“…1) was not typical of very well crystallized and large particles of gibbsite (Hsu, 1989). Thus, the asymmetry in peak B in the organic acid/Al MR = 0 system was ascribed to gibbsite particles containing some adsorbed Al (i.e., partial crystallization) (Shen et al, 2006) and/or smaller particles than the gibbsite reference material. The Al L-edge spectra of the precipitation products formed at the malate/Al MR = 0.001 was similar to that of gibbsite, with peak B only slightly broader and of similar symmetry (Fig.…”
“…1) was not typical of very well crystallized and large particles of gibbsite (Hsu, 1989). Thus, the asymmetry in peak B in the organic acid/Al MR = 0 system was ascribed to gibbsite particles containing some adsorbed Al (i.e., partial crystallization) (Shen et al, 2006) and/or smaller particles than the gibbsite reference material. The Al L-edge spectra of the precipitation products formed at the malate/Al MR = 0.001 was similar to that of gibbsite, with peak B only slightly broader and of similar symmetry (Fig.…”
“…Gibbsite and bayerite were prepared following previously published syntheses [22], modified from the procedures described in Shen et al [24] and Lefevre et al [25]. After synthesis, gibbsite and bayerite were washed repeatedly in deionized water (>18.2 MΩ·cm) to remove excess electrolytes.…”
Section: Mineral and Reagent Preparationmentioning
Adsorption processes at mineral-water interfaces control the fate and transport of arsenic in soils and aquatic systems. Mechanistic and thermodynamic models to describe this phenomenon only consider inner-sphere complexes but recent observation of the simultaneous adsorption of inner-and outer-sphere arsenate on single crystal surfaces complicates this picture. In this study, we investigate the ionic strength-dependence of the macroscopic adsorption behavior and molecular-scale surface speciation of arsenate bound to gibbsite and bayerite. Arsenate adsorption decreases with increasing ionic strength on both minerals, with a larger effect at pH 4 than pH 7. The observed pH-dependence corresponds with a substantial decrease in surface charge at pH 7, as indicated by ζ-potential measurements. Extended X-ray absorption fine structure (EXAFS) spectroscopy finds that the number of second shell Al neighbors around arsenate is lower than that required for arsenate to occur solely as an inner-sphere surface complex. Together, these observations demonstrate that arsenate displays macroscopic and molecular-scale behavior consistent with the co-occurrence of inner-and outer-sphere surface complexes. This demonstrated that outer-sphere species can be responsible for strong adsorption of ions and suggests that environments experiencing an increase in salt content may induce arsenic release to water, especially under weakly acidic conditions.
“…On the other hand, there is another well-known interaction for weak interlayer binding, namely, the hydrogen bonding. Al(OH) with interlayer hydrogen bonds is an example which has been studied both experimentally and theoretically before [ 18 , 19 , 20 , 21 , 22 ]. However, their properties as a quasi 2D layered material have not been sufficiently appreciated compared to the vdW-interaction-mediated materials.…”
In many layer-structured materials, constituent layers are bound through van der Waals (vdW) interactions. However, hydrogen bonding is another type of weak interaction which can contribute to the formation of multi-layered materials. In this work, we investigate aluminum hydroxide [Al(OH)3] having hydrogen bonding as an interlayer binding mechanism. We study the crystal structures and electronic band structures of bulk, single-layer, and multi-layer Al(OH)3 using density functional theory calculations. We find that hydrogen bonds across the constituent layers indeed give rise to interlayer binding stronger than vdW interactions, and a reduction of the band gap occurs for an isolated layer as compared to bulk Al(OH)3 which is attributed to the emergence of surface states. We also consider the alkali-halide intercalation between layers and examine how the intercalated atoms affect the atomic and electronic structures of Al(OH)3.
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