Additional OH Research Articles

Abiotic Foldamer Quaternary Structures.

Abiotic aromatic foldamer sequences have been previously shown to fold in helix-turn-helix motifs in organic solvents. Using simple computational tools, a new helix-turn-helix motif was designed that bears additional hydrogen bond donor OH groups to promote its aggregation into a genuine, trimeric, abiotic quaternary structure. This sequence was synthesized and its self-assembly in solution was investigated by Nuclear Magnetic Resonance (NMR), Circular Dichroism (CD) and Molecular Dynamics (MD) simulations. The existence of two stable discrete aggregates was evidenced, one assigned to the initially designed trimer, the other to a dimer including multiple water molecules. The two species may be quantitatively interconverted upon changing the water content of the solution or the temperature. These results represent important steps in the design of protein-like abiotic architectures.

Cadmium Iodide as a Catalyst for the Addition of Carbon Dioxide to Oxiranes

The CdI2-catalyzed addition of CO2 to oxiranes is presented. The catalysts are obtained by mixing amines with CdI2. It is found that amines with a large number of aliphatic groups provide the higher conversion; the presence of additional OH and NH groups negatively affects the conversion.

The characteristics and mechanism NO formation during hydroxylated fuels/NH3 oxidation in oxy-fuel atmospheres

Oxy-fuel combustion, as an important technology to realize CCUS in the field of combustion, needs to control the generation of pollutants such as NOx while realizing CO2 capture, and the conversion of fuel-N to N2 is crucial. Previous experiments have provided insights into the influence of different atmospheres on NO during oxy-fuel combustion of alcohols. However, the specific reaction mechanism underlying how the atmosphere and hydroxyl fuels impact NO generation through the free radical pool remains unclear. In this study, the formation and reduction of NO during the oxidation of CH3OH/NH3 and C2H5OH/NH3 in O2/CO2, O2/H2O and O2/CO2/H2O atmospheres with oxy-fuel condition were investigated by simulation. In the NO generation stage, different H2O, CO2, O2 and fuel types have little effect on the peak of NO although they change the NH3→NO reaction path. In the process of NO reduction, stage 1 is the main reaction phase of NO→N2, and both CO2 and H2O are beneficial for the reduction of NO. But the reduction of NO by H2O was more pronounced. In the case of simultaneous addition of H2O and CO2, the reducing effect of H2O and CO2 alone on NO was attenuated. On the other hand, the reduction effect exerted by H2O and CO2 was stronger in high than in low oxygen-fuel ratio, stronger in C2H5OH than in CH3OH. The reduction of NO by H2O and CO2 is based on the general equation NO→N2+O2. H2O is used to promote the reaction in the positive direction by consuming O2 to convert it to H and OH, so that more of the element O is converted to OH than O2 to inhibit the production of NO. The CO2 contributes to the formation of less O2 during the reduction of N2 from NO by promoting reaction NO + N→O + N2, while the additional OH increases the "capacity" of O2 in the NO→N2+O2 reaction.

Interactions of gliadins with flavonoids and their glycosides studied with application of FT-Raman spectroscopy

FT-Raman spectroscopy was applied to study interactions between wheat gliadins and three flavonoids and their glycosides. Complexes gliadins-flavonoids/glycosides were extracted from the model wheat dough. As flavonoids were used quercetin, naringenin, hesperetin and their glycosides rutin, naringin, hesperidin in the amount of 0.05%, 0.1% and 0.2%. The analysis of the FT-Raman spectra showed that the tested compounds caused changes in the secondary and tertiary structure of gliadins. In the case of gliadins, these changes concerned mainly α-helices. Quercetin induced a different type of structural changes compared to naringenin and hesperetin, which was probably due to the presence of a double bond on the C ring and an additional OH group on the B ring in the structure of this molecule. On the other hand, the interactions of glycosides with gliadins were affected by the place of attachment of the sugar part in the structure of the glycoside. Flavonoids/glycosides significantly increased the content of disulfide bridges in the g-g-g conformation. Changes in the amino acid microenvironment (tyrosine and tryptophan) indicate the formation of a more ordered structure in gliadins.

