Atmospheric Reactions Research Articles

Atmospheric Oxidation Capacity and Its Impact on the Secondary Inorganic Components of PM2.5 in Recent Years in Beijing: Enlightenment for PM2.5 Pollution Control in the Future

In recent years, the concentrations of PM2.5 in urban ambient air in China have been declining; however, the strong atmospheric oxidation capacity (AOC) represents challenges to the further reduction of PM2.5 concentration and the continuous improvement of ambient air quality in China in the future, since the overall AOC is still at a high level. For this paper, based on ground observation data recorded in Beijing from 2016 to 2019, the variation in AOC was characterized according to the concentration of odd oxygen (OX = O3 + NO2). The concentrations of the primary and secondary components of PM2.5 were analyzed using empirical formulas, the correlation between AOC and the concentrations of secondary PM2.5 and the secondary inorganic components (SO42−, NO3−, NH4+, and SNA) in Beijing were explored, the impact of atmospheric photochemical reaction activity on the generation of atmospheric secondary particles was evaluated, and the impact of atmospheric oxidation variations on PM2.5 concentrations and SNA in Beijing was investigated. The results revealed that OX concentrations reached their peak in 2016 and reached their lowest point in 2019. The OX concentrations followed a descending seasonal trend of summer, spring, autumn, and winter, along with a spatial descending trend from urban observation stations to suburban stations and background stations. The degree of photochemical activity and the magnitude of the AOC have a large influence on the production of atmospheric secondary particles. When the photochemical reaction was more active and the AOC was stronger, the mass concentrations of the secondary generated PM2.5 fraction were higher and accounted for a higher proportion of the total PM2.5 mass concentrations. In the PM2.5 fraction, SNA accounted for 50.7% to 94.4% of the total mass concentrations of water-soluble inorganic ions in the field observations. Higher concentrations of the atmospheric oxidant OX in ambient air corresponded to a higher sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR), suggesting that the increase in AOC could promote the increase of PM2.5 concentration. Based on a relationship analysis of SOR, NOR, and OX, it was inferred that the relationship between OX and SOR and the relationship between OX and NOR were both nonlinear. Therefore, when establishing PM2.5 control strategies in Beijing in the future, the impact of the AOC on PM2.5 generation should be fully considered, and favorable measures should be taken to properly regulate the AOC, which would be more effective when carrying out further control measures regarding PM2.5 pollution.

Unraveling surface structures of gallium promoted transition metal catalysts in CO2 hydrogenation

Gallium-containing alloys have recently been reported to hydrogenate CO2 to methanol at ambient pressures. However, a full understanding of the Ga-promoted catalysts is still missing due to the lack of information about the surface structures formed under reaction conditions. Here, we employed near ambient pressure scanning tunneling microscopy and x-ray photoelectron spectroscopy to monitor the evolution of well-defined Cu-Ga surfaces during CO2 hydrogenation. We show the formation of two-dimensional Ga(III) oxide islands embedded into the Cu surface in the reaction atmosphere. The islands are a few atomic layers in thickness and considerably differ from bulk Ga2O3 polymorphs. Such a complex structure, which could not be determined with conventional characterization methods on powder catalysts, should be used for elucidating the reaction mechanism on the Ga-promoted metal catalysts.

Understanding of the synergy effect of DBD plasma discharge combined to photocatalysis in the case of Ethylbenzene removal: Interaction between plasma reactive species and catalyst

Hybrid non-thermal plasma combined with photocatalysis is an efficient technology for the degradation of volatile organic compounds (VOCs) and leads to a synergetic boosting effect of the degradation process. Herein, the degradation of ethylbenzene (EB) in a hybrid lab-scale reactor was performed. In the combined mode (plasma DBD and photocatalysis [TiO2 + UVA]), the degradation of EB was synergetically boosted, and a higher degradation efficiency was reached. In this study, the behavior of the synergetic effect was investigated whilst varying several operational conditions, including the UV light source (UVA and UVC), the TiO2 weight (7.5–22.51 g·m-²), the addition of metallic dopants to the TiO2 at different weight ratios (x%Cu-TiO2 and x%MnO2-TiO2, where x = 1, 3, 5 and 10 for the weight ratios of Cu:TiO2 and MnO2:TiO2) and the catalyst support (glass fiber tissue [GFT] and nickel foam [NF] with different thicknesses [0.3–3.3 mm]). Moreover, the oxygen content (0–100%) in the reactor atmosphere was examined. The results showed an enhancement of the synergetic effect under UVC (TiO2 + UVC + DBD), which may be a consequence of intensive ozone decomposition under UVC and the generation of reactive atomic oxygen. The improvement of the synergetic effect under 1% Cu-TiO2 and 10% MnO2-TiO2 catalysts is assumed to reflect the role of metallic species in the production of oxygen species on the TiO2 surface via the ozone depletion mechanism. Furthermore, TiO2/NF (3.3 mm) showed the highest synergetic effect, likely due to the conductive character and the 3D porous structure of NF. Finally, the rich oxygen composition had an apparent impact on the synergetic effect.

