Rafael Marangoni

New multifunctional materials obtained by the intercalation of anionic dyes into layered zinc hydroxide nitrate followed by dispersion into poly(vinyl alcohol) (PVA)

Different anionic blue and orange dyes have been immobilized on a zinc hydroxide nitrate (Zn(5)(OH)(8)(NO(3))(2)nH(2)O--Zn-OH-NO(3)) by anion exchange with interlayer and/or outer surface nitrate ions of the layered matrix. Orange G (OG) was totally intercalated, orange II (OII) was partially intercalated, while Niagara blue 3B (NB) and Evans blue (EV) were only adsorbed at the outer surface. Several composite films of poly(vinyl alcohol)--PVA were prepared by casting through the dispersion of the hybrid material (Zn-OH-OG) into a PVA aqueous solution and evaporation of water in a vacuum oven. The obtained composite films were transparent, colored, and capable of absorbing UV radiation. Improved mechanical properties were also obtained in relation to the nonfilled PVA films. These results demonstrate the onset of a new range of potential applications for layered hydroxide salts in the preparation of polymer composite multifunctional materials.

Zn2Al layered double hydroxides intercalated and adsorbed with anionic blue dyes: a physico-chemical characterization.

Three different anionic blue organic dyes have been intercalated into the structure of Zn(2)Al layered double hydroxides, using the co-precipitation method at constant pH. Using the same synthetic procedure, Zn(2)Al-Cl has been prepared and used as an adsorptive phase to retain the blue dyes from an aqueous solution. All the organic/inorganic (O/I) hybrid LDH compounds were analyzed by X-ray powder diffraction (XRPD), thermal analysis (TG/DTA), elemental analysis, solid state (13)C nuclear magnetic resonance (CPMAS (13)C NMR), and Fourier transform infrared spectroscopy (FTIR). In the adsorption experiments, Gibbs free energy DeltaG values for the temperatures in a range between 10 and 40 degrees C were found to be negative, which indicates that the nature of adsorption is spontaneous and shows the affinity of LDH material towards the blue anionic dyes. Additionally a decrease in DeltaG values at higher temperature further indicates that this process is even more favorable at these conditions. The enthalpy DeltaH values were between physisorption and chemisorption, and it may be concluded that the process was a physical adsorption enhanced by a chemical effect, characterized by a combined adsorption/intercalation reaction, making these O/I assemblies reminiscent of the Maya blue.

Organic inorganic dye filler for polymer : Blue-coloured layered double hydroxides into polystyrene

A series of blue dye molecules, Evans blue (EB), Chicago sky blue (CB), Niagara blue (NB) were incorporated by direct co-precipitation within the galleries of negatively charge layered double hydroxide (LDH). The materials of cation composition Zn/Al = 2 lead to well-defined organic inorganic assemblies. The molecular arrangement of the interleaved dye molecule is proposed by 1D electronic density projection along the stacking direction for the hydrothermally treated samples with alternatively a highly inclined orientation of EB and CB and a parallel-bilayer arrangement for NB. Blue coloured LDH assemblies were subsequently dispersed into polystyrene (PS). It was found that the hybrid fillers do not interfere in the radical polymerization of styrene, giving rise to similar molecular weight and polydispersity than filler free PS, while higher glass transition temperatures were obtained for the nanocomposites. This was consistent with the rheological behaviour with the observation for LDH/NB filler based nanocomposite of shear thinning exponent different from zero, underlining frictional interaction between filler and PS chain. The absorption maximum slightly blue-shifted for the hybrid filler in comparison to the corresponding organic dye was found unmodified for the PS nanocomposite, thus giving rise to blue coloured plastic films, reminiscent somehow of the blue Maya effect.

Effect of adsorbed/intercalated anionic dyes into the mechanical properties of PVA: layered zinc hydroxide nitrate nanocomposites.

Zinc hydroxide nitrate (ZHN) was adsorbed with anions of blue dyes (Chicago sky blue, CSB; Evans blue, EB; and Niagara blue, NB) and intercalated with anions of orange dyes (Orange G, OG; Orange II, OII; methyl orange, MO). Transparent, homogeneous and colored nanocomposite films were obtained by casting after dispersing the pigments (dye-intercalated/adsorbed into LHSs) into commercial poly(vinyl alcohol) (PVA). The films were characterized by XRD, UV-Vis spectroscopy, and mechanical testing. The mechanical properties of the PVA compounded with the dye-intercalated/adsorbed ZHN were evaluated, and reasonable increases in Youngs modulus and ultimate tensile strength were observed, depending on the amount and choice of layered filler. These results demonstrate the possibility of using a new class of layered hydroxide salts intercalated and adsorbed with anionic dyes to prepare multifunctional polymer nanocomposite materials.

