Depositional Model and Controlling Factors of High-Quality Shales of the Wufeng and Longmaxi Formations in Western Chongqing, Sichuan Basin, China.

The enrichment of organic matter is the foundation for a high-quality shale deposition. It is generally believed that high productivity and persistent anoxic conditions facilitate the preservation and enrichment of organic matter. However, there is a lack of investigation into how the dynamic combination of productivity and anoxia affects organic matter enrichment. Here, the black shales of the Wufeng Formation and Longmaxi Formation in the western Chongqing area were selected, where oceanic anoxia and high productivity evolved as a function of the water depth. The main findings were as follows: (1) the distribution of high-quality shales in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation is closely related to the oxygen minimum zone (OMZ), indicating that the physicochemical conditions within the OMZ zone facilitated the development of high-quality shale; (2) in the late period of the Wufeng Formation, intense ocean upwelling in the middle shelf and outer shelf regions caused high productivity where thick-bedded high-quality shales were deposited; and (3) in the early period of the Longmaxi Formation, ocean upwelling weakened, accompanied by the expansion of the OMZ to shallow water regions, and high-quality shales were widely distributed. Based on the above findings, two depositional models were proposed to account for the formation of high-quality shales, and it is suggested that intense ocean upwelling during the late period of the Wufeng Formation and OMZ expansion during the early period of the Longmaxi Formation played crucial roles in facilitating the formation of high-quality shales. These two models present the spatial and temporal variability of high-quality shale development for the first time and can guide shale gas exploration and development strategies.

Applications of X-Ray-Based Characterization in MXene Research.

X-rays are a penetrating form of high-energy electromagnetic radiation with wavelengths ranging from 10 pm to 10 nm. Similar to visible light, X-rays provide a powerful tool to study the atoms and elemental information of objects. Different characterization methods based on X-rays are established, such as X-ray diffraction, small- and wide-angle X-ray scattering, and X-ray-based spectroscopies, to explore the structural and elemental information of varied materials including low-dimensional nanomaterials. This review summarizes the recent progress of using X-ray related characterization methods in MXenes, a new family of 2D nanomaterials. These methods provide key information on the nanomaterials, covering synthesis, elemental composition, and the assembly of MXene sheets and their composites. Additionally, new characterization methods are proposed as future research directions in the outlook section to enhance understanding of MXene surface and chemical properties. This review is expected to provide a guideline for characterization method selection and aid in precise interpretation of the experimental data in MXene research.

Natural Polymer Template for Low-Cost Producing High-Performance Ti3C2Tx MXene Electrodes for Flexible Supercapacitors.

MXenes, two-dimensional (2D) transition-metal carbides and nitrides with high electrical conductivity, show outstanding potential for energy storage applications. However, the aggregation and restacking of 2D MXene nanosheets seriously decrease the performance of MXene-based electrodes. Instead of using high-cost artificial templates, herein, we select natural rubber (NR) latex-containing uniform sub-macroparticles as sacrificial templates and successfully construct three-dimensional interconnected porous MXene foam. This porous structure effectively prevents the restacking of MXene nanosheets and accelerates the transfer of electrolyte ions during charging and discharging, which significantly enhances capacitance and rate performance. By adjusting the loading of latex, we find that MXene foam (MXF)-70% provides both improved specific capacitance of 480 F g-1 at 2 mV s-1 and superior rate performance (42.1% residual at 1 V s-1) with excellent cycling stability of 97.1% capacitance retention after 10000 cycles at 50 mV s-1. Additionally, the low cost of natural rubber latex provides an alternate route to produce foam electrodes on a large scale for portable and integrated supercapacitors.

Design and Fabrication of an Additively Manufactured Aluminum Mirror with Compound Surfaces.

Microsatellites have a great attraction to researchers due to their high reliability, resource utilization, low cost, and compact size. As the core component of the optical payload, the mirror directly affects the system package size. Therefore, the structural design of mirrors is critical in the compact internal space of microsatellites. This study proposes a closed-back mirror with composite surfaces based on additive manufacturing (AM). Compared with the open-back mirror, it provides excellent optomechanical performance. In addition, AM significantly reduces the intricate mechanical parts' manufacturing difficulty. Finally, the roughness was better than 2 nm. The surface shape of the AM aluminum mirror reached RMS 1/10λ (λ = 632.8 nm) with the aid of ultra-precision machining technologies such as single-point diamond turning (SPDT), surface modification, and polishing, and the maximum deviation of the surface shape was about RMS 1/42λ (λ = 632.8 nm) after the thermal cycle test, which verified the optical grade application of AM.

