Batch Adsorption Study for the Removal of Heavy Metal Ions Using Cucurbita pepo Seed Starch–based Resin

Abstract

Heavy metal contamination of aqueous systems poses significant environmental and health concerns, highlighting the need for effective and environmentally compatible adsorbent materials. Starch-based biopolymers have attracted attention as cost-effective and biodegradable materials for heavy metal removal. However, the adsorption potential of pumpkin seed starch–ascorbic acid resin for Zn(II), Ni(II), Cd(II), and Pb(II), particularly under varying pH conditions, remains insufficiently explored. A starch-based resin derived from Cucurbita pepo seed was synthesised using epichlorohydrin and ascorbic acid and evaluated for the removal of selected heavy metal ions from standard aqueous solutions. The resulting pumpkin seed starch-ascorbic acid (PSSAA) resin was characterised by Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric-differential thermal analysis. FTIR analysis showed characteristic bands associated with hydroxyl, carbonyl, C-H, and C-O-C functionalities, while SEM observations indicated a rough and heterogeneous surface morphology. Thermal analysis showed that major degradation occurred at elevated temperature, with the maximum degradation rate occurring at approximately 406 °C. Batch adsorption experiments were conducted for Zn(II), Ni(II), Cd(II), and Pb(II) over a pH range of 2-8. Adsorption increased progressively from acidic conditions to pH 7 and declined at pH 8. At pH 7, percentage removal reached 90.95% for Zn(II), 82.12% for Ni(II), 83.04% for Cd(II), and 83.99% for Pb(II). The corresponding distribution coefficients were also highest at approximately pH 7. These findings indicate that solution pH substantially influences the interaction of the studied metal ions with the PSSAA resin. Under the experimental conditions examined, the synthesised material demonstrated measurable adsorption of all four metal ions, with Zn(II) showing the highest removal at the optimum pH.