Synthesis and applications of MXene-based composites: a review

Tailoring the ion storage of MXene by aramid nanofibers towards self-standing electrodes for flexible solid-state supercapacitors

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) are a class of 2D nanomaterials that can offer excellent properties for high-performance supercapacitors. Nevertheless, irreversible restacking of MXene sheets decreases the interlayer spacing, which inhibits the ion intercalation between the MXene nanosheets and finally deteriorates the electrochemical performance of supercapacitors. Herein, aramid nanofibers (ANFs) are mixed with Ti3C2TxMXene to prepare MXene/ANFs composite films. The restacking of MXene sheets is inhibited by the electrostatic repulsion between ANFs and MXene. The ANFs act as intercalation agents to increase the interlayer spacing of the composite films, which can improve the ion storage ability of supercapacitors. Furthermore, the ANFs enhance the mechanical strength of the composite films due to the strong hydrogen bonding interaction and nanomechanical interlocking between ANFs and MXene, endowing the composite films with self-standing property. The resultant composite films are used as electrodes for flexible solid-state supercapacitors to achieve high specific capacitance (996.5 mF cm-2at 5 mV s-1) and outstanding cycling stability. Thus, this work provides a potential strategy to regulate the properties of 2D nanomaterials, which may expand the application of them in energy storage, ionic separation, osmotic energy conversion and beyond.

MXene: A wonderful nanomaterial in antibacterial

Increasing bacterial infections and growing resistance to available drugs pose a serious threat to human health and the environment. Although antibiotics are crucial in fighting bacterial infections, their excessive use not only weakens our immune system but also contributes to bacterial resistance. These negative effects have caused doctors to be troubled by the clinical application of antibiotics. Facing this challenge, it is urgent to explore a new antibacterial strategy. MXene has been extensively reported in tumor therapy and biosensors due to its wonderful performance. Due to its large specific surface area, remarkable chemical stability, hydrophilicity, wide interlayer spacing, and excellent adsorption and reduction ability, it has shown wonderful potential for biopharmaceutical applications. However, there are few antimicrobial evaluations on MXene. The current antimicrobial mechanisms of MXene mainly include physical damage, induced oxidative stress, and photothermal and photodynamic therapy. In this paper, we reviewed MXene-based antimicrobial composites and discussed the application of MXene in bacterial infections to guide further research in the antimicrobial field.

Recent Advances and Strategies in MXene-Based Electrodes for Supercapacitors: Applications, Challenges and Future Prospects

With the growing demand for technologies to sustain high energy consumption, supercapacitors are gaining prominence as efficient energy storage solutions beyond conventional batteries. MXene-based electrodes have gained recognition as a promising material for supercapacitor applications because of their superior electrical conductivity, extensive surface area, and chemical stability. This review provides a comprehensive analysis of the recent progress and strategies in the development of MXene-based electrodes for supercapacitors. It covers various synthesis methods, characterization techniques, and performance parameters of these electrodes. The review also highlights the current challenges and limitations, including scalability and stability issues, and suggests potential solutions. The future outlooks and directions for further research in this field are also discussed, including the creation of new synthesis methods and the exploration of novel applications. The aim of the review is to offer a current and up-to-date understanding of the state-of-the-art in MXene-based electrodes for supercapacitors and to stimulate further research in the field.

MXenes vs. clays: emerging and traditional 2D layered nanoarchitectonics

Although MXene materials are considered an emerging research topic, they are receiving considerable interest because, like metals and graphene, they are good electronic conductors but with the particularity that they have a marked hydrophilic character. Having a structural organization and properties close to those of clay minerals (natural silicates typically with a lamellar morphology), they are sometimes referred to as "conducting clays" and exhibit colloidal, surface and intercalation properties also similar to those of clay minerals. The present contribution aims to inform and discuss the nature of MXenes in comparison with clay phyllosilicates, taking into account their structural analogies, outstanding surface properties and advanced applications. The current in-depth understanding of clay minerals may represent a basis for the future development of MXene-derived nanoarchitectures. Comparative examples of the preparation, and studies on the properties and applications of various nanoarchitectures based on clays and MXenes have been included in the present work.

Progress of 2D MXene as an Electrode Architecture for Advanced Supercapacitors: A Comprehensive Review

Supercapacitors, designed to store more energy and be proficient in accumulating more energy than conventional batteries with numerous charge-discharge cycles, have been developed in response to the growing demand for energy. Transition metal carbides/nitrides called MXenes have been the focus of researchers' cutting-edge research in energy storage. The 2D-layered MXenes are a hopeful contender for the electrode material due to their unique properties, such as high conductivity, hydrophilicity, tunable surface functional groups, better mechanical properties, and outstanding electrochemical performance. This newly developed pseudocapacitive substance benefits electrochemical energy storage because it is rich in interlayer ion diffusion pathways and ion storage sites. Making MXene involves etching the MAX phase precursor with suitable etchants, but different etching methods have distinct effects on the morphology and electrochemical properties. It is an overview of the recent progress of MXene and its structure, synthesis, and unique properties. There is a strong emphasis on the effects of shape, size, electrode design, electrolyte behavior, and other variables on the charge storage mechanism and electrochemical performance of MXene-based supercapacitors. The electrochemical application of MXene and the remarkable research achievements in MXene-based composites are an intense focus. Finally, in light of further research and potential applications, the challenges and future perspectives that MXenes face and the prospects that MXenes present have been highlighted.