Study of a catalytic technology for syngas/H2 production from raw biogas self-reforming in presence of sulphur

A synthetic biogas stream was effectively reformed in the presence of dimethyl sulphide (used as a model sulphur-containing molecule) by a multi-metallic catalyst main composed by Ni and Ce, with Sn and Rh as promoters, supported over high surface alumina. Prior to reaction, a thermodynamic equilibrium calculation indicated that dimethyl sulphide decomposes to H2S and CO2 at the reaction temperature inside the reactor. This sulphur, that strongly attaches to Ni catalyst causing deactivation, was overcome during 35 h by the studied catalyst when a moderate content was fed, 15 ppm (30 ppm of dimethyl sulphide DMS). The obtained H2/CO was close to 2/1 and methane conversion almost reached 60%. On the other hand, in the case of a higher concentration present at the reaction atmosphere, 50 ppm of sulphur (90 ppm of DMS), it was observed a continuous decay in activity. The analysis of the used catalysts by TEM, XRD, Raman and TGA indicated that sulphur promoted the formation of graphitic carbon, mostly nanotubes, removing the isolated nickel particles of the alumina surface, whilst a long time on stream favoured the sintering of the active phase, indicating a combination of different deactivation effects. In fact, the case of feeding 50 ppm of sulphur, different deactivation mechanisms were observed: sintering, coke deposition, fouling and leaching, whilst in the case of moderate concentration the catalyst was capable of tolerating the sulphur presence.

Assessment of atmospheric pollution by oxygenated and nitrated derivatives of polycyclic aromatic hydrocarbons in two regions of the Czech Republic

In this study, a method for monitoring 16 representatives of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) and six oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) in airborne particulate matter (PM) was developed and validated. Soxhlet extraction, followed by solid phase extraction (SPE) on silica, was used to isolate the target compounds. Instrumental analysis was performed by gas chromatography coupled with (tandem) mass spectrometry (GC-MS(/MS)) operated in electron impact (EI) and negative ion chemical ionization (NICI) modes. GC-EI-MS/MS was selected for further experiments due to its higher selectivity of measurement and ability to measure derivatives simultaneously with 20 commonly analyzed PAHs (EU + US EPA priority list). This is the first study documenting the simultaneous analysis of OPAHs, NPAHs, and parent PAHs in a single run. This analysis strategy was successfully validated at two concentration levels of artificial contamination, i.e., 0.8 and 4 ng per filter, with recoveries in the 70–104% range and less than 23% repeatability. The newly developed method was used for the analysis of 45 air samples from two cities in the Czech Republic, namely Ceske Budejovice and Most (a place with heavy industry), and two sampling seasons (February vs. May 2017). Five representatives were found in all samples from the oxy-PAH group, with 9,10-anthraquinone (9,10-ANTQ) being the most abundant (0.010–2.49 ng m−3 air). Three major nitro-PAHs, namely 9-nitroanthracene (9-nANT), 2-nitrofluoranthene (2-nFA), and 1-nitropyrene (1-nPYR), were found in 89%, 96%, and 33% of the samples, respectively, found in concentration ranges of <0.60–902, <0.60–276, and <0.60–117 pg m−3 air. Slightly higher levels of oxy- and nitro-PAHs were found in Ceske Budejovice compared to Most, but the difference was not statistically significant (p-value >0.05). A statistically significant difference was observed between February and May, where the concentrations in February were up to 20 and 50 times higher for individual oxy- and nitro-PAHs, respectively, in both regions. The diagnostic ratio 2-nFA/1-nPYR >5 showed that indirect emissions were the primary nitro-PAH source in Most of nitro-PAHs in Most and in both sampling campaigns. In Ceske Budejovice, the opposite trend was observed in winter, i.e. 2-nFA/1-nPYR <5, indicating direct emissions as the main source. In summary, direct emissions of OPAHs and NPAHs originate from fossil (transportation-related) and solid fuel (heating-related) combustion. In contrast, indirect emissions are related to atmospheric reactions of PAHs with OH radicals (spring, winter) and NO3 radicals (winter). The total TEQB[a]P was higher in winter than spring, with higher inhalation cancer risk.

