MXene - Nature, Properties, Chemical Reactions and Effect on Fibre
Muhammad Wajahat
CEO of LegerSoft | Aspiring Textile Engineer Technologist| Trainee Finishing Dye at Gulshan Fabrics| Software Company | AutoCAD Freelancer | WordPress
MXenes are a class of 2D transition metal carbides, nitrides, and carbonitrides, typically represented by the formula Mn+1XnTx, where M is an early transition metal (e.g., Ti, V, Nb), X is either carbon (C) or nitrogen (N), T represents surface terminations (–OH, –O, –F), and n is an integer (1, 2, or 3). First discovered in 2011, MXenes have gained attention for their remarkable electrical, mechanical, and electrochemical properties, making them promising candidates for applications in energy storage, sensors, catalysis, and flexible electronics.
Nature and Properties of MXenes
1. Layered Structure and High Conductivity:
MXenes have a layered structure similar to that of graphene, with metal layers (M) interspersed with carbon or nitrogen (X) layers. This structure gives MXenes metallic-level electrical conductivity, which is critical for applications in supercapacitors and batteries. For example, Ti?C?Tx is one of the most studied MXenes, offering high conductivity (up to 10,000 S/cm in thin films) and pseudocapacitance, making it ideal for high-performance capacitors(
).
2. Surface Functionalization:
One of the key characteristics of MXenes is their rich surface chemistry. The surface of MXene flakes is terminated with various functional groups such as –O, –OH, and –F, resulting from their synthesis via etching. These groups affect properties such as hydrophilicity, ionic conductivity, and electrochemical performance. Surface functionalization can also be tailored to specific applications, such as improving ion transport in energy storage devices.
3. Mechanical Flexibility:
MXenes, particularly Ti?C?Tx, are mechanically flexible due to their 2D nature, making them suitable for wearable devices and flexible electronics. MXenes can form thin films or be embedded into fibers without compromising flexibility, a critical property for integrating MXenes into textiles(
).
4. Hydrophilicity and Processability:
Unlike graphene, MXenes are naturally hydrophilic, which makes them easy to disperse in water and other solvents. This property allows for the processing of MXenes into thin films, coatings, or fibers via techniques such as vacuum filtration, spin coating, and spray deposition. Hydrophilicity is also advantageous for creating strong bonds with various fibers, especially when fabricating fiber supercapacitors(
).
5. Energy Storage and Pseudocapacitance:
MXenes can store electrical energy through both electrochemical double-layer capacitance (EDLC) and pseudocapacitance. EDLC occurs when ions from an electrolyte are adsorbed onto the surface of MXenes, while pseudocapacitance is due to fast surface redox reactions between the transition metal atoms and electrolyte ions. This combination of storage mechanisms allows MXenes to deliver high energy and power densities, crucial for high-performance fiber-based energy storage devices(
)(
).
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Chemical Reactions of MXenes
MXenes are typically produced by selectively etching out the A-layer (e.g., aluminum) from MAX phases, which are ternary carbides or nitrides (Mn+1AXn). The etching process involves hydrofluoric acid (HF) or other fluoride-containing reagents (e.g., ammonium bifluoride). The chemical reaction for etching a typical MXene, Ti?C?Tx, from its MAX phase precursor, Ti?AlC?, is as follows:
Ti3AlC2+3HF→Ti3C2Tx+AlF3+3H2\text{Ti}_3\text{AlC}_2 + 3HF \rightarrow \text{Ti}_3\text{C}_2T_x + AlF_3 + 3H_2Ti3AlC2+3HF→Ti3C2Tx+AlF3+3H2
The surface terminations (Tx) (e.g., –OH, –O, –F) result from this etching process, which greatly influences the properties of MXenes, such as their hydrophilicity and electrochemical performance(
).
In addition, MXenes can undergo intercalation reactions with various ions (e.g., Li?, Na?, K?), allowing them to function as ion storage materials in batteries and supercapacitors. The ease with which MXenes can undergo ion intercalation contributes to their high rate performance and cycling stability in energy storage applications.
Effect of MXenes on Different Types of Fibers
When incorporated into fibers, MXenes improve electrical conductivity, mechanical strength, and electrochemical properties. Depending on the fiber material, MXenes can be integrated in various ways, enhancing the overall performance of fiber-based devices.
1. Polymeric Fibers (e.g., Nylon, Polyurethane):
MXenes can be coated or embedded into polymer fibers to enhance their conductivity without sacrificing flexibility. These fibers are often used in wearable electronics and textile-based supercapacitors. For instance, MXene-coated polyurethane fibers can act as flexible electrodes in supercapacitors, maintaining high capacitance even when bent or twisted(
).
2. Carbon-Based Fibers (e.g., Carbon Nanotube (CNT) Fibers):
MXenes can be combined with carbon nanotube (CNT) fibers to create highly conductive, flexible fibers with enhanced energy storage capabilities. The large surface area and excellent conductivity of both materials allow for rapid charge and discharge cycles, making them ideal for high-performance supercapacitors(
).
3. Natural Fibers (e.g., Cotton, Silk):
MXenes can be coated onto natural fibers like cotton or silk to create conductive fabrics. These fabrics can be used in smart textiles, where flexibility, comfort, and conductivity are required. MXene-coated natural fibers retain the feel of traditional textiles while gaining electronic properties, making them suitable for wearable sensors or energy-harvesting garments(
).
Conclusion
MXenes, with their unique combination of metallic conductivity, surface functionalization, and mechanical flexibility, are emerging as key materials for flexible electronics and fiber-based energy storage systems. By interacting with different fiber types, MXenes improve the conductivity and energy storage performance of fibers, opening new possibilities for wearable electronics, smart textiles, and supercapacitors. MXenes' rich surface chemistry and ability to undergo various chemical reactions allow for customizable fibers with enhanced performance in a wide range of applications.