Optical Properties of Few-Layer Ti3CN MXene: From Experimental Observations to Theoretical Calculations

Ternary ReS2(1-x)Se2xalloys of different composition for Q-switched and mode-locked all-fiber laser

This paper systematically studied the composition-controlled nonlinear optical properties and pulse modulation of ternary ReS2(1-x)Se2xalloys for the first time. The compositionally modulated characteristics of ReS2(1-x)Se2xon the band gap were simulated based on the first principles. We investigated the effect of the band gap on the saturable absorption properties. In addition, we demonstrated the modulation characteristics of different components ReS2(1-x)Se2xon 1.5μm Q-switched pulse performance. The Q-switched threshold, repetition rate, and pulse duration increase as the S(sulfur)-element composition rise. And pulse energy also was affected by the S(sulfur)-element composition. The ReS0.8Se1.2SA was selected to realize a conventional soliton with high energy in the all-fiber mode-locked laser. The pulse was centered at 1562.9 nm with a pulse duration of 2.26 ps, a repetition rate of 3.88 MHz, and maximum pulse energy of 1.95 nJ. This work suggests that ReS2(1-x)Se2xhas great potential in laser technology and nonlinear optics, and widely extends the material applications in ultrafast photonics.

Advanced Insights on MXenes: Categories, Properties, Synthesis, and Applications in Alkali Metal Ion Batteries

The development and optimization of promising anode material for next-generation alkali metal ion batteries are significant for clean energy evolution. 2D MXenes have drawn extensive attention in electrochemical energy storage applications, due to their multiple advantages including excellent conductivity, robust mechanical properties, hydrophilicity of its functional terminations, and outstanding electrochemical storage capability. In this review, the categories, properties, and synthesis methods of MXenes are first outlined. Furthermore, the latest research and progress of MXenes and their composites in alkali metal ion storage are also summarized comprehensively. A special emphasis is placed on MXenes and their hybrids, ranging from material design and fabrication to fundamental understanding of the alkali ion storage mechanisms to battery performance optimization strategies. Lastly, the challenges and personal perspectives of the future research of MXenes and their composites for energy storage are presented.

Charge-transfer-driven ultrasensitive SERS sensing in a two-dimensional titanium carbonitride MXene

Two-dimensional (2D) MXenes stand out as promising platforms for surface-enhanced Raman scattering (SERS) sensing owing to their metallic feature, various compositions, high surface area, compatibility with functionalization, and ease of fabrication. In this work, we report a high-performance 2D titanium carbonitride (Ti3CN) MXene SERS substrate. We reveal that the abundant electronic density of states near the Fermi level of Ti3CN MXene boosts the efficiency of photo-induced charge transfer at the interface of Ti3CN/molecule, resulting in significant Raman enhancement. The SERS sensitivity of Ti3CN MXene is further promoted through a 2D morphology regulation and molecular enrichment strategies. Moreover, prohibited drugs are detectable on this substrate, presenting the potential of trace-amount analysis on Ti3CN MXene. This work provides a deep insight of the SERS mechanisms of Ti3CN MXene and broadens the practical application of transition metal carbonitride MXene SERS substrates.

Influence of MXene Composition on Triboelectricity of MXene-Alginate Nanocomposites

MXenes are highly versatile and conductive 2D materials that can significantly enhance the triboelectric properties of polymer nanocomposites. Despite the growing interest in the tunable chemistry of MXenes for energy applications, the effect of their chemical composition on triboelectric power generation has yet to be thoroughly studied. Here, we investigate the impact of the chemical composition of MXenes, specifically the Ti3CNTx carbonitride vs the most studied carbide, Ti3C2Tx, on their interactions with sodium alginate biopolymer and, ultimately, the performance of a triboelectric nanogenerator (TENG) device. Our results show that adding 2 wt % of Ti3CNTx to alginate produces a synergistic effect that generates a higher triboelectric output than the Ti3C2Tx system. Spectroscopic analyses suggest that a higher oxygen and fluorine content on the surface of Ti3CNTx enhances hydrogen bonding with the alginate matrix, thereby increasing the surface charge density of the alginate oxygen atoms. This was further supported by Kelvin probe force microscopy, which revealed a more negative surface potential on Ti3CNTx-alginate, facilitating high charge transfer between the TENG electrodes. The optimized Ti3CNTx-alginate nanogenerator delivered an output of 670 V, 15 μA, and 0.28 W/m2. Additionally, we demonstrate that plasma oxidation of the MXene surface further enhances triboelectric performance. Due to the diverse surface terminations of MXene, we show that Ti3CNTx-alginate can function as either tribopositive or tribonegative material, depending on the counter-contacting material. Our findings provide a deeper understanding of how MXene composition affects their interaction with biopolymers and resulting tunable triboelectrification behavior. This opens up new avenues for developing flexible and efficient MXene-based TENG devices.

