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M.C. Santos

Bio: M.C. Santos is an academic researcher from Universidade Federal do ABC. The author has contributed to research in topics: Electrocatalyst & Cyclic voltammetry. The author has an hindex of 22, co-authored 30 publications receiving 1358 citations. Previous affiliations of M.C. Santos include National Nuclear Energy Commission & The Advisory Board Company.

Papers
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Journal ArticleDOI
01 Jul 2011-Carbon
TL;DR: A comparative study of two different conductive carbon-black pigments, Vulcan XC-72 R and Printex L6, for the electrogeneration of hydrogen peroxide (H2O2) by reducing dissolved oxygen in an alkaline solution was performed.

156 citations

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TL;DR: The use of tetramethylammonium hydroxide, tertiary amines and strongly alkaline reagents for sample treatment involving extraction and digestion procedures is discussed in this paper.

116 citations

Journal ArticleDOI
TL;DR: The changes observed on Pt surfaces during a potential incursion into the underpotentially deposited (UPD) hydrogen and double layer ranges (0.05 to 0.8 V versus HESS) were analyzed in perchloric, sulfuric, phosphoric and hydrochloric acid media as mentioned in this paper.

108 citations

Journal ArticleDOI
TL;DR: In this paper, a comparative study using different proportions of CeO 2 /C (4, 9% and 13% ) was performed to produce H 2 O 2, a reagent used in the oxidation of organic pollutants and in electro-Fenton reactions for the production of the hydroxyl radical (OH ), a strong oxidant agent used in electrochemical treatment of aqueous wastewater.
Abstract: A comparative study using different proportions of CeO 2 /C (4%, 9% and 13% CeO 2 ) was performed to produce H 2 O 2 , a reagent used in the oxidation of organic pollutants and in electro-Fenton reactions for the production of the hydroxyl radical (OH ), a strong oxidant agent used in the electrochemical treatment of aqueous wastewater. The CeO 2 /C materials were prepared by a modified polymeric precursor method (PPM). X-ray diffraction analysis of the CeO 2 /C prepared by the PPM identified two phases, CeO 2 and CeO 2− x . The average size of the crystallites in these materials was close to 7 nm. The kinetics of the oxygen reduction reaction (ORR) were evaluated by the rotating ring-disk electrode technique. The results showed that the 4% CeO 2 /C prepared by the PPM was the best composite for the production of H 2 O 2 in a 1 mol L −1 NaOH electrolyte solution. For this material, the number of electrons transferred and the H 2 O 2 percentage efficiency were 3.1 and 44%, respectively. The ring-current of the 4% CeO 2 /C was higher than that of Vulcan carbon, the reference material for H 2 O 2 production, which produced 41% H 2 O 2 and transferred 3.1 electrons per molecule of oxygen. The overpotential for this reaction on the ceria-based catalyst was substantially lower (approximately 200 mV), demonstrating the higher catalytic performance of this material. Gas diffusion electrodes (GDE) containing the catalyst were used to evaluate the real amount of H 2 O 2 produced during exhaustive electrolysis. The 4% CeO 2 /C GDE produced 871 mg L −1 of H 2 O 2 , whereas the Vulcan carbon GDE produced a maximum amount of only 407 mg L −1 . Thus, the 4% CeO 2 /C electrocatalyst prepared by the PPM is a promising material for H 2 O 2 electrogeneration in alkaline media.

97 citations

Journal ArticleDOI
TL;DR: In this article, the formation of core-shell nanoparticles (SnO2@Pt/C) was measured by UV-vis spectrophotometry, and the results showed that the nano-particle formation was associated with an increase in the electrochemically active surface area.
Abstract: This paper presents a study on the ethanol oxidation reaction using SnO2@Pt/C core–shell structures as electrocatalysts. All the materials used, including Pt/C and PtSn/C E-tek, were 20% (w/w) metal on carbon. The formation of core–shell nanoparticles (SnO2@Pt/C) was measured by UV–vis spectrophotometry. X-ray diffraction measurements showed Pt (shell) diffraction patterns without influence from the SnO2 core and without any shift in 2θ values for Pt. The diameters of the core–shell particle structures, measured using high-resolution transmission electron microscopy images, were in the range of 3–16 nm. The electrochemical profile for SnO2@Pt/C in an acidic medium (H2SO4 at a concentration of 0.5 mol L−1) was almost the same as the typical electrochemical behavior for Pt in an acidic medium. Furthermore, the onset potential for the ethanol oxidation reaction using SnO2@Pt/C was almost the same as that for PtSn/C E-tek (0.23 V versus the reversible hydrogen electrode). However, the mass current peak densities for ethanol oxidation were 50% higher on SnO2@Pt/C than on PtSn/C E-tek. In the polarization curve, the mass current density for ethanol oxidation was higher at all potentials for SnO2@Pt/C when compared to Pt/C and PtSn/C E-tek. At 0.5 V, the current mass density for ethanol oxidation on SnO2@Pt was 2.3 times of that for the same process on the commercial material. The electrocatalytic activity of SnO2@Pt/C for ethanol oxidation was associated with an increase in the electrochemically active surface area. However, an electronic effect should also be considered because the Pt shell changes its electronic structure in the presence of the foreign core.

