Ion Implantation as an Approach for Structural Modifications and Functionalization of Ti3C2Tx MXenes

Metastructure and strain-defect engineered Cu-doped TiO x coating to enhance antibacterial sonodynamic therapy

Sonodynamic therapy (SDT) has attracted widespread attention in treatment of implant-associated infections, one of the key factors leading to implant failure. Nevertheless, constructing efficient ultrasound-triggered coatings on implant surfaces remains a challenge. Herein, an acoustic metastructure Cu-doped defective titanium oxide coating (Cu-TiO x ) with lattice strain was constructed in situ on titanium implant to realize effective sonocatalysis. The redistribution of Cu atoms broke the pristine lattice of TiO2 during the thermal reduction treatment to regulate its energy structure, which favored separation of electron-hole pairs generated by ultrasound radiation to enhance the sonocatalytic generation of reactive oxygen species. In addition, the acoustic metastructure enhanced the absorption of ultrasound by Cu-TiO x metastructure coating, which further promoted its sonocatalytic effect. Thus, Cu-TiO x metastructure coating could efficiently eliminate Staphylococcus aureus and Escherichia coli infections under ultrasonic irradiation in 10 min. Besides, the osteogenic property of implant was significantly improved after infection clearance in vivo. This work provides a fresh perspective on the design of SDT biosurfaces based on metastructure and strain-defect engineering.

MXene-Mediated Electronic State Engineering of Nickel Hydroxide for Efficient Piezo-Catalytic Hydrogen Peroxide Synthesis

The piezo-catalytic synthesis of hydrogen peroxide (H2O2) offers a sustainable alternative to the traditional anthraquinone process by enhancing both the water oxidation reaction (WOR) and oxygen reduction reaction (ORR). However, conventional high-dielectric-constant piezoelectric materials, despite their superior piezoelectric responses, generally feature wide band gaps, low electrical conductivity, and a limited number of active sites─catalytically unfavorable characteristics that restrict their piezocatalytic efficiency. To address this, we developed a 2D Ni(OH)2-Ti3C2Tx MXene composite for efficient H2O2 production in pure water. The Ti3C2Tx MXene modifies the electronic states of Ni(OH)2, enhancing its deprotonation ability (Ni2+ to Ni3+) and creating hypervalent nickel active sites that boost H2O2 synthesis. Theoretical and experimental studies confirm that H2O2 generation occurs through combined WOR and ORR pathways, with ORR being dominant. The hierarchical 2D nanosheet structure facilitates crystal deformation under mechanical stress, amplifying the piezoelectric effect and reducing the energy input required for redox reactions. As a result, the Ni(OH)2-Ti3C2Tx composite achieves an impressive H2O2 yield of 351.1 μmol·g-1·h-1. This work provides a novel design strategy for high-performance piezo-catalysts in sustainable H2O2 production.

The Future of MXenes: Exploring Oxidative Degradation Pathways and Coping with Surface/Edge Passivation Approach

The MXene, which is usually transition metal carbide, nitride, and carbonitride, is one of the emerging family of 2D materials, exhibiting considerable potential across various research areas. Despite theoretical versatility, practical application of MXene is prohibited due to its spontaneous oxidative degradation. This review meticulously discusses the factors influencing the oxidation of MXenes, considering both thermodynamic and kinetic point of view. The potential mechanisms of oxidation are systematically introduced, based on experimental and theoretical models. Typically, the surfaces and edges of MXenes are susceptible to oxidation, as the surface terminal groups are easily attacked by oxygen and water molecules, ultimately leading to structural deformation. To retard oxidative degradation, ligand mediated surface/edge passivation is suggested as a promising strategy. In this regard, detailed passivation strategies for MXenes are systematically explained based on the types of chemistry at the MXene-ligand interface-covalent bonding, electrostatic interactions, and hydrogen bonding-and the type of stabilizing moieties-organic, inorganic, biomolecules, and polymers. The retardation of oxidation is discussed in relation with the interaction type and passivating moiety. This review aims to catalyze future research to identify efficient and cost-effective ligands for the surface engineering of MXenes, enhancing their oxidation stability.

