Fast-thermoresponsive carboxylated cellulose nanofibers/Ti3C2/exfoliated montmorillonite-poly(N-isopropylacrylamide) with switchable wettability for oil-water separation

Abstract

Oil absorbed by aerogels was an effective method for achieving efficient oil–water separation. However, absorbent regeneration and recovery of oil were key issues that limited the practical application of aerogels. In this work, carboxylated cellulose nanofibers/Ti3C2/exfoliated montmorillonite/poly(N-isopropylacrylamide) (CNF-C/Ti3C2/MMTex-PNI) with switchable wettability was exploited through coordinately introduced exfoliated montmorillonite (MMTex), Ti3C2-MXene and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) into carboxylated cellulose nanofibers (CNF-C) by a facile one-step hydrothermal and in-situ co-precipitation process. CNF-C/Ti3C2/MMTex-PNI was capable of reversible transformation between hydrophobic/oleophilic and hydrophilic/oleophobic, when the environmental temperature was above or below the lower critical solution temperature (LCST: 32 °C) of PNIPAAm. CNF-C/Ti3C2/MMTex-PNI could absorb oil within 5 s (54–98 g⋅g−1) under 45 °C and desorb oil within 10 min (recovery efficiency exceeds 78 %) at 25 °C. Moreover, the addition of MMTex inhibited the oxidation of Ti3C2, and Ti3C2/MMTex synergistically enhanced the mechanical properties (complete recovery under 60 % strain) and thermal stability of CNF-C/Ti3C2/MMTex/PNI. After 20 cycles, the absorption and desorption capacities of CNF-C/Ti3C2/MMTex/PNI for oils all decreased by 15 %. Moreover, the synthesis and fast-thermoresponsive mechanism for CNF-C/Ti3C2/MMTex/PNI were proposed. In conclusion, this work provides a new reference for the synthesis and recycling of smart aerogels for oil–water separation.