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In this study, a spectrophotometric-chemometric (Spec-Chem) approach was applied as an alternative to chromatography to monitor ATZ and by-products after photolytic and photocatalytic oxidation aiming to unveil the ATZ degradation mechanism. Spec-Chem is an accessible, easy-to-operate, low-cost analytical approach to monitor atrazine (ATZ) and by-products, and its applicability was validated by HPLC, the reference technique for the evaluation of pollutant degradation mechanisms. The chromatographic (DChro) and spectrophotometric (DSpec) data found 95% and 57% ATZ removal after 30 min, respectively, proving that the DSpec erroneously induces a 38% loss in removal efficiency. When DSpec was treated by multivariate curve resolution (MCR) analysis for providing chemometric data (DChem), it found ATZ removal and hydroxyatrazine (HAT) formation statistically equal to DChro (t-test, p = 0.05). After unraveling the ATZ degradation mechanism using Spec-Chem, a new hypothesis for the kinetic calculation of ATZ degradation was presented, where the concentrations of ATZ and HAT were used to find k and R2 values representative for the ATZ degradation mechanism. The values found for k were compatible with the literature under similar conditions of ATZ degradation, and the linear correlation coefficients (R2 = 0.99) showed an optimal fit for the proposed hypothesis. Thus, Spec-Chem was successfully applied to unravel the mechanism of photocatalytic degradation of ATZ in the presence of TiO2, while k was obtained by the new hypothesis proposed that considered ATZ and HAT concentration as parameters of kinetic interest. Therefore, the importance of monitoring quantitatively ATZ and HAT were provided in this study, providing new information for the scientific community.

Among the electrochemical methods, potentiostatic electrosynthesis is the most common method for polymer deposition. In this case, it is possible to avoid undesirable reactions occurring by controlling the synthesis potential. However, this method does not control the kinetics itself, since the measured current values are not real, due to the fact that the polymer surface area changes considerably during the polymerization. In this way, it is essential to develop a method to normalize the current using instantaneous area values to have precise data about the polymer growth. Then, this work describes a method to calculate the electroactive area change during the electrochemical polymerization. For this purpose, PPy films were synthesized electrochemically at different potentials to study their effect on the synthesis process. Electrochemical impedance data was taken in several growth charges to characterize the growth curve completely. Also, electrochemical quartz crystal microbalance (EQCM) and scanning electron microscopy (SEM) were used. Analyzing the impedance complemented with EQCM data, it was possible to obtain the relative area change during the polymer formation. Furthermore, with this information, it was possible to understand the steps that occur during the synthesis and relate them to the measured current curve, which was impossible before, since it is a function of an unknown area. Therefore, it has been observed that depending on the potential applied on potentiostatic synthesis, the deposition mechanism changes, which consequently modifies the polymer morphology, as well as electrochemical properties.

Made available in DSpace on 2020-12-12T01:30:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Herein, to balance the overall performance of SPEEK membrane, the imidazolium hydrogen sulfate (Im.HSO4), 1-methylimidazolium hydrogen sulfate (MI.HSO4), and 1-butyl-3-methylimidazolium hydrogen sulfate (BMI.HSO4) ionic liquids (ILs) were used as dopants in polymer matrix. A series of SPEEK/ionic liquid composite membranes were successfully fabricated by casting method and evaluated. Comparative studies showed that the membranes doped with 5 wt.% of MI.HSO4 or BMI.HSO4 ILs showed an increase in the proton conductivity of 50% and 30% at 80 °C, respectively, compared with the pristine SPEEK membrane. The proton exchange membrane fuel cell (PEMFC) performance demonstrated that the membrane doped with 5 wt.% of BMI.HSO4 IL (SBMI5) has the highest current density value and the highest power density without loss of performance as temperature increases. This result indicates that this membrane is promising for fuel cells application. Chemistry Department Federal University of São Carlos, P. O. Box 676 Department of Chemistry Universidade Estadual Paulista–Unesp, P.O. Box 473 LRC-Institute of Chemistry Universidade Federal do Rio Grande do Sul, P. O. Box 15003 Department of Chemistry Universidade Estadual Paulista–Unesp, P.O. Box 473

The effect of quinones on the deactivation of four- and five-coordinate Co-Schiff base catalysts used for the oxidation of lignin models is systematically studied. 2,6-Dimethoxy-1,4-benzoquinone does not affect the catalytic activity of any of the studied Co-Schiff base catalysts, but 1,4-benzoquinone and 2-methoxy-1,4-benzoquinone have a strong effect on the catalytic activity. Quinone solubility in the reaction solvent does not correlate with catalyst deactivation, but added pyridine (a basic axial ligand) promotes catalyst deactivation by quinone. The synthesis and characterization of a catalytically inactive Co-Schiff base-quinone complex is presented and preliminary computational analysis of this complex in comparison to a dimeric Co-Schiff base peroxo complex is also discussed. Quinone and the Co-Schiff base redox potentials are found to correlate with catalyst deactivation. Thus, catalysts with a lower redox potential were more susceptible to deactivation, and quinones with a higher redox potential deactivate the catalysts. Based on these results, two mechanisms for deactivation of the catalyst are proposed. The first mechanism describes how the formation a Co-Schiff base-quinone complex prevents formation of the key catalytically active Co-superoxo complex. The second proposed mechanism suggests that quinones inhibit the Co-Schiff base catalyst by scavenging intermediate Co-superoxo radicals.

Pt is still the state of the art electrocatalyst for the oxidation of ethanol but it is poisoned by the CO-intermediates resulting in a slow ethanol oxidation reaction kinetic. Here, we show that the electrocatalytic activity of unsupported Pt nanoparticles for the ethanol electro-oxidation in acid medium can be significantly enhanced by the addition of small amounts of CeO2 nanoparticles (≤5 wt%). Comparative studies on bare Pt, Pt-CeO21 wt% and Pt-CeO2—5 wt% catalysts composed of Pt nanoparticles with different sizes (from 10 to >40 nm for bare Pt, and from 6 and 20 nm for the Pt-CeO2 composites) revealed an increase of the microstrain with the decrease of the Pt's average particle size. Besides, there is a strong electronic interaction between the Pt and CeO2 nanoparticles, demonstrated by a systematic shift of the Pt 4f7/2 peak to lower binding energy with the addition of CeO2. Chronoamperometric data showed that the steady state current density normalized to Pt's electrochemical surface area for ethanol electro-oxidation is mainly governed by the microstrain, and it decreases with increasing strain. This trend is explained in terms of a more facile activation of the ethanol molecule at the surface of less strained Pt nanoparticles. Thus, the best performance was obtained with Pt-CeO2 1 wt% formed by Pt nanoparticles with an average size of 18 nm, reaching 1.0 A·m−2 after 900 s at 0.6 V vs SCE.

