In this work, some of the synthesis methods already reported for aluminum(III) hydroxide polymorphs with layered structure like gibbsite are revisited. Gibbsite was synthesized with high purity and yield by a simple route developed from modifications of a heating method proposed in the literature, making it possible to prepare gibbsite in regular glassware, avoiding the use of hydrothermal reactor and oven, as described in the literature. The proposed synthesis was conducted with a heating system under reflux conditions in a glass heating flask, using an oil bath, without the need for more sophisticated equipment. This is an accessible alternative method for crystalline gibbsite synthesis, with yield (76 wt.%). The obtained gibbsite was used as a precursor for the synthesis of a lithium/aluminum layered double hydroxide (LDH) from the intercalation method of Al(OH)3 in aqueous solution of lithium chloride. Gibbsite and the obtained LDH Li/Al were used for the immobilization of an anionic porphyrin with a loading on the order of 10-5 mol g-1 of solid, thus being alternative solid supports for catalytic species such as porphyrins.

Phenylphosphonates of zinc (Zn-PPh), calcium (Ca-PPh) and magnesium (Mg-PPh) were synthesized by the hydrothermal method. Samples showed characteristic X-ray diffraction (XRD) patterns of layered compounds with basal spacing in the range of 14-15 Å. According to Fourier transform infrared spectroscopy (FTIR), all compositions showed the presence of characteristic bands attributed to phenyl aromatic rings, phosphonate and lattice metal-oxygen (M-O) vibrations. Different concentrations of phenylphosphonate particles were applied to stabilize water-in-oil Pickering emulsions using vaseline oil in different w/o fractions. The three particle types showed greater affinity for the oil phase (wettability) and the ability to stabilize the emulsions via the Pickering effect. Ca-PPh particles contained a greater emulsified fraction after 20 days of evaluation. This result can be attributed to the particle morphology observed by scanning electron microscopy (SEM). The fibrous morphology of Ca-PPh particles is believed to increase the steric hindrance effect at the surface around the droplets, while the Zn-PPh and Mg-PPh layered particles tended to form clusters.

Layered double hydroxides (LDH) with the composition Zn2Cr, intercalated with acetate and chloride ions were synthesized by co-precipitation with increasing pH and characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). The samples synthesized at optimized pH showed XRD patterns with basal diffraction peaks typical of layered structures, with basal distances of 7.88 and 12.69 Å for intercalated chloride (Zn2Cr/Cl) and acetate (Zn2Cr/Ac), respectively. After optimization experiments, exchange reactions were performed with different anions, using an excess of five times the anions to be intercalated. Zn2Cr/Cl was exchanged with CH3COO-, F-, Br-, I-, SO42- and NO3-, and Zn2Cr/Ac was exchanged with F-, Cl-, Br-, I-, SO42- and NO3-. Not all reactions were effective, indicating that among the evaluated anions, CH3COO- was preferred for exchange, mainly attributed to the pre-expansion with bigger anions, facilitating the exchange with smaller anions.

Layered double hydroxides (LDHs) with the compositions (Cs+/NH4+)0.111[M2+0.667Al0.333(OH)2.0 (SO4)0.222] (M2+ = Mn, Zn) and basal distance of ca. 11 Å were obtained by co-precipitating Mn/Al and Zn/Al sulfate salts with aqueous NH3, using excess of Cs2SO4. [Mn0.667Al3+0.333(OH)2]Cl0.333.nH2O and [M2+0.667Al3+0.333(OH)2](NO3)0.333.nH2O (M2+ = Mn, Zn) were also synthesized by co-precipitation, presenting respective basal distances of 8.92 and 7.92 Å. After applying exchange reactions with excess of Cs2SO4, materials with basal distances of ca. 11 Å were obtained, indicating the exchange of chloride and nitrate with sulfate, without incorporation of Cs+. When Na+0.111[M2+0.667Al0.333(OH)2.0(SO4)0.222](M2+ = Mn, Zn) obtained by co-precipitation and having basal distances of ca. 11 Å was exchanged with excess of Cs2SO4, the content of sulfate remained constant and Na+ was partially replaced with Cs+, but the amount was lower, indicating the probable composition (Na+/Cs+)y[M2+0.667Al0.333(OH)2-y(SO4)y/2(SO4)0.222-(y/2)](M2+ = Mn, Zn), where some of the hydroxide anions were replaced with grafted SO42-.