Optomechanical Performances of Advanced Lightweight Mirrors Based on Additive Manufacturing.

Additive manufacturing (AM)-layer-by-layer printing-completely changes the conventional manufacturing method. The design freedom for mirrors is increased without the limits of the manufacturing process. Advanced lightweight mirrors (ALM), new-type mirrors designed using the generative method and lattice technologies, have emerged as the times require. Contrasting with conventional lightweight mirrors (CLM), the performances of ALM are drastically improved. This paper took the Voronoi mirrors as an ALM case study and introduced a design flow. In addition, a conventional honeycomb mirror was designed using the analytical method as the control. The optomechanical performances of the two were further compared through finite element analysis (FEA). Finally, ALM's optomechanical performances outperformed CLM's, including the area density, structural stiffness, surface stability, and quilting deflection.

Understanding the Effect of Pore Size on Electrochemical Capacitive Performance of MXene Foams.

Wearable electronics demand energy storage devices with high energy density and fast charging-discharging rates. Although various porous electrodes have been constructed, the effect of pore size on the capacitive performance of 2D nanomaterials has been rarely studied. Herein, flexible MXene foams with significantly different pore structures are fabricated using varying diameter polystyrene (PS) spheres (80, 310, and 570 nm), which shows uniform pores and interconnected pores providing enough active sites and a good electrical connection for electron transfer. Noteworthy, when MXene flakes and templates (310 nm) have a similar size, the foam delivers the highest gravimetric capacitance of 474 ± 12 F g-1 at 2 mV s-1 than others. Additionally, the mass ratio between MXene and PS controls the packing density of foams influencing the inner resistance of foam electrodes. A carbon nanotube is introduced to further improve the electrical conductivity of foams to achieve a capacitance of 462 ± 8 F g-1 at 2 mV s-1 and retains 205 ± 10 F g-1 at 1000 mV s-1 , demonstrating promises in energy storage applications and providing an insightful guidance for designing 2D nanomaterials-based porous electrodes for supercapacitors.

Environmentally stable MXene ink for direct writing flexible electronics.

MXene inks are promising candidates for fabricating conductive circuits and flexible devices. Here, MXene inks prepared from solvent mixtures demonstrate long-term stability and can be employed in commercial rollerball pens to write electronic circuits on flexible substrates. Such circuits exhibit a fast and accurate capacitive response for touch-boards and water level measurement, indicating the excellent potential of these MXene inks in electrical device fabrication.

Tough and Fatigue Resistant Cellulose Nanocrystal Stitched Ti3 C2 Tx MXene Films.

Ti3 C2 Tx MXene (or "MXene" for simplicity) has gained noteworthy attention for its metal-like electrical conductivity and high electrochemical capacitance-a unique blend of properties attractive toward a wide range of applications such as energy storage, healthcare monitoring, and electromagnetic interference shielding. However, processing MXene architectures using conventional methods often deals with the presence of defects, voids, and isotropic flake arrangements, resulting in a trade-off in properties. Here, a sequential bridging (SB) strategy is reported to fabricate dense, freestanding MXene films of interconnected flakes with minimal defects, significantly enhancing its mechanical properties, specifically tensile strength (≈285 MPa) and breaking energy (≈16.1 MJ m-3 ), while retaining substantial values of electrical conductivity (≈3050 S cm-1 ) and electrochemical capacitance (≈920 F cm-3 ). This SB method first involves forming a cellulose nanocrystal-stitched MXene framework, followed by infiltration with structure-densifying calcium cations (Ca2+ ), resulting in tough and fatigue resistant films with anisotropic, evenly spaced, and strongly interconnected flakes - properties essential for developing high-performance energy-storage devices. It is anticipated that the knowledge gained in this work will be extended toward improving the robustness and retaining the electronic properties of 2D nanomaterial-based macroarchitectures.

Toughening Wet-Spun Silk Fibers by Silk Nanofiber Templating.

