Novel bio-fertilizer based on nitrogen-fixing bacterium immobilized in a hydrotalcite/alginate composite material.

The bacterium Streptomyces sp. is a common genus of the actinomycetes class found in soils and rhizospheres. This bacterium can produce substances with bio-stimulant capacity through the fixation of nitrogen from the air. In this work, the Streptomyces sp. bacterium was immobilized on a ZnMgAl-hydrotalcite clay and embedded in calcium alginate beads to generate a novel bio-composite that functions as a bacterial reservoir and as a controlled release material for bacteria to be used as a bio-fertilizer.The results showed that the novel bacterium-hydrotalcite/alginate bio-composite was very efficient as a bio-fertilizer showing a plant length of 64 mm in only 14 days of growing, which corresponds to an increase of ca. 760% in the lettuce plant growth in comparison with the materials without bacteria. In short, the present results demonstrate that the hydrotalcite and alginate served as an excellent container to keep the bacteria alive, providing nutrients to them and controlling their delivery.

Sorption of BTEX on a nanoporous composite of SBA-15 and a calcined hydrotalcite.

Benzene, toluene, ethylbenzene, and p-xylene (BTEX) are hazardous volatile organic compounds mostly released from fuel combustion, paint gas emissions, and biomass burning. In this work, it is studied the BTEX sorption influence on the surface reactivity of a new kind of nanoporous composite, prepared via an in situ functionalization of SBA-15 with a Mg-Al calcined hydrotalcite (HTC). During its preparation, Mg/Al mixed oxides are indeed formed and dispersed on the SBA-15 surface with non-blockage porosity. Furthermore, the physicochemical surface properties are exalted from its precursors and it is synergistically favorable for the BTEX sorption at low pressure and temperature.

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

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.

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

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.

Zeolitic polyoxometalates metal organic frameworks (Z-POMOF) with imidazole ligands and epsilon-Keggin ions as building blocks; computational evaluation of hypothetical polymorphs and a synthesis approach.

We investigate here a new family of zeolitic Metal Organic Frameworks (MOFs) based on imidazole (im) as the ligand and epsilon-type Keggin PolyOxoMetalates (POMs) as building units. The POM used in this study is the epsilon-{PMo(12)O(40)} Keggin isomer capped by four Zn(ii) ions (noted epsilon-Zn) in tetrahedral coordination. We describe here our methods to first construct and then evaluate the stability of hypothetical 3-D POMOFs possessing a tetrahedral network, typified by dense silica polymorphs and zeotypes and referred here to as Z-POMOFs. We use the analogy between the connectivity of silicon ion in dense minerals or zeolites and the epsilon-Zn, using imidazolate ligands to mimic the role of oxygen atoms in zeolites. Handling the epsilon-Keggin and imidazole as the constitutive building-blocks, a selection of 40 polymorphs were constructed and their relative stabilities computed. Among these Z-POMOFs, the cristobalite-like and zni-structure were identified as the most stable candidates. In parallel, we have attempted to synthesize Z-POMOF structures with epsilon-Zn POMs, synthesized in situ under hydrothermal conditions, and imidazole ligands. We present our first experimental result, the extended material [NBu(4)][PMo(V)(8)Mo(VI)(4)O(37)(OH)(3)Zn(4)(im)(Him)], named epsilon(im)(2). The structure of the hybrid framework is built by the connection of dimerized epsilon-Zn POMs to imidazole ligands in two directions. The obtaining of the first POMOF based on imidazole ligand is an encouraging step towards the synthesis of a new family of POMOFs.

Zeolitic polyoxometalate-based metal-organic frameworks (Z-POMOFs): computational evaluation of hypothetical polymorphs and the successful targeted synthesis of the redox-active Z-POMOF1.

The targeted design and simulation of a new family of zeolitic metal-organic frameworks (MOFs) based on benzenedicarboxylate (BDC) as the ligand and epsilon-type Keggin polyoxometalates (POMs) as building units, named here Z-POMOFs, have been performed. A key feature is the use of the analogy between the connectivity of silicon in dense minerals and zeolites with that of the epsilon-type Keggin POMs capped with Zn(II) ions. Handling the epsilon-Keggin as a building block, a selection of 21 zeotype structures, together with a series of dense minerals were constructed and their relative stabilities computed. Among these Z-POMOFs, the cristobalite-like structure was predicted to be the most stable structure. This prediction has been experimentally validated by the targeted synthesis of the first experimental Z-POMOF structure, which was strikingly found to possess the cristobalite topology, with three interpenetrated networks. Crystals of [NBu(4)](3)[PMo(V)(8)Mo(VI)(4)O(36)(OH)(4)Zn(4)(BDC)(2)].2H(2)O (Z-POMOF1) have been isolated under hydrothermal conditions from the reduction of ammonium heptamolybdate in the presence of phosphorous acid and Zn(II) ions. Tetrabutylammonium cations play the role of counterions and space-filling agents in this tridimensional interpenetrated framework. Moreover, the electrochemistry of the epsilon-Keggin POM is maintained and can be exploited in the insoluble Z-POMOF1 framework, as demonstrated by the electrocatalytic reduction of bromate.

On the acid-base properties of microwave irradiated hydrotalcite-like compounds containing Zn2+ and Mn2+.

Microwave irradiated lamellar double hydroxides containing different divalent metals (Mn2+, Zn2+, or Mg2+) were prepared with Al3+ as the trivalent metal. Samples containing Mn2+ and Zn2+ were unstable at 400 degrees C, leading to formation of mixed oxides and spinel phases. Acid-base properties of the samples were characterized by nitromethane and CO2 adsorption followed by FTIR spectroscopy. Decomposition of adsorbed nitromethane leads to isocyanate species that acts as probe molecules of acid-base sites at the surface. These properties determine the ability of materials to retain CO2. Indeed, whereas Mn-O sites are able to interact directly with CO2 molecules, Mg-O and Zn-O are able to form carbonate species as a result of the CO2 sorption.