OH Formation Research Articles

Effect of CO<sub>2</sub> Additives on the Non-Catalytic Conversion of Natural Gas into Syngas and Hydrogen

Abstract—A kinetic analysis of the non-catalytic carbon dioxide reforming of CH4 has been carried out in the temperature range of 1500–1800 K under conditions of variable temperature behind the reflected shock wave. The stages of conversion of methane into synthesis gas, the characteristic time intervals corresponding to these stages, and the most important elementary reactions have been established. At the first stage, as a result of thermal pyrolysis, methane molecules are sequentially converted into ethane, ethylene, and then acetylene, the most stable hydrocarbon in this temperature range. At the second stage, acetylene is normally converted into CO and H2, being accompanied by the formation soot particles in the case of rich mixtures. The conversion of CO2 proceeds at the second and third stages, when CH4 conversion is almost complete. It occurs as a result of the interaction of CO2 molecules with H● atoms arising in the reacting system and leads to the formation of CO molecules and OH● radicals. Acetylene is predominantly consumed in the reaction with OH radicals. A high concentration of acetylene during methane reforming promotes the intensive formation of soot nuclei, for which acetylene makes the highest contribution to the rate of their surface growth. At the same time, acetylene itself is not a precursor of soot particle nuclei, which are mainly formed from \({{{\text{C}}}_{{\text{3}}}}{\text{H}}_{3}^{\centerdot }\) radicals.

Boosting 5-hydroxymethylfurfural electrooxidation in neutral electrolytes via TEMPO-enhanced dehydrogenation and OH adsorption

5-Hydroxymethylfurfural (HMF) electrooxidation in neutral conditions is a promising strategy to suppress the formation of humins and corrosive effects on electrochemical devices. However, scarce studies have been reported in neutral media due to the deficiency in electrophilic oxygen (eg OH–) required for the activation of HMF. Herein, 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO)/Co3O4 was utilized to co-catalyze HMF in neutral media, successfully achieving 2,5-furandicarboxylic acid (FDCA) with yield > 99%. It was found that TEMPO could promote HMF dehydrogenation to 2,5-diformylfuran (DFF) and simultaneously activated water via hydrogen-bonding interactions. As a result, the formation of OH* in neutral electrolytes was favored, which was absorbed by electrogenerated active Co species to facilitate subsequent conversion of formyl-group-involved intermediates to FDCA. This work provides a current understanding of the catalytic mechanism for HMFOR in neutral media and guides the design of highly efficient electrocatalysts for biomass upgrading.

Kinetic modeling of advanced starch oxidation with ozone in basic solutions

ABSTRACT The growing use of ozone (O3) in the last years to clean and enhance the physicochemical properties of starches, widely used as additives in food, beverage, and pharmaceutical industries, calls for a better understanding of their oxidation process. High pH, however, decomposes O3 rapidly, forming highly-oxidant radicals, thus increasing the complexity of the reaction system. In this study, a kinetic model for the ozonation reaction of starch in an alkaline medium was developed and experimentally validated. Firstly, the concentration of hydroxyl radicals (●OH) over the reaction time is evaluated through the degradation of pCBA (a probe compound) to later evaluate and model the oxidation process of starch based on Chemical Oxygen Demand (COD) measurements. By using a semi-batch reactor containing alkaline solutions at pH = 13, different O3 concentrations (0–42.30 g/Nm3) and temperatures (20–60 °C), a pseudo first-order kinetic model was proposed to model the pCBA-ozone reaction. This model estimates the ●OH formation, being [●OH] constant and proportional to the O3 continuous dose. Therefore, under the conditions studied, ●OH is a non-limiting reactant independent of temperature. The activation energy was estimated at 14.2 ± 2.1 and 14.5 ± 0.6 KJ/mol for 21.15 and 42.30 gO3/Nm3, respectively. Then, COD data were used to propose a kinetic model for ozone-starch oxidation in alkaline media, where besides O3 concentration and temperature, starch concentration (600–1700 mg/L) was also varied. According to the results, higher temperatures and longer reaction times resulted in a greater COD reduction, being it more pronounced at lower initial starch concentration. The activation energy of the ozone radicals-starch reaction was estimated at 8.1 ± 0.4 KJ/mol, being significantly lower than those reported for the reaction between pCBA and ●OH.

