Pedro H C Camargo

University of São Paulo, San Paulo, São Paulo, Brazil

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Publications (69)379.41 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The synthesis of trimetallic nanoparticles represents an emerging strategy to maximize catalytic performances in noble metal-based catalysts. However, the controllable synthesis of trimetallic nanomaterials as well as the exact role played by the addition of a third metal in their composition over catalytic performances remains unclear. In this paper, we describe the synthesis of trimetallic nanoshells having AgAuPd, AgAuPt, and AgPdPt compositions by a sequential galvanic replacement reaction approach between Ag nanospheres as sacrificial templates and the corresponding metal precursors, i.e., AuCl4−(aq), PdCl42−(aq), and/or PtCl62−(aq). In each of these systems, the composition could be systematically tuned by varying the molar ratios between Ag and each metal precursor. Nanoshells having Ag56Au28Pd16, Ag78Au9Pt13, and Ag71Pd16Pt13 compositions were employed as model systems to investigate the effect of the addition of the third metal in their composition over the catalytic activities toward the 4-nitrophenol reduction. Our data demonstrate a significant enhancement in conversion percentages and thus the catalytic activities relative to the sum of their bimetallic counterparts, and this increase was dependent on the nature of the metals, corresponding to 826, 135, and 56 % for Ag56Au28Pd16, Ag78Au9Pt13, and Ag71Pd16Pt13 nanoshells relative to their bimetallic analogs. The results presented herein demonstrate the strong correlation between catalytic activity and composition in multimetallic nanoshells, and that the incorporation of a third metal may represent a promising approach to boost catalytic activities for a variety of transformations.
    Journal of Materials Science 08/2015; 50(16). DOI:10.1007/s10853-015-9114-x · 2.37 Impact Factor
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    ABSTRACT: New AgAu tadpole nanocrystals were synthesized in a one-step reaction involving simultaneous galvanic replacement between Ag nanospheres and AuCl4 (-) (aq.) and AuCl4 (-) (aq.) reduction to Au in the presence of citrate. The AgAu tadpoles display nodular polycrystalline hollow heads, while their undulating tails are single crystals. The unusual morphology suggests an oriented attachment growth mechanism. Remarkably, a 1 nm thick Ag layer was found to segregate so as to cover the entire surface of the tadpoles. By varying the nature of the seeds (Au NPs), double-headed Au tadpoles could also be obtained. The effect of a number of reaction parameters on product morphology were explored, leading to new insights into the growth mechanisms and surface segregation behavior involved in the synthesis of bimetallic and anisotropic nanomaterials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Chemistry - A European Journal 07/2015; 21(35). DOI:10.1002/chem.201501704 · 5.70 Impact Factor
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    ABSTRACT: TiO2–Au hybrid materials are promising as electrocatalysts for the in situ production of H2O2 via the oxygen reduction reaction (ORR). However, the synthesis of uniform and well-controlled TiO2–Au materials, which is crucial to establish morphology–performance relationships, remains challenging. We describe herein the synthesis of hybrid materials composed of TiO2 colloidal spheres and wires decorated with Au nanoparticles. We employed TiO2 colloidal spheres and wires as physical templates for Au deposition, which enabled the uniform deposition of Au NPs with monodisperse sizes over the TiO2 surface. Then, the electrocatalytic activities toward the electrogeneration of H2O2 by the ORR were investigated as a function of the TiO2 shape and TiO2–Au loading on Vulcan XC-72R carbon. We found that the electrocatalytic activities were strongly dependent on the TiO2 shape and TiO2–Au loading in the catalysts. The utilization of TiO2 colloidal spheres led to higher activities relative to pure carbon and commercial Pt/C, and the optimal TiO2–Au loading corresponded to 3%. Conversely, the TiO2 wires led to detrimental effects over the catalytic performances for all hybrid materials. These results could be explained based on the morphological and conductivity differences among TiO2–Au/C electrode materials. We believe the results described herein can have important implication for the design of TiO2-based hybrid nanostructures for the electrogeneration of H2O2 by the ORR.
