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Exploring the photocatalytic conversion mechanism of gaseous formaldehyde degradation on TiO2-x-OV surface
No full textTo understand the conversion mechanism of photocatalytic gaseous formaldehyde (HCHO) degradation, strontium (Sr)-doped TiO2-x-OV catalysts was designed and synthesized in this study, with comparable HCHO removal performance. Our results proved that foreign-element doping reduced Ti4+ to the lower oxidation state Ti(4-x)+, and that the internal charge kinetics was largely facilitated by the unbalanced electron distribution. Oxygen vacancies (OVs) were developed spontaneously to realize an electron-localized phenomenon in TiO2-x-OV, thereby boosting O-2 adsorption and activation for the enhanced generation of reactive oxygen species (ROS). At the chemisorption stage, in-situ DRIFTS spectra and density functional theory calculation results revealed that surface adsorbed O-2 (O-ads) and lattice O (O-lat) engaged in the isomerisation of HCHO to dioxymethylene (DOM) on TiO2-x-OV and TiO2, respectively. Time-resolved DRIFTS spectra under light irradiation revealed that the DOM was then converted to formate and thoroughly oxidized to CO2 and H2O in TiO2-x-OV. While bicarbonate byproducts were detected from DOM hydroxylation or possible side conversion of CO2 in TiO2, owing to insufficient consumption of surface hydroxyl. Our study enhances the understanding on the photocatalytic oxidation of HCHO, thereby promoting the practical application in indoor air purification
Optical properties of mountain primary and secondary brown carbon aerosols in summertime
No full textBrown carbon (BrC) can affect atmospheric radiation due to its strong absorption ability from the near ultraviolet to the visible range, thereby influencing global climate. However, given the complexity of BrC's chemical composition, its optical properties are still poorly understood, especially in mountainous areas. In this study, the black carbon (BC) tracer method is used to explore the light-absorbing properties of primary and secondary BrC at Mount Hua, China during the 2018 summer period. The primary BrC absorption contributes to 10-15% of the total BrC absorption at a wavelength of 370 nm. From the positive matrix factorization analysis, traffic emissions are found to be a major source of primary BrC absorption (44%), followed by industry and biomass-burning emissions (29%). The secondary BrC accounts for 87% of the total BrC absorption at a wavelength of 370 nm, indicating that BrC is dominated by secondary formation. The observation of a higher secondary BrC absorption diurnal pattern at Mount Hua can be affected by secondary BrC in the residual layer after sunrise and the formation of light-absorbing chromophores by photochemical oxidation in the afternoon. The estimated average mass absorption efficiencies of primary and secondary BrC (MAE(_pri) and MAE(_sec), respectively) are 0.4 m(2)/g and 2.1 m(2)/g at wavelengths of 370 nm, respectively, indicating a stronger light-absorbing ability for secondary BrC than for primary BrC. There is no significant difference in MAE(_pri) within a daily variation, but the daytime MAE(_sec) value is higher than that during the night. Our study shows that secondary BrC is important to light absorption in mountainous areas. (C) 2021 Elsevier B.V. All rights reserved
Controls on seasonal erosion behavior and potential increase in sediment evacuation in the warming Tibetan Plateau
No full textGlobal warming and intensified climate variability have greatly affected Earth's surface processes and continental sediment evacuation. River suspended sediment is a sensitive indicator for tracing seasonal surface erosion, but details of the rates of sediment generation and evacuation, and their connections with nowadays warming climate are not entirely clear, particularly in Tibet and other high-altitude areas where field observations remain scarce. Here, we investigate daily to seasonal river sediment transport dynamics between the cold, permafrost-dominated northeastern Tibetan Plateau and warm, non-permafrost Sichuan and Taiwan regions. Our results show that at a given river water discharge, greater river suspended sediment was evacuated during the pre-monsoon season (April-Mid June) relative to other seasons in the cold NE Tibetan catchments. In contrast, no such phenomenon was observed in the warm, non-permafrost regions. These comparisons likely indicate a center role of freeze-thaw processes on loose sediment generation, which enhanced sediment output. Hydmmeteorological records show up to similar to 2 degrees C warming in the NE Tibetan Plateau since the past 30 years, coupled with an 8-fold increase in sediment transport. We suggest that continuous warming climate may further accelerate sediment and soil carbon release in the Tibetan Plateau and other global permafrost-dominated areas, which in turn influences climate feedback
Geochemistry of evaporitic deposits from the Cenomanian (Upper Cretaceous) Maha Sarakham Formation in the Khorat Basin, northeastern Thailand
