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Ligands can control the surface chemistry, physicochemical properties, processing, and applications of nanomaterials. MXenes are the fastest growing family of two-dimensional (2D) nanomaterials, showing promise for energy, electronic, and environmental applications. However, complex oxidation states, surface terminal groups, and interaction with the environment have hindered the development of organic ligands suitable for MXenes. Here, we demonstrate a simple, fast, scalable, and universally applicable ligand chemistry for MXenes using alkylated 3,4-dihydroxy-l-phenylalanine (ADOPA). Due to the strong hydrogen-bonding and π-electron interactions between the catechol head and surface terminal groups of MXenes and the presence of a hydrophobic fluorinated alkyl tail compatible with organic solvents, the ADOPA ligands functionalize MXene surfaces under mild reaction conditions without sacrificing their properties. Stable colloidal solutions and highly concentrated liquid crystals of various MXenes, including Ti

Two-dimensional (2D) MXenes have attracted significant attention in electromagnetic interference (EMI) shielding applications due to their unique properties, such as excellent metallic conductivity, high surface area, 2D geometry, tunable surface chemistry, and solution processability. In this study, we present a simple and versatile way for introducing multiple internal interfaces into the Ti3C2T x MXenes using insulating graphene oxide (GO) intercalants to enhance internal scattering, resulting in improved absorption loss and EMI shielding effectiveness (SE). Amine-functionalized MXene flakes exhibit a positive surface charge, while GO flakes have a negative charge at acidic pH levels. The functionalized MXene and GO flakes electrostatically self-assemble to form 2D/2D heterostack of MXene/GO nanosheets, and simultaneously generate multiple internal interfaces with significant impedance mismatch. The 2D/2D alternating heterostack of MXene/GO enhances the internal scattering of incident EM waves. Interestingly, despite their inferior electrical conductivity, the MXene/GO heterostack films exhibit higher EMI SE values than the randomly mixed hybrid films, and even outperform pristine MXene with larger electrical conductivity. This enhancement is attributed to enhanced absorption of electromagnetic waves resulting from strong internal scattering at the multiple internal interfaces in the heterostack film.

Nano-hydroelectric technology utilizes hydraulic flow through electronically conducting nanomaterials to generate electricity in a simple, renewable, ubiquitous, and environmentally friendly manner. To date, several designs of nano-hydroelectric devices have been devised to maximize the electrokinetic interactions between water molecules and nanomaterials. However, the reported power generation of the state-of-the-art nano-hydroelectric generators is not sufficient for practical use, as tens of thousands of units were required to operate low-power electronics on a mW scale. Here, we utilize titanium carbide (Ti3C2Tx) MXene nanosheets, which have advantageous properties including metal-like conductivity and hydrophilicity, to facilitate the electrokinetic conversion of the transpiration–driven electrokinetic power generator (TEPG) with a remarkably improved energy generation efficiency compared to that of carbon-based TEPG. The Ti3C2Tx MXene-based TEPG delivered a high pseudo-streaming current of 120 μA by the fast capillary flow promoted by MXene sheets coated on cotton fabric. The strong cationic affinity of Ti3C2Tx enables the generator to achieve an output of 0.68 V and 2.73 mA when NaCl solution is applied. Moreover, incorporation of a conducting polymer (i.e., Ti3C2Tx/polyaniline composite) enhanced the ionic diffusivity while maintaining the electrical network of Ti3C2Tx. The optimized Ti3C2Tx/polyaniline composite TEPG generated a maximum voltage of 0.54 V, a current of 8.2 mA, and a specific power density of 30.9 mW cm−3, which was sufficient to successfully charge a commercial Li-ion battery as well as low-power electronics and devices with a volume of 6.72 cm3.

High conductivity and transparency and sheet-like two-dimensional morphology of MXenes make them attractive for use as functional transparent thin films. In addition, because of the dense surface f...