Fabrication of a novel PbO2 electrode with rare earth elements doping for p-nitrophenol degradation

A novel PbO2 electrode modified with rare earth elements (La, Ce, Gd and Er) doping (named as Re-PbO2) was prepared by electrodeposition in the present study. The micro-morphology and crystal structure of Re-PbO2 were characterized by scanning electronic microscopy (SEM), energy dispersive spectroscope (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Their electrochemical properties were determined by linear sweep voltammetry (LSV), cyclic voltammetry (CV), accelerated life test and hydroxyl radicals (•OH) formation analysis. Electrochemical oxidation of p-nitrophenol (p-NP) by Re-PbO2 compared with un-doped PbO2 has been investigated and the degradation rate followed the order of Er-PbO2 > Gd-PbO2 > La-PbO2 > Ce-PbO2 > PbO2. Especially for Er-PbO2, the pseudo-first order kinetic for p-NP (kp-NP) degradation was 0.41, which was only 0.19 for un-doped PbO2. Rare earths elements doping improved the oxidation ability of Re-PbO2 mainly through reducing grain size, increasing oxygen evolution potential, enlarging electrochemical active surface area and enhancing •OH formation ability. In addition, existing formation of oxygen species on PbO2 electrode surface was investigated by XPS. For Re-PbO2, percentage of lattice oxygen species (Oads) were higher than that on the un-doped one. These results demonstrated that rare earth elements can enhance the oxidation ability of PbO2 electrode significantly.

Understanding the Coordination Chemistry of AmIII/CmIII in the DOTA Cavity: Insights from Energetics and Electronic Structure Theory.

The minor actinides Am/Cm show multiple possibilities for coordination, providing great opportunities for their extraction and adsorption separation. Herein, we report complexation in an aqueous medium of AmIII/CmIII in the DOTA (H4DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) cavity with axial ligands (OH-, F-, and H2O), based on the energetics and electronic structure properties using density functional theory (DFT). The formation and substitution reactions of OH--capped complexes are more likely to occur due to their enhanced hydration Gibbs free energies, followed by F-, and then H2O. Both the longer An-ODOTA bond lengths and the larger bite angle (∠O-An-O) in the OH--capped complexes reflect the enhanced coordination provided by the axial ligand, slightly less so for F-. Energy decomposition analysis based on the electronic structure supports the preference for OH--capped complexes with a near-perfect balance between attractive and repulsive contributions toward the interaction. Furthermore, molecular orbital analysis revealed that the frontier molecular orbitals of Am and Cm complexes are substantially different; that is, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) compositions of the Am complexes are all contributed by 5f, while the HOMO and LUMO compositions of the Cm complexes are derived from 5f and 6d, respectively. Finally, the metal-exchange reactions demonstrate competitive complexation of DOTA toward AmIII over CmIII for the OH--capped system. These results imply the importance of coordination chemistry in actinide chemistry in general and specifically in AmIII/CmIII solution chemistry.

To promote catalytic ozonation of toluene by tuning Brönsted acid sites via introducing alkali metals into the OMS-2-SO42-/ZSM-5 catalyst

Although free hydroxyl radical (·OH) generated on OMS-2-based catalysts during the catalytic ozonation process have been shown as important reactive oxygen species (ROSs) for toluene degradation, improvement of surface ·OH formation ability remains challenging. Here, Na, K, Rb, and Cs-OMS-2-SO42-/ZSM-5 catalysts were prepared, characterized and evaluated for catalytic ozonation of toluene. Both characterizations and DFT calculations showed that the appropriate alkali metal introduction made the catalyst possess with appropriate crystalline, reducibility, and acidity, which was favorable for catalytic ozonation of toluene. Characterizations also showed that alkali metal introduction resulted in water molecule adsorption on Brönsted acid sites of the catalysts, which made water molecule activation by ozone to form ·OH more easily. The introduction of K+ content of ∼ 5.9 wt% yielded K-OMS-2-SO42-/ZSM-5 catalyst with the highest Brönsted acid sites and thus formed the most ·OH among the five prepared catalysts. As a result, the catalyst exhibited excellent toluene conversion and COx selectivity for catalytic ozonation of toluene at room temperature and ambient humidity. Furthermore, the catalytic activity of deactivated K-OMS-2-SO42-/ZSM-5 catalyst was recovered after regeneration by a combination of water washing and heat treatment. Finally, a complete mechanism for toluene catalytic ozonation, catalyst deactivation, and regeneration was proposed.

