Dimensional MXene Research Articles

Preparation and Study of Ti3C2Tx MXene–Deficient In Situ Anchored Fe−Co Alloy Nanoparticle Electrocatalyst for Hydrolysis and Hydrogenolysis

AbstractThe novel two–dimensional MXene material Ti3C2Tx has the advantages of a large specific surface area, adjustable band gap, good electrical conductivity, and high stability. However, the precipitation of hydrogen via electrolytic water splitting over Ti3C2Tx has unacceptably slow kinetics. In this paper, Co nanoparticles were incorporated on the Ti3C2TxMXene surface via electrostatic adsorption by utilizing the intrinsic MXene defects generated during the etching process. Next, a Fe−Co alloy structure was also constructed on the Ti3C2TxMXenesurface by wet chemical impregnation method using the principle of galvanic coupling substitution. The prepared catalyst had an overpotential of 118 mV at a current density of 10 mA‐cm−2 and a Tafel slope of 97.56 mV dec−1. The Fe−Co alloy structure accelerated the kinetic hydrogen precipitation step, and Fe−Co/Ti3C2Txshowed excellent stability when used in a water electrolysis process for 11 h. This work offers a promising strategy for the synthesis of intrinsically defective synthetic alloy MXene structures.

NiCo2O4/MXene Hybrid as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reaction

AbstractFor the advancement of electrochemical energy conversion and storage technologies, bifunctional electrocatalysts are crucial for efficiently driving both the oxygen evolution (OER) and reduction reactions (ORR). Cobalt‐based spinel oxides are a class of promising bifunctional electrocatalysts. However their low electrical conductivity and stability may hinder further improvement. A novel composite material composed of NiCo2O4 nanoparticles integrated with emerging two dimensional MXene nanosheets (NiCo2O4/MXene) was developed. The successful integration of NiCo2O4 with MXene brings about a number of attractive structural features. This includes synergistic effects between NiCo2O4 and MXene, highly accessible surface areas, complete exposure of numerous active sites, and excellent electronic conductivity, all of which collectively contribute to the desirability of composite material for OER and ORR. The synthesized NiCo2O4/MXene composite showed extraordinary OER electrocatalytic activity with a lower overpotential of 360 mV at a current density of 10 mA/cm2, and a small Tafel slope of 64 mV/dec compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed). Additionally, NiCo2O4/MXene displays an ORR limiting current density of −4 mA/cm2 and exhibited highest onset potential and half wave potential of 0.92 V and 0.72 V vs. RHE, respectively, for the ORR in alkaline media compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed).

A novel microfluidic chip integrating with microcolumn array electrodes for rapid and ultrasensitive detection of alpha-fetoprotein

BackgroundCancer posed a serious threat to human health, and early diagnosis of cancer biomarker was extremely important for the treatment and control of cancer. Electrochemistry-based assays were low-cost, responsive and easy to operate, but there were some challenges in terms of accuracy, detection limit, efficiency and portability. The combination of microfluidic devices and electrochemical methods was expected to construct a high-performance sensing platform, but long-time antigen-antibody incubation was still required. Therefore, a novel microfluidic chip needs to be developed, which has the advantages of good portability, short incubation time, high accuracy, low detection limit and great application to point-of-care testing. ResultsA microfluidic sensor based on microcolumn array electrodes was developed, in which microcolumns could create local mixed flow to reduce the incubation time of target molecules and enhance their interaction with the sensing interface. Besides, three dimensional Mxene fibers-gold nanoparticles (3D MF-Au) was modified on the microcolumn array electrodes to increase active sites and provide more electrolyte shuttle holes. The electrolyte turbulence caused by the microcolumn array electrodes could heighten the contact between the target molecules and sensing interface and accelerate the transfer of redox pairs, thus reducing the incubation time of the target molecules and improving the electrochemical responses in synergy with the 3D MF-Au. Herein, the detection of AFP was chosen as a model, and the microfluidic sensor possessed superior performance for analysis of AFP in the range of 0.1 pg mL−1 - 200 ng mL−1 with a low detection limit (LOD) of 0.0648 pg mL−1. SignificanceThis microfluidic chip integrating with microcolumn array electrodes has been successfully implemented to detect AFP in human serum, and the results were consistent with that of electrochemical chemiluminescence method. The microfluidic chip provided a new strategy of portability, shortening incubation time and enhancing electrical signals for antigen detection of real samples, which showed great utilization potentiality in point-of-care testing.

