Romeu C. Rocha-Filho

Universidade Federal de São Carlos, São Carlos do Pinhal, São Paulo, Brazil

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Publications (91)139.11 Total impact

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    ABSTRACT: Oxidation of anthraquinonic dye Acid Blue 62 by electrolysis with conductive-diamond electrodes is studied in this work. COD, TOC, and color have been selected to monitor the degradation of the molecule as a function of several operating inputs (current density, pH, temperature, and NaCl concentration). Results show that the electrochemical oxidation of this model of large molecules follows a first order kinetics in all the conditions assessed, and it does not depend on the pH and temperature. The occurrence of chloride ions in wastewaters increases the rate of color and COD removal as a consequence of the mediated oxidation promoted by the chlorinated oxidizing species. However, chloride occurrence does not have an influence on the mineralization rate. First-order kinetic-constants for color depletion (attack to chromophores groups), oxidation (COD removal), and mineralization (TOC removal) were found to depend on the current density and to increase significantly with its value. A single model was proposed to explain these changes in terms of the mediated oxidation processes. Rate of mineralization remained very close to that expected for a purely mass transfer-controlled process. This was explained assuming that mediated oxidation does not have a significant influence on the mineralization in spite it has some effect on intermediate oxidation stages. The efficiency of the oxidation was found to depend mainly on the concentration of COD being negligible the effect of the other inputs assessed except for the occurrence of chloride ions. Opposite, the efficiency of mineralization depends on concentration of TOC and current density and it did not depend on the chloride occurrence. This observation was found to have an important influence on the power required to remove a given percentage of the initial TOC or COD. To decrease COD efficiently, the occurrence of chloride in the solution is very important, while to remove TOC efficiently, it is more important to work at low current densities and chloride effect is negligible. Energy consumption could be decreased by folds using the proper conditions.
    Environmental Science and Pollution Research 03/2014; · 2.76 Impact Factor
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    ABSTRACT: Hybrid thermal heating induced by a microwave oven was unprecedentedly used to successfully attain rapid and facile crystallization into the anatase phase of amorphous TiO2 nanotubes grown on a Ti substrate. Amorphous TiO2 nanotubes were obtained by anodic oxidation of a Ti foil either in aqueous or organic medium. Afterward, these TiO2 nanotubes were thermally treated by hybrid heating in a common commercial microwave oven. The as-grown amorphous nanotubes were characterized by SEM and XRD, whereas the evolution of the nanotubes crystallization with thermal treatment time was followed by XRD. The crystallization into the anatase phase of the amorphous TiO2 nanotubes occurred after only 2 or 3 min of hybrid thermal treatment, which is very short and convenient as compared with several hours that are needed when conventional thermal treatment is used.
    Materials Letters. 01/2014; 126:52–54.
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    ABSTRACT: The electrochemical degradation of a real textile effluent was carried out using Ti–Pt/β-PbO2 and Ti/Ti0.7Ru0.3O2 (DSA®) anodes in a filter-press flow cell, in the presence and absence of chloride ions, varying the pH (3, 7, 11) and temperature (25 °C and 45 °C) of the effluent, and monitoring the removal of its turbidity and chemical oxygen demand (COD). The best experimental conditions for turbidity and COD removal were attained in neutral and basic conditions, independently of temperature. Higher COD removal values were attained with the Ti–Pt/β-PbO2 anode, as a consequence of its higher oxidation power; the electric charge applied per unit volume of effluent significantly decreased in the presence of chloride ions, when instantaneous current efficiencies as high as 0.5 were attained in the initial electrooxidation stages. Under these conditions, the electric energy consumption necessary to oxidize the real textile effluent was as low as 50 kW h m−3. The use of chloride ions enabled higher COD removal efficiencies using the Ti–Pt/β-PbO2 and DSA® anodes than a purely mass-transport controlled process due to indirect oxidation processes mediated by the active chloro species.
    Chemical Engineering Journal. 01/2014; 251:138–145.
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    ABSTRACT: The growth of oxides on the surfaces of pure Ti and two of its ternary alloys, Ti-6Al-4V and Ti-6Al-7Nb, by micro-arc oxidation (MAO) in a pH 5 phosphate buffer was investigated. The primary aim was to form thick, porous, and aluminum-free oxide layers, because these characteristics favor bonding between bone and metal when the latter is implanted in the human body. On Ti, Ti-6Al-4 V, and Ti-6Al-7Nb, the oxides exhibited breakdown potentials of about 200 V, 130 V, and 140 V, respectively, indicating that the oxide formed on the pure metal is the most stable. The use of the MAO procedure led to the formation of highly porous oxides, with a uniform distribution of pores; the pores varied in size, depending on the anodizing applied voltage and time. Irrespective of the material being anodized, Raman analyses allowed us to determine that the oxide films consisted mainly of the anatase phase of TiO2, and XPS results indicated that this oxide is free of Al and any other alloying element.
