Nanocellulose Building Block for the Construction of Hygroscopic Aerogels

Abstract

Moisture, a ubiquitous component in the atmosphere, offers a wealth of opportunities and presents various challenges in our daily lives and the surrounding environment. On the one hand, people can obtain clean drinking water from air and use the moisture to create new energy sources. On the other hand, many people across the world still face long-term drought or damp hazards caused by extremely low or high humidity. Therefore, the sustainable management of atmospheric moisture is crucial for creating a comfortable lifestyle for humanity. Cooling condensation and desiccant drying are established methods for adjusting atmospheric humidity, yet they still face a range of challenges including energy usage, efficiency levels, operational simplicity, and broad applicability. Recently, hygroscopic materials, which can regulate environmental humidity, material performance, and collect water by adsorbing moisture from air and managing the adsorbed moisture, are attracting increasing attention. For the efficient and scalable production of hygroscopic materials, it is fundamental to carefully select and ingeniously assemble the building blocks that dictate their performance.

Nanocellulose, an emerging biopolymer nanofiber, is predominantly biosynthesized by higher plants, positioning it as an ideal building block for constructing hygroscopic materials. Its appeal lies in the sustainable and plentiful nature of its raw materials, coupled with its distinctive one-dimensional nanostructure, abundant surface hydroxyl groups, and outstanding mechanical strength. Furthermore, its capacity to readily assemble into diverse structures through straightforward processes makes it a compelling choice for advancing the development of next-generation biopolymer-based hygroscopic materials. Lightweight and self-standing hygroscopic aerogels can be fabricated after integration nanocellulose with various hygroscopic salts through a series of methods. As well as adsorbing atmospheric moisture, they can transform gaseous water into liquid water, and transport it to their interiors for storage. Water evaporation and release are realized by simply exposing the moisture-adsorbed aerogels to sunlight. These properties qualify plant material-derived hygroscopic aerogels as sustainable moisture management platform that are useful in many fields.

In the present Account, we describe recent progress in the use of nanocellulose as a building block for constructing hygroscopic aerogels. We will begin with the introduction of some fundamental knowledge about nanocellulose, with a specific focus on the extraction of nanofibrillated cellulose, a kind of nanocellulose mainly individualized from wood powders by chemical pretreatment combined with mechanical nanofibrillation, as well as its nanostructure characteristics. We will then describe the methods for manufacturing various types of nanocellulose hygroscopic aerogels and their hierarchical structures. Subsequently, we will analyze the hygroscopic performance of the aerogels through some basic data. Next, we will thoroughly discuss the use of the hygroscopic aerogels for dehumidification, atmospheric water harvesting, and moisture-induced power generation. Finally, we will elaborate the challenges and prospects of this emerging field.