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Although clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can be considered a promising strategy, this approach remains challenging by the dependence on high loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or alloying) or replace them completely in these systems. The present investigation shows that high catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs) deposited onto MnO

We develop herein plasmonic-catalytic Au-IrO

Manganese oxide (MnO2) nanomaterials represent a promising low-cost electrocatalyst material for hydrogen peroxide (H2O2) production by the oxygen reduction reaction (ORR). In this material, the introduction of oxygen vacancies is an effective strategy for boosting their electrocatalytic activities. Although the importance of oxygen defects in MnO2-based catalysts has been shown in some electrochemical systems, a facile strategy for controlling the number oxygen vacancies in MnO2-based catalysts and the systematic investigation of the effect of the vacancies on their electrocatalytic activities towards the ORR and H2O2 electrogeneration remains limited. Here, we describe the synthesis of hybrid materials composed of MnO2 nanoflowers supported on Vulcan XC-72 carbon in which the concentration of the surface oxygen vacancy sites was increased. Surprisingly, we found a volcano-type relationship between the activity and the MnO2 loading. RRDE experiments showed the greatest formation of hydroperoxide ion in alkaline media for MnO2/C 3% on carbon, displaying the highest electrocatalytic activity. This result was maintained for hydrogen peroxide during the electrolytic process using gas diffusion electrodes in acidic media. We suggest that the optimized catalytic activities observed for the MnO2/C 3% catalyst are a result of (i) the high concentrations of oxygen vacancies at the catalyst surface, which promote the generation of highly catalytically active sites towards the ORR; (ii) their strong metal oxide-carbon interactions with modification of the carbon surface; (iii) the high surface area observed for the MnO2 nanoflowers supported on Vulcan XC-72; and (iv) the use of a MnO2 nanostructure displaying well-defined shapes and uniform sizes (with petals measuring 10 ± 5 nm in width) displaying a uniform dispersion over the carbon support. We believe the results described herein shed new light on the understanding of the role of the oxygen vacancies in the electrogeneration of H2O2, which has important implications for the design of MnO2-based electrocatalysts.

We described herein the facile synthesis of sub-15 nm CeO2 nanowires based on a hydrothermal method without the use of any capping/stabilizing agent, in which an oriented attachment mechanism took place during the CeO2 nanowire formation. The synthesis of sub-15 nm CeO2 nanowires could be achieved on relatively large scales (∼2.6 grams of nanowires per batch), in high yields (>94%), and at low cost. To date, there are only a limited number of successful attempts towards the synthesis of CeO2 nanowires with such small diameters, and the reported protocols are typically limited to low amounts. The nanowires displayed uniform shapes and sizes, high surface areas, an increased number of oxygen defects sites, and a high proportion of Ce3+/Ce4+ surface species. These features make them promising candidates for oxidation reactions. To this end, we employed the selective oxidation of aniline as a model transformation. The sub-15 nm CeO2 nanowires catalyzed the selective synthesis of nitrosobenzene (up to 98% selectivity) from aniline at room temperature using H2O2 as the oxidant. The effect of solvent and temperature during the catalytic reaction was investigated. We found that such parameters played an important role in the control of the selectivity. The improved catalytic activities observed for the sub-15 nm nanowires could be explained by: i) the uniform morphology with a typical dimension of 11 ± 2 nm in width, which provides higher specific surface areas relative to those of conventional catalysts; ii) the significant concentration of oxygen vacancies and high proportion of Ce3+/Ce4+ species at the surface that represent highly active sites towards oxidation reactions; iii) the crystal growth along the (110) highly catalytically active crystallographic directions, and iv) the mesoporous surface which is easily accessible by liquid substrates. The results reported herein demonstrated high activities under ambient conditions, provided novel insights into selectivities, and may inspire novel metal oxide-based catalysts with desired performances.

