The reaction of carbonyl-to-imine/hemiaminal conversion in the atmospheric aqueous phase is a critical pathway to produce the light-absorbing N-containing secondary organic compounds(SOC).The formation mechanism of th...The reaction of carbonyl-to-imine/hemiaminal conversion in the atmospheric aqueous phase is a critical pathway to produce the light-absorbing N-containing secondary organic compounds(SOC).The formation mechanism of these compounds has been wildly investigated in bulk solutions with a low ionic strength.However,the ionic strength in the aqueous phase of the polluted atmosphere may be higher.It is still unclear whether and to what extent the inorganic ions can affect the SOC formation.Here we prepared the bulk solution with certain ionic strength,in which glyoxal and ammonium were mixed to mimic the aqueous-phase reaction.Molecular characterization by High-resolution Mass Spectrometry was performed to identify the N-containing products,and the light absorption of the mixtures was measured by ultraviolet-visible spectroscopy.Thirty-nine N-containing compounds were identified and divided into four categories(N-heterocyclic chromophores,high-molecular-weight compounds with N-heterocycle,aliphatic imines/hemiaminals,and the unclassified).It was observed that the longer reaction time and higher ionic strength led to the formation of more N-heterocyclic chromophores and the increasing of the lightabsorbance of the mixture.The added inorganic ions were proposed to make the aqueous phase somewhat viscous so that the molecules were prone to undergo consecutive and intramolecular reactions to form the heterocycles.In general,this study revealed that the enhanced ionic strength and prolonged reaction time had the promotion effect on the lightabsorbing SOC formation.It implies that the aldehyde-derived aqueous-phase SOC would contribute more light-absorbing particulate matter in the industrial or populated area where inorganic ions are abundant.展开更多
The conversion of biomass-derived products to fine chemicals and fuels is extremely important for the utilization of renewable energy sources.Water is not only a by-product formed during the hydrogenation of biomass-d...The conversion of biomass-derived products to fine chemicals and fuels is extremely important for the utilization of renewable energy sources.Water is not only a by-product formed during the hydrogenation of biomass-derived oxygenated chemicals,but also an inexpensive and nontoxic solvent.The instability of solid catalysts for aqueous-phase reactions caused by metal leaching and the collapse of a catalyst support represents a significant challenge.In this work,various catalyst stabilization strategies including the nanospace and interfacial confinements that prevent sintering and leaching of metal nanoparticles as well as modification methods for increasing the support stability are summarized and systemically discussed.In addition,feasible approaches to designing stable and efficient heterogeneous catalysts for aqueous-phase reactions are proposed.展开更多
This work reports a facile and efficient seed-mediated method for the synthesis of dendritic platinum （Pt） nanoparticles （NPs） at low temperatures of 55-60 ℃ in water, using L-ascorbic acid as a reducing agent an...This work reports a facile and efficient seed-mediated method for the synthesis of dendritic platinum （Pt） nanoparticles （NPs） at low temperatures of 55-60 ℃ in water, using L-ascorbic acid as a reducing agent and sodium citrate as a capping agent. It is found that the dendritic Pt NPs （10-150 nm） are composed of tiny Pt nanocrystals, which nucleate and grow through the introduced smaller Pt seeds with diameters of 3-5 nm. Further investigation shows that the dendritic Pt nanostructures display excellent catalytic performance in an aqueous-phase aromatic ketone hydrogenation reaction, including： （i） acetophenone conversion rate of 〉 90%, with smaller dendritic Pt NPs （10-46 nm） offering a higher conversion efficiency; （ii） high chemoselectivity toward carbonyl group （90.6%-91.5%）, e.g., the selectivity to l-phenylethanol is -90.1% with nearly 100% acetophenone conversion for 10 nm dendritic Pt NPs within 60 rain, under mild reaction conditions （20 ℃, 1.5 bar H2 pressure, and 1.5 tool% catalyst）. The high catalytic activity, selectivity and stability of the dendritic Pt nanostructures under the organic solvent-free conditions make them promising for many potential applications in green catalytic conversion of hydrophilic biomass derived compounds.展开更多
A green protocol for the synthesis of quinoxalines has been developed from catalytic oxidative cyclization of deoxybenzoins with 1,2-phenylenediamines in water.The optimal conditions are involved in the use of a water...A green protocol for the synthesis of quinoxalines has been developed from catalytic oxidative cyclization of deoxybenzoins with 1,2-phenylenediamines in water.The optimal conditions are involved in the use of a water-soluble mononuclear copper（Ⅱ） complex of a zwitterionic calix[4]arene[Cu（Ⅱ）LCH2O）]I2（1,H4L=[5,ll,17,23-tetrakis（trimethylammonium）-25,26,27,28-tetrahydroxycalix[4]arene]） as a catalyst in alkali solution after refluxing for 15 h in O2.The target quinoxaline and its derivatives were obtained in good yields（up to 88%）.The procedure described in this paper is simple,practical and environmentally benign.展开更多
Perovskite solar cells(PSCs)based onα-phase FAPbI_(3)(α-FAPbI_(3))microcrystals precursor outperform those withδ-phase mi-crocrystals due to their superior crystallinity and fewer defects,makingα-phase microcrysta...Perovskite solar cells(PSCs)based onα-phase FAPbI_(3)(α-FAPbI_(3))microcrystals precursor outperform those withδ-phase mi-crocrystals due to their superior crystallinity and fewer defects,makingα-phase microcrystals precursor more advantageous for high-per-formance PSCs.However,most reported synthesis methods of perovskite microcrystals,especially for aqueous synthesis,fail to reach the energy threshold required forα-phase transformation and therefore exhibit theδphase.In this study,we introduce a novel aqueous syn-thesis method to fabricateα-FAPbI_(3) microcrystals.Our approach overcomes the energy barrier by properly heating the reaction system,enabling the direct formation ofα-FAPbI_(3) in water.This direct one-step aqueous synthesis route yieldsα-FAPbI_(3) microcrystals with su-perior phase purity,crystallinity,and minimal defect density.Combined with green anti-solvent,the high-qualityα-FAPbI_(3) microcrystals serving as exceptional precursors endow perovskite films with reduced nonradiative recombination.The PSC achieves a remarkable power conversion efficiency(PCE)of 24.43%,which is one of the highest PCE reports for using the green anti-solvent in ambient air condition.This aqueous synthesis approach shows a significant potential for scalable production of high-performance PSCs.展开更多