Thermodynamic and Kinetic Investigation on Electrogeneration of Hydroxyl Radicals for Water Purification

The water oxidation reaction (WOR) is of fundamental importance for the development of promising technologies in the field of energy conversion and environmental remediation. Although effort has been devoted to uncovering the mechanism of the oxygen evolution reaction (OER) by four-electron WOR, little attention has been paid to an in-depth understanding of one-electron WOR for •OH formation, which is the key to the electrochemical advanced oxidation process (EAOP) for environmental applications. Currently, oxygen evolution potential (OEP) is generally regarded as an important thermodynamic descriptor responsible for •OH production, but the kinetic descriptor has been overlooked; thus, the trade-off between thermodynamic and kinetic factors remains unclear. In this study, the thermodynamic feasibility and kinetic activity of electrogeneration of •OH were regulated by doping three kinds of low-electronegativity elements (Ce, Al, and In) into the prototype PbO2 nonactive anode. We investigated these electrodes in terms of •OH production and electrochemical decontamination performance in the context of sulfamethoxazole (SMX) removal. The results showed that 0.8%Ce-PbO2 anode (OEP = 3.67 V vs Ag/AgCl) achieved the highest SMX removal performance (∼100%; kobs = 0.027 min–1) and the highest •OH production with a relatively high number of •OH = 2.7 × 107. In comparison, the highest OEP (5.98 V vs Ag/AgCl) for the 1.6%Ce-PbO2 anode exhibited the lowest SMX removal (∼59%; kobs = 0.008 min–1) and 1 order of magnitude lower •OH production (relative number of •OH = 1.5 × 106). This suggested that the electrogeneration of •OH was unlikely to be always positively correlated to the OEP of the anode. Both experimental results and theoretical calculations verified the importance of suitably high OEP and relative fast electron transfer rate toward WOR to generate H2O+ (oxidation intermediate of H2O) for the ideal anode of EAOP. This study not only demonstrates the trade-off existing between thermodynamic (OEP) and kinetic (charge/electron transfer) factors responsible for electrogeneration of •OH via WOR fundamentally but also suggests a possible strategy for developing a high-efficiency anode by doping low-electronegativity elements to optimize one-electron WOR for environmental applications.

Tuning the optical properties of SnO2 by doping Cu2+ for enhancing solar irradiated photodegradation of dye effluents and underlying mechanism

Water pollution due to industrial dye effluents is a major concern to society. To tackle with this situation, Sn1-xCuxO2 (x = 0, 0.1 & 0.2) nanocomposites were synthesized by co– precipitation technique. The phase structure, morphology and optical properties of prepared nanocomposites were determined using XRD, FTIR, SEM-EDAX with elemental mapping, electrical resistivity, UV– VIS- DRS, Photoluminescence and XPS methods. Sn1-xCuxO2 crystallizes in tetragonal structure without phase segregation up to x = 0. 2. As compared to pristine SnO2, Sn1-xCuxO2 exhibit red shift in the visible region. XPS study confirm the presence of Cu2+ and Sn4+ ions in Sn1-xCuxO2. Visible light harvesting efficiency was evaluated by photodegradation of Amido Black dye under natural sunlight. 67 % degradation was observed with SnO2 in 60 min time which enhances to 100 % with Cu doping. Analysis of degradation product and the formation of reactive OH. radical was checked by fluorescence technique using terephthalic acid. Sn1-xCuxO2 composites also exhibit antibacterial action towards gram positive and gram-negative bacteria thereby preventing spread of water borne diseases.

Dumbbell Defect Containing Chromium-Rich Lithium-Vacant Layered LiyCr1–xFexO2(y≤ 1, 0 ≤x≤ 0.2): An Unexplored and Highly Efficient Electrocatalyst for the Oxygen Evolution Reaction

