[Show abstract][Hide abstract] ABSTRACT: Herein, we present a cross-linked ureasil-polyether-siloxane hybrid (labeled PEO500) that can function as a stimuli-sensitive material-it swells or shrinks in response to changes in the environmental conditions and it can also, effectively and selectively, remove dyes from water solution. We also developed a methodology to separate a mixture of cationic and anionic dyes present in water. Addition of PEO500 to an aqueous solution of the anionic orange II (OII) or the Ponceau S (PS) dye rendered the solution colorless, but an aqueous solution of cationic Methylene Blue (MB) remained unchanged after 2h of contact with the insoluble matrix. In situ small-angle X-ray scattering (SAXS) showed that the distance of siloxane nanodomains are strongly affected by the swelling or shriking. By in situ UV-vis adsorption experiments we found that the kinetics of OII and PS removal followed a pseudo-first-order rate equation. We accomplished B3LYP calculations, to establish which sites on the matrix interacted with the dyes and to investigate the nature of the matrix-dye chemical bonds. On the basis of the experimental and theoretical investigations, we proposed some mechanisms to explain how PEO500 adsorbs anionic dyes efficiently. This "smart" matrix is potentially applicable as an efficient, fast, selective, and convenient device in water treatment and stimuli-sensitive response materials.
[Show abstract][Hide abstract] ABSTRACT: Poly(methylmetacrilate)-maghemite (PMMA-gamma-Fe2O3) hybrid material was studied by the electron stimulated ion desorption (ESID) techniques coupled with time-of-flight mass spectrometry (TOF-MS) and theoretical investigation about its fragmentation. Moreover, atomic force microscopy was utilized to characterize the morphology before and after ionic desorption. ESID results indicated differences of pattern fragmentation for different compositions of hybrid material in comparison with neat PMMA. Theoretical studies suggest that kinetics effects can take place in the fragmentation process and electrostatic contributions were important in the stabilization of PMMA on maghemite after the grafting process.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 08/2013; 117C:276-283. · 1.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The XAS/WAXS time-resolved method was applied for unraveling the complex mechanisms arising from the evolution of several metastable intermediates during the degradation of chlorine layered double hydroxide (LDH) upon heating to 450 °C, i.e., Zn2Al(OH)6·nH2O, ZnCuAl(OH)6·nH2O, Zn2Al0.75Fe0.25(OH)6·nH2O, and ZnCuAl0.5Fe0.5(OH)6·nH2O. After a contraction of the interlamellar distance, attributed to the loss of intracrystalline water molecules, this distance experiences an expansion (T > 175–225 °C) before the breakdown of the lamellar framework around 275–295 °C. Amorphous prenucleus clusters with crystallo-chemical local order of zinc-based oxide and zinc-based spinel phases, and if any of copper-based oxide, are formed at T > 175–225 °C well before the loss of stacking of LDH layers. This distance expansion has been ascribed to the migration of ZnII from octahedral layers to tetrahedral sites in the interlayer space, nucleating the nano-ZnO or nano-ZnM2O4 (M = Al or Fe) amorphous prenuclei. The transformation of these nano-ZnO clusters toward ZnO crystallites proceeds through an agglomeration process occurring before the complete loss of layer stacking for Zn2Al(OH)6·nH2O and Zn2Al0.75Fe0.25(OH)6·nH2O. For ZnCuAl(OH)6·nH2O and ZnCuAl0.5Fe0.5(OH)6·nH2O, a cooperative effect between the formation of nano-CuO and nano-ZnAl2O4 amorphous clusters facilitates the topochemical transformation of LDH to spinel due to the contribution of octahedral CuII vacancy to ZnII diffusion.
Chemistry of Materials. 07/2013; 25(14):2855–2867.
