Easily constructed HNs/CNTs photothermal membrane with high-temperature resistance for efficient solar desalination and dye-polluted water purification

Utilizing abundant and renewable solar energy to produce clean freshwater from the existing seawater and wastewater has been considered a reliable and effective method to alleviate the severe shortage of freshwater currently. However, most of traditional desalination membranes usually showed insufficient photothermal conversion capacity, poor thermal stability, complex preparation procedure, and unsatisfactory water treatment efficiency. Therefore, we mixed as-prepared ultra-long hydroxyapatite nanowires (HNs) and carbon nanotubes (CNTs) for building HNs/CNTs membranes with high photothermal conversion efficiency, porous structure, high water transporting speed and remarkable high-temperature resistance in this work. Under one solar irradiation, the average light absorption of HNs/CNTs membrane was as high as 93%, and the evaporation rate of its integrated evaporator in simulated seawater (3.5 wt% NaCl) was 1.21 kg·m-2·h-1. Meanwhile, the HNs/CNTs membranes have good salt resistance and high Na+ removal rate, which makes their integrated evaporators suitable for solar-driven recirculation desalination process. Notably, the HNs/CNTs membranes also have excellent thermal stability, significant refractoriness and good thermal insulation, resulting in high temperature resistance and long-term solar evaporation stability. The water evaporation rate of HNs/CNTs integrated evaporator can be stabilized around 1.43 kg·m-2·h-1 and 3.74 kg·m-2·h-1 in 10 cycles of experiments under one and three solar irradiations. In addition, the removal rates of MB and RhB after photothermal purification via HNs/CNTs membranes reached up to 99.96% and 100%, respectively, displaying the promising and broad applications in solar desalination and dye wastewater purification.