Competitive chemisorption and physisorption processes of a walnut shell based semi-IPN bio-composite adsorbent for lead ion removal from water: Equilibrium, Kinetic and Thermodynamic studies

In this research, the effect of walnut shell (WS) as an effective bio-filler in poly acrylic acid (PAA) and poly vinyl alcohol (PVA) semi-IPN was studied for lead ion (Pb2+) removal from water. The prepared bio-composite adsorbent structure was investigated using FTIR, TGA, DSC, FESEM and N2 adsorption desorption analysis. Adsorption verification of lead ions was verified using energy-dispersive X-ray spectroscopy (EDS) technique. Swelling ability and adsorption efficiency of the adsorbents were studied in various conditions such as different adsorbent dosages, type of adsorbent used, contact time, pH and temperature. Regeneration studies were carried out for reusability of the adsorbents. Equilibrium, kinetic and thermodynamic studies were carried out. Chemisorption was found to be rather than physisorption. Excess amounts of WS, exhibited counter effect on adsorption efficiency due to aggregated WS within semi-IPN structure and inter-molecular hydrogen bonding. The results suggest that, adsorption was occurred chemically, the adsorbent exhibited high thermal stability, optimum amount of WS within bio-composite was 5 %wt, adsorbent was usable after 4 cycles of regeneration, up to 95% of lead ion removal was achieved at optimum conditions and a high monolayer adsorption capacity was obtained and the synergistic effect of other metal ions beside Pb2+ requires further research attention