Reaction of Bromide with Bromate in Thin-Film Water

Abstract

Thin-film water is ubiquitous in nature, occurring on virtually all surfaces exposed to the ambient environment. In particular, alkali halide salts below their deliquescence point are expected to be coated with water films from one molecular layer to a few nanometers thick. While salt ion mobility in thin-film water has been characterized in the literature, little is known about the chemistry occurring within these films. Here we investigate the surface chemistry change of a mixed bromine salt (KBr/KBrO(3)) using X-ray photoelectron spectroscopy, secondary electron microscopy, and energy-dispersive X-ray spectroscopy. At 68% relative humidity, the Br(-) surface concentration was observed to deplete with increasing water vapor exposure time. Known bulk solution kinetics for the reaction of Br(-) + BrO(3)(-) has a second-order dependence on H(+) concentrations. However, in the present experiments there was no addition of an external acid. These results suggest that the pH and chemical reactions within thin-film water are uniquely differently from bulk solution. Because bromine chemistry in the atmosphere is strongly influenced by pH, these results have implications for the cycling of bromine where thin-film water is present.

Size Effects in MgO Cube Dissolution

“…One must not forget, that in humid environments thin-film water is ubiquitous. 52 Nanomaterials are high surface area materials and become instantaneously coated with water films with thicknesses ranging between one molecular layer to few nanometers. 53 These films provide a less discussed reaction medium 54,55 with an essentially unexplored surface and solvent chemistry 52,53 that can be determining for functionality and fate of metal oxide nanomaterials in the ambient.…”

Thin water films and magnesium hydroxide fiber growth

“…4a). However, the interaction between chlorosiloxane covered MgO nanocubes and H 2 O vapor gives rise to the F5 phase Mg 3 (OH) 5 Cl$4H 2 O as concluded from the XRD powder pattern (Fig. 4c and S5 in ESI †).…”

“…An important aspect relates to the localization of these transformation processes, i.e. the base of Mg 3 (OH) 5 Cl$4H 2 O ber growth. Spatially conned reaction media 30 both in the mm range (agglomerates of functionalized MgO nanocubes) as well as in the range of few nanometers (thin liquid water lms for ion transport and reaction) were shown to determine the transformation and microstructure evolution.…”

“…6 Scheme illustrating the mechanism of fiber growth. Contact with water vapor leads to the instantaneous formation of condensed water films which sustain ion transport necessary to add new Mg 3 (OH) 5 Cl$4H 2 O units to the top of the growing crystalline fibers. As concluded from the characteristic and well-characterized morphology of oxychloride fibers 25 the [010] direction is proposed to be the growth direction with the (101) plane being subject to fast material addition and growth.…”

“…3,4 Resulting solids are metastable, highly dispersed and, as such, subject to their interface and the chemical composition of the surrounding gas or liquid phase. Under ambient conditions and in humid environments thin-lm water is ubiquitous 2,5,6 and nanomaterials become instantaneously covered by water lms with thicknesses ranging between one molecular layer to few nanometers. 7 While the water-mineral oxide chemistry has received much attention in earth and environmental science 6,8 as well as in surface and materials science 7,[9][10][11] signicantly less attention has been paid to interfacial water in the eld of nanomaterials chemistry.…”