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Carbon quantum dots or carbon dots (CDs) are a new class of nanomaterials with a nearly spherical shape and a size smaller than 10 nm. The literature reports on studying metallic composites using other carbon allotropes, such as carbon nanotubes and graphene oxide. However, no studies have applied carbon quantum dots to metallic coatings. Tin is a metal widely used industrially due to its resistance to oxidation, corrosion resistance, and weldability. However, the thickness and microstructure of the material can impact its resistance. Therefore, this work studied composite coatings of tin (Sn) and CDs at different concentrations to improve the material's corrosion resistance. Different concentrations of CDs were analyzed to obtain Sn – CD composite coatings: 0.03, 0,04, 0.05, 0.07, and 0.09 g L−1. Mild steel plates were used as substrate using electrodeposition in galvanostatic mode with j = 6.25 mA cm−2. The performance of the coatings was evaluated by electrochemical measurements such as open circuit potential, electrochemical impedance, and potentiodynamic polarization curve. In addition, characterizations of the CDs and composite films were carried out by Fourier Transform Infrared Spectroscopy (FTIR), Zeta Potential (ζ), Dynamic Light Scattering (DLS), UV-VIS Spectroscopy, Fluorimetry, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Excited Photoelectron Spectroscopy X-Ray (XPS). The electrochemical tests show an optimal working concentration equivalent to 0.05 g L−1of CDs in the bath. The SEM and XDR show that this concentration favored the growth of the film in a more uniform manner, providing a more homogeneous barrier when compared to the pure Sn film. The XPS indicated that the pure Sn film oxidized more than the composite film, suggesting that the addition of CDs improved the resistance of this material.

Developing a sustainable and environmentally friendly inhibitor remains an essential and challenging goal for corrosion control. Here, different extracts from the same biomass (Juçara - Euterpe edulis) were applied as a new inhibitor for mild steel in different corrosive medium: 1 mol L−1HCl (pH 0) and simulated CO2-saturated formation water (pH 5). Depending on the extraction process, the anticorrosive capacity of extracts may increase, a fact verified in gravimetric tests, reaching 94.4% maximum inhibition efficiency for the acidic medium (1000 mg L−1of Juçara pulp in 48 h of immersion) and 86.1% inhibition efficiency for the saline medium (600 mg L−1of Juçara pulp extract assisted by ultrasound in 24 h of immersion). Gravimetric tests, electrochemical tests, and surface and biochemical characterization analyses were carried out to better understand these extracts' performance. This work provides an interesting application of the same biomass effectively acting in different corrosive medium, depending on the extraction method.

In this work, an endogenous self-doping N,P,S-CQDs was synthesized by the acid hydrolysis of pumpkin seeds (Cucurbita maxima)and its performance as a corrosion inhibitor was evaluated. Mild steel (MS) is one of the most used materials in the industry; however, it has low corrosion resistance in acidic environments. Pumpkin is cultivated worldwide, and this compositional characteristic makes pumpkin seeds a great alternative as a raw material to produce CQDs. The results show that endogenous self-doping CQD was successfully obtained with a size distribution smaller than 10 nm. The N,P,S-CQDs presented 91.3% at 60 ppm and 94.6% at 10 ppm as maximum inhibition efficiency after 2 and 24 h immersion, respectively. Activation energy studies, XPS analysis, and isotherm studies show that the inhibition mechanism occurs through physical interaction. These results show an excellent alternative for using pumpkin seeds (Cucurbita maxima), an agroindustry waste, as a corrosion inhibitor.

The soybean (Glycine Max) meal extracts inhibitory action, the aqueous extract by infusion (AE), its high molecular weight fraction (HMWF) and the aqueous extract by infusion of a commercially isolated soy protein (CIP) towards the mild steel corrosion in 0.5 mol L−1H2SO4was investigated by weight loss measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves. Additionally, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used, respectively, to characterize morphologically and chemically the surface. The total content of proteins in the different extracts was determined by a quantitative method, the Biuret methods, as well as by two qualitative methods, the nuclear magnetic resonance (NMR) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis (SDS-PAGE). The AE, its HMWF and CIP extracts acted as good corrosion inhibitors, reaching inhibition efficiencies of 85.2%, 88.7% and 94.8% for 800 mg L−1, respectively, from the jcorrdata. The polarization curves show that these extracts act as mixed-type inhibitor with predominantly cathodic characteristics. The adsorption of components from AE, its HMWF, and CIP on the mild steel surface follows the Langmuir adsorption isotherm. The SEM results indicate that the surface was covered by the inhibitor and the XPS analyses confirm chemical interactions between the extracts components and the mild steel surface. The results obtained with HMWF from AE and CIP suggest that the proteins are probably responsible for the inhibitory action.

