Hudson W. P. Carvalho

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

Are you Hudson W. P. Carvalho?

Claim your profile

Publications (23)48.28 Total impact

  • Applied Catalysis B Environmental 11/2014; s 160–161:188–199. · 5.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Maghemite (γ-Fe2O3)-poly(methyl methacrylate) (PMMA) nanocomposites were prepared by grafting 3-(trimethoxy-silyl) propyl methacrylate on the surface of maghemite nanoparticles, this process being followed by methyl methacrylate radical polymerization. Three different hybrids with 0.1, 0.5, and 2.5 wt% of maghemite nanoparticles were studied. The results indicate that these nanocomposites consist of a homogeneous PMMA matrix in which maghemite nanoparticles with a bimodal size distribution are embedded. The existence of covalent bonding between silane monomers and atoms on the maghemite surface was evidenced. AFM images showed a clear increase in surface roughness for increasing maghemite content. The thermal stability of PMMA-maghemite nanocomposites is higher than that of pure PMMA and increases for increasing maghemite content. The results of our theoretical studies indicate that the electron density in the maghemite nanoparticle is not homogenous, the low electron density volumes being supposed to be radical trappers during PMMA decomposition, thus acting as a thermal stabilizer. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers
    Polymer Composites 07/2014; · 1.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: PMMA-polysilsesquioxane (PMMA-Sil) class II organic-inorganic hybrids were prepared by the sol-gel method from a PMMA-based polymer precursor containing trimethoxysilane groups. An analysis was made of the effect of siloxane content, adjusted by addition of tetraethyl orthosilicate (TEOS), on the structure and thermal stability of the dried gels. 13C nuclear magnetic resonance measurements confirmed PMMA as the organic phase, while 29Si measurements revealed the presence of both T and Q silicon species, the most abundant being T2 and Q3. X-ray diffraction results showed that the inorganic SiO2 phase was amorphous, while small angle X-ray scattering analyses indicated that the average gyration radius size of the silicate particles and the correlation distance between the particles increased with greater addition of TEOS. Thermal stability was improved by increasing the amount of the inorganic phase. This effect was more evident under an air atmosphere than under N2, indicating that the silicate phase acted to limit oxygen diffusion.
    Polymer Degradation and Stability 06/2014; · 2.77 Impact Factor
  • [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.
    Langmuir 03/2014; 30(13):3857. · 4.38 Impact Factor
  • Source
    [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: The structure and the thermodegradation behavior of both poly(methyl methacrylate)-co-poly(3-tri(methoxysilyil)propyl methacrylate) polymer modified with silyl groups and of intercalated poly(methyl methacrylate)-co-poly(3-tri(methoxysilyil)propyl methacrylate)/Cloisite 15A™ nanocomposite have been in situ probed. The structural feature were comparatively studied by Fourier transform infrared spectroscopy (FTIR), 13C and 29Si nuclear magnetic resonance (NMR), and small angle X-ray scattering (SAXS) measurements. The intercalation of polymer in the interlayer galleries was evidenced by the increment of the basal distance from 31 to 45 Å. The variation of this interlayer distance as function of temperature was followed by in situ SAXS. Pristine polymer decomposition pathway depends on the atmosphere, presenting two steps under air and three under N2. The nanocomposites are more stable than polymer, and this thermal improvement is proportional to the clay loading. The experimental results indicate that clay nanoparticles play several different roles in polymer stabilization, among them, diffusion barrier, charring, and suppression of degradation steps by chemical reactions between polymer and clay. Charring is atmosphere dependent, occurring more pronounced under air. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
    Polymer Engineering and Science 06/2013; 53(6). · 1.24 Impact Factor
  • Source
