Synthesis of N-Guanidinium-Chitosan/Silica Hybrid Composites: Efficient Adsorbents for Anionic Pollutants

A new chitosan derivative, N -guanidinium chitosan acetate, has been synthesized by direct guanylation of chitosan by cyanamide in presence of scandium(III) triflate under mild acidic condition. Starting from this material, N -guanidinium chitosan/silica microhybrids were prepared via a sol gel method using 3-glycidoxypropyl trimethoxysilane as silica precursor. Both N -guanidinium chitosan and the N -guanidinium chitosan/silica hybrid were characterized by a range of analytical techniques such as 29 Si/ 13 C solid state NMR, FT-IR, scanning electron microscopy, thermogravimetry and elemental analysis. The characterization of the chitosan/silica hybrid indicated that this material is a highly hydrophilic nanocomposite material containing an organic core and a highly condensed silica shell. The N -guanidinium chitosan/silica microhybrids display excellent adsorption properties for anionic dyes such as methyl orange (MO) with very high capacities up to 917 mg/g. The fixation of MO as anionic dye was investigated in detail as a function of contact time, pH and the MO concentration. The adsorption kinetics of MO on N -guanidinium chitosan/silica microhybrids was more accurately described by pseudo second-order model. Langmuir isotherm model exhibited a better fit with adsorption data than Freundlich isotherm model. This work opens new possibilities for using N -guanidinium chitosan as a reusable adsorbent for water purification. Graphical Abstract