Pt nanoparticles supported on carbon (Pt/C) and nitrogen-doped carbon (Pt/NC) were prepared by an alcohol-reduction process and used for ammonia electro-oxidation in alkaline media. Nitrogen-doped carbons were prepared by thermal treatment of urea and Carbon Vulcan XC72 at 800 °C under argon atmosphere. The obtained materials showed the presence of face centered cubic structure of Pt and mean particle sizes in the range of 3–3.7 nm. X-ray photoelectron spectroscopy results revealed that Pt/NC 5 (carbon prepared with 5% of urea) presents more Pt on the surface than Pt/C, and the nanoparticles are predominantly in the metallic state. The electrocatalytic activity was investigated by cyclic voltammetry and chronoamperometry experiments. Pt/NC materials showed a higher electrocatalytic activity for ammonia electro-oxidation than Pt/C, whereby the material Pt/NC 5 showed the peak current density 161% higher than Pt/C. The increase of activity might be related to the high electrochemically accessible area of Pt/NC and the improvement on the interaction with water due to the nitrogen onto the support which could contribute to the oxidation of intermediate products from ammonia electro-oxidation.

Palladium nanoparticles supported on carbon Vulcan XC72 (Pd/C) and on phosphorus-doped carbon (Pd/P-C) were prepared by an alcohol reduction process. X-ray diffractograms of Pd/C and Pd/P-C showed the typical face-centered cubic (fcc) structure of Pd. The crystallite sizes of Pd fcc phase were around 8 nm for both samples. X-ray photoelectron spectroscopy revealed to Pd/C and Pd/P-C that Pd was found predominantly in the metallic state and to Pd/P-C, the presence of P increases the amount of oxygen on the electrocatalyst surface. The activity and stability of the electrocatalyts for ethanol electro-oxidation in alkaline medium was investigated by cyclic voltammetry and chronoamperometry experiments. The peak current density on Pd/P-C was 50% higher than on Pd/C, while the current density measured after 30 min at − 0.35 V vs. Hg/HgO was 65% higher on Pd/P-C than on Pd/C. The enhancement of the catalytic activity of Pd/P-C electrocatalyst might be related to the presence of higher amounts of oxygen species on the surface, which could contribute to the oxidation of intermediates formed during ethanol electro-oxidation process.

We develop herein plasmonic-catalytic Au-IrO2 nanostructures with a morphology optimized for efficient light harvesting and catalytic surface area; the nanoparticles have a nanoflower morphology, with closely spaced Au branches all partially covered by an ultrathin (1 nm) IrO2 shell. This nanoparticle architecture optimizes optical features due to the interactions of closely spaced plasmonic branches forming electromagnetic hot spots, and the ultra-thin IrO2 layer maximizes efficient use of this expensive catalyst. This concept was evaluated towards the enhancement of the electrocatalytic performances towards the oxygen evolution reaction (OER) as a model transformation. The OER can play a central role in meeting future energy demands but the performance of conventional electrocatalysts in this reaction is limited by the sluggish OER kinetics. We demonstrate an improvement of the OER performance for one of the most active OER catalysts, IrO2, by harvesting plasmonic effects from visible light illumination in multimetallic nanoparticles. We find that the OER activity for the Au-IrO2 nanoflowers can be improved under LSPR excitation, matching best properties reported in the literature. Our simulations and electrocatalytic data demonstrate that the enhancement in OER activities can be attributed to an electronic interaction between Au and IrO2 and to the activation of Ir-O bonds by LSPR excited hot holes, leading to a change in the reaction mechanism (rate-determinant step) under visible light illumination.

Gold nanoparticles incorporated on ceria nanowires have been employed as efficient nanocatalysts for the selective oxidation of thioanisole. The control of both physical and chemical parameters as well as metal–support interactions are important factors that determine their performances. Considering their one-dimensional morphology with large surface area, thin diameters, high concentration of oxygen vacancies, and small Au NPs uniformly on the entire CeO2 surface with a high fraction of oxidized gold species, these characteristics make them favorable nanocatalysts for oxidation transformations. The CeO2-Au nanowires displayed improved performances towards the oxidation of thioanisole when compared to the pure CeO2 nanowires and commercial CeO2-Au catalysts. The CeO2-Au nanowires catalyzed the selective synthesis of methyl phenyl sulfoxide with up to 100 % of selectivity and high conversion. The impact of solvent and temperature during the catalytic reaction was also experimentally and theoretically investigated by DFT calculations, indicating a key role in the observed activities.

