Geolar Fetter

Comparison of the structural and acid–base properties of Ga- and Al-containing layered double hydroxides obtained by microwave irradiation and conventional ageing of synthesis gels

Structural and acid–base properties of Mg/Al and Mg/Ga layered double hydroxides (LDHs) obtained by microwave irradiation of the co-precipitated gels have been investigated and compared to those of samples conventionally aged by prolonged hydrothermal treatment of the gels. Similar crystallinities and chemical compositions were obtained whatever the synthesis method used. Besides, all samples, and remarkably the Ga-containing LDHs with a molar ratio Mg ∶ Ga = 4.5, exhibited pure lamellar phases. The acid–base properties of the mixed oxides obtained by calcination of the LDHs have been examined by microcalorimetric adsorption of CO2 and by FTIR spectroscopy upon CH3CN interaction. These techniques gave evidence that the number and strength of acid and basic sites were influenced by the nature and amount of the trivalent cation, as well as by the preparation method.

Effect of microwave irradiation time on the synthesis of zirconia-pillared clays

In this work, we present the synthesis, at different zirconia/clay ratios, of zirconia-pillared montmorillonite in presence of microwave irradiation. The effect of irradiation time (5, 10, 20 and 30 min) on the structure and properties of the solids was also studied. The samples were characterized by X-ray diffraction, nitrogen adsorption (BET surface area) and thermo-programmed desorption of ammonia. It is shown that the irradiation time is critical between 5 and 10 min. For times longer than 10 min, no effect on the pillared clay features is observed.

Detrital Mg(OH)2 and Al(OH)3 in Microwaved Hydrotalcites

Microwave irradiation power (90, 180, 270 or 360 W) determines the composition and the structure of the compounds obtained when pH is increased, decreased or maintained constant during preparation. Although in all cases the X-ray diffraction patterns show that the obtained compounds are hydrotalcite-like, the surface areas (40 up to 240 m2/g) as well as other microcrystalline compounds have to be inferred, such as Al(OH)3 or Mg(OH)2.

Twofold role of calcined hydrotalcites in the degradation of methyl parathion pesticide

Summary Methyl parathion (MP) is a very toxic organophosphate pesticide used as a non-systematic insecticide and acaricide on many corps. As MP and its by-products are highly toxic, they have to be retained to avoid pollution of rivers and lakes. Highly efficient sorbents are hydrotalcites (HTs) (or anionic clays). We have correlated the degradation of an aqueous solution of MP at room temperature, with the basicity of the adsorbing materials. It was found that the metal composition of hydrotalcites determines both the surface electronic properties (basic or acidic) and the sorption capacity. Depending on the basic strength, some calcined hydrotalcites can catalyze the transformation of MP to p-nitrophenol (p-NP) and retain its by-products. Such a process has the advantage of being able to be carried out at room temperature and at the pH of the pesticide solution.

Thermal stability of monometallic Co-hydrotalcite

Monometallic Co62+Co23+(OH)−16(NO3)−2·nH2O hydrotalcite-like compound was prepared by a careful precipitation from an aqueous solution of Co(NO3)2·6H2O in air atmosphere, followed by microwave irradiation. As comparison, an additional sample was prepared without microwave irradiation, employing aging in the crystallization step. Thermal evolution was studied by X-ray diffraction (XRD), FTIR, DTA/TGA and nitrogen physisorption. The microwaved sample (monometallic hydrotalcite) was stable up to 200 °C. The nonirradiated sample only showed the Co3O4 spinel phase.

Bactericidal Performance of Chlorophyllin-Copper Hydrotalcite Compounds

Copper hydrotalcites with and without adsorbed chlorophyllin exhibit a bactericidal effect that depends on the copper release and the basicity, which can be tuned through the chlorophyllin adsorption. The prepared solids performed well for the elimination of Escherichia coli, Enterobacter aerogenes, Salmonella enterica, and Staphylococcus aureus bacteria. The results showed that the copper-containing hydrotalcite with the adsorbed chlorophyllin is the most active material. Wastewaters from a metal industry were treated with these hybrid compounds, and the bactericidal effect was comparable with the results reported using more complex methods such as photocatalysis. Furthermore, one main advantage of these hybrid compounds is its low human toxicity compared with silver-containing materials.

Preparation of layered double hydroxide/chlorophyll a hybrid nano-antennae: a key step

In the first step to obtain an efficient nano-antenna in a bottom-up approach, new hybrid materials were synthesized using a set of layered double hydroxides (LDHs) with basic properties and pure chlorophyll a (Chl a). The stability of the adsorbed monolayer of Chl a was shown to be dependent on the nature and the ratio of the different metal ions present in the LDHs tested. The hybrid materials turned out to be adequate for stabilizing Chl a on Mg/Al LDHs for more than a month under ambient conditions while a limited catalytic decomposition was observed for the Ni/Al LDHs leading to the formation of pheophytin. These changes were followed by namely XRD, DR-UV-vis and fluorescence spectroscopies of the hybrid antennae and of the solutions obtained from their lixiviation with acetone or diethylether. On Mg/Al hydrotalcites the stability of the adsorbed Chl a was equivalent for values of the metal atom ratio ranging from 2 to 4. The latter hybrids should constitute a good basis to form efficient nanoscale light harvesting units following intercalation of selected dyes. This work describes an efficient preparation of Chl a that allows scale-up as well as the obtention of a stable Chl a monolayer on the surface of various LDHs.

Nanoporous composites prepared by a combination of SBA-15 with Mg-Al mixed oxides. Water vapor sorption properties.

Summary This work presents two easy ways for preparing nanostructured mesoporous composites by interconnecting and combining SBA-15 with mixed oxides derived from a calcined Mg–Al hydrotalcite. Two different Mg–Al hydrotalcite addition procedures were implemented, either after or during the SBA-15 synthesis (in situ method). The first procedure, i.e., the post-synthesis method, produces a composite material with Mg–Al mixed oxides homogeneously dispersed on the SBA-15 nanoporous surface. The resulting composites present textural properties similar to the SBA-15. On the other hand, with the second procedure (in situ method), Mg and Al mixed oxides occur on the porous composite, which displays a cauliflower morphology. This is an important microporosity contribution and micro and mesoporous surfaces coexist in almost the same proportion. Furthermore, the nanostructured mesoporous composites present an extraordinary water vapor sorption capacity. Such composites might be utilized as as acid-base catalysts, adsorbents, sensors or storage nanomaterials.

Microwave Effect on Clay Pillaring

Pillared clays may be prepared in presence of microwave irradiation as it has been extensively used in organic chemistry syntheses. Preparation time of the conventional intercalating solution takes about 2 days, but only 15 min when the preparation mixture is microwave-irradiated. The amount of water required to disperse and to dilute the pillar precursor salts is also significantly reduced. In this work, the properties of the pillared clays prepared in presence of microwave irradiation are compared to those prepared by the conventional way. Their performance as catalysts or as adsorbents is discussed.

Structure, thermal stability, and catalytic performance of MgO-ZrO2 composites

A composite constituted by zirconia supported on magnesia is thermally treated. Depending on temperature, several crystal sizes and crystalline zirconia structures are obtained. At low temperatures, cubic zirconia crystals are found to be deposited on the crystalline magnesia matrix. As temperature increases, the cubic zirconia phase transforms to the tetragonal and the monoclinic phases. They form clusters supported on the MgO matrix. All these results are supported by different analytical techniques and a catalytic test.