Flash heating process for efficient meat preservation.

Maintaining food safety and quality is critical for public health and food security. Conventional food preservation methods, such as pasteurization and dehydration, often change the overall organoleptic quality of the food products. Herein, we demonstrate a method that affects only a thin surface layer of the food, using beef as a model. In this method, Joule heating is generated by applying high electric power to a carbon substrate in <1 s, which causes a transient increase of the substrate temperature to > ~2000 K. The beef surface in direct contact with the heating substrate is subjected to ultra-high temperature flash heating, leading to the formation of a microbe-inactivated, dehydrated layer of ~100 µm in thickness. Aerobic mesophilic bacteria, Enterobacteriaceae, yeast and mold on the treated samples are inactivated to a level below the detection limit and remained low during room temperature storage of 5 days. Meanwhile, the product quality, including visual appearance, texture, and nutrient level of the beef, remains mostly unchanged. In contrast, microorganisms grow rapidly on the untreated control samples, along with a rapid deterioration of the meat quality. This method might serve as a promising preservation technology for securing food safety and quality.

A stable atmospheric-pressure plasma for extreme-temperature synthesis.

Plasmas can generate ultra-high-temperature reactive environments that can be used for the synthesis and processing of a wide range of materials1,2. However, the limited volume, instability and non-uniformity of plasmas have made it challenging to scalably manufacture bulk, high-temperature materials3-8. Here we present a plasma set-up consisting of a pair of carbon-fibre-tip-enhanced electrodes that enable the generation of a uniform, ultra-high temperature and stable plasma (up to 8,000 K) at atmospheric pressure using a combination of vertically oriented long and short carbon fibres. The long carbon fibres initiate the plasma by micro-spark discharge at a low breakdown voltage, whereas the short carbon fibres coalesce the discharge into a volumetric and stable ultra-high-temperature plasma. As a proof of concept, we used this process to synthesize various extreme materials in seconds, including ultra-high-temperature ceramics (for example, hafnium carbonitride) and refractory metal alloys. Moreover, the carbon-fibre electrodes are highly flexible and can be shaped for various syntheses. This simple and practical plasma technology may help overcome the challenges in high-temperature synthesis and enable large-scale electrified plasma manufacturing powered by renewable electricity.

A solution-processed radiative cooling glass.

Passive daytime radiative cooling materials could reduce the energy needed for building cooling up to 60% by reflecting sunlight and emitting long-wave infrared (LWIR) radiation into the cold Universe (~3 kelvin). However, developing passive cooling structures that are both practical to manufacture and apply while also displaying long-term environmental stability is challenging. We developed a randomized photonic composite consisting of a microporous glass framework that features selective LWIR emission along with relatively high solar reflectance and aluminum oxide particles that strongly scatter sunlight and prevent densification of the porous structure during manufacturing. This microporous glass coating enables a temperature drop of ~3.5° and 4°C even under high-humidity conditions (up to 80%) during midday and nighttime, respectively. This radiative "cooling glass" coating maintains high solar reflectance even when exposed to harsh conditions, including water, ultraviolet radiation, soiling, and high temperatures.

Depolymerization of plastics by means of electrified spatiotemporal heating.

Depolymerization is a promising strategy for recycling waste plastic into constituent monomers for subsequent repolymerization1. However, many commodity plastics cannot be selectively depolymerized using conventional thermochemical approaches, as it is difficult to control the reaction progress and pathway. Although catalysts can improve the selectivity, they are susceptible to performance degradation2. Here we present a catalyst-free, far-from-equilibrium thermochemical depolymerization method that can generate monomers from commodity plastics (polypropylene (PP) and poly(ethylene terephthalate) (PET)) by means of pyrolysis. This selective depolymerization process is realized by two features: (1) a spatial temperature gradient and (2) a temporal heating profile. The spatial temperature gradient is achieved using a bilayer structure of porous carbon felt, in which the top electrically heated layer generates and conducts heat down to the underlying reactor layer and plastic. The resulting temperature gradient promotes continuous melting, wicking, vaporization and reaction of the plastic as it encounters the increasing temperature traversing the bilayer, enabling a high degree of depolymerization. Meanwhile, pulsing the electrical current through the top heater layer generates a temporal heating profile that features periodic high peak temperatures (for example, about 600 °C) to enable depolymerization, yet the transient heating duration (for example, 0.11 s) can suppress unwanted side reactions. Using this approach, we depolymerized PP and PET to their monomers with yields of about 36% and about 43%, respectively. Overall, this electrified spatiotemporal heating (STH) approach potentially offers a solution to the global plastic waste problem.

