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<jats:title>Abstract</jats:title> <jats:p>In this work, a novel Ti3C2Tx MXene/ chitosan/lignosulfonate adsorbent (MCL), was prepared via a facile decoration of Ti3C2Tx MXene sheets with chitosan/lignosulfonate nanospheres as a renewable and biodegradable additive that can improve the biocompatibility and aqueous stability of MXenes. Chitosan/lignosulfonate nanospheres were stabilized on the surface of MXne sheets, endowing them with a variety of surface functionalities, high specific surface area, and antioxidant characteristics. The competitive adsorption of multi-metal systems revealed that MCL had a preferential adsorption affinity toward various heavy metal ions; the MCL removal efficiency for the quinary-metal ions adsorption followed a trend of Pb(II) &gt; Cr(VI) ≈ Cu(II) &gt; Ni(II) ≈ Co(II) in neutral pH conditions. A moderate reduction was observed for Cu(II) and Cr(VI) ions. For all metals, the kinetics data fitted well with the pseudo-second-order model, and the adsorption equilibrium was best described by the Langmuir model. The adsorption mechanism is suggested to be a synergic combination of electrostatic interaction, surface complexation, and ion exchange. The findings of this study provide a new approach for eco-friendly MXene surface modification and give a general pattern of metal pollutants interactions during adsorption.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Strong band engineering in two-dimensional (2D) materials can be achieved by introducing moiré superlattices, leading to the emergence of various novel quantum phases with promising potential for future applications. Presented works to create moiré patterns have been focused on a twist embedded inside channel materials or between channel and substrate. However, the effects of a twist inside the substrate materials on the unaligned channel materials are much less explored. In this work, we report the realization of superlattice multi-Dirac cones with the coexistence of the main Dirac cone in a monolayer graphene (MLG) on a ~0.14° twisted double-layer boron nitride (tBN) substrate. Transport measurements reveal the emergence of three pairs of superlattice Dirac points around the pristine Dirac cone, featuring multiple metallic or insulating states surrounding the charge neutrality point (CNP). Displacement field tunable and electron-hole asymmetric Fermi velocities are indicated from temperature dependent measurements, along with the gapless dispersion of superlattice Dirac cones. The experimental observation of multiple Dirac cones in MLG/tBN heterostructure is supported by band structure calculations employing a periodic moiré potential. Our results unveil the potential of using twisted substrate as a universal band engineering technique for 2D materials regardless of lattice matching and crystal orientations, which might pave the way for a new branch of twistronics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Li-S batteries have received much attention due to their high energy density, low cost and environmental friendliness. However, the poor conductivity of sulfur and the “shuttle effect” of polysulfides still impede their practical applications. In this study, thin layered MXene nanosheets sandwiched by conductive poly(m-phenylenediamine) with in-plane cylindrical mesochannels (mPmPD/MXene) are constructed as sulfur hosts for the cathode materials of Li-S batteries. The polar active sites on MXene and mesoporous conductive PmPD polymers synergistically alleviate the polysulfide shuttling through chemisorption and physical confinement; the high metallic conductivity of MXene and conductive PmPD ensure the transport of electrons and promote the redox kinetics; the in-plane cylindrical mesochannels on mPmPD/MXene provide hosting space for high sulfur loading (~71 wt%) and facilitate smooth electrolyte transport in the internal space of the cathode. Profiting from these advantages, the Li-S battery based on the mPmPD/MXene cathode exhibits a capacity decay of 0.0593% after 800 cycles at 1 C (53% capacity retention). The optimized battery shows stable cycling performance even at high sulfur loading (6.8 mg cm<jats:sup>-2</jats:sup>) with 5.6 mAh cm<jats:sup>-2</jats:sup> capacity remained after 60 cycles at 0.1 C. This study provides insights for the rational design of 2D heterostructures with in-plane mesochannels for high-performance Li-S batteries.