Advancement in modern electronic devices needs special requirements such as compact size, lightweight, and easy processing ability for the new innovative systems. This chapter describes the fundamentals of porous MXene composites (foams and aerogels) with the aim of inhibiting electromagnetic (EM) pollution. The first article that elucidated the EM shielding capabilities of MXene composites demonstrated superior performances to those of the existing materials, owing to their metallic conductivity, large surface area, surface modifiability, and ease of processability. Various approaches have been used to attenuate EM waves, including the application of laminate, porous, and hybrid structures. Among these, the porous morphology can contribute to the design of the absorption-dominant EM shield. Herein, the variations in electrical conductivity, mechanical stability, and electromagnetic interference shielding effectiveness (EMI SE) were explored with the use of a porous morphology. Subsequently, the theoretical and experimental results were analyzed to obtain new insights into the shielding mechanisms. This chapter will provide an overview of porous MXene composite materials and future challenges and strategies to design hybrid materials for next-generation EMI shielding applications.

While two-dimensional (2D) Ti

Two-dimensional transition metal carbide/nitride (MXene) conductive inks are promising for scalable production of printable electronics, electromagnetic devices, and multifunctional coatings. However, the susceptible oxidation and poor rheological property seriously impede the printability of MXene inks and the exploration of functional devices. Here, we proposed a controllable surface grafting strategy for MXene flakes (

An effective pathway to build macroscopic scale functional architectures bearing diverse structural dimensions is one of the critical challenges in the two-dimensional (2D) MXene research area. Unfortunately, assembling MXene without adhesive binder is largely limited due to its innate brittle nature and the relatively weak inter-flake van der Waals contact, in contrast to other mechanically compliant 2D materials such as graphene. Herein, an electrochemical self-assembly of pure Ti3C2Tx MXenes is presented for functional multidimensional MXene structures, effectively driven by layer-by-layer spontaneous interfacial reduction at metal template surfaces and subsequent defunctionalization. A three-dimensional open porous aerogel as well as 2D highly stacked thin film structures could be readily obtained in this approach, along with largely enhanced electrical properties induced by spontaneous removal of charge-trapping oxygen functional groups. Accordingly, supercapacitors and electromagnetic interference shielding films based on the multidimensional assembly demonstrate excellent performances.

MXenes (Ti3C2TX) are two-dimensional transition-metal carbides and carbonitrides with high conductivity and optical transparency. However, transparent MXene electrodes with high environmental stability suitable for various flexible organic electronic devices have rarely been demonstrated. By laminating a thin polymer film onto a solution-processed MXene layer to protect the MXene film from harsh environmental conditions, we present transparent and flexible MXene electronic devices. A thin polymer layer spin-coated onto a transparent MXene electrode provides environmental stability even under air exposure longer than 7 d at high temperatures (up to 70 °C) and humidity levels (up to 50%) without degrading the transparency of the electrode. The resulting polymer-laminated (PL) MXene electrode facilitates the development of a variety of field-driven photoelectronic devices by exploiting the electric field exerted between the MXene layer and the counter electrode through the insulating polymer. Field-induced electroluminescent displays, based on both organic and inorganic phosphors, with PL-MXene electrodes are demonstrated with high transparency and mechanical flexibility. Furthermore, our PL-MXene electrode exhibits high versatility through successful implementation in capacitive-type pressure sensors and triboelectric nanogenerators, resulting in field-driven sensing and energy harvesting electronic devices with excellent operation reliability.

Understanding the oxidation reaction of aqueous Ti3C2Tx MXene suspensions is very important for fostering fundamental academic studies as well as widespread industrial applications. Herein, we investigated the mechanism and kinetics of the oxidation reaction of aqueous Ti3C2Tx suspensions at various pH and temperature conditions. Through comprehensive analysis, the mechanism of the chemical oxidative degradation of aqueous Ti3C2Tx colloids was established. Chemical oxidation produces solid products such as TiO2 and amorphous carbon as well as various gaseous species including CH4, CO, CO2, and HF. Additionally, our comprehensive kinetic study proposes that aqueous Ti3C2Tx dispersions are degraded via an acid-catalyzed oxidation reaction, where, under acidic conditions, the protonation of the hydroxyl terminal groups on the Ti3C2Tx flakes induces electron localization on titanium atoms and accelerates their oxidation reaction. In contrast, under basic conditions, the electrostatically alkali-metalized hydroxyl intermediates forming a bulky solvent cage results in less electron localization on titanium atoms, and thus retards their oxidative degradation.

