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The SiO2/TiO2/Nb2O5 material was set by the sol–gel method and was characterized by several techniques through thermogravimetric, spectroscopic, and textural analyzes. For the two synthesized materials, the specific surface area was 350.0 and 494.0 m2 g−1 (SiTiNb-A and SiTiNb-B, respectively). An enhance of the crystalline order with the temperature increase of the thermal treatment was observed. Through X-ray Photoelectron Spectroscopy analysis, the binding energy values for the Ti 2p and Nb 3d levels showed the insertion of Ti and Nb atoms in the silica matrix. The Electron Dispersive Spectroscopy analyses also confirmed the high dispersion of the metals presented on the materials surface. The Thermogravimetric Analysis showed weight loss for the of 37.6% (SiTiNb-A) and 29.7% (SiTiNb-B). The presence of the crystalline phases TiO2-anatase and monoclinic-Nb2O5 in the materials was confirmed through the data obtained by association of powder X-ray Diffraction and FT-Raman. Values obtained from optical band-gap aimed the dependence of the oxides concentration and the calcination temperature. Finally, the pyridine adsorption studies have indicated the presence of Lewis and Brønsted acid sites. [ABSTRACT FROM AUTHOR]

An electroanalytical method for the determination of morpholine, a corrosion inhibitor, was developed at a cathodically pretreated boron-doped diamond electrode (BDDE). The voltammetric response of morpholine at the BDDE in 0.1 mol L−1 KCl (pH 10) shows an irreversible oxidation process at approximately 1.3 V vs. Ag/AgCl in 3.0 mol L−1 KCl. Using cyclic voltammetry, the number of electrons involved in the morpholine electroxidation mechanism was found to be 1. The application of chronoamperometry showed that the apparent diffusion coefficient (D0) was 2.99 × 10−6 cm2 s−1. Using square wave voltammetry under the optimized conditions (frequency of 30.0 Hz, pulse amplitude of 100 mV and step potential of 20 mV at pH 10.0), the developed method provided limits of detection and quantification of 2.1 and 6.9 mg L−1, respectively, with a linear range from 5.0 to 100.0 mg L−1 (r = 0.991). Intraday (n = 10) and interday (two consecutive day) precision values assessed as the relative standard deviation for solutions containing 30.0, 60.0, and 90.0 mg L−1 of morpholine were from 0.41 to 5.86% and 0.92 to 3.19%, respectively. The feasibility of the method for the interference-free determination of morpholine was verified by the analysis of synthetic boiler water samples containing CaCO3, Na2SO3, Na3PO4, FeCl3, and humic acid as organic matter. In addition, hydrazine was added as a possible interfering compound because of its widespread use in corrosion inhibition. Recovery values from 90.9 to 109.4% were obtained in the synthetic boiler water, thereby attesting to the accuracy of the method. [ABSTRACT FROM AUTHOR]

Abstract: The behavior of the Schiff base N,N′-bis(salicylidene)-1,2-ethylenediamine (Salen), its reduced form (N,N′-bis(2-hydroxybenzyl)-1,2-ethylenediamine) and a mixture of its preceding molecules, ethylenediamine and salicylaldehyde, as carbon steel corrosion inhibitors in 1molL−1 HCl solution was studied by corrosion potential measurements, potentiodynamic polarization curves, electrochemical impedance spectroscopy and spectrophotometry measurements. The experimental results showed that the reduced Salen presented the highest efficiency among the inhibitors studied. The results obtained in the presence of Salen were similar to those obtained in the presence of the salicylaldehyde and ethylenediamine mixture, showing that in acid medium the Salen molecule undergoes hydrolysis, regenerating its precursor molecules. [Copyright &y& Elsevier]

A mechanochemical approach through ball milling (BM) to produce NiO clusters supported on TiO 2 has been successfully applied, resulting in a NiO/TiO 2 p-n heterojunction as an efficient and sunlight-sensitive photocatalyst. Besides, the synergistic interaction between NiO and TiO 2 (P90) enhances charge separation, ultimately boosting the H 2 photoproduction. Notably, the material obtained by BM, denoted as NiO/P90-BM achieved an H 2 evolution rate that was over 12 times higher than that of Neat P90 (8.85 mmol h−1 g−1 vs. 0.73 mmol h−1 g−1). The predominance of the high-spin configuration for Ni2+ in NiO was ascribed as one of the main reasons for such performance. Additionally, photoelectrochemical measurements revealed that NiO addition was beneficial for the photoelectrochemical properties. The NiO/P90-BM exhibited the lowest charge transfer resistance, the highest photocurrent signal, and the highest electronic density. Furthermore, the achieved H 2 evolution rate is on par with that of materials produced using noble metals and energy-intensive approaches. Noticeably, cycling, long-term, and aging tests have shown that the reported photocatalyst is efficient after several cycles, prolonged use, and after long periods of storage. [Display omitted] • One-step ball milling process led to a NiO/TiO 2 p-n heterojunction. • The addition of NiO boosted sunlight absorption. • This noble metal-free photocatalyst exhibited an outstanding H 2 evolution rate. • High-spin of Ni2+ in NiO was crucial for such outstanding performance. • NiO/P90-BM performs comparably to noble metal-based and energy-intensive materials. [ABSTRACT FROM AUTHOR]