Two-Dimensional Molybdenum Boride (MBene) Mo4/3B2Tx with Broadband and Termination-Dependent Ultrafast Nonlinear Optical Response

Two-dimensional molybdenum borides (MBenes) comprise a new class of 2D transition metal borides that exhibit potential photonics applications. Recently, the synthesis of individual single-layer Mo4/3B2Tx (T = O, F, OH) MBene sheets has been realized, which attracted considerable attention in optoelectronics. However, there is still a lack of understanding and regulation of the photophysical processes of Mo4/3B2Tx MBene. Here, we demonstrate that Mo4/3B2Tx MBene exhibits a surface termination-dependent electronic structure, carrier dynamics, and nonlinear optical response over a wide wavelength range (500-1550 nm). As prepared 2D Mo4/3B2F2 MBene possesses a semimetal material property that exhibits a shorter intraband scattering process (<100 ps) and a considerable nonlinear optical response at a broadband cover optical communication C band at 1550 nm. These thrilling results are confirmed theoretically and experimentally. The analysis of these results adds to the regulating and understanding of the basic photophysical processes, which is anticipated to be beneficial for the further design of MBene-based photonics and nanoelectronics devices.

Enhancement of MXene optical properties towards medical applications via metal oxide incorporation

MXenes have garnered research attention in the field of biomedical applications due to their unique properties, such as a large surface area, low toxicity, biocompatibility, and stability. Their optical behavior makes them versatile for a wide range of biomedical applications, from diagnostics to therapeutics. Nonetheless, MXenes have some minor limitations, including issues with restacking, susceptibility to oxidation, and a non-semiconducting nature. These limitations have prompted researchers to explore the incorporation of metal oxides into MXene structures. Metal oxides possess advantageous properties such as a high surface area, biocompatibility, intriguing redox behavior, catalytic activity, semiconducting properties, and enhanced stability. Incorporating metal oxides into MXenes can significantly improve their conductivity, surface area, and mechanical strength. In this review, we emphasize the importance of incorporating metal oxides into MXenes for light-influenced biomedical applications. We also provide insights into various preparation methods for incorporating metal oxides into MXene structures. Furthermore, we discuss how the incorporation of metal oxides enhances the optical behavior of MXenes. Finally, we offer a glimpse into the future potential of metal oxide-incorporated MXenes for diverse biomedical applications.

Radiation-Induced Surface Modification of MXene with Ionic Liquid to Improve Electrochemical Properties and Chemical Stability

For the first time, an ionic liquid was grafted onto Ti3C2Tx MXene interlayers (MXene-g-IL) using a radiation technique. The IL was tightly immobilized on the surface of MXene nanosheets via chemical linkage, which exhibited excellent specific capacitance (160 F g-1 at 5 mV s-1) and improved structural stability (maintaining the sheet-like structure for 180 days). The facile, efficient, and scalable synthetic strategy derived from the radiation technique can open a new avenue for covalent functionalization of MXene-based materials and promote their further application.

Ambient Processed rGO/Ti3CNTx MXene Thin Film with High Oxidation Stability, Photosensitivity, and Self-Cleaning Potential

Solution-based processing offers advantages for producing thin films due to scalability, low cost, simplicity, and benignity to the environment. Here, we develop conductive and photoactivated self-cleaning reduced graphene oxide (rGO)/Ti3CNTx MXene thin films via spin coating under ambient conditions. The addition of a thin rGO layer on top of Ti3CNTx resulted in up to 45-fold improvement in the environmental stability of the film compared to the bare Ti3CNTx film. The optimized rGO/Ti3CNTx thin film exhibits an optical transmittance of 74% in the visible region of the spectrum and a sheet resistance of 19 kΩ/sq. The rGO/Ti3CNTx films show high rhodamine B discoloration activity upon light irradiation. Under UV irradiation, the electrically conductive MXene in combination with in situ formed semiconducting titanium oxide induces photogenerated charge carriers, which could potentially be used in photocatalysis. On the other hand, due to film transparency, white light irradiation can bleach the adsorbed dye via photolysis. This study opens the door for using MXene thin films as multifunctional coatings with conductive and potentially self-cleaning properties.