Pt nanoparticles (Pt NPs) supported on carbon have been widely employed as electrocatalysts toward oxygen reduction reaction. The development of more efficient electrocatalysts that enable one to reduce or even not require the use of Pt is a central challenge. In addition to the control over the physical and chemical features of Pt NPs, metal support interactions can be employed to enhance activities via the generation and exposure of surface-active sites. In this context, we report herein the development of electrocatalysts composed of Pt NPs supported on TiO2 microspheres, that were subsequently impregnated onto carbon. We have found that, by optimizing the loading of Pt at the TiO2 surface, the electrocatalytic activity toward the ORR could be improved compared to that of the commercial Pt/C (E-TEK) material, even at lower Pt loadings. The enhancement in activities could be assigned to the balance between Pt loading and generation of reactive surface sites, such as adsorbed oxygenated species. Moreover, the utilization of TiO2 as support enabled improved stabilities relative to Pt/C (E-TEK). We believe that the results described herein may inspire the development of electrocatalysts for the ORR with improved activities and stabilities.

Among the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO2 nanoflowers. They displayed hierarchical morphology, large specific surface areas, ultrasmall and uniform Au NPs sizes, no agglomeration, strong metal-support interactions, oxygen vacancies, and Auδ+ species at their surface. These features led to improved performances towards the green oxidations of CO, benzene, toluene, o-xylene, glucose, and fructose relative to the pristine MnO2 nanoflowers, commercial MnO2 decorated with Au NPs, and other reported catalysts. We believe that the catalytic activities, stabilities, and mild/green reaction conditions described herein for both gas and liquid phase oxidations due to the optimization of both the support and active phase may inspire the development of novel catalytic systems for a wealth of sustainable transformations.

Further improvements and mechanistic understanding of the electrocatalytic enhancements towards the oxygen reduction reaction (ORR) are required to meet cost/energy demands and thus enable their practical applications in polymer electrolyte fuel cells. An investigation of the electrocatalytic enhancement mechanisms and stability of controlled electrocatalysts comprised Pt nanoparticles supported on TiO2/C materials was herein performed. The catalysts were prepared by depositing Pt, over the surface of TiO2 colloidal spheres. These materials were then supported onto Vulcan carbon to produce Pt/TiO2/C. The effect of Pt coverage at the TiO2 surface as well as the Pt/TiO2 loading on carbon over their ORR activity and stability were investigated. Results indicate that the control over Pt coverage at the surface played a pivotal role on activity optimization, in which an association between Pt content at the TiO2 surface and ORR activity was established. The ORR activity and stability were superior as compared to commercial Pt/C (E-TEK). Variations in catalytic activity could be correlated with the morphological features and with the concentration of surface reactive groups. Results described herein suggest that the understanding of the electrocatalytic enhancement mechanism together with the controlled synthesis of Pt-based nanomaterials may lead to tailored surface properties and thus ORR activities.

Among the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO

In hybrid materials containing plasmonic nanoparticles such as Au and Ag, charge-transfer processes from and to Au or Ag can affect both activities and selectivity in plasmonic catalysis. Inspired by the widespread utilization of commercial Si wafers in surface-enhanced Raman spectroscopy (SERS) studies, we investigated herein the effect of the native SiO

This study demonstrates that the precursor reduction kinetics can be employed to control the morphology and composition of bimetallic metal/metal oxides systems obtained by galvanic replacement reaction using metal oxides as sacrificial templates. This work investigated Cu2O as a proof-of-concept example, in which the relative rates of Cu2O oxidation by O2 and by noble metal precursors determined the morphology and composition of the products. We focused on three metal precursors with fast, medium, and slow reduction kinetics in the presence of Cu2O under aerobic conditions: PdCl42–, AuCl4–, and Ru3+, respectively. It was found that metal-oxide-based bowls, rattles, or dendrites can be obtained by simply changing the precursor reduction kinetics. These results provide novel insights over the versatility and mechanistic understanding of galvanic replacement to the synthesis of metal/metal-oxide bimetallic nanoparticles.

