Selective Calixarene-Directed Synthesis of MXene Plates, Crumpled Sheets, Spheres, and Scrolls

1D MXenes: Synthesis, Properties, and Applications

The fascinating properties and versatile nature of 2D MXenes have generated significant interest in the scientific community. This has led to extensive research on expanding these materials into 1D and 0D forms. This review investigates the synthesis, properties, and applications of 1D MXenes, elucidating their potential across various fields. 1D MXenes, including nanowires, nanoribbons, nanorods, and nanotubes, inherit the remarkable properties of their 2D counterparts while also exhibiting unique anisotropic characteristics that enhance their performance in various applications. The review explores various methods for synthesizing 1D MXenes and examines their structural, electronic, and optical properties. The transition from 2D to 1D results in MXenes that offer superior properties, which are advantageous for various next-generation systems. The increased aspect ratio and surface area of 1D MXenes broaden their usage in energy storage, photothermal therapy, oxygen evolution reactions (OER), hydrogen evolution reactions (HER), oxygen reduction reactions (ORR), microwave absorption, filtration membranes, gas sensors, metal detection, etc. The review also addresses the challenges associated with 1D MXenes, such as limited synthesis methods, scalable production, size customization, preservation of structural integrity, and stability. Furthermore, potential opportunities and future directions in the field of 1D MXenes have also been proposed.

Enhancing the Ag-loading capacity on Ti3C2Tx sheets as hybrid fillers to form composite coatings with excellent antibacterial properties

The settlement of microorganisms is an unwanted process in various practical fields, where also the first attaching microorganisms could promote other bacterial adhesion, causing an acceleration of bioaccumulation on the solid surface and damage to the surface functions. Developing an advanced composite coating with anti-microorganism attachment features is still a big challenge, and the critical element in any such method is to find an efficient functional agent for use in the coating system that could extend the service period. MXenes have received increasing attentions owing to their unique layer structure and large specific surface area. Increasing studies have been devoted to the development of MXene/polymer composites with creatively designed structures to realize various specific functions. Herein, two-dimensional (2D) transition metal carbide material MXene as a carrier was etched and decorated with cellulose to enhance the anchor points to grasp functional Ag nanoparticles via a simple method. The MXene nanosheets (Ti3C2Tx) were modified by cellulose to graft hydroxy groups on their surface, and then they were incorporated into silver nanoparticles (Ag NPs). The results showed that the cellulose could increase the loading content of the Ag NPs on the MXene surface, and also could act as a stabilized material to form the composite filler MXene@cellulose@Ag NPs (MAC), which could serve as a functional agent. Furthermore, the obtained product MAC filler exhibited excellent dispersibility and stability among all the tested fillers (MXene and MA), and it could help avoid aggregation and promote homogenous dispersal in the coating network. Besides, MAC displayed outstanding antibacterial activities against E. coli and S. aureus at the same concentration among all the fillers. When the filler was embedded into the coating system, the composite coating PCB-MAC possessed abundant active Ag+ ions released by the Ag NPs, which could work against bacterial growth and achieve a favorable antibacterial inhibition effect. Therefore, we believe that the active MAC filler maintained high antibacterial efficiency, evincing its potential as a desirable agent for obtaining an excellent anti-adhesive behavior in numerous broad applications, such as the environment field or medical area.

MXenes Functionalized with Macrocyclic Hosts: From Molecular Design to Applications

Two-dimensional (2D) MXene has aroused wide attention for its excellent physical and chemical properties. The interlayer engineering formed by layer-by-layer stacking of MXene nanosheets can be employed for molecular sieving and water purification by incorporating specific groups onto the exterior surface of MXene. Macrocyclic hosts exhibiting unique structural features and recognition ability can construct smart devices for external stimuli with reversible features between macrocycles and guests. On that basis, macrocyclic hosts can be anchored to MXene to provide numerous insights into their compositions and intercalation states. In this review, the MXene prepared based on macrocyclic hosts from molecular design to applications is highlighted. Various MXenes functionalized with macrocyclic hosts are empowered in functional membrane (including water purification, organic solvent nanofiltration, and electromagnetic shielding), photocatalysis, sensing, and adsorption (interactions with specific guest). Hopefully, this review can bring new inspiration to the design of multifunctional MXene-based materials and improving its practical applications.

