Amino-alcohol functionalized porous polymer coupled with chromium hydroxide nanoparticles for efficient Cd(ii) adsorption from aqueous solutions

Abstract

Cadmium is one of the most hazardous heavy metal contaminants, and it is usually abundant in the wastewater released from paint and pigment industries. Such effluents urgently need to be treated before their proper reuse for various industrial and agricultural purposes. Therefore, in this study, the process of Cd(II) ion adsorption from waste aqueous-solutions was investigated using polystyrene (PS), ethanolamine-modified polystyrene (EA-PS), and chromium hydroxide-impregnated ethanolamine-modified polystyrene (Cr@EA-PS) as new effective sorbents. The structural and textual properties as well as the surface charges and particle sizes of the prepared sorbents were examined using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), N₂ adsorption–desorption surface area analysis, X-ray diffraction (XRD), dynamic light scattering (DLS) and zeta potential analysis. Herein, correlations between different features of the three adsorbents and their impacts on adsorption efficiency were extensively investigated. Adsorption kinetics and isotherm studies were also conducted to evaluate the sorption mechanisms and the achieved capacities of the presented adsorbents. Results showed that surface functionalization with ethanol amine particles significantly improved adsorption capacity owing to the introduction of amino groups, providing further interactions with heavy metal species. Moreover, the subsequent impregnation of Cr(OH)₃ into the EA-PS structure could successively enhance surface properties and porosity, leading to observation of the highest adsorption capacity (13.6 mg g⁻¹ for Cr@EA-PS). Such increased adsorption capacity is nearly 10-fold higher than the reported capacity of PS. Kinetic studies revealed that the adsorption process followed a pseudo-second-order model, indicating chemisorption as the primary adsorption mechanism. Isotherm analysis confirmed a favorable monolayer adsorption process exhibited by the three structures. The combination of chemical bonding and physical adsorption mechanisms was observed for Cr@EA-PS, explaining its performance superiority in removing Cd(II) ions. Thus, the inorganic–organic composite exhibits the highest potential among the three introduced sorbents for practical applications in the field of wastewater treatment.