Spatiotemporally Resolved pH Measurement in Aerosol Microdroplets Undergoing Chloride Depletion: An Application of In Situ Raman Microspectrometry.

Acidity is a defining property of atmospheric aerosols that profoundly affects environmental systems, human health, and climate. However, directly measuring the pH of aerosol microdroplets remains a challenge, especially when the microdroplets' composition is nonhomogeneous or dynamically evolving or both. As a result, a pH measurement technique with high spatiotemporal resolution is needed. Here, we report a spatiotemporally resolved pH measurement technique in microdroplets using spontaneous Raman spectroscopy. Our target sample was the microdroplets comprising sodium chloride and oxalic acid─laboratory surrogates of sea spray aerosols and water-soluble organic compounds, respectively. Our measurements show that the chloride depletion from the microdroplets caused a continuous increase in pH by ∼0.5 units in 2 hours. Meanwhile, the surface propensity of chloride anions triggers a stable pH gradient inside a single droplet, with the pH at the droplet surface lower than that at the core by ∼ 0.4 units. The uncertainties arising from the Raman detection limit (±0.08 pH units) and from the nonideal solution conditions (-0.06 pH units) are constrained. Our findings indicate that spontaneous Raman spectroscopy is a simple yet robust technique for precise pH measurement in aerosols with high spatiotemporal resolution.

Template-free synthesis of salmon pink tube-shaped structure carbon nitride with enhanced visible light photocatalytic activity.

Designing a highly active and stable photocatalyst to directly solve environmental pollution is desirable for solar energy conversion. Herein, an effective strategy, hydrothermal-calcination, for synthesizing extremely active carbon nitride (salmon pink) from a low-cost precursor melamine, is reported. The salmon pink carbon nitride with tube-shaped structure significantly enhanced response to visible light, improved efficiency of charge separation and remarkably enhanced efficiency of methyl orange (MO) degradation than bulk g-C3N4 (light orange). The M-10-200-24-600 composite possessed the most wonderful ability towards MO degradation irradiated by visible light, which could achieve a highest degradation efficiency of 84% within 120 min. Our findings may provide a promising and facile approach to highly efficient photocatalysis for solar-energy conversion.

Enhanced photocarriers separation of novel CdS/pt/Mo2C heterostructure for visible-light-driven hydrogen evolution.

The production of H2 from water using photocatalysts is a promising way of generating clean, renewable and alternative energy. The key issue is to develop active and stable photocatalysts. Here, we report a novel CdS/Pt/Mo2C heterostructure photocatalyst, where Pt nanoparticles are closely supported on CdS/Mo2C. The UV-vis spectrum and EIS Nyquist plots show that Mo2C can boost the absorption in the UV-vis region and improve the separation of the photogenerated electron-hole pairs from CdS. The Pt nanoparticles act as the active co-catalyst that promotes the transient photocurrent response. As a result, the CdS/Pt/Mo2C photocatalyst exhibits an excellent H2 evolution activity up to 1828.82 µmol h-1 g-1 under visible-light irradiation, 8.5 and 16.2 times higher than that of pristine CdS and CdS/Mo2C, respectively. Moreover, a high apparent quantum yield (AQY) of 9.39% is obtained at 400 nm for the CdS/Pt/Mo2C heterostructure photocatalyst.