No full textThe Cenomanian (Upper Cretaceous) Maha Sarakham Formation of the Khorat Basin, northeasternThailand consists of three evaporite units (Lower, Middle and Upper Salt) interbedded with clasticsediments and exhibits abundant deposits of potash. Although numerous studies have been carried outon the Khorat potash deposit, results are still equivocal with regard to the origin of the rock salt, whetherit was marine or non-marine (hydrothermal and/or mixedfluids). The purpose of this study is to examinethe origin of rock salt based on elemental compositions and boron isotope analyses in the southwesternpart of the Khorat Basin. A stratigraphic correlation offive boreholes (K-201e205) located in BamnetNarong and Chaturat districts, Chaiyaphum province, Thailand, revealed a salt dome structure. Theelemental composition andd11B values in the longest borehole K-203 indicate a precipitation of haliteand carnallite from seawater. Rare earth elements (REE) of claystone and siltstone fromfive boreholes (K-201e205) are comparable to the REE of sandstone from the Simao Basin in China, which suggest asimilar provenance. Stratigraphic comparisons and geochemical signatures are important for a betterunderstanding of the recharge models of paleoseawater. In agreement with some previous studies, weconclude that the Cenomanian evaporites within the Khorat Basin are marine deposits. (c) 2021 Elsevier Ltd. All rights reserve
FeCo alloy encased in nitrogen-doped carbon for efficient formaldehyde removal: Preparation, electronic structure, and d-band center tailoring
No full textFormaldehyde is a typical indoor air pollutant that has posed severely adverse effects on human health. Herein, a novel FeCo alloy nanoparticle-embedded nitrogen-doped carbon (FeCo@NC) was synthesized with the aim of tailoring the transition-metal d-band structure toward an improved formaldehyde oxidation activity for the first time. A unique core@shell metal-organic frameworks (MOFs) architecture with a Fe-based Prussian blue analogue core and Co-containing zeolite imidazole framework shell was firstly fabricated. Then, Fe and Co ion alloying was readily achieved owing to the inherent MOF porosity and interionic nonequilibrium diffusion occurring during pyrolysis. High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectra confirm that small FeCo alloys in situ form in FeCo@NC, which exhibits a higher formaldehyde removal efficiency (93%) than the monometallic Fe-based catalyst and a remarkable CO2 selectivity (85%) at room temperature. Density functional theory calculations indicate the number of electrons transferred from the metal core to the outer carbon layer is altered by alloying Fe and Co. More importantly, a downshift in the d-band center relative to the Fermi level occurs from - 0.93 to - 1.04 eV after introducing Co, which could alleviate the adsorption of reaction intermediates and greatly improve the catalytic performance
Constructing Pd/ferroelectric Bi4Ti(3)O(12) nanoflake interfaces for O-2 activation and boosting NO photo-oxidation
No full textPhoto-oxidative NOx removal often encountered with sluggish charge carrier separation kinetics and poor selectivity. Herein, Pd/ferroelectric Bi4Ti3O12 nanoflakes (Pd/BTO NF) were constructed to investigate the photo-excited charge separation, O2 activation and the generated reactive oxygen species (ROS) in dictating NO removal. Results showed that the depolarization field of ferroelectric BTO NF significantly promoted bulk charge separation, leading to boosted NO removal reaction kinetics (10 times higher) for Pd/BTO NF comparing with Pd/TiO2. Revealed by electronic paramagnetic resonance and radical scavenging tests, it is observed that the primary O2 activation species differed among Pd, Ag and Pt supported BTO NF photocatalysts, which resulted in different selectivity. The underlying mechanism of NO photo-oxidative conversion pathway was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy. This work illustrate that metal/ferroelectric interfaces can be tuned to obtain differing O2 activation species, and notable selectivity changes in photocatalysis mediated environmental remediation reactions
Inflammatory and oxidative stress responses of healthy elders to solar-assisted large-scale cleaning system (SALSCS) and changes in ambient air pollution: A quasi-interventional study in Xi'an, China
No full textAn outdoor solar assisted large-scale cleaning system (SALSCS) was constructed to mitigate the levels of fine particulate matter (PM2.5) in urban areas of Xi'an China, providing a quasi-experimental opportunity to examine the biologic responses to the changes in pollution level. We conducted this outdoor SALSCS based real-world quasiinterventional study to examine the associations of the SALSCS intervention and changes in air pollution levels with the biomarkers of systemic inflammation and oxidative stress in healthy elders. We measured the levels of 8-hydrox-2-deoxyguanosine (8-OHdG), Interlukin-6 (IL-6). as well as tumor necrosis factor alpha (TNF-alpha) from urine samples, and IL-6 from saliva samples of 123 healthy retired participants from interventional/control residential areas in two sampling campaigns. We collected daily 24-h PM2.5 samples in two residential areas during the study periods using mini-volume samplers. Data on PM10, gaseous pollutants and weather factors were collected from the nearest national air quality monitoring stations. We used linear mixed-effect models to examine the percent change in each biomarker associated with the SALSCS intervention and air pollution levels, after adjusting for time trend, seasonality, weather factors and personal characteristics. Results showed that the SALSCS intervention was significantly associated with decreases in the geometric mean of biomarkers by 47.6% (95% confidence interval: 16.5-67.2%) for 8-OHdG, 66% (31.0-83.3%) for TNF-alpha, 41.7% (0.2-65.9%) and 43.4% (13.6-62.9%) for urinary and salivary IL-6, respectively. An inter-quartile range increase of ambient PM 2 . 5 exposure averaged on the day of the collection of bio-samples and the day before (34.1 mu g/m(3)) was associated, albeit non-significantly so, with 22.8%-37.9% increases in the geometric mean of these biomarkers. This study demonstrated that the SALSCS intervention and decreased ambient air pollution exposure results in lower burden of systemic inflammation and oxidative stress in older adults. (C) 2021 Elsevier B.V. All rights reserved
