Chromate uptake characteristics of the pristine layered double hydroxides of Mg with Al

Abstract

The layered double hydroxides (LDHs) of Mg with Al readily scavenge dissolved chromate ions under a wide range of conditions. While the chromate uptake is quantitative in the LDH containing 33 mol% Al, the uptake is only 58% of the stoichiometric value in the LDH containing 25 mol% Al. This indicates that the lower symmetry of the NO 3 À ions in the LDH with 33 mol% Al facilitates the intercalation of chromate ions even under conditions of equilibration with excess dissolved nitrate ions. The chromate uptake obeys the Langmuir adsorption isotherm suggesting that the entire interlayer region of the LDH behaves like a surface. This surface is structural rather than morphological as the chromate uptake correlates negatively with the BET surface area of the LDHs.

Structural Synthon Approach to Predict the Possible Polytypes of Layered Double Hydroxides

“…[2] Among the layered materials, layered double hydroxides (LDHs), have received a great deal of attention, on account of their applications in catalysis, sorption, anion exchange, water purification and in medicine, as agents for drug delivery. [3][4][5][6] The structure of the LDHs is derived from that of mineral brucite, Mg(OH) 2 . [7] Brucite comprises a hexagonal packing of OH -ions in which Mg 2+ ions occupy alternative layers of octahedral sites.…”

“…The nitrate LDHs exhibit two different interlayer spacings: 8.8 Å (x = 0.33) and 8.0 Å (x = 0.25). [18] 2. This difference in the interlayer spacings is associated with the orientation of the NO 3 -ion in the interlayer.…”

Interlayer structure of iodide intercalated layered double hydroxides (LDHs)

“…Given their structure, the LDHs are natural hosts for mineralization of a variety of anionic pollutants [4,5]. Radioactive iodine is one of the many hazardous elements discharged from nuclear reactors and is a serious health hazard.…”

Synthesis and characterization of arsenate-intercalated layered double hydroxides (LDHs): Prospects for arsenic mineralization

“…Layered double hydroxides (LDHs) are widely used for catalysis and sorption and are sinks for the mineralization of insidious anions such as chromates [2,3], selenates [4], fluorides [5], radioactive anions [6], and various organic pollutants [7]. LDHs exhibit anion exchange properties, which make them candidate materials for the immobilization of arsenate in the interlayer region of the LDHs.…”