    Materials Science and Engineering: C. 01/2014; 41:343–348.
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    ABSTRACT: The room-temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate, BMIM BF4, was employed as electrolyte in the electrosynthesis of thin polypyrrole (PPy) films on a Pt substrate, and the resulting PPy electrodes were electrochemically characterized. Electrochemical impedance spectroscopy (EIS) was used to comparatively investigate the electric behavior of PPy produced in the RTIL and the one produced in a traditional acetonitrile/lithium salt system, and charge–discharge curves in the range 2.0–4.0 V (vs. Li/Li+) were obtained in a 1.0 M LiBF4 propylene carbonate solution. Although a reduction of the specific capacity for the PPy obtained in the RTIL was observed, compared to that of the PPy film synthesized in the acetonitrilic electrolyte, its chronopotentiometric profile presented a plateau in the 2.7 V region. This is a remarkable result, considering that a linear decrease in this profile is usually observed for the majority of conducting polymer cathodes. PPy films obtained in BMIM BF4 presented globular morphology, with a special arrangement of nanoparticles constituting the globules; the EIS results indicated that this nanoscale structure may be contributing to a better definition of the redox characteristics during the PPy charge–discharge processes, as it happens for the well-organized structure of some metal oxides.
    Materials Chemistry and Physics. 01/2014; 147(s 1–2):99–104.
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    Journal of Electroanalytical Chemistry. 01/2014;
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    ABSTRACT: We report on the use of flow injection analysis with amperometric detection (FIA-EC) to evaluate the potential of using diamond electrodes for the analysis of three estrogenic compounds: estrone, 17-β-estradiol, and estriol. Amperometric detection was performed using a cathodically pretreated boron-doped diamond electrode that offered low background current, relatively low limits of detection, and good response reproducibility and stability. For all three compounds, response linearity was observed over the concentration range tested, 0.10 to 3.0μmolL(-1), the sensitivity was ca. 10mALmol(-1), and the minimum concentration detection (S/N≥3) was 0.10μmolL(-1) (~27μgL(-1)). The response variability with multiple injections was ca. 10% (RSD) over 20 injections. For estrone, the oxidation reaction on diamond does not proceed through an adsorbed state like it does on glassy carbon. After an initial current attenuation, the diamond electrode exhibited a stable response (oxidation current) for 3 days of continuous use, indicative of minimal surface contamination or fouling by reaction intermediates and products. The method for estrone was assessed using spiked city tap and local river water. Estrone recoveries in spiked city and river water samples presented standard deviations of less than 10%. In summary, the FIA-EC method with a diamond electrode enables sensitive, reproducible, stable, quick, and inexpensive determination of estrogenic compounds in water samples.
    Talanta 01/2014; 126:12–19. · 3.50 Impact Factor
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    ABSTRACT: Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CNx) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CNx electrode. Thus, an a-CNx film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1molL(-1) KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CNx electrode were 0.0656μmolL(-1) for DA and 1.05μmolL(-1) for AA, whereas with the BDD electrode these values were 0.283μmolL(-1) and 0.968μmolL(-1), respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CNx electrode in electroanalysis.
    Analytica chimica acta 10/2013; 797:30-9. · 4.31 Impact Factor
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    ABSTRACT: A simple procedure is described for the determination of propylthiouracil (PTU) by differential pulse voltammetry (DPV) using a cathodically pretreated boron-doped diamond (BDD) electrode. Cyclic voltammetry studies indicate that the oxidation of PTU is irreversible at a peak potential of 1.42 V (vs. Ag/AgCl (3.0 mol L-1 KCl)) in a Britton-Robinson (BR) buffer solution (pH 2.0). Under optimized conditions, the obtained analytical curve was linear (r = 0.9985) for the PTU concentration range of 1.0 to 29.1 mmol L-1 in a BR buffer solution (pH 2.0), with a detection limit of 0.90 mmol L-1. The proposed method was successfully applied in the determination of PTU in pharmaceutical samples, with results in agreement at a 95% confidence level with those obtained using an official titration method.