Characterizing Hydroxyl Radical Formation from the Light-Driven Fe(II)-Peracetic Acid Reaction, a Key Process for Aerosol-Cloud Chemistry.

The reaction of peracetic acid (PAA) and Fe(II) has recently gained attention due to its utility in wastewater treatment and its role in cloud chemistry. Aerosol-cloud interactions, partly mediated by aqueous hydroxyl radical (OH) chemistry, represent one of the largest uncertainties in the climate system. Ambiguities remain regarding the sources of OH in the cloud droplets. Our research group recently proposed that the dark and light-driven reaction of Fe(II) with peracids may be a key contributor to OH formation, producing a large burst of OH when aerosol particles take up water as they grow to become cloud droplets, in which reactants are consumed within 2 min. In this work, we quantify the OH production from the reaction of Fe(II) and PAA across a range of physical and chemical conditions. We show a strong dependence of OH formation on ultraviolet (UV) wavelength, with maximum OH formation at λ = 304 ± 5 nm, and demonstrate that the OH burst phenomenon is unique to Fe(II) and peracids. Using kinetics modeling and density functional theory calculations, we suggest the reaction proceeds through the formation of an [Fe(II)-(PAA)2(H2O)2] complex, followed by the formation of a Fe(IV) complex, which can also be photoactivated to produce additional OH. Determining the characteristics of OH production from this reaction advances our knowledge of the sources of OH in cloudwater and provides a framework to optimize this reaction for OH output for wastewater treatment purposes.

Incorporation mechanisms and infrared absorption coefficients of water in MgSiO3 orthoenstatite clarified via comprehensive NMR and vibrational spectroscopic measurements, and first-principles calculations

We performed 1H and 29Si NMR and infrared measurements, and first-principles calculations to clarify the nature of OH defects in MgSiO3 orthoenstatite. An orthoenstatite sample synthesized at 7 GPa and 1200 °C from a composition of MgSiO3 + 0.1 wt% H2O yielded two 1H MAS NMR peaks near 5.9 and 7.6 ppm that are correlated in 2D NMR spectra, and two infrared bands near 3361 and 3066 cm− 1 that correspond to the previously reported A3 and A4 bands. The first-principles calculations confirmed that they are due to a pair of protons in a Mg (M2) vacancy. The previously reported A1 and A2 infrared bands near 3687 and 3592 cm− 1 for orthoenstatite synthesized at low silica activities were confirmed to arise from four protons in a SiB vacancy. The latter is predicted to give two additional OH stretching bands associated with two strongly hydrogen-bonded O3b-H bonds with frequencies below the spectral range reported thus far. The previously reported infrared absorption coefficients were thus revised to account for the undetected bands. 1H NMR may be used to quantitatively detect all four protons (expected at 1–12 ppm). Other mantle minerals should also be examined for potentially overlooked OH defects with strong hydrogen bonding.

Additional HONO and OH Generation from Photoexcited Phenyl Organic Nitrates in the Photoreaction of Aromatics and NOx.

HONO acts as a major OH source, playing a vital role in secondary pollutant formation to deteriorate regional air quality. Strong unknown sources of daytime HONO have been widely reported, which significantly limit our understanding of radical cycling and atmospheric oxidation capacity. Here, we identify a potential daytime HONO and OH source originating from photoexcited phenyl organic nitrates formed during the photoreaction of aromatics and NOx. Significant HONO (1.56-4.52 ppb) and OH production is observed during the photoreaction of different kinds of aromatics with NOx (18.1-242.3 ppb). We propose an additional mechanism involving photoexcited phenyl organic nitrates (RONO2) reacting with water vapor to account for the higher levels of measured HONO and OH than the model prediction. The proposed HONO formation mechanism was evidenced directly by photolysis experiments using typical RONO2 under UV irradiation conditions, during which HONO formation was enhanced by relative humidity. The 0-D box model incorporated in this mechanism accurately reproduced the evolution of HONO and aromatic. The proposed mechanism contributes 5.9-36.6% of HONO formation as the NOx concentration increased in the photoreaction of aromatics and NOx. Our study implies that photoexcited phenyl organic nitrates are an important source of atmospheric HONO and OH that contributes significantly to atmospheric oxidation capacity.