Swift Droplet Manipulation on BTO/Polyimide Slippery Surfaces

Droplet manipulation on functional surfaces is an urgent problem to be solved. Fast and precise droplet manipulation plays an important role in many applications, such as microreactors and microfluidics. Although numerous techniques have been developed to manipulate droplets by injecting external stimuli, it remains a challenge to achieve high-precision, high-sensitivity, and fast droplet manipulation on smart, slippery response surfaces. Here, we report an intelligent slippery photopyroelectric response near-infrared-induced MXene-barium titanate/polyimide (SFMBPI) membrane. By using local near-infrared radiation (NIR), we can precisely control the droplet transport on the SFMBPI membrane, and SFMBPI uses electrospinning technology to better lock the dimethylsilicone oil, reducing the loss during the control process. Moreover, due to the presence of the pyroelectric layer, double external stimuli can be achieved. The thermal stimulation of the photothermal layer and the charge action of the pyroelectric layer make the manipulation of droplets on the SFMBPI surface more efficient and faster. Moreover, the experiment of negative gravity transport at an inclination angle of 6° demonstrates that the existence of the pyroelectric layer results in a greater driving force on the droplets, which can be more widely used. In addition, by inducing the direction of the NIR, programmable droplet transport and droplet merging can be achieved. Also, the SFMBPI membrane can be used for underwater bubble manipulation. This precise manipulation of droplets on the surface of SFMBPI membranes can be widely used in other fields, such as microfluidics.

2D versus 3D-Like Electrical Behavior of MXene Thin Films: Insights from Weak Localization in the Role of Thickness, Interflake Coupling and Defects

MXenes stand out from other 2D materials because they combine very good electrical conductivity with hydrophilicity, allowing cost-effective processing as thin films. Therefore, there is a high fundamental interest in unraveling the electronic transport mechanisms at stake in multilayers of the most conducting MXene, Ti3C2Tx. Although weak localization (WL) has been proposed as the dominating low-temperature (LT) transport mechanism in Ti3C2Tx thin films, there have been few attempts to model it quantitatively. In this work, the role of important structural parameters - thickness, interflake coupling, defects - on the dimensionality of the LT transport mechanisms in spin-coated Ti3C2Tx thin films is investigated through LT and magnetic field dependent resistivity measurements. A dimensional crossover from 2D to 3D WL is clearly evidenced when the film thickness exceeds the dephasing length lϕ, estimated here in the 50-100 nm range. 2D WL can be restored by weakening the coupling between adjacent flakes, the intrinsic thickness of which is lower than lϕ, hence acting as parallel 2D conductors. Alternatively, lϕ can be reduced down to the 10 nm range by defects. These results clearly emphasize the ability of WL quantitative study to give deep insights in the physics of electron transport in MXene thin films.

Wedge-Like Microstructure of Al2O3/i-Ti3C2Tx Electrode with "Nano-Pumping" Effect for Boosting Ion Diffusion and Electrochemical Defluoridation

Controlled synthesis and regulation of 2D nanomaterials with sufficient active sites are promising in electrochemical fluorine capture, but simultaneously achieving rapid rates and efficient activity of intercalation materials remains challengs. Herein, an integrated strategy of micro-regulation interlayer space and in situ modification of MXenes is proposed to enhance ion storage kinetics. The wedge-like microstructure of aluminum oxide/incomplete-Ti3C2Tx MXene (Al2O3/i-Ti3C2 Tx) is constructed by incomplete etching MAX and in situ derivation of A-layer element, in which the sub-nanoscale interlayer space is conducive to the small size ions intercalation, and the formation of "nanopump-like" effect boosted the ions diffusion. As evidenced by simulation calculations, Al2O3 nanoparticles not only shorten the migration distance of electrons/hydrated ions in interlayers but also contribute a lower adsorption energy barrier, bringing excellent capture kinetics and stability. Benefiting from the interfacial conversion-intercalation pseudocapacitance, such electrode is endowed with a high defluoridation capacity (69.9 mg g-1 at 1.6V) and an outstanding instantaneous adsorption rate (9.51 mg g-1 min-1), and shows satisfactory stability in more than 200 cycles. The physicochemical coupling strategy opens a novel approach to optimizing the interlayer structure and in situ modification interface of MXene, which also provids a universal idea for efficient capture of varisized ions of intercalation materials.

