Vertical macroporous chitosan aerogel adsorbents for simple and efficient enhancement of atmospheric water harvesting and air dehumidification

Abstract

Sorption-based atmospheric water harvesting (SAWH) has become one of the effective methods to extract water from the air in arid regions due to its high efficiency and low energy consumption. Hygroscopic salts have high water adsorption rates but their disadvantages such as easy leakage and slow kinetics limit their further application. Most of the reported aerogel porous materials loaded with hygroscopic salts can effectively solve the leakage problem, but the disordered pores limit the water vapour transport. It is therefore necessary to develop a simple method to further improve the adsorption kinetics and increase the rate of water vapour adsorption. In this paper, a low-cost, green, and high water adsorption LCSC-MC aerogel adsorbent is reported. The composite adsorbent is based on biomass chitosan and photothermal responsive nanocarbon as the aerogel skeleton structure, and the introduction of lithium chloride enables it to obtain excellent water-adsorption performance. In addition, we constructed a large number of vertical macroporous channel structures on the hygroscopic aerogel using a simple needle array template. Benefiting from the vertical macroporous channel structure, the diffusion resistance of water vapour in the aerogel is reduced, resulting in more efficient and faster water adsorption. The water adsorption rates of LCSC-MC after 12 h of moisture adsorption at 20% RH and 90% RH are as high as 0.75 g g⁻¹ and 3.85 g g⁻¹, respectively. In addition, LCSC-MC has excellent air dehumidification performance, reducing humidity from 75% RH to less than 30% RH in 50 minutes, which is superior to that of commercial desiccants such as silica gel, calcium chloride and 4A molecular sieves. Meanwhile, our prepared LCSC-MC showed good cycling stability in both long-term atmospheric water collection and passive air dehumidification practical applications. Moreover, we further improved the water adsorption efficiency of the aerogel adsorbent with a simple strategy, which is expected to be extended to other aerogel adsorbents.