A new dinuclear dioxidomolybdenum(VI) complex [(MoO2)2(BPA)2(μ-O)] was synthesized by the reaction between the tridentate N2O-donor ligand N-(2-hydroxybenzyl)-N-(pyridin-2-ylmethyl)amine (HBPA) and molybdenum trioxide (MoO3). This complex was analyzed by FT-IR, UV-visible, ESI-MS, elemental (CHN), thermogravimetric and electrochemical analyses. The crystal structure was solved by single crystal X-ray diffraction, which shows two non-equivalent molybdenum(VI) ions bridge-coordinated by an oxido ligand. The complex was studied using DFT calculations, resulting in a molecular structure with a geometry similar to the one obtained by X-ray diffraction. The dinuclear dioxidomolybdenum(VI) complex [(MoO2)2(BPA)2(μ-O)] was evaluated as a catalyst in the reaction involving the oxidation of sulfur compounds, at 25 and 50 °C, using hydrogen peroxide as an oxidant and acetonitrile as a solvent. The catalyst is able to oxidize thioanisole, diphenyl sulfide and dibenzothiophene producing sulfoxide and sulfone with conversions of 94%, 76% and 27%, respectively. [ABSTRACT FROM AUTHOR]

This article undertakes a critical evaluation of the literature regarding the use of the Langmuir isotherm, specifically in the context of inhibitor research. The Langmuir isotherm is frequently employed to derive thermodynamic and kinetic parameters, which are then used to gauge inhibitor performance. However, the validity of the Langmuir isotherm has been challenged, particularly by Walczak et al. (2019), whose work has served as a basis for others to reject its use as inadequate. Imposing limitations on the Langmuir isotherm would involve restrictions on heterogeneous kinetics, impedance interpretation, and other transient techniques. These aspects will be subjected to a more in-depth analysis in this discussion paper. ● Discussion on the use of the Langmuir isotherm in electrochemical studies. ● Analysis of the use of XPS as a tool for obtaining surface coverage. ● Study of heterogeneous kinetics and the use of the Langmuir isotherm. [ABSTRACT FROM AUTHOR]

The study aimed to develop an electrochemical sensor based on glassy carbon, mixed oxide (SiO2/TiO2/Sb2O5), and carbon black. The material was synthesized, characterized, and used to determine thiamethoxam in raw honey and water. The morphologic structure and electrochemical performance of the sensor was characterized by scanning electron microscopy and cyclic voltammetry. Differential pulse voltammetry with a concentration of 0.1 mol L−1 of Britton-Robinson buffer at pH 7.0 allowed the generation of a method to determine thiamethoxam in a linear range of 0.25 to 100.5 μmol L−1 and with a limit of detection of 0.012 μmol L−1. The system efficiently quantified traces of thiamethoxam in raw honey and tap water samples. The modified sensor did not present interferences of K+, Na+, Ca2+, Mg2+, glyphosate, imidacloprid, and carbendazim. In addition, the device showed good recovery values for thiamethoxam when applied directly to honey and water samples without any treatment, presenting an electrochemical sensor to monitor real-time hazardous substances in environmental and food matrices. [ABSTRACT FROM AUTHOR]

• Biomass-derived precursors can be great for preparing a green corrosion inhibitor. • Two aminoamides derived from maleic and succinic acid, named inhibitors (1) and (2) , showed excellent anticorrosive performance, with an inhibition efficiency of ∼90 % for gravimetric tests (2 h of immersion and 1 × 10–3 mol L–1). • XPS spectra, apparent activation energy, adsorption Gibbs free energy, and theoretical calculations show that the adsorption of the inhibitors on the metal surface is physical. Developing a sustainable and environmentally friendly inhibitor remains an essential and challenging goal for corrosion control. Here, aminoamide molecules were synthesized from maleic and succinic acids and applied as a novel biomass-derived corrosion inhibitor for mild steel in an HCl solution. The modification process of these molecules can increase their anticorrosive capacity, a fact verified in gravimetric tests, where inhibitors (1) and (2) achieved inhibition efficiency of ∼90 % (2 h immersion and 1 × 10–3 mol L–1). XPS spectra, apparent activation energy increase with inhibitor addition, adsorption Gibbs free energy of the inhibitors, and theoretical calculations show that the adsorption of the inhibitors on the metal surface is physical. This work provides a viable alternative to using a novel biomass-derived corrosion inhibitor. [ABSTRACT FROM AUTHOR]