Ultrafast Na-Ion Storage in Amorphization Engineered Hollow Vanadium Oxide/MXene Nanohybrids for High-Performance Sodium-Ion Hybrid Capacitors

Sodium ion hybrid capacitors (SIHCs) address the high power and energy requirements in energy storage devices but face significant challenges arising from the slow kinetics and cycling instability of the anode side. Introducing atomic disorder and employing structural engineering in anode materials proves to be effective strategies for achieving rapid charge storage. Here, it is demonstrated that N-doped MXene encapsulated amorphous vanadium oxide hollow spheres (VOx@N-MXene HSs) offer multidirectional open pathways and sufficient vacancies, enabling reversible and fast Na+ insertion/extraction. Machine learning potentials, coupled with molecular simulation techniques, confirm the presence of more abundant pores within the amorphous vanadium oxide (VOx) structure. The simulation of the charging/discharging process elucidates the authentic reaction path and structural evolutions of the VOx@N-MXene HSs, providing sufficient insight into the atomic-scale mechanisms associated with these structural superiorities. The full SIHCs devices demonstrate a high energy density of 198.3 Wh kg-1, along with a long-term cycling lifespan of 8000 cycles. This study offers valuable strategies into the intricate design and exploration of amorphous electrodes, contributing to the advancement of next-generation electrochemical energy devices.

Low-Temperature Plasma-Constructed Ni-Doped W18O49 Nanorod Arrays for Enhanced Electrocatalytic Oxygen Evolution and Urea Oxidation

Surface engineering by doping and amorphization is receiving widespread attention from the perspective of the regulation of the electrocatalytic activities of electrocatalysts. However, the effective modulation of active sites on catalysts is still challenging. Herein, a straightforward and efficient method combining hydrothermal treatment with low-temperature plasma processing is presented to synthesize Ni-doped W18O49 nanorod arrays on carbon cloth with abundant oxygen vacancies (CC/WO-Ni-x). Mild plasma doping with Ni modifies the electronic structure of the W18O49 nanorod arrays, resulting in the formation of an amorphous structure that significantly reduces the electron transfer resistance. Additionally, the coupling with high-valent W6+ (derived from W18O49) leads to the partial preoxidation of doped Ni to form active Ni3+ species and oxygen vacancies. These features are collectively responsible for the remarkable oxygen evolution reaction (OER) and urea oxidation reaction (UOR) properties of CC/WO-Ni-4, for example, 10 mA cm-2 current density, an overpotential of 265 mV required for the OER under 1.0 M KOH solution. The addition of 500 mM urea to the 1.0 M KOH solution decreases the overpotential required for the same current density from 265 to 93 mV. This study provides insights into the modification of surface structures and presents an effective strategy to optimize the electrocatalytic active sites and enhance the efficiency of multifunctional electrocatalysts.

Elastic properties and tensile strength of 2D Ti3C2Tx MXene monolayers

Two-dimensional (2D) transition metal nitrides and carbides (MXenes), represented by Ti3C2Tx, have broad applications in flexible electronics, electromechanical devices, and structural membranes due to their unique physical and chemical properties. Despite the Young's modulus of 2D Ti3C2Tx has been theoretically predicted to be 0.502 TPa, which has not been experimentally confirmed so far due to the measurement is extremely restricted. Here, by optimizing the sample preparation, cutting, and transfer protocols, we perform the direct in-situ tensile tests on monolayer Ti3C2Tx nanosheets using nanomechanical push-to-pull equipment under a scanning electron microscope. The effective Young's modulus is 0.484 ± 0.013 TPa, which is much closer to the theoretical value of 0.502 TPa than the previously reported 0.33 TPa by the disputed nanoindentation method, and the measured elastic stiffness is ~948 N/m. Moreover, during the process of tensile loading, the monolayer Ti3C2Tx shows an average elastic strain of ~3.2% and a tensile strength as large as ~15.4 GPa. This work corrects the previous reports by nanoindentation method and demonstrates that the Ti3C2Tx indeed keeps immense potential for broad range of applications.

Recent progresses on ion beam irradiation induced structure and performance modulation of two-dimensional materials

Two-dimensional (2D) materials are receiving significant attention for both fundamental research and industrial applications due to their unparalleled properties and wide application potential. In this case, the controllable modulation of their structures and properties is essential for the realization and further expansion of their applications. Accordingly, ion beam irradiation techniques, with large scope to adjust parameters, high manufacturing resolution, and a series of advanced equipment being developed, have been demonstrated to have obvious advantages in manipulating the structure and performance of 2D materials. In recent years, many research efforts have been devoted to uncovering the underlying mechanism and control rules regarding ion irradiation induced phenomena in 2D materials, aiming at fulfilling their application potential as soon as possible. Herein, we review the research progress in the interaction between energetic ions and 2D materials based on the energy transfer model, type of ion source, structural modulation, performance modification of 2D materials, and then their application status, aiming to provide useful information for researchers in this field and stimulating more research advances.