High-efficiency and simple synthesis of Ti3C2T x nanoscrolls by surface energy modulation and cryogenic freezing

To alleviate the restacking issue of 2D Ti₃C₂T _x itself, we purposefully explore a simple but efficient method for controllable construction of 1D Ti₃C₂T _x nanoscrolls with a high efficiency of ∼90.5%, with detailed regulation of the feed concentrations and surface energy of Ti₃C₂T _x . The involved transformation mechanism from 2D nanosheets to 1D nanoscrolls is reasonably proposed.

Ascorbic acid-induced fiber-scrolling of titanium carbide Ti3C2T x MXene

Changing the morphology of two-dimensional materials often offers an efficient and effective means to exploit their electronic and mechanical properties. Two-dimensional materials such as graphene can be scrolled into one-dimensional fibers via simple sonication. Unfortunately, scrolling MXene nanosheets into fibers is quite challenging, especially Ti₃C₂T _x composed of three layers of titanium atoms and two layers of carbon atoms. Herein, we report a new method to fabricate MXene fibers via ascorbic acid (AA) induced scrolling of Ti₃C₂T _x nanosheets. An unusual AA-Ti₃C₂T _x interaction is discovered in that intercalated AA molecules bind to and interact with the Ti₃C₂T _x surface in the form of a hydrogen bonding-bonded assembly instead of as individual molecules, and a sheet-scrolling mechanism is proposed based on this interaction. The as-obtained MXene fibers exhibit a compact cross-section, and the diameter can be tailored from hundreds of nanometers to several micrometers through tuning the MXene/AA ratio. Moreover, the storage modulus of the MXene-fiber sponge attains its maximum value of ∼1 MPa when a unique morphology comprising both fibers and not-yet-scrolled sheets is presented. This work offers a new strategy of fiber-shaping MXenes for applications in structural composites and flexible electronics.

The 10th anniversary of MXenes: Challenges and prospects for their surface modification toward future biotechnological applications

A broad family of two-dimensional (2D) materials - carbides, nitrides, and carbonitrides of early transition metals, called MXenes, became a newcomer in the flatland at the turn of 2010 and 2011 (over ten years ago). Their unique physicochemical properties made them attractive for many applications, highly boosting the development of various fields, including biotechnological. However, MXenes' functional features that impact their bioactivity and toxicity are still not fully well understood. This study discusses the essentials for MXenes's surface modifications toward their application in modern biotechnology and nanomedicine. We survey modification strategies in context of cytotoxicity, biocompatibility, and most prospective applications ready to implement in medical practice. We put the discussion on the material-structure-chemistry-property relationship into perspective and concentrate on overarching challenges regarding incorporating MXenes into nanostructured organic/inorganic bioactive architectures. It is another emerging group of materials that are interesting from the biomedical point of view as well. Finally, we present an influential outlook on the growing demand for future research in this field.

Hydrothermal-Assisted Synthesis and Stability of Multifunctional MXene Nanobipyramids: Structural, Chemical, and Optical Evolution