Significant Effect of 2nd Sphere Interactions on the Reductive Activation of O2 by non‐heme Iron(II) Complexes – Application to the Electroassisted Oxidation of Thioanisole

AbstractNew mononuclear non‐heme FeII complexes derived from a well‐known pentadentate amine/pyridine ligand were synthesized. The new ligand bears an additional OH group on one pyridyl aimed at developing second sphere hydrogen bonds. Two binding modes of the ligand were observed that can be selectively obtained through the choice of the counterion: the OH group develops an intramolecular H‐bond with the 6th exogenous ligand in the classical mode, or an intermolecular one with the unbound triflate counterion in the alternative mode. The complexes were studied by cyclic voltammetry in the reductive activation of O2. The addition of an H‐bond improves the O2 activation potential with a gain of 90 mV in the classical case and 220 mV in the alternative one. The difference is ascribed to the development of stabilizing H‐bonds within the FeIII‐peroxo intermediate with the proximal O atom of peroxo (classical mode) or the distal one (alternative mode). Ultimately, the complex in the alternative mode activates O2 at −0.5 V vs SCE (500 mV gain compared to free O2). We took advantage of this significantly reduced energetic cost to carry out and achieve the electroassisted oxidation of thioanisole by O2 at −0.5 V vs SCE.

Water Speciation and Storage Capacity of Olivine under the Reduced Fluid—Peridotite Interaction

The key features of the interaction between peridotites of the continental lithospheric mantle and reduced hydrocarbon-rich fluids have been studied in experiments conducted at 5.5 GPa and 1200 °C. Under this interaction, the original harzburgite undergoes recrystallization while the composition of the fluid changes from CH4-H2O to H2O-rich with a small amount of CO2. The oxygen fugacity in the experiments varied from the iron-wustite (IW) to enstatite-magnesite-olivine-graphite/diamond (EMOG) buffers. Olivines recrystallized in the interaction between harzburgite and a fluid generated by the decomposition of stearic acid contain inclusions composed of graphite and methane with traces of ethane and hydrogen. The water content of such olivines slightly exceeds that of the original harzburgite. Redox metasomatism, which involves the oxidation of hydrocarbons in the fluid by reaction with magnesite-bearing peridotite, leads to the appearance of additional OH absorption bands in the infrared spectra of olivines. The water content of olivine in this case increases by approximately two times, reaching 160–180 wt. ppm. When hydrocarbons are oxidized by interaction with hematite-bearing peridotite, olivine captures Ca-Mg-Fe carbonates, which are products of carbonate melt quenching. This oxidative metasomatism is characterized by the appearance of specific OH absorption bands and a significant increase in the total water content in olivine of up to 500–600 wt. ppm. These findings contribute to the development of criteria for reconstructing metasomatic transformations in mantle rocks based on the infrared spectra and water content of olivines.