The immobilization of plasmonic nanoparticles onto supports with suitable electronic properties represents an intuitive strategy for the modulation of nanoscale charge-transfer processes and thus the optimization of plasmonic catalytic performances. Here, we report the investigation of the effect of two kinds of bi-dimensional (2D) supports, i.e., partially reduced graphene oxide (prGO) and ultrathin titanate nanosheets (TixO2), on the plasmonic catalytic performances of Ag nanoparticles (NPs). As prGO and TixO2 act as electron donor and acceptor materials, respectively, when combined with plasmonic nanoparticles under 633 nm excitation, their similar 2D morphologies enabled us to systematically probe and compare how charge transfer to and from Ag NPs affected their plasmonic catalytic activities. By employing the SPR-mediated oxidation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) as a model reaction, we found that the performances of the hybrids were superior relative to unsupported Ag NPs and that the PATP oxidation mechanism and conversion were dependent on the nature of the support. We also prepared the tri-component hybrid comprised of Ag NPs, prGO and TixO2 nanosheets (Ag/TixO2/prGO), which displayed a similar performance to Ag/prGO. In this material, a mechanism based on the cooperative effect of the supports was proposed, in which charge transfer from prGO to Ag NPs is intensified by the presence of TixO2 nanosheets. We believe that our results expand the understanding on the electronic behavior of complex plasmonic systems, which can allow the rational design of nanoparticle systems with improved performances towards plasmonically triggered or enhanced transformations.

In hybrid materials containing plasmonic nanoparticles such as Au and Ag, charge-transfer processes from and to Au or Ag can affect both activities and selectivity in plasmonic catalysis. Inspired by the widespread utilization of commercial Si wafers in surface-enhanced Raman spectroscopy (SERS) studies, we investigated herein the effect of the native SiO2 layer on Si wafers over the surface plasmon resonance (SPR)-mediated activities of the Au and Ag nanoparticles (NPs). We prepared SERS-active plasmonic comprised of Au and Ag NPs deposited onto a Si wafer. Here, two kinds of Si wafers were employed: Si with a native oxide surface layer (Si/SiO2 ) and Si without a native oxide surface layer (Si). This led to Si/SiO2 /Au, Si/SiO2 /Ag, Si/Au, and Si/Ag NPs. The SPR-mediated oxidation of p-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB) was employed as a model transformation. By comparing the performances and band structures for the Si/Au and Si/Ag relative to Si/SiO2 /Au and Si/SiO2 /Ag NPs, it was found that the presence of a SiO2 layer was crucial to enable higher SPR-mediated PATP to DMAB conversions. The SiO2 layer acts to prevent the charge transfer of SPR-excited hot electrons from Au or Ag nanoparticles to the Si substrate. This enabled SPR-excited hot electrons to be transferred to adsorbed O2 molecules, which then participate in the selective oxidation of PATP to DMAB. In the absence of a SiO2 layer, SPR-excited hot electrons are preferentially transferred to Si instead of adsorbed O2 molecules, leading to much lower PATP oxidation.

The origin and influence of active sites on supported copper catalysts, and their catalytic properties for ethanol conversion, were investigated using Cu/SiO2, Cu2O/SiO2, and Cu/ZrO2. Diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO revealed that Cu1 + was more prevalent than Cu0 species at the Cu/SiO2 surface, and that Cu0 was the main species on Cu/ZrO2. The Cu1 +/Cu0 pair provided by Cu/SiO2 generates sites that are highly selective for the dehydrogenation of ethanol. Ethyl acetate can be formed from ethanol and acetaldehyde at ZrO2 or Cu surfaces. A combination of the Cu1 +/Cu0 pair and Cu0 interfaced to ZrO2 is needed to efficiently transform ethanol to ethyl acetate.

Although green catalytic transformations are very attractive, they often remain limited by low conversion percentages and selectivity. Here, we demonstrate that high catalytic performances (TOF = 590,000 h −1 ) could be achieved towards the green oxidation of silanes and H 2 production under ultralow Au loadings (0.001–0.0002 mol% in terms of Au) employing H 2 O as the oxidant, 25 °C as the reaction temperature, and MnO 2 nanowires decorated with ultrasmall Au NPs (3 nm) as catalysts. In addition to these high activities towards a variety of substrates, the MnO 2 –Au NPs displayed good stability/recyclability, in which no morphological changes or loss of activity were observed even after 10 reaction cycles. The improved catalytic activities observed for the MnO 2 –Au NPs can be assigned to: (i) the metal–support interactions, in which the presence of Au NPs could facilitate oxidative processes and thus yield high performances towards the oxidation of hydrosilanes; (ii) the significant concentration of Au δ+ species and oxygen vacancies at the catalyst surface that represent highly catalytically active sites towards oxidation reactions, and (iii) the Au NPs ultrasmall sizes at the MnO 2 surface that enable the exposure of high energy Au surface/facets, high surface-to-volume ratios, and their uniform dispersion. The MnO 2 –Au NPs could be synthesized by a facile approach based on the utilization of MnO 2 nanowires as physical templates for Au deposition without any prior surface modification/functionalization steps. The utilization of supported ultrasmall Au NPs having controlled sizes and dispersion may inspire the design of novel catalysts capable of enabling high catalytic performances towards green transformations at ultralow metal loadings.

