Amino-functionalized manganese oxide for effective hexavalent chromium adsorption

Abstract

This study explores the use of functionalized manganese oxide (K-MnO₂-NH₂) for the removal of hexavalent chromium (Cr(VI)) ions, a highly toxic heavy metal contaminant, from wastewater. The synthesis of K-MnO₂-NH₂ was achieved through a two-step process, followed by comprehensive characterization using various analytical techniques, which confirmed the material’s formation as a pure phase. The K-MnO₂-NH₂ exhibited exceptional chromium removal efficiency, achieving up to 90% (4.53 mg/g) of Cr(VI) removal at pH 2. This high efficiency is attributed to the incorporation of amine groups via functionalization with 3-aminopropyltriethoxysilane (APTES), which introduces active sites with a strong affinity for Cr(VI) ions. Kinetics studies indicated that a chemical reaction governs the adsorption process, while thermodynamic data suggested it to be exothermic, and thermodynamic data reveal the process to be exothermic. The Freundlich isotherm best described the adsorption behavior. The Cr(VI) adsorption capacity of K-MnO₂-NH₂ was determined to be 45.17 mg/g. K-MnO₂-NH₂ effectively removed Cr(VI) from industrial wastewater, achieving a removal efficiency of around 41% (25.5 mg/g) and visible discoloration showing excellent reusability, maintaining over 80% removal efficiency after five cycles without requiring regeneration. This innovative approach highlights the potential of K-MnO₂-NH₂ as a sustainable and effective solution for Cr(VI) removal in environmental remediation and water purification.