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Cathodoluminescence spectroscopy in conjunction with second-order auto-correlation measurements of g_2(τ) allows to extensively study the synchronization of photon emitters in low-dimensional structures. Co-existing excitons in two-dimensional transition metal dichalcogenide monolayers provide a great source of identical photon emitters which can be simultaneously excited by an electron. Here, we demonstrate large photon bunching with g_2(0) up to 156±16 of a tungsten disulfide monolayer (WS2), exhibiting a strong dependence on the electron-beam current. To further improve the excitation synchronization and the electron-emitter interaction, we show exemplary that the careful selection of a simple and compact geometry -- a thin, monocrystalline gold nanodisk -- can be used to realize a record-high bunching g_2(0) of up to 2152±236. This approach to control the electron excitation of excitons in a WS2 monolayer allows for the synchronization of photon emitters in an ensemble, which is important to further advance light information and computing technologies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A polyol-assisted solvothermal route is used to synthesize NixFey nanoalloys supported on a highly electron conductive 2D transition metal Mo2CTx MXene. Structural, morphological and chemical characteristics of the materials are determined using several physicochemical techniques. The MXene support allows not only the formation of a nanostructured metallic NixFey nanoalloys, but also favors the interfacial charge transfer for the OER. The NixFey@Mo2CTx material with a Ni/Fe ratio of 2.66 leads to the outstanding activity for the OER with an amazingly low Tafel slope value of 34 mV dec-1 and a current density of 10 mA.cm-2 at a potential of only 1.50 V vs. RHE. In situ Raman experiments show that β-NiOOH formed by oxidation of the nanoalloys under positive scan, likely containing a very small amount of Fe, is the active phase for the OER. This material exhibits also an excellent stability over 168 h in a 5 M KOH electrolyte. TEM-EELS analyses after 100 voltammetric cycles between 0.2 to 1.55 V vs. RHE evidence for the first time that the MXene support is not fully oxidized in the first cycle. Also, oxyhydroxide layer formed in the OER potential region at the surface of the NixFey nanoparticles can be reversibly reduced.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The capability to structure two-dimensional materials at the nanoscale with customizable patterns and over large areas is critical for a number of emerging applications, from nanoelectronics to 2D photonic metasurfaces. However, current technologies, such as photo- and electron beam lithography, often employing masking layers, can significantly contaminate the materials. Large-area CVD-grown graphene is known to have non-ideal properties already due to surface contamination resulting from the transferring process. Additional contamination through the lithographic process might thus reduce the performance of any device based on the structured graphene. Here, we demonstrate a contactless chemical-free approach for simultaneous patterning and cleaning of self-supporting graphene membranes in a single step. Using energetic ions passing through a suspended mask with pre-defined nanopatterns, we deterministically structure graphene with demonstrated feature size of 15 nm, approaching the performance of small-area focused ion beam techniques and extreme UV lithography. Our approach, however, requires only a broad beam, no nanoscale beam positioning and enables large area patterning of 2D-materials. Simultaneously, in regions surrounding the exposed areas, contaminations commonly observed on as-grown graphene targets, are effectively removed. This cleaning mechanism is attributed to coupling of surface diffusion and sputtering effects of adsorbed surface contaminants. For applications using 2D-materials, this simultaneous patterning and cleaning mechanism may become essential for preparing the nanostructured materials with improved cleanliness and hence, quality.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A significant challenge for graphene nanoplatelet (GNP) suppliers is the characterisation of platelet morphology in industrial environments. This challenge is further exacerbated to platelet surface chemistry when scalable functionalisation processes, such as plasma treatment, are used to modify the GNPs to improve the filler-matrix interphase in nanocomposites. The costly and complex suite of analytical equipment necessary for a complete material description makes quality control and process optimisation difficult. Raman spectroscopy is a facile and accessible characterisation technique, with recent advancements unlocking fast mapping for rapid data collection. In this study, we develop novel techniques to better characterise GNP morphology and changes in surface chemistry using Raman maps of bulk powders. Providing a bespoke algorithmic framework for the analysis of these advanced materials. An unsupervised peak fitting and processing algorithm was used to