• Biomass-derived precursors can be great for preparing a green corrosion inhibitor. • Two aminoamides derived from maleic and succinic acid, named inhibitors (1) and (2) , showed excellent anticorrosive performance, with an inhibition efficiency of ∼90 % for gravimetric tests (2 h of immersion and 1 × 10–3 mol L–1). • XPS spectra, apparent activation energy, adsorption Gibbs free energy, and theoretical calculations show that the adsorption of the inhibitors on the metal surface is physical. Developing a sustainable and environmentally friendly inhibitor remains an essential and challenging goal for corrosion control. Here, aminoamide molecules were synthesized from maleic and succinic acids and applied as a novel biomass-derived corrosion inhibitor for mild steel in an HCl solution. The modification process of these molecules can increase their anticorrosive capacity, a fact verified in gravimetric tests, where inhibitors (1) and (2) achieved inhibition efficiency of ∼90 % (2 h immersion and 1 × 10–3 mol L–1). XPS spectra, apparent activation energy increase with inhibitor addition, adsorption Gibbs free energy of the inhibitors, and theoretical calculations show that the adsorption of the inhibitors on the metal surface is physical. This work provides a viable alternative to using a novel biomass-derived corrosion inhibitor. [ABSTRACT FROM AUTHOR]

A higher surface-to-volume ratio typically enhances capacitance in supercapacitor electrodes. However, excessive porosity can increase electrical resistance, counteracting this benefit. This study optimized the compaction level of CFO (Cobalt Ferrite Oxide) nanoparticles for enhanced supercapacitor performance. Nanoparticle-assembled CFO films with varying compaction were produced via pulsed laser deposition while maintaining consistent crystal structure and particle size. Characterization using electron microscopy and electrochemical techniques revealed a strong correlation between compaction and capacitance. All CFO nanoparticle-assembled films exhibited superior pseudocapacitive behavior compared to CFO thin films, with the most compacted nanoparticle-assembled film achieving a high areal capacitance of 6 mF cm−2. • Electrochemical properties of pulse laser deposited (PLD) films depend on chamber pressure. • PLD can produce nanoparticle-assembled films of cobalt ferrite with higher porosity. • PLD chamber pressure modifies nanoparticle compaction but preserves their size. [ABSTRACT FROM AUTHOR]

Two electrochemical sensors based on modified glassy carbon electrodes with carbon nanostructures as graphene (GCE–EG) and carbon nanotubes (GCE–CNT) were evaluated for morpholine analysis. The carbon nanostructures were obtained and characterized using X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy and cyclic voltammetry. All spectroscopic and microscopic techniques confirmed the procurement of graphene and CNT. The electrochemical studies proved the efficient behaviour of both electrodes GCE–EG and GCE–CNT in sensing and detection of morpholine via differential pulse voltammetry. The area of the anodic peaks was correlated with the concentration of the analyte. It was observed that the implementation of a thin film of EG and CNT on the GCE promoted the electrocatalytic activity towards morpholine electro-oxidation, and a considerable increase in the corresponding oxidation peak was observed in both cases. Theoretical detection limits of 1.0 and 1.3 mg l–1 were obtained for GCE–EG and GCE–CNT, respectively. These merit figures, both satisfactorily meet the requirements of the Food and Drug Administration for morpholine detection in real applications. Finally, the sample recovery for GCE–EG and GCE–CNT sensors were, respectively, 107 and 103%, at 20.0 mg l–1 morpholine in the boiler water. [ABSTRACT FROM AUTHOR]

Abstract: The inhibitive action of the aqueous extracts of fruit peels against corrosion of carbon steel in a 1M HCl solution was investigated using electrochemical impedance spectroscopy, potentiodynamic polarization curves, weight loss measurements and surface analysis. We analyzed aqueous extracts of mango, orange, passion fruit and cashew peels in different concentrations and found that the extracts act as good corrosion inhibitors for the tested system. The inhibition efficiency increases with increasing extract concentration and decreases with temperature. The adsorption of components of the fruit peel extracts on the surface of the carbon steel follows the Langmuir adsorption isotherm. [Copyright &y& Elsevier]