MXene-based eutectic salt hydrate phase change material for efficient thermal features, corrosion resistance & photo-thermal energy conversion

Salt hydrate phase change materials (PCMs) possess low thermal conductivity, degree of supercooling, lack of corrosion resistance and poor photo thermal conversion ability. To overcome these challenges, a two dimensional, chemically stable, optically & thermally efficient MXene@eutectic salt hydrate composite PCM is developed for effective harnessing of solar energy and thermal energy storage (TES) applications. Low temperature eutectic salt hydrate PCM with phase transition temperature of 27.6 °C and 216 J/g melting enthalpy is developed using sodium sulphate decahydrate (SSD) and sodium phosphate dibasic dodecahydrate (SPDD) based on Schrader equation. Advanced 2D layered material, MXene (Ti3C2) is synthesised from MAX phase (Ti3AlC2). Furthermore, MXene based PCM nanocomposite is developed with binary eutectic PCM of SSD/SPDD at different weight fractions through two step technique. Developed nanocomposite PCM exhibits better chemical stability, high optical absorbance of (1.1), low transmissibility (10.2 %), reliable thermal conductivity (0.621 W/m⋅K), improved melting enthalpy (161.2 J/g) and considerable cycle stability. The optical absorbance and thermal conductivity demonstrated a superior photo-thermal conversion capability and thermal networks for the developed MXene based composite sample at 0.9 wt% of MXene. The above properties are experimentally inferred by evaluating the developed MXene@ eutectic salt hydrate and base eutectic PCM under the solar simulator. The interfacial attraction between the two dimensional MXene nano flakes and the developed eutectic PCM ensures a promising ability to trap solar energy effectively for thermal regulation in a sustainable direction. Subsequently, the effect of MXene with SSD/SPDD in regard to the issue of corrosion is explored for copper and aluminium metal surface.

Green synthesis of fluorine-free MXene via hydrothermal process: A sustainable approach for proton supercapacitor electrodes

The electrochemical properties of carbides and nitrides dominated two dimensional MXenes can be effectively engineered for a wide variety of applications. Herein, we report a hydrothermal Alkali etching process to prepare Ti3C2Tx@Al-NaOH (Tx= -OH, -O) MXene without fluorine from Sodium hydroxide (NaOH) and MAX solution. The Ti3C2Tx@Al-NaOH sample etched for 15 h in NaOH solution exhibits optimal electrochemical properties. Also, the Ti3C2Tx@Al-NaOH samples, which have NaOH concentrations of 22.5, 25, 30, 35 and 40 M, respectively, show higher rates of charge-discharge and pseudocapacitive effect in 1 M sulfuric acid electrolyte solution, while the corresponding specific capacity values are 378, 445, 565, 365 and 176 Cg−1, respectively. Meanwhile, their retention rates are still retained at 94 %, 119 %, 150 %, 113 % and 29 %, after continuous cycling of about 8000 times. It is demonstrated that the Ti3C2TX@Al-NaOH (30 M) for 15 h shows great potential as a candidate electrode for supercapacitors and other energy storage devices, since its capacitance value surpasses (by ∼465 %) to that of the multilayer Ti3C2Tx MXene prepared via normal hydrofluoric acid etching. As a consequence, our Alkali-assisted hydrothermal reaction treatment is a highly advantageous process to realize fine-tune of surface chemistry.

Assembly of MXene/ZnO heterojunction onto electrospun poly(arylene ether nitrile) fibrous membrane for favorable oil/water separation with high permeability and synergetic antifouling performance

The two dimensional MXene nanosheets lamellar membranes have emerged as the promising candidates for oil/water separation. However, to deal with the large-scale discharge of complicated oily wastewater (including oils, organics, microorganism, etc), developing advanced membrane materials with high permeate flux and enhanced antifouling is still big challenge. Herein, the MXene/ZnO heterojunction was prepared by electrostatic attraction, which was modified by tannic acid (TA) and further self-assembled onto the poly (arylene ether nitrile) (PEN) fibrous mat to construct the multi-functional separation membrane (ZnO/M-TA@PEN fibrous composite membrane). In the hierarchical functional layer, the improved hydrophilicity of TA and the hierarchical micro-/nano-roughness build by ZnO NPs contributed to the super-hydrophilic/underwater super-oleophobic feature (WCA = 0°, UOCA>152°), leading to high separation efficiency and ultra-low oil adhesion. Uniquely, the decoration of ZnO NPs achieved the “intercalation effect” and effectively tuned the interlayer spacing between MXene nanosheets, which conquered the stacking problem of MXene nanosheets lamellar membrane and greatly enhanced the permeation flux of membrane. For separating various oil emulsions, the resulting ZnO/M-TA@PEN fibrous composite membrane displayed superior emulsion separation flux (1815.34 ± 44.73–2053.35 ± 42.62 L/m2·h) and separation efficiency (>99.4%), even in high-temperature and salty environments. More importantly, the heterojunction structure of MXene/ZnO hybrid endowed the fibrous composite membrane with enhanced antibacterial ability and photocatalytic self-cleaning performance toward the degradation of methylene blue, which realized the synergetic antifouling and favorable cycling ability of the fibrous composite membrane. This combination of anti-fouling and high permeability renders the membrane as attractive candidate for dealing with the oily wastewater containing multicomponent pollutants.

