A versatile platform of poly(acrylic acid) cryogel for highly efficient photothermal water evaporation

Abstract

Photothermal water evaporation, benefiting from solar energy, is one hot topic concerning seawater desalination, sewage treatment, and water recovery. Commonly, the photothermal evaporation system consists of photothermal material supported by certain matrices with fundamental necessities. Poly(acrylic acid) (PAAc) cryogels, prepared at the temperature below the freezing point of polymerization mixture, are hierarchically macro-porous and highly hydrophilic with rapid water uptake, speedy water transport, and low thermal conductivity. Moreover, PAAc has the acid-doping ability for polyaniline and polypyrrole (PPy), which faciliates the good incorporation of photothermal materials in a cryogel matrix. Thus, the PAAc cryogel is an excellent platform for photothermal water evaporation. In this research, we prepared PAAc cryogels, incorporated different photothermal materials, and constructed the modular water evaporation systems. The photothermal evaporation rate of pure water with the PAAc-PPy cryogel system reached as high as 1.819 kg m⁻² h⁻¹ while its apparent efficiency surprisingly exceeded 100%. These modular systems exhibited excellent long-term and recyclable utility. As for the photothermal evaporation of salty water, the precipitated salt solid could be spontaneously dissolved during the light turnoff due to the quick water transport, maintaining the high water-to-vapor conversion. This study represents an ideal matrix platform, PAAc cryogel, for photothermal evaporation and opens up a new route to improve the photothermal evaporation technique for water purification and seawater desalination.