Ti₃C₂ MXene: Characteristics, Synthesis and Emerging Applications

MXene represents a novel nanomaterial category which consists of two-dimensional transition metal carbides/nitrides following the chemical formula M_n+1X_nT_x where M stands for transition metal X for carbon or nitrogen and Tx for surface groups like -OH and -F. Selective etching of the A layer (e.g., Al) from the MAX phase produces this material which features a layered structure along with high conductivity and a large specific surface area that provides numerous surface active sites. Research into Ti₃C₂ MXene has rapidly expanded across energy storage, catalysis and sensing fields because of its affordability combined with straightforward functionalization capabilities and superior electronic attributes. Current research priorities center on studying the etching and stripping techniques for multilayer MXene (m-MXene) and improving its effectiveness for use in supercapacitors and lithium-ion batteries.

Characteristics of Ti₃C₂ MXene

Ti₃C₂ MXene possesses superior electrical conductivity compared to other MXenes like Mo2CTx and Ti₂CT_x due to its two-dimensional layered structure and high carrier mobility which allows conductivity to reach up to 10⁴ S/cm. Theoretical results demonstrate that Ti₃C₂ MXene has a very low Li ion diffusion barrier and exhibits a maximum lithium storage capacity of 447.8 mAh/g which qualifies it as an optimal negative electrode material for lithium-ion batteries.

The presence of active groups like —OH, =O and —F on the Ti₃C₂ surface leads to outstanding hydrophilicity and chemical modifiability. Its specific capacitance reaches 517 F/g through K⁺ intercalation combined with the removal of surface groups including F⁻ and OH⁻. The active surface groups enable Ti₃C₂ to bond with other materials like TiO₂ which results in the formation of Schottky junctions that improve photocatalytic efficiency.

Ti₃C₂ MXene demonstrates complete internal photothermal conversion efficiency at 100%. The solar-driven water evaporation system achieves light-water evaporation efficiency of 84% which leads among comparable materials.

The layered structure combined with dielectric loss and interface polarization effects of Ti₃C₂ MXene results in wide absorption bandwidth and strong reflection loss within the 2-18 GHz frequency band. Developing a MoS2/ Ti₃C₂ heterojunction leads to better impedance matching and enhances electromagnetic wave absorption capabilities.

Under argon conditions Ti₃C₂ MXene remains stable until 800°C but begins oxidizing at 200°C when exposed to oxygen and transforms entirely into anatase TiO₂ at 1000°C.

MXene surface active groups react readily with environmental oxygen which leads to both structural and performance degradation. Exposure of unprotected Ti₃C₂ to air results in significant oxidation after several days. Research demonstrates that the application of carbon nanocoating (e.g., MoS₂@C/Ti₃C₂) or surface passivation through hydroxylamine functionalization enhances the material's oxidation resistance to achieve sustained performance in lithium storage alongside hydrogen evolution reactions.

Synthesis Method of Ti₃C₂ MXene

Top-down etching method

Ti₃C₂ MXene synthesis primarily uses the top-down etching method where the A component like Al is removed from the MAX phase precursor Ti₃AlC₂ to produce two-dimensional layered MXene. This method achieves selective removal of the A layer from MAX phases through chemical etchants like HF or NaF-HCl.

Precursor selection

The MAX phase precursor Ti₃AlC₂ serves as the primary material for producing MXenes. The compound consists of Ti, Al and C atoms while demonstrating strong chemical stability alongside layered features. Selective etching of the Al layer leads to the production of Ti₃C₂ MXene.

Process optimization

HF stands as the primary etchant choice in etching operations although its toxic nature restricts practical use. Researchers have created multiple alternative solutions for etching including NaF-HCl solution and LiF-HCl mixed solution. The alternative etchants achieve both lower toxicity levels and better etching performance and purity. The NaF-HCl solution etching process yields high-purity (>99.999%) Ti₃C₂ layered structures by adjusting both etchant concentration and temperature while controlling processing time.

Post-treatment and functionalization

Intercalation exfoliation: The Ti₃C₂ layered structures develop larger agglomerates following the etching process. Urea and DMSO work as intercalation agents to separate layers. Ultrasonic treatment or mechanical stirring processes help exfoliate intercalation agents that are inserted between layers.

Surface modification: Surface modification techniques help enhance Ti₃C₂ MXene performance through structural optimization. The addition of surfactants leads to greater interlayer distance and boosts both conductivity and functionality. Nitrogen doping stands as a popular surface modification technique which enhances the electrochemical properties of MXene.

