Natural lignocellulosic kapok fiber/MXene constructed hydrogel evaporators for high efficiency solar steam generation.

Solar-driven interfacial evaporation (SDIE) is a green and sustainable technique for desalination. Hydrogel composite evaporators have been widely used for SDIE, but it is still challenging for the hydrogel evaporators to achieve uniform distribution of the light absorbing nanomaterials and at the same time possess satisfactory evaporation rate, durability and environmental applicability. We developed a 3D hydrogel evaporator with an asymmetric structure for high-efficiency SDIE. Natural kapok fibers, an important lignocellulosic plant fiber with a hollow structure, are decorated with MXene nanosheets for construction of one-dimensional photothermal conversion network. The top composite hydrogel serves as the light-absorption layer where MXene-modified kapok fibers are evenly dispersed in PVA hydrogel, while the bottom PVA hydrogel with an oriented structure acts as water delivery path. The evaporator exhibits a high solar evaporation rate and efficiency (2.49 kg·m·h and 91.5 %, respectively) under one sun irradiation (1 kW·m). Even in a high salinity brine, emulsion and corrosive solutions, the evaporator can work normally with a slightly decreased evaporation rate. The 3D hydrogel evaporator with long-term stability and durability shows promising applications in purification of seawater and different waste water.