Exfoliation Of MXene Research Articles

Confined interfacial self-assembly of graphene-like carbon/MXene composite electrodes for capacitive deionization

Electrodes that have high desalting capacity, fast desalting rates and stable desalination performance are needed in capacitive deionization (CDI) technologies for water security. Herein, confined interfacial self-assembly of lignin-based graphene-like carbon (GC) precursors in Ti3C2-MXene interlayers was developed for forming GC/MXene composites. The formation of GC was generated in-situ by KHCO3-assisted pyrolytic carbonization which leads to exfoliation of multilayered MXene thereby forming GC/MXene heterostructures having strong interfacial interactions. GC/MXene exhibited tremella-like nanosheets morphology, accompanied by the formation of a TiO2 phase at the interface of GC and MXene hybridization, which confirmed formation of a heterostructure. Crystallographic phase identification of GC/MXene showed the exfoliation of MXene. GC/MXene had an ultra-negative surface charge of −39.3 mV, making it favorable for application as a cathode for Na+ removal. The GC/MXene heterostructure had high desalting capacity (54.2 mg g−1), high desalting rate (2.7 mg g−1 min−1), and stable cycling performance (90 % SAC retention after 30 cycles). The interfacial self-assembly strategy developed in this work is expected to enable green synthesis routes for graphene/MXene-based composite materials that allow construction of 2D/2D heterostructures for multilayer MXene and their analogues.

Joint Exfoliation of MXene by Dimensional Mismatched SiC/ZIF-67 Toward Multifunctional Flame Retardant Thermoplastic Polyurethane.

The single-layer MXene fully demonstrates the advantages of 2D materials, especially catalytic, conductive, and mechanical properties. However, the high energy consumption and low efficiency faced by MXene in the divestiture process are still challenges that need to be solved urgently. In this article, dimension mismatch and collaborative stripping strategies are skillfully combined to easily realize the transformation from multi-layer MXene to single layer. In addition, the functionalized MXene@SiC@polyaniline (MXene@SiC@PANI) nano-hybrid materials are used as fillers to improve the thermal conductivity, flame retardant, and antibacterial properties of thermoplastic polyurethane (TPU). The surface temperature of TPU/MXene@SiC@PANI composites increased from 33.4°C to 59.8°C within 10 s. In addition, the antibacterial efficiency of TPU composites against Escherichia coli and Staphylococcus aureus is 69.6% and 88.9%, respectively. Compared with pure TPU, the peak heat release rate and total heat release are reduced by 71.4% and 34.6%, respectively. The flame-retardant mechanism of MXene hybrid materials is systematically discussed. It is worth noting that the introduction of PANI enhances the compatibility between the filler and the polymer, effectively maintaining the mechanical properties of the TPU itself. This work provides a convenient method for the multi-functional practical application of TPU.

Integrating the 2D/2D heterostructure of the MXene monolayer and BiOBr nano-sheets for superior photo-catalysis

The highly efficient photo-oxidation of alcohols has sparked significant potential to cope with environmental pollution and the ever-increasing energy crisis. This study reports a unique Ti3C2/BiOBr (TB) heterojunction with a rich inter-face based on in situ exfoliation of MXene and subsequently anchored onto BiOBr sheets. The TB nano-composites exhibited substantially improved photo-catalytic activity towards the photo-oxidation of benzyl alcohol (BA) to benzaldehyde and achieved a formation rate of 1.73 mmol g−1 h−1, greater than pristine BiOBr. The ultra-thin inter-facial contact boosted the oxygen vacancies (Ov) and Ti3+ and possessed the most negative adsorption energy, which boosted the transfer and separation of inter-facial charge carriers and the adsorption and dissociation of BA. Overall, the successful synthesis of TB composite, along with its exceptional photo-catalytic performance, offers valuable insights for applications in green chemistry and environmental remediation.

