Electric Field Effects in Flash Joule Heating Synthesis.

Flash Joule heating has emerged as an ultrafast, scalable, and versatile synthesis method for nanomaterials, such as graphene. Here, we experimentally and theoretically deconvolute the contributions of thermal and electrical processes to the synthesis of graphene by flash Joule heating. While traditional methods of graphene synthesis involve purely chemical or thermal driving forces, our results show that the presence of charge and the resulting electric field in a graphene precursor catalyze the formation of graphene. Furthermore, modulation of the current or the pulse width affords the ability to control the three-step phase transition of the material from amorphous carbon to turbostratic graphene and finally to ordered (AB and ABC-stacked) graphene and graphite. Finally, density functional theory simulations reveal that the presence of a charge- and current-induced electric field inside the graphene precursor facilitates phase transition by lowering the activation energy of the reaction. These results demonstrate that the passage of electrical current through a solid sample can directly drive nanocrystal nucleation in flash Joule heating, an insight that may inform future Joule heating or other electrical synthesis strategies.

Nonlethal Molecular Nanomachines Potentiate Antibiotic Activity Against Gram-Negative Bacteria by Increasing Cell Permeability and Attenuating Efflux.

Antibiotic resistance is a pressing public health threat. Despite rising resistance, antibiotic development, especially for Gram-negative bacteria, has stagnated. As the traditional antibiotic research and development pipeline struggles to address this growing concern, alternative solutions become imperative. Synthetic molecular nanomachines (MNMs) are molecular structures that rotate unidirectionally in a controlled manner in response to a stimulus, such as light, resulting in a mechanical action that can propel molecules to drill into cell membranes, causing rapid cell death. Due to their broad destructive capabilities, clinical translation of MNMs remains challenging. Hence, here, we explore the ability of nonlethal visible-light-activated MNMs to potentiate conventional antibiotics against Gram-negative bacteria. Nonlethal MNMs enhanced the antibacterial activity of various classes of conventional antibiotics against Gram-negative bacteria, including those typically effective only against Gram-positive strains, reducing the antibiotic concentration required for bactericidal action. Our study also revealed that MNMs bind to the negatively charged phospholipids of the bacterial inner membrane, leading to permeabilization of the cell envelope and impairment of efflux pump activity following light activation of MNMs. The combined effects of MNMs on membrane permeability and efflux pumps resulted in increased antibiotic accumulation inside the cell, reversing antibiotic resistance and attenuating its development. These results identify nonlethal MNMs as pleiotropic antibiotic enhancers or adjuvants. The combination of MNMs with traditional antibiotics is a promising strategy against multidrug-resistant Gram-negative infections. This approach can reduce the amount of antibiotics needed and slow down antibiotic resistance development, thereby preserving the effectiveness of our current antibiotics.

Distinguishing Molecular Mechanical Action from Photothermal and Photodynamic Behavior.

Molecular motors (MM) are molecular machines, or nanomachines, that rotate unidirectionally upon photostimulation and perform mechanical work on their environment. In the last several years, it has been shown that the photomechanical action of MM can be used to permeabilize lipid bilayers, thereby killing cancer cells and pathogenic microorganisms and controlling cell signaling. The work contributes to a growing acknowledgement that the molecular actuation characteristic of these systems is useful for various applications in biology. However, the mechanical effects of molecular motion on biological materials are difficult to disentangle from photodynamic and photothermal action, which are also present when a light-absorbing fluorophore is irradiated with light. Here, an overview of the key methods used by various research groups to distinguish the effects of photomechanical, photodynamic, and photothermal action is provided. It is anticipated that this discussion will be helpful to the community seeking to use MM to develop new and distinctive medical technologies that result from mechanical disruption of biological materials.

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.

Oxidized Activated Charcoal Nanozymes: Synthesis, and Optimization for In Vitro and In Vivo Bioactivity for Traumatic Brain Injury.

Carbon-based superoxide dismutase (SOD) mimetic nanozymes have recently been employed as promising antioxidant nanotherapeutics due to their distinct properties. The structural features responsible for the efficacy of these nanomaterials as antioxidants are, however, poorly understood. Here, the process-structure-property-performance properties of coconut-derived oxidized activated charcoal (cOAC) nano-SOD mimetics are studied by analyzing how modifications to the nanomaterial's synthesis impact the size, as well as the elemental and electrochemical properties of the particles. These properties are then correlated to the in vitro antioxidant bioactivity of poly(ethylene glycol)-functionalized cOACs (PEG-cOAC). Chemical oxidative treatment methods that afford smaller, more homogeneous cOAC nanoparticles with higher levels of quinone functionalization show enhanced protection against oxidative damage in bEnd.3 murine endothelioma cells. In an in vivo rat model of mild traumatic brain injury (mTBI) and oxidative vascular injury, PEG-cOACs restore cerebral perfusion rapidly to the same extent as the former nanotube-derived PEG-hydrophilic carbon clusters (PEG-HCCs) with a single intravenous injection. These findings provide a deeper understanding of how carbon nanozyme syntheses can be tailored for improved antioxidant bioactivity, and set the stage for translation of medical applications.

