Magnetically engineered MXenes: interfacial design, coordination chemistry, and emerging opportunities for sustainable water remediation

Magnetically engineered MXenes (MMXenes) have recently emerged as a versatile class of multifunctional materials that integrate the exceptional surface chemistry of MXenes with the magnetic recoverability of ferrite-based nanostructures, offering significant opportunities for water purification. Despite the rapidly growing number of studies on MMXenes, a comprehensive understanding of the structure-property-performance relationships governing their hazardous metal-ion adsorption and oil-separation behavior, as well as their use in the valorization of used cooking oil (UCO), remains limited. This review critically examines recent advances in the design, characterization, and environmental applications of MMXene-based composites for heavy-metal treatment, oil-water separation, and UCO conversion to fuels. We systematically examine the fundamental mechanisms governing heavy metal capture, including surface complexation, ion exchange, electrostatic interactions, thermodynamic properties, redox transformations, and coordination-driven adsorption. We critically discuss the interfacial phenomena responsible for efficient oil-water separation, including wettability modulation, selective permeability, and magnetically assisted transport. In addition to oil separation, we highlight the MXene-based catalyst for converting UCO into biodiesel and its role in the circular economy. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations are emphasized to elucidate adsorption energetics, charge-transfer processes, diffusion behavior, and atomic-scale interactions between contaminants and MMXene surfaces, thereby bridging theoretical predictions with experimental observations. Comparative analyses of adsorption performance, selectivity, recyclability, and environmental stability identify current limitations and knowledge gaps. Finally, emerging opportunities in artificial intelligence-assisted materials design and practical wastewater treatment underscore the potential of MMXenes as a transformative platform for next-generation, sustainable water remediation technologies.