2D Ti3C2 MXene Research Articles

Ti3C2-Based MXene Oxide Nanosheets for Resistive Memory and Synaptic Learning Applications.

MXene, a new state-of-the-art two-dimensional (2D) nanomaterial, has attracted considerable interest from both industry and academia because of its excellent electrical, mechanical, and chemical properties. However, MXene-based device engineering has rarely been reported. In this study, we explored Ti3C2 MXene for digital and analog computing applications by engineering the top electrode. For this purpose, Ti3C2 MXene was synthesized by a simple chemical process, and its structural, compositional, and morphological properties were studied using various analytical tools. Finally, we explored its potential application in bipolar resistive switching (RS) and synaptic learning devices. In particular, the effect of the top electrode (Ag, Pt, and Al) on the RS properties of the Ti3C2 MXene-based memory devices was thoroughly investigated. Compared with the Ag and Pt top electrode-based devices, the Al/Ti3C2/Pt device exhibited better RS and operated more reliably, as determined by the evaluation of the charge-magnetic property and memory endurance and retention. Thus, we selected the Al/Ti3C2/Pt memristive device to mimic the potentiation and depression synaptic properties and spike-timing-dependent plasticity-based Hebbian learning rules. Furthermore, the electron transport in this device was found to occur by a filamentary RS mechanism (based on oxidized Ti3C2 MXene), as determined by analyzing the electrical fitting curves. The results suggest that the 2D Ti3C2 MXene is an excellent nanomaterial for non-volatile memory and synaptic learning applications.

Electrocatalytic Synthesis of Ammonia Using a 2D Ti3 C2 MXene Loaded with Copper Nanoparticles.

As an energy-saving and environmentally friendly ammonia synthesis method, electrocatalytic nitrogen reduction reaction (NRR) has received a great deal of attention. There is thus an urgent need to find high-efficiency electrocatalysts for the NRR. In this work, a Cu/Ti3 C2 composite catalyst was prepared and demonstrated excellent selectivity under environmental conditions, which could efficiently convert N2 into NH3 electrochemically. In 0.1 M KOH, Cu/Ti3 C2 can achieve a high Faradaic efficiency of 7.31 % and a high NH3 production rate of 3.04 μmol h-1 cm-2 at -0.5 V vs. RHE. Moreover, the material also exhibits superior electrochemical stability and durability. At the same time, density functional theory (DFT) shows that, compared with Ti3 C2 , Cu/Ti3 C2 exhibits a wider conduction and valence band and a larger Fermi level, thus indicating that Cu plays a vital role in the enhancement of the catalytic activity and conductivity of Ti3 C2 -based materials. This work provides a feasible strategy for designing high-efficiency MXene-based NRR electrocatalysts.

Photocatalytic Applications of Two-Dimensional Ti3C2 MXenes: A Review

Two-dimensional (2D) Ti3C2 MXenes have aroused tremendous attention as frontier materials for energy storage, solar energy conversion, and environmental remediation because they exhibit high elemen...

2D Ti3C2 MXene embedded with Co(II)(OH)n nanoparticles as the cathode material for hybrid magnesium–lithium-ion batteries

MXene, the 2D layered material, is intensively investigated for application in the energy storage field due to its multiple advantages of the high electrical conductivity, hydrophilicity and the plastic layer structure. Herein, a composite (M(II)(OH)n@Ti3C2) of Ti3C2 MXene matrices embedded with ultrafine M(II)(OH)n (M = Fe/Co/Ni) particles is in-situ prepared. M(II)(OH)n particles are tightly grown on the surface and between the interlayers of Ti3C2 MXene by strong Ti–O–Co covalent bonds. Co(II)(OH)n@Ti3C2 exhibits the remarkable performance in hybrid magnesium–lithium batteries (HMLBs) due to the redox capacitive contribution and “pillar effect” of Co(II)(OH)n particles between the interlayers of Ti3C2 MXene. It exhibits a promising reversible capacity and excellent cycling stability. Its reversible capacity maintains 81.1 mAh g−1 after 600 cycles at 100 mA g−1, and the coulombic efficiency is nearly 100%. Therefore, it is an effective strategy to enhance the electrochemical performance of HMLBs by increasing redox capacitance of MXene cathodes. The Co(II)(OH)n nanoparticles decorated Ti3C2 nanocomposite (M(II)(OH)n@Ti3C2) was successfully synthesized by three processing steps. The Co(II)(OH)n@Ti3C2 nanocomposite exhibits the superior performance in HMLBs due to the synergistic effect of the Co(II)(OH)n nanoparticles and the Ti3C2 matrix.