Growth of Nanocolumnar TiO2 Bilayer by Direct Current Reactive Magnetron Sputtering in Glancing-Angle Deposition Configuration for High-Quality Electron Transport Layer.

The electron transport layer (ETL) plays a crucial role in solar cell technology, particularly in perovskite solar cells (PSCs), where nanostructured TiO2 films have been investigated as superior ETLs compared to compact TiO2. In this study, we explored the nanocolumnar growth of TiO2 in the anatase phase for bilayer thin films by DC reactive magnetron sputtering (MS) technique and glancing-angle deposition (GLAD). For the growth of the compact TiO2 layer, it was found that the crystalline quality of the films is strongly dependent on the sputtering power, and the samples deposited at 120 and 140 W are those with the best crystalline quality. However, for the nanocolumnar layer, the reactive atmosphere composition determined the best crystalline properties. By optimizing the growth parameters, the formation of TiO2 nanocolumns with a cross-sectional diameter ranging from 50 to 75 nm was achieved. The average thickness of the films exceeded 12.71 ± 0.5 µm. All nanostructured films were grown at a constant GLAD angle of 70°, and after deposition, the measured inclination angle of the nanocolumns is very close to this, having values between 68 and 80°. Furthermore, a correlation was observed between the quality of the initial layer and the enhanced growth of the TiO2 nanocolumns. All bilayer films are highly transparent, allowing light to pass through up to 90%, and present a band gap with values between 3.7 and 3.8 eV. This article offers the experimental parameters for the fabrication of a nanocolumnar TiO2 using the magnetron sputtering technique and the glancing-angle deposition configuration.

Impact of Hunga Tonga-Hunga Ha’apai Volcanic Eruption on Stratospheric Water Vapour, Temperature, and Ozone

Despite being rare, large volcanic eruptions can have a long-lasting impact on the chemistry, radiation, and dynamics of the stratosphere. This study attempts to quantify the changes in the stratospheric water vapour and its relationship to temperature and ozone observed from space-based Microwave Limb Sounder (MLS) observations during the submarine volcano eruption Hunga Tonga-Hunga Ha’apai that occurred on 15 January 2022. The most notable aspect of this eruption is the plumes, which are water vapour columns that reached higher altitudes (1 hPa (47.6 km)) than earlier eruptions. We discovered that the eruption injected a record amount of water vapour (6–8 ppmv) directly into the stratosphere from 38–10 hPa vertically, which is present even after one year. The majority of water vapour is confined to the Southern Hemisphere (SH) tropics, i.e., 30°S to 5°N, and gradually descends to the SH polar latitudes over time. The WV from the lower stratosphere reaches mesospheric altitudes during January 2023. We quantify the impact of increased water vapour on temperature and ozone as well. Temperatures begin to fall during the month of March in the regions where there is an increase in water vapour. A ~5 K cooling occurs in July and August as a result of the thermal adjustment to the extra water vapour IR cooling. Our analysis shows a decrease in ozone caused by an increase in water vapour. Significant variability is observed in all three parameters at 26 km compared to other levels. Further, we noticed that after one year of eruption, the water vapour, Temperature and Ozone did not reach the background values. It is possible that this unusual eruption produced a different atmospheric reaction than other significant volcanic eruptions that have been well investigated.

Experimental and theoretical study on the photoionization of styrene.