Toward Smart Sensing by MXene

The Internet of Things era has promoted enormous research on sensors, communications, data fusion, and actuators. Among them, sensors are a prerequisite for acquiring the environmental information for delivering to an artificial data center to make decisions. The MXene-based sensors have aroused tremendous interest because of their extraordinary performances. In this review, the electrical, electronic, and optical properties of MXenes are first introduced. Next, the MXene-based sensors are discussed according to the sensing mechanisms such as electronic, electrochemical, and optical methods. Initially, biosensors are introduced based on chemiresistors and field-effect transistors. Besides, the wearable pressure sensor is demonstrated with piezoresistive devices. Third, the electrochemical methods include amperometry and electrochemiluminescence as examples. In addition, the optical approaches refer to surface plasmonic resonance and fluorescence resonance energy transfer. Moreover, the prospects are delivered of multimodal data fusion toward complicated human-like senses. Eventually, future opportunities for MXene research are conveyed in the new material discovery, structure design, and proof-of-concept devices.

Two-dimensional nanomaterial MXenes for efficient gas separation: a review

Transition metal carbides/nitrides (MXenes) are emerging two-dimensional (2D) materials that have been widely investigated in recent years. In general, these materials can be obtained from MAX phase ceramics after intercalation, etching, and exfoliation to obtain multilayer MXene nanosheet structures; moreover, they have abundant end-group functional groups on their surface. In recent years, the excellent high permeability, fine sieving ability and diverse processability of MXene series materials make the membranes prepared using them particularly suitable for membrane-based separation processes in the field of gas separation. 2D membranes enhance the diversity of the pristine membrane transport channels by regulating the gas transport channels through in-plane pores (intrinsic defects), in-plane slit-like pores, and planar to planar interlayer channels, endowing the membrane with the ability to effectively sieve gas energy efficiently. Herein, we review MXenes, a class of 2D nanomaterials, in terms of their unique structure, synthesis method, functionalization method, and the structure-property relationship of MXene-based gas separation membranes and list examples of MXene-based membranes used in the field of gas separation. By summarizing and analyzing the basic properties of MXenes and demonstrating their unique advantages compared to other 2D nanomaterials, we lay a foundation for the discussion of MXene-based membranes with outstanding carbon dioxide (CO₂) capture performance and outline and exemplify the excellent separation performances of MXene-based gas separation membranes. Finally, the challenges associated with MXenes are briefly discussed and an outlook on the promising future of MXene-based membranes is presented. It is expected that this review will provide new insights and important guidance for future research on MXene materials in the field of gas separation.

The Covalent Functionalization of Surface-Supported Graphene: An Update

In the last decade, the use of graphene supported on solid surfaces has broadened its scope and applications, and graphene has acquire a promising role as a major component of high-performance electronic devices. In this context, the chemical modification of graphene has become essential. In particular, covalent modification offers key benefits, including controllability, stability, and the facility to be integrated into manufacturing operations. In this Review, we critically comment on the latest advances in the covalent modification of supported graphene on substrates. We analyze the different chemical modifications with special attention to radical reactions. In this context, we review the latest achievements in reactivity control, tailoring electronic properties, and introducing active functionalities. Finally, we extended our analysis to other emerging 2D materials supported on surfaces, such as transition metal dichalcogenides, transition metal oxides, and elemental analogs of graphene.

Maximizing Electron Channels Enabled by MXene Aerogel for High-Performance Self-Healable Flexible Electronic Skin

Among the increasingly popular miniature and flexible smart electronics, two-dimensional materials show great potential in the development of flexible electronics owing to their layered structures and outstanding electrical properties. MXenes have attracted much attention in flexible electronics owing to their excellent hydrophilicity and metallic conductivity. However, their limited interlayer spacing and tendency for self-stacking lead to limited changes in electron channels under external pressure, making it difficult to exploit their excellent surface metal conductivity. We propose a strategy for rapid gas foaming to construct interlayer tunable MXene aerogels. MXene aerogels with rich interlayer network structures generate maximized electron channels under pressure, facilitating the effective utilization of the surface metal properties of MXene; this forms a self-healable flexible pressure sensor with excellent sensing properties such as high sensitivity (1,799.5 kPa-1), fast response time (11 ms), and good cycling stability (>25,000 cycles). This pressure sensor has applications in human body detection, human-computer interaction, self-healing, remote monitoring, and pressure distribution identification. The maximized electron channel design provides a simple, efficient, and scalable method to effectively exploit the excellent surface metal conduction of 2D materials.