Abstract: The bioelectrochemical oxidation of two polyaromatic hydrocarbons (PAH): anthracene (ANT) and pyrene (PYR), using horseradish peroxidase (HRP) resulting in the synthesis of photoactive polyaromatic quinones in organic media was studied. The electrochemical generation of hydrogen peroxide was compared with its direct addition in concentrations of up to 0.0012molL−1. In addition, three different chemical redox mediators were evaluated: ABTS, thionin and ortho-aminophenol. In a reaction medium containing 30% acetone and ABTS as mediator with a molar ratio mediator/PAH of 1:10, HRP attained the highest level of oxidation of PAH (1×10−3 molL−1): ANT (94%) and PYR (91%), producing 9,10-anthraquinone and mainly 1,2 and 4,5-pyrenequinones, respectively. [Copyright &y& Elsevier]

An electrode for monoethylene glycol analysis was developed based on the modification of the surface of the glassy carbon electrode with electrochemically reduced graphene oxide and gold and palladium nanoparticles (GCE/rGO/AuPd-np). Its analytical performance was assessed by determining some analytical figures of merit. Graphene oxide was reduced electrochemically as well as the metal particles with gold deposited by chronopotentiometry and palladium by cyclic voltammetry (CV). The electrode was characterized by MET, TEM and EDS techniques. The study of alcohol behaviour was performed electrochemically using CV technique. The positive synergistic effect of metals provided greater electrocatalytic response, stability and resistance to poisoning. The GCE/rGO/AuPd-np sensor presented a detection limit equal to 31.48 µmol l–1 for a linear range of 89.5–179 µmol l–1 with a linear correlation coefficient of 0.9096 and high stability, not losing response even after 650 cycles. [ABSTRACT FROM AUTHOR]

The present work reports the development of a new analytical method for the determination of free glycerol in biodiesel samples using enzymatic-spectrophotometric assay combined with solid phase extraction (SPE) by molecularly imprinted poly(methacrylic acid) (MIP). The spectrophotometric method was performed using a commercial enzyme kit. The enzymatic-spectrophotometric method showed good analytical performance in terms of the linearity (0.998), limit of detection (7.70 × 10−6% w/w), limit of quantification (2.54 × 10−5% w/w), repeatability (0.42% to 7.91%), and recovery (99.4% to 112%). The analyses of several biodiesel samples by SPE and enzymatic-spectrophotometric method provided recovery values between 91.4% and 105%. Therefore, the high selectivity of molecularly imprinted polymer (MIP) was successfully applied to isolate free glycerol from biodiesel samples containing acylglycerols and methyl esters, and thereby allow enzymatic-spectrophometric based quantification. The developed method using SPE with MIP was efficient for the determination of free glycerol in biodiesel and the obtained results are in agreement with gas chromatrography (GC) that was used as a reference protocol. [ABSTRACT FROM AUTHOR]

In this work, we developed a method for the quantification of free glycerol in biodiesel using electrochemical detection and solid phase extraction (SPE). SPE was performed using commercial stationary silica phase cartridges to isolate free glycerol from the combined glycerol (such as acylglycerols) and the methyl esters. The electrochemical method was performed by cyclic voltammetry in KOH solution using a glassy carbon electrode modified with Pd nanoparticles. The electrodeposition of palladium nanoparticles was optimized with a complete 32 factorial design with triplicate at the central point. The analytical performance of the method was evaluated in terms of linearity, limit of detection (LOD), limit of quantification (LOQ), precision (repeatability), and accuracy (recovery). The proposed method exhibits good linearity (R2 = 0.99525). The LOD and LOQ values were determined visually, the LOD was1.00 × 10−6% w/w, and the LOQ was 3.30 × 10−6% w/w, presenting better performance compared with other methods described in the literature. The precision was determined by the relative standard deviation (RSD%), and the values obtained were less than 5%. The recovery ranged between 95.8 and 101%. The proposed method proved to be efficient in the quantification of free glycerol in biodiesel, and the results correlate well with the reference method (GC). The results indicate that the method is presented as an alternative to costly and slow GC-based techniques. [ABSTRACT FROM AUTHOR]