Preparation and performance of perovskite solar cells with two dimensional MXene as active layer additive

In this paper, two-dimensional titanium carbide (Ti3C2Tx) and vanadium carbide (V2CTx) MXene with appropriate mass content are incorporated into PbI2 precursor solution to fabricate perovskite film via one-step coating method. The effects of the addition of MXene with different mass ratio on the morphology, crystallinity, light absorption property and stability of the CH3NH3PbI3 film and the photovoltaic performance and stability of the corresponding devices are further investigated. The results demonstrate that the introduction of Ti3C2Tx and V2CTx additive can improve the morphology of perovskite film, increase the grain size of perovskite film, enhance the hydrophobicity of the perovskite layer. As a result, improved photovoltaic performance can be achieved. By modifying the proportion of additives, the power conversion efficiency (PCE) of V2CTx MXene modified solar cells is better than those of the devices with Ti3C2Tx additive and the pristine one. Compared with the control device without additive, perovskite solar cells incorporating V2CTx additive with an optimized concentration of 0.0013 wt% achieve a PCE of 17.61% (increased by 17%). Moreover, for perovskite film incorporating V2CTx additive, unique morphology with uniform grain size and ordered layered crystal particle can be noted. This means the V2CTx additive can regulate the perovskite crystal film growth. In addition, the V2CTx additive incorporated devices can retain 68.29% of the initial PCE after 15 days, which is higher than the devices without additives (by 9.69%) and with Ti3C2Tx as additive (by 47.16%), owing to the better crystallinity and higher quality of perovskite film. Our work provides an effective method for improving performance of perovskite solar cells and expands the applications areas of V2CTx in photovoltaics.

Dirac-like band structure and strain-tunable electronic structure of Zr2CCl2 monolayer

Two dimensional MXenes is a general term for transition metal carbides and their derivatives. Different MXenes materials have attracted much attention due to their unique electronic properties, which have the potential applications in spintronic devices. With the synthesis of two dimensional Zr-containing materials, the related two dimensional Zr MXenes materials have gradually been paid more attention, so theoretical research based on first principles has also been enriched. In this paper, the electronic structure of the two dimensional MX Zr2C material after adsorption of Cl functional groups at different symmetrical positions on both sides is studied systematically by using the density functional theory. The bare Zr2C is a metal with magnetism, while the Zr2CCl2 structure becomes a non-magnetic metal. Three adsorption structures of Zr2CCl2 have been studied. The Zr2CCl2-I monolayer is the most stable structure, but the Zr2CCl2-II monolayer is the only unstable structure among the three structure. Additionally, a Dirac-like structure with a tiny gap appears in Zr2CCl2-III monolayer, where the position of gap can be further tailored by biaxial strain. As the compressive strain increases, the Dirac-like will move up. Moreover, at a compressive strain of −0.9%, the Dirac-like structure of Zr2CCl2-III will move to the Fermi level with an indirect-band-gap of 7.3 meV. At the same time, considering the influence of SOC, its band gap value will become 29.3 meV. The Dirac-like structure with a band gap also makes up for the shortcoming of graphene's zero band gap. And Zr2C with different functional groups has different electronic properties, since Zr2C MXenes have potential applications in electronic devices.