New materials can be developed using a known compound with enhanced properties modifying and controlling its microstructure, morphology, and density of defects. In this work, a new material was produced by the addition of ionic liquid (IL) to the poly(o-methoxyaniline) (POMA) conductive polymer, in the form of esmeraldine salt. The polymer impregnated with IL was tested as an electrode for use in supercapacitors. The results show that the charge storage properties of the materials are dependent on the length of the alquil substituent of imidazolium ring of ionic liquid cation. The best results, obtained by the addition of 1-butyl-3-methylimidazolium triflate IL to the polymer, improved electrical charge storage and electrochemical stability, making the material a promising electrode for supercapacitor devices. This compound has specific capacitance of 205 F/g, five times larger than pure POMA and was stable for 3000 cycles of charge/discharge experiments carried out at 1.0 A/g.

ACKNOWLEDGMENTS The support of this research by FAPESP (grants: 2013/07296-2, 2014/50249-8, 2015/12851-0, 2017/11986-5), Shell, CsF-PVE (99999.007708/2015-07), Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - Brasil (CAPES) - Finance Code 001 and CNPq is gratefully acknowledged.

A fast, efficient, and non-chromatographic method was presented in this study for nitrite, nitrate, and p-nitrophenol (N-compounds) extraction and speciation analysis of environmental samples. By applying ultrasound-assisted solid–liquid extraction (USLE), analytes were efficiently extracted from water, soil, or sediment collected in areas of environmental disaster. These analytes were selectively converted to NO(g) through UV photolysis (NO3−), H2O2/UV photocatalysis (PNP), and direct conversion (NO2−). Following conversion, NO(g) was separated from the liquid phase and determined by high-resolution continuum source molecular absorption spectrometry (HR-CS MAS). The LODs obtained were 0.097 ± 0.004 mg L−1 for nitrite, 0.119 ± 0.004 mg L−1 for nitrate, and 0.090 ± 0.006 mg L−1 for p-nitrophenol. On applying this speciation method to environmental samples, concentrations were found to be up to 0.99 ± 0.03 mg L−1 (NO2−), 49.80 ± 2.5 mg L−1 (NO3−), and 0.10 ± 0.02 mg L−1 (PNP). Finally, addition/recovery study of real water, soil, and sediment samples showed 101 ± 2% recovery for NO2−, 100 ± 1% for NO3−, and 96 ± 5% for PNP.

Two ionic liquids (ILs) with different alkyl chains, 1-butyl-3-methylimidazolium chloride (BMI.Cl) and 1-hexadecyl-3-methylimidazolium chloride (C16MI.Cl), were incorporated into ZnO particles using the microwave-assisted hydrothermal (MAH) method. The morphology and microstructure of ZnO and ZnO/IL composites were characterized along with their photocatalytic effect for dye degradation. While the incorporation of ILs into the ZnO particles did not alter their morphology, it converted the shallow defects into deep defects. These changes improved Rhodamine B (RhB) photodegradation efficiency. The dye degradation reached 62% when ZnO/C1640 was used, whereas it reached 30% when pure ZnO was used, during the same time interval.

We developed Ptpc/Co/Pt nanostructured metallic multilayers (MM) electrodes for methanol and carbon monoxide electro-oxidation. This material uses as an intermediate layer a non-noble metal (cobalt), which is a low cost material. Cyclic voltammetry was used to characterize the electrode electrochemical behaviour for methanol and carbon monoxide. In addition, electrochemical impedance spectroscopy (EIS) was used to study the methanol oxidation on these multilayers. An increase in the peak current density of about 35% for Ptpc/Co10/Pt5 nanostructured metallic multilayer compared to Ptpc electrode was observed for methanol oxidation reaction (MOR). Carbon monoxide electro-oxidation showed large current density for all multilayers electrodes and the onset potentials for this reaction was displaced toward more negative potentials, which indicates weaker adsorption energy for CO over the surface of the materials compared to Ptpc. EIS data indicated a lower charge transfer resistance (Rct) for Ptpc/Co10/Pt5 MM nanostructured during the methanol electro-oxidation, that indicates higher electrocatalytic activity for this electrode compared to Ptpc. Computational modelling results indicate that the presence of a Co-underlayer for Pt/Co/Pt (111) nanostructured system decrease the center of d-band and, consequently, increase the catalytic activity compared to Pt (111) system.

This paper reports the RuO2-SnO2 binary film synthesis and the influence of the SnO2 composition increase in the ion transport and pseudocapacitive properties of RuO2. The binary oxide was synthesized by polymeric precursors method followed deposition on a titanium substrate. XRD analysis showed the phases formed and the crystallites size of the samples. SEM allowed studying the morphology variation of the films with the addition of SnO2. The material obtained was evaluated by electrochemical techniques in 1 M H2SO4 electrolyte solution. The voltammograms showed that the pseudocapacitive characteristic of the RuO2 – SnO2 binary film remained even for greater amount of SnO2 in the binary mixture. The electrochemical impedance spectroscopy results are discussed in terms of complex capacitance and complex power. The relaxation time constant of the systems and capacitance values at low frequency, were determinate from complex capacitance plots.

ZnO particles synthesized by the microwave-assisted hydrothermal method were sensitized with different amounts of ionic liquid (IL) 1.3-dimethylimidazolium iodide (MMI.I). The structure of the modified and unmodified ZnO particles were characterized by X-ray diffraction, Raman spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM), ultraviolet-visible (UV–vis) absorption spectroscopy, photoluminescence (PL), and photoelectrochemical measurements. While the sensitization of ZnO particles by the ionic liquid does not change the ZnO phase, it reduces the particle size and converts shallow defects to deep defects. These changes cause the photocurrent density of the ZnO/IL films to increase significantly from 0.05 mA cm−2 for pure ZnO to 0.52 and 1.24 mA cm−2 for the ZnO films containing 20% and 35% by mass of the IL, respectively, at 1.08 V vs. Ag/AgCl. This about 24-fold increase in the photocurrent density of the ZnO/IL35 sample may indicate that the MMI.I IL may be acting as a dye, since it is constituted by an organic part, MMI+. This good performance presented by this sample indicates that this is a promising material for photoanode in solar cells.