Efficient physical delamination of Ti3C2Tx MXene under periodic and constant shear field of Taylor vortex flow

Employing Taylor vortex flow (TVF), we have devised an innovative technique for the delamination of MXene without using a chemical intercalant and demonstrated the enhanced optoelectronic characteristics of this delaminated MXene through their successful implementation in light emitting diode (LED). The pairwise toroidal fluid motion of TVF was induced by the rotation of the inner cylinder in the Couette-Taylor (CT) reactor. Due to periodic and constant shear field, TVF was highly efficient for the exfoliation of MXene. So, the continuous exfoliation process using CT reactor always showed 8.1 ∼ 12.5 times higher delaminated MXene (d-Ti3C2Tx) yield than that using a conventional mixing tank (MT) reactor which generated turbulent eddy flow (TEF) by impeller agitation. As such, 8.26 mgּ/mL (42.90 % of recovery ratio) of d-Ti3C2Tx was obtained in CT reactor at 1300 rpm of inner cylinder rotation speed and 24 min of mean residence time (MRT). In comparison, d-Ti3C2Tx in MT reactor at 3000 rpm of agitation speed and 24 min of MRT was 0.66 mgּ/mL (3.42 % of recovery ratio). In addition, d-Ti3C2Tx in TVF was thinner and wider than that in TEF. So, the d-Ti3C2Tx was homogeneously suspended without sedimentation and oxidation in aqueous suspension over 30 days. In addition, d-Ti3C2Tx in the TVF was applied to the transparent conducting electrode of inorganic CsPbBr3 perovskite light emitting diodes (PeLEDs). The transparent conducting oxide-free PeLED had 62.52 cd/A of maximum current efficiency and 14.48 % of maximum external quantum efficiency, which is comparable to the best performance of ITO-based inorganic CsPbBr3 PeLEDs.

Synchronously Enhanced Removal Ability and Stability of MXene through Biomimetic Modification.

Increasing environmental problems intensify the demand for high-performance environmental purification materials. MXene is a typical transition-metal carbide/nitride material with a two-dimensional geometric feature and a good deal of functional groups, and it is considered as an efficient adsorbent for removing pollutants from wastewater. However, the easy oxidation and relatively low adsorption capacity greatly restrict its application. In this study, the MXene/polydopamine (PDA) composite particles were fabricated through the biomimetic modification method of inducing the self-polymerization of dopamine in an MXene aqueous solution. Microstructure characterizations demonstrate that PDA facilitates the exfoliation of MXene. Adsorption measurements show that MXene and PDA exhibit an apparent synergistic effect in removing chromium hexavalent Cr(VI) from aqueous solution, and more PDA content leads to a larger synergistic effect. Consequently, the composite particles exhibit an ultrahigh adsorption capacity (862.3 mg/g). Specifically, even if the composite particles were stored in aqueous solution for 2 months, they still exhibit high adsorption ability with only a 3.3% loss in adsorption capacity, indirectly confirming the enhanced stability of MXene induced by PDA. Furthermore, the composite particles also show reduction ability to Cr(VI) and about 54.3% Cr(VI) can be reduced to harmless chromium trivalent Cr(III). This study provides a new method for the preparation of MXene-based adsorbents with excellent adsorption capacity and high stability, which has broad application prospects in the field of wastewater treatment.

Mildly Peeling Off and Encapsulating Large MXene Nanosheets with Rigid Biologic Fibrils for Synchronization of Solar Evaporation and Energy Harvest.

Efficient and nondestructive liquid exfoliation of MXene with large lateral size has drawn growing research interest due to its outstanding properties and diverse potential applications. The conventional sonication method, though enabling a high production yield of MXene nanosheets, broke them down into submicrometric sizes or even quantum dots, and thus sacrificed their size-dependent properties, chemical stability, and wide applications. Herein, rigid biological nanofibrils in combination of mild manual shake were found to be capable of peeling off MXene nanosheets by attaching on MXene surfaces and localizing the shear force. With comparison to sonication, this efficient and nondestructive exfoliation approach produced the MXene nanosheets with the lateral size up to 4-6 μm and a comparable yield of 64% within 2 h. The resultant MXene nanosheets were encapsulated with these biological fibrils, and thus enabled super colloidal and chemical stability. A steam generation efficiency of ∼86% and a high evaporation rate of 3.3 kg m-2 h-1 were achieved on their aerogels under 1-Sun irradiation at ∼25 °C. An evaporation rate of 0.5 kg m-2 h-1 still maintained even at the atmospheric temperature of -5 °C. More importantly, an electricity generation up to ∼350 mV also accompanied this solar evaporation under equivalent 5-Sun irradiation. Thus, this fibrous strategy not only provides an efficient and nondestructive exfoliation method of MXene, but also promises synchronization of solar-thermal evaporation and energy harvest.

