Sandwich-Structured Ordered Mesoporous Polydopamine/MXene Hybrids as High-Performance Anodes for Lithium-Ion Batteries

2D MXene-Based Nanoscale Materials for Electrochemical Sensing Toward the Detection of Hazardous Pollutants: A Perspective

MXenes (Mn+1XnTx), a subgroup of 2-dimensional (2D) materials, specifically comprise transition metal carbides, nitrides, and carbonitrides. They exhibit exceptional electrocatalytic and photocatalytic properties, making them well-suited for the detection and removal of pollutants from aqueous environments. Because of their high surface area and remarkable properties, they are being utilized in various applications, including catalysis, sensing, and adsorption, to combat pollution and mitigate its adverse effects. Different characterization techniques like XRD, SEM, TEM, UV-Visible spectroscopy, and Raman spectroscopy have been used for the structural elucidation of 2D MXene. Current responses against applied potential were measured during the electrochemical sensing of the hazardous pollutants in an aqueous system using a variety of electroanalytical techniques, including differential pulse voltammetry, amperometry, square wave anodic stripping voltammetry, etc. In this review, a comprehensive discussion on structural patterns, synthesis, properties of MXene and their application for electrochemical detection of lethal pollutants like hydroquionone, phenol, catechol, mercury and lead, etc. are presented. This review will be helpful to critically understand the methods of synthesis and application of MXenes for the removal of environmental pollutants.

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.

MXene as Promising Anode Material for High-Performance Lithium-Ion Batteries: A Comprehensive Review

Broad adoption has already been started of MXene materials in various energy storage technologies, such as super-capacitors and batteries, due to the increasing versatility of the preparation methods, as well as the ongoing discovery of new members. The essential requirements for an excellent anode material for lithium-ion batteries (LIBs) are high safety, minimal volume expansion during the lithiation/de-lithiation process, high cyclic stability, and high Li+ storage capability. However, most of the anode materials for LIBs, such as graphite, SnO2, Si, Al, and Li4Ti5O12, have at least one issue. Hence, creating novel anode materials continues to be difficult. To date, a few MXenes have been investigated experimentally as anodes of LIBs due to their distinct active voltage windows, large power capabilities, and longer cyclic life. The objective of this review paper is to provide an overview of the synthesis and characterization characteristics of the MXenes as anode materials of LIBs, including their discharge/charge capacity, rate performance, and cycle ability. In addition, a summary of the potential outlook for developments of these materials as anodes is provided.

Bacteria-targeted photothermal therapy for combating drug-resistant bacterial infections

Photothermal therapy is an ideal non-invasive treatment for bacterial infections. However, if photothermal agents are unable to target bacteria, they can also cause thermal damage to healthy tissue. This study describes the fabrication of a Ti3C2Tx MXene-based photothermal nanobactericide (denoted as MPP) that targets bacteria by modifying MXene nanosheets with polydopamine and the bacterial recognition peptide CAEKA. The polydopamine layer blunts the sharp edges of MXene nanosheets, preventing their damage to normal tissue cells. Furthermore, as a constituent of peptidoglycan, CAEKA can recognize and penetrate the bacterial cell membrane based on similar compatibility. The obtained MPP exhibits superior antibacterial activity and high cytocompatibility compared to the pristine MXene nanosheets. In vivo studies showed that MPP colloidal solution under 808 nm NIR light can effectively treat a subcutaneous abscess caused by multi-drug resistant bacterial infection without adverse effects.

Scalable functionalized liquid crystal elastomer fiber soft actuators with multi-stimulus responses and photoelectric conversion

Liquid crystal elastomer (LCE) fibers exhibit large deformation and reversibility, making them an ideal candidate for soft actuators. It is still challenging to develop a scalable strategy and endow fiber actuators with photoelectric functions to achieve tailorable photo-electro-thermal responsiveness and rapid large actuation deformation. Herein, we fabricated a multiresponsive actuator that consists of LCE long fibers obtained by continuous dry spinning and further coated it with polydopamine (PDA)-modified MXene ink. The designed PDA@MXene-integrated LCE fiber is used for shape-deformable and multi-trigger actuators that can be photo- and electro-thermally actuated. The proposed LCE fiber actuator combines an excellent photothermal and long-term electrically conductive PDA@MXene and a shape-morphing LCE fiber, enabling their robust mechanical flexibility, multiple fast responses (∼0.4 s), and stable and large actuation deformation (∼60%). As a proof-of-concept, we present near-infrared light-driven artificial muscle that can lift 1000 times the weight and an intelligent circuit switch with stable controllability and fast responsiveness (∼0.1 s). Importantly, an adaptive smart window system that integrates light-driven energy harvesting/conversion functions is ingeniously constructed by the integration of a propellable curtain woven by the designed fiber and solar cells. This work can provide insights into the development of advanced intelligent materials toward soft robotics, sustainable energy savings and beyond.