83 citations


Cited by
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Journal ArticleDOI
01 Feb 2018
TL;DR: In this article, a facile and general approach to catalyst development via surface oxidation of abundant carbon materials to significantly enhance both the activity and selectivity for H2O2 production by electrochemical oxygen reduction was demonstrated.
Abstract: Hydrogen peroxide (H2O2) is a valuable chemical with a wide range of applications, but the current industrial synthesis of H2O2 involves an energy-intensive anthraquinone process. The electrochemical synthesis of H2O2 from oxygen reduction offers an alternative route for on-site applications; the efficiency of this process depends greatly on identifying cost-effective catalysts with high activity and selectivity. Here, we demonstrate a facile and general approach to catalyst development via the surface oxidation of abundant carbon materials to significantly enhance both the activity and selectivity (~90%) for H2O2 production by electrochemical oxygen reduction. We find that both the activity and selectivity are positively correlated with the oxygen content of the catalysts. The density functional theory calculations demonstrate that the carbon atoms adjacent to several oxygen functional groups (–COOH and C–O–C) are the active sites for oxygen reduction reaction via the two-electron pathway, which are further supported by a series of control experiments. The direct synthesis of hydrogen peroxide via oxygen reduction is an attractive alternative to the anthraquinone process. Here, a general trend linking oxygenation of carbon surfaces with electrocatalytic performance in peroxide synthesis is demonstrated, and computational studies provide further insight into the nature of the active sites.

967 citations

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TL;DR: In this paper, a review of surface-modified TiO2 photocatalysis based on photo-induced interfacial charge transfer has been conducted, which is mainly focused on environmental remediation, and various surface modifiers are classified according to the kind of surface modifiers and their effects on photocatalytic reaction mechanism and kinetics are discussed in detail.
Abstract: This paper reviews recent studies on the semiconductor photocatalysis based on surface-modified TiO2 of which application is mainly focused on environmental remediation. TiO2 photocatalysis that is based on the photoinduced interfacial charge transfer has been extensively studied over the past four decades. A great number of modification methods of semiconductor photocatalysts have been developed and investigated to accelerate the photoconversion, to enable the absorption of visible light, or to alter the reaction mechanism to control the products and intermediates. In this regard, various modification methods of TiO2 are classified according to the kind of surface modifiers (metal-loading, impurity doping, inorganic adsorbates, polymer coating, dye-sensitization, charge transfer complexation) and their effects on photocatalytic reaction mechanism and kinetics are discussed in detail. Modifying TiO2 in various ways not only changes the mechanism and kinetics under UV irradiation but also introduces visible light activity that is absent with pure TiO2. Each modification method influences the photocatalytic activity and mechanism in a way different from others and the observed modification effects are often different depending on the test substrates and conditions even for the same modification method. Better understanding of the modification effects on TiO2 photocatalysis is necessary to obtain reliable results, to assess the photoconversion efficiency more quantitatively, and to further improve the modification methods.

