The goal of chemical destruction of perfluoroalkyl substances (PFAS) is mineralization of fluorine as free aqueous fluoride. The carbon-fluorine (C-F) bond has relatively high kinetic stability but is thermodynamically unstable with respect to hydrofluoric acid (HF) at moderate partial pressures of hydrogen. If the activation barrier can be overcome, then hydrogen gas is capable of completely mineralizing the fluorine from fluorocarbons. As an example, in this work we explore the mineralization of fluorine from bulk polytetrafluoroethylene (PTFE), which is one of the most inert fluorocarbons known. Hydrogen gas (H2) activated by a nonequilibrium plasma in the temperature range from 330 to 470 degrees C results in PTFE destruction rates from 1 to 10 g h-1 and batch conversion as high as 80% in 12 h. Greater than 90% fluorine mineralization was reproducibly achieved. For comparison, thermal reaction without plasma at 500 degrees C using the same hydrogen gas composition and pressure resulted in similar mass loss rate from the PTFE feedstock but negligible fluorine mineralization. The results support the perspective that PFAS destruction in reducing environments is about overcoming a reaction barrier to allow the exergonic reaction to proceed toward HF. HF is then straightforward to neutralize.

Sulfur-containing species are suggested as the UV-absorbers in Venus's atmosphere, which can be generated by photochemistry or electrochemistry. Here we report an electrical discharge experiment in gas mixtures of SO2 with CO2 and N-2, under the pressure and temperature conditions relevant to the Venus cloud layer. We directly observed the primary breakdown products of SO2 as free radicals SO*, S-I*, S-II*, S-2*, O-I*, O-II* using plasma spectroscopy; and the stable ending products as S-8 particles and H2SO4 droplets using Raman spectroscopy. Their co-exhibitions after a few minutes of electrical discharge imply the formation of short-lived intermediate phases (from the radicals as precursors), including polysulfur and sulfur-oxides, both are recognized candidates for the mysterious UV-absorber. The simultaneous observations of plasma lines of SO*and S-2* under all experimental conditions suggest that the two major breakdown paths of SO2, which require similar electron energy, are likely to occur simultaneously. In Venus's cloud layer where electric activity may occur, the high breakdown rate of SO2 by glow-to-arc electric discharge would generate various S-bearing radicals with very high transient density regionally, similar to 3 orders of magnitude higher than the global mixing ratio of similar species from photochemistry. The high density of reactive S-species from regional electrochemistry could be responsible for the inhomogeneous distribution and temporal changes of dark features in Venus UV images.

Non-thermal plasma-liquid reaction converts carbon monoxide (CO) into organic acids at ambient conditions, bolstering the potential for a two-step CO 2 to organic acids conversion via CO to improve chemical yields.

Coal is an abundant natural resource and there is motivation to find new uses for it that do not intrinsically involve combustion. One approach is to explore new ways of processing coal, and in this work, we focus on the transformation of coal in a nonequilibrium plasma generated from an equimolar mixture of nitrogen and hydrogen. The outcome of the nonequilibrium plasma reaction is fundamentally different than a thermal control reaction carried out using the same gas composition, pressure, and temperature range. The nonequilibrium plasma produces a gas mixture that is enriched in acetylene and its derivatives. Furthermore, when compared to the thermal control experiment, the solid char byproduct of the nonequilibrium plasma has a very reactive surface and is spontaneously combustible at ambient temperature. Experiments performed to characterize the reaction kinetics of coal in the plasma suggest that the mechanism proceeds through a sequential process by which the coal particle temperature rises to a point where devolatilization can occur, the devolatilization reaction happens, followed by parallel reactions of released organic vapors in the plasma phase and surface activation. The reaction rate appears to be limited by the time it takes for the coal particle temperature to rise, consistent with previous results reported for reactions of coal in thermal plasma.