Rational Design of High-Performance PEO/Ceramic Composite Solid Electrolytes for Lithium Metal Batteries

Composite solid electrolytes (CSEs) with poly(ethylene oxide) (PEO) have become fairly prevalent for fabricating high-performance solid-state lithium metal batteries due to their high Li+ solvating capability, flexible processability and low cost. However, unsatisfactory room-temperature ionic conductivity, weak interfacial compatibility and uncontrollable Li dendrite growth seriously hinder their progress. Enormous efforts have been devoted to combining PEO with ceramics either as fillers or major matrix with the rational design of two-phase architecture, spatial distribution and content, which is anticipated to hold the key to increasing ionic conductivity and resolving interfacial compatibility within CSEs and between CSEs/electrodes. Unfortunately, a comprehensive review exclusively discussing the design, preparation and application of PEO/ceramic-based CSEs is largely lacking, in spite of tremendous reviews dealing with a broad spectrum of polymers and ceramics. Consequently, this review targets recent advances in PEO/ceramic-based CSEs, starting with a brief introduction, followed by their ionic conduction mechanism, preparation methods, and then an emphasis on resolving ionic conductivity and interfacial compatibility. Afterward, their applications in solid-state lithium metal batteries with transition metal oxides and sulfur cathodes are summarized. Finally, a summary and outlook on existing challenges and future research directions are proposed.

2D Titanium carbide printed flexible ultrawideband monopole antenna for wireless communications

Flexible titanium carbide (Ti₃C₂) antenna offers a breakthrough in the penetration of information communications for the spread of Internet of Things (IoT) applications. Current configurations are constrained to multi-layer complicated designs due to the limited conformal integration of the dielectric substrate and additive-free Ti₃C₂ inks. Here, we report the flexible ultrawideband Ti₃C₂ monopole antenna by combining strategies of interfacial modification and advanced extrusion printing technology. The polydopamine, as molecular glue nano-binder, contributes the tight adhesion interactions between Ti₃C₂ film and commercial circuit boards for high spatial uniformity and mechanical flexibility. The bandwidth and center frequency of Ti₃C₂ antenna can be well maintained and the gain differences fluctuate within ±0.2 dBi at the low frequency range after the bent antenna returns to the flat state, which conquers the traditional inelastic Cu antenna. It also achieves the demo instance for the fluent and stable real-time wireless transmission in bending states.

Three-dimensional N-doped mesoporous carbon–MXene hybrid architecture for supercapacitor applications

NMC@MXene exhibits excellent rate capability as electrode material for supercapacitors.

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.

Interfacial Assembly and Applications of Functional Mesoporous Materials

Functional mesoporous materials have gained tremendous attention due to their distinctive properties and potential applications. In recent decades, the self-assembly of micelles and framework precursors into mesostructures on the liquid-solid, liquid-liquid, and gas-liquid interface has been explored in the construction of functional mesoporous materials with diverse compositions, morphologies, mesostructures, and pore sizes. Compared with the one-phase solution synthetic approach, the introduction of a two-phase interface in the synthetic system changes self-assembly behaviors between micelles and framework species, leading to the possibility for the on-demand fabrication of unique mesoporous architectures. In addition, controlling the interfacial tension is critical to manipulate the self-assembly process for precise synthesis. In particular, recent breakthroughs based on the concept of the "monomicelles" assembly mechanism are very promising and interesting for the synthesis of functional mesoporous materials with the precise control. In this review, we highlight the synthetic strategies, principles, and interface engineering at the macroscale, microscale, and nanoscale for oriented interfacial assembly of functional mesoporous materials over the past 10 years. The potential applications in various fields, including adsorption, separation, sensors, catalysis, energy storage, solar cells, and biomedicine, are discussed. Finally, we also propose the remaining challenges, possible directions, and opportunities in this field for the future outlook.