Constructing Ti3C2 MXene/ZnIn2S4 heterostructure as a Schottky catalyst for photocatalytic environmental remediation

It is highly demanded to steer the charge flow in semiconductor for efficient photocatalytic environmental remediation. Herein, we designed an interfacial contact Ti3C2 MXene/ZnIn2S4 nanosheets (TC/ZISNS) Schottky heterostructure which could greatly enhance photogenerated charge separation of ZnIn2S4 (ZIS). Through TEM and XPS measurement, the strong interface coupling between 2D ZnIn2S4 nanosheets and 2D Ti3C2 MXene were explained, and the formation of Schottky heterostructure was demonstrated by electrochemical method. To investigate the photocatalytic activity of as-prepared samples, the photocatalytic reduction of Cr(VI) and photocatalytic oxidation degradation tetracycline hydrochloride (TC-H) experiments were carried out. The results showed that the Schottky catalyst (10%-TC/ZISNS) possessed the optimum photocatalytic efficiency. Especially, the apparent rate constant of Cr(VI) reduction with 10%-TC/ZISNS was 3.9 times than that of pure ZIS. The photocatalytic performance of 10%-TC/ZISNS toward degradation rate of TC-H was 1.8 times than that of pure ZIS. Finally, a possible mechanism for great enhancement of visible-light driven photocatalytic activity in the TC/ZISNS system was provided. On the whole, this work provided a new insight on 2D/2D contact Schottky heterostructure for enhancing photocatalytic activity.

Ultrathin 2D Ti3C2 MXene Co-catalyst anchored on porous g-C3N4 for enhanced photocatalytic CO2 reduction under visible-light irradiation

Constructing an efficient photocatalyst is critical for photocatalytic carbon dioxide (CO2) into valuable fuel. Herein, a high-efficiency catalyst was synthesized by a simple one-step electrostatic self-assembly method, in which Ti3C2 (TC) was anchored on porous g-C3N4 (PCN) with rich –NHx via NHx-Ti bond. Such a chemical interaction made the optimized TC/PCN-2 with 2 wt% loading of Ti3C2 possess highest CH4 production (0.99 μmol·h−1·g−1catalyst) under visible light (>420 nm), which was 14 times higher than that of pure PCN (0.07 µmol·h−1·gcatalyst−1) at the same condition. More importantly, the TC/PCN-2 photocatalyst still maintained satisfied activity after four cycles. Besides the formation of NHx-Ti chemical bonding and superior conductivity of Ti3C2 as a co-catalyst, which facilitated interfacial charges separation and migration, the exceptional performance could also attribute to the enhanced CO2 adsorption/activation and improved light-harvesting capability. This work provided a potential application in energy conversion with MXene as an efficient co-catalyst.

Sacrificial Agent‐Free Photocatalytic Oxygen Evolution from Water Splitting over Ag3PO4/MXene Hybrids

Hybrid Photocatalysts In article number 1900434, Xiaofei Yang, Jingsan Xu, and co-workers demonstrate a new efficient and stable sacrificial agent–free water oxidation photocatalyst by integrating conductive few-layer 2D Ti3C2 MXene with a well-documented oxygen-evolving material. The constructed Ag3PO4/MXene Schottky heterojunctions exhibit increased light utilization efficiency, accelerated interfacial charge transfer, improved oxygen evolution performance, and highly enhanced photo-stability.