In this study, three raw Brazilian clays from João Pessoa, Paraíba State (Aço AP, AVL and Verde Lodo) were characterized before and after purification and acid activation. Several instrumental techniques were used, and the raw clays were classified as dioctahedral smectites with different compositions, where the AVL sample had the highest content of montmorillonite. In addition, analyses showed modification in clay mineral compositions, mainly due to removal of impurities and octahedral sheet cation leaching during acid activation, which resulted in specific areas ranging from 42 to 93 m2 g-1 and increase of the Brønsted/Lewis acid site ratio, until 1.52 (AVL). Then, methyl esterification reactions were performed using the acid-activated clays as catalysts. The maximum acid conversions obtained were of 92 and 64%, for acetic acid using activated AVL and for lauric acid using activated Verde Lodo, respectively, and these data were correlated mainly to the Brønsted-Lowry acidity.

Layered double hydroxides (LDHs) of Cu:Al in the molar ratio of 2:1, intercalated with sulfate, sulfate/(Li+, Na+, K+ or NH4+), NO3- and CO32-, were synthesized by co-precipitation with increasing pH. The materials were submitted to exchange reactions using B2SO4 (B = Li+, Na+, K+, NH4+) solutions in an attempt to replace previously intercalated cations or incorporated cations without removing intercalated sulfate. X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectra were consistent with the expected intercalated species and scanning electron microscopy (SEM) images indicated submicrometric platelet-like particles, typical of LDHs. The chemical compositions of all phases were confirmed by inductively coupled plasma optical emission spectrometry (ICP OES) and thermogravimetric analyses (TGA). In the exchange reactions, only in [Cu6Al3(OH)18][Na(H2O)6(SO4)2]·6H2O the sodium cations were almost totally replaced with lithium, potassium and ammonium, without removing the intercalated sulfate.

Zn2Al-Cl and Zn2Al-NO3 layered double hydroxides (LDHs) were synthesized through the fixed pH co-precipitation method and used as precursor materials for the intercalation of p-aminobenzoate through anion exchange reactions. Since chloride in Zn2Al-Cl was only partially exchanged with p-aminobenzoate, the phases Zn2Al-NO3 and Zn2Al-N -AB (nitrate exchanged with p-aminobenzoate) were used in different percentages as functional fillers to produce nanocomposites of low-density polyethylene doped with maleic anhydride (LDPE). Analysis of thermal properties showed that the melting and recrystallization temperatures were slightly increased in the nanocomposite containing 5 wt.% Zn2Al-N-AB. Weathering tests performed with neat LDPE and the nanocomposite films showed that the addition of the LDHs improved ultraviolet (UV) absorption and reduced the LDPE degradation by 25 and 76% when using Zn2Al-NO3 and Zn2Al-N-AB, respectively, as fillers, showing a promising UV-shielding effect. Preliminary results also showed a potential application of Zn2Al-N-AB as antioxidant in natural insulating oils (natural ester FR3 and castor oil), opening new opportunity of applications.

RESUMO A substituição parcial do óleo diesel pelo biodiesel tem contribuído para o aumento da disponibilidade de glicerina no mercado mundial. Cerca de 10 m3 e glicerina são obtidos para cada 100 m3 de triacilglicerídeos (principal componente de óleos vegetais e gorduras animais) processados na principal rota tecnológica para produção do biodiesel, a transesterificação alcalina em meio homogêneo. Naturalmente, a glicerina obtida como coproduto no processo precisa ser aproveitada em processos complementares. Isso usualmente é possível após a glicerina passar por vários processos de purificação. Com a intenção de evitar tais processos complementes para aproveitamento da glicerina, estamos propondo a síntese do biodiesel por interesterificação do óleo de soja com acetato de metila, uma rota tecnológica que possibilita a obtenção da glicerina na forma de triacetina, ou seja, já quimicamente modificada. Os catalisadores utilizados no processo foram o hidróxido duplo lamelar (HDL) Zn2 Al/NO3 e o estearato de zinco comercial (EZ), um carboxilato lamelar. Ambos estes materiais lamelares ainda não haviam sido testados como catalisadores em reações de interesterificação. Foram obtidas conversões em ésteres metílicos de ácidos graxos de 50,8±4,2 % e 82,9±1,0 % (m m-1) utilizando os catalisadores EZ e HDL, respectivamente; quando as reações foram conduzidas utilizando 5 % de catalisador (m m-1), por 10 h de reação e razão molar acetato de metila: óleo de soja de 24:1.