Replacement of Concrete Aggregates with Coal-Derived Flash Graphene.

Each year, the growth of cities across developing economies in Asia, Africa, and Latin America drives demand for concrete to house and serve their burgeoning populations. Since 1950, the number of people living in urban areas has quadrupled to 4.2 billion, with another predicted 2.5 billion expected to join them in the next three decades. The largest component of concrete by volume is aggregates, such as sand and rocks, with sand as the most mined material in the world. However, the extraction rate of sand currently exceeds its natural replenishment rate, meaning that a global concrete-suitable sand shortage is extremely likely. As such, replacements for fine aggregates, such as sand, are in demand. Here, flash Joule heating (FJH) is used to convert coal-derived metallurgical coke (MC) into flash graphene aggregate (FGA), a blend of MC-derived flash graphene (MCFG), which mimics a natural aggregate (NA) in size. While graphene and graphene oxide have previously been used as reinforcing additives to concrete, in this contribution, FGA is used as a total aggregate replacement for NA, resulting in 25% lighter concrete with increases in toughness, peak strain, and specific compressive strength of 32, 33, and 21%, respectively, with a small reduction in specific Young's modulus of 11%. FJH can potentially enable the replacement of fine NA with FGA, resulting in lighter, stronger concrete.

Synthesis of Clean Hydrogen Gas from Waste Plastic at Zero Net Cost.

Hydrogen gas (H2 ) is the primary storable fuel for pollution-free energy production, with over 90 million tonnes used globally per year. More than 95% of H2 is synthesized through metal-catalyzed steam methane reforming that produces 11 tonnes of carbon dioxide (CO2 ) per tonne H2 . "Green H2 " from water electrolysis using renewable energy evolves no CO2 , but costs 2-3× more, making it presently economically unviable. Here catalyst-free conversion of waste plastic into clean H2 along with high purity graphene is reported. The scalable procedure evolves no CO2 when deconstructing polyolefins and produces H2 in purities up to 94% at high mass yields. The sale of graphene byproduct at just 5% of its current value yields H2 production at a negative cost. Life-cycle assessment demonstrates a 39-84% reduction in emissions compared to other H2 production methods, suggesting the flash H2 process to be an economically viable, clean H2 production route.

Molecular machines stimulate intercellular calcium waves and cause muscle contraction.

Intercellular calcium waves (ICW) are complex signalling phenomena that control many essential biological activities, including smooth muscle contraction, vesicle secretion, gene expression and changes in neuronal excitability. Accordingly, the remote stimulation of ICW could result in versatile biomodulation and therapeutic strategies. Here we demonstrate that light-activated molecular machines (MM)-molecules that perform mechanical work on the molecular scale-can remotely stimulate ICW. MM consist of a polycyclic rotor and stator that rotate around a central alkene when activated with visible light. Live-cell calcium-tracking and pharmacological experiments reveal that MM-induced ICW are driven by the activation of inositol-triphosphate-mediated signalling pathways by unidirectional, fast-rotating MM. Our data suggest that MM-induced ICW can control muscle contraction in vitro in cardiomyocytes and animal behaviour in vivo in Hydra vulgaris. This work demonstrates a strategy for directly controlling cell signalling and downstream biological function using molecular-scale devices.

Visible-Light-Activated Molecular Machines Kill Fungi by Necrosis Following Mitochondrial Dysfunction and Calcium Overload.

Invasive fungal infections are a growing public health threat. As fungi become increasingly resistant to existing drugs, new antifungals are urgently needed. Here, it is reported that 405-nm-visible-light-activated synthetic molecular machines (MMs) eliminate planktonic and biofilm fungal populations more effectively than conventional antifungals without resistance development. Mechanism-of-action studies show that MMs bind to fungal mitochondrial phospholipids. Upon visible light activation, rapid unidirectional drilling of MMs at ≈3 million cycles per second (MHz) results in mitochondrial dysfunction, calcium overload, and ultimately necrosis. Besides their direct antifungal effect, MMs synergize with conventional antifungals by impairing the activity of energy-dependent efflux pumps. Finally, MMs potentiate standard antifungals both in vivo and in an ex vivo porcine model of onychomycosis, reducing the fungal burden associated with infection.

