Tamarindus indica L. Seed Starch Ascorbic Acid Resin: Microwave Assisted Synthesis, Characterization, and Batch Adsorption Study for Removal of Heavy Metal Ions from Aqueous Solutions

Abstract

This study investigated the microwave-assisted synthesis and batch-adsorption performance of tamarind seed starch ascorbic acid (TISSAA) resin for the removal of Zn(II), Ni(II), Cd(II), and Pb(II) from standard aqueous solutions. Tamarind seed starch was functionalised through a microwave-assisted procedure with ascorbic acid, and the resulting resin was characterised by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), thermogravimetric-differential thermal analysis (TGA-DTA), and scanning electron microscopy (SEM). FTIR and ¹H NMR data were used to assess the functional features of the prepared resin, while TGA-DTA described its thermal behaviour and SEM micrographs showed a rough, heterogeneous, and porous surface morphology. Batch adsorption experiments were conducted across pH 2–8, and distribution coefficients, percentage adsorption, and metal exchange capacities were determined. Adsorption increased with pH up to pH 6 for all investigated ions and declined at higher pH values. At pH 6, removal efficiencies were 77.21% for Zn(II), 75.01% for Ni(II), 87.27% for Cd(II), and 82.15% for Pb(II). The observed adsorption affinity followed the order Cd(II) > Pb(II) > Zn(II) > Ni(II). Under the investigated batch conditions, TISSAA resin therefore exhibited measurable pH-dependent affinity for the four divalent metal ions, with the highest measured removal obtained for Cd(II).