RESUMO

In the last decades, the growth of world agricultural activity has significantly contributed to the increased presence of emerging pollutants such as atrazine (ATZ) in aquatic ecosystems. Due to its high stability to the natural or artificial degradation processes, the ATZ environmental remediation by adsorption has been investigated. In this study, a graphitic-porous-carbon- (GPC) based material with magnetic domains was applied to remove ATZ from aqueous solution. ATZ high adsorption efficiency in a reduced time was achieved in the presence of the GPC adsorbent, leading to a detailed investigation of the mechanisms involved in the adsorption processes. Pseudo-first-order (PFO), pseudo-second-order (PSO), Ritchie, Elovich, and Weber-Morris models were applied to calculate the kinetic process efficiency. Likewise, adsorption isotherms based on Langmuir, Freundlich, Temkin, and Redlich-Peterson models were applied for a detailed understanding of the adsorption mechanisms. GPC was successfully applied for ATZ remediation in natural waters, confirming its high potential for treating natural waters contaminated by ATZ using adsorption process. The material can also be recovered and reused for up to 4 application cycles due to its magnetic properties, showing that in addition to ATZ adsorption efficiency, its sustainable use can be achieved.

Assuntos

RESUMO

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.

Assuntos

RESUMO

In this paper, we study theoretically and experimentally the effect of induced charging currents on the fast-scan cyclic voltammetry. As explained in this paper, the phenomenon originates from the coupling between faradaic and capacitive currents in the presence of uncompensated resistance. Due to the existence of induced charging currents, the capacitive contribution to the total current is different from the capacitive current measured in the absence of electroactive species. In this paper, we show that this effect is particularly important when the ratio of the capacitive current and the total current is close to unity, even for a relatively low cell time constant. Consequently, the conventional background subtraction method may be inaccurate in these situations. In this work, we develop a method that separates the faradaic and capacitive currents, combining simulation and experimental data. The method is applicable even in the presence of potential-dependent capacitance. The theoretical results are compared with some previously reported results and with experiments carried out on the potassium ferrocyanide/ferricyanide redox couple. Platinum disk electrodes of different diameters and NaClO4 support electrolyte of different concentrations were used to obtain different cell time constants. The proposed method allowed us to separate the real capacitive current even in the situations where the conventional background subtraction used in many published papers is clearly inappropriate.

RESUMO

In this study, a novel material for the electrochemical determination of 17ß-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 17ß-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 17ß-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 17ß-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.

Assuntos

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We merged the microwave synthesis approach with an extension of the nonhydrolytic sol-gel method to induce highly selective crystallization of MoS(2) layers over graphene sheets. This hybrid material showed superior electrocatalytic activity in hydrogen evolution reactions.

RESUMO

Potentiodynamic electrochemical synthesis was used to controllably synthesize nanofibers (mean diameter 48 nm) and/or nanoparticles (mean diameter 88 nm) of polyaniline (PANI) on gold electrodes. The films were characterized by cyclic voltammetry (CV), field emission gun scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The type and dimensions of the nanostructures depend on deposition conditions such as monomer concentration and scan rate. This study shows that the nucleation and growth steps play a key role on the film development and its nano-morphology.

Assuntos

RESUMO

Nanostructured films from two conducting polymers, poly(o-methoxyaniline) (POMA) and poly(3-thiopheneacetic acid) (PTAA), were fabricated with the layer-by-layer (LBL) technique. The electrochemical response of the LBL films differs from that of a POMA cast film, even in a potential range where PTAA is inactive. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated by quartz crystal microbalance measurements. The results show that the transport properties of conducting polymers can be changed by alternation with layers of appropriate materials in LBL films.