ABSTRACT The partial replacement of diesel oil with biodiesel has contributed to the increased availability of glycerin on the world market. About 10 m3 of glycerol is obtained for every 100 m3 of triacylglycerides (main component of vegetable oils and animal fats) processed in the main technological route for biodiesel production, the alkaline transesterification in homogeneous medium. Of course, the glycerin obtained as a coproduct in the process needs to be harnessed in complementary processes. This is usually possible after the glycerin undergoes several purification processes. With the intention of avoiding such complementary processes, we are proposing the synthesis of biodiesel by interesterification of soybean oil with methyl acetate, a technological route that makes it possible to obtain glycerol in the form of triacetin, that is, already chemically modified. The catalysts used in the process were the layered double hydroxide (HDL) Zn2 Al/NO3 and the commercial zinc stearate (EZ), a layered carboxylate. Both these layered materials had not yet been tested as catalysts in interesterification reactions. Conversions were obtained in fatty acid methyl esters of 50.8 ± 4.2% and 82.9 ± 1.0% (m m-1) using the EZ and HDL catalysts, respectively; when reactions were conducted using 5% catalyst (m m-1), for 10 h reaction and molar ratio methyl acetate: soybean oil of 24:1.

Abstract This work presents the processing of a high-acidity oil through sequential reactions of esterification using montmorillonite K10 and transesterification using zinc monoglycerolate. Since these solids had not been employed along with this approach beforehand, the objective of this work is to provide a general insight of the proposed process and demonstrate its technical feasibility. In this sense, the processing of a synthetic mixture containing soybean oil and lauric acid provided a reduction of the free fatty acid content from (40.8±0.1) % to (3.1±0.4) % after the esterification reaction and a fatty acid methyl ester yield of (95.4±0.2) % was obtained after the transesterification reaction. As compared to traditional homogeneous catalysts, the solid catalysts employed in this work require higher reaction times to achieve satisfactory ester yields but, on the other hand, they are less sensitive to the presence of both water and free fatty acids in the raw materials and can be easily recovered and reused. Therefore, the results accomplished may help the development of a technology for processing high-acidity fatty materials in order to obtain biodiesel, although its economic feasibility still needs a further assessment.

Chrysotile:cement roofing sheets were milled with and without K2HPO4. As indicated by X-ray diffraction (XRD), the samples crystallinities were reduced with the increasing milling time. The same tendency was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), with disaggregation of the chrysotile fiber bundles and formation of non-fibrous micrometric agglomerate particles. After milling for 16 min, most of the phases present in the cement and chrysotile were transformed into amorphous materials, except quartz, in which the structure integrity was preserved, and calcium carbonate, where the particles were reduced to nanometric size. Both milled samples were submitted to release experiments in water, where the characteristics of a potential slow release fertilizer and acid soil conditioner were observed. The process is a viable alternative not only to eliminate the hazard of chrysotile fibers without the need to remove them from the cement matrix, but also as aggregation value to the milled almost amorphous mixture.