Largely enhanced adsorption performance and stability of MXene through in-situ depositing polypyrrole nanoparticles

Due to the high presence of active functional groups, two-dimensional transition metal carbide/nitride materials that are usually named MXene have been thought as an efficient adsorbent for the removal of organic contaminants from wastewater. However, the poor stability of MXene originated from the high oxidization performance greatly restricts their application. In this work, few-layered MXene was firstly prepared and then the in-situ polymerization of polypyrrole (PPy) was induced in the MXene solution to prepare the MXene/PPy composite particles. The microstructure, adsorption behaviors toward methylene blue (MB) and the stability during the storage process were systematically investigated. The results show that introducing PPy nanoparticles promotes the further exfoliation of MXene. Consequently, the adsorption ability of the MXene/PPy composite particles is significantly enhanced, and the maximum adsorption capacity reaches 553.57 mg/g. The MXene/PPy composite particles also show high adsorption selectivity and it can exclusively remove MB from the solution mixing both cationic and anionic dyes simultaneously. The stability of the MXene is greatly enhanced and nearly no oxidization is observed for the MXene/PPy composite particles. This study offers an additional way to fabricate the MXene-based adsorbents with high stability, and the composite particles exhibit promising applications in effluent water remediation.

Microwave-assisted efficient exfoliation of MXene and its composite for high-performance supercapacitors

MXene, as a promising electrode material, exhibits outstanding performance in supercapacitors because of its excellent chemical and physical properties. However, the conventional inefficient exfoliation methods and the blocked ion transmission channels caused by self-weight accumulation of MXene nanoflakes all severely limit its development. Here, this work reports an efficient microwave exfoliation method that requires only 90s to exfoliate multilayered MXene into few-layer MXene (2–3 nm) with large-size (4∼6 μm). Additionally, to enhance its capacitance and cycling stability, the exfoliated MXene was composited with graphene quantum dots, which shows a larger specific surface area, and importantly performs ultrahigh capacitance (343 F/g at a current density of 1 A/g) and excellent capacitance retention (100% after 10,000 cycles at a current density of 5 A/g). When using composite material as an anode, the assembled supercapacitor exhibits an excellent energy density of 35 Wh/kg at a power density of 384 W/kg with 107% capacitance retention after 10,000 cycles. Not only does this work provide an efficient approach to exfoliate MXene, but it also prepares a highly promising material for energy storage materials.

An efficient water-assisted liquid exfoliation of layered MXene (Ti3C2Tx) by rationally matching Hansen solubility parameter and surface tension

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) have spurred great attention in many applications due to their outstanding electronic or mechanical properties. The exfoliation into single and fewer layer nanosheets of MXene is a requisite step for performance study in many cases. Herein this study aims to propose a facile and convenient liquid phase exfoliation (LPE) method to fabricate fewer-layer MXene nanosheets in large scale. The Hansen solubility parameters (HSPs) and surface tension component ratio are estimated and further applied to detect a green low-boiling-point water/acetone cosolvent for the better exfoliation of MXene. It has been found that the exfoliation efficiency is improved efficiently by matching HSPs and surface tension component ratio of MXene to that of solvents. A high concentrated MXene dispersion up to 1.727 mg/ml in the optimum composition of the water/acetone mixture which is approximately 78 and 5 times higher than that in pure acetone and water, respectively. Detailed characterization of morphology and suspension stability of exfoliated MXene are implemented which exhibit that the high quality and more stable MXene nanosheets are obtained in the suitable cosolvent. In addition, the determined HSPs and surface tension component ratio of MXene here will make a contribution to finding other new efficient solvents for MXene conveniently in specific fields.