Aerosol liquid water content(ALWC)plays an important role in secondary aerosol formation.In this study,a whole year field campaign was conducted at Shanxi in north Zhejiang Province during 2021.ALWC estimated by ISORR...Aerosol liquid water content(ALWC)plays an important role in secondary aerosol formation.In this study,a whole year field campaign was conducted at Shanxi in north Zhejiang Province during 2021.ALWC estimated by ISORROPIA-Ⅱ was then investigated to explore its characteristics and relationship with secondary aerosols.ALWC exhibited a highest value in spring(66.38μg/m^(3)),followed by winter(45.08μg/m^(3)),summer(41.64μg/m^(3)),and autumn(35.01μg/m^(3)),respectively.It was supposed that the secondary inorganic aerosols(SIA)were facilitated under higher ALWC conditions(RH>80%),while the secondary organic species tended to form under lower ALWC levels.Higher RH(>80%)promoted the NO_(3)^(-)formation via gas-particle partitioning,while SO_(4)^(2-)was generated at a relative lower RH(>50%).The ALWC was more sensitive to NO_(3)^(-)(R=0.94)than SO_(4)^(2-)(R=0.90).Thus,the self-amplifying processes between the ALWC and SIA enhanced the particle mass growth.The sensitivity of ALWC and OX(NO_(2)+O_(3))to secondary organic carbon(SOC)varied in different seasons at Shanxi,more sensitive to aqueous-phase reactions(daytime R=0.84;nighttime R=0.54)than photochemical oxidation(daytime R=0.23;nighttime R=0.41)in wintertime with a high level of OX(daytime:130-140μg/m^(3);nighttime:100-140μg/m^(3)).The self-amplifying process of ALWC and SIA and the aqueous-phase formation of SOC will enhance aerosol formation,contributing to air pollution and reduction of visibility.展开更多
Water-assisted proton hopping(WAPH)plays an important role in the aqueous-phase hydrogenation of levulinic acid(LA)toγ-valerolactone(GVL).In this study,based on a strategy of spontaneously polarized ceramic(SPCE)-rei...Water-assisted proton hopping(WAPH)plays an important role in the aqueous-phase hydrogenation of levulinic acid(LA)toγ-valerolactone(GVL).In this study,based on a strategy of spontaneously polarized ceramic(SPCE)-reinforced WAPH,a Ni-Co/SPCE-C catalyst was constructed by high-temperature calci-nation of a dual mechanical activation-treated precursor.Ni-Co/SPCE-C with favorable structural char-acteristics,intimate interfacial compatibility,and unique spontaneous polarization effect enhanced the migration efficiency of active hydrogen and activated water to form small water clusters,contributing to outstanding catalytic activity for aqueous-phase hydrogenation of LA to produce GVL at relatively low re-action temperature and H2 pressure.A LA conversion of 99.9%and a GVL yield of 92.3%were achieved at 160℃ and 1.5 MPa H2 over the Ni-Co/SPCE-C catalyst,which were significantly higher than those catalyzed by contrastive catalysts.A variety of tests and theoretical calculations reveal that SPCE with far-infrared emission and surface electric field was conducive to the reduction in the hydrogen spillover energy barrier,the stabilization of the transition state,and the facile exchange of H2 and water for ac-celerating WAPH.Moreover,a reasonable SPCE-reinforced WAPH mechanism was proposed to explain the enhanced aqueous hydrogenation of LA.This research can provide valuable insights into the design and development of high-performance non-noble metal catalysts for aqueous hydrogenation applications.展开更多
Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China.During this study, a haze episode(haze days) and a typical haze proce...Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China.During this study, a haze episode(haze days) and a typical haze process mixed with sandstorm(sandy haze days)were observed in Zhengzhou with a series of high-time-resolution monitoring instruments from November 22 to December 8, 2018.Concentrations of PM10 and crustal elements clearly increased in the sandy haze days.Concentrations of gaseous pollutants, metallic elements emitted from anthropogenic sources, nitrate, and ammonium during sandy haze days were slightly lower than those during the haze days but still obviously higher than those during the non-haze days.The sulfate concentrations, the sulfate fractions in PM2.5,and the sulfur oxidation ratios significantly increased in the sandy haze days.Heterogeneous reactions dominated the conversion of SO2 during the haze and sandy haze days.Enhanced SO2 conversion during the sandy haze days may be attributed to the high concentrations of transition metal ions from the sandstorm when the values of relative humidity(RH) were in 30%–70%, and high O3 at certain time points.Gas-phase NO2 oxidation reactions were the main pathways for nitrate formation.In the sandy haze days,higher nitrogen oxidation ratio(NOR) at daytime may be associated with higher RH and lower temperature than those in the haze days, which facilitate the gas-to-particle partitioning of nitrate;higher NOR values at night may be attributed to the higher O3 concentrations, which promoted the formation of N2O5.展开更多
Current bio-ethanol production entails the enzymatic depolymerization of cellulose,but this process shows low efficiency and poor economy.In this work,we developed a consecutive aqueous hydrogenolysis process for the ...Current bio-ethanol production entails the enzymatic depolymerization of cellulose,but this process shows low efficiency and poor economy.In this work,we developed a consecutive aqueous hydrogenolysis process for the conversion of corn-stalk cellulose to produce a relatively high concentration of bio-ethanol(6.1 wt%)without humin formation.A high yield of cellulose(ca.50 wt%)is extracted from corn stalk using a green solvent(80 wt%1,4-butanediol)without destroying the structure of the lignin.The first hydrothermal hydrogenolysis step uses a Ni–WO_(x)/SiO_(2)catalyst to convert the high cumulative concentration of cellulose(30 wt%)into a polyol mixture with a 56.5 C%yield of ethylene glycol(EG).The original polyol mixture is then subjected to subsequent selective aqueous-phase hydrogenolysis of the C–O bond to produce bioethanol(75%conversion,84 C%selectivity)over the modified hydrothermally stable Cu catalysts.The added Ni component favors the good dispersion of Cu nanoparticles,and the incorporated Au3+helps to stabilize the active Cu^(0)-Cu^(+)species.This multi-functional catalytic process provides an economically competitive route for the production of cellulosic ethanol from raw lignocellulose.展开更多