[Show abstract][Hide abstract] ABSTRACT: In this study, the short-and long-range chem-ical environments of Cu dopant in TiO 2 photocatalyst have been investigated. The Cu-doped and undoped TiO 2 spec-imens were prepared by the sol–gel approach employing CuSO 4 Á5H 2 O and Ti(O-iPr) 4 precursors and subjecting the dried gels to thermal treatment at 400 and 500 °C. The photocatalytic activity, investigated by methylene blue degradation under sunlight irradiation, showed a signifi-cantly higher efficiency of Cu-doped samples than that of pure TiO 2 . The X-ray diffraction results showed the pres-ence of anatase phase for samples prepared at 400 and 500 °C. No crystalline CuSO 4 phase was detected below 500 °C. It was also found that doping decreases the crys-tallite size in the (004) and (101) directions. Infrared spectroscopy results indicated that the chemical environ-ment of sulfate changes as a function of thermal treatment, and UV–vis spectra showed that the band gap decreases with thermal treatment and Cu doping, showing the lowest value for the 400 °C sample. X-ray absorption fine struc-ture measurements and analysis refinements revealed that even after thermal treatment and photocatalytic assays, the Cu 2? local order is similar to that of CuSO 4 , containing, however, oxygen vacancies. X-ray photoelectron spec-troscopy data, limited to the near surface region of the catalyst, evidenced, besides CuSO 4 , the presence of Cu 1? and CuO phases, indicating the active role of Cu in the TiO 2 lattice.
[Show abstract][Hide abstract] ABSTRACT: Mn-incorporated Fe3O4 photocatalysts were prepared by a simple co-precipitation method. Photocatalytic discoloration of Methylene Blue (MB) was used to evaluate the performance of these catalysts. The DSC results have shown that the insertion of Mn into Fe3O4 lattice has increased converting Fe3O4 to γ-Fe2O3. This is accompanied by a decrease of surface area and of crystallinity, as detected by XRD. The analysis of the chemical environment by XPS has shown that Mn2+ replaces Fe2+ preferentially in the octahedral sites while Mn3+ replaces Fe3+ of inverse spinel sites. The Mn-incorporated samples were significantly more efficient in MB discoloration assisted by UVA irradiation and H2O2. It was also found that ascorbic acid prevents H2O2 decomposition, by scavenging preferentially OOH radicals produced at Mn sites. Finally, the results reported here can contribute for a better comprehension of the activity of composite catalysts and the design of efficient systems for discoloration of organic pollutants.
[Show abstract][Hide abstract] ABSTRACT: In this work the effect of doping concentration and depth profile of Cu atoms on the photocatalytic and surface properties of TiO(2) films were studied. TiO(2) films of about 200 nm thickness were deposited on glass substrates on which a thin Cu layer (5 nm) was deposited. The films were annealed during 1s to 100°C and 400°C, followed by chemical etching of the Cu film. The grazing incidence X-ray fluorescence measurements showed a thermal induced migration of Cu atoms to depths between 7 and 31 nm. The X-ray photoelectron spectroscopy analysis detected the presence of TiO(2), Cu(2)O and Cu(0) phases and an increasing Cu content with the annealing temperature. The change of the surface properties was monitored by the increasing red-shift and absorption of the ultraviolet-visible spectra. Contact angle measurements revealed the formation of a highly hydrophilic surface for the film having a medium Cu concentration. For this sample photocatalytic assays, performed by methylene blue discoloration, show the highest activity. The proposed mechanism of the catalytic effect, taking place on Ti/Cu sites, is supported by results obtained by theoretical calculations.
Journal of hazardous materials 12/2010; 184(1-3):273-80. · 4.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, we study the effect of doping depth profile on the photocatalytic and surface properties of TiO2 films. Two thin film layers of TiO2 (200nm) and Co (5nm), respectively, were deposited by physical evaporation on glass substrate. These films were annealed
for 1s at 100 and 400°C and the Co layer was removed by chemical etching. Atomic force microscopy (AFM) phase images showed
changes in the surface in function of thermal treatment. The grazing-incidence X-ray fluorescence (GIXRF) measurements indicated
that the thermal treatment caused migration of Co atoms to below the surface, the depths found were between 19 and 29nm.