III-Nitride materials such as gallium nitride (GaN) and indium nitride (InN) are critical for applications in electronics and optoelectronics due to their exceptional properties. However, their high-temperature stability is often limited by decomposition into constituent elements at low nitrogen pressures near or below ambient. This work investigates the use of nonequilibrium nitrogen plasma to stabilize GaN and InN at elevated temperatures and low pressures. Bulk nitride synthesis was demonstrated via plasma-assisted nitridation of Ga and In metals. Following synthesis, the suppression of nitride decomposition at temperatures exceeding the predicted equilibrium limits was accomplished by means of a nonequilibrium nitrogen plasma. Experimental results revealed that the nonequilibrium plasma imparted an additional chemical potential onto the ground state nitrogen by electron impact excitation, stabilizing GaN at 1000 °C and InN at 600 °C for nitrogen partial pressures as low as 10 Pa. With this experimental approach, the chemical potential of excited nitrogen species in the plasma was estimated to be 1.8 eV higher than the ground state value. These findings highlight the potential for plasma-based processing to enable scalable synthesis and stabilization of III-nitrides at high temperatures for advanced material applications.

Plasma has been proposed as an alternative strategy to treat organic contaminants in brines. Chemical degradation in these systems is expected to be partially driven by halogen oxidants, which have been detected in halide-containing solutions exposed to plasma. In this study, we characterized specific mechanisms involving the formation and reactions of halogen oxidants during plasma treatment. We first demonstrated that addition of halides accelerated the degradation of a probe compound known to react quickly with halogen oxidants (i.e., para-hydroxybenzoate) but did not affect the degradation of a less reactive probe compound (i.e., benzoate). This effect was attributed to the degradation of para-hydroxybenzoate by hypohalous acids, which were produced via a mechanism involving halogen radicals as intermediates. We applied this mechanistic insight to investigate the impact of constituents in brines on reactions driven by halogen oxidants during plasma treatment. Bromide, which is expected to occur alongside chloride in brines, was required to enable halogen oxidant formation, consistent with the generation of halogen radicals from the oxidation of halides by hydroxyl radical. Other constituents typically present in brines (i.e., carbonates, organic matter) slowed the degradation of organic compounds, consistent with their ability to scavenge species involved during plasma treatment.

In this work, satellite data from the Clouds and Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments is analyzed to determine how the global absorbed sunlight and global entropy generation rate have changed during the time period from 2002 to 2023. The data is used to test hypotheses derived from the Maximum Power Principle (MPP) and Maximum Entropy Production Principle (MEP) about the evolution of earth’s surface and atmosphere. The results indicate that the amount of absorbed sunlight has increased over the last 20 years but rising surface temperatures have caused the entropy generation rate to remain approximately constant despite that decrease in albedo. The results are simpler to explain using the MPP but do not completely rule out the MEP. Given the acceptance of the MPP or MEP, some extensions and nuances are discussed.

In this work, satellite data from the Clouds and Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are analyzed to determine how the global absorbed sunlight and global entropy production rates have changed from 2002 to 2023. The data is used to test hypotheses derived from the Maximum Power Principle (MPP) and Maximum Entropy Production Principle (MEP) about the evolution of Earth’s surface and atmosphere. The results indicate that both the rate of absorbed sunlight and global entropy production have increased over the last 20 years, which is consistent with the predictions of both hypotheses. Given the acceptance of the MPP or MEP, some peripheral extensions and nuances are discussed.