The chemical composition of the essential oil from leaves of Croton wagneri Mull. Arg. grown in Ecuador was studied. A total of 135 volatile compounds were identified in the essential oil, of which the most prominent were cis-chrysanthenol (27.5%) and myrcene (19.2%). Furthermore, we assessed the antioxidant properties using the DPPH and the ferric reducing antioxidant power assays and found that the extract had a moderate scavenging effect.

Although macromolecules such as polymers are in widespread industrial use, pure formulations rarely have precisely the properties new applications demand. Pure polymer is often too brittle and inflexible, necessitating plasticizers to soften or toughen films and bulk polymer materials. In practice, new formulations are developed by extensive trial-and-error methods, as no general molecular explanations exist for the mechanism of plasticization to aid in determining the optimal structure and concentration of plasticizers. Here, through atomistic molecular simulations augmented with advanced sampling techniques, we develop an atomic-level picture of the processes in plasticization by directly calculating free energies that govern the interaction between polymers and small-molecule plasticizers. This work focuses on the influence of two common plasticizer molecules-glycerol and sorbitol-interacting with polyvinyl alcohol (PVA), a frequently used component of polymer films. In particular, we focus on conformational and hydrogen bond structure changes induced in globules of PVA by the plasticizer molecules, with the hypothesis that hydrogen bonding plays a role in the incorporation of these plasticizers into PVA and, thus, in the observed mechanical properties. While we focus on nanoscopic systems, we observe distinct preferences in the conformational free energy that can be connected to the performance of polymer materials at laboratory and industrial scales. This work presents a new molecular perspective from which effective plasticizers can be developed and presents a firm basis from which important analyses of plasticization in complex chemical environments relevant to industry may be developed.

In this study, we have assessed directed carbon-hydrogen activation (CHA) for alkylation of monomeric, dimeric, and polymeric lignin models using Murai's catalyst [RuH2(CO)(PPh3)3]. Based on related work from our laboratory showing that isolated organosolv lignin bears benzylic directing groups ideal for CHA reactions, this approach could offer new methodology for the valorization of biorefinery lignin. Monomeric and dimeric models bearing a keto group at the benzylic position undergo Ru-catalyzed alkylation in good to excellent yield. Similarly, models bearing a benzylic OH group also undergo alkylation via a tandem oxidation/alkylation process enabled by the Ru catalyst. Polymeric models show low levels of functionalization as a result of the poor solubility of the starting polymer. With unsymmetrical models, functionalization occurs first at the least sterically hindered ortho-site, but a subsequent alkylation, leading to disubstituted products can occur at the more sterically hindered site, leading to hexasubstituted arenes. The reaction shows sensitivity to free phenolic OH groups, which appears to reduce the yield in some reactions, and is also a contributing factor to the low yields observed with polymeric lignin models. Combining CHA methodology with lignin isolation technology able to introduce appropriate directing groups for catalytic functionalization will form the basis for improved conversion of lignin to high value chemical products.

Fuel quality control has gained interest in many countries owing to the potential damage of low-quality fuel to engines, the environment, and economy. Thus, the application of analytical techniques to verify quality control of fuels has become crucial. The portable micro-spectrometer in the near infrared region (microNIR) has gained credibility as a successful analytical technique in several quality control sectors. The possibility of real-time analysis using a nondestructive and reliable method is the main advantage of this methodology. In this work, chemometric models (PLS) were developed using microNIR data to determine the amount of biodiesel in diesel (LODBio = 0.5wt%; LOQBio = 1.8wt%; and RMSEPBio = 1.8wt%); sulfur in diesel (LODS = 2.4mgL-1; LOQS = 8.0mgL-1; and RMSEPS = 13.2mgL-1); gasoline, ethanol, and methanol in C-type gasoline (LODgas = 0.55wt%; LOQgas = 1.84wt%; and RMSEPgas = 0.81wt%; LODeth = 0.75wt%; LOQeth = 2.5wt%; and RMSEPeth = 3.81wt%; and LODmet = 0.85wt%; LOQmet = 2.84wt%; and RMSEPmet = 1.80wt%); and water, methanol, and ethanol in ethanol-hydrated fuel (EHF) (LODH2O = 0.04wt%; LOQH2O = 1.29wt%; and RMSEPH2O = 1.05wt%; LODmet = 0.52wt%; LOQmet = 1.73wt%; and RMSEPmet = 2.78wt%; and LODeth = 1.22wt%; LOQeth = 4.07wt%; and RMSEPeth = 4.41wt%). A total of 181 blends were prepared, with biodiesel and sulfur contents ranging from 0 to 100wt% and 10-500mgL-1, respectively. For gasoline blends, the gasoline, ethanol, and methanol contents ranged from 0.0 to 75.0wt%, 25.0-75.0wt%, and 0.0-50.0wt%, respectively. In the EHF control, the ethanol, water, and methanol contents ranged from 0.0 to 100.0wt%, 0.0-50.0wt%, and 0.0-50.0wt%, respectively. The proposed method presented high precision and accuracy in all cases, and the results showed that the microNIR technique had excellent performance in fuel quality control.

Different materials have been proposed as active electrode in electrochemical capacitors, including conducting polymers. Among them, several papers describe the use of polyaniline and its derivatives for such purpose. However, the use of poly(o-methoxyaniline), a polyaniline derivative, in ionic liquid electrolytes as pseudocapacitors has never been proposed in the literature. Therefore, the objective of this work is to investigate the electrochemical properties and stability of POMA casting film in ionic liquid electrolyte as electrode for supercapacitors. Cyclic voltammetry and galvanostatic charge/discharge experiments have been used to analyze the behavior of the films. The results show that POMA films have high specific capacitance and good electrochemical stability during 3000 cycles. Its initial value is 260 F g−1 in a mixture of ionic liquid and polyethylene glycol (80:20 v/v). The specific energy shows 70% retention from the initial value after 3000 cycles. Furthermore, the specific power remains remarkably stable during 3000 cycles, as well as the coulombic efficiency, which is about 99%. For these reasons this work opens up the possibilities of using conducting polymers in ionic liquids and illustrates its good behavior and stability for supercapacitor application.

