Abstract
Hydrotalcite-type anionic clays are a group of important materials used in adsorption processes, mainly for organic pollutants removal due the layered double hydroxide structure. The layer-interlayer interactions provide a structural memory even after dehydration and dehydroxylation process, since a very stable interlayer anions are part of material composition, like the carbonate one. A limited numbers of trivalent modifier cations can replace the aluminium cation due the ionic radii mismatch or oxidation state restrictions. Transition metal cations can replace the aluminium one in octahedral site of hydroxide lamellas in order to improve the adsorptive behaviors. In this work, we have investigate three compositions of carbonated magnesium-aluminium hydrotalcite with dif-ferent iron (III) contents through the co-precipitation method at pH 11 and aging step at 60°C for 6 hours. Thermal analysis was performed aiming the determination of the hydration water and hydroxyl amounts in dried precipitate samples, taking in account the results obtained for X-ray diffractometry, infrared spectroscopy, and nitrogen adsorption-desorption characterization for several thermally treated samples. All of synthesized samples showed high surface areas, even for high temperature of thermal treatment. The co-substitution with iron (III) reduced the temperature of dehydration and dehydroxylation process, but the co-substitution at 5 mol% provides other desirables characteristics, like a more amount of rhombohedral HDL phase and higher porosity, even after the thermal treatment at 500°C for 4 hours. This result makes that composition very applicable as a reusable adsorbent material in order to removal several types of micro-pollutant compounds in aqueous media.
Highlights
One of the most versatile adsorbent material groups is the synthetic hydrotalcite anionic clays due their wide applications as adsorbents and catalyst support materials, named Layered Double Hydroxide (LDH) [1] [2] [3]
Hydrotalcite-type anionic clays are a group of important materials used in adsorption processes, mainly for organic pollutants removal due the layered double hydroxide structure
We have investigate three compositions of carbonated magnesium-aluminium hydrotalcite with different iron (III) contents through the co-precipitation method at pH 11 and aging step at 60 ̊C for 6 hours
Summary
One of the most versatile adsorbent material groups is the synthetic hydrotalcite anionic clays due their wide applications as adsorbents and catalyst support materials, named Layered Double Hydroxide (LDH) [1] [2] [3]. In aqueous media, water and mineral anions, like the carbonate, are able to form an intricate arrangement of hydrogen bonds in order to connect the sheets through the interlayer species and give rise to LDH structure [4] [5] [6]. The typical hydrotalcite structures possess some of the Mg2+ cation replaced by trivalent cation, like Al3+ one, which causes a charge unbalancing among the mixed cation centers and terminal OH− groups, leading to the formation of highly positively charged sheets. To stabilize this type of hydrotalcite LDH structure, a proportional amount of interlayer anions is required to compensate the positive charge in the layer.
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