A highly efficient A-site deficient perovskite interlaced within two dimensional MXene nanosheets as an active electrocatalyst for hydrogen production

We report a unique composite of La0.4Sr0.4Ti0.9Ni0.1O3-δ (LSTN) nanoparticles interlaced with two dimensional Ti3C2Tx (MXene) nanosheets, providing high conductivity. LSTN heterostructure synthesized by the sol-gel method produces a large oxygen vacancy and creates a variable valence state while, MXene synthesized from Hydrofluoric acid (HF) treatment resulted in a highly hydrophilic and conductive surface, thereby enhancing the charge transferability. For OER, the LSTN/MXene 66.67% electrode exhibits a benchmark of 10 mA cm−2 at a potential of 1.56 (V vs RHE) in 1 M KOH. It has exhibited the lowest Tafel slope of 44 mV dec−1 and highest mass activity (60 mA g−1 @ 1.59 V) due to quicker ions diffusion and increased available exposed area. Moreover, the efficient LSTN/MXene 66.67% electrode showed good long-term durability during a 24 h stability test at a current density of 100 mA cm−2. The strong interfacial interaction and high charge transfer among LSTN nanoparticles and 2D MXene nanosheets not only provide good structural strength to the composite but also improves the redox activity of LSTN/MXene 66.67% catalyst towards OER. This work provides improved conductive properties of perovskite by developing a composite of perovskite and MXene, that has significantly enhanced electrochemical properties of the catalyst by undergoing fast kinetics.

Two dimensional MXenes as emerging paradigm for adsorptive removal of toxic metallic pollutants from wastewater

Effective methods for removing harmful metals from wastewater have had a huge impact on reducing freshwater scarcity. Because of its excellent removal effectiveness, simplicity and low cost at ambient conditions, adsorption is one of the most promising purifying approaches. MXene-based nanoarchitectures have proven to be effective adsorbents in a variety of harmful metal removal applications. This owes from the distinctive features such as, hydrophilicity, high surface area, electron-richness, great adsorption capacity, and activated metallic hydroxide sites of MXenes. Given the rapid advancement in the design and synthesis of MXene nanoarchitectures for water treatment, prompt updates on this research area are needed that focus on removal of toxic metal, such as production routes and characterization techniques for the advantages, merits and limitations of MXenes for toxic metal adsorption. This is in addition to the fundamentals and the adsorption mechanism tailored by the shape and composition of MXene based on some representative paradigms. Finally, the limits of MXenes are highlighted, as well as their potential future research directions for wastewater treatment. This manuscript may initiate researchers to improve unique MXene-based nanostructures with distinct compositions, shapes, and physiochemical merits for effective removal of toxic metals from wastewater.

Multiwalled carbon nanotubes modified two dimensional MXene with high antifouling property for sensitive detection of ochratoxin A

Electrochemical sensor has great potential in the detection of small molecules by virtues of low cost, fast response, and easy to miniaturization. However, electrochemical sensing of ochratoxin A (OTA) was seriously hindered by the heavy electrode-fouling effect and poor electrochemical activity inherent from OTA molecular. Herein, two-dimensional titanium carbide (2D Ti3C2) MXene incorporated with carboxylic multiwalled carbon nanotubes (cMWCNTs) was developed as a glassy carbon electrode modifier for rapid and sensitive detection of OTA. Physical characterizations combined with electrochemical techniques revealed that cMWCNTs can not only prevent the restacking of 2D Ti3C2 nanosheets but also facile its electron transfer, leading to a nanohybrid with a high specific surface and good electrocatalytic activity to OTA. Under optimal conditions, the electrochemical sensor showed a good linear response to OTA in a concentration range from 0.09 to 10 μmol·l−1 and a low detection limit (LOD) of 0.028 μmol·l−1. The proposed sensor was impelled successive times to detect OTA, a good repeatability was obtained, indicating the constructed sensor possessed good anti-fouling property. Moreover, satisfactory recoveries between 91.8% and 103.2% were obtained in the real sample analysis of grape and beer, showing that the developed sensing technique is reliable for the screening of trace OTA in food resources.

Two Dimensional Mxene (Ti3C2) Decorated By SnO2 Nanocrystals for Enhanced Chemical Gas Sensors at Room Temperature

