Engineering Fe-based MOF functioned 3D polyvinyl alcohol-agar scaffolds for highly efficient solar-driven desalination without salt accumulation

Solar-driven interfacial evaporation is a promising way to produce desalinated freshwater. However, the evaporation flux of the evaporators is still insufficient to meet practical demands. In this paper, a kind of highly efficient evaporator with vertical channels based on a metal–organic framework (MOF) is designed and prepared. First, 3D polyvinyl alcohol-agar (PVA-Agar) scaffolds were fabricated via the ice template method at a temperature of −18 ℃. They possess hierarchical pores from the bottom surface to the top surface, improving upward water-pumping and inhibiting salt accumulation. In addition, the PVA-Agar scaffolds were further in situ decorated by Fe-MIL88A microrods with a length of 1.8 ± 0.2 μm and a diameter of 401.0 ± 27.5 nm, forming the PVA-Agar/MIL88A evaporators. It can be found that the loading yield of MIL88A and the agar content strongly affect the upward water-pumping performance, hydrogen bonding, water vaporization enthalpy, and absorptivity of the evaporators. The optimum PVA-Agar/MIL88A evaporator with a MIL88A loading yield of 17.4 wt% and an agar content of 70.0 wt% has an ultrahigh pure water evaporation flux of 5.0 kg m -2 h −1 and 4.2 kg m -2 h −1 in 3.5 wt% NaCl under sun illumination at 1000 W m −2 . Moreover, the outdoor solar-driven desalination tests suggest that the PVA-Agar/MIL88A evaporator exhibits good solar-driven desalination performances and stability. PVA-Agar/MIL88A evaporators will greatly promote the development of seawater desalination because of their high evaporation flux and good salt resistance.