Cellulose, as the most abundant biopolymer in nature, has attracted extensive interest from both academia and industry in recent years due to its specific properties such as biocompatibility, biodegradability, thermal and chemical stability. Nowadays, cellulose aerogel, which possesses extremely low density, large open pores, and a high specific surface area, has become one of topical polymer materials that are based on this sustainable resource. The combination of the advantages and characteristics of the renewable biopolymer and highly porous material has made cellulose aerogel as the new generation succeeding the inorganic and synthetic polymer-based aerogel. In this review, recent research progress in cellulose aerogel materials is summarized based on about 70 relevant papers. The preparation of cellulose aerogel materials is mainly focused on the dissolving solvents of cellulose, including hydrous and anhydrous systems, and aqueous dispersion media of cellulose nanofibers, which are separated from native lignocellulose biomass and bacterial cellulose. The recent development to enhance the mechanical properties of cellulose aerogel by improving the strength of solid network via addition of inorganic components, is described, along with that to introduce functionality (hydrophobicity, superoleophobicity, electrical and magnetic properties, etc.) in cellulose aerogel. Finally, a perspective on the cellulose aerogel materials and the research directions in the future is briefly discussed.

Contents
1 Introduction
2 Preparation of cellulose aerogels
2.1 Dissolution of cellulose by non-derivative solvents
2.2 Dispersion of cellulose nanofibers in water
3 Modification of cellulose aerogels
3.1 Enhancement of mechanical properties
3.2 Modification of hydrophobicity and oleophobicity
3.3 Electrical and magnetic functionalization
3.4 Loading of active compounds on aerogels
4 Perspective