Stratospheric Temperature and Ozone Impacts of the Hunga Tonga‐Hunga Ha'apai Water Vapor Injection

AbstractThe January 2022 eruption of the Hunga Tonga‐Hunga Ha'apai underwater volcano injected a large amount of water vapor into the mid‐stratosphere. This study uses model simulations to investigate the resulting stratospheric impacts out to 2031. Maximum radiatively‐driven model temperature changes occur in the Southern Hemisphere (SH) subtropics in April–May 2022, with warming of ∼1 K in the lower stratosphere and cooling of 3 K in the mid‐stratosphere. The radiative cooling combined with adiabatic cooling driven by the quasi‐biennial oscillation meridional circulation explains the near‐record cold anomaly observed in the SH subtropical mid‐stratosphere. Projected ozone responses maximize in 2023–2024 as the water vapor plume is transported globally throughout the stratosphere and mesosphere. The excess H2O increases the OH radical, causing a negative global ozone response (2%–10%) in the upper stratosphere and mesosphere due to increased odd hydrogen‐ozone loss, and a small positive ozone response (0.5%–1%) in the mid‐stratosphere due to interference of the NOx catalytic loss cycle by the additional OH. In the lower stratosphere, the excess H2O is projected to increase polar stratospheric clouds and springtime halogen‐ozone loss, enhancing the Antarctic ozone hole by 25–30 DU in 2023. Arctic impact is small, with maximum additional ozone loss of 4–5 DU projected in spring 2024. These responses diminish after 2024 to be quite small by 2031, as the excess H2O is removed from the stratosphere with a 2.5‐year e‐folding time. Given the year‐to‐year variability of the stratosphere, the magnitudes of these ozone responses may be below the threshold of detectability in observations.

Increase of OH radical yields due to the decomposition of hydrogen peroxide by gold nanoparticles under X-ray irradiation.

We elucidate the decomposition mechanism of hydrogen peroxide, which is formed by water radiolysis, by gold nanoparticles (GNPs) under X-ray irradiation. The variations in yields of hydrogen peroxide generated in the presence of GNPs are evaluated using the Ghormley technique. The increase of yields of OH radicals has been quantified using Ampliflu® Red solutions. Almost all hydrogen peroxide generated by irradiation of <25 Gy is decomposed by GNPs, while the yield of OH radicals increases by 1.6 times. The amount of OH radicals thus obtained is almost equivalent to that of the decomposed hydrogen peroxide. The decomposition of hydrogen peroxide is an essential reaction to produce additional OH radicals efficiently in the vicinity of GNPs.

Titanium and Vanadium Complexes of Tridentate Phenoxy-Imine and Phenoxy-Amine Ligands and Their Application in the Ring-Opening Polymerization of Cyclic Esters.

Phenoxy-imine and phenoxy-amine proligands, with the additional OH donor groups 2,4-tBu2-6-(2-CH2(OH)-C6H4N=CH)C6H3OH (L1H2), 6-(2-CH2(OH)-C6H4N=CH)C6H3OH (L2H2), and 2,4-tBu2-6-(2-CH2(OH)-C6H4NH-CH)C6H3OH (L3H2), were synthesized and their titanium (Ti-L1-Ti-L3) and vanadium (V-L1-V-L2) complexes were prepared in reactions with Ti(OiPr)4 and VO(OiPr)3, respectively. All new compounds were characterized with the use of FTIR, 1H, and 13C NMR spectroscopy; X-ray crystallography was also used to study proligands. All the complexes proved to be active catalysts in the ring-opening polymerization (ROP) of ε-caprolactone, rac-lactide, and L-lactide in the melt. The effects of the complex structure (transition metal type, presence of tBu substituents, and type of nitrogen donor group), as well as the polymerization time and temperature, on the monomer conversion and polymer properties were investigated in detail.

(Invited) Physical Analysis and Modeling of Wafer-to-Wafer Copper Hybrid Bonding at Sub-Micron Pitches