Bismuth Nano-Nest/Ti3CN Quantum Dot-Based Surface Plasmon Coupling Electrochemiluminescence Sensor for Ascites miRNA-421 Detection

In this study, a novel surface plasmon-coupled electrochemiluminescence (SPC-ECL) biosensor was developed based on bismuth nano-nest and Ti₃CN quantum dots (Ti₃CN QDs). First, MXene derivative QDs (Ti₃CN QDs) with excellent luminescence performance were prepared as the ECL luminescent. The N doping in Ti₃CN QDs can effectively improve the luminescence performance and catalytic activity. Therefore, the luminescence performance of QDs has been effectively improved. Furthermore, the bismuth nano-nest structure with a strong localized surface plasmon resonance effect has been designed as the sensing interface via the electrochemical deposition method. It was worth noticed that the morphology of bismuth nanomaterials can be controlled effectively on the electrode surface by the step potential method. Due to the abundant surface plasmon hot spots generated between the bismuth nano-nests, the isotropic ECL signal of Ti₃CN QDs can be not only significantly enhanced by 5.8 times but also converted into polarized emission. Finally, the bismuth nano-nest/Ti₃CN QD-based SPC-ECL sensor was used to quantify miRNA-421 in the range of 1 fM to 10 nM. The biosensor has been successfully used for miRNA in ascites samples from gastric cancer patients, which indicated that the SPC-ECL sensor developed in this study has great potential for clinical analysis.

Surface hopping modeling of charge and energy transfer in active environments

An active environment is any atomic or molecular system changing a chromophore's nonadiabatic dynamics compared to the isolated molecule. The action of the environment on the chromophore occurs by changing the potential energy landscape and triggering new energy and charge flows unavailable in the vacuum. Surface hopping is a mixed quantum-classical approach whose extreme flexibility has made it the primary platform for implementing novel methodologies to investigate the nonadiabatic dynamics of a chromophore in active environments. This Perspective paper surveys the latest developments in the field, focusing on charge and energy transfer processes.

Roles of MXenes in biomedical applications: recent developments and prospects

....With the development of nanomedical technology, the application of various novel nanomaterials in the biomedical field has been greatly developed in recent years. MXenes, which are new inorganic nanomaterials with ultrathin atomic thickness, consist of layered transition metal carbides and nitrides or carbonitrides and have the general structural formula M_n+1X_nT_x (n = 1-3). Based on the unique structural features of MXenes, such as ultrathin atomic thickness and high specific surface area, and their excellent physicochemical properties, such as high photothermal conversion efficiency and antibacterial properties, MXenes have been widely applied in the biomedical field. This review systematically summarizes the application of MXene-based materials in biomedicine. The first section is a brief summary of their synthesis methods and surface modification strategies, which is followed by a focused overview and analysis of MXenes applications in biosensors, diagnosis, therapy, antibacterial agents, and implants, among other areas. We also review two popular research areas: wearable devices and immunotherapy. Finally, the difficulties and research progress in the clinical translation of MXene-based materials in biomedical applications are briefly discussed.

Cathode materials for lithium-sulfur battery: a review

Lithium-sulfur batteries (LSBs) are considered to be one of the most promising candidates for becoming the post-lithium-ion battery technology, which would require a high level of energy density across a variety of applications. An increasing amount of research has been conducted on LSBs over the past decade to develop fundamental understanding, modelling, and application-based control. In this study, the advantages and disadvantages of LSB technology are discussed from a fundamental perspective. Then, the focus shifts to intermediate lithium polysulfide adsorption capacity and the challenges involved in improving LSBs by using alternative materials besides carbon for cathode construction. Attempted alternative materials include metal oxides, metal carbides, metal nitrides, MXenes, graphene, quantum dots, and metal organic frameworks. One critical issue is that polar material should be more favorable than non-polar carbonaceous materials in the aspect of intermediate lithium polysulfide species adsorption and suppress shuttle effect. It will be also presented that by preparing cathode with suitable materials and morphological structure, high-performance LSB can be obtained.

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Nonlinear Absorption Response of Zirconium Carbide Films

Zirconium carbide (ZrC), a novel representative of the MXene family, has attracted considerable interest because of its outstanding physicochemical properties and potential applications in optoelectronic devices. For improving its performance as an optical modulator for ultrashort lasers, there is a call to continue studying the nonlinear optical behavior of MXene ZrC. Herein, for the first time, MXene ZrC films were fabricated on fused silica by magnetron sputtering deposition technology and used as a saturable absorber (SA) optical modulator in a passive Q-switched Nd:YAG laser. The saturation absorption behaviors of the prepared ZrC films were characterized by the Z-scan method. Their morphology, band structure, damage threshold, carrier recovery time, and saturation absorption properties were analyzed. The experimental results show that the MXene ZrC SA films exhibit excellent nonlinear optical characteristics, with a saturation intensity of 48.4 MW/cm², a large modulation depth of 6.9%, and an ultrashort recovery time of 2.72 ps. In addition, the damage threshold of MXene ZrC SA films was estimated to be greater than 0.2516 J/cm². By integrating the ZrC SA film optical modulator into the oscillator of the Nd:YAG laser, we achieved stable operation of the Q-switched laser with a central wavelength at 1.06 μm, with the shortest pulse width of 78 ns. The results of this study demonstrate the potential use of MXene ZrC SA films as optical modulators in ultrashort lasers.