Facile preparation of Yb3+/Tm3+ co-doped Ti3C2/Ag/Ag3VO4 composite with an efficient charge separation for boosting visible-light photocatalytic activity

A novel Yb3+/Tm3+ co-doped Ti3C2/Ag/Ag3VO4 composite with stable and robust photodegradation performance was synthesized by in-situ partially reduction along with hydrothermal strategy. In the composite, block-like Ag3VO4 particles are self-assembled on the surface of 2D Ti3C2 MXene accompanied by partial reduction of Ag+ to Ag0. Photodegradation results showed that the resulting Yb3+/Tm3+ co-doped Ti3C2/Ag/Ag3VO4 composite with optimal Yb/Tm proportion (Y/T:0.3/0.005) presented a boosting photocatalytic performance for degradation of tetracycline (TC) and organic dyes under visible light irradiation. The removal efficiency was 97% for TC in 20 min, 96% for rhodamine B in 25 min, and 99% for methylene blue in 20 min, which was higher than that of Ag/Ag3VO4 composite. As manifested by photoelectrochemical measurements, the enhanced photocatalytic performance of the Y/T:0.3/0.005 composite was attributed to the improved light absorption and excellent charge separation induced by the formation of intermediate energy states after co-doping Yb3+/Tm3+ ions. Meanwhile, the photocatalytic mechanism of the photocatalyst was also investigated through electron spin resonance (ESR) spectra and trapping experiments, which verified that the active species of h+ and ·O2− play the important role for photodegradation of tetracyline and organic dyes.

Engineering of 2D Ti3C2 MXene Surface Charge and Its Influence on Biological Properties.

Current trends in the field of MXenes emphasize the importance of controlling their surface features for successful application in biotechnological areas. The ability to stabilize the surface properties of MXenes has been demonstrated here through surface charge engineering. It was thus determined how changing the surface charges of two-dimensional (2D) Ti3C2 MXene phase flakes using cationic polymeric poly-L-lysine (PLL) molecules affects the colloidal and biological properties of the resulting hybrid 2D nanomaterial. Electrostatic adsorption of PLL on the surface of delaminated 2D Ti3C2 flakes occurs efficiently, leads to changing an MXene’s negative surface charge toward a positive value, which can also be effectively managed through pH changes. Analysis of bioactive properties revealed additional antibacterial functionality of the developed 2D Ti3C2/PLL MXene flakes concerning Escherichia. coli Gram-negative bacteria cells. A reduction of two orders of magnitude of viable cells was achieved at a concentration of 200 mg L−1. The in vitro analysis also showed lowered toxicity in the concentration range up to 375 mg L−1. The presented study demonstrates a feasible approach to control surface properties of 2D Ti3C2 MXene flakes through surface charge engineering which was also verified in vitro for usage in biotechnology or nanomedicine applications.

A simple, low-cost and green method for controlling the cytotoxicity of MXenes.

MXene phases are a member of the intriguing 2D material family, beyond graphene. They are good candidates for many applications, however, their potential toxicity is of crucial importance for future development. Herein, we present a simple, low-cost and fully green approach for controlling the potential cytotoxicity of 2D MXenes after delamination by harnessing the interactions that occur between the surface of MXene phases and natural biomacromolecule - collagen. We also demonstrate that the step-by-step adsorption and desorption of collagen from the surface of 2D MXenes is easily controlled using in situ zeta potential measurements coupled with dynamic light scattering (DLS) method. The obtained results demonstrated that the electrostatically driven unprecedented susceptibility of the MXenes' surfaces to collagen. Surface-modification reduces toxicity of MXenes in vitro i.e. adjust cells' viabilities as well as reduce their oxidative stress. This indicates enhanced biocompatibility of 2D Ti3C2 and Ti2C MXenes surface-modified with collagen, which is involved in many bio-interactions as important building blocks in the human body. The presented study opens new avenues for designing MXenes with defined surface properties and paves the way for their future successful management in nano-medicinal applications.

On tuning the cytotoxicity of Ti3C2 (MXene) flakes to cancerous and benign cells by post-delamination surface modifications