Oxycarbide MXenes and MAX phases identification using monoatomic layer-by-layer analysis with ultralow-energy secondary-ion mass spectrometry

The MXene family of two-dimensional transition metal carbides and nitrides already includes ~50 members with distinct numbers of atomic layers, stoichiometric compositions and solid solutions, in-plane or out-of-plane ordering of atoms, and a variety of surface terminations. MXenes have shown properties that make them attractive for applications ranging from energy storage to electronics and medicine. Although this compositional variability allows fine-tuning of the MXene properties, it also creates challenges during the analysis of MXenes because of the presence of multiple light elements (for example, H, C, N, O, and F) in close proximity. Here, we show depth profiling of single particles of MXenes and their parent MAX phases with atomic resolution using ultralow-energy secondary-ion mass spectrometry. We directly detect oxygen in the carbon sublattice, thereby demonstrating the existence of oxycarbide MXenes. We also determine the composition of adjacent surface termination layers and show their interaction with each other. Analysis of the metal sublattice shows that Mo₂TiAlC₂ MAX exhibits perfect out-of-plane ordering, whereas Cr₂TiAlC₂ MAX exhibits some intermixing between Cr and Ti in the inner transition metal layer. Our results showcase the capabilities of the developed secondary-ion mass spectrometry technique to probe the composition of layered and two-dimensional materials with monoatomic-layer precision.

Room-Temperature Detection of Perfluoroisobutyronitrile with SnO2/Ti3C2Tx Gas Sensors

Ti₃C₂T_x MXene is an emerging two-dimensional transition-metal carbide/nitride with excellent properties of large specific surface and high carrier mobility for room-temperature gas sensing. However, achieving high sensitivity and long-term stability of pristine Ti₃C₂T_x-based gas sensors remains challenging. SnO₂ is a typical semiconductor metal oxide with high reaction activity and stable chemical properties ideal for a dopant that can comprehensively improve sensing performance. Ti₃C₂T_x and SnO₂ are investigated for the first time in this study as functional materials for hybridization and room-temperature detection of the gas insulating medium fluorinated nitrile (C₄F₇N) with microtoxicity. A Ti₃C₂T_x-SnO₂ nanocomposite sensor exhibits superior sensitivity, high selectivity, strong anti-interference ability, and excellent long-term stability. The enhanced sensing mechanism is ascribed to the synergistic effect between SnO₂ and Ti₃C₂T_x and the strong adsorption ability of SnO₂ to C₄F₇N similar to bait for fish. We also established an actual leakage scene and demonstrated the feasibility of the Ti₃C₂T_x-SnO₂ sensor to provide distribution rules with high sensing efficiency for actual engineering applications. The results of this work can expand the gas sensing application of Ti₃C₂T_x MXene and provide a reference for maintaining C₄F₇N-based eco-friendly gas-insulated equipment.

Enhanced ion transport in nanochannels of MXenes by Mg2+ pre-intercalation

How to enhance the ion transport between MXene layers is a critical topic in the fields of electrochemical storage (especially supercapacitors) and water treatment. Vertical structure design of MXene nanosheets and single-molecule organic pre-intercalation are proposed, but the methods to enhance the ion transport through MXene nanochannels by modulating MXene's surface state have not been investigated yet. The interaction mechanism between Mg²⁺ and MXene 2D nanochannels during the transport process has not been thoroughly explored. In our work, we used a facile infiltration method to immerse the Ti₃C₂T_x membranes in MgCl₂ solution for ion pre-intercalation. We found that the pre-intercalation of Mg²⁺ has a significant effect on the increase of the ion transport rate of Ti₃C₂T_x membranes, especially for Li⁺ which reached 268.49% compared with those of non-intercalation membranes. Through multiple characterization methods, we discovered that the enhancement of ion transport rate by pre-intercalation of Mg²⁺ mainly originated from the fact that the pre-intercalation of Mg²⁺ increased the layer spacing of MXene films as the channel support between layers while Mg²⁺ increased the work function (WF) of 2D nanochannels thereby reducing the interaction of other ions with the channel surface. The acceleration phenomenon of ion transport by surface state modulation proposed in our work will provide new strategies for the design of structure and regulation of surface states, revealing the mechanism of capacity improvement.