The ability of nitrogenated derivatives of furfural to act as corrosion inhibitors for mild steel in 1molL−1HCl solution was evaluated using weight-loss measurements, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The imine 2-((furan-2-ylmethylene)amino)ethan-1-ol (1)and the mixture of 2-(furan-2-yl)-1,3-oxazinane and 3-((furan-2-ylmethylene)amino)propan-1-ol (2a+b)presented, respectively, 81.9% and 84.4% of inhibition efficiency towards the mild steel acidic corrosion at 5×10−3molL−1, room temperature and 2-h immersion time. Polarization curves showed more effective inhibition in the cathodic process. EIS plots indicated an increase in the polarization resistance with enhancement of inhibitor concentration. The adsorption of the evaluated inhibitors obeyed the Langmuir adsorption isotherm. The ΔG°adsand ΔH°adsvalues obtained suggest a physical nature adsorption of inhibitors (1)and (2a+b). The physisorption could be explained by the coulombic interaction between the protonated forms of the inhibitor molecules due to the acid medium with the negatively charged surface. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphologically and chemically, respectively. Quantum chemical calculations were applied to correlate electronic structure parameters of inhibitors with their corrosion inhibition efficiency.

Background: Chagas disease, also known as American trypanosomiasis, is classified as one of the 17 most important neglected diseases by the World Health Organization. The only drugs with proven efficacy against Chagas disease are benznidazole and nifurtimox, however both show adverse effects, poor clinical efficacy, and development of resistance. For these reasons, the search for new effective chemical entities is a challenge to research groups and the pharmaceutical industry. Objective: Synthesis and evaluation of antitrypanosomal activities of a series of thiosemicarbazones and semicarbazones containing 1,2,3-1H triazole isatin scaffold. Method: 5'-(4-alkyl/aryl)-1H-1,2,3-triazole-isatins were prepared by Huisgen 1,3-dipolar cycloaddition and the thiosemicarbazones and semicarbazones were obtained by the 1:1 reactions of the carbonylated derivatives with thiosemicarbazide and semicarbazide hydrochloride, respectively, in methanol, using conventional reflux or microwave heating. The compounds were assayed for in vitro trypanocidal activity against Trypanosoma cruzi, the aetiological agent of Chagas disease. Beyond the thio/semicarbazone derivatives, isatin and triazole synthetic intermediates were also evaluated for comparison. Results: A series of compounds were prepared in good yields. Among the 37 compounds evaluated, 18 were found to be active, in particular thiosemicarbazones containing a non-polar saturated alkyl chain (IC50 = 24.1, 38.6, and 83.2 μM; SI = 11.6, 11.8, and 14.0, respectively). To further elucidate the mechanism of action of these new compounds, the redox behaviour of some active and inactive derivatives was studied by cyclic voltammetry. Molecular docking studies were also performed in two validated protein targets of Trypanosoma cruzi, i.e., cruzipain (CRZ) and phosphodiesterase C (TcrPDEC). Conclusion: A class of thio/semicarbazones structurally simple and easily accessible was synthesized. Compounds containing thiosemicarbazone moieties showed the best results in the series, being more active than the corresponding semicarbazones. Our results indicated that the activity of these compounds does not originate from an oxidation-reduction pathway but probably from the interactions with trypanosomal enzymes.

