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The discovery of two-dimensional (2D) transition metal carbides and nitrides (MXenes) in 2011 has expanded the pool of nanomaterials available for a variety of applications. ...Characteristic properties of MXenes, such as high conductivity, hydrophilicity, and catalytic activity have led to a growing research interest for their use in environmental remediation and water treatment applications. This review summarizes recent advances in the synthesis and applications of MXenes as adsorbents, desalination membranes, electrodes for electrochemical deionization, and catalytic or antibacterial agents for water purification and other environmental remediation processes. The overview also features discussions on the computational attempts, biocompatibility, and environmental impact in the exploration of MXenes for water applications, highlighting the challenges and opportunities of these advanced 2D materials.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Two-dimensional (2D) carbides, nitrides, and carbonitrides known as MXenes are emerging materials with a wealth of useful applications. However, the range of metals capable of forming stable MXenes ...is limited mostly to early transition metals of groups 3–6, making the exploration of properties inherent to mid or late transition metal MXenes very challenging. To circumvent the inaccessibility of MXene phases derived from mid-to-late transition metals, we have developed a synthetic strategy that allows the incorporation of such transition metal sites into a host MXene matrix. Here, we report the structural characterization of a Mo2CT x :Co phase (where T x are O, OH, and F surface terminations) that is obtained from a cobalt-substituted bulk molybdenum carbide (β-Mo2C:Co) through a two-step synthesis: first an intercalation of gallium yielding Mo2Ga2C:Co followed by removal of Ga via HF treatment. Extended X-ray absorption fine structure (EXAFS) analysis confirms that Co atoms occupy Mo positions in the Mo2CT x lattice, providing isolated Co centers without any detectable formation of other cobalt-containing phases. The beneficial effect of cobalt substitution on the redox properties of Mo2CT x :Co is manifested in a substantially improved hydrogen evolution reaction (HER) activity, as compared to the unsubstituted Mo2CT x catalyst. Density functional theory (DFT) calculations attribute the enhanced HER kinetics of Mo2CT x :Co to the favorable binding of hydrogen on the oxygen terminated MXene surface that is strongly influenced by the substitution of Mo by Co in the Mo2CT x lattice. In addition to the remarkable HER activity, Mo2CT x :Co features excellent operational and structural stability, on par with the best performing non-noble metal-based HER catalysts. Overall, our work expands the compositional space of the MXene family by introducing a material with site-isolated cobalt centers embedded in the stable matrix of Mo2CT x . The synthetic approach presented here illustrates that tailoring the properties of MXenes for a specific application can be achieved via substitution of the host metal sites by mid or late transition metals.
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IJS, KILJ, NUK, PNG, UL, UM
Two-dimensional (2D) metal carbides and nitrides, called MXenes, have attracted great interest for applications such as energy storage. We demonstrate their potential as Schottky-barrier-free metal ...contacts to 2D semiconductors, providing a solution to the contact-resistance problem in 2D electronics. On the basis of first-principles calculations, we find that the surface chemistry strongly affects Fermi level of MXenes: O termination always increases the work function with respect to that of bare surface, OH always decreases it, whereas F exhibits either trend depending on the specific material. This phenomenon originates from the effect of surface dipoles, which together with the weak Fermi level pinning, enable Schottky-barrier-free hole (or electron) injection into 2D semiconductors through van der Waals junctions with some of the O-terminated (or all the OH-terminated) MXenes. Furthermore, we suggest synthetic routes to control surface terminations based on calculated formation energies. This study enhances understanding of the correlation between surface chemistry and electronic/transport properties of 2D materials, and also gives predictions for improving 2D electronics.
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IJS, KILJ, NUK, PNG, UL, UM
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•The preparation of pristine MXenes and MXenes hybrids are systematically summarized.•Green, efficient, and widely available synthetic routes are specifically highlighted.•The ...structure, microstructure and electronic structure of MXene are clearly revealed.•Microwave dielectric properties and attenuation mechanism are objectively reviewed.•Numbers research works on MXenes for MA and EMI shielding are demonstrated.
