Creating aligned porous structure with cobweb-like cellulose nanofibrils in MXene composite aerogel for solar-thermal desalination and humidity response

[Display omitted] •Cobweb-like CNF was formed to enhance thermal insulation of MXene-based aerogel.•Aerogel exhibited ultralow thermal conductivity and ultrahigh evaporation efficiency.•The swelling of PVA endowed humidity responsive properties to MXene-based aerogel. Aerogel with vertically aligned porous structure can effectively enhance sunlight absorption and continuously absorb seawater, which is ideal for solar-thermal desalination, but the oriented cell walls lead to rapid heat dissipation, reducing the evaporation efficiency. Herein, the multifunctional aerogels with enhanced thermal insulation property were fabricated through rational assembly of exfoliated Ti3C2Tx nanosheets, polyvinyl alcohol (PVA) and cellulose nanofibrils (CNF). The MXene composite aerogel (MCA) possessed the multiscale structure with parallel PVA/Ti3C2Tx cell walls served as the skeleton and cross-linked CNF filled in the aligned pores, which is responsible for the superior hydrophilicity, thermal insulation (56.54 mWm-1K-1) and solar absorption (97.9 %), suggesting high solar-thermal evaporation efficiency. Consequently, under exposure to 10 h natural sunlight irradiation, the maximum evaporation rate and efficiency of MCA reached 1.13 kgm-2h-1 and 82.93 %, respectively. Moreover, the swelling of polymers with dipped water causes the structure change and conductivity variation of MCA, which can monitor the changing humidity by the generation of water-induced electrical signal, showing great prospects in solar-thermal desalination and intelligent detection fields.