Development of MXene-decorated sodium alginate/SiO2@n-docosane hierarchical phase-change microcapsules for solar-driven sustainable seawater desalination

A novel type of MXene-decorated and sodium alginate (SA)-coated phase-change microcapsules (hereafter named “MXene/SA/SiO2-MEPCM”) was designed as a bifunctional solar absorber for the interfacial evaporator to realize sustainable seawater desalination. The MXene/SA/SiO2-MEPCM was fabricated by encapsulating n-docosane as a phase change material (PCM) in the SiO2 shell, followed by depositing a SA layer and decorating MXene nanosheets. An innovative integration of SA and MXene nanosheets enables the microcapsules to achieve a high light absorption capability of over 97 % together with good wettability, promoting a high evaporation rate of 2.11 kg·m−2·h−1 under one-sun illumination. The MXene/SA/SiO2-MEPCM exhibits a high latent heat capacity of over 150 J·g−1 for consecutive and high-efficient evaporation under intermittent solar illumination. Compared to the evaporator without a PCM core, the MXene/SA/SiO2-MEPCM-based evaporator achieved an increase in evaporation mass by 1.4 kg·m−2 through 5-cycle consecutive evaporation processes under solar illumination and natural cooling. Furthermore, its total water production was increased by 1.01 kg·m−2 under natural solar illumination for 7.5 h on a semi-cloudy day. The MXene/SA/SiO2-MEPCM also exhibits good recyclability for long-term use in solar-driven seawater desalination thanks to the good structural stability of its shell and highly stable reversible phase transitions of its PCM core.