Hudson W. P. Carvalho

Karlsruhe Institute of Technology, Carlsruhe, Baden-Württemberg, Germany

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Publications (14)26.76 Total impact

  • Applied Catalysis B: Environmental. 01/2014; s 160–161:188–199.
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    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
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    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.
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    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.
    Materials Science and Engineering: B. 01/2013;
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    ABSTRACT: To contribute to the development of antibacterial products from propolis produced by native Brazilian bees, twenty-nine samples of propolis collected from hives in the state of Minas Gerais, Brazil, were screened for in vitro activity against Aeromonas hydrophila, Bacillus subtilis, Pseudomonas aeruginosa, and Staphylococcus aureus. Among the samples from native Brazilian bees, only that from Frieseomelitta varia (Lepeletier, 1836) inhibited in vitro bacterial growth. Consequently, this propolis underwent fractionation by chromatographic methods monitored through Agar-diffusion assays with these bacteria, which resulted in the isolation and identification of 3,5-diprenyl-4-hydroxycinnamic acid (artepillin C), which showed MIC of 62.5 and 250 µg/mL against B. subtilis and S. aureus, respectively. This result indicates the potential of F. varia to produce therapeutic propolis.
    Ciência e Agrotecnologia 12/2011; 35(6):1043-1049. · 0.40 Impact Factor
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    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
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    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. · 2.16 Impact Factor
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    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
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    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
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    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
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    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
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    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.
    Fitoterapia 03/2007; 78(2):142-5. · 2.23 Impact Factor
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    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. · 2.16 Impact Factor
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Publication Stats

37 Citations
26.76 Total Impact Points

Institutions

  • 2013–2014
    • Karlsruhe Institute of Technology
      • Institute of Technical and Polymer Chemistry
      Carlsruhe, Baden-Württemberg, Germany
    • Federal University of Minas Gerais
      Cidade de Minas, Minas Gerais, Brazil
  • 2010–2013
    • São Paulo State University
      • Institute of Chemistry
      San Paulo, São Paulo, Brazil
  • 2007–2011
    • Universidade Federal de Lavras (UFLA)
      • Departamento de Química
      Lavras, Minas Gerais, Brazil