Amphiphilic silica monomers induced superhydrophilic and flexible silica aerogels for radiative cooling and atmospheric water harvesting

Abstract

Silica aerogels have attracted extensive attention owing to their exceptional porous structures and crucial applications for sustainable environments. However, the inherent fragility and complex manufacturing process of silica aerogels present a challenge for their prolonged applications. In this study, an amphiphilic silica monomer, triethoxysilane end-capped poly(ethylene oxide) (PEO-TES), is designed and synthesized, which can co-gelled with methyltrimethoxysilane in water and gives birth to flexible and superhydrophilic silica aerogels via ambient pressure drying (APD). PEO-TES plays a dual role as both co-monomers and surfactants, effectively stabilizing the sol–gel transition, adjusting the porous structure of hydrogels, and imparting superhydrophilicity. The silica aerogel has low density (0.147 g cm−3), zero water contact angle, high elasticity (80 % compression), high solar reflectance (0.888), and high IR emissivity (0.967). These features make them robust all-day passive radiative cooling materials with 10.5 °C sub-ambient cooling capacity and atmospheric water harvesting capacities for both vapor (a water harvesting rate of 0.041 kg m−2h−1) and fog (harvesting capacity of 2.9 g g−1). The strategy provides a simple APD method for synthesizing flexible and superhydrophilic silica aerogels with controllable porous structures, passive cooling, and water harvesting performance, which may help address global climate change and water scarcity challenges.