Silicon carbide-assisted co-existence of magnetic phases in well-optimized Ti3SiC2-etched MXene

Here, we report the first successful exfoliation of two-dimensional Ti3C2Tx MXene through selective etching of silicon from titanium silicon carbide (Ti3SiC2) MAX. The successful etching and exfoliation of MXene are confirmed through the shifting of all (00l) peaks to lower angles along with the increase in the c-lattice parameter as determined by X-ray diffraction to detail the material structure. The c-lattice parameter of multilayered MXene was found to be 19.34 Å which was increased to 26.22 Å after the delamination process indicating the successful intercalation of TMA+ ions within the MXene Sheets. The scanning electron microscopy (SEM) images show the formation of a 2D layered structure. The magnetic measurement of the etched MXene sample was measured using a superconducting quantum interference device (SQUID: Quantum Design). The magnetization versus magnetic (M − H) curves indicate the ferromagnetic-dominant hysteresis loops at low-temperature as well as at room temperature along with the presence of a small silicon carbide (SiC) diamagnetic phase. The presence of the SiC phase is confirmed through XRD and Raman spectra that show the vibrational modes of SiC within the 2D MXene structure. The present work shows the co-existence of ferromagnetic and diamagnetic phases, making it suitable for 2D material for future spintronics devices.

Large-scale production of simultaneously exfoliated and Functionalized Mxenes as promising flame retardant for polyurethane

The low yield of MXenes nanosheets and its poor interfacial compatibility with polymer matrix have been an unavoidable obstruction for the fabrication of related polymer nanocomposites. Here, we reported a facile and large-scale route for the simultaneous organic modification and exfoliation of MXene by utilizing the wet ball milling process. Due to the electrostatic attraction effect, positively charged poly(diallyldimethylammonium chloride) (PDDA) long chains would attach to negatively charged MXene, which prevented the newly peeled-off MXene sheets from agglomerating and reduced the collision from the steel balls. Also, the attached PDDA molecule may act as protective shield for MXene nanosheets, leading to the delay of oxidation on the surface of MXene nanosheets in atmosphere. Notably, with the incorporation of 3 wt% PDDA modified MXene in thermoplastic polyurethane (TPU) matrix, the peak heat-release rate (decreased by 50%) and total smoke production (decreased by 47%) were significantly decreased. Moreover, mechanical performance (tensile strength at break was raised by 31.2%) and thermal conductivities (increased by 88.6%) of TPU nanocomposites were evidently enhanced. This novel strategy provide a simple and effective way to obtain exfoliated and functionalized MXenes nanosheets, enriching the application of MXenes in polymeric material field.

Water Transport and Thermomechanical Properties of Ti3C2Tz MXene Epoxy Nanocomposites.

Herein, we present the fabrication of dispersed, 5.0 wt % (1.74 vol %) Ti3C2Tz MXene epoxy nanocomposites (NCs), and report on their water transport and mechanical properties. To make the composites, Li+ ions between Ti3C2Tz MXene multilayers, MLs, present after the etching step were exchanged with either 12-aminolauric acid, ALA, or di(hydrogenated tallow)benzyl methyl ammonium chloride, DHT. After drying, the resulting ML powders were added at room temperature to the epoxy resin (diglycidyl ether of bisphenol A), followed by the curing agent, triethylenetetramine. The NCs were characterized by X-ray diffraction, thermogravimetric analysis, dynamic vapor sorption, dynamic mechanical analysis, scanning and transmission electron microscopies, and infrared spectroscopy. From XRD, the lack of signature MXene basal peaks, as well as evidence of exfoliation supported by TEM micrographs, we conclude that the MXene ML had indeed been intercalated by the epoxy. The distribution of the exfoliated multilayers, MLs, however, was not uniform. Nevertheless, our relative permeabilities, with a 1.74 vol % loading, are 5 times lower than results obtained in the carbon- or clay-reinforced epoxy NC literature. The lower permeabilities are due to reductions in both solubilities and diffusivities relative to the neat polymer. In the case of DHT, the water solubility at all temperatures was almost halved. The mechanical properties and thermal stability are found to be slightly improved with the addition of DHT-MXene. As far as we are aware, this is the first report of exfoliation of MXene in an epoxy matrix. Additionally, this study is the first to measure the diffusion of water in MXene epoxy NCs. More work on better dispersion of the MLs is indicated and ongoing.