    Journal of Catalysis 06/2015; 326. DOI:10.1016/j.jcat.2015.04.007 · 6.07 Impact Factor
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    ABSTRACT: Hybrid materials in which reduced graphene oxide (rGO) is decorated with Au nanoparticles (rGO-Au NPs) were obtained by the in situ reduction of GO and AuCl4 (-) (aq) by ascorbic acid. On laser excitation, rGO could be oxidized as a result of the surface plasmon resonance (SPR) excitation in the Au NPs, which generates activated O2 through the transfer of SPR-excited hot electrons to O2 molecules adsorbed from air. The SPR-mediated catalytic oxidation of p-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB) was then employed as a model reaction to probe the effect of rGO as a support for Au NPs on their SPR-mediated catalytic activities. The increased conversion of PATP to DMAB relative to individual Au NPs indicated that charge-transfer processes from rGO to Au took place and contributed to improved SPR-mediated activity. Since the transfer of electrons from Au to adsorbed O2 molecules is the crucial step for PATP oxidation, in addition to the SPR-excited hot electrons of Au NPs, the transfer of electrons from rGO to Au contributed to increasing the electron density of Au above the Fermi level and thus the Au-to-O2 charge-transfer process. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Chemistry - A European Journal 05/2015; DOI:10.1002/chem.201500677 · 5.70 Impact Factor
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    ABSTRACT: We describe the synthesis of AgPt hollow nanodendrites employing Ag nanospheres as seeds by combining a galvanic replacement reaction between Ag and PtCl62− and PtCl62− reduction to Pt in the presence of hydroquinone. AgPt hollow nanodendrites comprised of several Pt islands ≈6 nm in diameter could be obtained in only 15 s following the addition of PtCl62− to a suspension containing Ag nanospheres, and their size and composition could be tuned as a function of the growth time. The synthesis could be scaled up by 100 folds, which enabled us to uniformly support the AgPt nanostructures onto commercial silica. The AgPt nanodendrites displayed good catalytic activities for both the 4-nitrophenol reduction and the BTX oxidation reactions. The results presented herein may inspire the synthesis of noble metal nanostructures displaying attractive features for catalysis, such as hollow interiors, ultrathin walls, and uniform dispersion over solid supports (solid supported catalysts).
    05/2015; 1(1):46-51. DOI:10.1002/cnma.201500025
  • Jiale Wang · Romulo A. Ando · Pedro H. C. Camargo
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    ABSTRACT: Although catalytic processes mediated by surface plasmon resonance (SPR) excitation have emerged as a new frontier in catalysis, the selectivity of these processes remains poorly understood. Here, the selectivity of the SPR-mediated oxidation of p-aminothiophenol (PATP) employing Au NPs as catalysts was controlled by the choice of catalysts (Au or TiO2 -Au NPs) and by the modulation of the charge transfer from UV-excited TiO2 to Au. When Au NPs were employed as catalyst, the SPR-mediated oxidation of PATP yielded p,p-dimercaptobenzene (DMAB). When TiO2 -Au NPs were employed as catalysts under both UV illumination and SPR excitation, p-nitrophenol (PNTP) was formed from PATP in a single step. Interestingly, PNTP molecules were further reduced to DMAB after the UV illumination was removed. Our data show that control over charge-transfer processes may play an important role to tune activity, product formation, and selectivity in SPR-mediated catalytic processes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Angewandte Chemie 04/2015; 54(23). DOI:10.1002/ange.201502077
  • Jiale Wang · Peixuan Chen · Pedro H. C. Camargo
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    ABSTRACT: We report herein the synthesis of Pd nanostructures ~64–95-nm range in size displaying controlled surface morphologies by a seeded-growth method employing Pd nanoparticles as seeds. Interestingly, we found that the surface texture and thus the surface area of the produced Pd nanomaterials could be tuned by varying the seeded-growth temperature. Pd nanostructures displaying increasingly higher surface textures were obtained as the seeded-growth temperature was decreased from 95 to 30 °C. These results could be explained based on the variations in the relative rates of atom deposition (V deposition) and surface diffusion (V diffusion) during the Pd growth. The catalytic activities of the Pd nanostructures toward the reduction of 4-nitrophenol augmented with the increase in the surface texture of the produced nanostructures. The results presented herein can have important implications for designing facile approaches to the synthesis of Pd nanostructures with desired features and optimized catalytic performances that can be highly accessible and attractive for large scale production.