The behavior of the gorse extract has been investigated as a new corrosion inhibitor by weight-loss measurements, potentiodynamic polarization curves, electrochemical impedance spectroscopy and scanning electron microscopy. Weight-loss measurements showed an increase in inhibition efficiency (IE) with the immersion time and the concentration of the extract. At 800 mg L−1, the extract IE ranged from 72.5% to 93.8% for 2 and 48 h, respectively. TheEadecreased slightly with the addition of the extract, characterizing the chemical adsorption by the molecules present in the extract on the surface. The measurements of electrochemical impedance spectroscopy showed an increase inRctand a decrease inCdl, reaching 96.6% of IE at 1600 mg L−1. The polarization curves indicated that the gorse extract served as an adsorption inhibitor, reducing both the anodic and cathodic current density. The high-molecular-weight fraction isolated from the gorse extract also showed high inhibition efficiencies. [ABSTRACT FROM PUBLISHER]

The anticorrosive activity of furfural derivatives, by ex-situ and in-situ syntheses, on mild steel immersed in CO 2 -saturated formation water solution was evaluated using mass loss measurements, polarization curves, X-ray photoelectron spectroscopy, quantum chemical calculation, and electrochemical impedance. Furfural thiosemicarbazone presented inhibition efficiency reaching 90.2% for 72 h in immersion. The same molecule, synthesized in-situ by the mixture of the precursors in the corrosive medium, also produced good efficiency, 82.2% for 24 h of immersion, but it decreased over the time due to incomplete conversion of the precursors in furfural thiosemicarbazone. [Display omitted] • In-situ synthesis of furfural thiosemicarbazone occurred in the corrosive medium. • Furfural thiosemicarbazone presented great inhibition efficiency for mild steel. • The presence of S atom plays a crucial role in the interaction of the inhibitor with the metallic surface. [ABSTRACT FROM AUTHOR]

A statistical treatment was carried out on electrochemical methods intended for iodide determination as a tracer in seawater reservoirs. Comparison was made for amperometric and potentiometric detection, including the use of a modified carbon electrode. The potentiometric method showed a good linear correlation coefficient (r = 0.9926) with a Nernstian behavior in a concentration range of 10 − 5 to 1 mol L − 1 (1.3 mg L − 1 to 127 g L − 1 ) and a limit of detection of 1.3 mg L − 1 (10 μmol L − 1 ). The amperometric method showed a good linear correlation coefficient (r = 0.9988) with a linear response over a concentration range of 1 to 4 mg L − 1 (8 to 31.5 μmol L − 1 ) and a limit of detection of 0.5 mg L − 1 (4 μmol L − 1 ). The statistic treatment has shown that the potentiometric method is promising to measure the iodide concentration in samples with high iodide content and the amperometric method is appropriate to measure the iodide concentration in samples with low iodide content, for example, in the case of produced water from petroleum reservoirs. Moreover, the salophen modified electrode can be readily used for routine analysis in laboratory. [ABSTRACT FROM AUTHOR]

In this work the complexation of the guest molecule (dibenzylthiourea-DBT) with α and β forms of hydroxypropylated cyclodextrins was evaluated in solution and in the solid state by different techniques. It was shown that the inclusion complexes were obtained and the aromatic moieties of DBT are points of interaction in the structure of the guest. The inhibitory action of these inclusion compounds in carbon steel corrosion in acidic medium was evaluated by polarization curves, electrochemical impedance diagrams and weight loss measurements. There is an enhancement of the inhibitory action against the carbon steel corrosion in HCl solution when the DBT was encapsulated in inclusion compounds whereas the alone hydroxypropylated cyclodextrins did not present an inhibitory effect. It was concluded that these inclusion compounds could be a good alternative to introduce molecules with low solubility in aqueous media and still increase their inhibitory action. [ABSTRACT FROM AUTHOR]

The inhibitory effect of thiourea-based compounds was evaluated using carbon steel body specimens in hydrochloric acid media. Thiourea derivatives,N-(pyrimidin-2-ylcarbamothioyl)benzamide andN-(6-methylpyridin-2-ylcarbamothioyl)benzamide, were synthesized using a simple route with good yields of approximately 70%. The inhibitory efficiencies were obtained by means of weight-loss experiments and electrochemical techniques (e.g., polarization curves and electrochemical impedance spectroscopy). The presence of a methyl functional group showed a better inhibitory efficiency compared with the derivate inhibitor without such modification. Analyzing Langmuir isotherms, ΔG0adsvalues indicate the chemical adsorption of thiourea-based compounds. TheECorrvalues obtained for the thiourea derivative with the methyl functionality was cathodically shifted by approximately −0.08 V, with an inhibition efficiency of 81%. [ABSTRACT FROM AUTHOR]

