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991.
J. C. M. Silva R. F. B. De Souza G. S. Buzzo E. V. Spinacé A. O. Neto M. H. M. T. Assumpção 《Ionics》2014,20(8):1137-1144
Platinum nanoparticles supported on physical mixtures of Vulcan carbon and TiO2 (Pt/(C?+?TiO2)) were prepared by the borohydride method and tested for methanol electro-oxidation in alkaline media. X-ray diffraction (XRD) analyses showed peaks characteristic of Pt face-centered cubic (fcc) structure and peaks associated with TiO2 and carbon. Transmission electron microscopy (TEM) images showed the Pt nanoparticles distributed preferentially over the TiO2 support with average particle sizes between 5 and 6 nm. Cyclic voltammograms showed a decrease of Pt surface area with increasing TiO2 load while linear sweep in the presence of methanol showed Pt/(C?+?TiO2) (60:40) with the highest current density in accordance with chronoamperometry. The results were attributed to Pt-based nanoparticles on TiO2 which show enhanced catalytic activities for methanol oxidation due to a metal-support interaction. Furthermore, TiO2 is a semiconductor with low conductivity when compared to carbon. Thus, it is expected that an intermediate proportion of carbon and TiO2 as substrate could improve the activity of Pt nanoparticles without substantial loss of conductivity, resulting in a synergic effect. 相似文献
992.
The electrochemical behavior of Hg2+ was investigated in poly(Eriochrome Black T)-modified carbon paste electrode (CPE) using cyclic voltammetry (CV). Poly(Eriochrome Black T) was prepared in an alkaline medium on the surface of the CPE using a solution of Eriochrome Black T with the CV technique. The electrochemical impedance study revealed a better charge transfer kinetics at the modified electrode. The effects of variation of the experimental conditions, such as the concentration of electrolytes, pH, deposition time, and the deposition potential, which maximize current efficiency were studied. The optimum response of Hg2+ was observed in 1.0 M KCl solution. The differential pulse anodic stripping voltammetric technique was employed successfully to detect Hg2+, which gave a good linear response at low concentration levels of Hg2+. The detection limit was found to be 2.2?×?10?10 M (S/N?=?3), which is comparable with that achieved in multiwall carbon nanotube-modified electrode. The remarkable electroanalytical performance of the modified electrode makes it amenable to employ it successfully as an electrochemical sensor for the determination of hazardous pollutant Hg2+ in environmental samples. 相似文献
993.
为研究超高韧性水泥基复合材料(ultra-high toughness cementitious composites, UHTCC)在内埋炸药爆炸下的抗爆性能和损伤破坏规律,对不同炸药埋深下的UHTCC和高强混凝土(high-strength concrete, HSC)进行了内埋炸药抗爆实验。得到了两种材料靶体的破坏状态,并利用接触爆炸的实验结果计算出了两种材料的抗爆性能参数。结果表明,在相同条件下,UHTCC抗爆性能优于高强混凝土。为了进一步探究UHTCC的抗压强度、抗拉强度以及拉伸韧性对靶体在内埋炸药下抗爆性能的影响,首先,采用改进的K&C模型对炸药埋深为40 mm的超高韧性水泥基复合材料靶体进行数值模拟,模拟结果与实验结果基本吻合,并根据数值模拟的结果得到了爆炸冲击波沿靶体径向衰减速度大于轴向衰减速度这一规律,验证了数值模型的有效性;然后,通过调整改进K&C模型中与抗压强度、抗拉强度以及拉伸韧性相关的参数,数值预测了不同抗压强度、抗拉强度以及拉伸韧性下UHTCC靶体的破坏状态,发现增强UHTCC的韧性可以有效防止靶体发生整体性破坏,增大UHTCC的抗拉强度可以减小靶体迎爆面的开坑直径,增大UHTCC的抗压强度对减小开坑直径效果不明显。 相似文献
994.
Ribeiro Camila de Lima Santos João G. M. Souza Jurandir R. Paterno Leonardo G. 《Journal of Solid State Electrochemistry》2019,23(3):783-793
Journal of Solid State Electrochemistry - The present work reports the performance and the mechanism of detection of a voltammetric sensor for salicylic acid (SA) in a skin care product employing a... 相似文献
995.
Eric de Souza Gil Severino Carlos B. de Oliveira Ana Maria de Oliveira‐Brett 《Electroanalysis》2012,24(11):2079-2084
The anodic oxidation of the hydroxyanthraquinones carminic acid (CA) and chrysazin (CR) was investigated. The oxidation of CA proceeds in a pH‐dependent cascade mechanism, concerning the hydroquinone, the catechol and the 3‐OH groups in the anthraquinone moiety. The oxidation of the hydroquinone following the catechol electron‐donating groups occurs first at low positive potentials, the 3‐OH group is oxidized irreversibly at a higher potential. The oxidation of CR is pH‐dependent and occurs in successive steps. Oxidation of the hydroquinone tautomer in the CR‐ring occurs first, and the symmetrical 1‐OH and 8‐OH groups are irreversibly oxidized at the same higher potential. 相似文献
996.