Carbon nanocoating: Surface coating with carbon nanomaterial layers serves to prevent oxidation and improve composite material interfacial coupling on Ti₃C₂. The material becomes more stable and its practical application performance is enhanced through this process.

Although top-down etching is currently the main method for MXene synthesis, it still faces some challenges: The effectiveness of HF is limited by its high toxicity for practical applications. A variety of fluorine-free etching techniques like electrochemical etching and alkali treatment have been created by researchers. MXene performance depends directly on its interlayer spacing and interlayer forces. The performance of structures can be optimized through interlayer spacing adjustments which are achieved by employing intercalation agents or surface modification techniques. High-performance applications require MXene materials that possess both high purity and high crystallinity. The purity and crystallinity of MXene sees substantial enhancement when etching conditions (including factors like temperature, duration and concentration) are meticulously optimized.

Emerging Applications of Ti₃C₂ MXene

1. Energy Storage and Conversion

Lithium-ion Batteries: The superior conductivity and structural stability of Ti₃C₂ MXene make it an ideal material for use in lithium-ion batteries. Experimental results demonstrate that MXene/carbon composite electrodes deliver superior cycling performance through sustained high capacity retention and minimal capacity loss over 3000 cycles. MXene-based composite electrodes achieve better energy density and longer cycle life in lithium-ion batteries when SiO₂ nanoparticles are integrated with other materials.

Hydrogen Evolution Reaction (HER): Ti₃C₂ MXene demonstrates strong catalytic performance in the Hydrogen Evolution Reaction. The CoP@3D Ti₃C₂ MXene catalyst exhibits low overpotential alongside excellent long-term stability which positions it as the perfect material for efficient HER. The combination of MXene with other transition metal phosphides like CoP enhances both the activity and stability of HER performance.

Supercapacitors: The widespread use of Ti₃C₂ MXene in supercapacitors stems from its excellent conductivity and extensive specific surface area. Research demonstrates that MXene-based composites achieve high levels of energy density along with power density performance. The TMF2DHNM hybrid nanomaterial based on Ti₃C₂ MXene demonstrates a specific capacitance of 62.51 F/g together with a capacity of 268.53 mAh/g.

2. Photocatalysis and clean energy

Photocatalytic hydrogen production: Ti₃C₂ MXene proves to be an effective photocatalyst for water decomposition and hydrogen production applications. The photocatalytic hydrogen evolution performance of Ti₃C₂ MXene improves when it is combined with Cd_0.5Zn_0.5S nanorods. Hydrogen production performance gets enhanced when MXene is combined with semiconductor materials like G-C₃N₄ due to improved photogenerated carrier separation efficiency.

Solar evaporation: The photothermal conversion efficiency of self-floating MXene films reaches up to 84% in solar evaporation applications which creates new possibilities for efficient solar-driven water evaporation technologies.

3. Electronics and sensor technology

Conductive film: The combination of Ti₃C₂ MXene with materials like silver nanowires results in flexible transparent conductive films that possess high conductivity and mechanical flexibility which makes them ideal for flexible electronic devices.

Resistive memory: Neuromorphic computing gains a fresh material foundation from Al/ Ti₃C₂/Pt memristors which reproduce synaptic plasticity and perform brain-like calculations.

4. Biomedical applications

Antibacterial materials: The unique antibacterial properties of small-sized Ti₃C₂ nanosheets enable them to effectively kill both Gram-positive and Gram-negative bacteria.

Photothermal therapy: The Fe(II)- Ti₃C₂ composites demonstrate photothermal conversion efficiency while offering MRI functionality which enables them to serve as a multifunctional platform for tumor diagnosis and treatment.

5. Composite materials and multifunctional platforms

Polymer composites: Melt-mixing Ti₃C₂ MXene with TPU leads to composite materials with improved mechanical strength and thermal stability enabling application in high-performance engineering plastics.

Microwave absorption: MXene/paraffin composites demonstrate effective broadband electromagnetic shielding capabilities while providing superior microwave absorption performance which offers a fresh approach to electromagnetic interference shielding.

The recently discovered two-dimensional material Ti₃C₂ MXene holds significant promise across various technological areas. The combination of great conductivity alongside large surface area and chemical stability positions MXene as a prime material choice for applications in energy storage and conversion as well as photocatalysis, electronic devices, biomedicine and composite materials. The practical application of MXene encounters several obstacles including difficulties in large-scale synthesis as well as stability at interfaces and synergistic interactions with other materials. Research going forward must aim to enhance MXene performance and functional strategies in order to facilitate its broad application across practical domains.