Role of WSOCs and pH on Ammonium Nitrate Aerosol Efflorescence: Insights into Secondary Aerosol Formation.

Efflorescence of ammonium nitrate (AN) aerosols significantly impacts atmospheric secondary aerosol formation, climate, and human health. We investigated the effect of representative water-soluble organic compounds (WSOCs) (sucralose (SUC), glycerol (GLY), and citric acid (CA) on AN:WSOC aerosol efflorescence using vacuum Fourier transform infrared spectroscopy. Combining efflorescence relative humidity (ERH) measurements, heterogeneous nucleation rates, and model predictions, we found that aerosol viscosity, correlating with molecular diffusion, effectively predicted ERH variations among the AN:WSOC aerosols. WSOCs with higher viscosity (SUC and CA) hindered efflorescence, while GLY with a lower viscosity showed a minor effect. At a low AN:CA molar ratio (10:1), CA promoted ERH, likely due to CA crystallization. Increasing the droplet pH inhibited AN:CA aerosol efflorescence. In contrast, for AN:SUC and AN:GLY aerosols, efflorescence is pH-insensitive. With the addition of trivial sulfate, AN:SUC droplets exhibited two-stage efflorescence, coinciding with ammonium sulfate and AN efflorescence. Given the atmospheric abundance, the morphology, phase, and mixing state of nitrate aerosols are significant for atmospheric chemistry and physics. Our results suggest that AN:WSOCs aerosols can exist in the amorphous phase in the atmosphere, with efflorescence behavior depending on the aerosol composition, viscosity, pH, and the cation and anion interactions in a complex manner.

Facile synthesis of the Z-scheme graphite-like carbon nitride/silver/silver phosphate nanocomposite for photocatalytic oxidative removal of nitric oxides under visible light.

In this study, a novel ternary Z-scheme Graphite-like Carbon Nitride (g-C3N4)/Silver (Ag)/Silver Phosphate (Ag3PO4) photocatalyst was designed and prepared using a two-step method (sodium chloride (NaCl) template-assisted strategy plus selective deposition). Its photocatalysts performance against removing 400 ppm of Nitric Oxides (NOx) was then investigated. We found 50 wt% g-C3N4/Ag/Ag3PO4(AP-CN 2:1) catalyst removes up to 74% of NO in 90 min under the illumination of visible light (>420 nm), which is respectively 3.5 and 1.8 times higher than using g-C3N4 or Ag3PO4, alone. This improved performance was attributed to the formation of Z-scheme g-C3N4/Ag/Ag3PO4 heterojunction, driven by the built-in electric field across the g-C3N4/Ag/Ag3PO4 interface. These separated the electron-hole but enhanced the original strong oxidation and reduction performance of related components. The superior performance is also attributed to the improved surface area, enhanced hydrophilicity (H2O2) and better visible-light-harvesting capability of the composite compound. More importantly, the AP-CN 2:1 sample maintained a NO removal rate of more than 73% even after four rounds of recycling. The photocatalytic oxidation removal mechanism was evaluated using the radical-capture experiments, electron spin resonance (ESR) and ion-exchange high-performance liquid chromatography (HPLC) analysis. The findings of this work offer a simple but effective design of a highly reactive and practical ternary Z-scheme heterojunction photocatalysts for the removal of toxic NO.