Despite intensive research on the application of two-dimensional (2D) materials, including MXenes, in nanomedicine, the knowledge concerning the mechanisms responsible for their observed bio-effects is far from being understood. Here we present insight into the mechanism of toxicity in vitro of the 2D Ti3C2 MXene. The most important results of this work are that using simple, inexpensive, post-delamination treatments, such as ultrasonication or mild thermal oxidation it is possible to ‘tune’ the cytotoxicity of the Ti3C2Tz flakes. Sonication of Ti3C2Tz flakes, or sonication followed by mild oxidation in the water at 60 °C, renders them selectively toxic to cancer cells as compared to non-malignant ones. It relates to the appearance of superficial titanium (III) oxide (Ti2O3) layer corresponding to the type of post-treatment. The presence of surface-Ti2O3 results in a noticeably higher generation of oxidative stress compared to pristine 2D Ti3C2. Our findings give evidence that the sonication and thermal treatments were successful in changing the nature of the surface terminations on the Ti3C2Tz surfaces. This study makes a significant contribution to the future rationalized surface-management of 2D Ti3C2 MXene as well as encourages new rationalized applications in biotechnology and nanomedicine.Bullet points:1. First study on 2D Ti3C2 MXene superficially oxidized to titanium (III) oxide i.e. Ti2O3.2. By sonication Ti3C2Tz MXene flakes followed by mild thermal oxidation in the water at 60 °C for 24 h, it is possible to ‘tune’ the toxicity of the flakes to cancerous cell lines.3. Decreases in cell viabilities were dose-dependent.4. Highest cytotoxic effect was observed for thermally oxidized samples.5. The thermally oxidized samples were also selectively toxic towards all cancerous cell lines up to 375 mg l−1.6. Reactive oxygen species generation was identified as a mechanism of toxicity.

Anchoring Co3O4 nanoparticles on MXene for efficient electrocatalytic oxygen evolution

Rational design and controllable synthesis of efficient electrocatalysts for water oxidation is of significant importance for the development of promising energy conversion systems, in particular integrated photoelectrochemical water splitting devices. Cobalt oxide (Co3O4) nanostructures with mixed valences (II,III) have been regarded as promising electrocatalysts for the oxygen evolution reaction (OER). They are able to promote catalytic support of OER but with only modest activity. Here, we demonstrate that the OER performance of cubic Co3O4 electrocatalyst is obviously improved when they are anchored on delaminated two-dimensional (2D) Ti3C2 MXene nanosheets. Upon activation the overpotential of the hybrid catalyst delivers 300 mV at a current density of 10 mA cm−2 in basic solutions, which is remarkably lower than those of Ti3C2 MXene and Co3O4 nanocubes. The strong interfacial electrostatic interactions between two components contribute to the exceptional catalytic performance and stability. The enhanced OER activity and facile synthesis make these Co3O4 nanocubes-decorated ultrathin 2D Ti3C2 MXene nanosheets useful for constructing efficient and stable electrodes for high-performance electrochemical water splitting.

Highly safe and ionothermal synthesis of Ti3C2 MXene with expanded interlayer spacing for enhanced lithium storage

Abstract MXene is a rising star of two-dimensional (2D) materials for energy relative applications, however, the traditional synthesis of MXene etched by hazard HF acid or LiF+HCl mixed solution is highly dangerous with the risk of splashing or pouring liquid solutions. In this work, we developed a water-free ionothermal synthesis of 2D Ti3C2 MXene via etching pristine Ti3AlC2 MAX in low-cost choline chloride and oxalic acid based deep eutectic solvents (DES) with the presence of NH4F, thus it was highly safe and convenient to operate solid precursor and product materials at room temperature. Benefited from the low vapor pressure and solvating properties of DES, the prepared Ti3C2 (denoted as DES-Ti3C2) possessed a high purity up to 98% compared with 95% for HF etched Ti3C2 (denoted as HF-Ti3C2). Notably, an expanded interlayer spacing of 1.35 nm could be achieved due to the intercalation of choline cations in DES-Ti3C2, larger than that of HF-Ti3C2 (0.98 nm). As a result, the DES-Ti3C2 anodes exhibited enhanced lithium storage performance, such as high reversible capacity of 208 mAh g−1 at 0.5 A g−1, and long cycle life over 400 times, outperforming most reported pure MXene anodes. The ionothermal synthesis of MXene developed here may pave a new way to safely prepare other MXene for various energy relating applications.

2D MXene-Integrated 3D-Printing Scaffolds for Augmented Osteosarcoma Phototherapy and Accelerated Tissue Reconstruction.