The contact angle showed distinct values in function of the doped profile or Co surface concentration. The UV–vis spectra
presented a red shift with the increasing of thermal treatment. Photocatalytical assays were performed by methylene blue discoloration
and the higher activity was found for TiO2–Co treated at 400°C, the ESI-MS showed the fragments formed during the methylene blue decomposition.
Journal of Materials Science 01/2010; 45(20):5698-5703. · 2.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In order to evaluate the interactions between Au/Cu atoms and clean Si(111) surface, we used synchrotron radiation grazing incidence X-ray fluorescence analysis and theoretical calculations. Optimized geometries and energies on different adsorption sites indicate that the binding energies at different adsorption sites are high, suggesting a strong interaction between metal atom and silicon surface. The Au atom showed higher interaction than Cu atom. The theoretical and experimental data showed good agreement.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 07/2009; 74(1):292-6. · 1.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The rhizobacterium Paenibacillus macerans was grown in tryptic soy broth and after separating the cells by centrifugation the activity of fractions of the supernatant
was tested against Meloidogyne exigua juveniles. From HPLC analyses and spectral data, the most active fractions were found to contain alanine, glutamic acid,
glycine, histidine, threonine and valine, which were probably produced by bacterial hydrolysis of proteic nutrients. Amino
acids from commercial sources were then assayed to confirm these results and to evaluate their potential for the control of
nematodes. LC50 of 26 and 283μg ml−1 were shown for the nematicide aldicarb and L-cysteine respectively when tested on M. exigua juveniles. At a concentration 38.4 times>LC50, the amino acid diminished the nematode population on coffee plants to values statistically equal to those obtained with
aldicarb at a concentration 19.2 times>LC50.
European Journal of Plant Pathology 01/2009; 124(1):57-63. · 1.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A series of Nb-containing hematites, Fe2−xNbxO3 (%Nb=0.00, 1.49, 5.00 and 9.24) was prepared using the conventional co-precipitation method. Mössbauer and temperature-programmed reduction (TPR) measurements suggested the formation of the crystalline phase with partial substitution of Fe3+ by Nb5+ in the structure. N2 adsorption/desorption revealed that the presence of Nb has a remarkable effect on the textural properties of the material with an increase in the BET surface area. The reactivity of Fe2−xNbxO3 was investigated using the oxidation of the methylene blue dye used as a model pollutant. The obtained results showed that the presence of Nb seems not to act directly promoting the H2O2 decomposition, but improving the dye oxidation. The analysis using the ESI-MS technique showed partial oxidation observed through different intermediates before the mineralization. This suggests the use of Nb-doped hematite as an efficient catalyst in degradation reactions in the presence of H2O2 or ultraviolet light.
Applied Catalysis A General 01/2009; 357(1):79-84. · 3.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: a b s t r a c t Novel materials based on niobia (Nb 2 O 5) destined to oxidize an organic compound in aqueous medium via heterogeneous photocatalysis after chemical modification were synthesized. Niobia was modified by the doping with molybdenum or tungsten and also treated with H 2 O 2 . The analysis of the products from methylene blue dye oxidation, with electrospray ionization mass spectrometry, showed that the dye was successively oxidized to different intermediate compounds. These results strongly suggest that the oxidation of the organic dye involves oxidizing species mainly generated after the modification of the niobia with Mo or W and also the previous treatment with H 2 O 2 .
Applied Catalysis B Environmental 10/2008; 83:169. · 5.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Since the methanol extract of Lantana lilacina leaves collected in the city of Lavras (MG, Brazil) showed antibacterial properties in a preliminary study, a fractionation process guided by agar diffusion assays with Aeromonas hydrophila, Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus was carried out to purify and identify the active compounds. After solvent partition and several chromatographic steps, [ß-3,4-dihydroxyphenyl)-ethyl]-(3'-O-α-L-rhamnopyranosyl)-(4'- O-cafeoyl)-β-D-glycopyranoside, known as acteoside, was isolated. The minimal inhibition concentration and the minimal bactericidal concentration of such substance against A. hydrophila, B. subtilis, P. aeruginosa and S. aureus were 0.12, 1.00, 1.00 and 0.25 mg/mL, respectively.
