Freeze v/s air-dried alginate-pectin gel beads modified with sodium dodecyl sulphate for enhanced removal of copper ions.

This work presents a novel polymer-based adsorbent, Sodium Dodecyl Sulphate modified alginate-pectin gel beads (APS221) prepared via controlled freeze drying & air drying, for the removal of copper ions from the aqueous solution. This work also critically discusses the role played by various components and their concentrations in the success of APS221. Addition of pectin to alginate resulted into approximately 150 % increase in the metal removal performance of the adsorbent while addition of SDS into alginate-pectin complex enhanced the performance by 14 % approximately, taking the maximum adsorption capacity of final complex APS221 to 111.11 mg/g. Our characterization studies revealed that the adsorption happened predominantly by complexation and ion-exchange mechanisms, and hence despite having a higher surface area, freeze-dried variant showed lesser adsorption capacity than air-dried variant as there was a loss of ion-exchange sites resulting from breakage of crosslinking bonds due to chain elongation. The adsorption process was found to follow Langmuir isotherm and pseudo-second order kinetics with a good fit of experimental data. Further, operating parameters have been optimized via RSM to, simultaneously, maximize the utilization of the adsorbent and minimize the cost of the process. Stability studies showed that APS221 beads could be used up to eight cycles.