Studies on selective adsorbents for oxo-anions. Nitrate ion-exchange properties of layered double hydroxides with different metal atoms

Abstract

Layered double hydroxides (LDHs) with different kinds of metal ions (Mg-Al, Co-Fe, Ni-Fe, and Mg-Fe) in the brucite layers were prepared and their anion exchange properties were studied by measurements of distribution coefficient (K d ) and ion exchange capacity. The basal spacing of LDHs varied depending on the kind of metal ions in the brucite layer. A relatively high K d value for NO 3 2 ions was observed on Ni-Fe type LDHs, and a markedly high K d value for the hydrothermally-treated Ni-Fe type LDHs (Ni-Fe (HT)), prepared at 120 °C. These high K d values correlated with the basal spacing of 0.81 nm observed for this sample, where the interlayer distance (0.33 nm) is suitable for the stable fixing of NO 3 2 ions (ionic size = 0.33 nm). A chemical analysis study showed a Cl 2 /NO 3 2 ion-exchange mechanism for NO 3 2 adsorption on Ni-Fe (HT). The NO 3 2 uptake by Ni-Fe (HT) was nearly constant (NO 3 /Fe = 0.7) over a pH range between 5 and 10, which also supports the adsorption mechanism of Cl 2 /NO 3 2 ion exchange. The Ni-Fe (HT) could remove NO 3 2 ions from seawater effectively (NO 3 2 uptake = 168 mmol g 21 ) even though seawater contains an extremely large amount of coexisting anions. This novel adsorbent thus has a NO 3 2 ion-sieve property and will prove beneficial for the selective removal of NO 3 2 ions from industrial effluents and seawater to clean the environment.

Anion Selectivity of Layered Double Hydroxides: Effects of Crystallinity and Charge Density

“…It is therefore very questionable whether LDHs could be used as nitrate adsorbents. However, several recent studies have reported that certain LDHs with specific compositions [21][22][23][24][25][26][27][28] show high selectivity for nitrate ions. Those reports, however, did not address the question of whether only the nitrate anion among monovalent anions and anions of low charge densities has a high affinity for LDHs under certain conditions.…”

Co—Fe Prussian Blue Analogue Intercalated into Diamagnetic Mg—Al Layered Double Hydroxides

“…The absorption peak at 1,380 cm -1 was observed in LDH-NO 3 , which is attributable to the symmetric vibration of the interlayer nitrate anion (Figure 1Ba). [28][29][30][31]36] LDH-Fe(CN) 6 showed that an absorption peak at 1,380 cm [25,37,38] SEM images of the LDH-NO 3 and LDH-Fe(CN) 6 are shown in Figure 1C. As can be seen, the rosette aggregation for LDH-NO 3 was observed (Figure 1Ca).…”

“…The d 003 = 8.8 Å and a = 3.04 Å were consistent with well-known LDHs containing the nitrate anion (Table 1). [23,24,[28][29][30][31] 6 , and (c) LDH-PB. BS is basal spacing.…”

Geomaterials: their application to environmental remediation

“…Harmful anions such as phosphate, arsenic and nitrate ions can be absorbed in the interlayers of LDHs [121][122][123]. We focused on preparing multifunctional composites with adsorption properties, which can be used to simultaneously remove harmful cations and anions.…”