The residual of malignant tumor cells and lack of bone‐tissue integration are the two critical concerns of bone‐tumor recurrence and surgical failure. In this work, the rational integration of 2D Ti3C2 MXene is reported with 3D‐printing bioactive glass (BG) scaffolds for achieving concurrent bone‐tumor killing by photonic hyperthermia and bone‐tissue regeneration by bioactive scaffolds. The designed composite scaffolds take the unique feature of high photothermal conversion of integrated 2D Ti3C2 MXene for inducing bone‐tumor ablation by near infrared‐triggered photothermal hyperthermia, which has achieved the complete tumor eradication on in vivo bone‐tumor xenografts. Importantly, the rational integration of 2D Ti3C2 MXene is demonstrated to efficiently accelerate the in vivo growth of newborn bone tissue of the composite BG scaffolds. The dual functionality of bone‐tumor killing and bone‐tissue regeneration makes these Ti3C2 MXene‐integrated composite scaffolds highly promising for the treatment of bone tumors, which also substantially broadens the biomedical applications of 2D MXenes in tissue engineering, especially on the treatment of bone tumors.

In situ fabrication of 1D CdS nanorod/2D Ti3C2 MXene nanosheet Schottky heterojunction toward enhanced photocatalytic hydrogen evolution

Benefiting from excellent metallic conductivity, full-spectrum solar energy absorption and rich active sites on the surface, atomically thin two-dimensional transition metal carbide (2D MXene) shows great promise in improving solar-to-hydrogen efficiency and has drawn intense interest in the field of photocatalysis. However, controllable construction of ultrathin 2D MXene-based heterojunction photocatalysts still remains a significant challenge. Herein, one-dimensional (1D) CdS nanorod/2D MXene nanosheet heterojunctions with well-defined nanostructures and strong interfacial coupling are fabricated by in situ assembling solvothermally-generated CdS nanorods on ultrathin Ti3C2 MXene nanosheets. Due to their specific interface characteristics, 1D/2D Schottky heterojunction is capable of providing accelerated charge separation and a lower Schottky barrier for solar-driven hydrogen evolution from water splitting. As expected, the Schottky-based photocatalyst is 7-fold more active in the illuminated hydrogen evolution reaction (HER) than pristine CdS nanorods, implying the synergistic effects between n-type semiconductor CdS and highly conductive 2D Ti3C2 MXene nanosheets.

Triggering Sequential Catalytic Fenton Reaction on 2D MXenes for Hyperthermia-Augmented Synergistic Nanocatalytic Cancer Therapy.

The unique characteristics of a tumor microenvironment (TME) enable the development of new tumor-therapeutic modalities with high efficiency, biosafety, and tumor specificity. In this work, we report on the construction of photothermal-enhanced and nanocatalyst-enabled sequential catalytic reaction for TME-specific cancer therapy. This conceptual advance is achieved by engineering the surface of two-dimensional Ti3C2 MXene with two separate catalysts, including natural glucose oxidase (GOD) as glucose catalysts and superparamagnetic iron oxide nanoparticles (IONPs) as Fenton-reaction nanocatalysts. A sequential catalytic reaction is triggered by using GOD for catalyzing the tumor-overtaken glucose to generate large amounts of hydrogen peroxide molecules. Subsequently IONPs can catalyze the transformation of pregenerated hydrogen peroxide into large amounts of highly toxic hydroxyl radicals to kill the cancer cells subsequently in TME-enabled acidity condition. The two-dimensional (2D) Ti3C2 MXene matrix efficiently converts the near-infrared light into thermal energy to synergistically enhance the catalytic efficiency of this sequential catalytic reaction and therefore achieve the high synergistic cancer-therapeutic outcome, accompanied with the high biocompatibility of the constructed composite nanocatalysts. Both in vitro cancer-cell evaluation and in vivo tumor xenograft on nude mice with complete tumor eradication demonstrate the high synergistic efficiency of photothermal-enhanced sequential nanocatalytic cancer therapy. Therefore, this work substantially broadens the biomedical applications of 2D MXenes to nanocatalytic cancer therapy by enhancing the Fenton reaction-based nanocatalytic therapy via converting the near-infrared light into thermal energy and subsequently elevating the local Fenton-reaction temperature.

