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The nitrate depletion and HNO3 release in internally mixed nitrate and dicarboxylic acids (DCAs) particles have been widely detected in field and laboratory studies. Nevertheless, considerable discrepancies are still present among these measurements, and the influence factors for this acid-displacement reaction have not yet been elucidated. In this work, the hygroscopic growth and chemical composition evolution of mixtures of NaNO3 and DCAs, i.e., oxalic acid (OA), malonic acid (MA), and glutaric acid (GA), were measured using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and vacuum FTIR techniques. The HNO3 release from NaNO3/OA mixtures was observed in both the measurements, owing to the relatively high acidity of OA. At the same time, the NaNO3 phase state was found to act as a key regulator of nitrate depletion. Amorphous NaNO3 solids at relative humidity (RH) < 5% were inert to liquid OA. With increasing RH, the mixtures experienced three interesting stages of phase changes showing different HNO3 release rates, e.g., at around 15% RH, the slow HNO3 release was detected by the vacuum IR spectra, potentially indicating the transformation of amorphous solids to semisolid NaNO3; in the second stage (sudden RH increase from ~ 15% to 61%), the HNO3 release rate was increased by about an order of magnitude; when NaNO3 deliquescence occurred in the third stage, this displacement reaction proceeded due to more available NO3" ions formation. Compared to OA, MA and GA reacted with nitrate only in vacuum FTIR measurement, while in ATR-FTIR measurement, the mixtures tended to be effloresced completely without nitrate depletion. Further, the influences of ambient pressure, chemical composition, and water activity on HNO3 release rates were estimated via Maxwell steady-state diffusive mass transfer equation. The results showed that weaker acidity of MA and GA as well as relatively lower HNO3 diffusion rate in ambient gas phase mainly contributed to the unobserved nitrate depletion in ATR-FTIR measurement. Our findings reveal that chemical component, phase state, and water activity of particles, as well as HNO3 gas phase diffusion play crucial roles on HNO3 release from nitrate and DCAs mixtures. This work may provide a new perspective on nitrate depletion in the aging processes during transport of atmospheric aerosols. [ABSTRACT FROM AUTHOR]

In ambient air, aqueous-phase oxidation may turn precursors into more light-absorbing and toxic products, leading to air quality deterioration and adverse health effects. In this study, we investigated eugenol degradation in the aqueous phase by direct photolysis, and triplet excited organic (³C*) and hydroxyl radical (OH) as oxidants. Results showed degradation rates of eugenol followed the order of ³C* > OH>direct photolysis. Relative contributions of reactive oxygen species (ROS) and ³C* were evaluated via quenching and O2-free experiments. ³C* played a dominant role in eugenol degradation for ³C*-initiated oxidation, while both O2 and O2⋅ -generated were important for eugenol degradation for OH-initiated oxidation. Rate constants under O2, air and N2 followed the order of kO2 > kAir > kN2 for both direct photolysis and OH oxidation, and it changed to kAir > kN2 > kO2 for ³C*-initiate oxidation. Light absorption spectra showed absorbance at 300-400 nm, and intenstiy increased as photolysis progressed, and there were new broad fluorescent spectra at excitation/emission (Ex/Em)=250/(400-500) nm, suggesting the formation of new chromophores and fluorophores, such as humic-like substances (HULIS). Additionally, distinct fluorescence peaks appeared at Ex/Em=(300-350)/300 nm different oxidation stages. Concentration of generated HULIS increased gradually over time, then leveled off. Dithiothreitol (DTT) assay was applied to assess oxidation potential of the products, which was greater than that of pure eugenol, suggesting more harmful species were produced during oxidation. Detailed reaction pathways were elucidated via analyses of chemical characteristics of the products. [ABSTRACT FROM AUTHOR]

This work reports the day-night differences of a suite of chemical species including elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), water-soluble organic nitrogen (WSON), selected polycyclic aromatic hydrocarbons (PAHs), and secondary inorganic ions (NO3-, SO42-, NH4+) in ambient fine particles (PM2.5) collected from 23 July to 23 August 2016 in Changzhou, China. Mass concentrations of PM2.5 and SO42- show a 10-20% increase during daytime, while NO3- concentration decreases by a factor of three from nighttime to daytime due to its semi-volatile nature. PAHs, EC, and WSON show higher mass concentration in the night too. Mass ratios of WSOC to OC are high in both day and night, indicating that secondary organic aerosol (SOA) formation could occur throughout the day, while the slightly higher ratio during daytime suggests a more significant contribution from daytime photochemical oxidation. Strong positive correlations between HULIS-C and WSOC, and HULIS-C with O3 both in day and night, imply that HULIS-C, similar to WSOC, is mainly composed of secondary species. HULIS-C accounted for a large fraction of WSOC, with an average of ~60%. Moreover, the average WSON concentrations are 1.08 and 1.46 μg/m³, constituting ~16% and ~18% of water-soluble total nitrogen in day and night, respectively. Correlation analyses suggest that WSON is also predominantly produced from secondary processes. PAHs concentrations are found to be very low in summer aerosols. Overall, our findings highlight the dominant contribution of secondary processes to the major aerosol components in Changzhou, suggesting proper measures to effectively reduce gaseous precursors are also important to improve air quality. [ABSTRACT FROM AUTHOR]