In this work, a method was developed for the quantification of total glycerol in biodiesel using solid phase extraction (SPE) coupled with enzymatic-spectrophotometric determination. An aminopropylsilane stationary phase was used for the separation of the main contaminants of biodiesel (monoacylglycerol (MAG), diacylglycerol (DAG), triacylglycerol (TAG) and free glycerol (FG)) from its main components, fatty acid methyl esters (FAMEs). A biodiesel sample from a high-conversion transesterification reaction was used, and the separation of contaminants was monitored by non-aqueous, reversed-phase high-performance liquid chromatography (HPLC-NARP). After SPE, the samples were analyzed by spectrophotometry using a commercial enzyme kit widely used to measure total triglyceride levels in blood. The method showed good analytical performance for linearity (R2= 0.9919), limit of detection (9.81 × 10−4%, w/w), limit of quantification (3.24 × 10−3%, w/w), repeatability (RSD% ranged from 1.22% to 4.80%), intermediate precision and recovery (96.8% to 100%). The proposed method efficiently determined the total glycerol in biodiesel, and the paired t-test demonstrated strong correlation with the reference method (GC).

Biodiesel is a strong candidate to replace diesel and has its origin in renewable resources. The guarantee of biodiesel quality is a matter of utmost importance in order to take its place in the global energy matrix. One of the parameters that stand out in the monitoring of its quality is the acid number. The evaluation of this parameter is of paramount importance by considering the raw material used in the production of biodiesel up to its storage, since the presence of free fatty acids leads to the formation of deposits in the injector nozzles. The standardized method in Europe, Brazil and the USA is based on potentiometric titration, using KOH as a base. This method has some drawbacks such as long analysis time, parallel reactions with possible contaminants or additives, etc. Recently, our group proposed a method based on the voltammetric reduction of 2-methyl-1,4-naphthoquinone in the presence of acids. The generated pre-peak current is proportional to the concentration of acids in the medium. This paper reports a comparison of the conventional and our method considering analysis conditions, repeatability, limits of detection and quantification, recovery, selectivity, reproducibility and determination of acidity in various biodiesel samples. [ABSTRACT FROM AUTHOR]

In the present work, two mixed oxides, namely, SiO2/Al2O3/Nb2O5and SiO2/Al2O3/TiO2(designated as SiAlNb and SiAlTi, respectively), obtained using the sol–gel method were used to immobilize chloroperoxidase. Hydrogen peroxide was quantified using potassium hexacyanoferrate(ii) as a redox-mediator and amperometric measurements at 0.0 V vs.Ag/AgCl/Cl−(3 M). The SiAlTi biosensor presented higher sensitivity than the SiAlNb biosensor, however, the first one did not present a good response regarding time. The developed biosensor using the SiAlNb mixed oxide provided good signal levels, good linearity, good stability (retaining approximately 70% of its original response after 6 weeks of usage), a low detection limit (3 μM), good sensitivity, a suitable working range (from 4 to 19 μM), fast response and good repeatability. The recovery of the amperometric method for the detection of hydrogen peroxide in synthetic samples was approximately 100 ± 2%, and for Listerine® Whitening Pre-Brush Rinse samples fortified with 1, 2 and 3% (v/v) of hydrogen peroxide, it was 100 ± 3%.

In this work, an electroenzymatic methodology based on two coupled enzymatic activities (glycerokinase and glycerol‐3‐phosphate oxidase) was developed using an oxygen Clark‐type electrode for the determination of free and total glycerol in biodiesel samples. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark‐type electrode and correlated with the concentration of glycerol in the sample. The electroenzymatic method proposed showed a good linear correlation coefficient (R=0.9990) with a linear response in the concentration range of 6.25×10−5to 6.25×10−4% (w/v) and limits of detection and quantification at 1.0×10−5% and 3.0×10−5% (w/v), respectively. Good correlations were found between the results obtained in this work and those by the gas chromatography technique (R=0.9994). The proposed method was shown to be promising for the analysis of glycerol in biodiesel samples, with a simple and inexpensive methodology compared with the gas chromatography technique.

Many factors can affect the quality of diesel oil, in particular the degradation processes that are directly related to some organosulfur compounds. During the degradation process, these compounds are oxidized into their corresponding sulfonic acids, generating a strong acid content during the process. p‐Toluene sulfonic acid analysis was performed using the linear sweep voltammetry technique with a platinum ultramicroelectrode in aqueous solution containing 3 mol L−1potassium chloride. An extraction step was introduced prior to the voltammetric detection in order to avoid the adsorption of organic molecules, which inhibit the electrochemical response. The extraction step promoted the transference of sulfonic acid from the diesel oil to an aqueous phase. The method was accurate and reproducible, with detection and quantification limits of 5 ppm and 15 ppm, respectively. Recovery of sulfonic acid was around 90%.