Lightweight, Superelastic, and Hydrophobic Polyimide Nanofiber /MXene Composite Aerogel for Wearable Piezoresistive Sensor and Oil/Water Separation Applications

Abstract

Inspired by the ultralight and structurally robust spider webs, flexible nanofibril‐assembled aerogels with intriguing attributes have been designed for achieving promising performances in various applications. Here, conductive polyimide nanofiber (PINF)/MXene composite aerogel with typical “layer‐strut” bracing hierarchical nanofibrous cellular structure has been developed via the freeze‐drying and thermal imidization process. Benefiting from the porous architecture and robust bonding between PINF and MXene, the PINF/MXene composite aerogel exhibits an ultralow density (9.98 mg cm−3), intriguing temperature tolerance from ‐50 to 250 °C, superior compressibility and recoverability (up to 90% strain), and excellent fatigue resistance over 1000 cycles. The composite aerogel can be used as a piezoresistive sensor, with an outstanding sensing capacity up to 90% strain (corresponding 85.21 kPa), ultralow detection limit of 0.5% strain (corresponding 0.01 kPa), robust fatigue resistance over 1000 cycles, excellent piezoresistive stability and reproductivity in extremely harsh environments. Furthermore, the composite aerogel also exhibits superior oil/water separation properties such as high adsorption capacity (55.85 to 135.29 g g−1) and stable recyclability due to its hydrophobicity and robust hierarchical porous structure. It is expected that the designed PINF/MXene composite aerogel can supply a new multifunctional platform for human bodily motion/physical signals detection and high‐efficient oil/water separation.

Piezotronics in two‐dimensional materials

“…The entrance of piezotronics from 2D materials was opened thoroughly since the first experimental confirmation from 2D MoS 2 by Hone and Wang groups in 2014, where piezo‐voltage and output current were detected only from MoS 2 flakes with odd number of atomic layers 31 . Then, piezotronics based on 2D materials has been grown into forest since the expansion from black phosphorus (BP), 55–59 hexagonal boron nitride (h‐BN), 60–63 transition metal dichalcogenide (TMDCs) and Janus TMDCs, 63–72 II‐VI semiconductors, 73–79 III‐V, 80–88 Group‐III monochalcogenides (III‐VI), 89,90 and Janus III‐VI, 91,92 Group‐IV monochalcogenides (IV‐VI), 93–97 Group‐V (V‐V), 98 and so on 99–109 . At the same time, the variety of applications of piezotronics from 2D materials were achieved on flexible optoelectronics, piezotronic catalysis, biological medicine, information storage, and so forth.…”

Recent Advances in Multidimensional (1D, 2D, and 3D) Composite Sensors Derived from MXene: Synthesis, Structure, Application, and Perspective

“…The researches on MXene-based sensors have shown a booming growth trend since its advent in 2015, according to the current reported articles, it is not difficult to find that most of MXene-based sensors are applied to intelligent wearable devices, working in the form of physical sensor (strain/pressure/piezoresistive sensor), regardless of 1D, 2D, and 3D MXene-based senor. 1D MXene-based fibers are commonly weaved into smart clothes for human health monitoring, besides this, it can be used for other special monitoring in other external stimuli such as working as the thermal sensor [196] MXene/ANFs aerogel Freeze-drying Pressure 128 kPa −1 0.01-623 kPa 320 [194] MXene/rGO aerogel Freeze-drying Pressure 22.56 kPa −1 0.01-3.5 kPa <200 [192] MXene/CSx aerogel Freeze-casting Pressure 80.4 kPa −1 0-5 kPa 109.6 [195] MXene sponge Dipping-coating Pressure/strain 442 kPa −1 0-18.56 kPa 138 [197] MXene sphere Ultrasonic spray pyrolysis NO 2 gas -5-100 ppm - [198] and optical fiber sensor. In addition, 2D and 3D MXene-based sensors have been successfully assembled into an array of circuits and then connected to a Bluetooth system for real-time detection on human activities, these are not far from practical commercial applications.…”

“…In 2021, Liu et al fabricated MXene/polyimide nanofiber (PINF) composite aerogel by freeze-drying assisted with thermal treatment, which endows MXene/PINF with typical "layer-strut" bracing hierarchical nanofibrous cellular structure. [196] To endure stable combination between MXene and PINF, oxygen plasma treatment used to improve the hydrophilicity of PINF, to obtain the homogenous MXene/PINF mixture successfully. And then water-soluble polyacrylic acid (PAA) as a binder, finally converted to PI and thus led to a great improvement in the elastic bonding between MXene and PINF, greatly improved the structural stability of composite aerogel.…”

“…And then water‐soluble polyacrylic acid (PAA) as a binder, finally converted to PI and thus led to a great improvement in the elastic bonding between MXene and PINF, greatly improved the structural stability of composite aerogel. [ 196 ] As a result, MXene/PINF composite aerogels with low density of 9.98 mg cm −3 exhibit good compressibility and recovery even in the compression strain range of up to 90%, which endowed the composite excellent oil–water separation performance and the responding adsorption capacity of up to 55.85–135.29 g g −1 . The good structure stability, elasticity, and antifatigue performance built a good basis for the sensing property, as a pressure sensor, it showed low detection limit (10 Pa), wide sensing range of up to 85.21 kPa even under the different high temperatures varying from 50 to 250 °C.…”

Dodecyl Mercaptan Functionalized Copper Mesh for Water Repellence and Oil-water Separation

“…The adsorbent materials are mainly 3D porous foams [28] , sponges [29,30] , aerogels [31,32] , powders or particles [33] , which are suitable for the adsorption and transfer of oil spills on water surface. In contrast, filtering is more desired for the separation of collectible oil-water mixtures, and porous metal mesh [34][35][36] , membranes [37,38], fiber fabrics [39,40] and filter papers [41] are always selected as the substrates to create surfaces with super wettability for filtering type separation. Among them, metal meshes (e.g., Copper Mesh (CM)) are characterized with good mechanical strength, cheapness and easy availability, etc.…”