MXene, a shining star of two-dimensional (2D) materials, perfectly showcases layered structure, outstanding electrical conductivity, tunable active surface, and excellent mechanical strength, all of which make it extremely attractive in various applications, in particular for the ever growing market of microwave absorption (MA) and electromagnetic interference (EMI) shielding technology. Herein, we introduce the synthetic strategies, structure and properties of MXene-based materials. The current research progresses on the dielectric properties of MXene are comprehensively summarized and analyzed. We objectively overview and evaluate the state-of-the-art in electromagnetic wave absorbing and shielding of MXene-based matrials and dissect the major problems and bottlenecks. In addition, prospective research opportunities are highlighted toward the development of advanced MXene-based materials for MA and EMI shielding.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The hydrogen evolution reaction plays a decisive role in a range of electrochemical and photoelectrochemical devices. It requires efficient and robust electrocatalysts to lower the reaction ...overpotential and minimize energy consumption. Over the last decade, we have witnessed a rapid rise in new electrocatalysts, particularly those based on non-precious metals. Some of them approach the activity of precious metal benchmarks. Here, we present a comprehensive overview of the recent developments of heterogeneous electrocatalysts for the hydrogen evolution reaction. Detailed discussion is organized from precious metals to non-precious metal compounds including alloys, chalcogenides, carbides, nitrides, borides and phosphides, and finally to metal-free materials. Emphasis is placed on the challenges facing these electrocatalysts and solutions for further improving their performance. We conclude with a perspective on the development of future HER electrocatalysts.
In this review, the fundamental, current status and challenges of different types of HER electrocatalysts are highlighted.
Scalable Synthesis of Ti3C2Tx MXene Shuck, Christopher E.; Sarycheva, Asia; Anayee, Mark ...
Advanced engineering materials,
March 2020, Volume:
22, Issue:
3
Journal Article
Peer reviewed
Scaling the production of synthetic 2D materials to industrial quantities has faced significant challenges due to synthesis bottlenecks whereby few have been produced in large volumes. These ...challenges typically stem from bottom‐up approaches limiting the production to the substrate size or precursor availability for chemical synthesis and/or exfoliation. In contrast, MXenes, a large class of 2D transition metal carbides and/or nitrides, are produced via a top‐down synthesis approach. The selective wet etching process does not have similar synthesis constraints as some other 2D materials. The reaction occurs in the whole volume; therefore, the process can be readily scaled with reactor volume. Herein, the synthesis of 2D titanium carbide MXene (Ti3C2Tx) is studied in two batch sizes, 1 and 50 g, to determine if large‐volume synthesis affects the resultant structure or composition of MXene flakes. Characterization of the morphology and properties of the produced MXene using scanning electron microscopy, X‐ray diffraction, dynamic light scattering, Raman spectroscopy, X‐ray photoelectron spectroscopy, UV–visible spectroscopy, and conductivity measurements show that the materials produced in both batch sizes are essentially identical. This illustrates that MXenes experience no change in structure or properties when scaling synthesis, making them viable for further scale‐up and commercialization.
Herein, a reactor used for MXene synthesis and the scalable production (50 g) of 2D Ti3C2Tx in one batch is demonstrated. The large‐scale Ti3C2Tx produced in this study has identical properties to conventional laboratory synthesis, implying that Ti3C2Tx and other MXenes can be produced in industrial quantities without a loss of properties.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In this review, we categorized the explosive progress of research related to emerging 2D materials (e.g. 2D transition metal nanomaterials, graphitic nitride materials, black phosphorus, and emerging ...2D organic polymers) and highlighted their biosensing and bioimaging applications in recent three years.
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The great success of graphene throws new light on discovering more two-dimensional (2D) layered nanomaterials that stem from atomically thin 2D sheets. Compared with a single element of graphene, emerging graphene-like 2D materials composed of multiple elements that possess more versatility, greater flexibility and better functionality with a wide range of potential applications. In this review, we provide insights into the rapidly emerging 2D materials and their biosensing and bioimaging applications in recent three years, including 2D transition metal nanomaterials, graphitic nitride materials, black phosphorus, and emerging 2D organic polymers. We first briefly highlight their unique 2D morphology and physicochemical properties and then focus on their recent applications in electrochemical biosensing, optical biosensing and bioimaging. The challenges and some thoughts on future perspectives in this field are also addressed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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•MSP foams were prepared via preforming MXene/SA aerogels and coating of PDMS layers.•The highly conductive MXene/SA aerogel shows ultrahigh EMI shielding effectiveness.•Durable MSP ...foam exhibits stable shielding performance under long-term compression.•MSP foam is promising as EMI shielding gaskets and piezoresistive devices.