The rate constants of reactions between the SO4^- radical and some common anions in atmospheric aqueous droplets e.g. Cl^-,NO^-, HSO3^- and HCO3^- were determined using the laser flash photolysis technique.Absorption ...The rate constants of reactions between the SO4^- radical and some common anions in atmospheric aqueous droplets e.g. Cl^-,NO^-, HSO3^- and HCO3^- were determined using the laser flash photolysis technique.Absorption spectra of SO4^- and the product radicals were also reported.The chloride ion was evaluated among all the anions to be the most efficient scavenger of SO4^-.The results may supply useful information for a better understanding of the vigorous radical-initiated reactions in atmospheric aqueous droplets such as clouds, rains or fogs.展开更多
We herein report a new lanthanide metal-organic framework(MOF) that exhibits excellent chemical stability,especially in the aqueous solution over a wide pH range from 1 to 14.In contrast to many reported lanthanide MO...We herein report a new lanthanide metal-organic framework(MOF) that exhibits excellent chemical stability,especially in the aqueous solution over a wide pH range from 1 to 14.In contrast to many reported lanthanide MOFs,this Tb-based MOF emits cyan fluorescence inherited from the integrated AIEactive ligand,rather than Ln3+ ions.More remarkably,its fluorescence signal features a highly selective and sensitive "turn-off" response toward CrO_(4)^(2-),Cr_(2)O_(7)^(2- )and Fe^(3+) ions,highlighted with the low detection limits down to 68.18,69.85 and 138.8 ppm,respectively.Thus,the exceptional structural stability and sensing performance render this material able to be a superior luminescent sensor for heavy metal ions in wastewater.展开更多
Trans-sobrerol （Sob） and 8-p-menthen-1,2-diol （Limo-diol） are the primary products in the atmospheric oxidation of α-pinene and limonene, respectively. Because of their low volatility, they associate more likely ...Trans-sobrerol （Sob） and 8-p-menthen-1,2-diol （Limo-diol） are the primary products in the atmospheric oxidation of α-pinene and limonene, respectively. Because of their low volatility, they associate more likely to the liquid particles in the atmosphere, where they are subject to the aqueous phase oxidation by the atmospheric oxidants. In this work, through experimental and theoretical study, we first provide the rate constants of Sob and Limo-diol reacting with hydroxyl radical （.OH） in aqueous solution at room temperature of 3044-3 K and 1 atm pressure, which are （3.05±0.5）×10 9 and （4.57±0.2）×10 9 L/（mol.s）, respectively. Quantum chemistry calculations have also been employed to demonstrate the solvent effect on the rate constants in aqueous phase and the calculated results agree well with the measurements. Some reaction products have been identified based on liquid chromatography combined with mass spectroscopy and theoretical calculations.展开更多
Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformati...Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states.The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water.A perspective is also provided for future research in this vibrant field.展开更多
An efficient, environmentally friendly procedure is developed for the condensation of aldchydcs/kctoncs and activated methylene compounds by using an aminopropyl-functionalized MCM-41 catalyst in aqueous solution. Dif...An efficient, environmentally friendly procedure is developed for the condensation of aldchydcs/kctoncs and activated methylene compounds by using an aminopropyl-functionalized MCM-41 catalyst in aqueous solution. Different aldchydcs/kctoncs and activated methylene compounds gave the corresponding alkcncs in 78-97% isolated yields in mild reaction conditions. In comparison with organic solution, the aqueous solution gives higher yields in the same reaction conditions. Further more, the aminopropyl-functionalizcd MCM-41 in aqueous system can be reused for 8 flints without significant decrease of activity.展开更多
Many problems regarding structure-function relationships have remained unsolved in the field of respiratory physiology. In the present review, we highlighted these uncertain issues from a variety of anatomical and phy...Many problems regarding structure-function relationships have remained unsolved in the field of respiratory physiology. In the present review, we highlighted these uncertain issues from a variety of anatomical and physiological viewpoints. Model A of Weibel in which dichotomously branching airways are incorporated should be used for analyzing gas mixing in conducting and acinar airways. Acinus of Loeschcke is taken as an anatomical gas-exchange unit.Although it is difficult to define functional gas-exchange unit in a way entirely consistent with anatomical structures, acinus of Aschoff may serve as a functional gas-exchange unit in a first approximation. Based on anatomical and physiological perspectives, the multiple inert-gas elimination technique is thought to be highly effective for predicting ventilation-perfusion heterogeneity between acini of Aschoff under steady-state condition. Changes in effective alveolar P_(O2), the most important parameter in classical gas-exchange theory, are coherent with those in mixed alveolar P_(O2) decided from the multiple inert-gas elimination technique. Therefore, effective alveolar-arterial P_(O2) difference is considered useful for assessing gas-exchange abnormalities in lung periphery.However, one should be aware that although alveolar-arterial P_(O2) difference sensitively detects moderately low ventilation-perfusion regions causing hypoxemia, it is insensitive to abnormal gas exchange evoked by very low and high ventilation-perfusion regions. Pulmonary diffusing capacity for CO (D_(LCO))and the value corrected for alveolar volume (V_(AV)), i.e., D_(LCO)/V_(AV) (K_(CO)), are thought to be crucial for diagnosing alveolar-wall damages. D_(LCO)-related parameters have higher sensitivity to detecting abnormalities in pulmonary microcirculation than those in the alveolocapillary membrane. We would like to recommend four categories derived from combining behaviors of D_(LCO) with those of K_(CO) for differential diagnosis on anatomically morbid states in alveolar walls:type-1abnormality defined by decrease in both D_(LCO) and K_(CO); type-2 abnormality by decrease in D_(LCO) but increase in K_(CO); type-3 abnormality by decrease in D_(LCO) but restricted rise in K_(CO); and type-4 abnormality by increase in both D_(LCO) and K_(CO).展开更多
Nighttime aqueous oxidation of fossil fuel emissions is a significant source of atmospheric secondary organic aerosols.However,the underlying mechanism of the aqueous processing remains unclear.Utilizing ultrahigh-res...Nighttime aqueous oxidation of fossil fuel emissions is a significant source of atmospheric secondary organic aerosols.However,the underlying mechanism of the aqueous processing remains unclear.Utilizing ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry of watersoluble organic carbon samples,we present field observations that reveal the aqueous-phase conversion of nitroaromatic compounds(NACs)and sulfur-containing aerosols from fossil fuel combustion at high relative humidity during a severe haze event in Beijing in the winter of 2016.We have confirmed that the ring-breaking oxidation of NACs can generate nitrous acid in the aqueous phase,which rapidly oxidizes sulfur dioxide(SO_(2))to sulfate.Subsequently,reactions between sulfate and unsaturated compounds contribute to the formation of aliphatic organosulfates.Our results elucidate a molecular-level understanding of the aqueous production of sulfur-containing aerosols from NACs and SO_(2) in wintertime urban haze.展开更多