Element-Doped Mxenes: Mechanism, Synthesis, and Applications

Heteroatom doping can endow MXenes with various new or improved electromagnetic, physicochemical, optical, and structural properties. This greatly extends the arsenal of MXenes materials and their potential for a spectrum of applications. This article comprehensively and critically discusses the syntheses, properties, and emerging applications of the growing family of heteroatom-doped MXenes materials. First, the doping strategies, synthesis methods, and theoretical simulations of high-performance MXenes materials are summarized. In order to achieve high-performance MXenes materials, the mechanism of atomic element doping from three aspects of lattice optimization, functional substitution, and interface modification is analyzed and summarized, aiming to provide clues for developing new and controllable synthetic routes. The mechanisms underlying their advantageous uses for energy storage, catalysis, sensors, environmental purification and biomedicine are highlighted. Finally, future opportunities and challenges for the study and application of multifunctional high-performance MXenes are presented. This work could open up new prospects for the development of high-performance MXenes.

MXene based saturation organic vertical photoelectric transistors with low subthreshold swing

Vertical transistors have attracted enormous attention in the next-generation electronic devices due to their high working frequency, low operation voltage and large current density, while a major scientific and technological challenge for high performance vertical transistor is to find suitable source electrode. Herein, an MXene material, Ti₃C₂T_x, is introduced as source electrode of organic vertical transistors. The porous MXene films take the advantage of both partially shielding effect of graphene and the direct modulation of the Schottky barrier at the mesh electrode, which significantly enhances the ability of gate modulation and reduces the subthreshold swing to 73 mV/dec. More importantly, the saturation of output current which is essential for all transistor-based applications but remains a great challenge for vertical transistors, is easily achieved in our device due to the ultra-thin thickness and native oxidation of MXene, as verified by finite-element simulations. Finally, our device also possesses great potential for being used as wide-spectrum photodetector with fast response speed without complex material and structure design. This work demonstrates that MXene as source electrode offers plenty of opportunities for high performance vertical transistors and photoelectric devices.

The modulation of Schottky barrier, which dominates the carrier injection in vertical organic field-effect transistors, strongly depends on the source electrode. Here, Chen et al. utilize MXene as a source electrode, achieving a subthreshold swing down to 73 mv/dec and a large gate control ability.

Constructing MXene-PANI@MWCNTs heterojunction with high specific capacitance towards flexible micro-supercapacitor

Micro-supercapacitors (MSCs) are considered as the promising energy supply of miniaturized electronic devices. The electrode material, as one integral part, play a crucial role on the energy storage performance of MSCs. In our work, we constructed a heterojunction in MXene-PANI@MWCNTs (MPM) ternary composite, benefitting for the synergistic enhancement effect among MXene, polyaniline (PANI) and multiwall carbon nanotubes, an outstanding specific capacitance of 414 F g^-1(at 1 A g^-1) has been achieved. MPM shows high capacitance retention at large current density (86.7%, at 10 A g^-1) and long-term cycling stability of 90.4% for 10 000 cycles. Furthermore, we obtained MPM self-standing films, and constructed a flexible all-solid-state MSC based on the film electrode. A competitive charge storage capability of 30.2 mF cm^-2and long-term stability of 70.2% retention for 10 000 cycles was obtained in the MSC. Meanwhile, the MSC shows excellent flexibility, maintaining most capacitance under bending conditions. Moreover, using an integrated strategy, MSCs can obtain tunable voltages and currents that meet various practical requirements. All these results indicate that the MPM is an excellent charge storage material and will become a potential candidate for flexible energy-storage devices.

