Kinetically Controlled Synthesis of Metallic Glass Nanoparticles with Expanded Composition Space.

Nanoscale metallic glasses offer opportunities for investigating fundamental properties of amorphous solids and technological applications in biomedicine, microengineering, and catalysis. However, their top-down fabrication is limited by bulk counterpart availability, and bottom-up synthesis remains underexplored due to strict formation conditions. Here, a kinetically controlled flash carbothermic reaction is developed, featuring ultrafast heating (>105 K s-1) and cooling rates (>104 K s-1), for synthesizing metallic glass nanoparticles within milliseconds. Nine compositional permutations of noble metals, base metals, and metalloid (M1─M2─P, M1 = Pt/Pd, M2 = Cu/Ni/Fe/Co/Sn) are synthesized with widely tunable particle sizes and substrates. Through combinatorial development, a substantially expanded composition space for nanoscale metallic glass is discovered compared to bulk counterpart, revealing that the nanosize effect enhances glass forming ability. Leveraging this, several nanoscale metallic glasses are synthesized with composition that have never, to the knowledge, been synthesized in bulk. The metallic glass nanoparticles exhibit high activity in heterogeneous catalysis, outperforming crystalline metal alloy nanoparticles.

Automated Laboratory Kilogram-Scale Graphene Production from Coal.

The flash Joule heating (FJH) method converts many carbon feedstocks into graphene in milliseconds to seconds using an electrical pulse. This opens an opportunity for processing low or negative value resources, such as coal and plastic waste, into high value graphene. Here, a lab-scale automation FJH system that allows the synthesis of 1.1 kg of turbostratic flash graphene from coal-based metallurgical coke (MC) in 1.5 h is demonstrated. The process is based on the automated conversion of 5.7 g of MC per batch using an electrical pulse width modulation system to conduct the bottom-up upcycle of MC into flash graphene. This study then compare this method to two other scalable graphene synthesis techniques by both a life cycle assessment and a technoeconomic assessment.

High-temperature electrothermal remediation of multi-pollutants in soil.

Soil contamination is an environmental issue due to increasing anthropogenic activities. Existing processes for soil remediation suffer from long treatment time and lack generality because of different sources, occurrences, and properties of pollutants. Here, we report a high-temperature electrothermal process for rapid, water-free remediation of multiple pollutants in soil. The temperature of contaminated soil with carbon additives ramps up to 1000 to 3000 °C as needed within seconds via pulsed direct current input, enabling the vaporization of heavy metals like Cd, Hg, Pb, Co, Ni, and Cu, and graphitization of persistent organic pollutants like polycyclic aromatic hydrocarbons. The rapid treatment retains soil mineral constituents while increases infiltration rate and exchangeable nutrient supply, leading to soil fertilization and improved germination rates. We propose strategies for upscaling and field applications. Techno-economic analysis indicates the process holds the potential for being more energy-efficient and cost-effective compared to soil washing or thermal desorption.

NaGdF4:Eu3+ nanocrystalline: an in-depth study of energy transfer processes and Judd-Ofelt analysis using the luminescence excitation spectrum.

NaGdF4 nanocrystalline doped with different concentrations of Eu3+ ions were synthesized using the precipitation method. The structure and morphology of the material were investigated through the measurements of the XRD patterns and SEM images, respectively. The optical properties of the NaGdF4:Eu3+ nanocrystalline were studied in the framework of the Judd-Ofelt theory in which the Ωλ parameters were calculated by two methods: the traditional method using the luminescence spectra and the self-referenced method using the luminescence excitation spectra. In NaGdF4:Eu3+ nanocrystalline, the Gd3+ ions in the lattice act as sensitizer centers for the luminescence of Eu3+ ions under excitation at 272 and 310 nm. The energy transfer process from Gd3+ to Eu3+ causes the emission enhancement of Eu3+ ions. Upon excitation by the characteristic wavelengths of Gd3+, the luminescence efficiency of the Eu3+ ions in NaGdF4:Eu3+ is affected by two mechanisms: the emission of Gd3+ ions and the trapping of excited energy by the Eu3+ ions. The energy transfer between Eu3+ ions was also discussed in detail. This process leads to the enhancement of the luminescence bands originating from the 5D0 level. The dominant interaction between the Eu3+ ions in the energy transfer process is the dipole-dipole mechanism, which is determined by fitting the decay curve of the 5D2 level to the Inokuti-Hirayama model.

Environmental contamination with Clostridioides (Clostridium) difficile in Vietnam.