Chiral covalent organic frameworks(COFs)have shown promising applications in asymmetric catalysis,enantiomer separation and chiral recognition due to their tunable structures and permanent porosity.Currently,synthesis...Chiral covalent organic frameworks(COFs)have shown promising applications in asymmetric catalysis,enantiomer separation and chiral recognition due to their tunable structures and permanent porosity.Currently,synthesis of chiral COFs mainly relies on direct-synthesis method which requires asymmetric monomers to polymerize and crystallize with symmetric monomers and post-synthesis method which has been greatly limited to having complete reactions with the micro-/meso-sized pores of COFs.Recently,the synthesis of two-dimensional COFs by covalent replacement of chiral competitor has been reported.Herein,we present the synthesis of three types of 3D COFs with tunable chirality using chiral amino acid derivative surfactant as inducer in water under ambient conditions.The hydrogen bonds and electrostatic interactions between amino acid derivative surfactant and monomers as well as their precursors facilitate the transfer of the chirality.展开更多
On the basis that endothermic aqueous-phase reforming of oxygenated hydrocarbons for H2 produc- tion and exothermic liquid phase hydrogenation of organic compounds are carried out under extremely close conditions of t...On the basis that endothermic aqueous-phase reforming of oxygenated hydrocarbons for H2 produc- tion and exothermic liquid phase hydrogenation of organic compounds are carried out under extremely close conditions of temperature and pressure over the same type of catalyst, a novel liquid system of catalytic hydrogenation has been proposed, in which hydrogen produced from aqueous-phase re- forming of oxygenated hydrocarbons is in situ used for liquid phase hydrogenation of organic com- pounds. The usage of active hydrogen generated from aqueous-phase reforming of oxygenated hy- drocarbons for liquid catalytic hydrogenation of organic compounds could lead to increasing the se- lectivity to H2 in the aqueous-phase reforming due to the prompt removal of hydrogen on the active centers of the catalyst. Meanwhile, this novel liquid system of catalytic hydrogenation might be a po- tential method to improve the selectivity to the desired product in liquid phase catalytic hydrogenation of organic compounds. On the other hand, for this novel liquid system of catalytic hydrogenation, some special facilities for H2 generation, storage and transportation in traditional liquid phase hydrogenation industry process are yet not needed. Thus, it would simplify the working process of liquid phase hy- drogenation and increase the energy usage and hydrogen productivity.展开更多
Alloy nanocrystals （NCs） of Pt with 3d transition metals, especially Ni, are excellent catalysts for the oxygen reduction reaction （ORR）. In this work, we, for the first time, demonstrated the water phase colloida...Alloy nanocrystals （NCs） of Pt with 3d transition metals, especially Ni, are excellent catalysts for the oxygen reduction reaction （ORR）. In this work, we, for the first time, demonstrated the water phase colloidal synthesis of Pt-M （M = Ni, Co and Fe） alloy NCs with tunable composition and morphology through a facile hydrothermal method. Pt-Ni alloy NCs synthesized with this method presented better ORR activity than commercial Pt/C catalysts. The X-ray energy dispersive spectra （EDS） mapping technique revealed that Pt-enriched shells existed on the as-synthesized Pt-Ni alloy NCs. About two atom thick layered Pt-enriched shells formed on Pts0Nis0 NCs and the thickness of the Pt-enriched shells increased as the Ni content increased. Furthermore, X-ray photoelectron spectroscopy analysis revealed that the oxidation level of the surface Pt atoms on the Pt-Ni alloy NCs decreased compared with monometallic Pt NCs, implying a decrease in the oxophilicity of the surface Pt atoms. Pt-Ni alloy NCs with lower oxophilicity of the surface Pt atoms give higher ORR activity. The most active alloy sample showed 13 times higher specific activity and six times higher mass activity at 0.9 V vs. a reversible hydrogen electrode when compared with commercial Pt/C. Pt-Ni alloy NCs also showed better durability than commercial Pt/C in long term ORR tests.展开更多
To investigate the impacts of relative humidity(RH) on secondary organic aerosol(SOA) concentrations and chemical reactions, the carbonaceous aerosol components [i.e., organic carbon(OC) and element carbon(EC)] were q...To investigate the impacts of relative humidity(RH) on secondary organic aerosol(SOA) concentrations and chemical reactions, the carbonaceous aerosol components [i.e., organic carbon(OC) and element carbon(EC)] were quantified in daily PM2.5 samples collected at a background site in East China during summer 2015. Based on the method of EC-tracer, the concentration of secondary organic carbon(SOC) demonstrated an obvious negative relationship with RH higher than 60%. Moreover, the ratio of SOC/EC also exhibited obvious decreasing trends with increasing RH, indicating negative effects for chemical production of SOA under high RH conditions. Due to high RH,photochemistry was weakened, gaseous oxidant concentrations was lowered(e.g., significantly decreased O3 levels),and the production rates of SOA were relatively low. On the other hand, because of more water uptake under higher RH conditions, the aerosol droplet acidity was reduced and enhancement of SOA formation by acidity was accordingly absent. In addition, high RH also plays an important role in changing viscosity of pre-existing aerosol coatings,which can affect reactive uptake yield of SOA. Overall, the results from this study imply that SOA production may be more associated with photochemical processes, while aqueous-phase chemistry is not very important for some SOA formation in a moist ambient environment. In the ambient atmosphere, oxidant concentrations, reaction rates,airborne species, etc., are highly variable. How do these factors affect SOA yields under given ambient environment warrants further detailed investigations.展开更多
基金supported by the National Natural Science Foundation of China(Nos.21976034,42077193,92044301,and21906024)the Shanghai Municipal Health Commission Science and Research Fund(No.202040185)+1 种基金the Shanghai Pudong New District Bureau of Ecology and Environment Research Project(No.PDHJ20210008)the Guangdong Provincial Observation and Research Station for Coastal Atmosphere and Climate of the Great Bay Area(No.2021B1212050024)。
