Ultrahigh fluid sorption capacity of superhydrophobic and tough cryogels of cross-linked cellulose nanofibers, cellulose nanocrystals, and Ti3C2Tx MXene nanosheets

Abstract

In this study, we present superhydrophobic, hierarchical, and nanostructured cryogels made from a nanocellulose (NC) skeleton comprising cellulose nanofibers (CNFs) and nanocrystals (CNCs), double cross-linked with Ti₃C₂T_x MXene nanosheets and poly(vinyl alcohol) (PVA) in the presence of tetradecylamine. Compared to pure CNCs or CNFs, cryogels with a combination of CNCs and CNFs possessed significantly better mechanical performance. Unlike many green natural based nanoporous solids, the prepared mixed cryogels displayed rigid and durable structure, and possessed ultrahigh sorption capacity for several organic fluids, among the highest reported for aerogels/cryogels in the literature. By taking advantage of the synergistic effects of crosslinking between long-entangled CNFs with short-needle-like CNCs as well as the strong interaction between NCs, MXene nanosheets and PVA, highly porous (>92%), lightweight (∼20 mg cm⁻³), and superhydrophobic cryogels with a water contact angle of ∼150° were designed. The hybrid cryogels possessed ultrahigh sorption capacity toward various oils/organic solvents ranging from approximately 110–320 times their weight. The cryogels were reused in more than ten cycles of sorption–squeezing without significantly reducing sorption capacity. Hence, these nanostructured porous solids have a high potential to be used in various purposes in environmental remediation, such as oil spill response and removal of water-insoluble organic solvents.