This paper presents the results obtained in the integration of the cartographic product with field works during a course in São Vicente-SP in January, 2004. The study was inserted in the project "Univerão - Unesp" that developed activity with teachers, scientists, students and local beach population, on the summer vacation. The course "Special workshop of the models for Support the citizenship" allowed a connection between cartographic material and field work. The students made two models about the city, the first presented the use and occupation of the urban territory, the second one emphasized the environmental impacts. The models was prepared through the theoretical classes, practical classes, thematic maps exploring, images, photographs and field work, as well as, they permitted the observation of the reality. The study contributed for conscientiousness the urban planning, citizenship, environmental impacts, urban expansion and territory development and its changes.

In this work, a simple but powerful method for controlling the size and surface morphology of AgAu nanodendrites is presented. Control of the number of Ag nanoparticle seeds is found to provide a fast and effective route by which to manipulate the size and morphology of nanoparticles produced via a combined galvanic replacement and reduction reaction. A lower number of Ag nanoparticle seeds leads to larger nanodendrites with the particles' outer diameter being tunable in the range of 45-148 nm. The size and surface morphology of the nanodendrites was found to directly affect their catalytic activity. Specifically, we report on the activity of these AgAu nanodendrites in catalyzing the gas-phase oxidation of benzene, toluene and o-xylene, which is an important reaction for the removal of these toxic compounds from fuels and for environmental remediation. All produced nanodendrite particles were found to be catalytically active, even at low temperatures and low metal loadings. Surprisingly, the largest nanodendrites provided the greatest percent conversion efficiencies.

Este trabalho teve por objetivo identificar a associação existente entre classe social e retardo do crescimento físico, ocorrido nos primeiros anos de vida. Com base em um censo de estatura, envolvendo alunos ingressantes em todas as escolas (públicas e particulares) do Município de Osasco, região metropolitana de São Paulo, Brasil, realizado no início do ano letivo de 1989, foram selecionados casos e controles para a investigação retrospectiva dos determinantes sociais do retardo do crescimento. Os casos, totalizando 125 ingressantes de sete a oito anos de idade, foram caracterizados pelo índice altura/idade inferior a -2 escores Z da população de referência do NHCS/OMS. Os controles, totalizando 139 ingressantes da mesma idade, foram caracterizados pelo índice altura/idade superior a -1 escore Z. Escolaridade do chefe da casa e da mãe, renda familiar per capita, condições de habitação e saneamento, ou seja, variáveis que devem mediar a relação entre classe social e déficit de estatura, foram fatores que se associaram significativamente com o risco de retardo do cresimento. Quanto à inserção da família no processo social de produção, avaliada através da classe social do chefe, as crianças do subproletariado apresentaram uma chance sete vezes maior de retardo do crescimento quando comparadas com as dos grupos da pequena burguesia, refletindo os efeitos biológicos da recessão econômica dos anos 80. Cases and controls were selected for this retrospective investigation of the social determinants of growth retardation, from a Height Census carried out in the 1989 school year,involving children attending the first grade of all public and private schools in Osasco (in the Greater Metropolitan Area of São Paulo, Brazil). The cases, totalling 125 children entering school aged 7-8 years old, were characterized by a height-for-age index below -2 z score of the NCHS/WHO reference. The controls, totalling 139 children entering school at the same age, were characterized by a height-for-age index above -1 z score. Socioeconomíc variables such as family income, head-of-family's level of schooling, mother's schooling, environmental sanitation, and housing conditions were significant factors associated with the stunting process. Risk of linear growth retardation tended to be higher with lower social class (odds ratio = 7.3 for sub-proletariat vs. petit bourgeois; p < 0,001 for overall trend), suggesting the biological impact of Brazil's economic slowdown during the 1980s.