Enhancing hexavalent chromium removal using amino-functionalized manganese oxide (birnessite) for improved adsorption efficiency

Abstract

This study investigates the use of functionalized manganese oxide (K-MnO2-NH2) for removing Cr(VI) ions, a notably hazardous heavy metal contaminant,, from wastewater. The synthesis of K-MnO2-NH2 occurred in two steps followed by comprehensive characterization using various techniques, confirming its formation as pure-phase. The material demonstrated a high chromium removal efficiency (up to 90% at pH 2) attributed primarily to the introduction of amine groups through functionalization with 3-aminopropyltriethoxysilane (APTES). These amine groups create active sites displaying a strong affinity towards Cr(VI) ions. Kinetic studies suggest a chemical reaction governs the adsorption process, while thermodynamic data indicate it to be exothermic. Freundlich isotherm best describes the adsorption behaviour compared to Langmuir and Temkin models. K-MnO2-NH2 effectively removed Cr(VI) from real wastewater, achieving a removal efficiency of around 41% and causing a visible discoloration. Remarkably, the material exhibits excellent reusability, maintaining over 80% removal efficiency after five cycles without any regeneration procedures. This innovative approach provides a sustainable and efficient method for removing Cr(VI) from wastewater, showcasing the considerable potential of K-MnO2-NH2 in environmental remediation and water purification efforts.