Recent developments in mesoporous polydopamine-derived nanoplatforms for cancer theranostics

Polydopamine (PDA), which is derived from marine mussels, has excellent potential in early diagnosis of diseases and targeted drug delivery owing to its good biocompatibility, biodegradability, and photothermal conversion. However, when used as a solid nanoparticle, the application of traditional PDA is restricted because of the low drug-loading and encapsulation efficiencies of hydrophobic drugs. Nevertheless, the emergence of mesoporous materials broaden our horizon. Mesoporous polydopamine (MPDA) has the characteristics of a porous structure, simple preparation process, low cost, high specific surface area, high light-to-heat conversion efficiency, and excellent biocompatibility, and therefore has gained considerable interest. This review provides an overview of the preparation methods and the latest applications of MPDA-based nanodrug delivery systems (chemotherapy combined with radiotherapy, photothermal therapy combined with chemotherapy, photothermal therapy combined with immunotherapy, photothermal therapy combined with photodynamic/chemodynamic therapy, and cancer theranostics). This review is expected to shed light on the multi-strategy antitumor therapy applications of MPDA-based nanodrug delivery systems.

Dye-loaded mesoporous polydopamine nanoparticles for multimodal tumor theranostics with enhanced immunogenic cell death

BACKGROUND

Tumor phototherapy especially photodynamic therapy (PDT) or photothermal therapy (PTT), has been considered as an attractive strategy to elicit significant immunogenic cell death (ICD) at an optimal tumor retention of PDT/PTT agents. Heptamethine cyanine dye (IR-780), a promising PDT/PTT agent, which can be used for near-infrared (NIR) fluorescence/photoacoustic (PA) imaging guided tumor phototherapy, however, the strong hydrophobicity, short circulation time, and potential toxicity in vivo hinder its biomedical applications. To address this challenge, we developed mesoporous polydopamine nanoparticles (MPDA) with excellent biocompatibility, PTT efficacy, and PA imaging ability, facilitating an efficient loading and protection of hydrophobic IR-780.

RESULTS

The IR-780 loaded MPDA (IR-780@MPDA) exhibited high loading capacity of IR-780 (49.7 wt%), good physiological solubility and stability, and reduced toxicity. In vivo NIR fluorescence and PA imaging revealed high tumor accumulation of IR-780@MPDA. Furthermore, the combined PDT/PTT of IR-780@MPDA could induce ICD, triggered immunotherapeutic response to breast tumor by the activation of cytotoxic T cells, resulting in significant suppression of tumor growth in vivo.

CONCLUSION

This study demonstrated that the as-developed compact and biocompatible platform could induce combined PDT/PTT and accelerate immune activation via excellent tumor accumulation ability, offering multimodal tumor theranostics with negligible systemic toxicity.

Two-Dimensional MXene-Polymer Heterostructure with Ordered In-Plane Mesochannels for High-Performance Capacitive Deionization

The application of traditional electrode materials for high-performance capacitive deionization (CDI) has been persistently limited by their low charge-storage capacities, excessive co-ion expulsion and slow salt removal rates. Here we report a bottom-up approach to the preparation of a two-dimensional (2D) Ti₃ C₂ T_x MXene-polydopamine heterostructure having ordered in-plane mesochannels (denoted as mPDA/MXene). Interfacial self-assembly of mesoporous polydopamine (mPDA) monolayers on MXene nanosheets leads to the mPDA/MXene heterostructure, which exhibits several unique features: (1) MXene undergoes reversible ion intercalation/deintercalation and possesses high conductivity; (2) mPDA layers establish redox capacitive characteristics and Na⁺ selectivity, and also help to prevent self-stacking and oxidation of MXene; (3) in-plane mesochannels enable the smooth transport of ions at the internal spaces of this stacked 2D material. When applied as an electrode material for CDI, mPDA/MXene nanosheets exhibit top-level CDI performance and cycling stability compared to those of the so far reported 2D materials. Our study opens an avenue for the rational construction of MXene-organic hybrid heterostructures, and further motivates the development of high-performance CDI electrode materials.