The water photo-oxidation to oxygen on iron oxyhydroxide (FeOOH) deposited on a surface of semiconductor materials play a crucial role in the enhancement of different devices. In order to investigate how FeOOH works to produce O2 from water splitting, we have investigated the role of a deposited layer of FeOOH on the bismuth vanadate (BiVO4) films. The simple-modified method based on polyethylene glycol was applied to produce BiVO4 nanostructures and a FeOOH photoelectrodeposition methodology was used to cover the BiVO4 film surface. The photoelectrochemistry study for FeOOH modified BiVO4 revealed a 3.4 times increase in the photocurrent at 1.23 V vs. RHE. A possible explanation to the FeOOH mechanism is that it is actually a green rust containing a mixture of Fe (II) and Fe (III) that acts as center of charge transfer mediation and not as a catalyst itself. This hypothesis has been supported by a change absence in the onset potential, no photocurrent saturation, and no change in the charge carrier density. Moreover, the FeOOH also passivated the surface states of BiVO4 as the open circuit potential shifted 70 mV vs. RHE to more positive potentials.

Anatase titanium dioxide nanoparticles were synthesized via fast microwave-hydrothermal route and they were characterized by BET, SEM, XRD and EIS. The synthesis process took barely 20 s, which means a low sintering time which provides a decrease in the cost and energy required in the synthesis process. Pure anatase colloidal TiO2 particles were obtained under these synthesis conditions. Particulate TiO2 films were deposited onto high porous graphite substrates and their catalytic activity toward the oxygen reduction reaction in alkaline media was qualitatively demonstrated by cyclic voltammetry and linear sweep voltammetry. The ORR mechanism showed to follow the two-electron pathway via hydrogen peroxide production and further reduction to water.

The elucidation of photocatalysis and adsorption mechanisms in the pollutant removal, as well as the efficiency for each process, provide key information for polluted water remediation. In this respect, the present study analyzed the application of nanomaterials based on niobium pentoxide (Nb2O5) and hydroxyapatite (HAP) during Prozac® and 4-(trifluoromethyl)phenol (TFMP) photodegradation. Removals for Prozac® and TFMP were respectively 93% after 2 min and 64% after 5 min. The photodegradation kinetic constants by Nb2O5 nanoparticles were 2.1 min‐1 (R2 = 0.943) and 0.185 min‐1 (R2 = 0.994), respectively, for Prozac® and TFMP, using a Hg-MDEL reactor operating at 70 W microwave power. A detailed study of the mechanisms for Prozac® and TFMP photodegradation was carried out, confirming that the adsorptive, oxidative, and photolytic processes work together to remove and/or convert the compounds into by-products. Therefore, Prozac® and the main by-products were quantified, and the cytotoxicity response was evaluated using the Lepidium sativum and Allium cepa plants. The results showed that 3-phenyl-propyl-methylamine (PPMA) by-product was more toxic than Prozac® to plant growth, exhibiting seed seability of 4% (PPMA), 33% (Prozac®), 77% (α-[2-(Methylamino) ethyl] benzyl-alcohol, MAEB), and 81% (TFMP). Furthermore, the presence of these contaminants may increase phytotoxicity at the cellular level, fostering mutation, and cell death.

In this work, one-step electrochemical synthesis of a supercapacitor with high performance and stability based on carbon nitride and polypyrrole is described. The new composite was easily obtained through the electrodeposition of polypyrrole on the surface of carbon nitride using an aqueous suspension. This material was fully characterized using both theoretical studies and experimental techniques. The sample showed a capacitance value of 810 F g−1 (at 0.2 A g−1), retaining 92% of its initial value after 6000 charge-discharge cycles at 6.0 A g−1. Furthermore, the composite material has a capacitance value of 610 F g−1 at 9.0 A g−1. To explain these results, it was used impedance spectroscopy and DFT calculations. The computational calculations showed the formation of hydrogen bonds between the N H of the polypyrrole and the π-system of the carbon nitride which stabilized the structures. Besides, a planarization effect could also be observed over the polypyrrole chains. Both results are supported by the experimental data collected from the impedance experiments.

In this work, a new material was developed to be used as the active electrode in an electrochromic device based on layer-by-layer poly(o-methoxyaniline) and poly(3-thiopheneacetic acid) films. Its properties were compared to a poly(o-methoxyaniline) film prepared by casting with similar electrochemical properties. The film preparation technique, layer-by-layer, guarantees molecular interaction between layers. In this case, the interaction leads to a self-doping effect, inhibiting the ion transport from the solution to the polymer which is the rate limiting step during the device operation. The results show both a decrease in the time constant for color change as well as a strong increase in the coloration efficiency, from 144.7 to 542 cm2 C−1 for POMA casting and LBL films, respectively.

Poly(3-hexylthiophene) has been used in different photoelectrochemical devices as active material. However, its efficiency regarding photo-conversion is low and the coupling with a second compound is necessary to reduce the electron-hole recombination effect on the generation of photocurrent. The low efficiency could be related to the organization of the polymer. In this work, we propose the use of reduced graphene oxide as modifier to P3HT to enhance its photocatalytic properties. The results here obtained strong suggest, both theoretically and experimentally, an important change in the polymer chain organization from twisted to planar configuration. As consequence, an important increase in the photoelectrochemical properties were observed. In the present case an improvement of over 50% in the value of the photocurrent comparing the pure material and the binary one, processed under the same conditions. In addition, the half-life of the charge carrier increased substantially from 0.781 ms to 9.54 ms. The results are promising because they demonstrate that a higher organization level of the polymer chains increases the photocatalytic properties of the material. Furthermore, the theoretical study not only explains why the properties are improved, but also leads to new understanding of the electronic structure obtained in a binary material.