    [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: We report on a novel transparent, flexible, rubbery, and insoluble tri-ureasil organic–inorganic hybrid material with multifunctional characteristics and potential application in drug delivery, water purification, and photochromic materials. We obtained the tri-ureasil gels by the one-pot sol–gel route using 3-isocyanatopropyltriethoxysilane and glyceryl poly(oxypropylene)triamine of molecular weight 5000 g mol−1 (Jeffamine® T5000). This approach generated a silica backbone covalently connected with poly(oxyalkylene) chains PPO(OCH–CH3CH2)n through urea bridges. We characterized the obtained materials by DSC, swelling tests, XRD, 29Si NMR, and small-angle X-ray scattering (SAXS). The results attested that the tri-ureasil hybrids are potentially applicable as photochromic devices, drug delivery systems, and adsorbents of pollutants from contaminated waters.
    Polym. Chem. 02/2013; 4(5):1575-1582.
  • Source
    [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.
    Materials Science and Engineering B 01/2013; · 1.85 Impact Factor
  • Source
    Journal of Materials Science. 01/2013; 48(11):3904.
  • Source
    [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. · 4.33 Impact Factor
  • Source
    [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 10/2010; 45(20):5698-5703. · 2.31 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Fractionation of the methanolic extract from Gochnatia barrosii Cabrera (Asteraceae) leaves resulted in the isolation of the flavonol glycoside trans-tiliroside [kaempferol 3-O- -D-(6''-O-E-p-coumaroyl)-glucopyranoside], which had never been found in such plant species. Such substance at 500 μg/mL caused no in vitro effect on the mortality of second-stage juveniles of the nematode Meloidogyne exigua Goeldi.
    Ciência e Agrotecnologia 10/2010; 34(5):1224-1231. · 0.40 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A photocatalyst based on CuO/SiO2 was prepared, and evaluated for the degradation of methylene blue in aqueous medium. The photocatalyst was obtained by calcination method of copper salt, in the presence of silica. The characterization by XRD, FTIR, and TPR techniques confirmed the formation of CuO as active phase. SEM studies showed CuO deposited on the surface of SiO2. By ESI-MS, it was demonstrated that the degradation of methylene blue occurs through successive hydroxylations. Photodegradation assays showed that CuO/SiO2 was efficient for degradation, and that the material worked better in the presence of UV light.
    Environmental Chemistry Letters 01/2010; 8(1). · 1.62 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Polysaccharide natural seed coat from the tree Magonia pubescens, in the form of hydrogel was used to remove metals in aqueous solution. Swelling tests indicate that seed coat presents hydrogel behavior, with maximum water absorption of 292g water/g. Adsorption experiments performed using Na+, Mg2+, K+, Ca2+, Cr3+, Fe3+ and Zn2+ demonstrated that the polysaccharide structure has a high capacity to extract these ions from the aqueous solution. Scanning electron microscopy revealed significant morphological changes of the material before and after water contact. Differential scanning calorimetry measurements indicate a signal shift of the water evaporation temperature in the material with adsorbed zinc. X-ray photoelectron spectroscopy analysis combined with theoretical studies by the density functional theory and on Hartree–Fock (HF) level evidence that the metallic ions were adsorbed through coordination with hydroxyl groups of polysaccharide. In the case of Zn2+ the lowest HF energy was observed for the tetracoordination mode, where Zn2+ is coordinated by two hydroxyl groups and two water molecules. KeywordsHydrogel-Polysaccharide-Metallic ions-Adsorption-Hartree–Fock
    Environmental Chemistry Letters 12/2009; 8(4):343-348. · 1.62 Impact Factor
  • Source
    [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: 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. · 1.71 Impact Factor
  • Source
    [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
  • Source
    [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

Publication Stats

51 Citations
48.28 Total Impact Points

Institutions

  • 2013–2014
    • Karlsruhe Institute of Technology
      Carlsruhe, Baden-Württemberg, Germany
    • Federal University of Minas Gerais
      Cidade de Minas, Minas Gerais, Brazil
  • 2009–2013
    • São Paulo State University
      • • Institute of Chemistry
      • • Departamento de Físico Química
      San Paulo, São Paulo, Brazil
  • 2007–2010
    • Universidade Federal de Lavras (UFLA)
      • Departamento de Química
      Lavras, Minas Gerais, Brazil