Plasmonic optical fiber gratings based on few-layer Ta2C MXenes for refractive index sensing

Tilted fiber Bragg grating (TFBG) is a widespread approach for developing refractive index (RI) sensors. The unique optoelectronic properties exhibited by MXene are expected to enhance the performance of TFBG-SPR sensors. In this study, a Ta₂C coating appropriate for sensing was obtained by optimizing the photo-deposition time, which addressed the challenge of preparing large areas of MXene. The uniform coating of the few-layer Ta₂C increases the wavelength sensitivity and FOM of the sensor to 229.5 nm/RIU and 2228.15 respectively. This significant enhancement was attributed to an ordered MXene phase of the grown Ta₂C. The energy band theory verified the metallic nature of the Ta₂C and the amplification effect on the RI response. Finite element analysis demonstrated that the stronger absorption band of Ta₂C facilitated the generation of surface plasmon polariton. Based on the above benefits, the sensor detected melamine in milk with a detection limit of 7.9 × 10^-9M. The TFBG/Au/Ta₂C sensor is a promising approach for biochemical analysis and trace detection.

van der Waals integration of mixed-dimensional CeO2@Bi heterostructure for high-performance self-powered photodetector with fast response speed

Heterostructures have been extensively investigated for optoelectronic devices owing to their fantastic physicochemical properties. Herein, a mixed-dimensional van der Waals heterostructure (vdWH) CeO₂@Bi, 1D ceria (CeO₂) loaded with 0D bismuth quantum dots (Bi QDs), is synthesized through a facile hydrothermal bottom-up method. It is found that the fabricated CeO₂@Bi-based photoelectrochemical (PEC)-type photodetector (PD) shows self-powered photodetection capability with a fast photoresponse speed of 0.02 s. Besides, a photocurrent of 2.00 μA cm^-2 and a photoresponsivity of 888.89 μA W^-1 under 365 nm illumination are obtained. Furthermore, good long-term cycle stability is also observed after 1 month in a harsh environment, indicating the great potential for practical applications. These results are further supported by density functional theory (DFT) calculations. We believe that the presented work is expected to provide a new pathway for the future utilization of vdWHs for high-performance optoelectronics.

Mixed-dimensional V2CTx/Ti3C2Tx composite interlayer to boost electrochemical performance of Li-S batteries

Abstract: A mixed-dimensional V₂CT_x/Ti₃C₂T_x composite interlayer was successfully prepared to tackle severe polysulfide (LiPS) shuttling and sluggish sulfur redox kinetics for high-performance lithium–sulfur batteries. In the unique nanoarchitecture, two-dimensional Ti₃C₂T_x nanosheets served as a stable skeleton with superb electronic conductivity, good mechanical strength, and high polysulfide adsorption, whereas one-dimensional V₂CT_x nanorods played a crucial role in chemisorbing LiPSs and catalyzing the conversion of LiPSs due to their high polarity and electrocatalysis. With the synergistic effect of V₂CT_x and Ti₃C₂T_x composite nanostructures, the cells with the mixed-dimensional V₂CT_x/Ti₃C₂T_x composite interlayer showed an impressive long-term cycling stability and small capacity decay rate of 0.062% per cycle over 600 cycles at 1 C and exhibited an outstanding rate capability of 935.3 mAh·g⁻¹ at 2 C.

Intercalation of Nanoscale Multiferroic Spacers between the Two-Dimensional Interlayers of MXene

We report a facile synthesis of MXene/bismuth ferrite (Ti₃C₂T _x @ BiFeO₃) nanocomposites using hydrazine hydrate induced with the hydrothermal method. Preparation of the composite with hydrazine hydrate prevents the formation of Bi₂₅FeO₃₉ inside the matrix. The 25 wt % loading of BiFeO₃ acts as spacers for the multilayer restacking of MXene flakes by retaining the (002) plane. This promotes large dc conductivity with interfacial and defect dipole polarization mechanisms inside the composite material. The thinner M-H loop also indicates the minimal magnetic loss inside the composites. The facile synthesis strategy provides outstanding properties in Ti₃C₂T _x @ BiFeO₃ composites as two-dimensional multiferroic materials.