Isotherm, kinetics, and adsorption mechanism studies of diethylenetriaminepentaacetic acid-modified banana/pomegranate peels as efficient adsorbents for removing Cd(II) and Ni(II) from aqueous solution.

Two novel absorbents were synthesized for the first time by banana and pomegranate peels using diethylenetriaminepentaacetic acid (DTPA) modification to eliminate Cd(II) and Ni(II) of sewage. The DTPA-modified peels performed significantly higher adsorption capacity than unmodified materials. The maximum adsorption capacities of DTPA-modified banana/pomegranate peel were 46.729/46.296 mg/g for Cd(II), and 29.240/16.611 mg/g for Ni(II). Adsorption isotherm and kinetics models were simulated to determine their removal efficiency and potential for recovery of these two heavy metals. As the results, the adsorption reached equilibrium within 5 min and was well described by the pseudo-second order model and Langmuir isotherm. The surface morphology analysis of the synthetic materials by Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy, Fourier Transform Infrared spectroscopy, and X-ray Photoelectron Spectroscopy, implied that ion exchange, complexation, and physical adsorption may together contribute to Cd(II) and Ni(II) loading on DTPA-modified peels. This study demonstrates the feasibility of waste peels as cost-efficient bio-absorbents to remove Cd(II) and Ni(II) in sewage systems, and discovers potential adsorption mechanism of efficiency improvements after DTPA modification.