Role of freeze-drying in cellulose-based aerogels: Freezing optimization strategies and diverse water treatment applications

Cellulose-based biomass aerogels recently have garnered significant attentions as emerging materials for water treatment, due to their excellent characteristics of high porosity, lightweight structure, chemical modifiability and environmental friendliness. However, conventional freeze-drying methods have resulted in disordered pore structures of aerogels, reducing their mechanical property and water treatment efficiency. This article aims to provide a comprehensive review on the role of freeze-drying in cellulose-based aerogels. Special emphases are placed on freezing optimization strategies in aerogels preparations, such as co-solvent addition, directional freezing, freeze-thaw and soft-ice freezing, and water treatment applications of aerogels including oil-water separation, dye and heavy metal ions adsorptions, and seawater desalination via photothermal interfacial evaporation. The ordered pore structure constructed by freezing optimization can significantly increase the specific surface area and enhance the mechanical property of aerogels, thus improving the mass transfer rate and recyclability. The high-performance biomass aerogels prepared through freezing optimizations have shown a great application promise for biomass resources to achieve green and sustainable water treatment processes.