extract crystallinity data and correlate it with laser-diffraction-derived lateral size values for a commercial set of GNPs rapidly and accurately. Classical machine learning was used to identify the most informative Raman features for classifying the plasma-functionalised GNPs. The initial material properties were found to affect the peak features that were the most useful for classification. In low defect density and low specific surface area GNPs, the D peak FWHM is found to be the most useful, whereas the I2D/IG ratio is the most useful in the opposite case. Finally, a convolutional neural network was trained to discern between different GNP grades with 86% accuracy. This work demonstrates how computer vision could be deployed for rapid and accurate quality control on the factory floor.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Transition metal dichalcogenides integrated within a high-quality microcavity support well-defined exciton polaritons. While the role of intralayer excitons in 2D polaritonics is well studied, interlayer excitons have been largely ignored due to their weak oscillator strength. Using a microscopic and material-realistic Wannier-Hopfield model, we demonstrate that MoS<jats:sub>2</jats:sub> homobilayers in a Fabry-Perot cavity support polaritons that exhibit a large interlayer exciton contribution, while remaining visible in linear optical spectra. Interestingly, with suitable tuning of the cavity length, the hybridization between intra- and interlayer excitons can be 'unmixed' due to the interaction with photons. We predict formation of polaritons where &gt;90% of the total excitonic contribution is stemming from the interlayer exciton. Furthermore, we explore the conditions on the tunneling strength and exciton energy landscape to push this to even 100%. Despite the extremely weak oscillator strength of the underlying interlayer exciton, optical energy can be effectively fed into the polaritons once the critical coupling condition of balanced radiative and scattering decay channels is met. These findings have a wide relevance for fields ranging from nonlinear optoelectronic devices to Bose-Einstein condensation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The performance of electronic and optoelectronic devices is dominated by charge carrier injection through metal–semiconductor contacts. Therefore, creating low-resistance electrical contacts is one of the most critical challenges to the development of devices based on new materials, especially in the case of two-dimensional semiconductors. Here, we report a strategy to reduce contact resistance to MoS2 via local pressurization. We make electrical contacts using an Atomic Force Microscopy tip and apply variable pressure ranging from 0 to 25 GPa. By measuring transverse electronic transport properties, we show that MoS2 under pressure undergoes a reversible semiconducting-metallic transition. Planar devices in field effect configuration with electrical contacts performed at pressures above ~15 GPa show an up to 30-fold reduced contact resistance and an up to 25-fold improved field-effect mobility when compared to those measured at low pressure. Theoretical simulations show that this enhanced performance is due to an improved charge injection to the MoS2 semiconductor channel through the metallic MoS2 phase obtained by pressurization. Our results suggest a novel strategy for realizing improved contacts to MoS2 devices by local pressurization and to explore emergent phenomena under mechano-electric modulation.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The synthesized MoSi2N4 marks a new-born two-dimensional (2D) MA2Z4 family. In this work, we present a comprehensive study on the MA2Z4 family as anodes for Li- and Na-ion batteries (LIBs and SIBs) based on first-principle calculations. There exists a linear relationship between the ion adsorption energy E_ads and the energy level of the lowest unoccupied states E_LUS of MA2Z4, and a lower E_LUS leads to more energetically favourable electron occupation and hence stronger adsorption. E_LUS acts as a simple and useful descriptor, which allows for the straightforward prediction of ion adsorption based solely on the substrate electronic properties. Through evaluating the theoretical capacities and diffusion barriers, NbGe2N4 is predicted to be the most promising candidate for LIBs while VSi2P4 is better for SIBs, with maximum theoretical capacities of 547 mAh·g−1 and 696 mAh·g−1 and ion diffusion barriers of 0.34 eV and 0.10 eV, respectively. Moreover, NbGe2N4 and VSi2P4 show good phase stabilities by the analysis of their phase transformations. This study explores the application prospects of novel MA2Z4 in LIBs and SIBs and provides a deep understanding of intrinsic electronic mechanisms.</jats:p>