Engineering salt-rejecting solar evaporator from naturally hierarchical tree root for sufficient clean water production

Solar desalination has been recognized as one of the most promising technologies for solving current freshwater scarcity. However, enhancement of the photothermal conversion efficiency and prohibiting salt crystallization on the top light-absorbing surface are the two major critical challenges for developing highly-efficient and stable solar evaporators. Here, we have discovered that tree roots, often as processing waste when utilizing woods, can serve as a high-efficient solar evaporation device for continuous desalination. The naturally occurring hierarchical structure of tree roots possesses multilevel longitudinal channels from micrometer to millimeter-scale and interconnected porous microstructures, which allows excellent water transport and multidirectional salt exchange, exhibiting a superior anti-salt-accumulation capability even in 21% brine. Together with a mountain-shaped hydrophobic absorber surface obtained from the in situ synthesized Fe3O4 nanoparticles, the designed tree root-based solar evaporator demonstrates an evaporation rate of 1.64 kg m−2 h−1 and ultra-high conversion efficiency of 96% at 1 solar irradiation, rendering it as one of the best performing wood-based solar evaporators. Furthermore, such a high-efficacy, techno-economic and long-term stable seawater desalination platform provided by the architectures of multi-level channel-array in tree root will inspire material scientists and engineers to tailor structurally similar materials from building blocks of broader selections.