    Journal of the Brazilian Chemical Society 09/2013; 24(9):1504-1511. · 1.28 Impact Factor
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    ABSTRACT: Carbon fiber (CF) composites of organometallic intercalated polyaniline (Pani) and polypyrrole (Ppy) doped with polystyrene sulfonate (PSS) were electrochemically synthesized and tested as electrodes for lithium-ion batteries. From the results obtained by cyclic voltammetry, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy, it was concluded that the incorporation of copper(II) ions in the polymeric composite was successfully attained by adsorption of Cu2+ ions and 2,5-dimercapto-1,3,4-thiadiazole (DMcT) monomers on the carbon microfibers. The experimental electrochemical impedance response of the obtained Pani(DMcT–Cu ion)/CF composite was simulated by adequate equivalent electrical circuits. After 20 charge/discharge cycles, the experimental discharge specific capacity of the Pani(DMcT–Cu ion)/CF composite was 118 mA h g−1 (100% coulombic efficiency) using a 1 mol L−1 LiClO4 solution in propylene carbonate, and 110 mA h g−1 when a polymeric electrolyte was used. In the charge/discharge tests of the Ppy-PSS/Pani/CF composite as anode, a high discharge specific capacity of 225 mA h g−1 was obtained after 20 cycles. The resulting Ppy-PSS/Pani/CF/polymeric electrolyte/Pani(DMcT–Cu ion)/CF battery presented a specific capacity of 62 mA h g−1 and could be charged up to 2.0 V, yielding an energy density 425 W h g−1, with a coulombic efficiency of about 98%.
    Materials Chemistry and Physics. 04/2013; 139(1):47–54.
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    ABSTRACT: The determination of bezafibrate (BZF) using square-wave voltammetry (SWV) and a cathodically pretreated boron-doped diamond electrode is proposed. Cyclic voltammetry results showed one irreversible oxidation peak for BZF at 1.20V (vs. Ag/AgCl (3.0molL(-1) KCl)) in a 0.04molL(-1) Britton-Robinson (BR) buffer solution (pH 2.0). Under optimized SWV conditions, a linear analytical curve is obtained for the BZF concentration range 0.10-9.1μmolL(-1) in the BR buffer solution (pH 2.0), with a detection limit of 0.098μmolL(-1). The obtained recoveries range from 93.4 to 108%. The proposed novel method was successfully applied in the determination of the BZF content in several pharmaceutical formulations (tablets) and the results are in close agreement (at a 95% confidence level) with those obtained using a comparative spectrophotometric method.
    Talanta 01/2013; 103:201-6. · 3.50 Impact Factor
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    ABSTRACT: The anodic oxidation of estrone was comparatively investigated at glassy carbon (GC), nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) and boron-doped diamond (BDD) electrodes. The ta-C:N and BDD electrodes are characterized by a wider working potential window and lower background current that that for GC. The latter is because of a reduced level of pseudocapacitance on the former electrodes due to the absence of significant levels of redox-active surface carbon-oxygen functionalities. The irreversible oxidation of estrone was recorded as a similar potential for all three electrodes (0.9-0.95 V) in 0.5 mol L-1 H2SO4. The voltammetric peak current decreased some for all the electrodes with potential cycling suggestive of some response attenuation by reaction product adsorption (or slow desorption). From the dependence of the oxidation peak potential and current with solution pH, it was possible to conclude that the electrooxidation of estrone involves the transfer of two electrons accompanied by the loss of two protons at pH < 10. Voltammetric and chronocoulometric data indicated the oxidation reaction kinetics on all three electrodes were under mixed control by both diffusion and adsorption. This was most apparent for GC where estrone adsorption was greatest (145 pmol cm-2). The greater adsorption on GC can be explained by electronic and or chemical effects associated with the graphitic edge plane sites. In contrast, the estrone adsorption on ta–C:N and BDD was significantly lower, about 1/10 of that on GC. This behavior is due to the differences in the types and density of functional groups and the absence of an extended π–electron system in both materials. In summary, the here-reported properties of the ta–C:N and BDD electrodes suggest that both could be excellent candidates for electroanalytical measurements involving the detection and/or determination of estrone and similar hormones.
    Journal of Electroanalytical Chemistry. 01/2013;
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    ABSTRACT: A single-line flow injection system and multiple pulse amperometric detection using a boron-doped diamond electrode were employed to develop and optimize a simple, low-cost, and rapid method for the simultaneous determination of two pairs of food colorants: tartrazine and sunset yellow (TT-SY) or brilliant blue and SY (BB-SY). A dual-potential waveform was used: E(det.1)=-150mV (400ms duration) and E(det.2)=-450mV (100ms duration) vs. Ag/AgCl (3.0molL(-1) KCl). Polarization at E(det.1) or E(det.2) causes reduction of SY or the respective pair of colorants, TT-SY or BB-SY; hence, with proper current correction, both colorants in each pair can be determined. The obtained linear response ranges (detection limits) were 5.0-60.0 (2.5) and 1.0-50.0 (0.80)μmolL(-1), for TT and SY, or 5.0-60.0 (3.5) and 1.0-50.0 (0.85)μmolL(-1), for BB and SY, respectively. Investigation of possible interferents (other food colorants or additives) showed no significant interference with the methods here proposed, which were then used to simultaneously determine the pairs of colorants in industrialized food samples, with results that showed good agreement with those obtained using a comparative HPLC method.
