Comparison of Cadmium Adsorption from Water Using Same Source Chitosan and Nanochitosan: Is It Worthwhile to Go Nano?

Industrial effluents and stormwater runoff pose a significant threat to the environment and public health. Consequently, the water quality guidelines set strict limitations on the heavy metal content due to their toxicity. Among heavy metals, cadmium is one of the most hazardous, and its maximum permissible concentration is 10 μg/L. Therefore, the improvement of wastewater treatment technology is a prominent and ongoing task. The present study deals with the adsorption of cadmium onto chitosan beads and nanochitosan, a natural polysaccharide polymer derived from seafood shell waste. The chitosan beads and the nanochitosan were derived from the same source chitosan in order to compare their capacities and their kinetic performances on an equal basis. Both cadmium adsorption capacities are extremely high with 1.65 mmol Cd/g chitosan beads and 1.90 mmol Cd/g on nanochitosan—with nanochitsosan showing a 15% higher uptake. Several kinetic models were compared and the kinetics of both chitosan beads and nanochitosan followed both the pseudo-second-order and the Elovich models very closely but the uptake of cadmium on nanochitosan was faster. A comparison of benefits and disadvantages of using the two chitosans is presented.