Less Is More - Partial Thiolation of Porous Chitosan Beads to Enhance Cu(II) Adsorption.

Chitosan gel beads has a high uptake capacity due to its affinity to Cu(II) ion. However, its use as absorbent in flow column is affected by swelling and low stability in acidic condition. Even though crosslinking of chitosan beads increases resistance to acid attack, it also decreases their sorption capacity. In this study, modified chitosan beads (ETB) with dithiocarbamate derivatives were thermally decomposed to form thiourea and disulfide crosslinks to enhanced stability in acidic condition. Sorption of ETB beads with varying degree of thiolation were studied using 1 mM copper nitrate solution at 0.5 and 2.0 g/L sorbent/solution ratio. Cu(II) ions is adsorbed to amine, thiol and sulfonate groups of ETB. The coordinated Cu(II) ion has been reduced to Cu(I) ion and has oxidized thiol to sulfonate groups. The Cu(II) uptake of partially modified ETB is greater than highly modified ETB. The Cu(II) uptake (mmol/g) is inversely correlated to total sulfur of ETB with a linear correlation coefficient of 0.8835 (ETB/solution ratio: 2.0 g/L). Greater formation of crosslinks in highly modified ETB may have decreased the number of amine binding site for Cu(II). The Cu(II) uptake of partially modified ETB is similar to pristine chitosan beads with greater stability.