    Journal of Nanoparticle Research 12/2014; 16(12). DOI:10.1007/s11051-014-2763-x · 2.28 Impact Factor
  • J. L. Wang · Romulo A. Ando · Pedro H. C. Camargo
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    ABSTRACT: The surface plasmon resonance (SPR) excitation by visible light in plasmonic nanostructures can be put to work to mediate catalytic processes. However, the role of composition in bimetallic nanoparticles over the SPR-mediated catalytic activity remains unclear. We investigated herein the SPR-mediated catalytic activity of AgAu nanoparticles as a function of composition toward the oxidation of p-aminothiophenol to p,p′-dimercaptoazobenzene. Our results showed that a “volcano-type” relationship between composition and product conversion was observed, with a maximum activity observed for Ag0.19Au0.81 nanoparticles. The variations in catalytic activity could be explained by the balance between the matching of the excitation wavelength with SPR position and the plasmonic damping due to interband transitions above 500 nm. These data suggest that the precise control over composition allows the fine-tuning of catalytic activity in SPR-mediated catalytic processes.Keywords: nanoparticles; bimetallic; silver; gold; SPR; plasmon-mediated catalysis; SERS
    ACS Catalysis 11/2014; 4(11):3815-3819. DOI:10.1021/cs501189m · 7.57 Impact Factor
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    ABSTRACT: Metallic nanomaterials displaying hollow interiors as well as sharp tips/branches at their surface (such as hollow nanodendrites) are attractive, because these features enable higher surface-to-volume ratios than their solid and/or rounded counterparts. This paper describes a simple strategy for the synthesis of Ag–Au nanodendrites in 15 s using Ag nanospheres prepared in a previous synthetic step as seeds. Our approach was based on the utilization of Ag nanospheres as seeds for Au deposition by a combination of galvanic replacement reaction between Ag and AuCl4−(aq) and AuCl4−(aq) reduction using hydroquinone in the presence of polyvinylpyrrolidone (PVP) as a stabilizer and water as the solvent. The produced Ag–Au nanodendrites presented monodisperse sizes, and their surface morphologies could be tuned as a function of growth time. Owing to their hollow interiors and sharp tips, the Ag–Au nanodendrites performed as effective substrates for surface-enhanced Raman scattering (SERS) detection of 4-MPy (4-mercaptopyridine) and R6G (rhodamine 6G) as probe molecules. We believe that the approach described herein can serve as a protocol for the fast and one-step synthesis of Ag–Au hollow nanondendrites with a wide range of sizes, compositions, and surface morphologies for applications in SERS and catalysis.
    Chemistry - A European Journal 10/2014; 20(46). DOI:10.1002/chem.201404739 · 5.70 Impact Factor
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    ABSTRACT: We report the controlled alloying, oxidation, and subsequent reduction of individual AgAu nanoparticles in the scanning transmission electron microscope (STEM). Through sequential application of electron beam induced oxidation and in situ heating and quenching, we demonstrate the transformation of Ag-Au core-shell nanoparticles into: AgAu alloyed, Au-Ag core-shell, hollow Au-Ag2O core-shell, and Au-Ag2O yolk-shell nanoparticles. We are able to directly image these morphological transformations in real-time at atomic resolution and perform energy dispersive X-ray (EDX) spectrum imaging to map changing elemental distributions with sub-nanometre resolution. By combining aberration corrected STEM imaging and high efficiency EDX spectroscopy we are able to quantify not only the growth and coalescence of Kirkendall voids during oxidation but also the compositional changes occurring during this reaction. This is the first time that it has been possible to track the changing distribution of elements in an individual nanoparticle undergoing oxidation driven shell growth and hollowing.
    Nanoscale 09/2014; 6(22). DOI:10.1039/C4NR04837G · 7.39 Impact Factor
  • T J A Slater · P H C Camargo · M G Burke · N J Zaluzec · S J Haigh
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    ABSTRACT: We have investigated the use of x-ray energy dispersive spectroscopy during tomographic hyperspectral imaging experiments in the scanning transmission electron microscope. In this work, we have found that for an analytical system employing a commercial high-tilt tomography holder the measured x-ray signal is limited by shadowing caused by the penumbra of the holder relative to the x-ray detector system. This limits the ability to perform quantitative, elemental tomographic analysis.
    Journal of Physics Conference Series 06/2014; 522(1):012025. DOI:10.1088/1742-6596/522/1/012025
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    ABSTRACT: Sub-nanosecond charge dynamics in monodisperse Au nanoparticles (NPs) supported on TiO2 colloidal spheres are studied as a function of NP diameter using ultrafast transient absorption spectroscopy. The decay of the transmittance changes observed in the region of the plasmon resonance of the Au NPs following photoexcitation of the TiO2 spheres are well-described by a bi-exponential function consisting of a fast component of 2 ps duration associated with electron-phonon scattering, followed by a slow and relatively weak component associated with phonon-phonon scattering. The decay constant characterising the latter component was found to be dependent on the size of the Au NPs, rising from 49 ± 3 to 128 ± 6 ps as the diameter of the Au NPs increased from 12.2 ± 2.2 nm to 24.5 ± 2.8 nm, respectively.