    Talanta 09/2012; 99:883-9. · 3.50 Impact Factor
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    ABSTRACT: Differential pulse voltammetry (DPV) and a cathodically pretreated boron-doped diamond (BDD) electrode were used to simultaneously determine two pairs of synthetic food colorants commonly found mixed in food products: tartrazine (TT) and sunset yellow (SY) or brilliant blue (BB) and sunset yellow (SY). In the DPV measurements using the BDD electrode, the reduction peak potentials of TT and SY or BB and SY were separated by about 150 mV. The detection limit values obtained for the simultaneous determination of TT and SY or BB and SY were 62.7 nmol L(-1) and 13.1 nmol L(-1) or 143 nmol L(-1) and 25.6 nmol L(-1), respectively. The novel proposed voltammetric method was successfully applied in the simultaneous determination of these synthetic colorants in food products, with results similar to those obtained using a HPLC method at 95% confidence level.
    Talanta 08/2012; 97:291-7. · 3.50 Impact Factor
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    ABSTRACT: Tyrosinase (Tyr)-based biosensors might be interesting devices for fast analytical screening of phenols, espe-cially if gold nanoparticles (AuNPs) are used as mediators of the direct electron transfer (DET) reaction be-tween enzyme and electrode substrate. Therefore, by immobilizing Tyr on AuNPs electrodeposited on a boron-doped diamond (BDD) electrode. The best conditions (applied potential and deposition time) to elec-trodeposit AuNPs on BDD were selected by factorial design; homogeneously distributed quasi-spherical AuNPs (33 nm average diameter) were obtained by applying − 0.4 V vs. Ag/AgCl (3 M KCl) for 40 s. Then, Tyr was immobilized on AuNPs previously modified using cystamine and glutaraldehyde. The occurrence of DET between the electrode surface and the Tyr active site was verified by cyclic voltammetry, yielding the fol-lowing parameter values: formal redox potential, 115 mV vs. Ag/AgCl (3 M KCl); transfer coefficient, 0.45; het-erogeneous electron transfer rate constant, 0.032 s − 1 . Using square-wave voltammetry (SWV), a sensitive electrochemical reduction of phenol was attained: concentration range, 0.10–11.0 μM; detection limit, 0.07 μM; intra-day and inter-day repeatability RSDs, 3.4% and 4.24%, respectively; reasonably good stability (only 15% response decrease after 30 days). Furthermore, the obtained apparent Michaelis–Menten kinetic constant for phenol (13.0 μM) is quite good when compared to the ones reported in the literature. Hence, the developed Tyr-AuNPs/BDD biosensor exhibits good sensitivity, stability, and reproducibility for the deter-mination of phenol by SWV.
    Diamond and Related Materials 04/2012; · 1.71 Impact Factor
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    ABSTRACT: Tyrosinase biosensor Enzyme electrode direct electron transfer Gold nanoparticle electrodeposition Phenol determination Tyrosinase (Tyr)-based biosensors might be interesting devices for fast analytical screening of phenols, espe-cially if gold nanoparticles (AuNPs) are used as mediators of the direct electron transfer (DET) reaction be-tween enzyme and electrode substrate. Therefore, by immobilizing Tyr on AuNPs electrodeposited on a boron-doped diamond (BDD) electrode. The best conditions (applied potential and deposition time) to elec-trodeposit AuNPs on BDD were selected by factorial design; homogeneously distributed quasi-spherical AuNPs (33 nm average diameter) were obtained by applying − 0.4 V vs. Ag/AgCl (3 M KCl) for 40 s. Then, Tyr was immobilized on AuNPs previously modified using cystamine and glutaraldehyde. The occurrence of DET between the electrode surface and the Tyr active site was verified by cyclic voltammetry, yielding the fol-lowing parameter values: formal redox potential, 115 mV vs. Ag/AgCl (3 M KCl); transfer coefficient, 0.45; het-erogeneous electron transfer rate constant, 0.032 s − 1 . Using square-wave voltammetry (SWV), a sensitive electrochemical reduction of phenol was attained: concentration range, 0.10–11.0 μM; detection limit, 0.07 μM; intra-day and inter-day repeatability RSDs, 3.4% and 4.24%, respectively; reasonably good stability (only 15% response decrease after 30 days). Furthermore, the obtained apparent Michaelis–Menten kinetic constant for phenol (13.0 μM) is quite good when compared to the ones reported in the literature. Hence, the developed Tyr-AuNPs/BDD biosensor exhibits good sensitivity, stability, and reproducibility for the deter-mination of phenol by SWV.
