Tailored magnetic hybrid composites with recoverable properties for efficient Cr(vi) adsorption and reduction: a synergistic experimental and theoretical study

Abstract

Despite polyaniline's simple synthesis methods and proven capabilities pollutant removal applications, its recovery from solutions remains a major challenge that hampers its application. Therefore, developing approaches for synthesizing an efficient and easily recoverable polyaniline (PANI) adsorbent is crucial. In this study, we designed a magnetic Fe₃O₄–cysteine-functionalized PANI (Fe₃O₄–Cys–PANI) adsorbent via in situ polymerization. The resulting magnetic adsorbent was characterized by several analytical techniques (e.g., FTIR spectroscopy, XRD, porosity measurements and SEM-EDS), and the results indicated that it exhibited tunable features for Cr(VI) detoxification. A systematic experimental study revealed that the maximum Cr(VI) detoxification yield (98.12%) was achieved with an adsorbent dose of 0.25 g L⁻¹ and at pH 2.0. The Freundlich isotherm models and the pseudo-second-order kinetics were appropriate for predicting the Cr(VI) removal process. The Monte Carlo simulations further elucidated the Cr(VI) adsorption process, revealing an adsorption energy of E_ads = −55.613 kcal mol⁻¹ on Fe₃O₄–Cys–PANI. The significantly negative adsorption energy further supported the experimental findings, confirming the spontaneity of the process and high energy efficiency. Additionally, the Fe₃O₄–Cys–PANI magnetic composite showed excellent decontamination, outstanding regeneration capacity and prominent reusability, making it a promising candidate for industrial wastewater treatment.