Fluids and Electrolytes under Confinement in Single-Digit Nanopores.

Confined fluids and electrolyte solutions in nanopores exhibit rich and surprising physics and chemistry that impact the mass transport and energy efficiency in many important natural systems and industrial applications. Existing theories often fail to predict the exotic effects observed in the narrowest of such pores, called single-digit nanopores (SDNs), which have diameters or conduit widths of less than 10 nm, and have only recently become accessible for experimental measurements. What SDNs reveal has been surprising, including a rapidly increasing number of examples such as extraordinarily fast water transport, distorted fluid-phase boundaries, strong ion-correlation and quantum effects, and dielectric anomalies that are not observed in larger pores. Exploiting these effects presents myriad opportunities in both basic and applied research that stand to impact a host of new technologies at the water-energy nexus, from new membranes for precise separations and water purification to new gas permeable materials for water electrolyzers and energy-storage devices. SDNs also present unique opportunities to achieve ultrasensitive and selective chemical sensing at the single-ion and single-molecule limit. In this review article, we summarize the progress on nanofluidics of SDNs, with a focus on the confinement effects that arise in these extremely narrow nanopores. The recent development of precision model systems, transformative experimental tools, and multiscale theories that have played enabling roles in advancing this frontier are reviewed. We also identify new knowledge gaps in our understanding of nanofluidic transport and provide an outlook for the future challenges and opportunities at this rapidly advancing frontier.

Highly stable, antiviral, antibacterial cotton textiles via molecular engineering.

Cotton textiles are ubiquitous in daily life and are also one of the primary mediums for transmitting viruses and bacteria. Conventional approaches to fabricating antiviral and antibacterial textiles generally load functional additives onto the surface of the fabric and/or their microfibres. However, such modifications are susceptible to deterioration after long-term use due to leaching of the additives. Here we show a different method to impregnate copper ions into the cellulose matrix to form a copper ion-textile (Cu-IT), in which the copper ions strongly coordinate with the oxygen-containing polar functional groups (for example, hydroxyl) of the cellulose chains. The Cu-IT displays high antiviral and antibacterial performance against tobacco mosaic virus and influenza A virus, and Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa and Bacillus subtilis bacteria due to the antimicrobial properties of copper. Furthermore, the strong coordination bonding of copper ions with the hydroxyl functionalities endows the Cu-IT with excellent air/water retainability and superior mechanical stability, which can meet daily use and resist repeated washing. This method to fabricate Cu-IT is cost-effective, ecofriendly and highly scalable, and this textile appears very promising for use in household products, public facilities and medical settings.

A cellulose-derived supramolecule for fast ion transport.

Supramolecular frameworks have been widely synthesized for ion transport applications. However, conventional approaches of constructing ion transport pathways in supramolecular frameworks typically require complex processes and display poor scalability, high cost, and limited sustainability. Here, we report the scalable and cost-effective synthesis of an ion-conducting (e.g., Na+) cellulose-derived supramolecule (Na-CS) that features a three-dimensional, hierarchical, and crystalline structure composed of massively aligned, one-dimensional, and ångström-scale open channels. Using wood-based Na-CS as a model material, we achieve high ionic conductivities (e.g., 0.23 S/cm in 20 wt% NaOH at 25 °C) even with a highly dense microstructure, in stark contrast to conventional membranes that typically rely on large pores (e.g., submicrometers to a few micrometers) to obtain comparable ionic conductivities. This synthesis approach can be universally applied to a variety of cellulose materials beyond wood, including cotton textiles, fibers, paper, and ink, which suggests excellent potential for a number of applications such as ion-conductive membranes, ionic cables, and ionotronic devices.

Ultrahigh-temperature melt printing of multi-principal element alloys.