IntroductionA low-cost chemical sensor for ammonia (NH3) detection is highly demanded nowadays for several important applications. Two-dimensional (2D) nanomaterials such as graphene/reduced graphene oxide (rGO), transitional metal dicharcogenides, black phosphor and transition metal carbonitride (MXene) have found a promising application in the fields of gas sensing electronics at room temperature due to their unique microstructure, electrical properties and excellent gas adsorptions ability. Decoration of the secondary phase such as noble metals and metal oxide nanocrystals to form heterojunctions with two-dimensional materials can effectively improve the inadequacy of two-dimensional materials based gas sensors. It takes advantages of the difference in the Fermi level of each phase to make the electrons transfer from one material to the other and thus enriching the electron concentration on the surface of one material that is dominant in the electrical transport. In this way, more ionized oxygen is chemisorbed, leading to the improvement of the gas sensing properties [1].In this work, 2D MXene heterojunctions incorporated with SnO2 nanoparticles have been synthesized by using hydrothermal method. The as-fabricated MXene/SnO2 heterojunction based chemiresistive-type sensor showed excellent sensitivity to different concentrations of ammonia from 0.5-100 ppm at room temperature. The response has about 20 times higher than those reported in literature to 100 ppm NH3 and an excellent selectivity.Preparation and characterizations The Ti3AlC2 was purchased directly from Beijing Forsman Corp. The concentrated hydrochloric acid (HCl) was diluted to 9 M. 2 g of lithium fluoride (LiF) was added into 20 ml diluted hydrochloric acid and stirred with magnetic mixer. 2 g Ti3AlC2 was slowly and evenly dispersed in the solution over a period of several minutes and subsequently stirred at 35 ℃ for 48 h to obtain the MXene. 70 mg of MXene powder was dispersed in 30 ml of deionized water after grinding and sonicated for 30 min. 73.5 mg of stannic chloride pentahydrate (SnCl4·5H2O) was added into the suspension and stirred with magnetic stirrer at room temperature. The suspension was then loaded in a 50 ml Teflon-lined autoclave. The autoclave was sealed and heated in an KSL-1200X hydrothermal system at 180 ℃ for 12 h to obtain the MXene-SnO2 hybirds. The samples were then characterized by XRD, SEM, XPS, Raman and TEM-ED. The MXene/SnO2 based chemirestive-type sensor was measured by a static volumetric method. The resistance of the sensor is directly measured by a digital multimeter (Agilent 34410A). The responses of the sensors were defined as the relative change in the resistances of the sensors in the air and those in the tested gas. Results and Conclusions Fig.1a shows the XRD of the prepared samples. Appearance and down-shift of the peak at ~10 oC indicates the successful achievements of MXene and thus the MXene-SnO2 composite heterojunctions [2-3].Fig.1 (b-c) show the micrographs of the surface morphology of the MXene and heterojunctions. The etched MXene material has obvious layered structure with sizes ranging from 2 μm to 4 μm. The thickness of MXene is about 75 nm indicating the sample contains about 100 single layers of MXene. The granular SnO2 nanoparticles are intimately attached to the surface of MXene. Fig.2 (b) shows the Raman spectra of MXene and Mxene/SnO2 heterojunction. The appearance of both D-band and G-band in the MXene/SnO2 heterojunction sample indicated that MXene remained well during the hydrothermal reaction. Fig.2(c) shows the Ti core level (2p) spectra of the MXene and MXene/SnO2. Ti - X corresponds to titanium carbide or titanium oxynitride. Fig.2d indicates that the peaks at 530.1 and 532 eV correspond to oxygen vacancies and O=C-OH, respectively, suggesting that these and surface-adsorbed oxygen tend to form more active sites, thereby enhancing sensing capability.The sensors using MXene/SnO2 heterojuction shows excellent response and selectivity to low-level NH3 from 0.5-9 ppm at RT (Fig.3). Since the work function of MXene (3.4 eV) was slightly lower than that of SnO2 (4.7 eV), Schottky-type junctions were formed across MXene/SnO2 interfaces (Fig.4). Electrons would transfer from SnO2 to MXene, and the depletion layer was deepened on the surface of MXene. MXene could then chemically adsorb more oxygen, and the response of the MXene/SnO2 heterojunction was thus significantly enhanced.

Unique intermediate adsorption enabled by anion vacancies in metal sulfide embedded MXene nanosheets overcoming kinetic barriers of oxygen electrode reactions in lithium-oxygen batteries

Designing electrode materials with optimized surface electronic structure and fully exposed active sites is urgently desired to improve oxygen electrode reaction kinetics in lithium-oxygen batteries (LOBs). Herein, sulfur vacancy-rich Ni 3 S 2 on two dimensional MXene (V S -Ni 3 S 2 @MN) is fabricate as a bifunctional catalyst for LOBs. The introduction of sulfur vacancy via Ar plasma bombards exposes massive coordination unsaturated sites on the surface of V S -Ni 3 S 2 @MN, which is available for deposition and decomposition of uniformly distributed Li 2 O 2 during oxygen reduction reactions and oxygen evolution reactions, thus efficiently decreasing overpotentials and ameliorating round-trip efficiency. In addition, theoretical calculations confirm that sulfur vacancies as the active sites can memorably improve the intrinsic appetency of intermediates and thus fundamentally adjust the deposition mechanism of Li 2 O 2 . Specifically, LOBs with the V S -Ni 3 S 2 @MN electrode afford remarkably decreased overpotential (0.77 V) and improved long-term cyclic stability (200 cycles with current density 400 mA g −1 ). This work provides a unique view that the regulation of intermediate adsorption via surface vacancies is a practical strategy for enhancing the performance of the LOBs and sheds new light on designing oxygen electrode materials.