840 citations

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TL;DR: A high and growing prevalence of COPD is suggested, both globally and regionally, and there is a need for governments, policy makers and international organizations to consider strengthening collaborations to address COPD globally.
Abstract: In a follow–up to the 2011 United Nations (UN) high level political declaration on non-communicable diseases (NCDs) [1], the World Health Assembly, in 2012, endorsed a new health goal (the “25 by 25 goal”), which focuses on reduction of premature deaths from COPD and other NCDs by 25% by the year 2025 [2]. Despite this initiative, experts have reported that COPD remains a growing [3], but neglected global epidemic [4]. The World Health Organization (WHO) estimated that there were about 62 million people with moderate to severe COPD in 2002, with the total number of COPD cases predicted to increase to about 200 million in 2010 [5,6]. According to the 2010 Global Burden of Disease (GBD) study, COPD was responsible for about 5% of global disability–adjusted life years – DALYs (76.7 million) – and 5% of total deaths (2.9 million) [7,8]. COPD is currently rated the fourth most common specific cause of death globally and predicted to be the third by 2030, in the absence of interventions that address the risks – especially tobacco smoking, exposures to combustion products of biomass fuels and environmental pollution [9,10]. The burden of COPD has been reported to be high in some high–income countries (HIC), particularly due to high prevalence of smoking in these settings [11]. For example, between years 2000 and 2010, about 4%–10% of adults were diagnosed with non–reversible and progressive airway obstruction (a basic feature of COPD) in population–based surveys across many European countries, with smoking indicated as a major risk [12]. The WHO has estimated that in many HIC up to 73% of COPD deaths are related to tobacco smoking [6]. The European Union (EU) reported that the direct cost from COPD was over 38.6 billion Euros in 2005, representing about 3% of total health care expenditure [13,14]. In the United States (US), over 2.7 million adults were estimated to have COPD in 2011, with about 135 000 deaths reported [15]. In 2010, the US government spent nearly US$ 49.9 billion on COPD, including 29.5 billion spent on direct health care, 8.0 billion on indirect morbidity and 12.4 billion on indirect mortality costs, respectively [15]. Meanwhile, it has been estimated that despite a high prevalence of COPD in some HIC, 90% of COPD deaths still occur in low– and middle–income countries (LMIC)in the future [4] and 40% of these deaths are attributable to smoking [6]. The burden in LMIC has been comparatively high owing to relatively low COPD awareness, challenges with COPD diagnosis and increased exposures to additional risk factors, especially combustion products of biomass fuels [16]. Salvi and colleagues reported that about 3 billion people globally are exposed to smoke from biomass fuel, compared to 1 billion people who smoke tobacco globally [17]. In many developing countries COPD is neglected by governments, physicians, experts and the pharmaceutical industry, although it's been identified as an important public health problem [4]. In the last two decades, the Burden of Obstructive Lung Disease (BOLD) initiative has been collecting country–specific data on the prevalence, risk factors and socioeconomic burden of COPD, using standardized and tested methods for conducting COPD surveys in the general population [18]. This is expected to provide governments of many nations with country–specific evidence on which to develop policy on COPD prevention and management [18]. As noted above, this initiative is yet to take a full effect in many LMIC [19]. In addition, spirometry (the gold standard for COPD diagnosis) is not widely available in many LMIC [16]. Even when it is there, professionals in LMIC are often not being trained properly on how to use spirometers or interpret spirometry results. There is concern that COPD burden has been underestimated, owing to over–reliance on doctor’s diagnosis, with many diagnoses not being based on spirometry and international diagnostic guidelines [20]. The lack of routine COPD data collation and effective health information management system in many LMIC also implies that these settings could have been grossly under–represented in global burden of COPD estimates [11]. Some global and regional estimates of COPD burden have been published [1,21–23]. However, despite the fact that COPD is now prevalent in both HIC and LMIC, experts have raised concerns that reliable estimates of COPD prevalence are still few in many parts of the world. Moreover, many of the estimates are based on varying definitions and diagnostic criteria of COPD [9]. Also, some of the current estimates were reported before the BOLD surveys in several countries, thereby failing to account for the additional spirometry–based epidemiological data from the BOLD surveys. There is a need for a revised and updated estimate of COPD prevalence across world regions. We conducted a systematic review of COPD prevalence based on spirometry data across world regions. Our aim was to provide global and regional prevalence rates of COPD that could facilitate adequate policy response in these regions.

746 citations

Journal ArticleDOI
TL;DR: Most methods that are being exploited in nanoecotoxicology for analysis and characterization of nanomaterials are described, including electron microscopy and atomic force microscopy.
Abstract: Environmental risk assessments of engineered nanoparticles require thorough characterization of nanoparticles and their aggregates. Furthermore, quantitative analytical methods are required to determine environmental concentrations and enable both effect and exposure assessments. Many methods still need optimization and development, especially for new types of nanoparticles in water, but extensive experience can be gained from the fields of environmental chemistry of natural nanomaterials and from fundamental colloid chemistry. This review briefly describes most methods that are being exploited in nanoecotoxicology for analysis and characterization of nanomaterials. Methodological aspects are discussed in relation to the fields of nanometrology, particle size analysis and analytical chemistry. Differences in both the type of size measures (length, radius, aspect ratio, etc.), and the type of average or distributions afforded by the specific measures are compared. The strengths of single particle methods, such as electron microscopy and atomic force microscopy, with respect to imaging, shape determinations and application to particle process studies are discussed, together with their limitations in terms of counting statistics and sample preparation. Methods based on the measurement of particle populations are discussed in terms of their quantitative analyses, but the necessity of knowing their limitations in size range and concentration range is also considered. The advantage of combining complementary methods is highlighted.

590 citations

Journal ArticleDOI
TL;DR: This paper presents a practical guide on how to count and size nanoparticles using spICPMS, and an alternative protocol is provided for determining particle size that broadens the applicability of the technique to all types of inorganic nanoparticles.
Abstract: Currently there are few ideal methods for the characterization of nanoparticles in complex, environmental samples, leading to significant gaps in toxicity and exposure assessments of nanomaterials. Single particle-inductively coupled plasma-mass spectrometry (spICPMS) is an emerging technique that can both size and count metal-containing nanoparticles. A major benefit of the spICPMS method is its ability to characterize nanoparticles at concentrations relevant to the environment. This paper presents a practical guide on how to count and size nanoparticles using spICPMS. Different methods are investigated for measuring transport efficiency (i.e., nebulization efficiency), an important term in the spICPMS calculations. In addition, an alternative protocol is provided for determining particle size that broadens the applicability of the technique to all types of inorganic nanoparticles. Initial comparison, using well-characterized, monodisperse silver nanoparticles, showed the importance of having an accurate...

582 citations