    Physical Chemistry Chemical Physics 06/2014; 16(27). DOI:10.1039/c4cp01475h · 4.20 Impact Factor
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    ABSTRACT: This paper describes the development of a facile and environmentally friendly strategy for supporting palladium nanoparticles (Pd NPs) on multiwalled carbon nanotubes (MWCNTs) with ethanol as the solvent/reducing agent, potassium tetrachloropalladate(II) (K2PdCl4) as the Pd precursor, and polyvinylpyrrolidone (PVP) as the surface modifier. More specifically, our approach was based on the nonbonding interaction between MWCNTs and PVP, which is a cheap, nontoxic, and commercial polymer. As PVP can serve not only as a surface modifier but also as a stabilizing agent for Pd NPs, the utilization of additional functionalization steps, reducing agents, and stabilizers was not required to achieve uniform Pd deposition over the MWCNTs. Our results demonstrate that Pd NPs below 5 nm in diameter can be directly supported on MWCNTs by this route. Also, sequential Pd-reduction steps can be employed to improve the coverage of Pd NPs at the MWCNT surfaces, although this can also lead to the formation of larger Pd particles or aggregates. The electrocatalytic activity for ethanol oxidation was investigated as a function of the composition and structure of the materials produced, in which MWCNTs decorated with Pd NPs of smaller sizes and lower coverages displayed the highest activities. The results described herein suggest that our approach may serve as a simple platform for the synthesis of MWCNTs decorated with metal NPs with well-defined morphologies and uniform dispersion for electrochemical and catalytic applications.
    Berichte der deutschen chemischen Gesellschaft 03/2014; 2014(9). DOI:10.1002/ejic.201301585
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    ABSTRACT: Significant elemental segregation is shown to exist within individual hollow silver-gold (Ag-Au) bimetallic nanoparticles produced from the galvanic reaction between Ag particles and AuCl4-. Three dimensional compositional mapping using energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope (STEM) reveals that nanoparticle surface segregation inverts from Au-rich to Ag-rich as Au content increases. Maximum Au surface coverage was observed for nanoparticles with approximately 25at% Au which correlates to the optimal catalytic performance in a three-component coupling reaction between cyclohexanecarboxyaldehyde, piperidine and phenylacetylene. These results provide important fundamental insights towards optimizing the properties and reducing the cost of precious metal catalysts.
    Nano Letters 02/2014; 14(4). DOI:10.1021/nl4047448 · 13.59 Impact Factor
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    ABSTRACT: The synthesis of gold nanoparticles (Au NPs) 15, 26, and 34 nm in diameter, followed by the investigation of their size-dependent optical and catalytic properties, is described herein as an undergraduate level experiment. The proposed experiment covers concepts on the synthesis, stabilization, and characterization of Au NPs, their size-dependent optical and catalytic properties at the nanoscale, chemical kinetics, and the role of a catalyst. The experiment should be performed by groups of two or three students in three lab sessions of 3 h each and organized as follows: i) synthesis of Au NPs of different sizes and investigation of their optical properties; ii) evaluation of their catalytic activity; and iii) data analysis and discussion. We believe that this activity enables students to integrate these multidisciplinary concepts in a single experiment as well as to become introduced/familiarized with an active research field and current literature in the areas of nanoparticle synthesis and catalysis.
    Química Nova 01/2014; 37(10). DOI:10.5935/0100-4042.20140235 · 0.66 Impact Factor
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    ABSTRACT: Associating polyaniline and metallic nanoparticles may result in the combination/synergism of properties, which have been attracting great attention. This paper describes an investigation on the effectiveness of several gold nanostructures acting as surface enhanced Raman scattering (SERS) substrates using the emeraldine salt form of PANI (PANI-ES) as a probe-molecule was verified. The surface enhanced resonance Raman scattering (SERRS) spectra of PANI-ES at 1064 nm result from two enhancement effects: one from the PANI-ES resonance Raman and the other from localized surface plasmon resonance of the gold nanostructures when the plasmon wavelength approaches the NIR region. A considerable SERRS intensity for PANI-ES at the 10 nM level could be obtained using a gold nanoplates colloidal suspension as substrates. The SERRS spectra of PANI-ES and the high correlation between SERRS intensity and LSPR extinction of Au nanostructures at 1064 nm indicate that the enhancement was mostly due to the electromagnetic mechanism. These results indicate that PANI-ES can be employed as a general probe-molecule for the evaluation of SERRS substrates performance at 1064 nm excitation.