Recent advancements in two-dimensional materials have brought MXene (Ti₃C₂) into attention due to its exciting properties as a very promising material for various applications. In this work, we report a novel Ti₃C₂ nanobipyramid (Ti₃C₂ NB) structure obtained through a three-step process involving exfoliation, delamination, and subsequent hydrothermal treatment. The morphological and textural properties at each step of synthesis were studied using an array of experimental techniques such as transmission electron microscopy, scanning electron microscopy, and atomic force microscopy and the chemical properties through X-ray diffraction, Raman, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis. The Ti₃C₂ NBs exhibit fluorescence with an excitation-dependent emission. Further, the effect of temperature and pH on the fluorescence was also investigated, which opens up its scope in bioanalytical applications. Ti₃C₂ NBs showed a ∼43% increase in photoluminescence intensity from pH 3 to 11 while a ∼38% increase with the temperature from 20 to 80 °C. Usually, MXenes are highly susceptible to oxidation, but the Ti₃C₂ NBs were found to be chemically and optically stable even after 30 days. Bestowed with good hydrophilicity, the material exhibited high biocompatibility on the mouse fibroblast cell line L929. Further, L929 cells also showed good cellular adhesion on a Ti₃C₂ NB-modified glass substrate. These properties pave a way for its multifunctional ability as a sensor for pH and temperature as well as bioimaging.

Exploring the Influence of Critical Parameters for the Effective Synthesis of High-Quality 2D MXene

Recently, a new class of two-dimensional (2D) materials, called MXene, consisting of layers of transition-metal carbides and nitrides/carbonitrides has been introduced. MXene, a multifunctional material with hydrophilic nature and excellent electrical conductivity and chemical stabilities, can be applied in diverse research areas such as energy harvesting and its storage, water purification, thermal dissipation, and gas sensing. To achieve the best quality of MXene, optimization of some important synthetic parameters is highly required such as an optimized etchant concentration to remove an "A" element from the MAX phase and sonication time for the efficient exfoliation of MXene flakes. Besides, there is a need to disclose that particular solvent through which intercalation can easily be achieved. In this work, we optimized the abovementioned critical parameters for the synthesis of good-quality MXene. Our results clearly explain the variations in the quality of MXene under applied etchant concentrations, solvents for better intercalation, and optimization of sonication time for better exfoliation. The obtained results suggest that 30% HF as an etchant, dimethyl sulfoxide (DMSO) as a solvent, and 135 min as the sonication time are effective parameters for the synthesis of good-quality MXene. We expect that this report will be helpful for the young research community to synthesize good-quality MXene with the required properties.

Continuous flow vortex fluidic-mediated exfoliation and fragmentation of two-dimensional MXene

MXene (Ti₂CT _x ) is exfoliated in a vortex fluidic device (VFD), as a thin film microfluidic platform, under continuous flow conditions, down to ca 3 nm thin multi-layered two-dimensional (2D) material, as determined using AFM. The optimized process, under an inert atmosphere of nitrogen to avoid oxidation of the material, was established by systematically exploring the operating parameters of the VFD, along with the concentration of the dispersed starting material and the choice of solvent, which was a 1 : 1 mixture of isopropyl alcohol and water. There is also some fragmentation of the 2D material into nanoparticles ca 68 nm in diameter.

Chemical Functionalisation of 2D Materials by Batch and Continuous Hydrothermal Flow Synthesis

2D materials are single or few layered materials consisting of one or several elements with a thickness of a few nanometres. Their unique, tuneable physical and chemical properties including ease of chemical functionalisation makes this class of materials useful in a variety of technological applications. The feasibility of 2D materials strongly depends on better synthetic approaches to improve properties, increase performance, durability and reduce costs. As such, in the synthesis of nanomaterials, hydrothermal processes are widely adopted through a precursor-product synthesis route. This method includes batch or continuous flow systems, both employing water at elevated temperatures (above boiling point) and pressures to fine-tune the physical, chemical, optical and electronic properties of the nanomaterial. Both techniques yield particles with different morphology, size and surface area due to different mechanisms of particle formation. In this Minireview, we present batch and continuous hydrothermal flow synthesis of a selection of 2D derivatives (graphene, MXene and molybdenum disulfide), their chemical functionalisation as an advantageous approach in exploring properties of these materials as well as the benefits and challenges of employing these processes, and an outlook for further research.