A new electrode for the photoelectrochemical removal of 17β-estradiol from water using ruthenium oxide nanoparticles supported on reduced graphene oxide is proposed in this study. The morphology, microstructure and the electrochemical performance of the material were characterized using HRTEM, XRD and Raman spectroscopy. The characterization showed the formation of reduced graphene oxide from a micro-wave assisted hydrothermal method with a particle size of 5.0 nm + 2.4 nm. The electrochemical measurements point to a high performance of the electrode in the presence of a white light source. The hormone removal efficiency in water containing 50 μmol L−1 of 17β-estradiol was evaluated using chronoamperometry at +1.0 V and the process was monitored using liquid chromatography. The reaction is pseudo first order with the removal of 92.2% of 17β-estradiol after 60 min of photoelectrocatalytic treatment.

In this paper, the electrochemical ageing of poly(3-hexilthiophene) was studied using two different films electrodeposited under different experimental conditions. The first one has been was prepared in acetonitrile with 0.1 mol L −1 of monomer + 0.1 mol L −1 of LiClO 4 (Film I). The second one has been synthesized in the same solvent with 0.2 mol L −1 of monomer + 0.2 mol L −1 of LiClO 4 , plus the addition of 10 mmol L −1 of pure water (Film II). The electrochemical ageing has been carried out by the application of an overoxidation potential. At every 20 minutes, a cyclic voltammogram and electrochemical impedance experiments were measured. Each film has exhibited different pathway for the ageing process. Film II showed a smooth degradation of the electrochemical properties, mainly at the interface polymer chains and solution in the pores. The other one, Film I, has presented a two steps degradation process, been the first, up to 120 min, characterized by smooth changes in all the electrochemical parameters necessary to describe the polymer. After 120 min, the second degradation process occurs characterized by an abrupt change in in all the parameters, indicating an important change not only in the electrochemical degradation of the polymer but also in its morphology, measured by SEM micrographs. Furthermore, two electrode impedance electronic experiments confirmed an important degradation of the bulk polymer for Film I.

The study of metallic multilayers (MM) has presented interesting highlights to understand electrocatalytic properties for organic molecules oxidation. This work reports the preparation and characterization of MM using rhodium or ruthenium as an intermediate layer, Ptpc/Rh/Pt and Ptpc/Ru/Pt, aiming to evaluate the electrocatalytic activity toward methanol and ethanol oxidation in acid medium. For methanol electro-oxidation, the evaluated MM presented higher current density than Ptpc, especially Ptpc/Rh2/Pt1 and Ptpc/Ru5/Pt2, where the increase in peak current density was 283% and 422% compared to Ptpc. By in situ infrared spectroscopy (FTIR in situ), it was observed that in MM the CO2 formation from methanol oxidation occurred in lower potentials compared to Ptpc. In the ethanol oxidation, Ptpc/Rh2/Pt1 and Ptpc/Ru5/Pt2 increase in peak current density 32% and 67% compared to Ptpc, respectively. The bands referring to the acetaldehyde, acetic acid and CO2 were observed first to MM than for Ptpc. The better electroactivity of the metallic multilayers in the electro-oxidation of alcohols could be explained by the changes in the electronic interaction between the exposed platinum surface and the rhodium or ruthenium intermediate layer, which facilitated the oxidation of intermediates at lower potentials, and thus, increasing of the electrocatalytic activity of these materials.

Understanding the basic properties of pristine carbon nitride electrodes is of great importance for their further applications as supercapacitor materials. To this end, a comparative study of unmodified carbon nitride is crucial to understand the difference between the bare material and its composite counterparts described in the literature. Therefore, the aim of this paper is to explore the electrochemical behaviour of casting-produced C3N4 electrodes using cyclic voltammetry, charge/discharge curves and impedance spectroscopy. The results from this study show a capacitance value of 113.7 F g−1 at 0.2 A g−1 with an impressive retention of 89.2% after 5000 charge and discharge cycles at 3.0 A g−1. In addition, this material shows a large amount of specific energy (76.5 W h kg−1) at an operation power of 11.9 W kg−1, decreasing only 10.7% due to the electrochemical aging process. Hence, C3N4 constitutes a long-life pristine material with a large amount of energy and a moderate operation power with better performance than other C3N4-based composites found in the literature. These results are important to gain a better understanding of the inherent properties of carbon nitride – to further design composites with higher specific capacitance, longer lifetime, and specific energy.

The aim of the present work is to evaluate the impact of pure palm biodiesel fuel (B100) and biodiesel blends with 0.32% oleic, palmitic, acetic, myristic, and stearic acids on the properties of some polymeric materials used commonly in the manufacture of auto parts such as the polyamide 66 (PA66), polyoxymethylene (POM), and high-density polyethylene (HDPE). The effects of the B100 and B100–acid blends on polymeric materials were examined by comparing changes in the gain/loss of mass and by measuring the hardness, the impact strength, and the tensile strength of the materials at the end of the exposure. The characterization of the polymers was carried out before and after exposure by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). After the immersion in B100–acids blends, the HDPE exhibited an increase in mass of 5%, which was very similar in all blends. The PA66 showed a small decrease in weight (2% approx.) in all mixtures. The POM presented an increase in the percentage of weight in the mixture of B100 with acetic acid of 0.3%. A decrease was observed in the crystallinity of the HDPE when exposed to blends of B100–acids. This behavior may be associated with a plasticizing effect in the HDPE exposed to the blends. The mechanical properties of POM and HDPE showed no significant changes after immersion in the fuels. On the other hand, PA66 exhibited a significant decrease in maximum stress value after immersion in B100, B100–oleic acid and B100–palmitic acid blends. The variation of the mechanical properties of the PA66 after exposure to B100 was potentiated by addition of organic acids. The assessed polymers did not undergo appreciable changes in the chemical structure of the samples after immersion in the fuels, so the variation in the mechanical properties could be explained by physical absorption of the fuel into the polymers.