Preparation, microstructure and tensile properties of two dimensional MXene reinforced copper matrix composites

The dispersion homogeneity of particles has a significant influence on the mechanical properties of particle reinforced metal matrix composites. In this study, a new Cu matrix composites with uniform dispersion of submicron and nanoscale MXene reinforcement particles were fabricated by the methods of high energy ball milling and hot pressing sintering. The microstructure evolution of MXene-Cu composite powders were studied in detail. When the initial MXene content is less than 3 vol%, the MXene particles can be dispersed homogenously in Cu matrix after 12 h ball milling. The refinement and dispersion of the MXene particles are mainly achieved by the cold welding and plastic deformation of composite particles in ball milling process. The XRD and TEM results reveal that these MXene reinforcement particles have been transformed to cubic TiC x in the final MXene/Cu composites. The tensile test results indicate that the UTS and elongation of the MXene/Cu composites are closely related to the dispersion homogeneity of the MXene particles. The UTS and elongation of the 1MXene/Cu and 3MXene/Cu composites increase with increasing the ball milling time. The UTS of the 3MXene/Cu-12 h can reach to 314 MPa with an elongation of 11.1%. The maximum UTS of the 5MXene/Cu-6 h can reach to 354 MPa. However, further increase in milling time would result in the UTS and elongation decline. The fracture surface analysis further testifies that the 3MXene/Cu-12 h composite presents a typical plastic fracture feature, while the 5MXene/Cu composite with various ball milling time all present brittle fracture characteristic for the severe agglomeration of MXene particles.

Novel Prussian blue analogues@MXene nanocomposite as heterogeneous activator of peroxymonosulfate for the degradation of coumarin: The nonnegligible role of Lewis-acid sites on MXene

In this study, with two dimensional MXene as the substrate, Prussian blue [email protected] composite ([email protected]) was fabricated and utilized as a heterogeneous catalyst for the oxidative degradation of coumarin (COU) based on peroxymonosulfate activation. The initial pH strongly affected the degradation process, and the alkaline pH was beneficial to the COU degradation than the acidic pH. The kinetic rate constants were determined to be 0.030, 0.055, 0.121 and 0.246 min-1at pHs of 3.0, 5.0, 6.6 and 10.0, respectively. The TOC removal efficiency achieved at pH 10.0 was 70.9% in 20 min reaction time. Radical scavengers tests showed that in the presence of 500 mM tert-butyl alcohol (TBA), the rate constant was gradually enhanced from 0.004 to 0.040 min−1 with increasing the solution pH from 3.0 to 10.0; while with the addition of 500 mM Methanol (Me), the rate constants were determined to be 0.002, 0.001, 0.002, and 0.002 min−1 at pHs of 3.0, 5.0, 6.6, and 10.0, respectively. Mechanism study indicated that the differences in COU degradation at different pHs could be mainly ascribed to the unsaturated Ti-C-O (Lewis-acid site) and terminal F-Ti on the catalyst surface. This work not only demonstrated that [email protected] was a promisingly effective catalyst for PMS activation for COU degradation, but also clearly spelled out the role of Lewis-acid sites of MXene in MXene-based catalysts.

Surface treatment of two dimensional MXene for poly(vinylidene fluoride) nanocomposites with tunable dielectric permittivity

Dielectric polymer nanocomposites with high dielectric permittivity and low dielectric loss have great applications in energy storage field. In this study, a series of PVDF/MXene nanocomposites was prepared by solution method. The surface of MXene was functionalized with cetyltrimethylammonium bromide (MXene@CTAB) to achieve better dispersion in poly(vinylidene fluoride) (PVDF) matrix. The results revealed that the MXene@CTAB dispersed uniformly and had a good compatibility with PVDF matrix. In addition, the dynamical rheological test revealed that the viscosity and storage modulus of PVDF nanocomposites increased with the increasing of MXene@CTAB loading. The PVDF/MXene@CTAB nanocomposite containing 7 wt% MXene@CTAB exhibited a dielectric permittivity of 82.1 and a loss factor as low as 0.2 at 1 kHz. The presence of CTAB could serve as an insulating layer to suppress dielectric loss and AC conductivity of PVDF nanocomposites simultaneously. The PVDF/MXene@CTAB nanocomposite with high dielectric permittivity may find potential applications in energy storage capacitors for electronics. Moreover, the addition of MXene@CTAB contributed to the formation of Beta phase of PVDF.