AIMS: To investigate the prevalence, molecular type, and antimicrobial susceptibility of Clostridioides difficile in the environment in Vietnam, where little is known about C. difficile. METHODS AND RESULTS: Samples of pig faeces, soils from pig farms, potatoes, and the hospital environment were cultured for C. difficile. Isolates were identified and typed by polymerase chain reaction (PCR) ribotyping. The overall prevalence of C. difficile contamination was 24.5% (68/278). Clostridioides difficile was detected mainly in soils from pig farms and hospital soils, with 70%-100% prevalence. Clostridioides difficile was isolated from 3.4% of pig faecal samples and 5% of potato surfaces. The four most prevalent ribotypes (RTs) were RTs 001, 009, 038, and QX574. All isolates were susceptible to metronidazole, fidaxomicin, vancomycin, and amoxicillin/clavulanate, while resistance to erythromycin, tetracycline, and moxifloxacin was common in toxigenic strains. Clostridioides difficile RTs 001A+B+CDT- and 038A-B-CDT- were predominantly multidrug resistant. CONCLUSIONS: Environmental sources of C. difficile are important to consider in the epidemiology of C. difficile infection in Vietnam, however, contaminated soils are likely to be the most important source of C. difficile. This poses additional challenges to controlling infections in healthcare settings.

High-surface-area corundum nanoparticles by resistive hotspot-induced phase transformation.

High-surface-area α-Al2O3 nanoparticles are used in high-strength ceramics and stable catalyst supports. The production of α-Al2O3 by phase transformation from γ-Al2O3 is hampered by a high activation energy barrier, which usually requires extended high-temperature annealing (~1500 K, > 10 h) and suffers from aggregation. Here, we report the synthesis of dehydrated α-Al2O3 nanoparticles (phase purity ~100%, particle size ~23 nm, surface area ~65 m2 g-1) by a pulsed direct current Joule heating of γ-Al2O3. The phase transformation is completed at a reduced bulk temperature and duration (~573 K, < 1 s) via an intermediate δ'-Al2O3 phase. Numerical simulations reveal the resistive hotspot-induced local heating in the pulsed current process enables the rapid transformation. Theoretical calculations show the topotactic transition (from γ- to δ'- to α-Al2O3) is driven by their surface energy differences. The α-Al2O3 nanoparticles are sintered to nanograined ceramics with hardness superior to commercial alumina and approaching that of sapphire.

Robust Superhydrophobic Surfaces via the Sand-In Method.

Superhydrophobic surfaces have gained sustained attention because of their extensive applications in the fields of self-cleaning, anti-icing, and drag reduction systems. Water droplets must have large apparent contact angle (CA) (>150°) and small CA hysteresis (<10°) on these surfaces. However, previous research usually involves complex fabrication strategies to modify the surface wettability. It is also challenging to maintain the temporal and mechanical stability of the delicate surface textures. Here, we develop a one-step solvent-free sand-in method to fabricate robust superhydrophobic surfaces directly atop various substrates with an apparent CA up to ∼163.8° and hysteresis less than 5°. The water repellency can withstand 100 Scotch tape peeling tests and remain stable after being stored under ambient humid conditions in Houston, Texas, for 18 months or being heated at 130 °C in air for 24 h. The superhydrophobic surfaces have excellent anti-icing ability, including a ∼2.6× longer water freezing time and ∼40% smaller ice adhesion strength with the temperature as low as -35 °C. Since the surface layers are fabricated by sanding the substrates with the powder additives, the surface damage can be repaired by a direct re-sanding treatment with the same powder additives. Further sand-in condition screenings broaden surface wettability from hydrophilic to superhydrophobic. The sand-in method induces the surface modification and the formation of the tribofilm. Surface and materials characterizations reveal that both microstructures and nanoscale asperities of the tribofilms contribute to the robust superhydrophobic features of sanded surfaces.

Turbostratic Boron-Carbon-Nitrogen and Boron Nitride by Flash Joule Heating.

Turbostratic layers in 2D materials have an interlayer misalignment. The lack of alignment expands the intrinsic interlayer distances and weakens the optical and electronic interactions between adjacent layers. This introduces properties distinct from those structures with well-aligned lattices and strong coupling interactions. However, direct and rapid synthesis of turbostratic materials remains a challenge owing to their thermodynamically metastable properties. Here, a flash Joule heating (FJH) method to achieve bulk synthesis of boron-carbon-nitrogen ternary compounds with turbostratic structures by a kinetically controlled ultrafast cooling process that takes place within milliseconds (103  to 104 K s-1 ) is reported. Theoretical calculations support the existence of turbostratic structures and provide estimates of the energy barriers with respect to conversion into the corresponding well-aligned counterparts. When using non-carbon conductive additives, a direct synthesis of boron nitride is possible. The turbostratic nature facilitates mechanical exfoliation and more stable dispersions. Accordingly, the addition of flash products to a poly(vinyl alcohol) nanocomposite film coating a copper surface greatly improves the copper's resistance to corrosion in 0.5 m sulfuric acid or 3.5 wt% saline solution. FJH allows the use of bulk materials as reactants and provides a rapid approach to large quantities of the hitherto hard-to-access turbostratic materials.