The electrochemical process generated by simulation experiments of Venusian lightning Hongkun Qu1,3, Alian Wang1, and and Elijah Thimsen2 1Dept. of Earth and Planetary Sciences and the McDonnell Center for the Space Sciences, 2McKelvey School of Engineering, Washington University in St. Louis, One Brookings Drive, St. Louis, MO, 63130, USA. One Brookings Drive, St. Louis, MO, 63130, USA. 3Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences, Shandong University, Weihai, Shandong,264209, China. (hongkun.qu@wustl.edu ) Introduction Lightning (one type of electrostatic discharge), as an important electrical process for planets with atmosphere, which has been detected on many planets in our solar system, e.g., Earth, Jupiter [1], Saturn [2], Uranus [3], and Neptune [3], and might occur on Mars [4], Venus [5], and Tian [6]. The earliest observation of Venus lightning was reported by Ksanfomaliti … mission name [7]. Afterward, many more ground-based [8] and mission observations on electrical and optical evidence of Venus lightning were reported [9]. The Venus Climate Orbiter (VCO) and Planet-C, observed an intense optical flash that was assigned to lightning in 2020 [10]. Electrons with high kinetic energy generated by Venusian lightning would collide with atmospheric gaseous molecules and dissociate, excite these radicals, including atoms and molecules at excited states, have high chemical activity. Electrochemical reactions among these species would create new species that would not be produced in common Venusian chemical reactions. Experimental results We conducted a series of simulation experiments on Venusian lightning in a newly designed Venus-ESD-Chamber (VEC). We report here the radicals detected during ESD in VEC under CO2 and gas mixture of N2, O2, CO2, H2O, Ar. Different types of discharges would generate numbers of radical species which indicate that electrochemical reactions take place during and after discharge. In collected plasma spectra of ESD in gas mixture, the emission lines of N2, N2+, N, N+, NO, OH, O, O+, Ar, and Ha were observed and may be generated by the following reactions: N2 + e → N2* + e (1) N2 + e → N2+ + e (2) N2 + e → N + N + e (3) N + e → N+ + e (4) O2 + e → O + O + e (5) O + e → O+ + 2e (6) N2 + O → NO + N (7) H2O + e → OH + H + e (8) Ar + e → Ar* + e (9) Emission lines of CO2+, CO, CO+, C, C2, C+, O, O+, and OH were observed in spectra of CO2 electrostatic discharge, the possible electrochemical reactions are as follows: CO2 + e → CO2* + e (10) CO2 + e → CO2+ + 2e (11) CO2 + e → CO + O + e (12) CO2 + e → C+ + O2 + 2e (13) CO2 + e → CO+ + O + 2e (14) These active radicals would play significant rules in the evolutions of the Venusian atmosphere. Further Work: For the next step, we will conduct ESD in SO2 gas and in SO2 + CO2 gas with different concentrates for investigations of sulfur species generated in ESD. Acknowledgments: This work was supported by the CSC scholarship (NO. 201906220244) for HKQ to support his joint-training Ph.D. study at Washington University in St. Louis, and by spectral funding 94351A of WUSTL_MCSS to AW to maintain a collaboration with planetary scientists and students from Shandong University in China. Reference: [1] D. A. Gurnett, R. R. Shaw, R. R. Anderson, W. S. Kurth, and F. L. Scarf, Geophys. Res. Lett., 1979. [2] K. H. Baines et al., Planet. Space Sci., 2009. [3] K. Aplin, Springer Science & Business Media, 2013. [4] W. M. Farrell and M. D. Desch, J. Geophys. Res. Planets, 2001. [5] W. W. L. Taylor, F. L. SCARF, C. T. RUSSELL, and L. H. BRACE, Nature, 1979. [6] R. Lorenz, J. Phys. IV, 2002. [7] L. V Ksanfomaliti, F. L. Scarf, and W. W. L. Taylor, Venus, 1983. [8] S. A. Hansell, W. K. Wells, and D. M. Hunten, Icarus, 1995. [9] R. D. Lorenz, Prog. Earth Planet. Sci., 2018. [10] Y. Takahashi et al., Nat. Portf., 2021.

