A moisture-absorbing cellulose nanofibril-based foam via ambient drying for high-performance dehumidification

Hygroscopic salt is often used as an important functional component of moisture-absorbing materials because of its excellent capability of capturing water from the air. However, hygroscopic salt cannot store large amounts of condensed water and has poor structural stability, as it dissolves easily in the condensate. The droplets leak from porous composites, resulting in hygroscopic salt consumption and poor water uptake. Herein, we aimed to develop a porous moisture-absorbing foam, which consists of a hydrophilic cellulose nanofibril (CNF)/4A molecular sieve network functionalized by hygroscopic lithium chloride (LiCl), using an ambient drying method. The hygroscopic LiCl considerably enhanced the moisture absorption of the porous foam, while strong hydrophilic CNFs captured the adjacent water molecules via hydrogen bonding and transported the condensed water to the inner part of the foam. The synergistic effect of LiCl and the CNF/4A molecular sieve network was critical for the air dehumidification performance, conferring the foam with excellent water uptake ability of 0.74 g/g within 8 h at 50 % relative humidity (RH). The liquefied water was confined completely in the porous foam during the moisture sorption process, thereby achieving good cyclic stability (10 cycles). Even when the volume was equivalent to 120 x of the volume of one foam, the RH was reduced by the foam from 55 to 58 % to 28-31 % (within 23 min) and then maintained stably up to 8 h. The foam possessed better dehumidification ability than desiccant wheel and silica gel, indicating that it may be used for air dehumidification and environmental humidity management.