Preparation Strategies and Applications of MXene-Polymer Composites: A Review

As a new member of the 2D material family, MXene integrates high metallic conductivity and hydrophilic property simultaneously. It shows tremendous potential in fields of energy storage, sensing, electromagnetic shielding, and so forth. Due to the abundant surface functional groups, the physical and chemical properties of MXene can be tuned by the formation of MXene-polymer composites. The introduction of polymers can expand the interlayer spacing, reduce the distance of ion/electron transport, improve the surface hydrophilicity, and thus guide the assembly of MXene-polymer structures. Herein, the preparation strategies of MXene-polymer composites including physical mixing, surface modification, such as anchoring through TiN and Ti-O-C bonds, bonding through esterification, grafting functional groups through TiOSi/TiOP bonds, photograft reaction, as well as in situ polymerization are highlighted. In addition, the possible mechanisms for each strategy are explained. Furthermore, the applications of MXene-polymer composites obtained by different preparation strategies are summarized. Finally, perspectives and challenges are presented for the designs of MXene-polymer composites.

Surface Functionalization of Ti3C2Tx MXene Nanosheets with Catechols: Implication for Colloidal Processing

Precise tailoring of two-dimensional nanosheets with organic molecules is critical to passivate the surface and control the reactivity, which is essential for a wide range of applications. Herein, we introduce catechols to functionalize exfoliated MXenes (Ti₃C₂T_x) in a colloidal suspension. Catechols react spontaneously with Ti₃C₂T_x surfaces, where binding is initiated from a charge-transfer complex as confirmed by density functional theory (DFT) and UV-vis. Ti₃C₂T_x sheet interlayer spacing is increased by catechol functionalization, as confirmed by X-ray diffraction (XRD), while Raman and atomic force microscopy-infrared spectroscopy (AFM-IR) measurements indicate binding of catechols at the Ti₃C₂T_x surface occurs through metal-oxygen bonds, which is supported by DFT calculations. Finally, we demonstrate immobilization of a fluorescent dye on the surface of MXene. Our results establish a strategy for tailoring MXene surfaces via aqueous functionalization with catechols, whereby colloidal stability can be modified and further functionality can be introduced, which could provide excellent anchoring points to grow polymer brushes and tune specific properties.

Knittable and Sewable Spandex Yarn with Nacre-Mimetic Composite Coating for Wearable Health Monitoring and Thermo- and Antibacterial Therapies

The emerging personal healthcare has significantly propelled the development of advanced wearable electronics with novel functions of providing diagnostic information and point-of-care therapies for specific diseases. However, it is still challenging to simultaneously achieve high sensitivity for health biomonitoring and multifunction integration for point-of-care therapies in a one single flexible, lightweight yet robust fiber-based device. Here, a knittable and sewable spandex yarn with conductive nacre-mimetic composite coating has been developed through an alternant dip-coating method employing MXene nanosheets as the "brick" and polydopamine (PDA)/Ni²⁺ as the "mortar". The resultant spandex yarn coating with MXene/PDA/Ni²⁺ (MPNi@Spandex) can be assembled as a strain sensor with high sensitivity (up to 5.7 × 10⁴ for the gauge factor), wide sensing range (∼61.2%), and low detection limit (0.11%) to monitor the biological activities of the human body. Furthermore, MPNi@Spandex displays great potential to give on-demand thermotherapy by virtue of the fast response to near-infrared irradiation, controllable surface temperature, and applicability even under sewing conditions. In addition, MPNi@Spandex knitted textiles demonstrate a strong antibacterial effect due to the sharp edges, anionic, and hydrophilic nature of MXene nanosheets. Remarkably, near-infrared irradiation further improves the bacteria-killing efficiency of an MPNi@Spandex knitted textile to more than 99.9%. This work paves the way for the design of multifunctional wearable electronics with an all-in-one theranostic platform for personal healthcare.

Recent Advanced on the MXene-Organic Hybrids: Design, Synthesis, and Their Applications

With increasing research interest in the field of flexible electronics and wearable devices, intensive efforts have been paid to the development of novel inorganic-organic hybrid materials. As a newly developed two-dimensional (2D) material family, MXenes present many advantages compared with other 2D analogs, especially the variable surface terminal groups, thus the infinite possibility for the regulation of surface physicochemical properties. However, there is still less attention paid to the interfacial compatibility of the MXene-organic hybrids. To this end, this review will briefly summarize the recent progress on MXene-organic hybrids, offers a deeper understanding of the interaction and collaborative mechanism between the MXenes and organic component. After the discussion of the structure and surface characters of MXenes, strategies towards MXene-organic hybrids are introduced based on the interfacial interactions. Based on different application scenarios, the advantages of MXene-organic hybrids in constructing flexible devices are then discussed. The challenges and outlook on MXene-organic hybrids are also presented.