Tunable Hybridized Morphologies Obtained through Flash Joule Heating of Carbon Nanotubes.

Hybrid carbon nanomaterials, such as those that incorporate carbon nanotubes into graphene sheets, have been found to display interesting mechanical and electrical properties because of their covalent bonding and π-π stacking domains. However, synthesis of these hybrid materials is limited by the high energetic cost of techniques like chemical vapor deposition. Here, we demonstrate the solvent- and gas-free synthesis of a 2D carbon nanotube/graphene network through flash Joule heating of pristine carbon nanotubes. The relative proportion of each morphology in the hybrid material can be tuned by varying the pulse time, as confirmed by Raman spectroscopy and microscopy. Triboindentation of epoxy composites made with the hybrid material shows increases of 162% and 64% to the hardness and Young's modulus, respectively, compared with the neat epoxy. These results demonstrate that flash Joule heating can be used to inexpensively convert carbon nanotubes into a hybrid network of nanotubes and graphene for use as an effective reinforcing additive in epoxy composites.

Upcycling of Waste Plastic into Hybrid Carbon Nanomaterials.

Graphitic 1D and hybrid nanomaterials represent a powerful solution in composite and electronic applications due to exceptional properties, but large-scale synthesis of hybrid materials has yet to be realized. Here, a rapid, scalable method to produce graphitic 1D materials from polymers using flash Joule heating (FJH) is reported. This avoids lengthy chemical vapor deposition and uses no solvent or water. The flash 1D materials (F1DM), synthesized using a variety of earth-abundant catalysts, have controllable diameters and morphologies by parameter tuning. Furthermore, the process can be modified to form hybrid materials, with F1DM bonded to turbostratic graphene. In nanocomposites, F1DM outperform commercially available carbon nanotubes. Compared to current 1D material synthetic strategies using life cycle assessment, FJH synthesis represents an 86-92% decrease in cumulative energy demand and 92-94% decrease in global-warming potential. This work suggests that FJH affords a cost-effective and sustainable route to upcycle waste plastic into valuable 1D and hybrid nanomaterials.

Flash Recycling of Graphite Anodes.

The ever-increasing production of commercial lithium-ion batteries (LIBs) will result in a staggering accumulation of waste when they reach their end of life. A closed-loop solution, with effective recycling of spent LIBs, will lessen both the environmental impacts and economic cost of their use. Presently, <5% of spent LIBs are recycled and the regeneration of graphite anodes has, unfortunately, been mostly overlooked despite the considerable cost of battery-grade graphite. Here, an ultrafast flash recycling method to regenerate the graphite anode is developed and valuable battery metal resources are recovered. Selective Joule heating is applied for only seconds to efficiently decompose the resistive impurities. The generated inorganic salts, including lithium, cobalt, nickel, and manganese, can be easily recollected from the flashed anode waste using diluted acid, specifically 0.1 m HCl. The flash-recycled anode preserves the graphite structure and is coated with a solid-electrolyte-interphase-derived carbon shell, contributing to high initial specific capacity, superior rate performance, and cycling stability, when compared to anode materials recycled using a high-temperature-calcination method. Life-cycle-analysis relative to current graphite production and recycling methods indicate that flash recycling can significantly reduce the total energy consumption and greenhouse gas emission while turning anode recycling into an economically advantageous process.

Sustainable valorization of asphaltenes via flash joule heating.

The refining process of petroleum crude oil generates asphaltenes, which poses complicated problems during the production of cleaner fuels. Following refining, asphaltenes are typically combusted for reuse as fuel or discarded into tailing ponds and landfills, leading to economic and environmental disruption. Here, we show that low-value asphaltenes can be converted into a high-value carbon allotrope, asphaltene-derived flash graphene (AFG), via the flash joule heating (FJH) process. After successful conversion, we develop nanocomposites by dispersing AFG into a polymer effectively, which have superior mechanical, thermal, and corrosion-resistant properties compared to the bare polymer. In addition, the life cycle and technoeconomic analysis show that the FJH process leads to reduced environmental impact compared to the traditional processing of asphaltene and lower production cost compared to other FJH precursors. Thus, our work suggests an alternative pathway to the existing asphaltene processing that directs toward a higher value stream while sequestering downstream emissions from the processing.

Light-activated molecular machines are fast-acting broad-spectrum antibacterials that target the membrane.