Regenerated silk fibers typically fall short of silkworm cocoon fibers in mechanical properties due to reduced fiber crystal structure and alignment. One approach to address this has been to employ inorganic materials as reinforcing agents. The present study avoids the need for synthetic additives, demonstrating the first use of exfoliated silk nanofibers to control silk solution crystallization, resulting in all-silk pseudocomposite fibers with remarkable mechanical properties. Incorporating only 0.06 wt% silk nanofibers led to a ≈44% increase in tensile strength (over 600 MPa) and ≈33% increase in toughness (over 200 kJ kg-1 ) compared with fibers without silk nanofibers. These remarkable properties can be attributed to nanofiber crystal seeding in conjunction with fiber draw. The crystallinity nearly doubled from ≈17% for fiber spun from pure silk solution to ≈30% for the silk nanofiber reinforced sample. The latter fiber also shows a high degree of crystal orientation with a Herman's orientation factor of 0.93, a value which approaches that of natural degummed B. mori silk cocoon fiber (0.96). This study provides a strong foundation to guide the development of simple, eco-friendly methods to spin regenerated silk with excellent properties and a hierarchical structure that mimics natural silk.

Ti3C2Tx MXene: from dispersions to multifunctional architectures for diverse applications.

The exciting combination of high electrical conductivity, high specific capacitance and colloidal stability of two-dimensional Ti3C2Tx MXene (referred to as MXene) has shown great potential in a wide range of applications including wearable electronics, energy storage, sensors, and electromagnetic interference shielding. To realize its full potential, recent literature has reported a variety of solution-based processing methodologies to develop MXenes into multifunctional architectures, such as fibres, films and aerogels. In response to these recent critical advances, this review provides a comprehensive analysis of the diverse solution-based processing methodologies currently being used for MXene-architecture fabrication. A critical evaluation of the processing challenges directly affecting macroscale material properties and ultimately, the performance of the resulting prototype devices is also provided. Opportunities arising from the observed and foreseen challenges regarding their use are discussed to provide avenues for new designs and realise practical use in high performance applications.

Scalable Fabrication of Ti3C2Tx MXene/RGO/Carbon Hybrid Aerogel for Organics Absorption and Energy Conversion.

High aspect ratio two-dimensional Ti3C2Tx MXene flakes with extraordinary mechanical, electrical, and thermal properties are ideal candidates for assembling elastic and conductive aerogels. However, the scalable fabrication of large MXene-based aerogels remains a challenge because the traditional preparation method relies on supercritical drying techniques such as freeze drying, resulting in poor scalability and high cost. Herein, the use of porous melamine foam as a robust template for MXene/reduced graphene oxide aerogel circumvents the volume shrinkage during its natural drying process. Through this approach, we were able to produce large size (up to 600 cm3) MXene-based aerogel with controllable shape. In addition, the aerogels possess an interconnected cellular structure and display resilience up to 70% of compressive strain. Some key features also include high solvent absorption capacity (∼50-90 g g-1), good photothermal conversion ability (an average evaporation rate of 1.48 kg m-2 h-1 for steam generation), and an excellent electrothermal conversion rate (1.8 kg m-2 h-1 at 1 V). More importantly, this passive drying process provides a scalable, convenient, and cost-effective approach to produce high-performance MXene-based aerogels, demonstrating the feasibility of commercial production of MXene-based aerogels toward practical applications.

Pollution Assessment of Potentially Toxic Elements (PTEs) in Soils around the Yanzhuang Gold Mine Tailings Pond, Pinggu County, Beijing, China.

The accumulation of tailings from gold mining and smelting may result in PTE pollution. We investigated PTE contamination from a large amalgamated gold mine tailings pond in Pinggu County, Beijing. In November 2017, 30 soil samples were collected around the tailings pond. The concentrations and pollution degree of PTEs in the samples and the sources of Sb, As, Cd, Cu, Pb, Zn and Hg were analyzed. The average concentration of these elements in soil samples near the tailings pond (16.24, 28.29, 0.99, 171.04, 263.25, 99.73, 0.72 mg/kg, respectively) were higher than their corresponding standard values and background values of the study area. The geoaccumulation index showed that the pollution degree of As, Pb and Hg was moderate, while Sb and Cu present non-pollution to moderate pollution. The average EF values of the elements were Sb (38.31), As (4.23), Cd (0.71), Cu (3.68), Pb (21.24), Zn (0.82) and Hg (5.29), respectively. The environmental risk assessment developed throughout the PERI method indicated that Sb, As, Hg and Pb were the main pollutants in the study area. The three quantitative risk indicators (RI, Igeo and EF) were positively correlated, and all of them indicated that PTEs had significant pollution to the local area. Thus, Sb, As, Pb, Cu, and Hg pollution should be highly concerning. Multivariate statistical analysis shows that the pollution of PTEs was mainly caused by the accumulation of tailings ponds after gold mining and smelting. The research result is of great significance for the prevention and control of soil pollution of PTEs near the tailings pond.

Development and Applications of MXene-Based Functional Fibers.

