Vertically Aligned Janus MXene-Based Aerogels for Solar Desalination with High Efficiency and Salt Resistance.

Solar desalination is an effective way of converting solar energy to heat for seawater purification. The structure of absorbers and salt resistance are two crucial parameters for water transport and desalination stability. Here, we designed a vertically aligned Janus MXene aerogel (VA-MXA) with hydrophobic upper layer and hydrophilic bottom layer. Compared with irregular porous channels, such regulatable and well-ordered vertical array structure gives competitive advantage in the capillary water transport, light absorption, and vapor escape. MXene, which possesses a theoretical light-to-heat conversion efficiency of 100%, combined with the Janus structure, can efficiently convert light to heat and prevent the photothermal layer from "direct bulk water contact" with the hydrophobic upper layer, thus decreasing heat loss, while the hydrophilic bottom layer submerged in water can quickly pump water upward through the vertically aligned channels with low transport resistance and, meanwhile, enable effective inhibition of salt crystallization due to rapid dissolution with continuously pumping water. With a vertically aligned and Janus structure by flexible design, the Janus VA-MXA exhibited a high conversion efficiency (87%) and stable water yield for 15 days (∼1.46 kg·m-2·h-1) under 1 sun. About 6 L·m-2 of freshwater was output daily from seawater.