Adsorbed Water Promotes Chemically Active Environments on the Surface of Sodium Chloride

Abstract

Gas–particle interfaces are chemically active environments. This study investigates the reactivity of SO2 on NaCl surfaces using advanced experimental and theoretical methods with a NH4Cl substrate also examined for cation effects. Results show that NaCl surfaces rapidly convert to Na2SO4 with a new chlorine component when exposed to SO2 under low humidity. In contrast, NH4Cl surfaces have limited SO2 uptake and do not change significantly. Depth profiles reveal transformed layers and elemental ratios at the crystal surfaces. The chlorine species detected originates from Cl– expelled from the NaCl crystal structure, as determined by atomistic density functional theory calculations. Molecular dynamics simulations highlight the chemically active NaCl surface environment, driven by a strong interfacial electric field and the presence of sub-monolayer water coverage. These findings underscore the chemical activity of salt surfaces and the unexpected chemistry that arises from their interaction with interfacial water, even under very dry conditions.

Water-Catalyzed Formation of Reactive Oxygen Species from NO2 on a Weakly Hydrated Calcite Surface

“…Water has been shown to serve as a catalyst for some interfacial reactions . An interfacial electric field with intensities sufficient to catalyze reactions and promote water autoionization has been reported for other hydrated mineral surfaces in the literature. ,, Figure shows that on the calcite surface, the adsorbed water sublayer experiences an interfacial electric field of ∼4 V/Å, which is similar to those observed on other hydrated mineral surfaces ,, and is sufficient to promote the autoionization of water . Interestingly, hydroxyl formation on a wet calcite surface has previously been observed experimentally, , which strongly supports the occurrence of water autoionization on calcite.…”

“…The interfaces of weakly hydrated (or even transiently hydrated) minerals have been shown to serve as catalytic sites for heterogeneous chemical reactions that are unfeasible under standard or bulk conditions or to even support novel chemical pathways that had not previously been observed. − Investigating such heterogeneous chemical reactions at mineral surfaces under water-restricted hydration conditions may explain some chemical phenomena that are not yet fully understood. An important example is the chemistry of nitrogen dioxide (NO 2 ).…”

Marine Fuel Regulations and Engine Emissions: Impacts on Physicochemical Properties, Cloud Activity and Emission Factors

“…In Figure 5b the soot NEXAFS spectrum has a peak at around 532 eV corresponding to the carbonyl group, which is missing for the sulfate. Both spectra show a distinct peak above 537 eV, which signals the presence of sulfate particles and soot containing sulfate (Fauré et al, 2023;Kong, Gladich, et al, 2023;Zelenay et al, 2011). This peak is broader for the soot particle, which indicates the presence of oxygen atoms bonded to carbon atoms but other compounds cannot be excluded due to the complexity of this absorption region.…”