Fbio de Souza Barbosa Leonardo Capra Pezzi Marisa Tsao Tiago Franco de Oliveira Sandra Manoela Dias Macedo Elfrides E.S. Schapoval Andreas S.L. Mendez 《Biomedical chromatography : BMC》2019,33(4)
Carbapenems show recognized instability in aqueous solutions; therefore some care must be taken in their handling and preparation and their use in the hospital environment. The stability and degradation products of imipenem were investigated from conditions that simulate its clinical use. For this, a simple stability‐indicating method by HPLC‐DAD was validated with a focus on the quantitation of drug concentration remaining from infusion solutions (sodium chloride 0.9% and glucose 5%). The degradation products formed were identified by high‐resolution mass spectrometry (ESI‐Q‐TOF‐MS/MS), with detection of the [M + H]+ ions at m/z 318 (DP‐1), m/z 599 (DP‐2) and m/z 658 (DP‐3). The most probable elemental compositions were obtained with a high degree of confidence, where the error between the masses observed and calculated was 1.25 ppm for DP‐1, ?0.33 ppm for DP‐2 and 1.82 ppm for DP‐3. The DP‐1 degradation product resulted from cleavage of the β‐lactam ring; DP‐2 corresponded to the drug dimer; and DP‐3 was generated from the interaction between imipenem and cilastatin. The proposed method provides a safe and reliable alternative for the quantitation of imipenem, and the stability data obtained by ESI‐Q‐TOF help in understanding the drug behavior under the conditions of clinical use. 相似文献
997.
Particle Detachment Under Velocity Alternation During Suspension Transport in Porous Media 总被引:1,自引:0,他引:1
Pavel Bedrikovetsky Abbas Zeinijahromi Fernando D. Siqueira Claudio A. Furtado Antonio Luiz S. de Souza 《Transport in Porous Media》2012,91(1):173-197
Flow of suspensions in porous media with particle capture and detachment under alternate flow rates is discussed. The mathematical
model contains the maximum retention concentration function of flow velocity that governs the particle release and is used
instead of equation for particle detachment kinetics from the classical filtration model. An analytical model for suspension
injection with alternate rates was derived, and a coreflood by suspension with alternate rates was carried out. The modelling
and laboratory data are in a good agreement, which validates the modified particle detachment model with the maximum retention
function. 相似文献
998.
Thomaz R. S. de Souza C. T. Papaléo R. M. 《Applied Physics A: Materials Science & Processing》2011,104(4):1223-1227
We report on the effect of light-ion irradiation on the size distribution of etched tracks produced by medium energy heavy-ions
in polycarbonate. Makrofol KG polycarbonate foils were treated with 2 MeV H+ ions at different fluences φ either before or after a short irradiation with 18 MeV Au7+. The heavy ion irradiation was used to produce the latent tracks in the foils and the proton beam acted as a perturbation
to the matrix. The proton irradiation causes initially a decrease in the mean etched pore size, as compared to samples only
bombarded by Au ions, reaching a minimum at H+ fluences around 2–5×1013 cm−2, while at higher φ the pore size starts to grow again. This effect is attributed to the action of two competitive processes that dominate in
different fluence regimes. The decrease in the pore radii at low fluences is attributed to an increase in crystallinity induced
by the proton beam. As the total dose builds up, this effect is surpassed by chain scission and amorphization that grow at
a lower rate and cause the pore radii to increase again. 相似文献
999.
Mrcio Santos Soares Danielle Fernandes da Silva Jssica Cristina Amaral Michelli Masaroli da Silva Moacir Rossi Forim Edson Rodrigues‐Filho Maria Ftima das Graas Fernandes da Silva Joo Batista Fernandes Marcos Antnio Machado Alessandra Alves de Souza Carlos Henrique Gomes Martins 《Rapid communications in mass spectrometry : RCM》2020,34(Z3)
1000.
Letícia Coli Louvisse de Abreu Bárbara de Azevedo Abrahim-Vieira Alessandra Mendonça Teles de Souza Eduardo Costa Pinto Mariana da Silva Gonçalves Alice Simon Gil Mendes Viana Carlos Rangel Rodrigues Valeria Pereira de Sousa Lucio Mendes Cabral 《Biomedical chromatography : BMC》2020,34(7):e4832
Injectable solutions containing epinephrine (EPI) and norepinephrine (NE) are not stable, and their degradation is favored mainly by the oxidation of catechol moiety. As studies of these drugs under forced degradation conditions are scarce, herein, we report the identification of their degradation products (DP) in anesthetic formulations by the development of stability-indicating HPLC method. Finally, the risk assessment of the major degradation products was evaluated using in silico toxicity approach. HPLC method was developed to obtain a higher selectivity allowing adequate elution for both drugs and their DPs. The optimized conditions were developed using a C18 HPLC column, sodium 1-octanesulfonate, and methanol (80:20, v/v) as mobile phase, with a flow rate of 1.5 mL/min, UV detection at 199 nm. The analysis of standard solutions with these modifications resulted in greater retention time for EPI and NE, which allow the separation of these drugs from their respective DPs. Then, five DPs were identified and analyzed by in silico studies. Most of the DPs showed important alerts as hepatotoxicity and mutagenicity. To the best of our acknowledgment, this is the first report of a stability-indicating HPLC method that can be used with formulations containing catecholamines. 相似文献