The bonding process has four sequential steps: plasma surface treatment, rinsing, bonding, and annealing. It is important to understand the details of all these steps to enable high performance bonding at sub-micron pitches. A multi-level back-end-of-line test vehicles at 1um and 0.5um pitches have been produced to evaluate the execution of the Tokyo Electron wafer-to-wafer (W2W) bonding tool platform. Subsequently several simulation and modeling approaches have been developed to better comprehend the impacts of different process conditions on the physical hybrid bonding results.Figure 1 shows the scanning electron microscope (SEM) image of the 1um bonding pad pitch Kelvin-via test structure that was successfully bonded and electrically tested. A median resistance of 0.44Ω has been measured for well-aligned 1um pitch kelvin-via measurements. Multiple variations of the test structures purposefully shift the top and bottom wafer patterning up to 100% mis-aligned to study the impact on electrical results from the bonding alignment. The corresponding electrical resistance, leakage and yield results provide statistically relevant feedback to improve the design and process integration of the test vehicle and W2W bonding platform.Maintaining a proper composition of the copper bond pads during plasma activation is necessary, especially if a lower anneal temperature post bond is desired. At low thermal budget bonding the oxides are not able to diffuse through any thick layer of modified copper formed between the pads during bonding which can significantly impede the electrical properties of the contact. The impact of plasma gas composition on the formation of surface copper species was determined using X-Ray Photoelectron Spectroscopy. For low temperature bonding, a simultaneous O2/H2 plasma treatment produces the thinnest copper oxide with the lowest theoretical resistivity. The activation gas chosen is based on the dielectric being used, but it has a significant impact on copper oxidation.If the bonding dielectric material is SiCN, then an O2 or O2/H2 mixed gas is best used for the activation process. The Cu2O content is less than the diffusion length for low temperature bonding for both gases, but the concentration of both CuO and Cu(OH)2 is high for the O2 treatment. At these concentrations, a low temperature O2 activation would create a copper contact with significant resistance. These results will help develop a plasma treatment to achieve good electrical contacts between hybrid bonded wafers with low thermal budget.A quantum chemistry simulation was developed to study how O/N-radicals modify the surface of SiO2 to increase the bond density. O atoms binding with H, N and C in the SiO2 films to create OH, CH2O, CO, HNO and nitic oxides (NO) groups. NO-groups are hydrolyzed to form additional surface OH during the rinsing step, increasing the density of Si-O-Si formation and total bonding energy. Atomistic molecular dynamic simulation also confirmed how nitrogen atoms introduce silanol and siloxane group to the surface during the surface activation treatment and the hydration reaction. The population effects of N atoms on bond formation were also studied, which indicated when more N atoms exist it will lead to improved bonding.Several plasma conditions were tested for the surface activation process to bond thermal silicon dioxide (TOX) to each other, and the bonding strength was calculated by the Maszara-Method after the annealing process. Comparing the bonding strength between TOX/TOX bond with N2 and O2 plasma under the same plasma conditions, the bonding strength using N2 plasma treatment is 1.7 times stronger than the bonding strength using O2 plasma treatment, indicating that the N2 plasma treatment is superior to the O2 plasma treatment.Finally, a multi-physics finite element model to simulate the post-bond distortion resulting from the wafer-to-wafer bonding process in room conditions was evaluated. The axisymmetric simulation model includes both the solid mechanics of the silicon wafers and the fluid mechanics of the air gap to accurately simulate the bond propagation dynamics. The two wafers, which may be warped by stressed films in preceding process steps, are initially separated at a small, fixed gap. As the center of upper wafer is pushed down by a striker, an adhesion model like Lennard-Jones potential simulates the contact propagation behavior between the two wafers. The simulation also includes other bonder process parameters and hardware designs to provide accurate distortion results. The outputs of the simulation are validated against a numerical model. The simulation model is also validated against direct wafer bonding experiment results. Figure 1

Experimental and kinetic modeling study of the autoignition and oxidation of ammonia/ethane mixtures in a rapid compression machine and a jet-stirred reactor

