M. Li, Y. Boluk, M.G. El-Din
University of Alberta,
Keywords: cellulose, nanofiber, water purification, heavy metals
Summary:Water contaminant from heavy metal ions is a serious issue for environmental and economics around the world. Among different developed water treatment techniques, adsorption is a relatively cost effective approach with high removal efficiency and easy-operation features. Cellulose, one of the most abundant natural polymers, is environmental benign, biodegradable, and easy to be functionalized. These features make it as an excellent raw material for the preparation of low-cost adsorbents. In the present study, wood pulp was used as the raw material. TEMPO-oxidized cellulose nanofibers (TOCNF) were prepared and investigated for the removal of Cu (II) and Zn (II) from synthetic water and natural waters. Systematic adsorption performance tests were conducted, including kinetics, isotherms, effect of water matrix properties (ionic strength and pH) as well as the influence of TOCNF loading dosage. The adsorption equilibrium could be reached within 2 minutes and adsorption capacity as high as 167.5 mg/g was observed for Cu (II) and 71.3 mg/g for Zn (II). Elevated pH was preferred for higher metal ion removal. The ionic strength showed adverse effect on the adsorption capacity, however, TOCNF with higher carboxymethyl content was less influenced. A combined interaction mechanism, including ion exchange, coordination and possible accumulation, was proposed based on the isotherm and material characterization results. In competitive adsorption test, copper adsorption exhibited strong selectivity over potassium, magnesium and manganese ions and showed moderate selectivity over zinc and ferrous ions. Furthermore, calorimetric titration was, for the first time, applied to the adsorption thermodynamics study of TOCNF. Typical single-site binding curve was found. The modeling result showed that the adsorption of copper and zinc onto TOCNF were spontaneous and endothermic processes, which indicated that the complexation was the dominant adsorption mechanism instead of the electrostatic interaction between the metal ions and the carboxylic groups. All the above findings confirmed the great potential of TOCNF application in water purification and reclamation approaches.