Opposing Effects of Humidity on Rhodochrosite Surface Oxidation

Abstract

Rhodochrosite (MnCO3) is a model mineral representing carbonate aerosol particles containing redox-active elements that can influence particle surface reconstruction in humid air, thereby affecting the heterogeneous transformation of important atmospheric constituents such as nitric oxides, sulfur dioxides, and organic acids. Using in situ atomic force microscopy, we show that the surface reconstruction of rhodochrosite in humid oxygen leads to the formation and growth of oxide nanostructures. The oxidative reconstruction consists of two consecutive processes with distinctive time scales, including a long waiting period corresponding to slow nucleation and a rapid expansion phase corresponding to fast growth. By varying the relative humidity from 55 to 78%, we further show that increasing humidity has opposing effects on the two processes, accelerating nucleation from 2.8(±0.2) × 10(-3) to 3.0(±0.2) × 10(-2) h(-1) but decelerating growth from 7.5(±0.3) × 10(-3) to 3.1(±0.1) × 10(-3) μm(2) h(-1). Through quantitative analysis, we propose that nanostructure nucleation is controlled by rhodochrosite surface dissolution, similar to the dissolution-precipitation mechanism proposed for carbonate mineral surface reconstruction in aqueous solution. To explain nanostructure growth in humid oxygen, a new Cabrera-Mott mechanism involving electron tunneling and solid-state diffusion is proposed.

Infrared Signature of the Cation−π Interaction between Calcite and Aromatic Hydrocarbons

“…Aromatic hydrocarbons, such as BTE compounds, can enter soils and sediments by leakage or spills at facilities for producing, delivering, and distributing oil and oil products . The leakage and spill of oil and oil products can also release BTE compounds, given their high volatility, into the atmosphere, where they can interact with carbonate-containing aerosol particles originated from dust storms. − Our results suggest that the cation−π interaction is likely to occur under low relative humidity in soils and the atmosphere, where the mineral surface is not completely covered by water. For calcite, the incomplete coverage of the cleavage (101̅4) surface occurs under relative humidities below 50%, − a condition that is not difficult to encounter.…”

Features of the crystal structure and surface of superprotonic conductor caesium hydrogen sulfate phosphate

“…In air, the surface of samples is covered with adsorption layers and moisture, which can initiate heterogeneous chemical reactions with the formation of uncontrolled products, e.g. surface structures with different structure, chemical composition and physicochemical characteristics (conductivity, surface potential) from the bulk phase (Gouveia et al, 2012;Na et al, 2015;Kempaiah et al, 2019). AFM techniques were applied to obtain data on the surface layers of Cs 4 (HSO 4 ) 3 (H 2 PO 4 ) crystals.…”