Two enzymatic methods using amperometric and colorimetric detection based on two coupled activities (glyceroquinase and glycerol-3-phosphate oxidase) were compared for the glycerol content determination. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark-type electrode and correlated with the glycerol concentration. In addition to the enzymatic-colorimetric method, there is a third enzymatic reaction that can be used to form a coloured compound; this method involves the addition of peroxidase, 4-chlorophenol and 4-aminoantipyrine. The enzymatic methods studied showed good linearity in the range of 4 to 60 μmol L−1glycerol with a detection limit of 1 μmol L−1. Studies of glycerol recovery in fortified sugar cane liquor showed a recovery of 98 ± 2% for the enzymatic-amperometric method and of 96 ± 1% for the enzymatic-colorimetric method. These two methods were applied to the determination of glycerol in beverages and good correlations were found between these methods. [ABSTRACT FROM PUBLISHER]

International and Brazilian standards have in common the acid number as the main qualification parameter for biodiesel. Free fatty acids lead to engine corrosion and contribute to the formation of gum. The analytical methods specified for analysis are based on colorimetric and potentiometric titrations, which are characterised by lack of selectivity. This article proposes a new method based on the electrochemical reduction of quinones in the presence of the free fatty acids found in biodiesel on the glassy carbon electrode surface in the range of 0.4 V to −0.65 V versus Ag/AgCl/Cl− (3 mol L−1). The proposed method was validated. [ABSTRACT FROM AUTHOR]

Abstract: The effect of aqueous garlic peel extract on the corrosion process of carbon steel in 1molL−1 HCl was examined. The inhibition efficiency of C-steel in 1molL−1 HCl increased as the extract concentration and temperature increased. The inhibitory property of the extract is discussed in terms of the mechanism by which its components adsorb onto the C-steel surface. This adsorption process obeyed a Langmuir adsorption isotherm. HS-SPME GC analysis of the garlic peel extract suggests that sulphur compounds may play an important role in the inhibition process. [Copyright &y& Elsevier]

In this study, an electrochemical method was developed using flow injection analysis and amperometric detection with screen-printed electrodes for iodide determination as a tracer in seawater reservoirs. The amperometric method resulted in a good linear correlation coefficient ( r = 0.9966) with a linear response over a concentration range of 1-10 mg L, a limit of detection of 0.2 mg L and a quantification of 0.6 mg L. In addition, the method has been shown to be precise, linear and homoscedastic. The recovery for the amperometric method was 100 ± 3 %, and the recovery for the produced water samples fortified with iodide was 102 ± 2 %. The amperometric method did not show interference from other anions. Thus, the proposed method is promising for analysing the iodide content of seawater reservoir samples with simple and inexpensive methodologies compared with ion chromatography techniques. [ABSTRACT FROM AUTHOR]

This paper describes the applicability of a Hg-electroplated-Pt ultramicroelectrode in the quantification of elemental sulphur in naphtha samples by square-wave voltammetry. A reproducible deposition methodology was studied and is reported in this paper. This methodology is innovative and relies on the quality of the mercury stock solution to obtain reproducible surfaces required for the analytical methodology. All analyses were performed using a Hg-electroplated-Pt ultramicroelectrode (Hg-Pt UME) due to the low sensibility of such devices to ohmic drops in resistive solutions. The responses of the peak areas in voltammetric experiments were linear in all of the range studied. Themethod developed here is accurate and reproducible, with a detection limit of 0.010 mg L-1 and a good recovery range for both standard solutions of elemental sulphur (85 to 99%) and real naphtha sample (79%). These results attest to the potential for the application of this electroanalytical methodology in determining elemental sulphur in naphtha samples containing mercaptans and disulphides. [ABSTRACT FROM AUTHOR]

Abstract: The effects of aqueous extracts of spent coffee grounds on the corrosion of carbon steel in a 1molL−1 HCl were examined. Two methods of extraction were studied: decoction and infusion. The inhibition efficiency of C-steel in 1molL−1 HCl increased as the extract concentration and temperature increased. The coffee extracts acted as a mixed-type inhibitor with predominant cathodic effectiveness. In this study, the adsorption process of components of spent coffee grounds extracts obeyed the Langmuir adsorption isotherm. The chlorogenic acids isolated do not seem to explain the corrosion inhibition observed during the use of the coffee extracts. [Copyright &y& Elsevier]

