Aline O. Moura

Hexagonal mesoporous silica modified with copper phthalocyanine as a photocatalyst for pesticide 2,4-dichlorophenoxiacetic acid degradation

A new mesoporous catalyst was prepared by the reaction between 3-aminopropyltrimethoxisylane and Cu(II)-hexadecafluorophthalocyanine, followed by co-condensation of tetraethylorthosilicate around a micelle formed by n-dodecylamine. The surfactant was removed from the pores by continuous extraction with ethanol, giving the Si-CuF16Pc catalyst. This catalyst was characterized by SEM, FTIR, TGA, 29Si NMR, N2 adsorption and X-ray diffraction. SEM images confirmed that the catalyst material is formed by nanoaggregates with a diameter of 100 nm. N2 adsorption isotherms showed that Si-CuF16Pc has a surface area of approximately 200 m2 g(-1) and a porous diameter of 7.7 nm, characterizing the mesoporosity of this product. This novel material shows an excellent photocatalytic activity, degrading almost 90% of 2,4-dichlorophenoxyacetic acid (2,4-D) up to 30 min, while only approximately 40% of photodegradation was obtained in its absence.

Nanosized Silica Modified with Carboxylic Acid as Support for Controlled Release of Herbicides

Hexagonal mesoporous silica modified with carboxylic acid (SiAc) has been obtained by reaction between chloroacetic acid and 3-aminopropyltrimethoxysilane, which was immobilized on porous material by a sol-gel process in the presence of an n-dodecylamine template. SiAc was characterized by TG, FT-IR, (29)Si NMR, (13)C NMR, SEM, surface charge density, surface area and porous diameter, which proved that the carboxylic group was chemically bonded to an inorganic structure, and the material presented a nanometric structure with spheres <50 nm and porous diameter of 10 nm. Herbicides 2,4-D and picloram were anchored on SiAc porous gel to produce the materials named SiD and SiPi, respectively. The controlled release of picloram from the SiAc was less than that of 2,4-D. After 26 days of releasing, 4.43 × 10(-5) mol L(-1) of picloram was delivered by SiPi, and 5.0 × 10(-5) L(-1) was released from the SiD in 30 days.

Effect of thermal dehydration and rehydration on Na-magadiite structure

The effect caused by dehydration and rehydration of the synthetic Na-magadiite was investigated by TGA, XRD, SEM, and (29)Si NMR. Thermal analysis of Na-magadiite presented two well-defined loss mass stages between 20 and 150 degrees C and another between 270 and 310 degrees C, both related to the removal of interlayer water. The swelling behavior of Na-magadiite was studied by thermal dehydration data obtained at 150 and 300 degrees C, and respective rehydration by water addition. X-ray patterns showed that the dehydration of Na-magadiite at 150 and 300 degrees C provoked the basal spacing decrease. The XRD also showed that only the material treated at 150 degrees C returned to the original structure with the rehydration. (29)Si NMR spectra showed that after rehydration, the Q(3)/Q(4) relationship presented the same value for Na-magadiite treated at 150 degrees C. However, this Q(3)/Q(4) value decreased when the treatment was done at 300 degrees C. Kinetic studies of thermal decomposition showed that the dehydration of magadiite is based on a phase boundary-controlled reaction, caused by contracting areas. The exfoliation of lamellas with thermal treatment can explain this behavior, as observed in SEM images.

Magadiite as a support for the controlled release of herbicides

Diuron and 2,4-dichlorophenoxyacetic acid were intercalated into layered silicate magadiite and the presence of anchored herbicides within the lamellas was confirmed by Fourier transform infrared spectroscopy. X-ray diffraction patterns and surface area analysis showed that the intercalation of herbicides decreased basal lamellar spacing and the surface area of the silicate. According to the results obtained from surface charge analysis, the main interactions between magadiite and the herbicides were mediated by hydrogen bond formation. Controlled release studies demonstrated that the delivery of the herbicides occurred substantially faster at pH 9, while the difference in delivery rates at pH 1 and pH 4.6 (the point of zero charge) was far less marked, although release at the more acidic pH was slightly quicker. The use of magadiite as a herbicide support shows great potential for the development of controlled release systems and will contribute to more sustainable forms of weed control.

Estudos Cinéticos da aquação do trans-[Co(en)2Cl2]Cl

The trans-dichlorobis(ethylenediamine)cobalt(III) chloride was synthesized in an undergraduate laboratory and its aquation reaction was carried out at different temperatures. This reaction follows pseudo-first-order kinetics and the rate constants, determined at 25, 35, 45, 55 and 70 o C, are 1.44 x 10-3; 5.14 x 10-3; 1.48 x 10-2; 4.21 x 10-2 and 2.21 x 10-1 s-1, respectively. The activation energy is 93.99 ± 2.88 kJ mol-1.

Co-movimientos en mercados bursátiles en américa latina: la evidencia con el COVAR

The paper investigates comovements in equity markets in six Latin American Countries: Argentina, Brazil, Chile, Colombia, Mexico, and Peru. We used the CoVaR method to identify the contagion effect between those countries’ stock exchanges, estimated by quintile regression. It was possible to find out which country has suffered most and which one has caused the highest contagion effect to the others. The results have shown that Peru was the country most vulnerable to risk, Argentina the one that least influenced the risk of other countries analyzed, and Mexico, followed by Brazil, the countries that contributed most to the contagion of others.