Extrapolation of anthropogenic disturbances on hazard elements in PM2.5 in a typical heavy industrial city in northwest China
No full textBaoji is a typical heavy industrial city in northwest China. Its air quality is greatly impacted by the emission from the factories. Elements in fine particulate matter (PM2.5) that are greatly emitted from anthropogenic sources could pose diverse health impacts on humans. In this study, an online AMMS-100 atmospheric heavy metal analyzer was used to quantify 30 elements in PM2.5 under the weak and strong anthropogenic disturbance scenarios before the city lockdown period (from January 9(th) to 23(rd)) and the lockdown period (from January 26(th) to February 9(th)) due to the outbreak of COVID-19 in 2020. During the lockdown period, the average total concentration of total quantified elements was 3475.0 ng/m(3), which was 28% and 33% lower than that of the week and strong anthropogenic disturbance scenarios during the pre-lockdown period. The greatest reductions were found for the elements of chromium (Cr), titanium (Ti), manganese (Mn), and Zinc (Zn), consistent with the industrial structure of Baoji. The mass concentrations of most elements showed obvious reductions when the government post-alerted the industries to reduce the operations and production. Dust, traffic sources, combustion, non-ferrous metal processing, and Ti-related industrial processing that are the contributors of the elements in the pre-lockdown period were apportioned by the positive matrix factorization (PMF) model. Substantial changes in the quantified elements' compositions and sources were found in the lockdown period. Health assessment was conducted and characterized by apportioned sources. The highest non-carcinogenic risk (HQ) was seen for Zn, demonstrating the high emissions from the related industrial activities. The concentration level of arsenic (As) exceeded the incremental lifetime carcinogenic risk (ILCR) in the lockdown period. This could be attributed to the traditional firework activities for the celebration of the Chinese New Year within the lockdown period
Uncertainty in the projected changes of Sahel summer rainfall under global warming in CMIP5 and CMIP6 multi-model ensembles
No full textThe Sahel summer rainfall is of great significance to the local social, economic, and cultural environment. In the context of a long Sahel megadrought in the last thirty years of the twentieth century, the future change of Sahel summer rainfall under global warming has aroused wide attention. Based on the historical simulations and high emission scenario experiments from 20 Coupled Model Intercomparison Project phase-5 (CMIP5) models and 22 CMIP6 models, this study investigates the future projections of Sahel summer rainfall under global warming. The results show that the multi-model ensemble (MME) mean projects a slight increase (1-2%/celcius) of summer rainfall over the Sahel in the future which seems to be due to the thermodynamic changes and opposed by the dynamic changes, but that the inter-model spread is due to the latter. We find that, in particular, the inter-model spreads in the extratropical northern and tropical Atlantic sea surface temperature (SST) changes are two important sources of the uncertainty in the Sahel summer rainfall projections via two different atmospheric teleconnection processes. On the one hand, a warmer northern Atlantic SST would induce an anomalous large-scale cyclone over North Africa and Europe, and the southern branch would strengthen the western African monsoonal circulation, leading to a wetter Sahel. On the other hand, a warmer tropical Atlantic SST would weaken the regional circulation, resulting in a drier Sahel. Our results suggest that an improved projection of the future Atlantic warming, especially the differential warming between the northern and tropical Atlantic, is a priority for the reliable future projection of Sahel summer rainfall
Efficient charge separation of a Z-scheme Bi5O7-delta I/CeO2-delta heterojunction with enhanced visible light photocatalytic activity for NO removal
No full textIn this work, a novel Z-scheme Bi5O7-delta I/CeO2-delta heterojunction photocatalyst was prepared by combining hydrothermal synthesis and thermal treatment methods. Oxygen vacancies were in situ generated on the surface of Bi5O7-delta I and CeO2-delta nanostructures. The existence of oxygen vacancies significantly improved the light absorption of CeO2-delta and inhibited the recombination of photogenerated carriers. Based on the photocatalytic activity, the as-prepared Bi5O7-delta I/CeO2-delta photocatalyst exhibited excellent photocatalytic NO removal performance under visible light irradiation. The results of the capture experiment and electron spin resonance (ESR) spectroscopy show that super oxygen radicals (O-2(-)) and hydroxyl radicals (OH) are the main active species in the overall photocatalytic reaction process. Density functional theory (DFT) calculations and ESR results demonstrate that a Z-scheme heterojunction is formed between Bi5O7-delta I and CeO2-delta. Compared with the traditional type-II heterojunction, the Z-scheme heterojunction exhibited more efficient charge separation and robust redox capacity in the photocatalytic reaction