Fig. 4: Localized salt crystallization mechanism on the biomimetic 3D evaporator.

a–d Time sequence of optical captures displaying the localized crystallization process on the biomimetic 3D evaporator. e Optical image of the salt easy-removing property of the biomimetic 3D evaporator, the crystallized salt can be removed through leaning the evaporator. f Bottom view Micro-CT image of the removed NaCl crystal. g Side cross-sectional Micro-CT image of the detached crystal, which amplifies the conical hole morphology of the contacting interface. h Micro-CT image of the apex position of the biomimetic 3D evaporator. i Scheme of the continuous water film along the sidewall of the biomimetic 3D evaporator which extends to the localized crystal at the apex position. j Temperature profile along the sidewall of the biomimetic 3D evaporator with the existence of the localized crystal at the apex position. Inset is the corresponding infrared image. k Measured concentrations of Na⁺ in different brine samples (including 25, 20, 10, 1, and 0.1 wt% NaCl solution) before and after desalination. Orange and green columns represent the metal ion concentrations before and after purification, respectively. The broken line refers to the WHO Na⁺ concentration standards for drinkable water. l–n Optical image of the water sample with different heavy metal ions (including the aqueous solution of 10 wt% CoCl₂, 20 wt% CuSO₄, and mixed solution composed of 10 wt% NaCl and 10 wt% CuSO₄) before and after solar purification. o Measured concentrations of corresponding metal ions before and after purification. Orange and green columns represent the metal ion concentrations before and after purification, respectively.