MXene-decorated magnetic phase-change microcapsules for solar-driven continuous seawater desalination with easy salt accumulation elimination

Solar-driven interfacial evaporators provide a powerful means for rapid wastewater purification and seawater desalination. However, there is still an immense challenge in interfacial evaporators with efficient energy utilization and long-term evaporation stability due to intermittent solar illumination and salt accumulation. To address these issues, we developed a novel type of interfacial evaporator based on the microencapsulated n-tetracosane and n-eicosane as twin phase-change material (PCM) cores with a SiO2/Fe3O4 composite shell along with a surface-coated polypyrrole layer and surface-decorated MXene nanosheets. The resultant microcapsules act as both a solar absorber and a latent-heat storage material for sustainable evaporation of seawater. Benefiting from a rational combination of PCMs and solar absorbers, the evaporator based on the microcapsules achieved a high light absorption efficiency of 95.4 % together with evaporation rates of 2.04 and 4.11 kg·m−2·h−1 under 1.0-sun and 2.0-sun illumination, respectively. Owing to the photothermal energy released by the PCM cores, the developed evaporator exhibits a consecutive and stable evaporation behavior even without solar illumination. Compared to conventional evaporators without a PCM, there is an increase by 0.45 kg·m−2 in the yield of the distilled water obtained from the developed evaporator under 2.0-sun illumination and then in the dark environment. Based on magnetic Fe3O4 nanoparticles in the silica-matrix shell, the separability of the microcapsules from the accumulated salt crystals was improved through simple washing and magnetic separation. Through an innovative integration of magnetic phase-change microcapsules and solar absorbers, this study will provide a new idea and promising approach for the sustainable evaporation system design based on solar energy utilization for applications of seawater desalination and wastewater treatment.