MXene-Based Porous Monoliths

Abstract

In the past decade, a thriving family of 2D nanomaterials, transition-metal carbides/nitrides (MXenes), have garnered tremendous interest due to its intriguing physical/chemical properties, structural features, and versatile functionality. Integrating these 2D nanosheets into 3D monoliths offers an exciting and powerful platform for translating their fundamental advantages into practical applications. Introducing internal pores, such as isotropic pores and aligned channels, within the monoliths can not only address the restacking of MXenes, but also afford a series of novel and, in some cases, unique structural merits to advance the utility of the MXene-based materials. Here, a brief overview of the development of MXene-based porous monoliths, in terms of the types of microstructures, is provided, focusing on the pore design and how the porous microstructure affects the application performance.

Keywords: 2D nanomaterials; MXenes; assembly; porous architecture.

Figure 4

Digital photographs and SEM images of MXene/rGO (a) hydrogel and (b,c) aerogels with isotropic cellular microstructure. (d) Schematic illustration of EDA-MXene/rGO hydrogel. (e) SEM images of K⁺-MXene/rGO monolith and MXene/rGO monolith. (f) SEM image of MXene/PI aerogel. (g) SEM image of freeze-dried MXene/PAA/amorphous calcium carbonate (ACC) hydrogel. (h) Schematic illustration and SEM image of Fe²⁺-MXene monolith. (a) is reproduced with permission from ref. [34]. Copyright 2018, American Chemical Society. (b) is reproduced with permission from ref. [63]. Copyright 2018, Wiley-VCH. (c) is reproduced with permission from ref. [64]. Copyright 2019, The Royal Society of Chemistry. (d) is reproduced with permission from ref. [67]. Copyright 2019, Wiley-VCH. (e) is reproduced with permission from ref. [69]. Copyright 2021, Elsevier. (f) is reproduced with permission from ref. [33]. Copyright 2018, Wiley-VCH. (g) is reproduced with permission from ref. [79]. Copyright 2021, American Chemical Society. (h) is reproduced with permission from ref. [81]. Copyright 2019, Wiley-VCH.

Figure 6

(a) Schematic illustration of MXene/SA aerogel with aligned honeycomb microstructure prepared by UFC, and SEM images captured from the side view and top view. (b) Schematic illustration showing the 3D-printing MXene architecture, and SEM images showing the MXene architecture and the cross-section of one printed filament. (c) Schematic illustration of the MXene architecture prepared by 3D printing and UFC, and SEM images captured from the side view and top view. (a) is reproduced with permission from ref. [52]. Copyright 2019, Elsevier. (b) is reproduced with permission from ref. [103]. Copyright 2019, Wiley-VCH. (c) is reproduced with permission from ref. [109]. Copyright 2020, Wiley-VCH.

Figure 1

Growing importance of MXene-based porous monoliths in increasing number of SCI indexed publications (source: SciFinder 2022).

Figure 2

MXene-based porous monoliths: types and applications. Reproduced with permission from ref. [51]. Copyright 2016, Wiley-VCH. Reproduced with permission from ref. [52]. Copyright 2019, Elsevier. Reproduced with permission from ref. [53]. Copyright 2022, American Chemical Society. Reproduced with permission from ref. [54]. Copyright 2020, Elsevier. Reproduced with permission from ref. [55]. Copyright 2022, American Chemical Society.

Figure 3

Five typical microstructures in MXene-based porous monoliths: (a) isotropic cellular, (b) aligned honeycomb, (c) local oriented lamellar, (d) long-range ordered lamellar, and (e) radial lamellar structures. (a) is reproduced with permission from ref. [34]. Copyright 2018, American Chemical Society. (b) is reproduced with permission from ref. [59]. Copyright 2020, Wiley-VCH. (c) is reproduced with permission from ref. [55]. Copyright 2022, American Chemical Society. (d) is reproduced with permission from ref. [60]. Copyright 2019, American Chemical Society. (e) is reproduced with permission from ref. [53]. Copyright 2022, American Chemical Society.

Figure 5

(a) Schematic illustration of collaborative assembly of MXSs at toluene–water interface and the MXS aerogel; optical photographs showing the lightweight, robust, and hydrophobic MXS aerogel; and SEM images MXS aerogels prepared from emulsion templates with different MXene concentrations. (b) Schematic illustration of JMN aerogel; optical photograph showing the lightweight property; and SEM images of JMN aerogels prepared from emulsion templates with different JMN contents. (a) is reproduced with permission from ref. [93]. Copyright 2019, Wiley-VCH. (b) is reproduced with permission from ref. [96]. Copyright 2022, Elsevier.