This study employed a vacuum ultraviolet synchrotron radiation source and reflectron time-of-flight mass spectrometry (TOF-MS) to investigate the photoionization and dissociation of styrene. By analyzing the photoionization mass spectrum and efficiency curve alongside G3B3 theoretical calculations, we determined the ionization energy of the molecular ion, appearance energy of fragment ions, and relevant dissociation pathways. The major ion peaks observed in the photoionization mass spectra of styrene correspond to C8 H8 + , C8 H7 + and C6 H6 + . The ionization energy of styrene is measured as 8.46 ± 0.03 eV, whereas the appearance energies of C8 H7 + and C6 H6 + are found to be 12.42 ± 0.03 and 12.22 ± 0.03 eV, respectively, in agreement with theoretical values. The main channel for the photodissociation of styrene molecular ions is the formation of benzene ions, whereas the dissociation channel that loses hydrogen atoms is the secondary channel. Based on the experimental results and empirical formulas, the required dissociation energies (Ed ) of C8 H7 + , C8 H6 + and C6 H6 + are calculated to be (3.96 ± 0.06), (4.00 ± 0.06) and (3.76 ± 0.06) eV, respectively. Combined with related thermochemical parameters, the standard enthalpies of formations of C8 H8 + , C8 H7 + , C8 H6 + and C6 H6 + are determined to be 964.2, 1346.3, 1350.2 and 1327.0kJ/mol, respectively. Based on the theoretical study, the kinetic factors controlling the styrene dissociation reaction process are determined by using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. This provides a reference for further research on the atmospheric photooxidation reaction mechanism of styrene in atmospheric and interstellar environments.

Synergistic generation mechanisms of SOA and ozone from the photochemical oxidation of 1,3,5-trimethylbenzene: Influence of precursors ratio, temperature and radiation intensity

Aromatic hydrocarbons (AHs) are important anthropogenic precursors for both secondary organic aerosol (SOA) and ozone (O3) in urban areas. Knowledge about the synergistic processes and influence mechanisms of SOA and O3 during the photochemical oxidation of AHs is still relatively limited. In this study, the synergistic formation processes of SOA and O3 through the photochemical reactions of a representative AHs (1,3,5-trimethylbenzene, 135TMB) under different initial volatile organic compound/nitrogen oxides ([VOC]/[NOX]) ratios, temperatures and radiation intensities were investigated. The results showed that temperature and radiation significantly affected the reaction products and yields: the O3 production rates under high temperatures and radiation were greater than those under low temperatures and radiation, whereas the mass concentrations and yields of SOA under low temperatures and radiation were much higher than those under high temperatures and radiation. It was also found that the SOA yield increased with increasing NOX concentration within a specific initial [135TMB]/[NOX] ratio, but it decreased with increasing NOX concentration beyond a specific initial [135TMB]/[NOX] ratio. In addition, the concentrations of SOA and O3 in all the experiments increased simultaneously regardless of low temperatures or high temperatures. From these phenomena, it can be inferred that appropriate strategies for O3 precursor abatement can simultaneously reduce the concentration of SOA, which means that the coordinated control of fine particles and O3 could be achieved by taking coordinated emission reduction measures for VOCs and NOX precursors. The analysis of the organic components revealed that intramolecular hydrogen transfer occurred in some reactions in 135TMB photooxidation, and low-volatility and high-oxidative state organics were formed. The master chemical mechanism (MCM) results showed that the existing MCM mechanism does not yet fully meet the need to simulate the atmospheric photochemical reaction processes of 135TMB in the real atmosphere in China, and a localized MCM mechanism needs to be developed in the future.

Analytical (hydro)pyrolysis of pinewood and wheat straw in chloride molten salts: A route for 2-methyl furan production

2-methyl furan (MF) is a fuel additive with improved fuel characteristics compared to bio-ethanol. Unfortunately, the production of MF (from furfural (FF) hydrogenation) is not economically feasible. Interestingly, molten salts in biomass pyrolysis have shown to promote the formation of furans (mainly FF). Because molten salts hydropyrolysis could be an alternative route to both produce FF and convert it into MF, an assessment is indispensable. Molten salts pyrolysis and hydropyrolysis of pinewood and wheat straw and related model compounds were studied in a micro-reactor. The effect of hydropyrolysis process variables was assessed on the total detectable condensable vapors and MF formation.At low pressures (0.4 MPa), the chloride salts favored the production of FF and acetic regardless of the reaction atmosphere. Under a high pressure of hydrogen though (1.6 and 3.0 MPa), the conversion of FF to MF was enhanced through hydrogenation, hydrodeoxygenation and demethylation reactions. Molten salts hydropyrolysis at 350 °C and pressures of either 1.6 MPa (biomass mass fraction of 0.09) or 3.0 MPa (biomass mass fraction of 0.24) were optimal and yielded ca. 8 wt% to 9 wt% MF. Reaction temperatures >350 °C were unfavorable for the MF yield and instead promoted furfural decarbonylation to furan.