Brushed Metals for Rechargeable Metal Batteries.

Battery designs are swiftly changing from metal-ion to rechargeable metal batteries. Theoretically, metals can deliver maximum anode capacity and enable cells with improved energy density. In practice, these advantages are only possible if the parasitic surface reactions associated with metal anodes are controlled. These undesirable surface reactions are responsible for many troublesome issues, like dendrite formation and accelerated consumption of active materials, which leads to anodes with low cycle life or even battery runaway. Here, a facile and solvent-free brushing method is reported to convert powders into films atop Li and Na metal foils. Benefiting from the reactivity of Li metal with these powder films, surface energy can be effectively tuned, thereby preventing parasitic reaction. In-operando study of P2 S5 -modified Li anodes in liquid electrolyte cells reveals a smoother electrode contour and more uniform metal electrodeposition and dissolution behavior. The P2 S5 -modified Li anodes sustain ultralow polarization in symmetric cell for >4000 h, ≈8× longer than bare Li anodes. The capacity retention is ≈70% higher when P2 S5 -modified Li anodes are paired with a practical LiFePO4 cathode (≈3.2 mAh cm-2 ) after 340 cycles. Brush coating opens a promising avenue to fabricate large-scale artificial solid-electrolyte-interphase directly on metals without the need for organic solvent.

Heteroatom-Doped Flash Graphene.

Heteroatom doping can effectively tailor the local structures and electronic states of intrinsic two-dimensional materials, and endow them with modified optical, electrical, and mechanical properties. Recent studies have shown the feasibility of preparing doped graphene from graphene oxide and its derivatives via some post-treatments, including solid-state and solvothermal methods, but they require reactive and harsh reagents. However, direct synthesis of various heteroatom-doped graphene in larger quantities and high purity through bottom-up methods remains challenging. Here, we report catalyst-free and solvent-free direct synthesis of graphene doped with various heteroatoms in bulk via flash Joule heating (FJH). Seven types of heteroatom-doped flash graphene (FG) are synthesized through millisecond flashing, including single-element-doped FG (boron, nitrogen, oxygen, phosphorus, sulfur), two-element-co-doped FG (boron and nitrogen), as well as three-element-co-doped FG (boron, nitrogen, and sulfur). A variety of low-cost dopants, such as elements, oxides, and organic compounds are used. The graphene quality of heteroatom-doped FG is high, and similar to intrinsic FG, the material exhibits turbostraticity, increased interlayer spacing, and superior dispersibility. Electrochemical oxygen reduction reaction of different heteroatom-doped FG is tested, and sulfur-doped FG shows the best performance. Lithium metal battery tests demonstrate that nitrogen-doped FG exhibits a smaller nucleation overpotential compared to Cu or undoped FG. The electrical energy cost for the synthesis of heteroatom-doped FG synthesis is only 1.2 to 10.7 kJ g-1, which could render the FJH method suitable for low-cost mass production of heteroatom-doped graphene.

Rare earth elements from waste.

Rare earth elements (REEs) are critical materials in electronics and clean technologies. With the diminishing of easily accessible minerals for mining, the REE recovery from waste is an alternative toward a circular economy. Present methods for REE recovery suffer from lengthy purifications, low extractability, and high wastewater streams. Here, we report an ultrafast electrothermal process (~3000°C, ~1 s) based on flash Joule heating (FJH) for activating wastes to improve REE extractability. FJH thermally degrades or reduces the hard-to-dissolve REE species to components with high thermodynamic solubility, leading to ~2× increase in leachability and high recovery yields using diluted acid (e.g., 0.1 M HCl). The activation strategy is feasible for various wastes including coal fly ash, bauxite residue, and electronic waste. The rapid FJH process is energy-efficient with a low electrical energy consumption of 600 kWh ton-1. The potential for this route to be rapidly scaled is outlined.

Phase controlled synthesis of transition metal carbide nanocrystals by ultrafast flash Joule heating.

