Green fabrication of multifunctional polyimide aerogels for efficient solar-driven desalination by controlling polarity of side units

Polyimide (PI) aerogels have been widely used in desalination owing to their remarkable mechanical properties and thermal stability. However, their evaporation rates are poor. To improve this situation, a series of PI molecules bearing –CF 3 , –CH 3 , or –COOH pendant groups were synthesized to elucidate how molecular polarity affects interfacial water transport. The resulting PI films showed excellent tensile strength of beyond 100 MPa and high thermal decomposition temperature of beyond 250 °C. Among them, COOH-PI showed the strongest affinity for water: a water droplet completely infiltrated the corresponding aerogel within 4 s, whereas droplets remained on or were readily removed from the Me-PI and F-PI aerogels. And thus an evaporation rate of 3.23kg m -2 h −1 was achieved for carboxyl aerogel, which was far higher than methyl (0.58kg m -2 h −1 ) and trifluoromethyl (0.26kg m -2 h −1 ) aerogels. More encouragingly, the evaporate rate was nearly unaffected even it was suffered from 10 cyclic treatment. It is worthy to note that adsorption capacity of aerogel for both polar and nonpolar liquids was higher than 10 g g −1 and just slightly decreased after 20 cycles of testing. The compressive strength was up to 0.48 MPa, and this mechanical property was almost unaffected even they were exposed to heating (200 °C) or cooling (−20 °C) environment for 30 min. Overall, this work provided a meaningful insight for designing efficient aerogels for water evaporators.