An efficient, robust, and affordable photothermal membrane using polyvinyl alcohol encapsulated MXene/non-woven fibers for solar desalination/sewage purification

Abstract

Recently Ti₃C₂T_x (MXene) has become an ideal photothermal material for solar interface evaporation, due to its near unit photothermal conversion efficiency, unique layered structures, and abundant surface terminals. However, MXene photothermal membranes still face key issues including evaporation performance, stability, and cost, which restrict their commercialization. Hence, a composite photothermal membrane (MPF) of MXene/polyvinyl alcohol (PVA)/nonwoven fiber (NWF) is constructed in this study, simply by soaking NWF into a MXene solution to achieve saturated adsorption, followed by dropping PVA as an encapsulation layer. The evaporation rate and efficiency of MPF reach 1.84 kgm⁻²h⁻¹ and 99.82 %, respectively, at 1 sun in a siphon-model solar evaporator. The high evaporation performance is attributed to a synergistic effect of improved light absorption, water transport, and thermal management, as well as reduced evaporation enthalpy, by modulating the microstructures of MPF. MPF maintains stable evaporation after 15 cycles in 3.5 wt% simulated seawater, and in simulated seawater with different salinities (0–15 wt%). MPF also shows great light intensity adaptability (0.5–3 sun), and outstanding salt resistance and structural stability. The high stability of MPF is contributed by the encapsulation of PVA, which firmly welds MXene onto NWF and protect MXene from water and oxygen. In addition, MPF exhibits excellent water purification capabilities for different simulating seawater/wastewater. Finally, it is estimated that MPF has a low cost of 23.2 $m⁻² and a high cost-effectiveness of 79.3 gh⁻¹/$, showing significant cost advantages compared to other reported photothermal membranes. A large-area (e.g., 12 × 12 cm²) and flexible MPF can be easily obtained by cutting NWF into any size as needed. This work promotes the practical application of MXene photothermal membranes in solar water treatment.