In this study, we fabricated broadband anti-reflection coatings using a method based on layer-by-layer self assembly of positively charged layer double hydroxide (LDH) nanosheets and negatively charged silica nanoparticles via electrostatic interaction. Scanning electron microscopy and atomic force microscopy were used to observe the morphology, structure, and surface topography of LDH/SiO2 multilayer coatings. The anti-reflection properties of the coatings were investigated by UV visible spectrophotometry. Glass substrates covered with the LDH/SiO2 multilayer coatings exhibited broadband anti-reflection properties. The obtained [LDH(0.4 g/L)/SiO2(25 nm)]8, [LDH(0.4 g/L)/SiO2(50 nm)]10, and [LDH(0.8 g/L)/SiO2(25 nm)]6 coatings exhibited the best broadband anti-reflection properties among the as-prepared LDH/SiO2 multilayer coatings with different deposition cycles. Transmission levels of 97% were achieved in these optimal systems. Moreover, a maximum transmittance of 98% was achieved at a wavelength of 550 nm in the [LDH(0.4 g/L)/SiO2(25nm)]8 system and at 700 nm in the [LDH(0.8 g/L)/SiO2(25nm)]6 system. Different packing patterns of the two oppositely charged nanomaterials (dense packing of LDH nanosheets and loose stacking of silica nanoparticles) and the moderate textured surface of the coatings contributed to the enhanced light transmission and reduced wavelength dependence in the UV visible spectral range. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the effect of a water-soluble copolymer, Acrylic acid-Oxalic acid-Allypolyethoxy carboxylate-8-hydroxy-1,3,6-pyrene trisulfonic acid trisodium salt (pyranine) (AA-APEM-APTA), APEM, and APTA were copolymerized with acrylic acid (AA) to synthesize APTA-tagged no phosphate and nitrogen-free CaCO3 inhibitor, AA-APEM-APTA. Structures of APTA, APEM, and AA-APEM-APTA were carried out by FT-IR. The observation shows that the dosage of AA-APEM-APTA plays an important role on CaCO3 inhibition. It can be concluded that the order of preventing the precipitation from flask tests was AA-APEM > AA-APEM-APTA > HPMA > PAA≈PESA. Relationship between AA-APEMAPTA's fluorescent intensity and its dosage was studied. Correlation coefficient r of AA-APEM-APTA's is 0.99672. The effect on the formation of CaCO3 was investigated with combination of scanning electronic microscopy, transmission electron microscope, and X-ray powder diffraction analysis. AA-APEM-APTA can be used to accurately measure polymer consumption on line besides providing excellent CaCO3. [ABSTRACT FROM AUTHOR]

This manuscript describes the deposition of carbon on the surface of ZnO nanoparticles via a simple adsorption and calcination process. The prepared ZnO/C sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and thermogravimetric analysis (TGA); the results indicated that carbon was successfully doped on the surface of the ZnO nanoparticles. The photocatalytic activity and adsorption capacity were evaluated by photocatalytic decomposition and adsorption of the dye methylene blue (MB) in aqueous solution. The results showed that the obtained ZnO/C sample exhibited much higher photocatalytic properties and adsorption capacity for MB than pure ZnO and carbon because of the formation of heteroarchitectures, which might have improved the separation of photogenerated electrons and holes. In particular, the pseudo-first-order rate constant of the ZnO/C sample was 0.326 min-1, which was 10 times greater than that of pure ZnO. Moreover, the ZnO/C composites could remove dyes from different water sources like the Changjiang River water with high efficiency as well as from deionized water, greatly promoting their application in the area of environmental remediation. [ABSTRACT FROM AUTHOR]

ZnO/Ag[sub 2]O heterostructures were successfully synthesized via a simple one-step photochemical route. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). Photocatalytic activity toward degradation of a methylene blue (MB) aqueous solution under ultraviolet (UV) and visible light was investigated. The results showed that the as-prepared ZnO/Ag[sub 2]O heterostructures significantly enhanced the UV and visible photocatalytic activity compared with pure ZnO and Ag[sub 2]O. In particular, the rates of degradation using the as-prepared ZnO/ Ag[sub 2]O heterostructures were 27.4 and 15.6 times faster than that using bare ZnO nanoparticles under UV and visible light irradiation, respectively. Furthermore, the as-prepared ZnO/Ag[sub 2]O heterostructures could be easily recycled in UV and visible photocatalytic applications due to the low concentration of surface defects. Moreover, the ZnO/Ag[sub 2]O heterostructures could also degrade MB dye with high efficiency in various water types such as Changjiang river water, tap water, and deionized water, which will greatly promote their application in the area of environmental remediation. [ABSTRACT FROM AUTHOR]