Bifunctional MXene/carbon nanotube membranes with expanded interlayer nanochannels for efficient desulfurization wastewater treatment.

Desulfurization wastewater from coal-fired power plants contains high salinity and toxic heavy metals, posing significant environmental challenges. In this work, we developed an innovative solar membrane evaporation-crystallization system driven by solar energy and desulfurization waste heat, which converted desulfurization wastewater into clean water and fertilizer, enabling comprehensive management of wet flue gas desulfurization wastewater. The core component of this system, a bifunctional MXene/carbon nanotube (CNT) composite membrane, was prepared by vacuum-assisted self-assembly of Ti3C2Tx MXene and CNTs, which resulted in an expanded interlayer spacing of 1.67 nm and achieved an exceptional evaporation rate of 1.46 kg m-2 h-1 (1.87 times higher than that of the commercial microfiltration membrane). The enhanced performance stemmed from the decrease in water evaporation enthalpy from 2219.88 to 1222.65 kJ kg-1 through the formation of intermediate water within the hydrophilic network. Beyond water production, the membrane also enabled targeted decontamination, demonstrating a high removal efficiency of Hg2+ (≥95%) via selective adsorption, ensuring the production of high-quality (NH4)2SO4 crystals without mercury pollution, and achieving simultaneous pollution control and resource recovery. Compared to conventional thermal or chemical methods, this solar-powered operation and its compatibility with low-grade waste heat systems minimized the need for chemical additives or post-treatment steps. It could operate without requiring high-pressure or high-temperature external energy inputs, significantly reducing external energy consumption and carbon emissions. This proposed system offered a promising solution for sustainable water management in power plants and other industrial settings, with potential applications in disaster-affected, war-torn, and water-scarce regions.