Effects of process atmosphere on additively manufactured FeCrAl oxide dispersion strengthened steel: Printability, microstructure and tensile properties

In this study, the effects of using a reactive process atmosphere (premixed Ar–O2 mixture and N2) on additively manufactured FeCrAl oxide dispersion strengthened (ODS) steel are evaluated by investigating the oxygen/nitrogen content of the as-built material, geometric characteristics and stability of the molten pool, microstructural feature, second phase formation and tensile properties. It was found that the use of reactive process gas within the building chamber allowed for in-situ alloying in the molten pool. With increasing oxygen content in the building chamber, more oxygen was dissolved by the molten pool allowing for more oxide formation. However, oxide agglomeration and coarsening were also seen to occur. When printing under the N2 process atmosphere, the nitrogen content in the as-built material increased, and the oxide agglomeration and coarsening were alleviated. A smaller depth-to-width ratio of the molten pool and a more uniform low-angle grain boundaries (LAGBs) distribution in the as-built material were realized when printing under Ar-1% O2 or N2 process atmosphere. Nitrogen, as low-cost gas, can be considered to replace traditional Ar as shielding gas for improved mechanical properties of as-built parts.

Comparison of the heterogeneous reaction of NO2 on the surface of clay minerals and desert dust particles

Mineral particles in air could provide atmospheric chemical reaction interface for gaseous substances and participate in atmospheric chemical reaction process, and affecting the status and levels of gaseous pollutants in air. However, differences of the heterogenous reaction on the surface minerals particles are not very clear. Considering main mineral composition of ambient particles was from dust emission, therefore, typical clay minerals (chlorite, illite) and desert particles (Taklimakan Desert) were selected to analysize chemical reaction of NO2, one of major gaseous pollutants, on mineral particles by using of In-situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) under different condition. And In situ near-ambient pressure X-ray photoelectron spectroscopy (In situ NAP-XPS) was employed to investigate iron (one of the major metals) species variation on the surface of mineral dust particles during the heterogeneous reactions. Our data show that humidity controlled by deuterium oxide (D2O) has a greater effect on chemical reactions compared to light and temperature. Under dry conditions, the amount of heterogeneous reaction products of NO2 on the particles shows Xiaotang dust > chlorite > illite > Tazhong dust regardless of dark or light conditions. In contrast, under humidity conditions, the order of nitrate product quantity under moderate conditions was chlorite > illite > Xiaotang dust > Tazhong dust. In situ NAP-XPS results demonstrate that specie variation of the Fe could promote the heterogenous reactions. These data could provide useful information for understanding the formation mechanism of nitrate aerosols and removal of nitrogen oxides in the atmosphere.

Fundamental study of in-situ strengthening and formation of continuous gradient titanium alloys via laser directed energy deposition

Current heterostructured materials have significant potential for improving the strength-ductility trade-off, but the interfacial bonding capabilities are limited. In this research, composites with TiN/Ti6Al4V interlayer structure were in-situ synthesized by atmospheric remelting using laser directed energy deposition (LDED). The elemental diffusion, microstructure, and mechanical properties of TiN/Ti6Al4V interlayer structure composites were investigated. The mechanical properties of the composites were improved after nitrogen remelting due to the strengthening of internal TiN ceramic particles. The microhardness of TiN/Ti6Al4V composites increased by up to 209.8% to 1141 HV0.2, ultimate tensile strength by 6% and elongation by 34.5% to 1071.4 MPa and 15.6%, respectively. This research demonstrates that a flexible combination of the LDED process and reaction atmosphere can synthesize new periodic layered ceramic/metal composites with excellent mechanical properties. This research offers the groundwork for the fabrication of in-situ strengthening continuous gradient materials.