Figure 7

(a) Schematic illustration of MXene/rGO aerogel with aligned lamellar microstructure prepared by UFC, and SEM images captured from the side view and top view. (b) Schematic illustration of spectrally modified MXene/PVA aerogel with local oriented lamellar structure prepared by freezing/thawing, UFC, and freeze drying, and SEM image captured from the top view of this aerogel. (c) Schematic illustration of patterned MXene aerogel prepared by drop-on-demand inkjet printing and UFC, and SEM images captured from the side view and top view of this aerogel. (a) is reproduced with permission from ref. [49]. Copyright 2018, American Chemical Society. (b) is reproduced with permission from ref. [110]. Copyright 2022, Wiley-VCH. (c) is reproduced with permission from ref. [111]. Copyright 2021, Wiley-VCH.

Figure 8

(a) Schematic illustration of BFC device and process. (b) SEM images of Ti₃C₂T_x/PI aerogel with long-range ordered lamellar structure captured from different views. (a) is reproduced with permission from ref. [60]. Copyright 2019, American Chemical Society. (b) is reproduced with permission from ref. [54]. Copyright 2020, Elsevier.

Figure 9

(a) Schematic illustration of RFC process and MXene/PI aerogel with radial lamellar structure. SEM images of the aerogel captured from the (b) top view and (c) side view, and (d) SEM image of a single lamella. Reproduced with permission from ref. [53]. Copyright 2022, American Chemical Society.

Figure 10

(a) SEM and Micro-CT images of MXene monoliths with local oriented lamellar structure prepared from suspensions with varying concentrations (15 and 50 mg mL⁻¹). (b) SEM images showing the enlarged spacing of MXene hydrogels under reduced freezing rate. (c) Virtual CT section and 3D segmented rendering of the aerogel sheets (up left); virtual CT section and 3D segmented showing the domain orientations (up right); and microstructure evolution under compression (down). (a) is reproduced with permission from ref. [117]. Copyright 2019, American Chemical Society. (b) is reproduced with permission from ref. [118]. Copyright 2020, American Chemical Society. (c) is reproduced with permission from ref. [55]. Copyright 2022, American Chemical Society.

Figure 11

Schematic illustration of EMI shielding mechanism of MXene-SA composite films. Reproduced with permission from ref. [22]. Copyright 2016, the American Association for the Advancement of Science.

Figure 12

Resistance changes of MXene/PVA hydrogel in response to (a) finger bending, (b) different hand gestures, (c) human pulse, insert showing a typical dicrotic notch, and (d,e) facial expressions. Reproduced with permission from ref. [70]. Copyright 2018, the American Association for the Advancement of Science.

Figure 13

(a) Cyclic compressive stress–strain curves and (b) finite element analysis of MXene aerogel with aligned honeycomb structure. Reproduced with permission from ref. [145]. Copyright 2021, Elsevier.

Figure 14

(a) Schematic diagram of the wireless device and signal codes. (b) Morse code signals represent different words. Reproduced with permission from ref. [148]. Copyright 2022, Elsevier.

Figure 15

(a) Schematic illustration showing the MXene aerogel with sandwich-like structure, and the shrinking process of the multilevel cellular wall with bottlebrush-like PGPDMS crosslinked MXene nanochannels under compression. (b) Equivalent circuit diagram of this piezoresistive sensor. Reproduced with permission from ref. [149]. Copyright 2022, Springer Nature.

Figure 16

(a) Schematic illustration of a solar steam generation system and the salt resistance strategy based on a Janus-type MXene aerogel. (b) Schematic illustration of the solar-vapor generation from the solar absorber of MXene foam decorated with vertical arrays of 2D carbon nanoplates with embedded Co nanoparticles. (c) Photograph and optical microscope image showing a penguin down-feather (left); and schematic illustration of MXene/PVA aerogel with this microstructure for solar-powered water evaporation. (d) Schematic illustration of the radial MXene aerogel, photothermal evaporation device, and the capillary force in the aligned channels for water transportation. (a) is reproduced with permission from ref. [50]. Copyright 2019, American Chemical Society. (b) is reproduced with permission from ref. [160]. Copyright 2020, Wiley-VCH. (c) is reproduced with permission from ref. [110]. Copyright 2022, Wiley-VCH. (d) is reproduced with permission from ref. [53]. Copyright 2022, American Chemical Society.

Figure 17

(a) Schematic illustration of the cell walls’/pore channels’ orientation-induced EMI shielding mechanism. (b) SEM images and (c) EMI shielding effectiveness of the MXene/CNF hybrid aerogels with various angles between the cell walls’ oriented direction and electric field direction of incident EM waves. Reproduced with permission from ref. [59]. Copyright 2020, Wiley-VCH.

Figure 18

Schematic illustrations of the EM absorption mechanism of Ni/MXene/rGO aerogel. Reproduced with permission from ref. [167]. Copyright 2021, American Chemical Society.