Abstract
In this study, by using first principles simulation techniques, we explored the basal spacings, interlayer structures, and dynamics of arsenite and arsenate intercalated Layered double hydroxides (LDHs). Our results confirm that the basal spacings of NO3−-LDHs increase with layer charge densities. It is found that Arsenic (As) species can enter the gallery spaces of LDHs with a Mg/Al ratio of 2:1 but they cannot enter those with lower charge densities. Interlayer species show layering distributions. All anions form a single layer distribution while water molecules form a single layer distribution at low layer charge density and a double layer distribution at high layer charge densities. H2AsO4− has two orientations in the interlayer regions (i.e., one with its three folds axis normal to the layer sheets and another with its two folds axis normal to the layer sheets), and only the latter is observed for HAsO42−. H2AsO3− orientates in a tilt-lying way. The mobility of water and NO3− increases with the layer charge densities while As species have very low mobility. Our simulations provide microscopic information of As intercalated LDHs, which can be used for further understanding of the structures of oxy-anion intercalated LDHs.
Highlights
As a common pollutant in water bodies, Arsenic (As) has been threatening water supplies all over the world for a long time [1]
The Layered double hydroxides (LDHs) structures used in this study were based on the powder X-ray diffraction data of
The LDH structures used in this study were based on the powder X-ray diffraction data of hydrotalcite after refinement using the Rietveld method [60]
Summary
As a common pollutant in water bodies, Arsenic (As) has been threatening water supplies all over the world for a long time [1]. The concentration of As in fresh water is often lower than 1 μg/L [2], while high concentrations up to 50 μg/L and even 500 μg/L can be found in groundwater, especially those in Bangladesh, Vietnam, Hungary, Argentina, Mexico, and some regions in China [2,3]. As holds several oxidation states (−3, 0, 3, 5) [2] and can exist in both organic and inorganic forms [4], while only As(III) and As(V) are of importance in water contamination [3,4]. High level concentrations of arsenite have been found in rivers close to As(III)-dominated industrial effluent [5] and in underground water systems, for example, groundwater from Bangladesh [6]
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