Gallium nitride quantum dots (GaN QDs) are a promising material for optoelectronics, but the synthesis of freestanding GaN QDs remains a challenge. To date, the size-dependent photonic properties of freestanding GaN QDs have not been reported. Here, we examine the photonic properties exhibited by thin films composed of GaN QDs synthesized by nonequilibrium plasma aerotaxy. Each film exhibited two photoluminescence peaks after exposure to ambient air. The first peak was in the ultraviolet spectral region, and the second peak was in the visible region. Both peak positions depended on the QD size. Our findings, supported by transient absorption spectroscopy experiments, suggest that conduction band to valence band recombination was the cause of the ultraviolet photoluminescence and that recombination between the conduction band and an acceptor level was the cause of visible photoluminescence. Furthermore, we show that coating the surface of fresh QDs with Al2O3 suppressed the visible region photoluminescence, corroborating the conclusion that the photoactive defect was caused by oxidation in air.

In this work, we demonstrate plasma-catalytic synthesis of hydrogen and acrylonitrile (AN) from CH and N. The process involves two steps: 1) plasma synthesis of CH and HCN in a nominally 1:1 stoichiometric ratio with high yield up to 90% and high methane conversion > 90%; and 2) downstream thermocatalytic reaction of these intermediates to make AN. The effect of process parameters on product distributions and specific energy requirements are reported. If the catalytic conversion of CH and HCN in the downstream thermocatalytic step to AN were perfect, which will require further improvements in the thermocatalytic reactor, then at the maximum output of our 1 kW radiofrequency 13.56 MHz transformer, a specific energy requirement of 73 kWh kgANwas determined. The expectation is that scaling up the process to higher throughputs would result in decreases in specific energy requirement into the predicted economically viable range less than 10 kWh kgAN.

A new Venus‐ESD‐Chamber (VEC) and peripheral systems were designed and built to simulate Venus lightning. It consists of three subsystems (a) electrostatic discharge (ESD) generation, (b) environmental pressure, temperature, gas composition control & monitoring, and (c) optical and non‐optical sensors. We conducted arc discharge experiments in air, in CO 2 , and in Venus major gas mixture (CO 2 ‐N 2 , 96.5% ± 1.5%:3.5% ± 1.5%) under 10, 350, 700, and 1,000 mbar pressures, that correspond to the 50–75 km altitude range in the cloud layer of Venus. Plasma and Raman spectra, plus gas sensors, and GC‐MS were used to identify the ESD products and to semi‐quantify CO and O 3 generated by ESD. We have found all species of free radicals that have been found in previous simulation studies using different discharge technologies, including some important species in CO 2 ‐N 2 system, nitrogen oxides and CN. In addition, we found three species (O 3 , N 2 + , and C 2 ) that have not been previously reported. Our results suggest that electron flux and kinetic energy are the determining factors for the type of generated free radical species and gas pressure plays a less important role. We found that the quantity of CO changes with the type of ESD. The detection of O 3 in this study suggests that lightning might be one of the sources of O 3 observed in the Venusian atmosphere. O I emission line at 777.4 nm is the most prominent line in our plasma spectra of FD, consistent with the intense optical flash observed by the Lightning and Airglow Camera (LAC) on the Akatsuki mission.

In this work, stationary states in nonequilibrium plasmas of chemical reactions that can produce hydrogen are explored, namely the water splitting and water gas shift reactions. For both reactions, the effluent from the reactor at long gas residence times in the plasma was found to be independent of the influent speciation. In other words, feeding the reactor either 0.1 H2O or 0.1H2+0.05O2 by mole produced the same effluent composition, and similarly, feeding the reactor 0.1CO+0.1H2O produced nominally the same effluent as 0.1CO2+0.1H2. For both reactions, the effluent from the plasma was found to be very far from local equilibrium at the total pressure and background temperature of the reactor. An important conclusion of this work is that special attention must be paid to the recombination zone in plasma chemical processes. The recombination zone tends to drive the gas composition from plasma stationary states back towards local equilibrium.

