Anion exchangers prepared from graft polymerisation of microfibrillated cellulose using the reactive ionic liquid

Microfibrillated cellulose (MFC) was functionalised using a reactive ionic liquid monomer, i.e., glycidyltriethylammonium chloride (GTEAC), via chain-growth polymerisation, resulting in a novel cationic polyelectrolyte-grafted quaternised MFC (QMFC). The degree of quaternisation and maximum ion exchange capacity of the resulting QMFC were 2.13 mmol/g (i.e., 132 mg/g) and 1.51 mmol/g (i.e., 94 mg/g), respectively. Small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) experiments confirmed the retention of monoclinic crystalline structure for cellulose I with the corresponding decrease in the degree of crystallinity from 85% to 56% and the increase in the spacing between cellulose crystallites by 35%. The presence of the amorphous and grafted polymers was confirmed by microscopy, thermal analysis, and water sorption experiments. QMFC filter cartridges were prepared and tested under dynamic flow conditions with a pressure of 0.2 MPa (retention time of 0.5 min). These cationic polyelectrolytes enhanced multi-site ion exchange interactions as evidenced by the Freundlich sorption isotherm. The QMFC filter cartridges demonstrated high anion removal efficiency values of 83.2%, 98.1%, and 94.9% for NO₃⁻, SO₄²⁻, and PO₄³⁻, respectively. This system achieved a process mass efficiency of 2.79, an E-factor of 1.97, and an energy efficiency score of 66.3, which conforms to the green chemistry principles and demonstrates high potential for sustainable water purification.