Nanoscale carbides enhance ultra-strong ceramics and show activity as high-performance catalysts. Traditional lengthy carburization methods for carbide syntheses usually result in coked surface, large particle size, and uncontrolled phase. Here, a flash Joule heating process is developed for ultrafast synthesis of carbide nanocrystals within 1 s. Various interstitial transition metal carbides (TiC, ZrC, HfC, VC, NbC, TaC, Cr2C3, MoC, and W2C) and covalent carbides (B4C and SiC) are produced using low-cost precursors. By controlling pulse voltages, phase-pure molybdenum carbides including ß-Mo2C and metastable α-MoC1-x and η-MoC1-x are selectively synthesized, demonstrating the excellent phase engineering ability of the flash Joule heating by broadly tunable energy input that can exceed 3000 K coupled with kinetically controlled ultrafast cooling (>104 K s-1). Theoretical calculation reveals carbon vacancies as the driving factor for topotactic transition of carbide phases. The phase-dependent hydrogen evolution capability of molybdenum carbides is investigated with ß-Mo2C showing the best performance.

Large-Scale Syntheses of 2D Materials: Flash Joule Heating and Other Methods.

In the past 17 years, the larger-scale production of graphene and graphene family materials has proven difficult and costly, thus slowing wider-scale commercial applications. The quality of the graphene that is prepared on larger scales has often been poor, demonstrating a need for improved quality controls. Here, current industrial graphene synthetic and analytical methods, as well as recent academic advancements in larger-scale or sustainable synthesis of graphene, defined here as weights more than 200 mg or films larger than 200 cm2 , are compiled and reviewed. There is a specific emphasis on recent research in the use of flash Joule heating as a rapid, efficient, and scalable method to produce graphene and other 2D nanomaterials. Reactor design, synthetic strategies, safety considerations, feedstock selection, Raman spectroscopy, and future outlooks for flash Joule heating syntheses are presented. To conclude, the remaining challenges and opportunities in the larger-scale synthesis of graphene and a perspective on the broader use of flash Joule heating for larger-scale 2D materials synthesis are discussed.

Folate Functionalized Lipid Nanoparticles for Targeted Therapy of Methicillin-Resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA), commonly called a superbug, is a highly alarming antibiotic-resistant population of Staphylococcus aureus (S. aureus) bacteria. Vancomycin (VAN) was first approved by the FDA in 1988, and it is still regarded as the treatment of choice for MRSA. The efficacy of VAN treatment has become less effective due to the development of VAN resistance in MRSA and the potential for nephrotoxicity. This study aims to improve the efficacy of VAN treatment by identifying the folate receptor for MRSA infected tissues and developing folate decorated lipid nanoparticles containing VAN (LVAN). In comparison to conventional VAN, LVAN showed a higher bactericidal effect and a superior ability to inhibit biofilm in MRSA with an enhanced accumulation in MRSA infected thigh tissues and a reduced accumulation in kidney. The results suggested that LVAN is a promising candidate to overcome the current limitations of bacterial resistance and adverse side effects in kidneys found in VAN.

Urban mining by flash Joule heating.

Precious metal recovery from electronic waste, termed urban mining, is important for a circular economy. Present methods for urban mining, mainly smelting and leaching, suffer from lengthy purification processes and negative environmental impacts. Here, a solvent-free and sustainable process by flash Joule heating is disclosed to recover precious metals and remove hazardous heavy metals in electronic waste within one second. The sample temperature ramps to ~3400 K in milliseconds by the ultrafast electrical thermal process. Such a high temperature enables the evaporative separation of precious metals from the supporting matrices, with the recovery yields >80% for Rh, Pd, Ag, and >60% for Au. The heavy metals in electronic waste, some of which are highly toxic including Cr, As, Cd, Hg, and Pb, are also removed, leaving a final waste with minimal metal content, acceptable even for agriculture soil levels. Urban mining by flash Joule heating would be 80× to 500× less energy consumptive than using traditional smelting furnaces for metal-component recovery and more environmentally friendly.

Ultrafast and Controllable Phase Evolution by Flash Joule Heating.

Flash Joule heating (FJH), an advanced material synthesis technique, has been used for the production of high-quality carbon materials. Direct current discharge through the precursors by large capacitors has successfully converted carbon-based starting materials into bulk quantities of turbostratic graphene by the FJH process. However, the formation of other carbon allotropes, such as nanodiamonds and concentric carbon materials, as well as the covalent functionalization of different carbon allotropes by the FJH process, remains challenging. Here, we report the solvent-free FJH synthesis of three different fluorinated carbon allotropes: fluorinated nanodiamonds, fluorinated turbostratic graphene, and fluorinated concentric carbon. This is done by millisecond flashing of organic fluorine compounds and fluoride precursors. Spectroscopic analysis confirms the modification of the electronic states and the existence of various short-range and long-range orders in the different fluorinated carbon allotropes. The flash-time-dependent relationship is further demonstrated to control the phase evolution and product compositions.