A composite of reduced graphene oxide (rGO) coated with metal-organic framework (MOF) HKUST-1 was synthesized using a facile hydrothermal method. The micro-frame of HKUST-1 was retained with the well-decorated octahedral framework on the surface of rGO sheets, resulting in the production of a scabrous, thorny trunk structure. The as-prepared composites exhibited the best shielding effectiveness at a weight ratio of 1:1 of the rGO:Cu(NO3)2.3H2O precursor, with a total shielding value (SET) greater than 36 dB over a wide frequency range (i.e., from 8.2 to 18 GHz). The maximum SET of the composite exceeded 46.1 dB at 18 GHz, compared to a value of 36.6 dB in pristine rGO. The introduction of the HKUST-1 MOF, which was anchored to the surface of rGO, prevented sheet layers from aggregating and decreased the impedance mismatching by limiting the value of shielding effectiveness by reflection. The mechanism of electromagnetic shielding was attributed mainly to dielectric loss and synergic effects between rGO and HKUST-1.

Two-dimensional graphene is of great interest for electromagnetic interference (EMI) shielding owing to its inherent electrical conductivity, lightweight, and excellent mechanical flexibility even at minor thicknesses. However, the complex synthesis and quality-control difficulties limit its application. In this study, we demonstrate that electrochemically exfoliated graphene (EEG) with post-reduction treatment is a promising candidate for lightweight EMI shielding materials. A facile electrochemical exfoliation approach produces a high-quality multilayer graphene with a high electrical conductivity of ∼600 S cm-1, owing to its low degree of oxidation. The reduction of EEG by three different methods, including chemical, thermal, and microwave treatments, causes the removal of surface functional groups as well as significant changes in the microstructure of the final films. The reduced graphene films by microwaves, which are driven by the improved electrical conductivity and large volume expansion, exhibit an EMI shielding effectiveness of 108 dB at a thickness of 125 μm, one of the largest EMI shielding values ever reported for graphene at comparable thicknesses.

Two-dimensional (2D) MXene has shown enormous potential in scientific fields, including energy storage and electromagnetic interference (EMI) shielding. Unfortunately, MXene-based material structures generally suffer from mechanical fragility and vulnerability to oxidation. Herein, mussel-inspired dopamine successfully addresses those weaknesses by improving interflake interaction and ordering in MXene assembled films. Dopamine undergoes in situ polymerization and binding at MXene flake surfaces by spontaneous interfacial charge transfer, yielding an ultrathin adhesive layer. Resultant nanocomposites with highly aligned tight layer structures achieve approximately seven times enhanced tensile strength with a simultaneous increase of elongation. Ambient stability of MXene films is also greatly improved by the effective screening of oxygen and moisture. Interestingly, angstrom thick polydopamine further promotes the innate high electrical conductivity and excellent EMI shielding properties of MXene films. This synergistic concurrent enhancement of physical properties proposes MXene/polydopamine hybrids as a general platform for MXene based reliable applications.

Lightweight, ultrathin, and flexible electromagnetic interference (EMI) shielding materials are needed to protect electronic circuits and portable telecommunication devices and to eliminate cross-talk between devices and device components. Here, we show that a two-dimensional (2D) transition metal carbonitride, Ti3CNTx MXene, with a moderate electrical conductivity, provides a higher shielding effectiveness compared with more conductive Ti3C2Tx or metal foils of the same thickness. This exceptional shielding performance of Ti3CNTx was achieved by thermal annealing and is attributed to an anomalously high absorption of electromagnetic waves in its layered, metamaterial-like structure. These results provide guidance for designing advanced EMI shielding materials but also highlight the need for exploring fundamental mechanisms behind interaction of electromagnetic waves with 2D materials.

