Superwetting monolithic hypercrosslinked polymers nanotubes with high salt-resistance for efficient solar steam generation

Abstract Solar-driven water evaporation is emerging as a promising strategy to utilize solar energy for the desalination and water purification. In this work, two kinds of monoliths based on hypercrosslinked polymers (HCPs) nanotubes, which were synthesized using inexpensive and conventional chemicals, i.e. benzene and methylbenzene as building blocks via Friedel-Crafts reaction, have been created as photothermal materials through a superhydrophilic modification followed by the coating of polypyrrole as light absorption layer. The as-synthesized HCPs possess large specific surface area (up to 773 m2 g-1) and low apparent density (0.011 g cm-3), which endow them very low thermal conductivity (0.029 W m-1 k-1). After modification with sodium alginate and polypyrrole, the resulting HCPs (named as PPy-M-HCPs) show surface superhydrophilicity (water contact angle ~0°), stronger light absorption (ca. 95%) and better mechanical properties. Taking advantages of these unique physicochemical properties mentioned above, the PPy-M-HCPs exhibit outstanding light-to-heat conversion performance with a high solar conversion efficiency of ca. 87% achieved under 1 kW m-2 irradiation. In addition, the PPy-M-HCPs also show excellent salt-resistant performance, e.g. a high energy conversion efficiency of more than 85% obtained in 20 wt% NaCl solution, due to their loosely porous structure coupling with their superhydrophilic wettability. Based on the merits of simple fabrication process, excellent stability and high solar conversion efficiency, the PPy-M-HCPs may have great potentials as efficient photothermal materials for real applications.