Multi-principal element alloys (MPEA) demonstrate superior synergetic properties compared to single-element predominated traditional alloys. However, the rapid melting and uniform mixing of multi-elements for the fabrication of MPEA structural materials by metallic 3D printing is challenging as it is difficult to achieve both a high temperature and uniform temperature distribution in a sufficient heating source simultaneously. Herein, we report an ultrahigh-temperature melt printing method that can achieve rapid multi-elemental melting and uniform mixing for MPEA fabrication. In a typical fabrication process, multi-elemental metal powders are loaded into a high-temperature column zone that can be heated up to 3000 K via Joule heating, followed by melting on the order of milliseconds and mixing into homogenous alloys, which we attribute to the sufficiently uniform high-temperature heating zone. As proof-of-concept, we successfully fabricated single-phase bulk NiFeCrCo MPEA with uniform grain size. This ultrahigh-temperature rapid melt printing process provides excellent potential toward MPEA 3D printing.

Programmable heating and quenching for efficient thermochemical synthesis.

Conventional thermochemical syntheses by continuous heating under near-equilibrium conditions face critical challenges in improving the synthesis rate, selectivity, catalyst stability and energy efficiency, owing to the lack of temporal control over the reaction temperature and time, and thus the reaction pathways1-3. As an alternative, we present a non-equilibrium, continuous synthesis technique that uses pulsed heating and quenching (for example, 0.02 s on, 1.08 s off) using a programmable electric current to rapidly switch the reaction between high (for example, up to 2,400 K) and low temperatures. The rapid quenching ensures high selectivity and good catalyst stability, as well as lowers the average temperature to reduce the energy cost. Using CH4 pyrolysis as a model reaction, our programmable heating and quenching technique leads to high selectivity to value-added C2 products (>75% versus <35% by the conventional non-catalytic method and versus <60% by most conventional methods using optimized catalysts). Our technique can be extended to a range of thermochemical reactions, such as NH3 synthesis, for which we achieve a stable and high synthesis rate of about 6,000 µmol gFe-1 h-1 at ambient pressure for >100 h using a non-optimized catalyst. This study establishes a new model towards highly efficient non-equilibrium thermochemical synthesis.

A high-performance hydroxide exchange membrane enabled by Cu2+-crosslinked chitosan.

Ion exchange membranes are widely used to selectively transport ions in various electrochemical devices. Hydroxide exchange membranes (HEMs) are promising to couple with lower cost platinum-free electrocatalysts used in alkaline conditions, but are not stable enough in strong alkaline solutions. Herein, we present a Cu2+-crosslinked chitosan (chitosan-Cu) material as a stable and high-performance HEM. The Cu2+ ions are coordinated with the amino and hydroxyl groups of chitosan to crosslink the chitosan chains, forming hexagonal nanochannels (~1 nm in diameter) that can accommodate water diffusion and facilitate fast ion transport, with a high hydroxide conductivity of 67 mS cm-1 at room temperature. The Cu2+ coordination also enhances the mechanical strength of the membrane, reduces its permeability and, most importantly, improves its stability in alkaline solution (only 5% conductivity loss at 80 °C after 1,000 h). These advantages make chitosan-Cu an outstanding HEM, which we demonstrate in a direct methanol fuel cell that exhibits a high power density of 305 mW cm-2. The design principle of the chitosan-Cu HEM, in which ion transport channels are generated in the polymer through metal-crosslinking of polar functional groups, could inspire the synthesis of many ion exchange membranes for ion transport, ion sieving, ion filtration and more.

High-entropy nanoparticles: Synthesis-structure-property relationships and data-driven discovery.

High-entropy nanoparticles have become a rapidly growing area of research in recent years. Because of their multielemental compositions and unique high-entropy mixing states (i.e., solid-solution) that can lead to tunable activity and enhanced stability, these nanoparticles have received notable attention for catalyst design and exploration. However, this strong potential is also accompanied by grand challenges originating from their vast compositional space and complex atomic structure, which hinder comprehensive exploration and fundamental understanding. Through a multidisciplinary view of synthesis, characterization, catalytic applications, high-throughput screening, and data-driven materials discovery, this review is dedicated to discussing the important progress of high-entropy nanoparticles and unveiling the critical needs for their future development for catalysis, energy, and sustainability applications.

Rapid Pressureless Sintering of Glasses.