The kinetics of oxygen reduction was studied on copper in tartarate solutions using a rotating disc electrode. The effect of pH on the cathodic reduction was examined. AC impedance and cathodic polarization curves showed that the reaction is partially controlled by mass transport. At high current densities, the limiting current values showed that O2 is reduced mainly through the four electron pathway. From measurements of density and viscosity and data taken from Levich and Tafel plots, diffusion coefficients for oxygen in tartarate medium were calculated. Peroxidase-mediated oxidation of methylene blue (MB) results using electrogenerated H2O2 on copper electrode showed that O2 reduction reaction occurs in two steps producing the adsorbed intermediate species H2O2 by k2. In the absence of peroxidase, the hydrogen peroxide elimination has to be rapid with k3 ≫ kM. The MB oxidation by lignin peroxidase using electrogenerated H2O2 was studied. After 24 h LiP is able to oxide the MB, producing different oxidized forms: azure C and thionine, with yield of 23% and 66%, respectively. [ABSTRACT FROM AUTHOR]

Amino acids and self assembled monolayers (SAM's) have been studied as to their inhibiting action on the corrosion of metallic materials. The objective of this work is to study the electrochemical behavior of the cisteincisteine, the diphosfonate and the mixture of both in inhibiting the action of corrosion on stainless steel 304 in HCl 1 molL-1. As the following techniques were used: open circuit potential (OCP), potenciostatic anodic polarization (AP), chronoamperometry (CA), electrochemical impedance spectroscopy (EIS) and optical microscopy (OM). The results of CA showed that cisteine has a double effect, catalytic and inhibiting, in function of the immersion time of the metallic part in the electrolytic solution. AP curves have shown lesser current density for the system containing cisteine + diphosfonate, suggesting an inhibiting synergic action. These results have been confi rmed by EIS and OM. [ABSTRACT FROM AUTHOR]

Sulfur compounds in petroleum have caused several problems such as corrosion of equipment, lack of high quality final products, and emission of toxic gases into the environment. Elemental sulfur can increase these problems, since small amounts of it turn mercaptans into potential corrosion agents. This paper describes the applicability of a voltammetric method to quantify elemental sulfur in Brazilian naphtha samples. Elemental sulfur was quantified in synthetic and real samples using square wave voltammetry and a hanging mercury drop electrode. The method was found to have low limits of detection (0.003 mg L−1) and quantification (0.009 mg L−1) and a good recovery range (94.0–108.6%). This voltammetric method has potential for use in elemental sulfur determination in naphtha samples containing mercaptans and aliphatic and aromatic disulfides. [ABSTRACT FROM AUTHOR]

Abstract: Conjugated dienes content is one of the factors for determining the quality of gasoline. Owing to their easy polymerization, the presence of these compounds decreases the quality of the product. Although UOP-326, the traditional method for their determination, is still in use, it has some disadvantages such as: long analysis time, incomplete reaction with some conjugated dienes, and the interference of primary alcohols. The main objective of this work is to propose a faster and more reliable method, using the voltammetric technique, for the determination of conjugated dienes value in Brazilian naphtha samples. The results point out some advantages of the proposed method, such as: less analysis time, better recovery, a good selectivity, the non-interference of alcohols, and the possibility of direct analysis of commercial gasoline. [Copyright &y& Elsevier]

Abstract: The content of conjugated dienes is one of the most important factors in determining the quality of gasoline. Owing to their easy polymerization, the presence of these compounds decreases the quality of the product. Although the Brazilian Petroleum Industry still uses the UOP-326 method to determine the content of conjugated dienes, this method has some disadvantages such as long analysis time, incomplete reaction with some conjugated dienes and the interference of primary alcohols. The main objective of this work is to compare and evaluate the three methods (UOP-326, voltammetric and gas chromatographic/mass spectrometric) used for the determination of the conjugated dienes values in naphtha samples. Our results show that the voltammetric and gas chromatographic/mass spectrometric methods can be applied for the determination of conjugated dienes in naphtha samples. However, the voltammetric method is recommended for daily routine analysis because, in addition to being faster and more precise than the UOP-326 method, it is less expensive if compared to the gas chromatographic/mass spectrometric. [Copyright &y& Elsevier]

Wacker oxidation of limonene, using PdCl2/CuCl2/O2 in glacial AcOH at 302 K with a 24 h reaction time, yielded cis-carvyl acetate, trans-carvyl acetate, trans-carveol, carvone and α-terpinyl acetate. Oxidation of limonene was also carried out in t-butanol using PdCl2/CuCl2/t-butyl hydroperoxide (molar ratio 1:2:360): the yields of oxidation products were higher in the presence of added chloride ion: conversion rates of about 80% after 36 h reaction time were observed at ratios of [PdCl]2]:[LiCl] = 1:4. t-Butylperoxy products resulted in the PdCl2/CuCl2/t-butyl hydroperoxide oxidations from η3-allyl-palladium intermediates. Generally, allylic oxidation was the predominant reaction. The reaction products were generally identified from their mass spectra and retention indices obtained using HRGC–MS. [Copyright &y& Elsevier]