    Diamond and Related Materials 03/2012; · 1.71 Impact Factor
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    ABSTRACT: A combined chemical-electrochemical oxidation method to obtain porous bioactive TiO2 films on titanium is reported. In this case, a titanium chemical pre-etching followed by the micro-arc oxidation (MAO) treatment is proposed and optimized, to obtain a high-roughness and porous surface which benefits the titanium/bone integration. The MAO treatment at various rates (different current densities) allowed to define the influence of the oxide growth rate on the surface morphology and to design the best features for each case. Titanium samples were pre-etched using a 2% HF solution as a function of the etching time, and then anodized by the MAO treatment in a 0.5 M H3PO4 solution at current densities in the 10 to 90 mA.cm–2 range. High porosity (0.5 to 1 µm-diameter pores) and higher phosphorous content for TiO2 films were achieved by first etching the Ti sample for 180 seconds in the HF solution, and then applying current densities in the 80 to 90 mA.cm–2 range for the micro-arc oxidation process.
    Materials Research 02/2012; 15(1):159-165. · 0.52 Impact Factor
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    ABSTRACT: The removal of Pb2+ ions from dilute solutions was investigated under galvanostatic conditions using a membrane-less flow-through cell with stainless steel wool (SSW) electrodes. The response surface methodology (independent variables: electric current and volumetric flow rate) was used to find the optimal conditions for Pb2+ removal from 2 L of an aqueous solution of 50 mg L-1 Pb(NO3)2 in 0.10 mol L-1 NaNO3 + 0.10 mol L-1 H3BO3 (pH 4.8). The obtained response surfaces revealed that the volumetric flow rate (59-341 L h-1) does not substantially affect the Pb2+ removal process. On the other hand, the electric current increase led to higher Pb2+ removal, with significantly improved values of specific energy consumption and current efficiency when compared with those reported in the literature. For an experiment carried out in the optimum-condition region (70 mA and 200 L h-1), a Pb2+ conversion of 99.6% was attained after 90 min of electrolysis. The use of the membrane-less flow-through cell with SSW electrodes, besides being significantly more energy efficient, led to Pb2+ removal on both electrodes, but predominantly in the SSW anode, on which more than 95% of the Pb2+ ions were converted to PbO2.
    Journal of the Brazilian Chemical Society 09/2011; 22(9):1686-1694. · 1.28 Impact Factor
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    ABSTRACT: Constant current electrolyses are carried out in a filter-press reactor using a boron-doped diamond (Nb/BDD) or a Ti-Pt/β-PbO(2) anode, varying current density (j) and temperature. The degradation of the real textile effluent is followed by its decolorization and chemical oxygen demand (COD) abatement. The effect of adding NaCl (1.5 g L(-1)) on the degradation of the effluent is also investigated. The Nb/BDD anode yields much higher decolorization (attaining the DFZ limit) and COD-abatement rates than the Ti-Pt/β-PbO(2) anode, at any experimental condition. The best conditions are j = 5 mA cm(-2) and 55 °C, for the system's optimized hydrodynamic conditions. The addition of chloride ions significantly increases the decolorization rate; thus a decrease of more than 90% of the effluent relative absorbance is attained using an applied electric charge per unit volume of the electrolyzed effluent (Q(ap)) of only about 2 kA h m(-3). Practically total abatement of the effluent COD is attained with the Nb/BDD anode using a Q(ap) value of only 7 kA h m(-3), with an energy consumption of about 30 kW h m(-3). This result allows to conclude that the Nb/BDD electrode might be an excellent option for the remediation of textile effluents.
    Journal of hazardous materials 07/2011; 192(3):1275-82. · 4.14 Impact Factor
  • 06/2011: pages 181 - 212; , ISBN: 9781118062364

Publication Stats

367 Citations
139.11 Total Impact Points

Institutions

  • 1987–2014
    • Universidade Federal de São Carlos
      • • Departamento de Química (DQ)
      • • Centro de Ciências Exatas e de Tecnologia (CCET)
      São Carlos do Pinhal, São Paulo, Brazil
  • 2009
    • University of São Paulo
      • Instituto de Química de São Carlos (IQSC)
      São Paulo, Estado de Sao Paulo, Brazil