Improved Thermophysical Properties and Energy Efficiency of Aqueous Ionic Liquid/MXene Nanofluid in a Hybrid PV/T Solar System.

In recent years, solar energy technologies have developed an emerging edge. The incessant research to develop a power source alternative to fossil fuel because of its scarcity and detrimental effects on the environment is the main driving force. In addition, nanofluids have gained immense interest as superior heat transfer fluid in solar technologies for the last decades. In this research, a binary solution of ionic liquid (IL) + water based ionanofluids is formulated successfully with two dimensional MXene (Ti3C2) nano additives at three distinct concentrations of 0.05, 0.10, and 0.20 wt % and the optimum concentration is used to check the performance of a hybrid solar PV/T system. The layered structure of MXene and high absorbance of prepared nanofluids have been perceived by SEM and UV–vis respectively. Rheometer and DSC are used to assess the viscosity and heat capacity respectively while transient hot wire technique is engaged for thermal conductivity measurement. A maximum improvement of 47% in thermal conductivity is observed for 0.20 wt % loading of MXene. Furthermore, the viscosity is found to rise insignificantly with addition of Ti3C2 by different concentrations. Conversely, viscosity decreases substantially as the temperature increases from 20 °C to 60 °C. However, based on their thermophysical properties, 0.20 wt % is found to be the optimum concentration. A comparative analysis in terms of heat transfer performance with three different nanofluids in PV/T system shows that, IL+ water/MXene ionanofluid exhibits highest thermal, electrical, and overall heat transfer efficiency compared to water/alumina, palm oil/MXene, and water alone. Maximum electrical efficiency and thermal efficiency are recorded as 13.95% and 81.15% respectively using IL + water/MXene, besides that, heat transfer coefficients are also noticed to increase by 12.6% and 2% when compared to water/alumina and palm oil/MXene respectively. In conclusion, it can be demonstrated that MXene dispersed ionanofluid might be great a prospect in the field of heat transfer applications since they can augment the heat transfer rate considerably which improves system efficiency.

Two Dimensional Mxene (Ti3C2) Decorated By SnO2 Nanocrystals for Enhanced Chemical Gas Sensors at Room Temperature