Lightweight and compressible electromagnetic interference (EMI) shielding polymer nanocomposites are urgently required to solve increasingly serious electromagnetic pollutions. Two-dimensional transition metal carbides and nitrides (MXenes), especially Ti3C2Tx, are ideal candidates for constructing highly efficient conduction networks in polymer matrices due to their intriguing layered structure and high electrical conductivity. Herein, compressible and electrically conductive polydimethylsiloxane (PDMS)-coated MXene foams are fabricated by preforming three-dimensional (3D) MXene aerogel architectures assisted with sodium alginate (SA) followed by coating a thin layer of PDMS to enhance structural stability and durability of the porous architectures. Consequently, the lightweight MXene/SA hybrid aerogel achieves an outstanding conductivity of 2211 S m−1 and a high average EMI shielding efficiency of 70.5 dB. Furthermore, the PDMS coating effectively endows the 3D conductance network with excellent compressibility and durability. The PDMS-coated MXene foam with 6.1 wt% of MXene reserves its high EMI shielding efficiency of 48.2 dB after 500 compression-release cycles. The lightweight, compressible and conductive PDMS-coated MXene foam is thus promising for applications in EMI shielding gaskets, wearable electronics, sensors and other specific areas.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The C 1s signal from ubiquitous carbon contamination on samples forming during air exposure, so called adventitious carbon (AdC) layers, is the most common binding energy (BE) reference in X‐ray ...photoelectron spectroscopy studies. We demonstrate here, by using a series of transition‐metal nitride films with different AdC coverage, that the BE of the C 1s peak EBF
varies by as much as 1.44 eV. This is a factor of 10 more than the typical resolvable difference between two chemical states of the same element, which makes BE referencing against the C 1s peak highly unreliable. Surprisingly, we find that C 1s shifts correlate to changes in sample work function ϕSA
, such that the sum EBF+ϕSA
is constant at 289.50±0.15 eV, irrespective of materials system and air exposure time, indicating vacuum level alignment. This discovery allows for significantly better accuracy of chemical state determination than offered by the conventional methods. Our findings are not specific to nitrides and likely apply to all systems in which charge transfer at the AdC/substrate interface is negligible.
Zeros matter: The C 1s signal from adventitious carbon (AdC) is the most common binding energy (BE) reference in X‐ray photoelectron spectroscopy. It is shown here that the BE of the C 1s peak EBF
is substrate dependent, which makes BE referencing highly unreliable. Surprisingly, C 1s shifts correlate to changes in the sample work function ϕSA
, such that the sum EBF+ϕSA
is constant irrespective of the materials system and air exposure time, indicating vacuum level alignment. This discovery allows for significantly better accuracy of chemical state determination.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Doping of nitrogen is a promising strategy to modulate chemical, electronic, and structural functionalities of graphene (G)and graphene quantum dots (GQDs) for their outstanding properties in energy ...and environmental applications.This paper reviews various synthesis approaches of nitrogen-doped graphene (N-G) and nitrogen-doped graphene quantum dots (N-GQDs).;Thermal, ultrasonic, solvothermal, hydrothermal, and electron-beam methods have been applied to synthesize N-G and N-GQDs.These nitrogen-doped carbon materials are characterized to obtain their structural configurations in order to achieve better performance in their applications compared to only either graphene or graphene quantum dots.Both N-G and N-GQDs may be converted into functional materials by integrating with other compounds such as metal oxides/nitrides, polymers, and semiconductors.These functional materials demonstrate superior performance over N-G and N-GQDs materials.Examples of applications of N-G and N-GQDs include supercapacitors, batteries, sensors, fuel cells, solar cells, and photocatalyst.
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•Doping of nitrogen to composites of N-G and N-GQDs tailors improves properties•Synthesis strategies include thermal, microwave, ultrasonication, catalysis•Applications of nitrogen-doped composites are in electronics, sensors, batteries•Photocatalytic degradation of pollutants by N-G and N-GQDs under visible light
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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