Atmospheric oxidation of ethyl methyl carbonate: Kinetics and reaction mechanism

Ethyl methyl carbonate (EMC, CH3CH2OC(O)OCH3) is used industrially as an electrolyte for lithium-ion batteries and its production and use is expected to increase in the coming years, with a consequent increase in its atmospheric emissions. In this work, the photo-oxidation of EMC initiated by chlorine atoms in the gas phase was studied. The rate coefficient of the reaction between EMC and chlorine atom was determined by the relative method giving a mean value of (6.1 ± 0.5) × 10-12 cm3 molec-1 s−1. The products resulting from atmospheric photo-oxidation of EMC at 298 K and 760 torr total pressure were identified and quantified by infrared spectroscopy: CH3C(O)OC(O)OCH3 (35 %), CH3OC(O)OC(O)H (14 %), CH3OH (30 %), HC(O)OH (12 %), HC(O)H (6 %), CO2 (84 %), and CO (28 %). Theoretical calculations were performed using the Gaussian09 program to obtain the infrared spectra of the products not available in the literature. Finally, from the kinetic analysis and the observed products, an atmospheric reaction mechanism is here proposed.

Torrefaction under Different Reaction Atmospheres to Improve the Fuel Properties of Wheat Straw

This study aimed to produce biochar with an energy value in the range of sub-bituminous carbon by investigating the effect of oxidative and non-oxidative torrefaction on the torrefaction yield and fuel properties of wheat straw. Three independent variables were considered at different levels: temperature (230, 255, 280, 305 °C), residence time (20, 40, 60 min), and reaction atmosphere (0, 3, 6 vol% O2; N2 balance); and three dependent variables: mass yield, energy yield, and percentage increase in higher heating value (HHV). The results showed that it is possible to produce a sub-bituminous carbon type C biochar using oxidative torrefaction, significantly reducing time and temperature compared with non-oxidative torrefaction. The optimum torrefaction conditions were 287 °C–20 min–6.0% O2, which increased the HHV of wheat straw from 13.86 to 19.41 MJ kg−1. The mass and energy yields were 44.11 and 61.78%, respectively. The physicochemical and fuel properties of the obtained biochar were improved compared with the raw biomass. The atomic O/C ratio was reduced from 1.38 to 0.86. In addition, the hydroxyl groups in the lignocellulosic structure decreased and the hemicellulose content decreased from 26.08% to 1.61%. This improved grindability, thermal stability, porosity, and hydrophobicity.

Thermal transformation of 1-(ferrocenyl)ethanol to iron oxide nanoparticles based on reaction atmosphere: analysis of the decomposition reaction using non-isothermal thermogravimetry

Thermal transformation of 1-(ferrocenyl)ethanol to iron oxide nanoparticles based on reaction atmosphere: analysis of the decomposition reaction using non-isothermal thermogravimetry

Tuning of photoluminescence by mixing valence of Eu2+/Eu3+ in Ca9Ln(PO4)7 (Ln = Y, La) phosphor for UV light-emitting diodes

A series of single-phased emission-tunable Ca9Ln(PO4)7:Eu2+/3+ (Ln = Y, La) phosphors were synthesized by a high temperature solid-state reaction in a CO atmosphere, and its luminescent properties have been investigated. The phosphors can be well excited in the wavelength range of 245–475 nm, which match well with the n-UV chip. Additionally, Eu2+ and Eu3+ ions exist in Ca9Ln(PO4)7: Eu2+/3+ (Ln = Y, La), although the samples are prepared at the reducing atmosphere. The tunable emission colors of the phosphors can be achieved by varying the Eu ion concentration or excitation wavelength. The corresponding color hue of Ca9Y(PO4)7: xEu (x = 0.01–0.2) phosphors shifts gradually from green to white and eventually to orange-red with the Eu concentration increases, whether at 252 nm, 300 nm or 395 nm excitation. While the colour coordinates of Ca9La(PO4)7: 0.08Eu phosphor by changing the excitation wavelength, varied the emission hue of the phosphor from orange-red to yellow-green to white, and eventually back to orange-red again. These results demonstrated that the single-component of Ca9Ln(PO4)7:Eu2+/3+ (Ln = Y, La) phosphor may be candidates for w-LED multi-color phosphors.