MXene-modified electrodes and electrolytes in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have attracted much attention as promising tools in renewable energy conversion technology. This is mainly because of their beneficial qualities, such as their impressive efficiency levels and low-cost fabrication techniques. An overview of MXene-modified electrodes in DSSCs is given in this review article. MXenes are two-dimensional (2D) transition metal carbides or nitrides with remarkable properties such as high conductivity and large surface area. MXenes' properties make them an appealing material for various applications, including energy storage, catalysis, and electronic devices. MXene integration enhances ion transport, dye adsorption, and charge transport in DSSC electrodes. In-depth analysis of the use of 2D Mxene and integration with carbon nanotubes (CNTs), reduced graphene oxide (rGO), 2D MoS2, and hybrids like 2D-2D heterostructures for electrode modification in photovoltaics (PVs), including anodes, photoanodes, composite decorated electrodes, counter electrodes (CEs), and electrolytes, is provided in this review article. The effects on the performance metrics of various deposition techniques are discussed and assessed. The use of MXene-modified electrodes in DSSCs suggests potential for enhancing the performance and efficiency of these solar cells in general. The article examines this strategy's potential advantages and implications, illuminating the fascinating advancements in the area and emphasizing MXenes' potential as a valuable substance for renewable energy applications. We also discuss the difficulties and potential benefits of using MXene-modified electrodes in DSSCs and emphasize the need for additional study to enhance stability, optimize MXene integration techniques, and enhance long-term device performance. The scalability and potential of MXene-based electrode modifications for commercial applications are also covered, addressing issues and prospects for the future, focusing on the necessity of more study. Electrodes modified with MXenes can improve DSSC performance and advance sustainable energy conversion.

Controlled synthesis and photocatalytic hydrogen evolution activities of cobalt carbides with different phase compositions

Cobalt carbides are emerging as promising materials for various magnetic and catalytic applications. However, exploring dedicated cobalt carbides with optimal catalytic properties via adjusting phase compositions remains a significant challenge. Herein, three different cobalt carbides, CoxC (Co2C-Co3C), Co2C-Co, and Co3C, were successfully prepared using a facile one-pot green method. The phase compositions of cobalt carbides could be easily controlled by varying the cobalt-based precursors and carbon sources. More remarkably, three different cobalt carbides could serve as reduction cocatalysts decorated CdS for improved hydrogen production under visible light. Intriguingly, the obtained Co3C/CdS nanocomposite displayed the highest photocatalytic hydrogen evolution activity among the three composites and superior photocatalytic stability. This work provides a fundamental approach to tuning the photocatalytic properties of cobalt carbides for energy conversion fields.

Role of MXenes in advancing soft robotics

MXenes with their unique electronic, optical, chemical, and mechanical properties have shown great promise in soft robotics. MXene-based soft actuators have been designed to display ultrafast actuations and recovery speeds as well as angle-independent structural colors in response to vapor. Several studies have developed soft actuators by combining MXenes with other materials to mimic the movement of natural organisms. Thus, MXene-based soft actuators have the potential to revolutionize the field of soft robotics and flexible electronics (e.g., wearable devices and artificial muscles). MXene-based artificial muscles have been explored for use in kinetic soft robotics as actuators in microsystems requiring exceptional compliance. MXene-based sensors and actuators have already been developed for human-like sensors and photodetection. However, there are still challenges that need to be addressed in such applications, such as the design of stretchable and compliant robotic skins with a high-level functional integration for soft robotics. The integration of various devices, such as power sources, sensors, and actuators, into soft robotics is another crucial challenge. Despite the excellent stretchability and tensile strength of MXene-based composites, there is a vital need to develop their mechanical and electrochemical features and grant them multi-functionalities. Herein, recent developments pertaining to the applications of MXenes and their composites in soft robotics are discussed with a focus on the important challenges and future perspectives.

Advances in MXene-Based Electrochemical (Bio)Sensors for Neurotransmitter Detection

Neurotransmitters are chemical messengers that play an important role in the nervous system's control of the body's physiological state and behaviour. Abnormal levels of neurotransmitters are closely associated with some mental disorders. Therefore, accurate analysis of neurotransmitters is of great clinical importance. Electrochemical sensors have shown bright application prospects in the detection of neurotransmitters. In recent years, MXene has been increasingly used to prepare electrode materials for fabricating electrochemical neurotransmitter sensors due to its excellent physicochemical properties. This paper systematically introduces the advances in MXene-based electrochemical (bio)sensors for the detection of neurotransmitters (including dopamine, serotonin, epinephrine, norepinephrine, tyrosine, NO, and H₂S), with a focus on their strategies for improving the electrochemical properties of MXene-based electrode materials, and provides the current challenges and future prospects for MXene-based electrochemical neurotransmitter sensors.