文摘The reaction of carbonyl-to-imine/hemiaminal conversion in the atmospheric aqueous phase is a critical pathway to produce the light-absorbing N-containing secondary organic compounds(SOC).The formation mechanism of these compounds has been wildly investigated in bulk solutions with a low ionic strength.However,the ionic strength in the aqueous phase of the polluted atmosphere may be higher.It is still unclear whether and to what extent the inorganic ions can affect the SOC formation.Here we prepared the bulk solution with certain ionic strength,in which glyoxal and ammonium were mixed to mimic the aqueous-phase reaction.Molecular characterization by High-resolution Mass Spectrometry was performed to identify the N-containing products,and the light absorption of the mixtures was measured by ultraviolet-visible spectroscopy.Thirty-nine N-containing compounds were identified and divided into four categories(N-heterocyclic chromophores,high-molecular-weight compounds with N-heterocycle,aliphatic imines/hemiaminals,and the unclassified).It was observed that the longer reaction time and higher ionic strength led to the formation of more N-heterocyclic chromophores and the increasing of the lightabsorbance of the mixture.The added inorganic ions were proposed to make the aqueous phase somewhat viscous so that the molecules were prone to undergo consecutive and intramolecular reactions to form the heterocycles.In general,this study revealed that the enhanced ionic strength and prolonged reaction time had the promotion effect on the lightabsorbing SOC formation.It implies that the aldehyde-derived aqueous-phase SOC would contribute more light-absorbing particulate matter in the industrial or populated area where inorganic ions are abundant.
文摘The conversion of biomass-derived products to fine chemicals and fuels is extremely important for the utilization of renewable energy sources.Water is not only a by-product formed during the hydrogenation of biomass-derived oxygenated chemicals,but also an inexpensive and nontoxic solvent.The instability of solid catalysts for aqueous-phase reactions caused by metal leaching and the collapse of a catalyst support represents a significant challenge.In this work,various catalyst stabilization strategies including the nanospace and interfacial confinements that prevent sintering and leaching of metal nanoparticles as well as modification methods for increasing the support stability are summarized and systemically discussed.In addition,feasible approaches to designing stable and efficient heterogeneous catalysts for aqueous-phase reactions are proposed.
基金the financial support of the Australian Research Council (ARC) projectsUSyd Early Career Researcher Scheme+2 种基金Major Equipment Schemethe scholarships provided by China Scholarship Council (CSC)the Commonwealth Scientific and Industrial Research Organization (CSIRO) OCE Top-up Scholarship
文摘This work reports a facile and efficient seed-mediated method for the synthesis of dendritic platinum （Pt） nanoparticles （NPs） at low temperatures of 55-60 ℃ in water, using L-ascorbic acid as a reducing agent and sodium citrate as a capping agent. It is found that the dendritic Pt NPs （10-150 nm） are composed of tiny Pt nanocrystals, which nucleate and grow through the introduced smaller Pt seeds with diameters of 3-5 nm. Further investigation shows that the dendritic Pt nanostructures display excellent catalytic performance in an aqueous-phase aromatic ketone hydrogenation reaction, including： （i） acetophenone conversion rate of 〉 90%, with smaller dendritic Pt NPs （10-46 nm） offering a higher conversion efficiency; （ii） high chemoselectivity toward carbonyl group （90.6%-91.5%）, e.g., the selectivity to l-phenylethanol is -90.1% with nearly 100% acetophenone conversion for 10 nm dendritic Pt NPs within 60 rain, under mild reaction conditions （20 ℃, 1.5 bar H2 pressure, and 1.5 tool% catalyst）. The high catalytic activity, selectivity and stability of the dendritic Pt nanostructures under the organic solvent-free conditions make them promising for many potential applications in green catalytic conversion of hydrophilic biomass derived compounds.
基金the financial supports from the National Natural Science Foundation of China(Nos.21271134, 21373142,21531006 and 21671144)the State Key Laboratory of Organometallic Chemistry,Shanghai Institute of Organic Chemistry(No.2015kf-07)+2 种基金supports from the "333" Project of Jiangsu Provincethe Priority Academic Program Development of Jiangsu Higher Education Institutionsthe "SooChow Scholar" Program of Soochow University
文摘A green protocol for the synthesis of quinoxalines has been developed from catalytic oxidative cyclization of deoxybenzoins with 1,2-phenylenediamines in water.The optimal conditions are involved in the use of a water-soluble mononuclear copper（Ⅱ） complex of a zwitterionic calix[4]arene[Cu（Ⅱ）LCH2O）]I2（1,H4L=[5,ll,17,23-tetrakis（trimethylammonium）-25,26,27,28-tetrahydroxycalix[4]arene]） as a catalyst in alkali solution after refluxing for 15 h in O2.The target quinoxaline and its derivatives were obtained in good yields（up to 88%）.The procedure described in this paper is simple,practical and environmentally benign.
基金financially supported by the National Key Research and Development Program of China(No.2022YFB3803300)the Major Scientific and Technological Project in 2022 of Changsha,China(No.kq2301002).
文摘Perovskite solar cells(PSCs)based onα-phase FAPbI_(3)(α-FAPbI_(3))microcrystals precursor outperform those withδ-phase mi-crocrystals due to their superior crystallinity and fewer defects,makingα-phase microcrystals precursor more advantageous for high-per-formance PSCs.However,most reported synthesis methods of perovskite microcrystals,especially for aqueous synthesis,fail to reach the energy threshold required forα-phase transformation and therefore exhibit theδphase.In this study,we introduce a novel aqueous syn-thesis method to fabricateα-FAPbI_(3) microcrystals.Our approach overcomes the energy barrier by properly heating the reaction system,enabling the direct formation ofα-FAPbI_(3) in water.This direct one-step aqueous synthesis route yieldsα-FAPbI_(3) microcrystals with su-perior phase purity,crystallinity,and minimal defect density.Combined with green anti-solvent,the high-qualityα-FAPbI_(3) microcrystals serving as exceptional precursors endow perovskite films with reduced nonradiative recombination.The PSC achieves a remarkable power conversion efficiency(PCE)of 24.43%,which is one of the highest PCE reports for using the green anti-solvent in ambient air condition.This aqueous synthesis approach shows a significant potential for scalable production of high-performance PSCs.