Ignition delay times and speciation data of ammonia/ethane (NH3/C2H6) fuel blends were measured in a rapid compression machine (RCM) and in a jet-stirred reactor coupled with molecular beam mass spectrometry (JSR-MBMS), respectively. Specifically, the RCM experiments were conducted at elevated pressures of 20 and 40 bar, intermediate temperatures between 890 and 1110 K, three equivalence ratios of 0.5, 1.0 and 2.0 and for three C2H6 mole fractions from 1% to 10%. Besides, the JSR measurements were conducted at atmospheric pressure, intermediate temperatures between 700 and 1180 K, three equivalence ratios of 0.5, 1.0 and 2.0 and three C2H6 mole fractions from 10% to 50%. The experimental results demonstrate that adding C2H6 into NH3 leads to a more reactive mixture. A kinetic model from our recent work on ammonia/ethanol fuel blends (M. Li et al., Proc. Combust. Inst., 2022) has been updated and validated with the new data obtained in this work. The updated model (PTB-NH3/C2 mech) can reproduce the effects of ethane fraction and equivalence ratio on IDT/speciation and show an overall satisfactory agreement between experimental results and predictions. Based on the kinetic analyses, for all conditions investigated in this study, the generation of OH radicals from HO2 and H radicals dominates the characteristic of the auto-ignition process in the RCM and the NH3 consumption process in the JSR, respectively. Apart from that, the addition of ethane provides additional OH from a relatively low temperature (e.g., around 850 K in a JSR condition) and triggers the interactions between hydrocarbon and ammonia systems, e.g., the reactions of C2H6/C2H4/CH3+NH2, which play an important role in the combustion of ammonia.

Direct Imaging of Local pH Reveals Bubble-Induced Mixing in a CO2 Electrolyzer.

Electrochemical CO2 reduction poses a promising pathway to produce hydrocarbon chemicals and fuels without relying on fossil fuels. Gas diffusion electrodes allow high selectivity for desired carbon products at high current density by ensuring a sufficient CO2 mass transfer rate to the catalyst layer. In addition to CO2 mass transfer, the product selectivity also strongly depends on the local pH at the catalyst surface. In this work, we directly visualize for the first time the two-dimensional (2D) pH profile in the catholyte channel of a gas-fed CO2 electrolyzer equipped with a bipolar membrane. The pH profile is imaged with operando fluorescence lifetime imaging microscopy (FLIM) using a pH-sensitive quinolinium-based dye. We demonstrate that bubble-induced mixing plays an important role in the Faradaic efficiency. Our concentration measurements show that the pH at the catalyst remains lower at -100 mA cm-2 than at -10 mA cm-2, implying that bubble-induced advection outweighs the additional OH- flux at these current densities. We also prove that the pH buffering effect of CO2 from the gas feed and dissolved CO2 in the catholyte prevents the gas diffusion electrode from becoming strongly alkaline. Our findings suggest that gas-fed CO2 electrolyzers with a bipolar membrane and a flowing catholyte are promising designs for scale-up and high-current-density operation because they are able to avoid extreme pH values in the catalyst layer.

Impact of Silver-Decorated Graphene Oxide (Ag-GO) towards Improving the Characteristics of Nanohybrid Polysulfone Membranes.

The utilization of membranes has been extensively employed in the treatment of water and wastewater. Membrane fouling, attributed to the hydrophobic nature of membranes, constitutes a noteworthy concern in the realm of membrane separation. The mitigation of fouling can be achieved through the modification of membrane characteristics, including but not limited to hydrophilicity, morphology, and selectivity. In this study, a nanohybrid polysulfone (PSf) membrane embedded with silver-graphene oxide (Ag-GO) was fabricated to overcome problems related to biofouling. The embedment of Ag-GO nanoparticles (NPs) is the aim towards producing membranes with antimicrobial properties. The fabricated membranes at different compositions of NPs (0 wt%, 0.3 wt%, 0.5 wt%, and 0.8 wt%) are denoted as M0, M1, M2, and M3, respectively. These PSf/Ag-GO membranes were characterized using FTIR, water contact angle (WCA) goniometer, FESEM, and salt rejection. The additions of GO significantly improved the hydrophilicity of PSf membranes. An additional OH peak at 3380.84 cm-1 of the nanohybrid membrane from FTIR spectra may be related to hydroxyl (-OH) groups of GO. The WCA of the fabricated membranes decreased from 69.92° to 54.71°, which confirmed the improvement in its hydrophilicity. In comparison to the pure PSf membrane, the morphology of the finger-like structure of the fabricated nanohybrid membrane slightly bent with a larger bottom part. Among the fabricated membranes, M2 achieved the highest iron (Fe) removal, up to 93%. This finding proved that the addition of 0.5 wt% Ag-GO NPs enhanced the membrane water permeability together with its performance of ionic solute removal (Fe2+) from synthetic groundwater. In conclusion, embedding a small amount of Ag-GO NPs successfully improved the hydrophilicity of PSf membranes and was able to achieve high removal of Fe at 10-100 mg L-1 towards purification of groundwater for safe drinking water.