Functional Group Regulated Ni/Ti3C2Tx (Tx = F, -OH) Holding Bimolecular Activation Tunnel for Enhanced Ammonia Borane Hydrolysis

Developing economical and efficient catalyst for hydrogen generation from ammonia borane (AB) hydrolysis is still a huge challenge. As an alternative strategy, the functional group regulation of metal nanoparticles (NPs)-based catalysts is believed to be capable of improving the catalytic activity. Herein, a series of Ni/Ti₃C₂T_x-Y (T_x = F, -OH; Y denotes etching time (d)) catalysts are synthesized and show remarkably enhanced catalytic activity on the hydrolysis of AB in contrast to the corresponding without regulating. The optimized Ni/Ti₃C₂T_x-4 with a turnover frequency (TOF) value of 161.0 min^-1 exhibits the highest catalytic activity among the non-noble monometallic-based catalyst. Experimental results and theory calculations demonstrate that the excellent catalytic activity benefits from the bimolecular activation channels formed by Ni NPs and Ti₃C₂T_x-Y. H₂O and AB molecules are activated simultaneously in the bimolecular activation tunnel. Bimolecular activation reduces the activation energy of AB hydrolysis, and hydrogen generation rate is promoted. This article provides a new approach to design effective catalysts and further supports the bimolecular activation model for the hydrolysis of AB.

Recent Advances in Oxidation Stable Chemistry of 2D MXenes

As an emerging star of 2D nanomaterials, 2D transition metal carbides and nitrides, named MXenes, present a large potential in various research areas owing to their intrinsic multilayer structure and intriguing physico-chemical properties. However, the fabrication and application of functional MXene-based devices still remain challenging as they are prone to oxidative degradation under ambient environment. Within this review, the preparation methods of MXenes focusing on the recent investigations on their thermal structure-stability relationships in inert, oxidizing, and aqueous environments are systematically introduced. Moreover, the key factors that affect the oxidation of MXenes, such as, atmosphere, temperature, composition, microstructure, and aqueous environment, are reviewed. Based on different scenarios, strategies for avoiding or delaying the oxidation of MXenes are proposed to encourage the utilization of MXenes in complicated environments, especially at high temperature. Furthermore, the chemistry of MXene-derived oxides is analyzed, which can offer perspectives on the further design and fabrication of novel 2D composites with the unique structures of MXenes being preserved.

Coupling of N-Doped Mesoporous Carbon and N-Ti3 C2 in 2D Sandwiched Heterostructure for Enhanced Oxygen Electroreduction

2D heterostructures provide a competitive platform to tailor electrical property through control of layer structure and constituents. However, despite the diverse integration of 2D materials and their application flexibility, tailoring synergistic interlayer interactions between 2D materials that form electronically coupled heterostructures remains a grand challenge. Here, the rational design and optimized synthesis of electronically coupled N-doped mesoporous defective carbon and nitrogen modified titanium carbide (Ti₃ C₂ ) in a 2D sandwiched heterostructure, is reported. First, a F127-polydopamine single-micelle-directed interfacial assembly strategy guarantees the construction of two surrounding mesoporous N-doped carbon monolayers assembled on both sides of Ti₃ C₂ nanosheets. Second, the followed ammonia post-treatment successfully introduces N elements into Ti₃ C₂ structure and more defective sites in N-doped mesoporous carbon. Finally, the oxygen reduction reaction (ORR) and theoretical calculation prove the synergistic coupled electronic effect between N-Ti₃ C₂ and defective N-doped carbon active sites in the 2D sandwiched heterostructure. Compared with the control 2D samples (0.87-0.88 V, 4.90-5.15 mA cm^-2 ), the coupled 2D heterostructure possesses the best onset potential of 0.90 V and limited density current of 5.50 mA cm^-2 . Meanwhile, this catalyst exhibits superior methanol tolerance and cyclic durability. This design philosophy opens up a new thought for tailoring synergistic interlayer interactions between 2D materials.

Ge Ion Implanted Photonic Devices and Annealing for Emerging Applications

Germanium (Ge) ion implantation into silicon waveguides will induce lattice defects in the silicon, which can eventually change the crystal silicon into amorphous silicon and increase the refractive index from 3.48 to 3.96. A subsequent annealing process, either by using an external laser or integrated thermal heaters can partially or completely remove those lattice defects and gradually change the amorphous silicon back into the crystalline form and, therefore, reduce the material’s refractive index. Utilising this change in optical properties, we successfully demonstrated various erasable photonic devices. Those devices can be used to implement a flexible and commercially viable wafer-scale testing method for a silicon photonics fabrication line, which is a key technology to reduce the cost and increase the yield in production. In addition, Ge ion implantation and annealing are also demonstrated to enable post-fabrication trimming of ring resonators and Mach–Zehnder interferometers and to implement nonvolatile programmable photonic circuits.