Silica glasses have wide applications in industrial fields due to their extraordinary properties, such as high transparency, low thermal expansion coefficient, and high hardness. However, current methods of fabricating silica glass generally require long thermal treatment time (up to hours) and complex setups, leading to high cost and slow manufacturing speed. Herein, to obtain high-quality glasses using a facile and rapid method, an ultrafast high-temperature sintering (UHS) technique is reported that requires no additional pressure. Using UHS, silica precursors can be densified in seconds due to the large heating rate (up to 102 K s-1 ) of closely placed carbon heaters. The typical sintering time is as short as ≈10 s, ≈1-3 orders of magnitude faster than other methods. The sintered glasses exhibit relative densities of > 98% and high visible transmittances of ≈90%. The powder-based sintering process also allows rapid doping of metal ions to fabricate colored glasses. The UHS is further extended to sinter other functional glasses such as indium tin oxide (ITO)-doped silica glass, and other transparent ceramics such as Gd-doped yttrium aluminum garnet. This study demonstrates an UHS proof-of-concept for the rapid fabrication of high-quality glass and opens an avenue toward rapid discovery of transparent materials.

Rapid Synthesis of High-Entropy Oxide Microparticles.

High-entropy nanoparticles have received notable attention due to their tunable properties and broad material space. However, these nanoparticles are not suitable for certain applications (e.g., battery electrodes), where their microparticle (submicron to micron) counterparts are more preferred. Conventional methods used for synthesizing high-entropy nanoparticles often involve various ultrafast shock processes. To increase the size thereby achieving high-entropy microparticles, longer reaction time (e.g., heating duration) is usually used, which may also lead to undesired particle overgrowth or even densified microstructures. In this work, an approach based on Joule heating for synthesizing high-entropy oxide (HEO) microparticles with uniform elemental distribution is reported. In particular, two key synthesis conditions are identified to achieve high-quality HEO microparticles: 1) the precursors need to be loosely packed to avoid densification; 2) the heating time needs to be accurately controlled to tens of seconds instead of using milliseconds (thermal shock) that leads to nanoparticles or longer heating duration that forms bulk structures. The utility of the synthesized HEO microparticles for a range of applications, including high-performance Li-ion battery anode and water oxidation catalyst. This study opens up a new door toward synthesizing high-entropy microparticles with high quality and broad material space.

Multi-principal elemental intermetallic nanoparticles synthesized via a disorder-to-order transition.

Nanoscale multi-principal element intermetallics (MPEIs) may provide a broad and tunable compositional space of active, high-surface area materials with potential applications such as catalysis and magnetics. However, MPEI nanoparticles are challenging to fabricate because of the tendency of the particles to grow/agglomerate or phase-separated during annealing. Here, we demonstrate a disorder-to-order phase transition approach that enables the synthesis of ultrasmall (4 to 5 nm) and stable MPEI nanoparticles (up to eight elements). We apply just 5 min of Joule heating to promote the phase transition of the nanoparticles into L10 intermetallic structure, which is then preserved by rapidly cooling. This disorder-to-order transition results in phase-stable nanoscale MPEIs with compositions (e.g., PtPdAuFeCoNiCuSn), which have not been previously attained by traditional synthetic methods. This synthesis strategy offers a new paradigm for developing previously unexplored MPEI nanoparticles by accessing a nanoscale-size regime and novel compositions with potentially broad applications.

Lightweight, strong, moldable wood via cell wall engineering as a sustainable structural material.

Wood is a sustainable structural material, but it cannot be easily shaped while maintaining its mechanical properties. We report a processing strategy that uses cell wall engineering to shape flat sheets of hardwood into versatile three-dimensional (3D) structures. After breaking down wood's lignin component and closing the vessels and fibers by evaporating water, we partially re-swell the wood in a rapid water-shock process that selectively opens the vessels. This forms a distinct wrinkled cell wall structure that allows the material to be folded and molded into desired shapes. The resulting 3D-molded wood is six times stronger than the starting wood and comparable to widely used lightweight materials such as aluminum alloys. This approach widens wood's potential as a structural material, with lower environmental impact for buildings and transportation applications.

Copper-coordinated cellulose ion conductors for solid-state batteries.

