Hydrophilic amphibious open-cell macroporous sponge by Hofmeister effect induced nanofibrils

Abstract

Hydrophilic macroporous sponge has been widely used in solar steam generation, catalysis, biosensing and other fields due to its high water transporting and adsorption ability. However, the synthesis step of hydrophilic sponge usually needs the assistance of a freezing process and toxic chemicals such as chemical crosslinkers or foaming agents. To solve these problems, herein, a novel and facile tactic based on the salting out effect was proposed to prepare hydrophilic amphibious open-cell macroporous sponge from the poly(vinyl alcohol) (PVA) solution. Glycerol, CaCl₂ and Na₃Cit were successively added into PVA solution. The sol–gel transition would occur due to the salting-out effect of Na₃Cit and hydrogen bond crosslinking of glycerol. Finally, the hydrophilic PVA sponge with different shapes and sizes could be easily prepared. Moreover, this hydrophilic wet sponge could be room temperature dried into dry sponge and this dry sponge could be quickly restored to wet sponge after immersing in water due to its ultra-rapid water absorption. The microstructure and mechanical properties of PVA wet and dry sponges were studied. The PVA wet sponge showed excellent mechanical properties with a tensile strength, Young's modulus, and fracture energy of 1.51 ± 0.01 MPa, 0.44 ± 0.02 MPa, and 113.2 ± 1.6 kJ m⁻², respectively. The wet sponge prepared in this work has an average porosity of up to 50 μm, and the pore structure can still be maintained during the conventional room temperature drying process. Moreover, the PVA sponge showed high stability in various aqueous media including acid, alkaline, and salt solutions. This work provided a simple and large-scale method to prepare amphibious open-cell hydrophilic PVA sponge.