Nanocrystalline Cr-2x Al2(1-x)O3 solid solutions offer a unique combination of chemical and thermal stabilities with optoelectronic and mechanical properties of interest for applications in catalysis, medicine, and structural materials. However, there exists an asymmetric miscibility gap in the range 0.02 < x < 0.7 at temperatures below 1000 degrees C Since sintering is extremely fast at high temperatures, synthesis of Al-rich corundum nanocrystals less than 50 nm in diameter has been elusive. In this work, we present a bottom-up synthesis of homogeneous alpha-Cr2xAl2(1-x)O3 nanocrystals with ultimate grain sizes as low as 20 nm. X-ray diffraction, electron microscopy, and energy-dispersive X-ray spectroscopy were used to demonstrate complete mixing of Cr and Al in the particles. Temperatures as low as 850 degrees C resulted in complete homogenization of alpha-Cr2xAl2(1-x)O3 nanocrystals. The ultrafine powders exhibited photoluminescence with a sharp emission line at 695 nm when excited by a 532 nm laser, characteristic of Cr3+ substitutions in the alpha-Al2O3 lattice. Additionally, the characteristic decay time of this emission was increased from 132.7 mu s to 278.5 mu s when the Cr concentration was diluted from Cr0.4Al1.6O3 to Cr0.02Al1.98O3.

Electrification of transportation and rising demand for grid energy storage continue to build momentum around batteries across the globe. However, the supply chain of Li-ion batteries is exposed to the increasing challenges of resourcing essential and scarce materials. Therefore, incentives to develop more sustainable battery chemistries are growing. Here we show an aqueous ZnCl2 electrolyte with introduced LiCl as supporting salt. Once the electrolyte is optimized to Li2ZnCl4⋅9H2O, the assembled Zn–air battery can sustain stable cycling over the course of 800 hours at a current density of 0.4 mA cm−2 between −60 °C and +80 °C, with 100% Coulombic efficiency for Zn stripping/plating. Even at −60 °C, >80% of room-temperature power density can be retained. Advanced characterization and theoretical calculations reveal a high-entropy solvation structure that is responsible for the excellent performance. The strong acidity allows ZnCl2 to accept donated Cl− ions to form ZnCl42− anions, while water molecules remain within the free solvent network at low salt concentration or coordinate with Li ions. Our work suggests an effective strategy for the rational design of electrolytes that could enable next-generation Zn batteries. Zinc batteries are receiving growing attention due to their sustainability merits not shared by lithium-ion technologies. Here the aqueous electrolyte design features unique solvation structures that render Zn–air pouch cell excellent cycling stability in a wide temperature range from −60 to 80 °C.

Metal pentazolate compounds that contain 5-nitrogen singly charged anion rings are an interesting class of materials from a thermodynamics perspective. These compounds are believed to be equilibrium phases only at extremely high pressures, and thus, they constitute exotic states of matter at ambient pressure and temperature. Moreover, the energy released by these pentazolate compounds upon relaxation to the equilibrium state at ambient conditions is in the range 1 to 10 MJ per kg, rivaling that of combustion reactions. The synthesis of pentazolates is not an easy task, and there are only two known methods, each of which has significant challenges. The development of new scalable synthesis routes could enable the production of these exotic materials in sufficient quantity to explore their properties more widely beyond the context of explosives and propellants. In this Perspective, it is argued that nonequilibrium plasma is a promising reaction medium for the synthesis of metal pentazolate compounds, for example from the corresponding metal azide and N-2 gas activated by the discharge at low background temperature.

