Model Behavior: Characterization of Hydroxyacetone at the Air-Water Interface Using Experimental and Computational Vibrational Sum Frequency Spectroscopy

Kinetics and Oligomer Products of the Multiphase Reactions of Hydroxyacetone with Atmospheric Amines, Ammonium Sulfate, and Cloud Processing

Hydroxyacetone (HA) is an atmospheric oxidation product of isoprene and other organic precursors that can form brown carbon (BrC). Measured bulk aqueous-phase reaction rates of HA with ammonium sulfate, methylamine, and glycine suggest that these reactions cannot compete with aqueous-phase hydroxyl radical oxidation. In cloud chamber photooxidation experiments with either gaseous or particulate HA in the presence of the same N-containing species, BrC formation was minor, with similar mass absorption coefficients at 365 nm (<0.05 m2 g-1). However, rapid changes observed in aerosol volume and gas-phase species concentrations suggest that the lack of BrC was not due to slow reactivity. Filter-based UHPLC/(+)ESI-HR-QTOFMS analysis revealed that the SOA became heavily oligomerized, with average molecular masses of ∼400 amu in all cases. Oligomers contained, on average, 3.9 HA, 1.5 ammonia, and 1.6 other small aldehydes, including, in descending order of abundance, acetaldehyde, glycolaldehyde, glyoxal, and methylglyoxal. PTR-ToF-MS confirmed the production of these aldehydes. We identify C17H26O5, C10H22O9, C15H27NO7, C17H23NO5, and C18H32N2O9 as potential tracer ions for HA oligomers. We hypothesize that efficient oligomerization without substantial BrC production is due to negligible N-heterocycle (e.g., imidazoles/pyrazines) formation. While HA photooxidation is unlikely a significant atmospheric BrC source, it may contribute significantly to aqueous SOA formation.

Halide-Salt-Free Synthesis of Silver Nanowires with High Yield and Purity for Transparent Conductive Films

To date, silver nanowires (AgNWs) are routinely synthesized. However, the controllable preparation of AgNWs without any halide salts has not reached a similar level. In particular, the halide-salt-free polyol synthesis of AgNWs commonly occurs above 413 K, and the property of AgNWs obtained is not so easy to control. In this study, a facile synthesis of AgNWs with a yield of up to ∼90% in an average length of 75 μm was successfully performed without any halide salts. The fabricated AgNW transparent conductive films (TCFs) show a transmittance of 81.7% (92.3% for the AgNW network only without substrate) at a sheet resistance of 12.25 Ω/square. In addition, the AgNW films show distinguished mechanical properties. More importantly, the reaction mechanism for AgNWs was briefly discussed, and the importance of reaction temperature, the mass ratio of poly(vinylpyrrolidone) (PVP)/AgNO3, and the atmosphere was emphasized. This knowledge will help enhance the reproducibility and scalability of polyol synthesis of high-quality AgNWs.

Vibrational Sum-Frequency Generation Hyperspectral Microscopy for Molecular Self-Assembled Systems

In this review, we discuss the recent developments and applications of vibrational sum-frequency generation (VSFG) microscopy. This hyperspectral imaging technique can resolve systems without inversion symmetry, such as surfaces, interfaces and noncentrosymmetric self-assembled materials, in the spatial, temporal, and spectral domains. We discuss two common VSFG microscopy geometries: wide-field and confocal point-scanning. We then introduce the principle of VSFG and the relationships between hyperspectral imaging with traditional spectroscopy, microscopy, and time-resolved measurements. We further highlight crucial applications of VSFG microscopy in self-assembled monolayers, cellulose in plants, collagen fibers, and lattice self-assembled biomimetic materials. In these systems, VSFG microscopy reveals relationships between physical properties that would otherwise be hidden without being spectrally, spatially, and temporally resolved. Lastly, we discuss the recent development of ultrafast transient VSFG microscopy, which can spatially measure the ultrafast vibrational dynamics of self-assembled materials. The review ends with an outlook on the technical challenges of and scientific potential for VSFG microscopy.