New ultrathin and multifunctional electromagnetic interference (EMI) shielding materials are required for protecting electronics against electromagnetic pollution in the fifth-generation networks a...

Solution-processed nanostructured mesoporous rutile phase titanium dioxides (TiO2) are a fascinating class of materials for energy applications owing to their remarkable properties, including thermal stability. The unique lattice structure of rutile TiO2 (R-TiO2) leads to multifaceted physicochemical properties, which influence its performances. We here report the preparation of mesoporous R-TiO2 via a simple and scalable solution process at a low temperature (

Non-aqueous lithium-ion redox flow batteries (Li-RFBs) have recently garnered much interest because of their high operating voltage and energy density. Albeit these outstanding advantages, challenges, such as poor cyclability and efficiency, still remain in employing the practical application. In an attempt to address these problems, a series of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and TEMPO derivatives catholytes were prepared and investigated as redox-active materials. Electrochemical evaluation exhibited that the introduction of polar and electron-withdrawing substituents to TEMPO was able to enhance the rate capability and cycling stability, when compared to those with the neat TEMPO. Extensive analysis of the electrochemical properties revealed that the electrophilic heteroatom stabilized the radical as well as alleviated the catholyte degradation. Overall, a careful selection of redox-active species demonstrates great promise in improving the current redox flow battery technology.

Herein, we demonstrate a simple and versatile way for preparing stable Ti3C2Tx MXene dispersions in nonpolar organic solvents through a simultaneous interfacial chemical grafting reaction and phase transfer method. Alkylphosphonic acid ligands were chemically grafted on the hydroxyl terminal groups of Ti3C2Tx flakes at the liquid-liquid interface between water and water-immiscible organic medium to form a covalent Ti-O-P bond via interfacial nucleophilic addition and sequential condensation reaction at room temperature; the surface-functionalized Ti3C2Tx flakes concurrently migrated from the aqueous phase to the organic phase. Unlike conventional surface chemical modification methods that require many complex and tedious steps, this is a simple and easy process for fabricating a Ti3C2Tx organic dispersion in various organic solvents, from highly polar to nonpolar. The nonpolar Ti3C2Tx dispersion in chloroform also exhibits strong oxidation resistance and stable long-term storage. This approach provides an opportunity for preparing MXene nanocomposites with nonpolar polymeric matrices that are soluble in organic media for future applications such as stretchable electrode.

Poly(2,6-dimethyl-1,4-phenylene ether) (PPE)/Nylon 66 blends have been considered as the potential heat resistant engineering plastics with high mechanical toughness and flame retardancy, suitable for high temperature applications. However, incompatibility between PPE and Nylon 66 and poor thermal stability of Nylon 66 degrade mechanical toughness and flame retardancy. In this work, for the first time, the PPE/Nylon 66 blends with high mechanical toughness and flame retardancy simultaneously have been prepared through newly synthesized compatibilizer of PPE grafted with fumaric acid (PPE-g-FA) and environmental-friendly non-halogen organic phosphinate flame retardant. The PPE/Nylon 66 blend achieved not only V0 grade flame retardancy with the help of improved fire resistance through the solid phase reaction of non-halogenic flame retardant, but also large impact strength larger than 10 kJ/m2 due to the strong compatibility of PPE-g-FA.

Herein, we demonstrate the selective sensing of Dopamine (DA), an important neurotransmitter, by using Nafion-stabilized two-dimensional transition metal carbides (Ti3C2Tx MXenes). Ti3C2Tx was deposited on a glassy carbon electrode followed by Nafion coating to achieve a robust sensitivity (∼3 nM), good selectivity, wide detection window (0.015–10 μM), high stability, reproducibility, and outstanding recoveries for DA detection in real samples. MXene-based biosensor exhibited much better electrochemical performance when compared with reduced graphene oxide-based biosensor under similar experimental conditions due to the MXenes good electrical conductivity and negatively charged surface which assisted in the selective and sensitive detection of DA.