Comparative study of ruthenium oxide loaded on amorphous UiO-66-NH2 and the derived ZrO2 in HCl oxidation to chlorine

The catalytic oxidation of HCl to Cl2 over RuO2-based catalysts is a significant process for chlorine recycling in chemical industry. In this study, an amorphous zirconium-based metal-organic framework (denoted by aUiO-66-NH2) and its derived metal oxide (denoted by ZrO2-aU) were utilized as carriers to construct RuO2-based catalysts. The XRD, XPS, SEM, STEM, H2-TPR, CO pulse, N2 adsorption-desorption and XAFS characterizations of RuO2/ZrO2-aU and RuO2/aUiO-66-NH2 catalysts indicated that, under the inducement of reaction atmosphere, the carrier aUiO-66-NH2 transforms to partially chlorinated t-ZrO2. Meantime, the RuO2 loaded on aUiO-66-NH2 diffuses into the crystal lattice of t-ZrO2, and finally form highly dispersed RuClxOy species stabilized in t-ZrO2, which leads to the higher activity than RuO2/ZrO2-aU. Comparatively, no structural transformation occurs for RuO2/ZrO2-aU catalyst, suggesting the advantage of the amorphous structure of aUiO-66-NH2 in constructing highly efficient catalysts.

Seasonal variations of O3 formation mechanism and atmospheric photochemical reactivity during severe high O3 pollution episodes in the Pearl River Delta region

In this study, the seasonal differences of O3 formation and photochemical reactivity were investigated during the high O3 episodes observed in autumn of 2014 and winter of 2017 at a downwind rural site of Pearl River Delta region (Heshan site). The mixing ratios of O3 and NO2 were highest in the Period I of autumn, followed by the Period II of autumn and the winter period. Though the total concentrations of VOCs were comparable in these periods, alkenes made greater fraction of VOCs during Period I of autumn, while those of OVOCs and aromatics were higher in winter period, resulting in the largest contributions of alkenes (ROH(alkenes)) and OVOCs (ROVOCs) to the photochemical reactivity in autumn and winter, respectively. The ozonolysis of alkenes (especially for 1-pentene and isoprene) dominated HOx production during Period I of autumn, while in winter period, photolysis of OVOCs increased before noon, and made the greatest contribution to HOx production in late afternoon. As for the HOx destruction, reaction of OH + NO2 dominated in both seasons, with higher rates in Period I of autumn because of higher levels of radical and NO2. Furthermore, the variations in O3 precursors and radical budget resulted in different O3 formation and destruction rates, with the highest contribution from RO2 and NO to O3 formation, as well as photolysis and ozonolysis of alkenes for O3 destruction in Period I of autumn. The net O3 production from photochemistry and contributions of physical processes indicated that local photochemistry dominated the O3 accumulation at noon and in the early afternoon, while dilution in O3 levels caused by physical process increased before noon and in the late afternoon. O3 formation sensitivity could be changed during the photochemical consumption of precursors, which was more NOx-limited in the late afternoon. Overall, our findings highlighted that control measures of photochemical pollution should consider the seasonal variations in the abundance of O3 and its precursors, and O3 formation sensitivity regime.

A novel additive manufactured reduced activation ferritic/martensitic steel enhanced by in-situ nanoparticles benefiting from oxygen addition

Reduced activation ferritic/martensitic (RAFM) steel emerging as the promising structural material of fusion reactors, has attracted considerable attention to improve its high-temperature performance. In the present study, a new-type RAFM steel (Fe-8.9Cr-0.82W-0.23Mn-0.086Si-0.27Ti-0.075C-0.032O) enhanced by in-situ nanoparticle constituents containing high-density and dispersed TiC, TiO and TiO@TiC (with core (TiO)-shell (TiC) structure) was manufactured using selective laser melting (SLM) with imposed oxygen atmosphere in the printing chamber. The novel TiO@TiC with core-shell structure is reported for the first time in RAFM steels. In addition, the high-temperature mechanical properties achieved in the present study are superior to those of other additive manufactured RAFM or oxide dispersion strengthened RAFM (ODS-RAFM) steels, which is attributed to the high-density and dispersed nanoparticles introduced by additional oxygen addition during SLM. The proposed idea for taking the reactive atmosphere into consideration for alloy design in this study could be extended to other alloys.