Introduction A low-cost chemical sensor for ammonia (NH3) detection is highly demanded nowadays for several important applications. Two-dimensional (2D) nanomaterials such as graphene/reduced graphene oxide (rGO), transitional metal dicharcogenides, black phosphor and transition metal carbonitride (MXene) have found a promising application in the fields of gas sensing electronics at room temperature due to their unique microstructure, electrical properties and excellent gas adsorptions ability. Decoration of the secondary phase such as noble metals and metal oxide nanocrystals to form heterojunctions with two-dimensional materials can effectively improve the inadequacy of two-dimensional materials based gas sensors. It takes advantages of the difference in the Fermi level of each phase to make the electrons transfer from one material to the other and thus enriching the electron concentration on the surface of one material that is dominant in the electrical transport. In this way, more ionized oxygen is chemisorbed, leading to the improvement of the gas sensing properties [1].In this work, 2D MXene heterojunctions incorporated with SnO2 nanoparticles have been synthesized by using hydrothermal method. The as-fabricated MXene/SnO2 heterojunction based chemiresistive-type sensor showed excellent sensitivity to different concentrations of ammonia from 0.5-100 ppm at room temperature. The response has about 20 times higher than those reported in literature to 100 ppm NH3 and an excellent selectivity. Preparation and characterizations The Ti3AlC2 was purchased directly from Beijing Forsman Corp. The concentrated hydrochloric acid (HCl) was diluted to 9M. 2g of lithium fluoride (LiF) was added into 20ml diluted hydrochloric acid and stirred with magnetic mixer. 2g Ti3AlC2 was slowly and evenly dispersed in the solution over a period of several minutes and subsequently stirred at 35℃ for 48h to obtain the MXene. 70 mg of MXene powder was dispersed in 30ml of deionized water after grinding and sonicated for 30min. 73.5mg of stannic chloride pentahydrate (SnCl4·5H2O) was added into the suspension and stirred with magnetic stirrer at room temperature. The suspension was then loaded in a 50ml Teflon-lined autoclave. The autoclave was sealed and heated in an KSL-1200X hydrothermal system at 180℃ for 12h to obtain the MXene-SnO2 hybirds. The samples were then characterized by XRD, SEM, XPS, Raman and TEM-ED. The MXene/SnO2 based chemirestive-type sensor was measured by a static volumetric method. The resistance of the sensor is directly measured by a digital multimeter (Agilent 34410A). The responses of the sensors were defined as the relative change in the resistances of the sensors in the air and those in the tested gas. Results and Conclusions Fig.1a shows the XRD of the prepared samples. Appearance and down-shift of the peak at ~10 oC indicates the successful achievements of MXene and thus the MXene-SnO2 composite heterojunctions [2-3].Fig.1 (b-c) show the micrographs of the surface morphology of the MXene and heterojunctions. The etched MXene material has obvious layered structure with sizes ranging from 2 μm to 4 μm. The thickness of MXene is about 75 nm indicating the sample contains about 100 single layers of MXene. The granular SnO2 nanoparticles are intimately attached to the surface of MXene. Fig.2 (b) shows the Raman spectra of MXene and Mxene/SnO2 heterojunction. The appearance of both D-band and G-band in the MXene/SnO2 heterojunction sample indicated that MXene remained well during the hydrothermal reaction. Fig.2(c) shows the Ti core level (2p) spectra of the MXene and MXene/SnO2. Ti - X corresponds to titanium carbide or titanium oxynitride. Fig.2d indicates that the peaks at 530.1 and 532 eV correspond to oxygen vacancies and O=C-OH, respectively, suggesting that these and surface-adsorbed oxygen tend to form more active sites, thereby enhancing sensing capability.The sensors using MXene/SnO2 heterojuction shows excellent response and selectivity to low-level NH3 from 0.5-9 ppm at RT (Fig.3). Since the work function of MXene (4.465 eV) was slightly lower than that of SnO2 (4.7 eV), Schottky-type junctions were formed across MXene/SnO2 interfaces (Fig.4). Electrons would transfer from SnO2 to MXene, and the depletion layer was deepened on the surface of MXene. MXene could then chemically adsorb more oxygen, and the response of the MXene/SnO2 heterojunction was thus significantly enhanced.

Adsorption mechanisms of Mo2CrC2 MXenes as potential anode materials for metal-ion batteries: A first-principles investigation

Two dimensional MXene are attracting increasing interests as electrode materials for metal ion batteries (MIBs) because metal ions can diffuse in a 2D lattice surface. In this work, first-principles calculations were carried out to investigate the adsorption performance of monolayer Mo2CrC2 for Li, Na, and K. The results show strong storage ability for various metal cations. There are three layers of Li, two layers of Na, one layer of K, and four layers of Mg on both sides of the monolayer. The electrochemical and thermodynamics of the intercalation of metal ions on the Mo2CrC2 Mxene have been intensively investigated. There is no band gap at the Fermi level of any configuration indicating that it has excellent electronic conductivity leading to an asymmetric electron localization distribution. The binding energy of metal ions decreases as the ion concentration increases. The adsorption of metal ions on a mono-layer of Mo2CrC2 has been studied, and the results indicate that the metal ions obviously improved the diffusion of metal ions. The CI-NEB method was used to study the diffusion of a cation on a Mo2CrC2 surface and search for its lowest energy along the diffusion pathway. Their structural transformations were studied via ab initio molecular dynamic (AIMD) simulations at a series of temperatures. The metal ions gradually evolved via thermal motion with increasing temperature. These results suggest that Mo2CrC2 could be a promising electrode material for Li- and Na-ion batteries in terms of Mo2CrC2 specific capacity, diffusion dynamics, and structural stability.

Cation-intercalated engineering and X-ray absorption spectroscopic characterizations of two dimensional MXenes

The geometrically multiplied development of 2D MXenes has already promoted the prosperity of various fields of scientific researches especially but not limited in energy storage and conversion. Notably, cation intercalation can improve the interlayer spacing of MXenes resulting in tunable physical and chemical properties. Moreover, the synchrotron radiation X-ray characterizations have also shown high potential on exploring the property and structure of cation intercalated MXenes. This review is mainly focused on the recent achievements of cation intercalated MXenes through different methods on energy storage systems. Synchrotron-based X-ray absorption spectroscopic characterizations are emphasized to probe the local coordination and electronic structure in intercalated MXenes. The outlook of cation intercalation on MXenes and their applications are also discussed.