Although solid-state lithium (Li)-metal batteries promise both high energy density and safety, existing solid ion conductors fail to satisfy the rigorous requirements of battery operations. Inorganic ion conductors allow fast ion transport, but their rigid and brittle nature prevents good interfacial contact with electrodes. Conversely, polymer ion conductors that are Li-metal-stable usually provide better interfacial compatibility and mechanical tolerance, but typically suffer from inferior ionic conductivity owing to the coupling of the ion transport with the motion of the polymer chains1-3. Here we report a general strategy for achieving high-performance solid polymer ion conductors by engineering of molecular channels. Through the coordination of copper ions (Cu2+) with one-dimensional cellulose nanofibrils, we show that the opening of molecular channels within the normally ion-insulating cellulose enables rapid transport of Li+ ions along the polymer chains. In addition to high Li+ conductivity (1.5 × 10-3 siemens per centimetre at room temperature along the molecular chain direction), the Cu2+-coordinated cellulose ion conductor also exhibits a high transference number (0.78, compared with 0.2-0.5 in other polymers2) and a wide window of electrochemical stability (0-4.5 volts) that can accommodate both the Li-metal anode and high-voltage cathodes. This one-dimensional ion conductor also allows ion percolation in thick LiFePO4 solid-state cathodes for application in batteries with a high energy density. Furthermore, we have verified the universality of this molecular-channel engineering approach with other polymers and cations, achieving similarly high conductivities, with implications that could go beyond safe, high-performance solid-state batteries.

Developing fibrillated cellulose as a sustainable technological material.

Cellulose is the most abundant biopolymer on Earth, found in trees, waste from agricultural crops and other biomass. The fibres that comprise cellulose can be broken down into building blocks, known as fibrillated cellulose, of varying, controllable dimensions that extend to the nanoscale. Fibrillated cellulose is harvested from renewable resources, so its sustainability potential combined with its other functional properties (mechanical, optical, thermal and fluidic, for example) gives this nanomaterial unique technological appeal. Here we explore the use of fibrillated cellulose in the fabrication of materials ranging from composites and macrofibres, to thin films, porous membranes and gels. We discuss research directions for the practical exploitation of these structures and the remaining challenges to overcome before fibrillated cellulose materials can reach their full potential. Finally, we highlight some key issues towards successful manufacturing scale-up of this family of materials.

Printable, high-performance solid-state electrolyte films.

Current ceramic solid-state electrolyte (SSE) films have low ionic conductivities (10-8 to 10-5 S/cm ), attributed to the amorphous structure or volatile Li loss. Herein, we report a solution-based printing process followed by rapid (~3 s) high-temperature (~1500°C) reactive sintering for the fabrication of high-performance ceramic SSE films. The SSEs exhibit a dense, uniform structure and a superior ionic conductivity of up to 1 mS/cm. Furthermore, the fabrication time from precursor to final product is typically ~5 min, 10 to 100 times faster than conventional SSE syntheses. This printing and rapid sintering process also allows the layer-by-layer fabrication of multilayer structures without cross-contamination. As a proof of concept, we demonstrate a printed solid-state battery with conformal interfaces and excellent cycling stability. Our technique can be readily extended to other thin-film SSEs, which open previously unexplores opportunities in developing safe, high-performance solid-state batteries and other thin-film devices.

Continuous Synthesis of Hollow High-Entropy Nanoparticles for Energy and Catalysis Applications.

Mixing multimetallic elements in hollow-structured nanoparticles is a promising strategy for the synthesis of highly efficient and cost-effective catalysts. However, the synthesis of multimetallic hollow nanoparticles is limited to two or three elements due to the difficulties in morphology control under the harsh alloying conditions. Herein, the rapid and continuous synthesis of hollow high-entropy-alloy (HEA) nanoparticles using a continuous "droplet-to-particle" method is reported. The formation of these hollow HEA nanoparticles is enabled through the decomposition of a gas-blowing agent in which a large amount of gas is produced in situ to "puff" the droplet during heating, followed by decomposition of the metal salt precursors and nucleation/growth of multimetallic particles. The high active sites per mass ratio of such hollow HEA nanoparticles makes them promising candidates for energy and electrocatalysis applications. As a proof-of-concept, it is demonstrated that these materials can be applied as the cathode catalyst for Li-O2 battery operations with a record-high current density per catalyst mass loading of 2000 mA gcat. -1 , as well as good stability and durable catalytic activity. This work offers a viable strategy for the continuous manufacturing of hollow HEA nanomaterials that can find broad applications in energy and catalysis.