Revista Brasileira de Farmacognosia 01/2008; 18(2). · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A screening was conducted with 26 plants collected in the Brazilian southeast region, to identify plant extracts with antibacterial properties against Aeromonas hydrophila, Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus. Initially, the agar diffusion method was employed. Then, those extracts presenting activity were submitted to a broth microdilution assay to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). It was observed that 13 of the tested extracts showed antibacterial activity. The best results were obtained with those from Lantana lilacina and Phyllanthus tenellus.
[Show abstract][Hide abstract] ABSTRACT: 2007. Atividade de carboidrato purificado a partir da cebola (Allium cepa L.) e de carboidratos comerciais sobre juvenis de Meloidogyne exigua Goeldi. Com vistas a identificar as substâncias ativas contra Meloidogyne exigua presentes em uma fração do extrato metanólico de cebola (Allium cepa), eluiu-se a referida fração por meio de coluna de sílica gel, o que resultou na purificação de uma substância ativa. Após análises por espectrometria de massas e por ressonância magnética nuclear de 1 H e 13 C, ela foi identificada como sacarose. Quando juvenis do segundo estádio (J 2) de M. exigua foram expostos durante 72 h a uma solução aquosa da substância isolada na concentração de 1.200 μg/ ml, observaram-se 85,5 % de mortes dos indivíduos, que é um valor estatisticamente igual ao obtido nas mesmas condições para o nematicida aldicarbe a 50 μg/ ml. Com vistas a corroborar os resultados, submeteu-se sacarose obtida de fonte comercial, bem como outros carboidratos e análogos, na concentração de 1.250 μg/ ml, a teste in vitro com J 2 de M. exigua nas mesmas condições. A sacarose causou mortes de 71,7 % de J 2 . Dentre as outras substâncias estudadas, as mais ativas foram lactose, manitol, D-galactose, ácido poligalacturônico e D-ácido lactoglucurônico, que, nas mesmas condições, causaram mortes de 70,7, 69,2, 65,0, 64,2, e 63,0 % de J 2 , respectivamente. Palavras-chaves: Meloidogyne exigua, sacarose, carboidrato, nematicida.. 2007. Activity against Meloidogyne exigua Goeldi by a carbohydrate isolated from onion (Allium cepa L.) and by commercially available carbohydrates and analogs. To identify the substances active against Meloidogyne exigua present in a fraction of the methanol extract of onion (Allium cepa), that fraction was eluted through a silica gel column, which resulted on the purification of an active substance. After analysis by mass spectrometry and 1 H and 13 C nuclear magnetic resonance, it was identified as sucrose. Mortality of 85.5 % was obtained after exposing M. exigua second stage juveniles (J 2) during 72 h to an aqueous solution of that substance at 1,200 μg/ ml. This mortality was statistically identical to the one obtained with the nematicide aldicarb at 50 μg/ ml, under the same conditions. In order to confirm these results, sucrose from commercial source, as well as other carbohydrates and analogs, at 1,250 μg/ ml, were submitted to the in vitro trial with M. exigua J 2 under the same conditions. Sucrose caused 71.7 % deaths. Among the other substances studied, the most active were lactose, manitol, D-galactose, polygalacturonic acid and D-lactoglucuronic acid, which caused the death of 70.7, 69.2, 65.0, 64.2 and 63.0 % J 2 , respectively.
[Show abstract][Hide abstract] ABSTRACT: In this work, we studied the photocatalytic and the structural aspects of silicon wafers doped with Au and Cu submitted to
thermal treatment. The materials were obtained by deposition of metals on Si using the sputtering method followed by fast
heating method. The photocatalyst materials were characterized by synchrotron-grazing incidence X-ray fluorescence, ultraviolet-visible
spectroscopy, X-ray diffraction, and assays of H2O2 degradation. The doping process decreases the optical band gap of materials and the doping with Au causes structural changes.
The best photocatalytic activity was found for thermally treated material doped with Au. Theoretical calculations at density
functional theory level are in agreement with the experimental data.
Journal of Materials Science 44(4):1029-1034. · 2.31 Impact Factor