Millisecond Conversion of Metastable 2D Materials by Flash Joule Heating.

Controllable phase engineering is vital for precisely tailoring material properties since different phase structures have various electronic states and atomic arrangements. Rapid synthesis of thermodynamically metastable materials, especially two-dimensional metastable materials, with high efficiency and low cost remains a large challenge. Here we report flash Joule heating (FJH) as an electrothermal method to achieve the bulk conversion of transition metal dichalcogenides, MoS2 and WS2, from 2H phases to 1T phases in milliseconds. The conversions can reach up to 76% of flash MoS2 using tungsten powder as conductive additive. Different degrees of phase conversion can be realized by controlling the FJH conditions, such as reaction duration and additives, which allows the study of ratio-dependent properties. First-principles calculations confirm that structural processes associated with the FJH, such as vacancy formation and charge accumulation, result in stabilization of the 1T phases. FJH offers rapid access to bulk quantities of the hitherto hard-to-access 1T phases, a promising method for further fundamental research and diverse applications of metastable phases.

Optical properties and energy transfer in KYF4:Sm3+ and KYF4:Tb3+,Sm3+ polycrystalline materials.

KYF4 polycrystalline materials singly doped with Sm3+ ions and co-doped with Tb3+/Sm3+ ions were synthesized by the hydrothermal technique. The optical spectra of all samples were measured at room temperature. The features of the ligand field and the optical properties of Sm3+ ions in KYF4 were studied via Judd-Ofelt theory. A three-level model was used to estimate the validity of the Judd-Ofelt analysis for KYF4:Sm3+. The luminescence quenching of KYF4:Sm3+ relates to energy transfer through cross relaxation between Sm3+ ions. For KYF4:Tb3+,Sm3+, the luminescence of Sm3+ ions is enhanced due to the energy transfer process from Tb3+ to Sm3+. The chromaticity features of the luminescence from KYF4:Tb3+,Sm3+ were estimated by the chromaticity coordinates and correlated color temperature (CCT). The dominant interaction mechanism and the energy transfer parameters for the Sm3+-Sm3+ and Tb3+-Sm3+ energy transfer processes were analyzed by using the Inokuti-Hirayama model.

Flash Graphene from Plastic Waste.

In this work, an approach to upcycling plastic waste (PW) products is presented. The method relies on flash Joule heating (FJH) to convert PW into flash graphene (FG). In addition to FG, the process results in the formation of carbon oligomers, hydrogen, and light hydrocarbons. In order to make high-quality graphene, a sequential alternating current (AC) and direct current (DC) flash is used. The FJH process requires no catalyst and works for PW mixtures, which makes the process suitable for handling landfill PW. The energy required to convert PW to FG is ∼23 kJ/g or ∼$125 in electricity per ton of PW, potentially making this process economically attractive for scale-up. The FG was characterized by Raman spectroscopy and had an I2D/IG peak ratio up to 6 with a low-intensity D band. Moreover, transmission electron microscopy and X-ray diffraction analysis show that the FG is turbostratic with an interlayer spacing of 3.45 Å. The large interlayer spacing will facilitate its dispersion in liquids and composites. Analysis of FG dispersions in 1% Pluronic aqueous solution shows that concentrations up to 1.2 mg/mL can be achieved. The carbon oligomers that distilled from the process were characterized by Fourier transform infrared spectroscopy and have chemical structures similar to the starting PW. Initial analysis of gas-phase products shows the formation of considerable amounts of hydrogen along with other light hydrocarbons. As graphene is naturally occurring and shows a low toxicity profile, this could be an environmentally beneficial method to upcycle PW.

Flash Graphene Morphologies.

Flash Joule heating (FJH) can convert almost any carbon-based precursor into bulk quantities of graphene. This work explores the morphologies and properties of flash graphene (FG) generated from carbon black. It is shown that FG is partially comprised of sheets of turbostratic FG (tFG) that have a rotational mismatch between neighboring layers. The remainder of the FG is wrinkled graphene sheets that resemble nongraphitizing carbon. To generate high quality tFG sheets, a FJH duration of 30-100 ms is employed. Beyond 100 ms, the turbostratic sheets have time to AB-stack and form bulk graphite. Atomistic simulations reveal that generic thermal annealing yields predominantly wrinkled graphene which displays minimal to no alignment of graphitic planes, as opposed to the high-quality tFG that might be formed under the direct influence of current conducted through the material. The tFG was easily exfoliated via shear, hence the FJH process has the potential for bulk production of tFG without the need for pre-exfoliation using chemicals or high energy mechanical shear.