MoS2-decorated 2D Ti3C2 (MXene): a high-performance anode material for lithium-ion batteries

MXenes can be invoked as anode materials for lithium-ion batteries because of low Li+ diffusion resistance, metal conductivity, and excellent mechanical properties. However, the lower specific capacity could restrict their application. Herein, MoS2@Ti3C2 composite material is synthesized using a simple hydrothermal method to increase layer space and specific capacity. The MoS2@Ti3C2 composite material yields a reversible discharge capacity of 355 mAh g−1 at 1000 mA g−1 over 1300 cycles, outstandingly higher than those of pure Ti3C2 and MoS2, which is 120 mAh g−1 and 52 mAh g−1, respectively. MoS2@Ti3C2 composite material electrode exhibited excellent performance.

Rapid preparation, thermal stability and electromagnetic interference shielding properties of two-dimensional Ti3C2 MXene

Abstract Two-dimensional (2D) MXenes have attracted much attention due to their unique structural characteristics and novel performance in a variety of functions. The fabrication of 2D Ti3C2 MXene by acid etching usually requires a long period of over 10 h. In this work, we report on the rapid preparation, thermal stability and electromagnetic interference (EMI) shielding effectiveness of 2D Ti3C2 MXene. With the processing conditions optimized by adjusting the etching time and temperature, Ti3C2 MXene with a scattered accordion-like structure has been successfully achieved by etching Ti3AlC2 powders with 40% HF at 50 °C for only 0.5 h. The as-synthesized Ti3C2 was stable at temperatures up to 300 °C in air, but stable in vacuum at temperatures up to 800 °C. The as-synthesized Ti3C2 MXene has good EMI shielding performance. The total shielding effectiveness of Ti3C2 in a WAX matrix exceeded 20 dB in the whole frequency ranging from 2 to 18 GHz. The maximum shielding effectiveness value achieved to 34 dB at 18 GHz as the Ti3C2 content was up to 70 wt%. This work provides an approach for the large scale preparation of the Ti3C2 MXene.

Novel Two-Dimensional Magnetic Titanium Carbide for Methylene Blue Removal over a Wide pH Range: Insight into Removal Performance and Mechanism.

Two-dimensional (2D) layer-structured titanium carbide MXenes (e.g., 2D Ti3C2 MXene) have received tremendous attention owing to their excellent properties and unique 2D planar topology. Nevertheless, there are still several challenges to be addressed for well dispersibility and easy separation from a heterogeneous system, hindering the practical applications. Herein, 2D Ti3C2 MXene, as the most typical member of 2D MXenes, is functionalized with magnetic Fe3O4 nanoparticles via an in situ growth approach (designated as MXene@Fe3O4), which exhibits the intriguing phenomenon on methylene blue (MB) adsorption in the environmental remediation realm. The maximum adsorption capacity of the MXene@Fe3O4 composites for MB is calculated to be 11.68 mg·g-1 by a Langmuir isotherm model. A thermodynamic study of the adsorption demonstrates that the reaction process is exothermic and entropy-driven. Attractively, the removal process is a pH-independent process, and the optimal MB adsorption capacity is achieved at pH = 3 or 11, which is ascribed to electrostatic interactions and the hydrogen bond effect. X-ray diffraction, Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculation results reveal that the adsorption process is based on a combination of Ti-OH···N bonding, electrostatic attraction, and reductivity. Furthermore, multiple cycle runs demonstrate an excellent stability and reusability of MXene@Fe3O4 composites. This study provides a promising approach for the alternative removal of MB and broadens the potential application of 2D MXene for the treatment of practical acidic or alkaline wastewater.

Strong interface effect induced high-k property in polymer based ternary composites filled with 2D layered Ti3C2 MXene nanosheets

High permittivity property is hard to achieve in the binary polymer based nanocomposites filled with wide-band-gap semiconductors unless substantial semiconductor fillers are introduced into polymer matrices. The overload of those semiconducting nanofillers usually results in the severe reduction of the mechanical and electric breakdown properties of the composite materials. In this work, the novel ternary polymer based nanocomposites were designed and further fabricated through adding a low concentration of 2D Ti3C2 MXene nanosheets into the binary polymer based nanocomposites containing alpha-SiC nanoparticles. In comparison with the binary composites, these ternary composites could exhibit the notably improved high permittivity properties due to significantly enhanced interface interaction from the introduction of MXene nanosheets. The desirable highly maintained comprehensive electrical properties and mechanical performances have been achieved in those ternary composites. This work might open the door to the large-scale preparation of promising high-permittivity nanocomposite dielectric materials based on building the ternary composite systems.