Controlling the nucleation and growth of nanoparticles in low temperature plasma systems is imperative for controlling nanoparticle size distributions; and for some applications such as deposition and etching in microelectronic processing, preventing particle contamination. In this work, silicon nanoparticle (NP) production from silane is used as a model system to investigate the nucleation process. Although the mechanisms responsible for silicon NP nucleation and growth have been studied, it is unclear how controllable system parameters (e.g., pressure, system geometry, and gas composition) can be used to inhibit or promote NP formation. For example, the transport of reactive silane species is expected to significantly affect the feed fraction of silane required to nucleate silicon NP (the nucleation onset fraction) due to losses at the reactor walls. In this work, NP mass density was determined as a function of system pressure, gas composition, and reactor diameter for a tubular flow-through radiofrequency plasma using Ar/H 2 /He/SiH 4 gas mixtures. A quartz crystal microbalance impactor was developed to measure the total aerosol mass density downstream of the plasma and thereby identify the nucleation onset and its dependence on process parameters. A reaction mechanism was developed and incorporated into a global plasma chemistry model to better understand the nucleation onset and NP growth.

Nonthermal plasmas in contact with liquids have been shown to generate a variety of reactive species capable of initiating reduction-oxidation (redox) reactions at the electrochemically active plasma-liquid interface. In conventional electrochemical cells, selective redox chemistry is achieved by controlling the reduction potential at the solid electrode-electrolyte interface by applying a bias via an external circuit. In the case of plasma-liquid systems, an analogous means of tuning the reduction potential near the interface has not clearly been identified. When treated as a floating surface, the liquid is expected to adopt a net negative charge to balance the flux of hot electrons and relatively cold positive ions. The reduction potential near the plasma-liquid interface is hypothesized to be proportional to the floating potential, which can be approximated using an analytical model provided the plasma parameters are known. Herein, we present a framework for correlating the electron density and electron temperature of a noble gas plasma jet to the reduction potential near the plasma-liquid interface. The plasma parameters were acquired for an argon atmospheric plasma jet in contact with an aqueous solution by means of laser Thomson scattering. The reduction potential was determined using identical reference electrodes to measure the potential difference between the plasma-liquid interface and bulk solution. Interestingly, the measured reduction potentials near the plasma-liquid interface were found to be in good agreement with the model-predicted values determined using the plasma parameters obtained from the Thomson scattering experiments.

Nonthermal atmospheric pressure plasma in contact with a liquid yields a variety of energetic photons, ions, and electrons, which can be transported into the plasma-liquid interface (PLI). Similar to the electrochemical interface formed between a solid electrode and electrolyte in conventional electrochemical systems, the charge-transfer process across the PLI is able to promote reduction-oxidation (redox) reactions. However, in the case of free plasma jets in contact with liquids, the absence of solid electrodes obscures the spatial locations of the electrochemical half-reactions. Herein, we present a spatial electrochemical measurement technique used to characterize an aqueous solution in contact with an atmospheric pressure plasma jet. The technique is based on measuring the potential difference between two identical Ag/AgCl electrochemical electrodes positioned at different locations within the solution. More specifically, electrochemical maps were made by measuring the potential of one electrochemical electrode positioned at different locations near the PLI with respect to the other electrochemical electrode positioned far away from the PLI in the bulk solution. Regions in the map with negative and positive potential differences between these electrochemical electrodes were used to identify the electrodeless cathode and anode, respectively. Visualization of the spatial distribution of molecular colorimetric redox indicators by multispectral imaging revealed that reduction was occurring near the plasma jet centerline while oxidation was occurring further away in solution, which constitutes an independent confirmation of the electrochemical maps.

Nanoparticles (a few to tens of nm) having controllable optical, compositional, and structural properties can be synthesized in flowing low temperature plasmas (LTPs). LTP produced Si nanoparticles (NPs) are being investigated for use in catalysis, optics, and medicine. On the other hand, nucleation of NPs is undesirable in microelectronics fabrication where, with shrinking feature sizes, particles of only a few nm can produce defects. In both cases, a key to controlling NP growth or preventing their formation, is the onset of nucleation. This is typically the point that a critical cluster size is achieved and NPs grow by reaction with radicals that increase the size of the NP instead of creating new NPs. However, conditions leading to the onset of nucleation are not well characterized.