Treatment of Pharmaceutical Industry Wastewater by PhotoelectroFenton Oxidation

The use of Photoelectro-Fenton oxidation to treat real pharmaceutical effluent is an attractiveoption for the elimination of complex and persistent organic contaminants. This advanced oxidation processcombines the electrochemical generation of highly reactive hydroxyl radicals (OH•) with the photochemicaldegradation of by-products, resulting in the efficient removal of pharmaceutical compounds fromwastewater. In the Photoelectro-Fenton process, an appropriate anode material, such as BDD or DSA, isused to generate OH•radicals through the electrochemical oxidation of Fe2+ ions. The addition of a smallamount of Fe2+ and H2O2 facilitates the Fenton reaction, leading to the production of additional OH•radicalsin the solution. The presence of these OH•radicals ensures the effective oxidation of pharmaceuticalpollutants, which are often resistant to conventional wastewater treatment methods. The use of UV orsunlight irradiation further enhances the Photoelectro-Fenton process by promoting thephotodecomposition of intermediate by-products formed during the oxidation process. This simultaneouselectrochemical and photochemical degradation mechanism provides synergistic effects, resulting inenhanced degradation and mineralization of pharmaceutical compounds. Studies have demonstrated thesuccessful application of Photoelectro-Fenton oxidation for the treatment of real pharmaceuticalwastewater, showing significant removal efficiencies for a wide range of pharmaceutical compounds,including antibiotics, analgesics, and hormones. Additionally, the process has been shown to effectivelydegrade recalcitrant by-products and reduce the overall toxicity of the wastewater. However, it is importantto consider factors such as optimal pH, Fe2+ and H2O2 dosages, irradiation intensity, and reaction time toachieve optimal treatment efficiency. Furthermore, the cost-effectiveness and scalability of thePhotoelectro-Fenton process need to be evaluated for its potential implementation in large-scale wastewatertreatment facilities.

Khurayyimite Ca7Zn4(Si2O7)2(OH)10·4H2O: a mineral with unusual loop-branched sechser single chains

The new mineral khurayyimite Ca7Zn4(Si2O7)2(OH)10·4H2O occurs in colorless spherulitic aggregates in small cavities of altered spurrite marbles located in the northern part of the Siwaqa pyrometamorphic rock area, Central Jordan. It is a low-temperature, hydrothermal mineral and is formed at a temperature lower than 100 °C. Synchrotron single-crystal X-ray diffraction experiments have revealed that khurayyimite crystallizes in space group P21/c, with unit cell parameters a = 11.2171(8), b = 9.0897(5), c = 14.0451(10) Å, β = 113.297(8)º, V = 1315.28(17) Å3 and Z = 2. The crystal structure of khurayyimite exhibits tetrahedral chains of periodicity 6. The sequence of SiO4 and ZnO2(OH)2-tetrahedra along the chain is Si–Si-Zn. The neighboring SiO4-tetrahedra of the corrugated chains are bridged by additional ZnO2(OH)2-tetrahedra to form 3-connected dreier rings. The chains can be addressed as loop-branched sechser single chains {lB, 11∞}[6Zn4Si4O21]. The chains are linked by clusters of five CaO6 and two CaO7 polyhedra with additional OH groups and H2O molecules in the coordination environment. Based on the connectedness and one-dimensional polymerisations of tetrahedra (TO4)n−, chains of khurayyimite belong to the same group as vlasovite Na2ZrSi4O11, since they can be described with geometrical repeat unit cTr = 2T43T4 and topological repeat unit cVr = 2V23V2.