Facile Preparation of Hierarchical AgNP-Loaded MXene/Fe3O4/Polymer Nanocomposites by Electrospinning with Enhanced Catalytic Performance for Wastewater Treatment

MXene as a kind of two-dimensional nanomaterial has aroused people's strong research interest because of its excellent properties. In the present study, we introduced a new poly(vinyl alcohol)/poly(acrylic acid)/Fe3O4/MXene@Ag nanoparticle composite film fabricated by electrospinning and heat treatment as well as self-reduction reaction process. The obtained composite films showed high self-reduction ability because of the incorporation of MXene flakes. The intercalated MXene flakes in the composite nanofibers were evenly distributed, which not only solved the aggregation problem from MXene dispersion but also could self-reduce Ag nanoparticles in situ in composite materials. In addition, the composite nanofiber films exhibited good fiber structure, thermal stability, and magnetic properties. Moreover, the composite nanofiber films demonstrated excellent catalytic ability and cycle stability to 4-nitrophenol and 2-nitroaniline.

Applications of 2D MXenes in energy conversion and storage systems

This article provides a comprehensive review of MXene materials and their energy-related applications.

Promoting Role of MXene Nanosheets in Biomedical Sciences: Therapeutic and Biosensing Innovations

MXene nanosheets have emerged as biocompatible transition metal structures, which illustrate desirable performance for various applications due to their unique structural, physicochemical, and compositional features. MXenes are currently expanding their usage territory from mechanical, optical, chemical, and electronic fields toward biomedical areas. This is mainly originated from their large surface area and strong absorbance in near-infrared region, which in combination with their facile surface functionalization with various polymers or nanoparticles, make them promising nanoplatforms for drug delivery, cancer therapy, precise biosensing and bioimaging. The facile surface modification of the MXenes can mediate the better in vivo performance of them through reduced toxicity, enhanced colloidal stability, and extended circulation within the body. Herein, the synthesis and state-of-the-art progresses of MXene nanosheets designed for biomedical applications, including structural- and dose-dependent antimicrobial activity, photothermal therapy, drug delivery, and implants are emphasized. Furthermore, biosensing applications are highlighted and a comprehensive discussion on photoacoustic imaging, magnetic resonance imaging, computed tomography imaging, and optical imaging of MXenes is presented. The challenges and future opportunities of applying MXene nanomaterials in the area of biomedicine are also discussed.

Recent Advances in Layered Ti3 C2 Tx MXene for Electrochemical Energy Storage

Ti₃ C₂ T_x , a typical representative among the emerging family of 2D layered transition metal carbides and/or nitrides referred to as MXenes, has exhibited multiple advantages including metallic conductivity, a plastic layer structure, small band gaps, and the hydrophilic nature of its functionalized surface. As a result, this 2D material is intensively investigated for application in the energy storage field. The composition, morphology and texture, surface chemistry, and structural configuration of Ti₃ C₂ T_x directly influence its electrochemical performance, e.g., the use of a well-designed 2D Ti₃ C₂ T_x as a rechargeable battery anode has significantly enhanced battery performance by providing more chemically active interfaces, shortened ion-diffusion lengths, and improved in-plane carrier/charge-transport kinetics. Some recent progresses of Ti₃ C₂ T_x MXene are achieved in energy storage. This Review summarizes recent advances in the synthesis and electrochemical energy storage applications of Ti₃ C₂ T_x MXene including supercapacitors, lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries. The current opportunities and future challenges of Ti₃ C₂ T_x MXene are addressed for energy-storage devices. This Review seeks to provide a rational and in-depth understanding of the relation between the electrochemical performance and the nanostructural/chemical composition of Ti₃ C₂ T_x , which will promote the further development of 2D MXenes in energy-storage applications.

Continuous hydrothermal flow synthesis of graphene quantum dots

A rapid, continuous hydrothermal flow synthesis route and life cycle assessment was employed for the synthesis of graphene quantum dots in the presence of calixarene.