Chemical modification of Moringa oleifera seed bioadsorbents for enhanced removal of Cd (II) ions from aqueous solutions

Abstract

This study assessed the potential of Moringa oleifera seeds as novel adsorbents for the removal of cadmium (Cd) (II) ions from synthetic wastewater. The seeds were chemically modified using calcium acetate and sodium hydroxide. Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR) were employed to characterise the bioadsorbents prepared from the Moringa oleifera seeds. The modified bioadsorbent (MOx) exhibited a BET surface area of 171.012 m²/g, a microporous pore size of 0.103 cm³/g, and a diameter of 2.138 nm. Results demonstrated that the removal efficiency of the biosorbents for Cd (II) ions was 51.1% for unmodified seeds (MO) and 57.6% for modified seeds (MOx) at a contact time of 90 minutes. At equilibrium, the maximal sorption capacities for MO and MOx were 4.50 and 4.89 mg/g, respectively. The strong coefficient of correlation (R²) of 0.9938 for the chemically modified seeds and 0.9603 for the unmodified seeds supported the applicability of the Freundlich model, indicating a robust sorption interaction with the Cd²⁺ ions. Pseudo-second-order sorption kinetics were found to be appropriate for Cd (II) sorption onto modified seeds under highly heterogeneous conditions.