Magnesium-aluminum Double Hydroxide Research Articles

Highly Stable Hybrid Pigments Prepared from Organic Chromophores and Fluorinated Hydrotalcites

Structural hydroxide groups in layered magnesium–aluminum double hydroxides were partially replaced by fluoride ions. Fluorinated and fluorine-free materials were used as hosts for two dyes, carminic acid and hydroxyl naphthol blue, resulting in a hybrid pigment color palette. The pigments were produced by two ways, either incorporating chromophore during the synthesis of the layered double hydroxide or in a post-synthesis step through the memory effect of the LDHs. Additionally, the pigments were protected with a magnesium hydroxide phase to prevent the color from fading over time. The pigments were stable for periods as long as 10 years. The color properties of the pigments were significantly influenced by the host of dye since the presence of fluorine directly influences the acid–base properties of the layered double hydroxides. The pigments conferred their color to white cream in the preparation of colored creams. The colored creams acquired the color of the layered pigment.

Energetics of order-disorder in layered magnesium aluminum double hydroxides with interlayer carbonate.

Laboratory synthesis of layered double hydroxides (LDH) often results in materials replete with stacking faults. Faults are known to affect several properties including sorption, electrochemical, and catalytic activity of this important class of materials. Understanding the occurrence of faults thus calls for a comprehensive analysis of formation and stability of ordered and faulted LDHs. High-temperature oxide melt solution calorimetric measurements made on an ordered and a faulted Mg-Al LDH with carbonate interlayer anion shows that ordered LDH is energetically more stable than the faulted one by ∼6 kJ/mol. The stacking faults are an intergrowth of 3R1 and 2H1 polytypes, and faults could thus mediate transformation of 3R1 to 2H1 polytypes. Several factors including pH and temperature of precipitation also affect layer stacking. The formation of stacking faults could therefore have its origin in kinetics. Water content in the interlayer also affects layer stacking, and hence it may affect properties of LDH. Improved understanding of the distribution of water molecules in LDH is also crucial in an environmental context, as LDH occur as minerals and are important for contaminant amelioration in the environment. Water adsorption calorimetry on dehydrated LDH shows a continuous decrease in the magnitude of adsorption enthalpy with increasing coverage, indicating the presence of energetically heterogeneous sites where the water molecules reside. The results also indicate that the energy of several sites where the water molecules may reside (whether in the interlayer or on the surface) overlaps, and hence it is hard to differentiate among them.

Sorption removal of Fe(CN)6 3− ion impurities from water and evaluation of water quality by the biotesting method

The sorption removal of Fe(CN)63− ion impurities from water was investigated. A specially synthesized magnesium-aluminum double hydroxide with the hydrotalcite-type structure was used as a sorbent. The biotesting method used for various test objects proved the efficiency of sorption removal of Fe(CN)63− from water.

AlN formation from a hydrotalcite-polyacrylonitrile intercalation compound by carbothermal reduction

As a precursor for AlN production by carbothermal reduction, a hydrotalcite (layered magnesium-aluminum double hydroxide)-polyacrylonitrile (PAN) intercalation compound has been prepared for the first time. After the layers were expanded by the replacement of the interlayer anions with the CH 3(CH 2) 11OSO 3 − ions, the acrylonitrile monomer was intercalated and subsequently polymerized. By the heat treatments at 1100°C–1600°C in N 2, AlN, MgO and MgS formed. MgO was detected in the products heated up to 1300°C. MgS formation was observed in the reactions below 1500°C. On heating at 1600°C, single phase submicron AlN grains were obtained.

Characterization of magnesium-aluminum double hydroxide prepared from alkoxides and its products of thermolysis

A magnesium-aluminum double hydroxide was prepared by the simultaneous hydrolysis of magnesium and aluminum alkoxides. Pure double hydroxide is obtained between 0.6 and 0.8 in the Mg 2+/(Mg 2+ + Al 3+) mole ratio. Infrared spectra were compared with those of 4Mg(OH) 2·Al(OH) 3 synthesized by Feitknecht and Gerber, and the naturally occurring mineral Mg 6Al 2(OH) 18·4H 2O. The compounds MgO and MgAl 2O 4 crystallize slowly above ≈ 500°C and ≈ 800°C, respectively. Powders for the double hydroxide gave large aggregates of small particles. Definite signs of particle growth and a marked increase in crystallite growth were seen in powders produced above 1100°C. Specific surface areas of powders heated at low temperatures are very high and did not fall below 10 m 2/g until the heating temperature was raised above 1100°C.