Synthesis and properties of thiol-modified CNC via surface tosylation

SH-containing polymers and nanoparticles are a significant direction in the creation of novel materials. The aim of this work is the synthesis of cellulose nanocrystals (CNC) with a surface modified by tosyl functions (CNC-Ts) and their further modification into SH-containing nanocrystals (CNC-SH). CNC-Ts were synthesized in an aqueous-organic emulsion from never-dried particles, while maintaining the size and supramolecular structure of CNC; the content of Ts-functions is up to 2.5 mmol·g^-1. Structure of the derivatives was analyzed by TEM, XRD, CP/MAS ¹³C NMR and FTIR spectroscopies. Nucleophilic substitution and hydrolysis of the obtained thioisouronium salts leads to the production of CNC-SH. To quantify SH-groups we used elemental analysis, potentiometric titration and Folin-Ciocalteu and Ellman's reagents. It is shown that SH-groups on the surface are partially oxidized and are involved in a dense network of hydrogen bonds. Rheological properties of CNC-SH hydrosols are close to those of CNC, addition of H₂O₂ at acidic pH leads to an increase in viscosity of the system; H₂O₂ added at neutral pH causes opposite effect - viscosity decreases. CNC-SH have a high capacity for sorption of Cr(VI) in acidic environments and exhibit photoreductive properties under UV irradiation.