A simple and sensitive photoelectrochemical sensor based on the bismuth vanadate (BiVO4) photoanode coupled to visible light excitation was developed for nitrite detection. The BiVO4 was prepared by hydrothermal methods and used as photoelectroactive sensor. Photoexcitation with visible light allows nitrite anions to act as highly efficient hole scavenger at low potential. The photocurrent response increases linearly with nitrite concentration in the solution. The proposed device operates in the range of detection (2.5 to 100.0 μmol L–1), with limit of detection (1.5 μmol L–1), and with good reproducibility (4.1%) for nitrite analysis. Keywords: Bismuth vanadate, Photoelectrochemical sensor, Nitrite, Hole scavenger

A systematic study of the electrochemical reduction of graphene oxide was performed. The graphene oxide was reduced electrochemically in phosphate buffer solution by applying potential of −0.8 V for different times. The graphene oxide and the electrochemically reduced graphene oxide were characterized using ex - situ field-emission gun scanning electron microscopy, in - situ Raman scattering and in - situ atomic force microscopy. Raman scattering showed that the reduction process is accompanied by an increase in the ratio between the D and the G bands of graphene, while the microscopies analyses revealed that the reduction procedure promotes changes in the morphology of the graphene oxide sheets that lead to an increase of the system roughness. Electrochemical impedance spectroscopy showed that reduction of graphene oxide promotes a decrease of the charge-transfer resistance upon electrochemical reduction. This observation was in agreement with the changes observed using cyclic voltammetry, which showed a reduction process improve the reversibility and increase the current peak. The increase in the roughness and an improvement of the electronic mobility brought upon electrochemical reduction are a function of the increase in the edge plane-like defects in the graphene layers.

In this study, a novel material for the electrochemical determination of 17β-estradiol using an electrode based on reduced graphene oxide and a metal complex porphyrin has been applied to environmental monitoring. The electrochemical profile of the proposed electrode was analyzed by differential pulse voltammetry, which showed a shift of the oxidation peak potential of 17β-estradiol to 150mV in a less positive direction compared to the bare reduced graphene oxide electrode. DPV experiments were performed in PBS at pH 7.0 to determine 17β-estradiol without any previous step of extraction, cleanup, or derivatization, in the range of 0.1-1.0μmolL(-1) with a detection limit archived at 5.3nmolL(-1) (1.4μgL(-1)). The proposed sensor was successfully applied in the determination of 17β-estradiol in a river water sample without any purification step and was successfully analyzed under the standard addition method. All the obtained results were in agreement with those from the HPLC procedure.

In this work, the corrosion process of AISI 1020 in crude oil, to which different amounts of sea water (0.5 and 4.0% v/v), naphthenic acid (500 and 3000 ppm), and H 2 S (50 and 1000 ppm) were added, was investigated using electrochemical noise at open circuit potential. The different oil samples were prepared using a 2 3 factorial design involving the three species described above. To analyze the obtained data, wavelet transform and energy distribution plot were used. Using this technique it was possible to separate the contributions of two types of corrosion, generalized and localized, in oil samples with different compositions and to analyze the effect of those variables on the changes that occurred during 55 days of immersion in the experiment. The results showed an increase in pitting formation in those steel samples studied in oil containing H 2 S at 50 ppm and 4.0% sea water. The contribution of generalized corrosion on the metallic surface is higher in oil containing 3000 ppm naphthenic acid than in the other experimental conditions. The results were confirmed by morphological analysis of the corroded samples.

The success of the biorefinery will depend on deriving value from the lignin fraction of lignocellulosic feedstocks. Thus, it will be necessary to develop procedures that provide a separate and usable lignin stream for chemical transformation. A wide range of processes have been developed that afford isolated lignin, but very few of these methods are practical for the biorefinery, as they target lignin analysis or lignin removal, and are largely impractical for large scale use or introduce severe structural changes in the lignin that significantly reduces its potential as a chemical feedstock. This chapter will introduce several methods that isolate lignin for analytical purposes, or for its removal from lignocellulose. The majority of the chapter then discusses processes for biomass fractionation – methodology that gives lignin streams in high yield and purity, and which offer potential utility within the biorefinery.

A glassy carbon electrode (GCE) was modified with multi-walled carbon nanotubes (MWCNT) and silver nanoparticles (AgNPs) and applied to the simultaneous determination of hydroquinone (HQ), catechol (CC), bisphenol A (BPA) and phenol by using square-wave voltammetry. The MWCNTs were deposited on the GCE and the AgNPs were then electrodeposited onto the MWCNT/GCE by the application of 10 potential sweep cycles using an AgNP colloidal suspension. The modified GCE was characterized by using SEM, which confirmed the presence of the AgNPs. The electrochemical behavior of the material was evaluated by using cyclic voltammetry, and by electrochemical impedance spectroscopy that employed hexacyanoferrate as an electrochemical probe. The results were compared to the performance of the unmodified GCE. The modified electrode has a lower charge-transfer resistance and yields an increased signal. The peaks for HQ (0.30 V), CC (0.40 V), BPA (0.74 V) and phenol (0.83 V; all versus Ag/AgCl) are well separated under optimized conditions, which facilitates their simultaneous determination. The oxidation current increases linearly with the concentrations of HQ, CC, BPA and phenol. Detection limits are in the order of 1 μM for all 4 species, and the sensor is highly stable and reproducible. The electrode was successfully employed with the simultaneous determination of HQ, CC, BPA and phenol in spiked tap water samples. Graphical abstract A glassy carbon electrode was modified with carbon nanotubes and silver nanoparticles and then successfully applied to the simultaneous determination of four phenolic compounds. The sensor showed high sensitivity in the detection of hydroquinone, catechol, bisphenol A and phenol in water samples.

In the present work, it is described the fabrication and characterization of TiO 2 nantotubes prepared potentiostatically using 1.0 or 5.0 vol.% ionic liquid electrolyte medium at 10 or 20 °C. These experimental conditions led to TiO 2 nanotubes with 63-77 nm pore diameter, crystallite sizes between 27-33 nm, and band-gap values in the 3.1-3.2 eV range. Although the morphology and band-gap values were similar, the water splitting reaction showed differences in terms of photocurrent, up to 300%. Besides, we report also important changes in those parameters related with electronic defects, such as carrier density ( N D ), width of depletion layer ( w ) and Debye length (λ D ). Then, the enhancement on photoelectrochemical properties could be related to a decrease in the rate of surface recombination processes. Finally, these proposition are in agreement with the open-circuit voltage-decay, where was observed a higher electron lifetime for TiO 2 NT obtained at higher vol.% of ionic liquid.