Oxygen electrochemistry plays a critical role in water electrolysis, fuel cells, and metal–air batteries as efficient energy storage and conversion technology to harness renewable energies. Dumbbell defects containing chromium-rich lithium-vacant layered structure LiCrO2 are envisaged here as an efficient oxygen evolution reaction (OER) electrocatalyst due to the presence of Cr6+ ions at interstitial sites that facilitates −Cr–O–OH formation in basic media. The presence of Cr6+ ions at the dumbbell interstitial sites of the hexagonal close-packed LiCrO2 lattice was confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy studies. The crystal structure, morphology, and composition of the materials were confirmed by powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and inductively coupled plasma–mass spectrometry analysis. Rhombohedral structure formation and formation of Cr6+ ion interstitials in the Li layer increase that varies with Fe doping in LiyCr1–xFexO2 (y ≤ 1, 0 ≤ x ≤ 0.2), and the best OER activity is achieved for Li0.6Cr0.9Fe0.1O2 (LCFO-10) with a Tafel slope of 50 mV dec–1 and an overpotential of 311 mV at a current density of 10 mA cm–2, better than that of the RuO2 (overpotential ∼336 mV) benchmark catalyst. At an overpotential of 350 mV, the OER current density of LCFO-10 is 28.07 mA cm–2, which is ∼2 times higher than the OER current density observed with commercial RuO2 (13.22 mA cm–2), indicating its superior electrocatalytic performances. The remarkable enhancement of OER performance may be attributed to the synergistic interaction of Cr6+ and Fe3+ ions present in the lattice.

Self-powered piezoelectric NaNbO3 induced band position rearrangement and electrocatalysis in MoS2/NaNbO3 heterojunction for generation of reactive oxygen species for organic pollutant removal

Piezocatalytic heterojunction was synthesized using sodium niobate (NaNbO3, NBO) and molybdenum disulfide sheets (MoS2, MS), and characterized via SEM, XRD, XPS, UPS, EPR, PFM, and EIS. Metronidazole (MET) removal using MS(x)/NBO heterojunction was tested via batch experiments in an ultrasonicator (40 kHz and 150 W) for 160 min. MET removal obtained under optimized MS(30)/NBO (30 wt% of MS) was 82.8%, and the removal mechanism was governed by .OH formed due to reduction of H2O2, electrocatalytic oxidation at MS anode, and oxidation by holes in depletion region at MS-water and MS-NBO interface. Scavenging and quantification studies confirmed the formation of H2O2 (∼27 µM) due to piezoelectric effect induced electrocatalysis. In the absence of piezoelectric effect, MET removal and .OH formation were insignificant. Moreover, COMSOL simulation revealed the role of orthorhombic NBO as parallel plate capacitor in the heterojunction that created electrocatalysis and formation of depletion and accumulation regions at MS-NBO and MS-water interface. Finally, effects of pH (2–12), competitive anions (Cl−, NO3–, SO42−, CO32–, and PO43−) and working temperature (28–63 ℃) on piezocatalytic MET removal were investigated through experiments and theoretical understanding. The increase in temperature due to ultrasonication improved efficiency of MET removal due to improvement in interfacial charge transfer, and increase in thermodynamic feasibility of .OH generation. Overall, MS(30)/NBO activity could be attributed to generation of charge carriers due to mechanical excitation and formation of piezoelectric effect due to cavitation under ultrasonic waves.

Hierarchical Fe3O4@LDH-incorporated composite anion exchange membranes for fuel cells based on magnetic field orientation

The trade-off between ionic conductivity and mechanical properties is the key issue facing anion exchange membranes (AEMs) at present. Herein, a new strategy combing three-dimensional (3D) hierarchical nanoarchitecture and magnetic field orientation was proposed to prepare imidazolium-functionalized poly(2,6-dimethyl phenylene oxide) (ImPPO)-based composite AEMs with simultaneously improved ionic conductivity and mechanical strength. Magnetic Fe3O4@LDH microspheres using Fe3O4 as the core and two-dimensional lamellar anion conductor, layered double hydroxide (LDH), as the shell were prepared through a simple co-precipitation method. The as-prepared Fe3O4@LDH was then incorporated into ImPPO matrix and induced by an external magnetic field to fabricate Fe3O4@LDH-orientated composite AEMs. The hierarchical-structured Fe3O4@LDH can not only effectively avoid the stacking of LDH laminates and thus fully play the ion conduction ability of LDH, but also contribute to the formation of continuous OH− ion transport pathway in the composite system after magnetic field induction. The magnetic-field-oriented membrane with 1% Fe3O4@LDH doping exhibited ionic conductivity of 128.9 mS cm−1 at 80 °C, which was 43.1% higher than that of pure ImPPO. Moreover, the high dry strength (30.7 MPa) and satisfactory wet strength and flexibility of the composite membrane were also obtained. The assembled direct methanol fuel cell demonstrated a peak power density of 11.7 mW cm−2, and showed an OCV retention of as high as 94.7% after continuous operation for 100 h, indicating their great potential for fuel cell applications.

