Cellulose modified to host functionalities via facile cation exchange approach

Properties of cellulose are typically functionalized by organic chemistry means. We progress an alternative facile way to functionalize cellulose by functional group counter-cation exchange. While ion-exchange is established for cellulose, it is far from exploited and understood beyond the most common cation, sodium. We build on our work that established the cation exchange for go-to alkali metal cations. We expand and further demonstrate the introduction of functional cations, namely, lanthanides. We show that cellulose nanocrystals (CNCs) carrying sulfate-half ester groups can acquire properties through the counter-cation exchange. Trivalent lanthanide cations europium (Eu³⁺), dysprosium (Dy³⁺) and gadolinium (Gd³⁺) were employed. The respective ions showed distinct differences in their ability of being coordinated by the sulfate groups; with Eu³⁺ fully saturating the sulfate groups while for Gd³⁺ and Dy³⁺, values of 82 and 41 % were determined by compositional analysis. CNCs functionalized with Eu³⁺ displayed red emission, those containing Dy³⁺ exhibited no optical functionality, while those with Gd³⁺ revealed significantly altered magnetic relaxation times. Using cation exchange to alter cellulose properties in various ways is a tremendous opportunity for modification of the abundant cellulose raw materials for a renewable future.