基金supported by the National Natural Science Foundation of China(Nos.91844301 and 42005087)the support from State Environmental Protection Key Laboratory of Formation and Prevention of Urban Air Pollution Complex,Shanghai Academy of Environment Sciences(No.CX2020080581)。
文摘Aerosol liquid water content(ALWC)plays an important role in secondary aerosol formation.In this study,a whole year field campaign was conducted at Shanxi in north Zhejiang Province during 2021.ALWC estimated by ISORROPIA-Ⅱ was then investigated to explore its characteristics and relationship with secondary aerosols.ALWC exhibited a highest value in spring(66.38μg/m^(3)),followed by winter(45.08μg/m^(3)),summer(41.64μg/m^(3)),and autumn(35.01μg/m^(3)),respectively.It was supposed that the secondary inorganic aerosols(SIA)were facilitated under higher ALWC conditions(RH>80%),while the secondary organic species tended to form under lower ALWC levels.Higher RH(>80%)promoted the NO_(3)^(-)formation via gas-particle partitioning,while SO_(4)^(2-)was generated at a relative lower RH(>50%).The ALWC was more sensitive to NO_(3)^(-)(R=0.94)than SO_(4)^(2-)(R=0.90).Thus,the self-amplifying processes between the ALWC and SIA enhanced the particle mass growth.The sensitivity of ALWC and OX(NO_(2)+O_(3))to secondary organic carbon(SOC)varied in different seasons at Shanxi,more sensitive to aqueous-phase reactions(daytime R=0.84;nighttime R=0.54)than photochemical oxidation(daytime R=0.23;nighttime R=0.41)in wintertime with a high level of OX(daytime:130-140μg/m^(3);nighttime:100-140μg/m^(3)).The self-amplifying process of ALWC and SIA and the aqueous-phase formation of SOC will enhance aerosol formation,contributing to air pollution and reduction of visibility.
基金supported by the National Natural Science Foundation of China(No.22008041)the Natural Science Foun-dation of Guangxi Province,China(Nos.2019GXNSFDA245020 and 2020GXNSFGA297001).
文摘Water-assisted proton hopping(WAPH)plays an important role in the aqueous-phase hydrogenation of levulinic acid(LA)toγ-valerolactone(GVL).In this study,based on a strategy of spontaneously polarized ceramic(SPCE)-reinforced WAPH,a Ni-Co/SPCE-C catalyst was constructed by high-temperature calci-nation of a dual mechanical activation-treated precursor.Ni-Co/SPCE-C with favorable structural char-acteristics,intimate interfacial compatibility,and unique spontaneous polarization effect enhanced the migration efficiency of active hydrogen and activated water to form small water clusters,contributing to outstanding catalytic activity for aqueous-phase hydrogenation of LA to produce GVL at relatively low re-action temperature and H2 pressure.A LA conversion of 99.9%and a GVL yield of 92.3%were achieved at 160℃ and 1.5 MPa H2 over the Ni-Co/SPCE-C catalyst,which were significantly higher than those catalyzed by contrastive catalysts.A variety of tests and theoretical calculations reveal that SPCE with far-infrared emission and surface electric field was conducive to the reduction in the hydrogen spillover energy barrier,the stabilization of the transition state,and the facile exchange of H2 and water for ac-celerating WAPH.Moreover,a reasonable SPCE-reinforced WAPH mechanism was proposed to explain the enhanced aqueous hydrogenation of LA.This research can provide valuable insights into the design and development of high-performance non-noble metal catalysts for aqueous hydrogenation applications.
基金supported by National Key R&D Program of China(No.2017YFC0212403).
文摘Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China.During this study, a haze episode(haze days) and a typical haze process mixed with sandstorm(sandy haze days)were observed in Zhengzhou with a series of high-time-resolution monitoring instruments from November 22 to December 8, 2018.Concentrations of PM10 and crustal elements clearly increased in the sandy haze days.Concentrations of gaseous pollutants, metallic elements emitted from anthropogenic sources, nitrate, and ammonium during sandy haze days were slightly lower than those during the haze days but still obviously higher than those during the non-haze days.The sulfate concentrations, the sulfate fractions in PM2.5,and the sulfur oxidation ratios significantly increased in the sandy haze days.Heterogeneous reactions dominated the conversion of SO2 during the haze and sandy haze days.Enhanced SO2 conversion during the sandy haze days may be attributed to the high concentrations of transition metal ions from the sandstorm when the values of relative humidity(RH) were in 30%–70%, and high O3 at certain time points.Gas-phase NO2 oxidation reactions were the main pathways for nitrate formation.In the sandy haze days,higher nitrogen oxidation ratio(NOR) at daytime may be associated with higher RH and lower temperature than those in the haze days, which facilitate the gas-to-particle partitioning of nitrate;higher NOR values at night may be attributed to the higher O3 concentrations, which promoted the formation of N2O5.
文摘Current bio-ethanol production entails the enzymatic depolymerization of cellulose,but this process shows low efficiency and poor economy.In this work,we developed a consecutive aqueous hydrogenolysis process for the conversion of corn-stalk cellulose to produce a relatively high concentration of bio-ethanol(6.1 wt%)without humin formation.A high yield of cellulose(ca.50 wt%)is extracted from corn stalk using a green solvent(80 wt%1,4-butanediol)without destroying the structure of the lignin.The first hydrothermal hydrogenolysis step uses a Ni–WO_(x)/SiO_(2)catalyst to convert the high cumulative concentration of cellulose(30 wt%)into a polyol mixture with a 56.5 C%yield of ethylene glycol(EG).The original polyol mixture is then subjected to subsequent selective aqueous-phase hydrogenolysis of the C–O bond to produce bioethanol(75%conversion,84 C%selectivity)over the modified hydrothermally stable Cu catalysts.The added Ni component favors the good dispersion of Cu nanoparticles,and the incorporated Au3+helps to stabilize the active Cu^(0)-Cu^(+)species.This multi-functional catalytic process provides an economically competitive route for the production of cellulosic ethanol from raw lignocellulose.