This work presents a method to study corrosion reactions in real time by the analysis of a temporal series of micrographs using in situ optical microscopy coupled to electrochemical techniques. The approach was applied to study the pitting corrosion of AISI 1040 steel during chronoamperometric measurements, in carbonate and chloride solutions. Using this coupled approach, it was possible to measure different pit parameters as well as to estimate the mean pit depth. The number of pits and the total pit area presented different behaviors as the chloride concentration increased and active and passive pits were detected.

In the present work, an innovative methodology is used to contribute in the elucidation of methanol electro-oxidation reaction on polycrystalline Pt surface. We coupled infrared spectroscopy to linear voltammetry and evaluate the data using parallel factor analysis (PARAFAC) to extract hidden information concerning the oxidation reaction. Five adsorbed species were simultaneously extracted and quantified at different applied potentials corresponding to: formate, sulfate, water, total CO and COL shift. It was observed that the CO adsorbed content starts at maximum on low potentials and gradually decreases up to 1.0 V. Meanwhile, the interfacial water content on the surface of the CO-free Pt increases, which causes the shift on the COL band, resulting in a further decrease of the interfacial water content. The water content increases again until up to 0.8 V, which it reaches a constant value, due to formate production and subsequent adsorption of sulfate. Using this technique, it was possible to determine the potential window where each chemical species is adsorbed on the surface, as well as the effect of methanol concentration and scan rate on the mechanism.

Platinum-loaded titanium oxide nanoparticles, Pt-TiO 2 , were prepared using the polymeric precursor method with titanium isopropoxide as metal precursor. Platinum ions were added to the titanium precursor solution with Pt/Ti molar ratios between 0.005 and 10 mol%. The characterization of the physical properties was carried out by BET-surface area, transmission electron microscopy (TEM) and X-ray diffraction (XRD) with Rietveld quantitative analysis. The XRD patterns indicated that Pt doping occurred only for samples containing less than 1.0 mol% of platinum, and a small amount of rutile phase was observed after doping. For 1.0 mol% or higher Pt concentration a metallic Pt phase was detected. On the other hand, TEM analysis showed that the doping/metallization limit is still lower. Samples with nominal Pt concentration of 0.1 mol% presented signal of Pt metal particles. The photocatalytic activities of the samples were studied using methyl orange (MO) as model compound under UV illumination. In all Pt-TiO 2 samples the photocatalytic activity was found to increase in comparison with pure TiO 2 samples, either by the doping mechanism (at a low Pt concentration level), or by charge transfer mechanism in the interface metal/oxide (at a high Pt concentration level). The increase in Pt content, up to 0.2 mol% of Pt, was found to enhance the photocatalytic activity of TiO 2 towards the decomposition of MO. At even higher concentrations, platinum no longer acted as a dopant: instead, metallic Pt particles decorated the oxide surface. Doped and metallized samples had similar photocatalytic activity.

In this work, TiO 2 nanotubes were prepared by anodization at a constant voltage in an electrolyte composed of fluoride species provided by ionic liquid (1 or 5 vol.%), applying 40 or 80 V. Different tube diameters (21.6, 34.8, 93 and 154.5 nm) were obtained, all of them presenting anatase crystalline phase with distinctive crystalline sizes and lattice strains. The Li-ion intercalation/deintercalation was studied and analysed in the light of crystalline structure changes. The amount of Li + irreversibly trapped was higher for the samples with larger TiO 2 nanotubes compared to narrower ones. This behaviour was correlated with the lattice strain observed in the samples.

Multilayered Pt/Ir/Pt films were electrodeposited over titanium substrates, controlling the film thickness by the deposition charge. Two probe molecules were used to perform the evaluation of catalytic activity, CH3OH and CO. Using a 22 factorial design with a central point, optimized intrinsic catalytic activity was obtained over the Ti/Pt25mC/Ir6mC/Pt electrode. An enhancement of the current density of up to 2.76 times was observed for the methanol oxidation reaction (MOR) compared with the reference sample (Ti/Pt electrodes), even though both samples had the same electroactive area. In addition to the methanol oxidation voltammetry, CO stripping voltammetry suggests that MM-like systems are less susceptible to the catalyst-poisoning phenomenon compared to the Ti/Pt ones. Impedance spectroscopy was mainly used to monitor the charge transference resistance (Rct), whose results showed a clear Rct reduction for the MOR process over MMs compared with Ti/Pt electrodes, corroborating the previous observations regarding the general catalytic improvement.

We report the microwave-assisted hydrothermal synthesis of bimetallic Pt-Au nanoparticles with different Pt/Au mole ratio, and investigate their performance towards the electro-oxidation of formic acid. The as-synthesized Pt-Au sol was dispersed on a graphite electrode, without any binding agents, which allowed us to control the mass of alloy deposited. Pt-Au alloys showed better activity than bulk Pt and/or Pt nanoparticles towards the oxidation of formic acid, as evidenced by the decrease in the onset potential and the higher currents in the corresponding cyclic voltammograms. The higher activity is due both to atomic-ensemble effects, which lead the reaction through the so-called direct pathway with insignificant CO poisoning, and to electronic effects, which optimised the interaction between the catalyst surface and the reactive intermediate in the direct path. Further insight into the individual contributions of atomic-ensemble and electronic effects and their effect on the catalytic activity was provided by the analysis of galvanostatic potential oscillations.

Human epidermal growth factor is a small peptide consisting of 53 amino acid residues, which stimulates cell proliferation and is associated with several human carcinomas. A simple sandwich-type ultramicroELISA assay (UMELISA), based on the advantages of high affinity reaction between streptavidin and biotin has been developed for the measurement of EGF in human serum samples. Strips coated with a high affinity monoclonal antibody directed against EGF are used as solid phase, to ensure the specificity of the assay. The EGF assay was completed in 18 hr, with a measuring range of 39–2500 pg/mL. The intra- and inter-assay coefficients of variation were 4.4–7.3% and 0–5.1%, respectively, depending on the EGF concentrations evaluated. Percentage recovery ranged from 96–104%. Regression analysis showed a good correlation with the commercially available Human EGF Immunoassay Quantikine® ELISA kit (n = 130, r = 0.92, P < 0.01). The analytical performance characteristics of our UMELISA EGF endorse its use ...

