Solvent-free functionalization of sawdust with quaternary ammonium groups: Application to the biosorption of two anionic dyes

The improvement of sawdust reactivity through simple chemical modification strategies represent an interesting method to extend the field of application or improve the natural performances of this abundant and available waste. In this work, sawdust was modified with Glycidyltrimethylammonium chloride (GTAC), an organic compound bearing a quaternary ammonium group. The objective was to obtain a modified sawdust with a permanent cationic charge. The modification of the material was confirmed by solid state 13C NMR and FTIR spectroscopy. The anion exchange capacity of modified sawdust (Sa-G) was demonstrated by the ability of sawdust to exclusively adsorb cations before modification and anions after modification. This anionic exchange property was applied for the adsorption of two anionic dyes (Procion Red MX-5B (PR) and Evans Blue (EB)). Generally, the material was more effective in acidic conditions due to the acid-base properties of sawdust. Compared to EB, the less charged and smaller PR adsorbs more quantitatively on the material and with faster kinetics (Equilibrium reached after only 30 min, while more than 24 h were needed in the case of EB). Thermodynamic study also reveals an exothermic process in the case of PR and endothermic in the case of EB. Under optimal conditions, the maximum adsorption capacities were 121.8 μmol g−1 for PR and 103.1 μmol g−1 for EB. Desorption tests showed that the material can be recycled by desorption of dyes in 0.1 M sodium hydroxide solution. After 5 adsorption-desorption cycles performance losses of only 15% for EB and 30% for PR were recorded.