Structural characterization of arsenate ion exchanged MgAl-layered double hydroxide

Interlayer Structures and Dynamics of Arsenate and Arsenite Intercalated Layered Double Hydroxides: A First Principles Study

“…H 2 AsO 4 − and HAsO 4 2− co-exist at near-neutral pH conditions and they both occurred in the experimental systems [31], so the basal spacings for As(V) are presented together in Figure 3. The calculated basal spacings (i.e., 9.10 Å and 8.90 Å for H 2 AsO 4 − and HAsO 4 2− , respectively) are consistent with some of the reported experiments [31,80] that are conducted under initial pH around 7 and 8 (range from 8.71 Å to 9.21 Å, Figure 3) at a Mg/Al ratio of 2:1, while large differences are found between our simulations and the other experiments [8,76] conducted under pH of 5 or higher than 9 (<8.48 Å, Figure 3 The basal spacing values of As LDHs with low layer charge densities from experiments are significantly smaller than those from our simulations, but they coincide with those of NO3 − -LDHs (~8.0 Å at 4:1 and 8.04 Å-9.0 Å at 3:1 [47]). This implies that these species may not enter the gallery spaces of LDHs in some experiments, that is, the systems measured by those experiments are in fact still NO3 − -LDHs.…”

“…The calculated basal spacings (i.e., 9.10 Å and 8.90 Å for H2AsO4 − and HAsO4 2− , respectively) are consistent with some of the reported experiments [31,80] that are conducted under initial pH around 7 and 8 (range from 8.71 Å to 9.21 Å, Figure 3) at a Mg/Al ratio of 2:1, while large differences are found between our simulations and the other experiments [8,76] conducted under pH of 5 or higher than 9 (<8.48 Å, Figure 3 [47]. This agreement validates our simulation set up.…”

“…β is the angle between η and Z and θ is the angle between μ and Z. [8,47,[72][73][74][75][76][77][78]; thus the NO3 − -LDHs can be used to validate our simulation settings. Here we did not include the experimental results obtained under very high pH conditions because the adsorptions of arsenic species are highly inhibited by OH − under high pH [79].…”

Thermal Analysis On The Kinetics Of Magnesium-Aluminum Layered Double Hydroxides In Different Heating Rates

“…(1) When the water molecules are dehydrated, the layered structure of LDHs is not destroyed, but basal spacing is slightly decreased. The dehydration process may involve several stages [11] : the breaking of bonds among brucite-layers, anions and water molecules, the slight deformation of initial crystal lattice; the formation of new crystal lattice; the adsorption and desorption of gaseous water, water diffusion; heat transfer. The rate of thermal dehydration is determined by the rate of one or more of these stages.…”

“…The second one is also an endothermic process at higher temperature, the transition of which is due to the losses of water form hydroxyl groups of brucite-like layer and carbon dioxide from carbonate ion. As a result, the layered structure is destroyed [9][10][11].…”