A kinetic investigation on low-temperature ignition of propane with ozone addition in an RCM

To extend the temperature for propane ignition to a lower region (< 680 K), ozone (O3) was used as an ignition promoter to investigate the low-temperature chemistry of propane. Ignition delay times for propane containing varying concentrations of O3 (0, 100, and 1000 ppm) were measured at 25 bar, 654–882 K, and equivalence ratios of 0.5 and 1.0 in a rapid compression machine (RCM). Species profiles during propane ignition with varying O3 concentrations were recorded using a fast sampling system combined with a gas chromatograph (GC). A kinetic model for propane ignition with O3 was developed. O3 shortened ignition delay times of propane significantly, and the NTC behavior was weakened. O atoms released from O3 reacted with propane through hydrogen abstraction reactions, which led to the fast production of OH radicals. The following oxidation of fuel radicals generated additional OH radicals. Consequently, the inhibition caused by the slow chemistry of hydrogen peroxide (H2O2) in the NTC region was weakened in the presence of O3. Experimental results with O3 addition can provide extra constraints on the low-temperature chemistry of propane. Species profiles during propane ignition at 730 K with 1000 ppm O3 addition showed the production of propanal (C2H5CHO), acetone (CH3COCH3), and acetaldehyde (CH3CHO) was promoted significantly. Model analyses indicated that O3 shifted the oxidation temperature of propane to a lower region, in which reactions of ROO radicals (NC3H7O2 and IC3H7O2) tend to generate RO radicals (NC3H7O and IC3H7O). The promotion of RO radicals led to the fast production of C2H5CHO, CH3COCH3, and CH3CHO. The corresponding species profile highlighted the reaction relevant to ROO and RO radicals (NC3H7O + O2 = C2H5CHO + HO2 and 2 IC3H7O2 = 2 IC3H7O + O2). Rate constants of these reactions were updated, which can potentially improve the performance of the core mechanism under lower temperatures and provide references for model development of larger hydrocarbons.

Deciphering the cooperative effect of base and N-substituents on the origin of enantioselectivity switching for Mannich reactions of glycinate by carbonyl catalysts

Chiral carbonyl catalysis has developed rapidly in recent years and provided reliable methods for the preparation of chiral molecules, while the effective catalyst model remains unclear, and the size effect of catalyst substituents on the reversal of enantioselectivity needs to be clarified. Herein, the N-quaternized pyridoxals catalyzed asymmetric Mannich reactions of glycinate were studied to obtain fundamental understanding on these issues. The calculations show that the dual activation model aided by base NaHCO3, which contributes additional beneficial OH···N and Na···O/N interactions, is energetically more favorable than the base-free models, and the multiple interactions among the three entities, the base NaHCO3, the catalyst, and the imine substrate, in the enantiocontrolling transition states (TS) are responsible for the high enantioselectivity, rendering the preferred chiral product of (R,R)-4 in reaction I and (S,S)-4 in reaction II. The origin of the reversed enantioselectivity upon the substitution of a methyl for the H on the N-functional group in the catalyst was analyzed, and was attributed to the variation of the preferred orientation of NaHCO3 from facing-up to facing-down owing to the substitution, which created governing interactions to drive the reversal of the enantioselectivity in the such asymmetric Mannich reactions. This understanding of the activation model and the reversed stereoinduction sheds light on the effective chiral N-quaternized pyridoxal catalyst form and role of base on the enantioselectivity, and offers new insights for the future design of related asymmetric catalysts and Mannich reactions.