• Isonitrosoacetanilide and isonitrosoacetanilide derivatives were evaluated as corrosion inhibitors for mild steel in 1 mol L−1 HCl; its maximum inhibition efficiency was 97.6% for 2-Bromoisonitrosoacetanilide at room temperature. • The isonitrosoacetanilides act as a mixed type inhibitor with predominantly cathodic effect. • Computational studies corroborated that the isonitrosoacetanilides are adsorbed on the mild steel surface by physisorption. • The bromo atom and methoxy group may play an important role in the inhibition process. • There is a good correlation between theoretical and experimental results. The isonitrosoacetanilide, 2-bromoisonitrosoacetanilide and 2-methoxyisonitrosoacetanilide were synthesized and investigated as mild steel corrosion inhibitors in 1 mol L−1 HCl solution by potentiodynamic polarization curves, electrochemical impedance, weight loss measurements, scanning electron microscopy analysis and theoretical calculations. The weight loss measurements varying temperature show that the isonitrosoacetanilides are adsorbed on the mild steel surface by physisorption. The adsorption of inhibitor obeys the Langmuir's adsorption isotherm and the adsorption is an exothermic process with a decrease in entropy. The Tafel polarization method reveals that the inhibitors act as mixed type inhibitor. The obtained experimental results suggested that the maximum inhibition efficiency of isonitrosoacetanilide derivatives were over 90% at 5 × 10−3 mol L−1 at 25 °C. The weight loss measurements and electrochemical results were confirmed with scanning electron microscopy (SEM). Quantum chemical calculation was applied to correlate electronic structure parameters of isonitrosoacetanilides molecules with their corrosion inhibition performances and showed that possibly the adsorption process is of the physical type. The 2-bromoisonitrosoacetanilide and 2-methoxyisonitrosoacetanilide results were slightly superior to those obtained in the presence of isonitrosoacetanilide, showing that the bromo atom and methoxy group enhances the inhibitory properties. [ABSTRACT FROM AUTHOR]

n electroenzymatic method based on two coupled enzymatic activities (glycerokinase and glycerol-3-phosphate oxidase) was developed using a platinum microelectrode for the determination of free glycerol in biodiesel samples. The electroenzymatic method proposed showed a good linear correlation coefficient (R = 0.9894), with a linear response in the concentration range of 8.2 × 10 to 5.7 × 10% (w/w) and a limit of detection of 6.0 × 10% (w/w). The results obtained for the free glycerol content of select biodiesel samples were compared with their gas chromatography (GC) analyses. The relative errors for glycerol determination using this enzymatic-amperometric method were in the range of −8.0 to 3.0%. The proposed method was shown to be promising for the analysis of glycerol in biodiesel samples and a simple and inexpensive method in comparison to gas chromatography. [ABSTRACT FROM AUTHOR]

• Selectively determination of ascorbic acid using molecularly imprinted polypyrrole. • Determination of ascorbic acid in presence of dopamine and uric acid interferers. • Molecularly imprinted polypyrrole rough surface favors recognition of the analyte. • Molecularly imprinted polypyrrole-graphene electrode induces electrocatalysis. Molecularly imprinted polymers are pushing the limits of sensing capabilities in electrochemical sensors. As a result, these sensors are driving the improvement of chemical species detection with applications in pharmaceutical, chemical and food industries as well as showing potential for bioanalytes sensing for applications in medical diagnostics. In particular, molecularly imprinted polymer-graphene sensors have great potential to increase the selectivity, sensitivity and detectability of electrochemical sensors for organic molecules determination, especially in the presence of interferers. In this work, we tested three different coatings on glassy carbon electrode for the purpose of ascorbic acid quantification: graphene, molecular imprinted polypyrrole-graphene and non-imprinted polypyrrole-graphene. Among the prepared electrodes, non-imprinted and molecularly imprinted polypyrrole on graphene, exhibited the highest sensitivity to ascorbic acid (6.14 and 5.87 μA/mmol L−1, respectively), although their detection limit (0.56 and 0.10 mmol L−1, respectively) was poore than the uncoated graphene one (0.02 mmol L−1). Besides that, graphene modified glassy carbon electrode showed better response for repetitive uses. However, in the case of a unique measurement to detect the presence of ascorbic acid in a solution containing interferers, as uric acid and dopamine, molecular imprinted polypyrrole-graphene electrode exhibits better response and selectivity in addition to, an electrocatalytic effect. [ABSTRACT FROM AUTHOR]