Abstract Cobalt/aluminum and nickel/aluminum layered double hydroxide (LDH - M+2:Al molar ratio of 3:1) were intercalated with dodecylsulphate (DDS), laurate (LAU), stearate (STE) and palmitate (PAL) and used as filler in low-density polyethylene (LDPE) in percentages between 0.2 and 7.0wt%. After injection molding, the samples were submitted to morphological characterization by scanning electron microscopy (SEM), analysis of thermal behavior by differential scanning calorimetry (DSC) and investigation of rheological properties. All Co/Al-LDPE samples showed the formation of a high temperature polymer crystal domain, induced by the LDH filler. The rheological properties indicated in general a reduction of shear modulus due to incompatibility between some regions of LDH and LDPE, which promoted phase separation. However, interaction with the LDH surface indicated higher affinity of the Ni/Al-LDH for the LDPE compared to Co/Al-LDH, forming permanent networks.

Green (Ni2+/Al+3) and pink (Co2+/Al+3) layered double hydroxides (LDH) (molar ratio of 3:1) were intercalated with several organic anions and used as functional colored fillers into low density polyethylene (LDPE) by melt mixing in amounts of 0.2 to 7 wt.%. Scanning electron microscopic (SEM) results of LDPE nanocomposites indicated that with low percentage of filler, all the LDH samples showed efficient delamination/exfoliation in the polymer matrix. Fillers added to LDPE with concentrations of 0.2, 0.5, 2 and 5% presented, in general, maintenance of Young's modulus and tensile strength, tending to the reduction with a loading of 7%. Most of the nanocomposites presented similar elongations, although NiUS stood out, with an elongation increase of 300%. Differential scanning calorimetry (DSC) indicated the effect of the Co/Al-LDH in inducing the formation of LDPE crystalline domains, especially at higher temperature than neat LDPE.

Rice husk ash (RHA) is a waste material produced in large quantities in many regions worldwide, and its disposal can be problematic. This work describes a method for using RHA to synthesize silicon and potassium slow-release fertilizer. The extraction of silica from RHA was accomplished by alkaline leaching with KOH. Different KOH concentrations and reaction times were evaluated and the best production of K2SiO3 solution was achieved using 6 mol L-1 and 6 h, respectively. The fertilizer was synthesized by the reaction of K2SiO3 with KAlO2 in aqueous medium, followed by calcination at 500 °C. X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses indicated that the fertilizer composition was similar to mineral kalsilite. Solubility essays indicated lower K+ and Si4+ release percentage in neutral medium. Kinetic mechanisms of release tests can be well explained by the pseudo-second order model. The proposed synthesis seems to be a viable process offering economic and environmental benefits.

This study reports the synthesis and characterization of a Ni/Zn layered double hydroxide salt intercalated with acetate ions and the subsequent replacement of the acetate ions with molybdate ions via an ion exchange reaction, conducted at two different pH values. Regardless of the pH employed during the synthesis, the basal spacing in the Ni/Zn layered double hydroxide salt decreased from 13.08 Å to approximately 9.5 Å, which agreed with intercalation of hydrated molybdate anions. The non-calcined material and the material submitted to heat treatment at 250 °C (basal spacing reduced to 7.35 Å, due to dehydration) were tested as catalyst for the methyl transesterification of soybean oil. Like sodium molybdate in homogeneous media, the solid materials were active catalysts. After reaction at 120 °C for 4 h, the materials afforded high conversions at an alcohol/soybean oil molar ratio of 35:1 and preserved the structure after three consecutive uses. In conclusion, intercalation of molybdate anion into the layered double hydroxide salt proved to be an efficient alternative to support the active species and transform a soluble catalyst into a solid with application in heterogeneous catalysis.

Isopropyl octanoate is an ester used in the formulation of cosmetics, foods, medicines, and other products. The peculiar thermodynamic and kinetic factors, allied with the demand for the applications mentioned above, justify the development of an optimized process for its synthesis. In the present article, the esterification of octanoic acid with isopropanol while using zinc n-octanoate as catalyst is reported. A factorial design was employed where variables such as molar ratio (alcohol:acid), percentage of catalyst (in relation to the acid mass) and temperature were investigated. It was observed that zinc octanoate showed promising catalytic activity, especially at 165 °C, with molar ratios of 8:1 and 6:1, and with 7 and 10% of catalyst, where conversions up to 75% were observed. Optimized conditions for the production of isopropyl octanoate were determined to be 165 °C, 6:1 molar ratio and 5.97% of catalyst.