Thermal Mineralization of Perfluorooctanesulfonic Acid (PFOS) to HF, CO2, and SO2

Utilizing air (O2) as the bath gas at reaction temperatures between 500 and 1000 °C, the thermal decomposition of perfluorooctanesulfonic acid (PFOS) in an α-alumina reactor was studied. It was found that in an air bath gas (and in the absence of water vapor), COF2 and trace amounts of C2F4 were detected. Quantum chemical calculations at the G4MP2 level of theory confirmed that CF2 radicals can react with O2 to form COF2 and an O (3P) atom. The inclusion of 2000 or 20 000 ppmv of water vapor (H2O(g)) to the air bath gas proved to be the key step to mineralizing all PFOS into hydrogen fluoride (HF), CO2, and SO2. At temperatures above 850 °C (0.95–0.84 s residence time), a feed of 20 000 ppmv of H2O(g) in air was observed to produce a product stream in which no gaseous fluorocarbon products were detected, with only HF, SO2, and CO2 being produced. A sulfur balance confirmed that 100 ± 5% of all the S in PFOS had converted into SO2 with a chemical kinetic model predicting in excess of 99.99999% destruction removal efficiency of PFOS at temperatures above 700 °C. Furthermore, from an elementary balance of F and C atoms, it was determined that at 1000 °C, approximately 99 ± 5% of F atoms present in PFOS have been converted into HF, and approximately 100 ± 5% of C atoms had been converted into CO2. A chemical kinetic model was developed to understand the importance of both O2 and water vapor in the overall thermal decomposition of PFOS, leading to complete mineralization. In the presence of both O2 and H2O(g), it was found that relatively high concentrations of OH radicals were produced, with significant contribution to OH formation attributed to the well-known chain branching reaction O(3P) + H2O → OH + OH.

Hydroxyl Molecular Line Shapes in Laser-Ignition of Air

This work communicates measurement and analysis of diatomic molecular hydroxyl (OH) spectra after generation of laser-induced plasma. A relative laboratory-air humidity of the order of 25% causes the occurrence of OH recombination radiation that is recorded with optical emission spectroscopy. A Q-switched, 150 mJ, 6 ns pulsed Nd:YAG laser beam at the fundamental wavelength of 1064 nm is focused in air with f/5 optics. Formation of OH is clearly discernible at time delays of several dozen microseconds after plasma initiation. Optical emissions are dispersed by a 0.64-m Czerny-Turner spectrometer and an intensified charge-coupled device records the data along the wavelength and slit dimensions.

Impact of ozonation on the optical properties and photo-reactivity of dissolved organic matter

With the increasing amount of wastewater discharges, the subsequent influence of treated effluent on the photochemistry of natural receiving waters has become more significant. Recently, the effect of treatment operations on the photo-reactivity of dissolved organic matter (DOM) has gained much attention. Meanwhile, some well-established correlations between spectroscopic measurements and photochemical behaviors become unreliable in treated DOM, thus requiring more robust relationships for better prediction. In the present research, the variations of optical and photochemical properties of DOM after ozonation were investigated. The correlations between fluorescence and reactive species photo-production were further explored through parallel factor analysis (PARAFAC). Results showed that ozonation induced the decline of aromaticity, molecular weight, and fluorescence intensities for all samples, which led to reduced photo-production of excited triplet states of DOM (3DOM*) and singlet oxygen (1O2). By contrast, the photo-formation of hydroxyl radical (•OH) was promoted. The correlations between optical parameters and quantum yields were evaluated. Furthermore, the max fluorescence intensity of PARAFAC components was used in linear regression modeling to predict the formation rate of 1O2 and •OH (R1O2 and R•OH). The contribution of each part was calculated. The good fit of R1O2 implied that ozonation would not affect the potential intrinsic relation between fluorophores and 1O2-producing chromophores. In contrast, the unsatisfactory modeling results of R•OH indicated a weak correlation between fluorescence and •OH formation. These findings suggest that ozonation influences the photo-reactivity of DOM and hint at the possibility of applying fluorescence combined with PARAFAC to explore 1O2 formation quantitatively.

