Enhancing Copper Ion Capture in MXene through Oxygen Content Modulation

MXenes are promising sorbents for heavy metal removal, yet their performance is often limited by surface oxidation. In this work, we engineered MXene membranes with tunable oxygen content via controlled etching to enhance redox activity and Cu 2+ adsorption. The optimized membrane retains a high density of exposed Ti active sites, facilitating interfacial electron transfer. Consequently, it achieves a superior maximum adsorption capacity of 593.66   mg/g, outperforming most reported MXene-based materials. Isotherm and kinetic modeling indicate a chemisorption-controlled, monolayer adsorption process (Langmuir and pseudo-second-order models). XPS analyses and DFT calculations confirm a redox-mediated pathway involving Cu 2+ reduction and Ti oxidation. Furthermore, the membrane exhibits excellent selectivity for Cu 2+ over competing ions (Pb²⁺, Mg²⁺, Fe²⁺, etc.) and maintains high efficiency across diverse pH and temperature conditions. These findings demonstrate that modulating oxygen content and Ti-site exposure is a scalable strategy for optimizing MXene-based water remediation.