Lightweight materials with high electrical conductivity and robust mechanical properties are highly desirable for electromagnetic interference (EMI) shielding in modern portable and highly integrated electronics. Herein, a three-dimensional (3D) porous Ti3C2Tx/carbon nanotube (CNT) hybrid aerogel was fabricated via a bidirectional freezing method for lightweight EMI shielding application. The synergism of the lamellar and porous structure of the MXene/CNT hybrid aerogels contributed extensively to their excellent electrical conductivity (9.43 S cm-1) and superior electromagnetic shielding effectiveness (EMI SE) value of 103.9 dB at 3 mm thickness at the X-band frequency, the latter of which is the best value reported for synthetic porous nanomaterials. The CNT reinforcement in the MXene/CNT hybrid aerogels enhanced the mechanical robustness and increased the compressional modulus by 9661% relative to that of the pristine MXene aerogel. The hybrid aerogel with high electrical conductivity, good mechanical strength, and superior EMI shielding performance is a promising material for inhibiting EMI pollution.

A mixture of ionic liquids, 1,3-dimethylimidazolium 2-methoxy(2-ethoxy(2-ethoxy(2-ethoxy)))ethylphosphite ([DMIm][MPEGP]) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which forms an ion...

Grafting nanotechnology on thermoelectric materials leads to significant advances in their performance. Creation of structural defects including nano-inclusion and interfaces via nanostructuring ac...

Prior to the advent of the next-generation heater for wearable/on-body electronic devices, various properties are required, including conductivity, transparency, mechanical reliability, and conformability. Expansion to two-dimensional (2D) structure of metallic nanowires based on network- and mesh-type geometries has been widely exploited for realizing these heaters. However, the routes led to many drawbacks such as the low-density cross-bar linking, self-aggregation of wire, and high junction resistance. Although 2D carbon nanomaterials such as graphene and reduced graphene oxide (rGO) have shown their potentials for the purpose, CVD-grown graphene with sufficiently high conductivity was limited due to its poor processability for large-area applications, while rGO fabricated with a complex reduction process involving the use of toxic chemicals suffered from a low electrical conductivity. In this study, we demonstrate a simple and robust process, utilizing electrostatic assembling of negatively charged MXene flakes on a positively treated surface of substrate, for fabricating a metal-like 2D MXene thin film heater (TFH). Our TFH showed a high optical property (>65%), low sheet resistance (215 Ω/sq), fast electrothermal response (within dozens of seconds) with an intrinsically high electrical conductivity, and mechanical flexibility (up to 180° bending). Its capability for forming a firm and stable ionic-type interface with a counterpart surface allows us to develop a shape-adaptable and patchable thread heater (TH) that can be shaped on diverse substrates even under harsh conditions of conventional sewing or weaving processes. This work suggests that our shape-adaptable MXene heaters are potentially suitable not only for wearable devices for local heating and defrosting but also for a variety of emerging applications of soft actuators and wearable/flexible healthcare monitoring and thermotherapy.

Silica nanoparticles were chemically grafted onto a porous polyethylene separator to improve the adhesion strength, thermal stability, and electrochemical performance of a polyolefin separator. A surface activation via UVO plasma treatment, followed by silane hybridization yielded a polymeric binder-free, thin coating of SiO2 nanoparticles onto the separator. The chemical grafting provided a much stronger adhesive strength (> 2.5 N/cm), reduced thermal shrinkage (

Herein, for the first time, FeSiAl (sendust)/metal hybrid materials were synthesized with a magnetic core and a highly electrically conductive metal shell for shielding electromagnetic interference (EMI) pollution. Soft magnetic sendust flakes were electroless-plated with electrically conductive Ag or Ni metal to form Ag-plated and Ni-plated sendust core-shell hybrids. The magnetic and metal hybrid-incorporated paraffin wax composites exhibited a better absorption-dominant EMI shielding performance of 65.6 dB and 58.5 dB, respectively, than that of the sendust wax composite and the composite with a mixture of sendust and electrically conductive Ag/Cu dendrite. The superior shielding performance was attributed to the synergistic combination of the effective magnetic loss, dielectric loss, and conduction loss. These exceptional properties of the new hybrid composite showed that it could be used in absorption-dominant EMI shielding applications.