文摘The rate constants of reactions between the SO4^- radical and some common anions in atmospheric aqueous droplets e.g. Cl^-,NO^-, HSO3^- and HCO3^- were determined using the laser flash photolysis technique.Absorption spectra of SO4^- and the product radicals were also reported.The chloride ion was evaluated among all the anions to be the most efficient scavenger of SO4^-.The results may supply useful information for a better understanding of the vigorous radical-initiated reactions in atmospheric aqueous droplets such as clouds, rains or fogs.
基金financially supported by the National Natural Science Foundation of China (Nos.21771113,22001132)China Postdoctoral Science Foundation (No.2019M651011)。
文摘We herein report a new lanthanide metal-organic framework(MOF) that exhibits excellent chemical stability,especially in the aqueous solution over a wide pH range from 1 to 14.In contrast to many reported lanthanide MOFs,this Tb-based MOF emits cyan fluorescence inherited from the integrated AIEactive ligand,rather than Ln3+ ions.More remarkably,its fluorescence signal features a highly selective and sensitive "turn-off" response toward CrO_(4)^(2-),Cr_(2)O_(7)^(2- )and Fe^(3+) ions,highlighted with the low detection limits down to 68.18,69.85 and 138.8 ppm,respectively.Thus,the exceptional structural stability and sensing performance render this material able to be a superior luminescent sensor for heavy metal ions in wastewater.
基金This work was supported by the National Natural Science Foundation of China （No.21177041 and No.21107026）, the Fundamental Research Funds for the Central Universities （No.2013ZZ0073）, and the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry.
文摘Trans-sobrerol （Sob） and 8-p-menthen-1,2-diol （Limo-diol） are the primary products in the atmospheric oxidation of α-pinene and limonene, respectively. Because of their low volatility, they associate more likely to the liquid particles in the atmosphere, where they are subject to the aqueous phase oxidation by the atmospheric oxidants. In this work, through experimental and theoretical study, we first provide the rate constants of Sob and Limo-diol reacting with hydroxyl radical （.OH） in aqueous solution at room temperature of 3044-3 K and 1 atm pressure, which are （3.05±0.5）×10 9 and （4.57±0.2）×10 9 L/（mol.s）, respectively. Quantum chemistry calculations have also been employed to demonstrate the solvent effect on the rate constants in aqueous phase and the calculated results agree well with the measurements. Some reaction products have been identified based on liquid chromatography combined with mass spectroscopy and theoretical calculations.
文摘Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states.The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water.A perspective is also provided for future research in this vibrant field.
文摘An efficient, environmentally friendly procedure is developed for the condensation of aldchydcs/kctoncs and activated methylene compounds by using an aminopropyl-functionalized MCM-41 catalyst in aqueous solution. Different aldchydcs/kctoncs and activated methylene compounds gave the corresponding alkcncs in 78-97% isolated yields in mild reaction conditions. In comparison with organic solution, the aqueous solution gives higher yields in the same reaction conditions. Further more, the aminopropyl-functionalizcd MCM-41 in aqueous system can be reused for 8 flints without significant decrease of activity.
文摘Many problems regarding structure-function relationships have remained unsolved in the field of respiratory physiology. In the present review, we highlighted these uncertain issues from a variety of anatomical and physiological viewpoints. Model A of Weibel in which dichotomously branching airways are incorporated should be used for analyzing gas mixing in conducting and acinar airways. Acinus of Loeschcke is taken as an anatomical gas-exchange unit.Although it is difficult to define functional gas-exchange unit in a way entirely consistent with anatomical structures, acinus of Aschoff may serve as a functional gas-exchange unit in a first approximation. Based on anatomical and physiological perspectives, the multiple inert-gas elimination technique is thought to be highly effective for predicting ventilation-perfusion heterogeneity between acini of Aschoff under steady-state condition. Changes in effective alveolar P_(O2), the most important parameter in classical gas-exchange theory, are coherent with those in mixed alveolar P_(O2) decided from the multiple inert-gas elimination technique. Therefore, effective alveolar-arterial P_(O2) difference is considered useful for assessing gas-exchange abnormalities in lung periphery.However, one should be aware that although alveolar-arterial P_(O2) difference sensitively detects moderately low ventilation-perfusion regions causing hypoxemia, it is insensitive to abnormal gas exchange evoked by very low and high ventilation-perfusion regions. Pulmonary diffusing capacity for CO (D_(LCO))and the value corrected for alveolar volume (V_(AV)), i.e., D_(LCO)/V_(AV) (K_(CO)), are thought to be crucial for diagnosing alveolar-wall damages. D_(LCO)-related parameters have higher sensitivity to detecting abnormalities in pulmonary microcirculation than those in the alveolocapillary membrane. We would like to recommend four categories derived from combining behaviors of D_(LCO) with those of K_(CO) for differential diagnosis on anatomically morbid states in alveolar walls:type-1abnormality defined by decrease in both D_(LCO) and K_(CO); type-2 abnormality by decrease in D_(LCO) but increase in K_(CO); type-3 abnormality by decrease in D_(LCO) but restricted rise in K_(CO); and type-4 abnormality by increase in both D_(LCO) and K_(CO).
基金supported by the National Natural Science Foundation of China(42130513,42221001,22276099,and U24A20515)the Harvard-NUIST Joint Laboratory on Air Quality and Climate(JLAQC)。
文摘Nighttime aqueous oxidation of fossil fuel emissions is a significant source of atmospheric secondary organic aerosols.However,the underlying mechanism of the aqueous processing remains unclear.Utilizing ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry of watersoluble organic carbon samples,we present field observations that reveal the aqueous-phase conversion of nitroaromatic compounds(NACs)and sulfur-containing aerosols from fossil fuel combustion at high relative humidity during a severe haze event in Beijing in the winter of 2016.We have confirmed that the ring-breaking oxidation of NACs can generate nitrous acid in the aqueous phase,which rapidly oxidizes sulfur dioxide(SO_(2))to sulfate.Subsequently,reactions between sulfate and unsaturated compounds contribute to the formation of aliphatic organosulfates.Our results elucidate a molecular-level understanding of the aqueous production of sulfur-containing aerosols from NACs and SO_(2) in wintertime urban haze.