The increasing occurrence of antibiotic-resistant bacteria and the dwindling antibiotic research and development pipeline have created a pressing global health crisis. Here, we report the discovery of a distinctive antibacterial therapy that uses visible (405 nanometers) light-activated synthetic molecular machines (MMs) to kill Gram-negative and Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus, in minutes, vastly outpacing conventional antibiotics. MMs also rapidly eliminate persister cells and established bacterial biofilms. The antibacterial mode of action of MMs involves physical disruption of the membrane. In addition, by permeabilizing the membrane, MMs at sublethal doses potentiate the action of conventional antibiotics. Repeated exposure to antibacterial MMs is not accompanied by resistance development. Finally, therapeutic doses of MMs mitigate mortality associated with bacterial infection in an in vivo model of burn wound infection. Visible light-activated MMs represent an unconventional antibacterial mode of action by mechanical disruption at the molecular scale, not existent in nature and to which resistance development is unlikely.

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.

Holey and Wrinkled Flash Graphene from Mixed Plastic Waste.

High surface area varieties of graphene have captured significant attention, allowing for improved performance in a variety of applications. However, there are challenges facing the use of graphene in these applications since it is expensive and difficult to synthesize in bulk. Here, we leverage the capabilities of flash Joule heating to synthesize holey and wrinkled flash graphene (HWFG) in seconds from mixed plastic waste feedstocks, using in situ salt decomposition to produce and stabilize pore formation during the reaction. Surface areas as high as 874 m2 g-1 are obtained, with characteristics of micro-, meso-, and macroporosities. Raman spectroscopy confirms the wrinkled and turbostratic nature of the HWFG. We demonstrate HWFG applications in its use as a metal-free hydrogen evolution reaction electrocatalyst, with excellent stability, competitive overpotential, and Tafel slope; in a Li-metal battery anode allowing for stable and high discharge rates; and in a material with high gas adsorption. This represents an upcycle of mixed plastic waste, thereby affording a valuable route to address this pressing environmental pollutant concern.

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.

Photochemical Synthesis and Spectroscopy of Covalent PAH Dimers.

Laser photochemistry of pressed-pellet samples of polycyclic aromatic hydrocarbons (PAHs) produces covalently bonded dimers and some higher polymers. This chemistry was discovered initially via laser desorption time-of-flight mass spectrometry experiments, which produced masses (m/z) of 2M-2 and 2M-4 (where M is the monomer parent mass). Dimers are believed to be formed from photochemical dehydrogenation and radical polymerization chemistry in the desorption plume. Replication of these ablation conditions at higher throughput allowed PAH dimers of pyrene, perylene, and coronene to be produced and collected in milligram quantities. Differential sublimation provided purification of the dimers and elimination of residual monomers. The purified dimers were investigated with UV-visible, IR, and Raman spectroscopy, complemented by computational studies using density functional theory at the CAM-B3LYP/def2-TZV level. Calculations and predicted spectra were calibrated by comparison with the corresponding monomers and used to determine the lowest energy dimer structures. Infrared and Raman spectroscopy provided few distinctive signatures, but UV-visible spectra detected new transitions for each dimer. The comparison of simulated and experimental spectra allows determination of the most prevalent structures for the PAH dimers. The work presented here provides interesting insights into the spectroscopy of extended aromatic systems and a new strategy for the photochemical synthesis of large PAH dimers.

Machine Learning Guided Synthesis of Flash Graphene.

Advances in nanoscience have enabled the synthesis of nanomaterials, such as graphene, from low-value or waste materials through flash Joule heating. Though this capability is promising, the complex and entangled variables that govern nanocrystal formation in the Joule heating process remain poorly understood. In this work, machine learning (ML) models are constructed to explore the factors that drive the transformation of amorphous carbon into graphene nanocrystals during flash Joule heating. An XGBoost regression model of crystallinity achieves an r2 score of 0.8051 ± 0.054. Feature importance assays and decision trees extracted from these models reveal key considerations in the selection of starting materials and the role of stochastic current fluctuations in flash Joule heating synthesis. Furthermore, partial dependence analyses demonstrate the importance of charge and current density as predictors of crystallinity, implying a progression from reaction-limited to diffusion-limited kinetics as flash Joule heating parameters change. Finally, a practical application of the ML models is shown by using Bayesian meta-learning algorithms to automatically improve bulk crystallinity over many Joule heating reactions. These results illustrate the power of ML as a tool to analyze complex nanomanufacturing processes and enable the synthesis of 2D crystals with desirable properties by flash Joule heating.