption studies corroborate the enhanced surface area and variable morphology of the cross-linked biopolymers. Equilibrium sorption studies at alkaline conditions with phenolic dyes, along with single component and mixed naphthenates in aqueous solution revealed variable uptake properties with the composites. The Freundlich isotherm model revealed that the composite at the highest levels of cross-linker, CGC3, had the highest sorption affinity (K_F; L mmol/g) for phenolphthalein (phth) followed by ortho-nitrophenyl acetic acid (ONPAA) and para-nitrophenol (PNP), as follows: Phth (5.03 × 10^-1) > ONPAA (2.28 × 10^-1) > PNP (8.49 × 10^-2). The Sips isotherm model provided a good description of the sorption profile of single component and naphthenate mixtures. The monolayer uptake capacity (Q_m; mg g^-1) is given in parentheses: 2-hexyldecanoic acid (S1; 115 mg/g) > 2-naphthoxyacetic acid (S3; 40.5 mg/g) > trans-4-pentylcyclohexylcarboxylic acid (S2; 13.7 mg/g). By comparison, the Q_m values for CGC3 with naphthenate mixtures (24.1 and 27.4 mg/g) according to UV spectroscopy and electrospray ionization mass spectrometry (ESI-HRMS). The sorbent materials generally show greater uptake with naphthenates that possess lower vs higher double bond equivalence (DBE) values. Kinetic studies revealed that the sorption of phth adopted behavior described by the pseudo-second order model, while uptake for S3 and naphthenate mixtures adopted pseudo-first order behavior. This study contributes to a greater understanding of the sorption properties of the two types of abundant biopolymers and their composites by illustrating their tunable sorption properties. The key role of hydrophobic interactions for CGC materials was evidenced by the controlled sorptive uptake of carboxylate anions with variable molecular structure.