    The Journal of Physical Chemistry C 09/2013; 117(35):18199. DOI:10.1021/jp406352r · 4.77 Impact Factor
  • 14th Brazilian Meeting on Organic Synthesis; 09/2013
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    ABSTRACT: We describe herein a systematic investigation on the optical properties of Ag, Au, and Cu triangular nanoprisms as a function of size and excitation wavelength using the discrete dipole approximation. Specifically, the edge length was varied from 40 to 100 nm while the thickness was kept at 10 nm. In the far field, our results suggest that the in-plane localized surface plasmon resonance (LSPR) peaks red-shifted as the edge length increased. In the near field, the magnitude of the electric fields generated close to the surface of the nanoprisms were calculated considering 514, 633, and 785 nm as the excitation wavelengths. The variation on the magnitude of the electric fields can be understood based on the matching between the excitation wavelength and the position of the in-plane dipole and quadrupole LSPR modes. We believe that these results can have important implications in the design of metal nanoprisms for plasmonic applications.
    Chemical Physics 09/2013; 423:142-150. DOI:10.1016/j.chemphys.2013.07.008 · 2.03 Impact Factor
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    Caio C S de Oliveira · Rômulo A Ando · Pedro H C Camargo
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    ABSTRACT: The polyol method has been widely employed for the synthesis of uniform silver nanowires (Ag NWs) in high yields. In this article, we describe the utilization of HCl oxidative etching as an effective strategy to control the width of Ag NWs produced by the polyol approach. More specifically, the width of the produced Ag NWs could be tuned from 65 to 765 nm by varying the HCl concentration in the polyol recipe. Our results indicate that the obtained widths displayed a linear and steady increase according to the HCl concentration employed in the reaction. Although the width was also dependent on other experimental parameters such as the AgNO(3) and polyvinylpirrolidone (PVP) concentrations and temperature, the HCl oxidative etching enabled the controlled synthesis of Ag NWs over the widest range of widths. The size-dependent optical property investigations revealed that the transverse mode surface plasmon resonance peak for the produced Ag NWs red-shifted from 378 to 467 nm as their width increased from 77 to 584 nm. The application of Ag NWs (77 nm) as SERS substrates for the detection of 4-mercaptopyridine was also demonstrated. As the properties of metal nanostructures are strongly dependent upon size, the results reported herein can have important implications for designing the synthesis of uniform Ag NWs in high yields displaying controlled and/or desired dimensions for applications in areas including plasmonics, electronics, and sensing.
    Physical Chemistry Chemical Physics 12/2012; 15(6). DOI:10.1039/c2cp43108d · 4.20 Impact Factor
  • Jean C. S. Costa · Paola Corio · Pedro H. C. Camargo
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    ABSTRACT: We report the synthesis of silver–gold nanotubes containing hot spots along their surface. The Ag–Au nanotubes exhibited exceptional SERS properties compared to silver nanowires, enabling the detection of crystal violet in the 10−10 M regime, as well as 9-nitroanthracene and benzo[a]pyrene at 3.3 × 10−7 M.
    RSC Advances 10/2012; 2(26):9801-9804. DOI:10.1039/C2RA21562D · 3.84 Impact Factor

Publication Stats

3k Citations
379.41 Total Impact Points

Institutions

  • 2011–2015
    • University of São Paulo
      • Departamento de Química Fundamental (IQ) (São Paulo)
      San Paulo, São Paulo, Brazil
  • 2014
    • The University of Manchester
      Manchester, England, United Kingdom
  • 2008–2011
    • Washington University in St. Louis
      • Department of Biomedical Engineering
      San Luis, Missouri, United States
  • 2010
    • Yonsei University
      • Department of Biomedical Engineering
      Sŏul, Seoul, South Korea
  • 2003–2009
    • Universidade Federal do Paraná
      • Department of Chemistry
      Pontal do Paraná, Paraná, Brazil
  • 2007–2008
    • University of Washington Seattle
      • Department of Chemistry
      Seattle, Washington, United States