Fast Kinetics Biosourced Carbon-Based Sorbents for Atmospheric Water Harvesting

Sorbent-based atmospheric water harvesting methods are emerging as promising techniques to address current and future water stress challenges. Recent advancements in sorbent design have shifted focus toward achieving both rapid sorption kinetics and high steady-state water uptake. Herein, daily water yields reaching 42, 15, 11, and 6.5 L·kg–1·day–1 are reported, respectively, at 95, 60, 30 and 10% relative humidity at 30 °C by employing activated, biosourced carbon-based sorbents. The specific dynamic vapor sorption performances of these biobased nanoporous sponges, Bio-NPS, were discussed as a function of their processing conditions, structures, and chemical compositions. The theoretical model proposed by Do et al. was applied to better understand the sorption mechanisms of water in different porous carbon media. The oxidation of hardwood charcoals using KOH at temperatures below 500 °C produced microporous sorbents rich in oxygen (18 atom %) and hydrophilic functions with a small specific surface. Type V water-sorption isotherms were obtained with no hysteresis. A moderate maximum water uptake (0.35 g·g–1 of sorbent at 95% relative humidity) was attained, with fast water sorption kinetics. At higher processing temperatures, sorbents presented a higher specific surface (2748 m2·g–1 for the sorbent processed at 900 °C) with reduced oxygen amount and hydrophilic functions. A higher maximum water uptake was obtained, reaching 1.3 g·g–1 at 95% relative humidity, but cycles were slower. Through Bio-NPS, a significant step demonstrating effective, sustainable, and robust water production performances across a wide range of conditions has been achieved, alongside low-environmental-impact and sustainable synthesis.