Sustainable removal of Cd(II) and Cr(VI) from aqueous solution via agro-waste derived biochar

This work explores agro-waste biochar derived from corn cob as a low-cost and sustainable adsorbent for the uptake of Cd(II) and Cr(VI) from aqueous solutions. The novelty of this study lies in the combined use of acid-washed corn cob precursors, inclusive structure–property–performance analysis, and evaluation under environmentally relevant concentration ranges, signifying that corncob biochar can achieve considerable adsorption performance without chemical activation. The biochar was produced via pyrolysis and characterized with Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area analysis. Batch adsorption experiments were carried out to assess the effects of pH, temperature, contact time, and adsorbent dosage on the metal ions sorption. FT-IR assessment confirmed the participation of –OH, C = O, and C–O functional groups in metal binding, while SEM images indicated a porous surface that became agglomerated after adsorption. Optimal removal efficiencies were achieved at pH 4.5 for Cd(II) and pH 5.0 for Cr(VI), with lower biochar dosages (0.35 g for Cd(II) and 0.3 g for Cr(VI)) enhancing adsorption due to increased availability of active sites. Adsorption kinetics followed a pseudo-second-order model, with maximum capacities of 70.2 mg/g for Cd(II) and 55.4 mg/g for Cr(VI). Thermodynamic analyses indicated that adsorption was spontaneous and endothermic. The adsorption mechanism is assigned to hydrogen bonding, electrostatic attraction, and ion-exchange interactions between metal ions and biochar functional groups. These findings demonstrate that corn cob biochar is an efficient and eco-friendly adsorbent for heavy metal remediation from wastewater.