Does the Oxygen Evolution Reaction follow the classical OH*, O*, OOH* path on single atom catalysts?

The Oxygen Evolution Reaction (OER) is a key part of water splitting. On metal and oxide surfaces it usually occurs via formation of three intermediates, M(OH), M(O), and M(OOH) (also referred to as OH*, O*, and OOH* species where * indicates a surface site). The last step consists of O2 release. So far, it has been generally assumed that the same path occurs on single atom catalysts (SACs). However, the chemistry of SACs may differ substantially from that of extended surfaces and is reminiscent of that of coordination compounds. This raises the question of whether on SACs the OER follows the classical mechanism or not. Using a DFT approach, we studied a set of 30 SACs made by ten metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Pd and Pt) anchored on three widely used 2D carbon-based materials, graphene, nitrogen-doped graphene and carbon nitride. In none of the cases examined the most favourable reaction path is the conventional one. In fact, in all cases other intermediates with higher stabilities form: M(OH)2, M(O)(OH), M(O)2, and M(O2) (OH* OH*, O* OH*, O* O*, O2* according to standard nomenclature). Therefore, the common assumption that on SACs the OER proceeds via formation of OH*, O*, and OOH* intermediates is not verified. Predictions of new catalysts based on the screening of large number of potential structures can lead to completely incorrect conclusions if these additional intermediates are not taken into consideration.

Effects of oxygen concentration on devolatilization and combustion behavior of coal particles: A multi-parameter study

The devolatilization and volatile combustion of lignite coal (LC), sub-bituminous coal (SBC) and bituminous coal (BC) with different O2 concentrations (21%-50%) were investigated on a concentrating photothermal experiment platform. The characteristics and mechanism of different coal particle combustion were analyzed by using multiple diagnostics, including Planar Laser Induced Fluorescence (PLIF) of OH radicals and polycyclic aromatic hydrocarbons (PAHs), high-speed cinematography and FT-IR. The results showed that, with increasing O2 concentration, the ignition delay time (tign) of different ranks of coal decreased, which was associated with the increase of OH concentrations during the ignition stage. The good correlation between tign and OH concentration was observed. For the volatile combustion, the OH concentration, volatile release amount and volatile flame duration time (tvol) significantly increased with the increasing of O2 concentration at low O2 concentrations. In the higher O2 concentrations, coals with different PAHs generation amount responded differently on the increasing of O2 concentration. On one hand, for the coals with lower PAHs generation amount, the OH concentration increased with the increasing of O2 concentration, while the tvol was not sensitive to changes of the O2 concentration. On the other hand, for the coals with higher PAHs generation amount, the OH concentration decreased with the increasing of O2 concentration while the tvol increased with the increasing of O2 concentration. It can be concluded that PAHs inhibited the OH generation, and the generation characteristics of OH and PAHs affected the sustained state of volatile combustion. The higher PAHs concentration consumed higher amount of OH during the volatile combustion. Meanwhile, with the increasing of PAHs concentration, the reaction rate of H + O2+M→HO2+M in which PAHs participate was increased, inhibiting the reaction H + O2→OH+O, and the increasing of polymer soot of PAHs will reduce the flame temperature through thermal radiation, which further inhibited the OH formation.

The acidic OER activation-decay process of highly active Ir–Ni mixed oxide modified by capping agent for both particle fining and Ir–OH formation

Developing highly active catalyst for oxygen evolution reaction (OER) with low noble metal loading is crucial for the application of proton exchange membrane (PEM) water electrolysis. Ir-transition metal (TM) binary catalyst with chemical leaching was reported to perform excellent activity with TM leaching. However, most of the studies on the activation-decay focused on the final status, and the variation process remains unclear. With cysteamine·HCl, a modified facile molten salt method was applied to prepared highly active Ir–Ni mixed oxide (c-xNiIrMO), which perform 5.5 times higher mass activity than commercial IrO2. The variation of active surface area, intrinsic activity, conductivity of prepared catalyst layer during the activation process are studied to unveil the key factors for the activity enhancement. With further stability test, c-xNiIrMO with Ni content lower than 67% performs decrease intrinsic activity and improved kinetic performance in the first hundred cycles. After obtaining a stable Ir0.95Ni0.05Ox structure, further cycling results in typical activity decay with dissolution of Ir.

Insight into the Photodegradation of Microplastics Boosted by Iron (Hydr)oxides.

