MXenes, discovered in 2011 at Drexel University, are one of the largest class of 2D materials ever known. Above image shows the scanning electron microscopy (SEM) image of MXene at 500 nm resolution. These are hydrophilic transition metal carbides, nitrides, and carbonitrides, having general structure formula as Mn+1XnTx, wherein
M: Transition metal (Ti, V, Nb, Mo, Cr, Ta, Hf)
X: C and/or N
Tx: Surface terminations (usually =O, -OH, -F, or -Cl), and n = 1-4
Usually, these are produced by selective etching, using HF, H2O2 + HF, HCl + LiF, HCl + Na, HCl + K, HCl + NH4F, NH4HF2, LiF + NaF + KF, NaOH, NaBF4, HCl, ZnCl2 at room temperature or higher temperatures – maximum being 550 oC; of Mn+1AXn phase precursors, wherein A is typically Al. They have two to four layers of M interleaved with carbon and/or nitrogen layers. Presence of O and/or OH terminations in Mxenes makes them hydrophilic compared to graphene.
Some MXenes reported until date are:
- M1.33X: Nb1.33C, Mo1.33C, W1.33C
- M2X: Ti2C, V2C, Nb2C, Mo2C, Ti2N, V2N, Mo2N, (Ti1/2,V1/2)2C, (Ti1/2Nb1/2)2C, (Mo2/3Y1/3)2C
- M3X2: Ti3C2, Ti3C2, Zr3C2, Hf3C2, (Ti1/2V1/2)3C2, (Cr1/2V1/2)3C2, (Cr2/3Ti1/3)3C2, (Cr2/3Ti1/3)3C2, (Mo2/3Ti1/3)3C2, (Mo2/3Sc1/3)3C2
- M4X3: Ti4N3, V4C3, Nb4C3, Ta4C3, (Nb4/5Ti1/5)4C3, (Nb4/5Zr1/5)4C3, (Mo1/2Ti1/2)4C3
Typical properties of MXenes are:
- Easy processability
- High mechanical strength
- High thermal stability
- Tunable plasmonic properties
- High capacitance
- High electrical conductance
Major application areas of MXenes are in:
- Energy Storage
- Tu et al. prepared MXene (Ti3C2 nanosheets) /poly(vinylidene fluoride) based percolative composites having enhanced dielectric permittivity, attributed to the charge accumulation caused by the formation of microscopic dipoles at the surfaces between the MXene sheets and the polymer matrix under an external applied electric field.
- Review by Gao et al. records various MXene/polymer composites found suitable for membrane applications especially for electromagnetic interference shielding, energy storage and wearable electronics.
- Hu et al. fabricated MXene (Ti3C2 nanosheets)/chitosan aerogels having ability to withstand extremely high strains (99%) and long term compression and bending tests.
- Shashzad et al. MXene (Ti3C2 nanosheets)/sodium alginate composite film prepared using vacuum assisted filtration starting from colloidal solutions, found to be suitable for electromagnetic interference shielding applications.
- Gund et al. MXene (Ti3C2 nanosheets)/ poly(3,4-ethylenedioxythiophene) polystyrene sulfonate hybrid thin films equipped with a spray drying method which were found applicable in making AC filtering electrochemical capacitor having high volumetric capacitance maintained up to a rate of 1,000 V s−1.
- Exhaustive review by Jimmy and Kandasubramanian elaborates various MXene/polymer composites ranging from polymers such as polyvinyl butyral, ultra high molecular weight polyethylene, polyether sulfone, chitosan, cellulose nanofibers, polysulfides, poly(vinylidene fluoride), polypyrrole, polyvinyl alcohol, poly(acrtylic acid), poly(2-(dimethylamino)ethyl methacrylate), polyurethane, polyaniline, low density polyethylene, polyesters, polyethyleneimine, polyacrylamides etc.
- Tu et al., prepared MXene (Ti3C2 large flakes)/ poly(vinylidene fluoride-trifluoro-ethylene-chlorofluoroehylene) composite to achieve very high dielectric permittivity in the orders of 105, caused by charge accumulation at the surfaces between the two dimensional (2D) MXene flakes and the polymer matrix.
There are many more example of MXene/Polymer composites. Have you come across any? Please mention in the comments section below.
However, few questions that pops in my mind are:
- Are they economically feasible materials?
- How much capable are we to produce the MXenes and their polymer composites in large scale?
- Can this material replace conventionally used conductive fillers?
- Is any research work happening in India?
Dear Readers, do go through the above literature and let me know your viewpoints in the Comments section.
Thanks for reading!
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- Bu, Fanxing, et al. “Porous MXenes: Synthesis, structures, and applications.” Nano Today 30 (2020): 100803.
- Shein, Igor R., and Alexander L. Ivanovskii. “Graphene-like nanocarbides and nanonitrides of d metals (MXenes): synthesis, properties and simulation.” Micro & Nano Letters 8.2 (2013): 59-62.
- Salim, O., et al. “Introduction to MXenes: synthesis and characteristics.” Materials Today Chemistry 14 (2019): 100191.
- Alhabeb, Mohamed, et al. “Guidelines for synthesis and processing of two-dimensional titanium carbide (Ti3C2T x MXene).” Chemistry of Materials 29.18 (2017): 7633-7644.
- Halim, Joseph, et al. “Synthesis and characterization of 2D molybdenum carbide (MXene).” Advanced Functional Materials 26.18 (2016): 3118-3127.
- Tu, Shaobo, et al. “Large dielectric constant enhancement in MXene percolative polymer composites.” ACS nano 12.4 (2018): 3369-3377.
- Gao, Lingfeng, et al. “MXene/polymer membranes: synthesis, properties, and emerging applications.” Chemistry of Materials 32.5 (2020): 1703-1747.
- Hu, Yijie, et al. “Biomass polymer-assisted fabrication of aerogels from MXenes with ultrahigh compression elasticity and pressure sensitivity.” Journal of Materials Chemistry A 7.17 (2019): 10273-10281.
- Shahzad, Faisal, et al. “Electromagnetic interference shielding with 2D transition metal carbides (MXenes).” Science 353.6304 (2016): 1137-1140.
- Monastyreckis, G., et al. “Micromechanical modeling of MXene-polymer composites.” Carbon (2020).
- Gund, Girish Sambhaji, et al. “MXene/polymer hybrid materials for flexible AC-filtering electrochemical capacitors.” Joule 3.1 (2019): 164-176.
- Jimmy, John, and Balasubramanian Kandasubramanian. “MXene functionalized polymer composites: Synthesis and applications.” European Polymer Journal 122 (2020): 109367.
- Tu, Shaobo, et al. “Enhancement of Dielectric Permittivity of Ti3C2T x MXene/Polymer Composites by Controlling Flake Size and Surface Termination.” ACS applied materials & interfaces 11.30 (2019): 27358-27362.
- Liu, Ruiting, et al. “Ultrathin biomimetic polymeric Ti3C2T x MXene composite films for electromagnetic interference shielding.” ACS applied materials & interfaces 10.51 (2018): 44787-44795.
- Boota, Muhammad, and Yury Gogotsi. “MXene—conducting polymer asymmetric pseudocapacitors.” Advanced Energy Materials 9.7 (2019): 1802917.