基金supported by the National Natural Science Foundation of China(52061135103,51873236,52203287)Fundamental Research Funds for the Central Universities,Sun Yat-sen University(No.23yxqntd002).
文摘Chiral covalent organic frameworks(COFs)have shown promising applications in asymmetric catalysis,enantiomer separation and chiral recognition due to their tunable structures and permanent porosity.Currently,synthesis of chiral COFs mainly relies on direct-synthesis method which requires asymmetric monomers to polymerize and crystallize with symmetric monomers and post-synthesis method which has been greatly limited to having complete reactions with the micro-/meso-sized pores of COFs.Recently,the synthesis of two-dimensional COFs by covalent replacement of chiral competitor has been reported.Herein,we present the synthesis of three types of 3D COFs with tunable chirality using chiral amino acid derivative surfactant as inducer in water under ambient conditions.The hydrogen bonds and electrostatic interactions between amino acid derivative surfactant and monomers as well as their precursors facilitate the transfer of the chirality.
基金Supported by the Program for New Century Excellent Talents in University (Grant No. NCET-04-0557) Specialized Research Fund for The Doctoral Program of High Education (Grant No. SRFDP-20060337001)
文摘On the basis that endothermic aqueous-phase reforming of oxygenated hydrocarbons for H2 produc- tion and exothermic liquid phase hydrogenation of organic compounds are carried out under extremely close conditions of temperature and pressure over the same type of catalyst, a novel liquid system of catalytic hydrogenation has been proposed, in which hydrogen produced from aqueous-phase re- forming of oxygenated hydrocarbons is in situ used for liquid phase hydrogenation of organic com- pounds. The usage of active hydrogen generated from aqueous-phase reforming of oxygenated hy- drocarbons for liquid catalytic hydrogenation of organic compounds could lead to increasing the se- lectivity to H2 in the aqueous-phase reforming due to the prompt removal of hydrogen on the active centers of the catalyst. Meanwhile, this novel liquid system of catalytic hydrogenation might be a po- tential method to improve the selectivity to the desired product in liquid phase catalytic hydrogenation of organic compounds. On the other hand, for this novel liquid system of catalytic hydrogenation, some special facilities for H2 generation, storage and transportation in traditional liquid phase hydrogenation industry process are yet not needed. Thus, it would simplify the working process of liquid phase hy- drogenation and increase the energy usage and hydrogen productivity.
基金We thank Prof. Dechun Zou and Mr. Ming Peng for their help with electrochemical characterization. This work was supported by the National Natural Science Foundation of China （Nos. 21025101, 21271011, and 21321001）. Y. W. Z. particularly appreciates the financial aid from the China National Funds for Distinguished Young Scientists from the National Natural Science Foundation of China （NSFC）. The work on micros- copy was partly carried out in the Center of Electron Microscopy of Zhejiang University, which was financially supported by the National Natural Science Foundation of China （No. 51222202）, the National Basic Research Program of China （No. 2014CB932500） and the Program for Innovative Research Teams in Universities of Ministry of Education of China （No. IRT13037） and the Fundamental Research Funds for the Central Universities （No. 2014XZZX003-07）.
文摘Alloy nanocrystals （NCs） of Pt with 3d transition metals, especially Ni, are excellent catalysts for the oxygen reduction reaction （ORR）. In this work, we, for the first time, demonstrated the water phase colloidal synthesis of Pt-M （M = Ni, Co and Fe） alloy NCs with tunable composition and morphology through a facile hydrothermal method. Pt-Ni alloy NCs synthesized with this method presented better ORR activity than commercial Pt/C catalysts. The X-ray energy dispersive spectra （EDS） mapping technique revealed that Pt-enriched shells existed on the as-synthesized Pt-Ni alloy NCs. About two atom thick layered Pt-enriched shells formed on Pts0Nis0 NCs and the thickness of the Pt-enriched shells increased as the Ni content increased. Furthermore, X-ray photoelectron spectroscopy analysis revealed that the oxidation level of the surface Pt atoms on the Pt-Ni alloy NCs decreased compared with monometallic Pt NCs, implying a decrease in the oxophilicity of the surface Pt atoms. Pt-Ni alloy NCs with lower oxophilicity of the surface Pt atoms give higher ORR activity. The most active alloy sample showed 13 times higher specific activity and six times higher mass activity at 0.9 V vs. a reversible hydrogen electrode when compared with commercial Pt/C. Pt-Ni alloy NCs also showed better durability than commercial Pt/C in long term ORR tests.
基金Supported by the National Key Research and Development Program of China(2016YFC0202300 and 2017YFC0212803)Beijing Natural Science Foundation(8192055)+1 种基金State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex(SCAPC201701)Basic Research and Operation Funds of Chinese Academy of Meteorological Sciences(2015Y001 and2017Z011)
文摘To investigate the impacts of relative humidity(RH) on secondary organic aerosol(SOA) concentrations and chemical reactions, the carbonaceous aerosol components [i.e., organic carbon(OC) and element carbon(EC)] were quantified in daily PM2.5 samples collected at a background site in East China during summer 2015. Based on the method of EC-tracer, the concentration of secondary organic carbon(SOC) demonstrated an obvious negative relationship with RH higher than 60%. Moreover, the ratio of SOC/EC also exhibited obvious decreasing trends with increasing RH, indicating negative effects for chemical production of SOA under high RH conditions. Due to high RH,photochemistry was weakened, gaseous oxidant concentrations was lowered(e.g., significantly decreased O3 levels),and the production rates of SOA were relatively low. On the other hand, because of more water uptake under higher RH conditions, the aerosol droplet acidity was reduced and enhancement of SOA formation by acidity was accordingly absent. In addition, high RH also plays an important role in changing viscosity of pre-existing aerosol coatings,which can affect reactive uptake yield of SOA. Overall, the results from this study imply that SOA production may be more associated with photochemical processes, while aqueous-phase chemistry is not very important for some SOA formation in a moist ambient environment. In the ambient atmosphere, oxidant concentrations, reaction rates,airborne species, etc., are highly variable. How do these factors affect SOA yields under given ambient environment warrants further detailed investigations.