Iron (hydr)oxides as a kind of natural mineral actively participate in the transformation of organic pollutants, but there is a large knowledge gap in their impacts on photochemical processes of microplastics (MPs). This study is the first to examine the degradation of two ordinary plastic materials, polyethylene (PE) and polypropylene (PP), mediated by iron (hydr)oxides (goethite and hematite) under simulated solar light irradiation. Both iron (hydr)oxides significantly promoted the degradation of MPs (particularly PP) with a greater effect by goethite than hematite, related to hydroxyl radical (•OH) produced by iron (hydr)oxides. Under light irradiation, the surface Fe(II) phase catalyzed the production of H2O2 and promoted the release of Fe2+, leading to the subsequent light-driven Fenton reaction which produced a large amount of •OH. As the iron (hydr)oxides were modified with NaF at various concentrations, the activity of the surface Fe(II) as well as the release of Fe2+ were greatly reduced, and thus the •OH formation and MP degradation were depressed remarkably. It is worth noting that the surface hydroxyl groups (especially ≡FeOH) affected the reaction kinetics of •OH by regulating the activity of Fe species. These findings unveil the distinct impacts and intrinsic mechanisms of iron (hydr)oxides in influencing the photodegradation of MPs.

Aerosol Oxidative Potential in the Greater Los Angeles Area: Source Apportionment and Associations with Socioeconomic Position.

Oxidative potential (OP) has been proposed as a possible integrated metric for particles smaller than 2.5 μm in diameter (PM2.5) to evaluate adverse health outcomes associated with particulate air pollution exposure. Here, we investigate how OP depends on sources and chemical composition and how OP varies by land use type and neighborhood socioeconomic position in the Los Angeles area. We measured OH formation (OPOH), dithiothreitol loss (OPDTT), black carbon, and 52 metals and elements for 54 total PM2.5 samples collected in September 2019 and February 2020. The Positive Matrix Factorization source apportionment model identified four sources contributing to volume-normalized OPOH: vehicular exhaust, brake and tire wear, soil and road dust, and mixed secondary and marine. Exhaust emissions contributed 42% of OPOH, followed by 21% from brake and tire wear. Similar results were observed for the OPDTT source apportionment. Furthermore, by linking measured PM2.5 and OP with census tract level socioeconomic and health outcome data provided by CalEnviroScreen, we found that the most disadvantaged neighborhoods were exposed to both the most toxic particles and the highest particle concentrations. OPOH exhibited the largest inverse social gradients, followed by OPDTT and PM2.5 mass. Finally, OPOH was the metric most strongly correlated with adverse health outcome indicators.

Exploring the chemistry behind low temperature auto-ignition of isopropyl nitrate in an RCM: An experimental and kinetic modeling study

The low-temperature auto-ignition chemistry of isopropyl nitrate (iPN) was experimentally and numerically investigated in the present study. The ignition delay times (IDTs) of iPN were measured stoichiometrically over a temperature range of 560–600 K at effective pressures of 5 and 10 bar in a rapid compression machine. A two-stage ignition phenomenon of iPN was observed. Both the first-stage IDTs and total IDTs vary rapidly within the narrow temperature range investigated (∼40 K). A recent iPN kinetic mechanism proposed by Fuller and Goldsmith for pyrolysis studies was extended. The reaction kinetics of CH3CHO + NO2 has been theoretically calculated at 500–1500 K and 0.01–100 atm. The rate information of CH3 + NO2 was updated based on previous theoretical results. The O2-addition channel of acetyl radical (CH3CO), which accounts for the first-stage IDT, was also considered in the present work. The extended iPN kinetic model predicts the two-stage IDTs well. Simulation results suggest that the IDTs are most sensitive to the following two reactions: (1) CH3 + NO2 = CH3O + NO; (2) CH3 + NO2 = CH3NO2. The former promotes the overall reactivity by yielding the reactive methoxy radical, while the latter forms a relatively stable product (i.e., CH3NO2). The reaction of CH3CHO + NO2 = CH3CO + HONO supplements the formation of CH3CO. The different consumption channels of CH3CO radicals (the O2-addition reaction and the decomposition reaction) lead to different chain reactions yielding OH radicals with increasing temperature in the ignition process. The “NONO2 loop” is the main route for OH formation in the studied conditions, which is mainly responsible for the iPN ignition.