Covalent grafting of phenylphosphonate groups onto layered silica derived from in situ-leached chrysotile fibers

The reaction of natural chrysotile fibers with phenylphosphonic acid leads to a new grafted material. The layered material, with an interplanar basal distance of 15.2 A, was characterized by powder X-ray diffraction, thermal analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis. The experimental data are consistent with the grafting of phenylphosphonate groups to the surface of the layered silica sheets, obtained by the in situ acidic leaching of brucite sheets, from chrysotile.

Microstructure and magnetism of Fe nanoparticles embedded in Al2O3?ZnO matrix

Nanoscaled Fe particles embedded in a double-oxide matrix were obtained by synthesizing a zinc?aluminium layered double hydroxide intercalated with a hexacyano Fe(III) complex under vacuum thermal annealing. Chemical and structural properties were investigated by Fourier transform infrared spectroscopy, x-ray photoemission spectroscopy, x-ray diffraction and transmission electron microscopy. The magnetic properties of the Fe nanoparticles were investigated using a SQUID magnetometer. Our measurements indicate a system of weakly interacting magnetic nanoparticles that are arranged in a multidomain state at low temperature.

LDHs Instability in Esterification Reactions and Their Conversion to Catalytically Active Layered Carboxylates

Layered double hydroxides (LDH) containing Zn/Al and Mg/Al with different counter-ions and M2+/M3+ ratios were synthesized and used as catalysts in the esterification of fatty acids with methanol. High conversion rates were obtained depending on the reaction conditions. However, LDHs were also converted in situ into layered carboxylates and this new material was responsible for the observed catalytic activity, which was preserved even after several consecutive reuse cycles.Graphical AbstractXRD patterns (A) and FTIR spectra (B) of synthetic LDHs.

Hidróxidos duplos lamelares como matrizes para fertilizantes de liberação lenta de nitrato

Due to the extensive use of nitrogen fertilizers in the agriculture e due to the elevate potential of nitrate leaching, there is a great demand for slow or controlled release fertilizers. Synthetic layered double hydroxides (HDLs) combine the characteristic that qualifies them to be used as matrixes for nitrate slow release fertilizers. The objectives of the present work are focused in the synthesis, characterization and investigation of the slow release of nitrate process in one structure of a HDL containing ions Mg2+ and Al3+ in its structure. The HDL with the formula Mg0,83Al0,17(OH)2(NO3)0,17.0,56H2O was synthesized by the co-precipitation method at constant alkaline pH, isolated by centrifugation and dried in an vacuum oven. Measurements of X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR) and thermal analysis (TGA/DTA) confirmed the obtaining of the compound containing the intercalated hydrated nitrate anions and the proposed formula. The compound was tested for release nitrate NaHCO3 solution buffered to pH 6.5, and distilled water. The representative curves demonstrated two complementary behaviors nitrate release a fast initial and a slow gradual. The compound investigated in this study demonstrates the potential to be used as a matrix for slow release fertilizer nitrate. The compound was submitted to the nitrate release tests using a NaHCO3 solution buffered at pH 6.5 and in distilled water. The obtained curves have shown two complementary events of nitrate release, one fast initial event and another slow and gradual. The compound investigated in the present work has shown a potential to be used as matrix for nitrate slow release fertilizers.

Poly(vinyl alcohol) composites containing layered hydroxide salts, intercalated with anionic azo dyes (tropaeolin 0 and tropaeolin 0)

Layered zinc hydroxide salts were intercalated with anionic azo dyes, obtaining orange pigments. The materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), thermal analysis (TGA/DTA/DSC) and X-ray photoelectron spectroscopy (XPS). After characterization, the layered pigments were dispersed into a matrix of poly(vinyl alcohol) - PVA, in variable concentrations, in relation to the PVA mass. Homogeneous, transparent and colorful films were obtained by wet casting method and kept in a desiccator at 65% of humidity for one week and evaluated in relation to their mechanical properties. Owing to the different intercalated anions polarities, different behaviors were observed for both pigments when used as fillers in PVA. This work opens a research front in the utilization of layered hydroxide salt intercalated with anionic dyes, as alternative fillers in polymer composite materials.

Compósitos de poli(álcool vinílico) contendo hidroxissais lamelares de zinco, intercalados com corantes aniônicos azo (tropaeolina 0 e tropaeolina 00)

Layered zinc hydroxide salts were intercalated with anionic azo dyes, obtaining orange pigments. The materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), thermal analysis (TGA/DTA/DSC) and X-ray photoelectron spectroscopy (XPS). After characterization, the layered pigments were dispersed into a matrix of poly(vinyl alcohol) - PVA, in variable concentrations, in relation to the PVA mass. Homogeneous, transparent and colorful films were obtained by wet casting method and kept in a desiccator at 65% of humidity for one week and evaluated in relation to their mechanical properties. Owing to the different intercalated anions polarities, different behaviors were observed for both pigments when used as fillers in PVA. This work opens a research front in the utilization of layered hydroxide salt intercalated with anionic dyes, as alternative fillers in polymer composite materials.