The increasing interest toward wearable and portable electronic devices calls for multifunctional materials and fibers/yarns capable of seamless integration with everyday textiles. To date, one particular gap inhibiting the development of such devices is the production of robust functional fibers with improved electronic conductivity and electrochemical energy storage capability. Recent efforts have been made to produce functional fibers with 2D carbides known as MXenes to address these demands. Ti3C2Tx MXene, in particular, is known for its metallic conductivity and high volumetric capacitance, and has shown promise for fibers and textile-based devices when used either as an additive, coating or the main fiber component. In this spotlight article, we highlight the recent exciting developments in our diverse efforts to fabricate MXene functionalized fibers, along with a critical evaluation of the challenges in processing, which directly affect macroscale material properties and the performance of the subsequent prototype devices. We also provide our assessment of observed and foreseen challenges of the current manufacturing methods and the opportunities arising from recent advances in the development of MXene fibers and paving future avenues for textile design and practical use in advanced applications.

Interfacial piezoelectric polarization locking in printable Ti3C2Tx MXene-fluoropolymer composites.

Piezoelectric fluoropolymers convert mechanical energy to electricity and are ideal for sustainably providing power to electronic devices. To convert mechanical energy, a net polarization must be induced in the fluoropolymer, which is currently achieved via an energy-intensive electrical poling process. Eliminating this process will enable the low-energy production of efficient energy harvesters. Here, by combining molecular dynamics simulations, piezoresponse force microscopy, and electrodynamic measurements, we reveal a hitherto unseen polarization locking phenomena of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) perpendicular to the basal plane of two-dimensional (2D) Ti3C2Tx MXene nanosheets. This polarization locking, driven by strong electrostatic interactions enabled exceptional energy harvesting performance, with a measured piezoelectric charge coefficient, d33, of -52.0 picocoulombs per newton, significantly higher than electrically poled PVDF-TrFE (approximately -38 picocoulombs per newton). This study provides a new fundamental and low-energy input mechanism of poling fluoropolymers, which enables new levels of performance in electromechanical technologies.

Superelastic Ti3C2Tx MXene-Based Hybrid Aerogels for Compression-Resilient Devices.

Superelastic aerogels with excellent electrical conductivity, reversible compressibility, and high durability hold great potential for varied emerging applications, ranging from wearable electronics to multifunctional scaffolds. In the present work, superelastic MXene/reduced graphene oxide (rGO) aerogels are fabricated by mixing MXene and GO flakes, followed by a multistep reduction of GO, freeze-casting, and finally an annealing process. By optimizing both the composition and reducing conditions, the resultant aerogel shows a reversible compressive strain of 95%, surpassing all current reported values. The conducting MXene/rGO network provides fast electron transfer and stable structural integrity under compression/release cycles. When assembled into compressible supercapacitors, 97.2% of the capacitance was retained after 1000 compression/release cycles. Moreover, the high conductivity and porous structure also enabled the fabrication of a piezoresistive sensor with high sensitivity (0.28 kPa-1), wide detection range (up to 66.98 kPa), and ultralow detection limit (∼60 Pa). It is envisaged that the superelasticity of MXene/rGO aerogels offers a versatile platform for utilizing MXene-based materials in a wide array of applications including wearable electronics, electromagnetic interference shielding, and flexible energy storage devices.

Spinning Regenerated Silk Fibers with Improved Toughness by Plasticizing with Low Molecular Weight Silk.

Low-molecular weight (LMW) silk was utilized as a LMW silk plasticizer for regenerated silk, generating weak physical crosslinks between high-molecular weight (HMW) silk chains in the amorphous regions of a mixed solution of HMW/LMW silk. The plasticization effect of LMW silk was investigated using mechanical testing, Raman spectroscopy, and wide-angle X-ray scattering (WAXS). Small amounts (10%) of LMW silk resulted in a 19.4% enhancement in fiber extensibility and 37.8% increase in toughness. The addition of the LMW silk facilitated the movement of HMW silk chains during drawing, resulting in an increase in molecular chain orientation when compared with silk spun from 100% HMW silk solution. The best regenerated silk fibers produced in this work had an orientation factor of 0.94 and crystallinity of 47.82%, close to the values of natural degummedBombyx mori silk fiber. The approach and mechanism elucidated here can facilitate artificial silk systems with enhanced properties.

Cathodic electrogenerated chemiluminescence of tris(2,2'-bipyridine)ruthenium(ii) and peroxydisulfate at pure Ti3C2Tx MXene electrodes.