The effect of the electropolymerization of seven poly(3-methylthiophene) (P3MT) films in the same used monomer solution have been investigated. Cyclic voltammetry, UV-Visible, scanning electron microscopy, and electrochemical impedance measurements were carried out to understand the effect of the solution reusing on the polymer electrochemical properties. The obtained results show that, as the solution is reused, the polymerization rate increase and the charge in of the cyclic voltammetry decrease. Besides, there are important changes in the sample's morphologies, with the increase of the synthesis number, the amount of fibers increase and this leads to lower the conductivity of the polymer film. In agreement to this, the impedance data analysis shown important changes in the interfacial electronic parameters, i.e., changer transfer resistance and double-layer capacitance, used to describe the films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44368.

M-doped TiO2 (M = Ag2+, Al3+, Ce4+, Nb5+) with different dopant contents have been prepared by the Pechini method using titanium IV isopropoxide as precursor. The effect of doping concentration on the photocatalytic activity for methyl orange (MO) photodegradation was investigated using UV radiation. The photocatalysts were characterized by surface area, X-ray diffraction and UV–Vis diffuse reflectance spectroscopy. An increase in the photoactivity of TiO2 nanoparticles was confirmed by MO photocatalytic degradation experiments, when the transition metal ions were incorporated into the semiconductor crystalline lattice, which could be attributed to an increase in the charge separation and reduction of e−/h+ recombination as a function of the substitutional defect generated at very low levels.

Plasma electrolytic oxidation (PEO) is a coating procedure that utilises anodic oxidation in aqueous electrolytes above the dielectric breakdown voltage to produce oxide coatings that have specific properties. These conditions facilitate oxide formation under localised high temperatures and pressures that originate from short-lived microdischarges at sites over the metal surface and have fast oxide volume expansion. Anodic ZrO2 films were prepared by subjecting metallic zirconium to PEO in acid solutions (H2C2O4 and H3PO4) using a galvanostatic DC regime. The ZrO2 microstructure was investigated in films that were prepared at different charge densities. During the anodic breakdown, an important change in the amplitude of the voltage oscillations at a specific charge density was observed (i.e., the transition charge density (Q T)). We verified that this transition charge is a monotonic function of both the current density and temperature applied during the anodisation, which indicated that Q T is an intrinsic response of this system. The oxide morphology and microstructure were characterised using SEM and X-ray diffraction experiments (XRD) techniques. X-ray diffraction analysis revealed that the change in voltage oscillation was correlated with oxide microstructure changes during the breakdown process.

This paper presents a study of the electro-oxidation of ethylene glycol (EG) at metallic multilayer electrodes: Pt pc /Ir x /Pt y (Pt pc = polycrystalline Pt, x and y denote the number of monolayers of Ir intralayer and Pt outer layer, respectively) and Pt pc /(Pt 1 Ir 1 ) x /Pt y (ie a 1:1 alloy of Pt and Ir was employed as intralayer). For comparison, data are also presented for Pt pc . Although Pt and Ir have similar crystallographic structures, the work reported shows for the first time that the electrocatalytic properties of the Pt outer layer are affected significantly by the composition of the intralayer. The voltammetry data show that the Pt pc /Ir 3.0 /Pt 3.0 metallic multilayer electrode exhibits a peak current density 78% higher than that observed using Pt pc , in agreement with activation energy measurements on the electro-oxidation of EG which showed: Pt pc /Ir 3.0 /Pt 3.0 (26 kJ mol −1 ) pc (44 kJ mol −1 ) pc /(Pt 1 Ir 1 ) 3.0 /Pt 3.0 (46 kJ mol −1 ). The FTIR experiments showed that the main products for the oxidation of the diol at the electrodes are similar: CO L , CO 2 and glycolic and/or oxalic acid over Pt pc and Pt pc /Ir 3.0 /Pt 3.0 metallic multilayer electrodes. However, significantly more CO 2 and CO L were observed at Pt pc /Ir 3.0 /Pt 3.0 compared to Pt pc electrodes.

In this work, Ptpc/Ir/Pt metallic multilayer nanostructured electrodes were prepared. The composition and number of the constituent metal layers were varied and the number of Ir and Pt layers studied were: 1.5:1.5, 1.5:10, 10:1.5, 10:10 and 250:250 Ir and Pt monolayers. The ethanol electrooxidation reaction and its products was studied using electrochemical in situ FTIR technique and could be observed as a selective cleavage of the ethanol CC bond in acidic electrolyte. Neither acetaldehyde nor acetic acid IR band could be observed for ethanol electrooxidation at 1.5 V vs. RHE over Ptpc/Ir250/Pt250 metallic multilayer electrodes. Also, the enhancement on CO2 production over this electrode was more than six times the amount observed using the Ptpc electrodes. Thus, the complete CC cleavage bond in ethanol molecule was observed, leading only CO2 as reaction product. Keywords: Metallic multilayers, Ethanol electrooxidation, CC cleavage

This work describes a detailed study of the ethanol electrooxidation on Ti/(RuO2)(x)Pt(1-x) electrodes using several compositions prepared by the polymeric precursor method. The results obtained using cyclic voltammetry and chronoamperometry showed that the best composition of Ti/(RuO2)(x)Pt(1-x) electrodes for CO and ethanol oxidation processes is Ti/(RuO2)0.50Pt0.50. On this electrode composition the onset of CO and the ethanol oxidation occurred at 380 mV and 220 mV more negative than on Ti/Pt, respectively. Besides, there was an increase of 2.5-fold in the current density for ethanol electrooxidation under constant potential polarization. The Ti/(RuO2)0.50Pt0.50 electrodes produced lower amount of acetic acid compared to Ti/Pt and polycrystalline Pt electrodes using in situ HPLC spectrometric analysis. Also, a non common product from ethanol oxidation could be observed on higher RuO2 loads: ethyl acetate. Finally, the impedance data showed that Ti/(RuO2)0.50Pt0.50 electrode composition had the smallest charge transfer resistance for ethanol oxidation among those compositions investigated

In this work, we present a new class of materials with non-linear electrical behaviour: the Organic Polymeric Varistors. These devices were built using a conducting polymer, polyaniline, and a conventional low-cost dielectric polymer, acrylonitrile–butadiene–styrene copolymer. The apparatus has low-voltage varistor behaviour with a breakdown field of around 10 V, and a non-linear coefficient of 5.0. They also remain stable after several voltage–current cycles and its preparation procedure is easy and inexpensive.