Nano-structured urchin-like photothermal covalent organic frameworks for efficient Solar-Driven interfacial water evaporation

Abstract

Solar-driven interfacial water evaporation is a promising sustainable technology to alleviate the global energy crisis and clean water shortage. The design of advanced photothermal materials play the critical role to utilize photothermal heat for water evaporation. Covalent organic frameworks (COFs) as a new class of crystalline porous polymer semiconductor materials have been deemed as an ideal nanoscale platform for designing photothermal materials with notable features like highly ordered structures, porous open channels, and tunable structure and functionality. In this work, we focus on the regulation of the multi-scale structure of COFs and design hierarchically nano-structured photothermal COFs for efficient solar-driven interfacial water evaporation. At the molecular scale, we synthesize a photothermal functionalized COF-366-OH using photosensitive 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (TAPP) and 2,5-dihydroxyterephthalaldehyde (DHTA) as building blocks. At the micro-nano scale, we introduce the π-conjugated catechol molecule 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to regulate COF polycondensation and assembly, which enable the shaping of COF-366-OH into urchin-like nano-morphologies (namely UCOF-366-OH). The synthesized UCOF-366-OH exhibits high crystallinity, large surface area, excellent photothermal conversion capacity, and strong hydrophilicity. Furthermore, UCOF-366-OH is processed into a photothermal composite membrane. With localized solar heating and optimized water transport at the water evaporation interface, a high evaporation rate of 2.51 kg m−2h−1 with solar-to-vapor efficiency of 97.3 % is achieved. This work paves a new way for the multi-scale structural design of COF-based photothermal materials and highlights their innovative application in solar water evaporation.