We demonstrate the first use of pure films of two-dimensional (2D) transition metal carbides and nitrides (Ti3C2Tx MXene) as an electrode material for electrogenerated chemiluminescence (ECL). The Ti3C2Tx MXene electrodes exhibited excellent electrochemical stability in the cathodic scan range and produced bright reductive-oxidation ECL using peroxydisulfate as a co-reactant with the tris(2,2'-bipyridine)ruthenium(ii) ([Ru(bpy)3]2+) luminophore.

Freezing Titanium Carbide Aqueous Dispersions for Ultra-long-term Storage.

Two-dimensional titanium carbide (Ti3C2Tx), or MXene, is a new nanomaterial that has attracted increasing interest due to its metallic conductivity, good solution processability, and excellent energy storage performance. However, Ti3C2Tx MXene flakes suffer from degradation through oxidation due to prolonged exposure to oxygenated water. Preventing the occurrence of oxidation, i.e., the formation of TiO2 particles, was found to be crucial in maintaining MXene quality. In the present work, we found that freezing aqueous MXene dispersions at a low temperature can effectively prevent the formation of TiO2 nanoparticles at the flake edge, which is known as the early stage of oxidation. The Ti3C2Tx flakes in frozen dispersion remain consistent in morphology and elemental composition for over 650 days, compared with freshly synthesized MXene, which in contrast exhibits flake edge degradation within two days when stored at room temperature. This result suggests that freezing a MXene dispersion dramatically postpones the oxidation of MXene flakes and that the stored MXene dispersion can be treated as freshly prepared MXene. This work not only fundamentally fulfilled the study on temperature dependence of MXene oxidation but has also demonstrated a simple method to extend the shelf life of MXene aqueous dispersion to years, which will be a cornerstone for large-scale production of MXene and ultimately benefit the research on MXenes.

Bath Electrospinning of Continuous and Scalable Multifunctional MXene-Infiltrated Nanoyarns.

Electroactive yarns that are stretchable are desired for many electronic textile applications, including energy storage, soft robotics, and sensing. However, using current methods to produce these yarns, achieving high loadings of electroactive materials and simultaneously demonstrating stretchability is a critical challenge. Here, a one-step bath electrospinning technique is developed to effectively capture Ti3 C2 Tx MXene flakes throughout continuous nylon and polyurethane (PU) nanofiber yarns (nanoyarns). With up to ≈90 wt% MXene loading, the resulting MXene/nylon nanoyarns demonstrate high electrical conductivity (up to 1195 S cm-1 ). By varying the flake size and MXene concentration, nanoyarns achieve stretchability of up to 43% (MXene/nylon) and 263% (MXene/PU). MXene/nylon nanoyarn electrodes offer high specific capacitance in saturated LiClO4 electrolyte (440 F cm-3 at 5 mV s-1 ), with a wide voltage window of 1.25 V and high rate capability (72% between 5 and 500 mV s-1 ). As strain sensors, MXene/PU yarns demonstrate a wide sensing range (60% under cyclic stretching), high sensitivity (gauge factor of ≈17 in the range of 20-50% strain), and low drift. Utilizing the stretchability of polymer nanofibers and the electrical and electrochemical properties of MXene, MXene-based nanoyarns demonstrate potential in a wide range of applications, including stretchable electronics and body movement monitoring.

Scalable Manufacturing of Free-Standing, Strong Ti3 C2 Tx MXene Films with Outstanding Conductivity.

Free-standing films that display high strength and high electrical conductivity are critical for flexible electronics, such as electromagnetic interference (EMI) shielding coatings and current collectors for batteries and supercapacitors. 2D Ti3 C2 Tx flakes are ideal candidates for making conductive films due to their high strength and metallic conductivity. It is, however, challenging to transfer those outstanding properties of single MXene flakes to macroscale films as a result of the small flake size and relatively poor flake alignment that occurs during solution-based processing. Here, a scalable method is shown for the fabrication of strong and highly conducting pure MXene films containing highly aligned large MXene flakes. These films demonstrate record tensile strength up to ≈570 MPa for a 940 nm thick film and electrical conductivity of ≈15 100 S cm-1 for a 214 nm thick film, which are both the highest values compared to previously reported pure Ti3 C2 Tx films. These films also exhibit outstanding EMI shielding performance (≈50 dB for a 940 nm thick film) that exceeds other synthetic materials with comparable thickness. MXene films with aligned flakes provide an effective route for producing large-area, high-strength, and high-electrical-conductivity MXene-based films for future electronic applications.