Study of selenium electrodeposition at gold electrode by voltammetric and rotating disc electrode techniques

Selenium (Se) recovery for technological applications from environmental matrices based on biotic and abiotic mechanisms

Selenium (Se) is an essential element with application in manufacturing from food to medical industries. Water contamination by Se is of concern due to anthropogenic activities. Recently, Se remediation has received increasing attention. Hence, different types of remediation techniques are listed in this work, and their potential for Se recovery is evaluated. Sorption, co-precipitation, coagulation and precipitation are effective for low-cost Se removal. In photocatalytic, zero-valent iron and electrochemical systems, the above mechanisms occur with reduction as an immobilization and detoxification process. In combination with magnetic separation, the above techniques are promising for Se recovery. Biological Se oxyanions reduction has been widely recognized as a cost-effective method for Se remediation, simultaneously generating biosynthetic Se nanoparticles (BioSeNPs). Increasing the extracellular production of BioSeNPs and controlling their morphology will benefit its recovery. However, the mechanism of the microbial production of BioSeNPs is not well understood. Se containing products from both microbial reduction and abiotic methods need to be refined to obtain pure Se. Eco-friendly and cost-effective Se refinery methods need to be developed. Overall, this review offers insight into the necessity of shifting attention from Se remediation to Se recovery.

Voltammetric and impedimetric determinations of selenium(iv) by an innovative gold-free poly(1-aminoanthraquinone)/multiwall carbon nanotube-modified carbon paste electrode

Selenite (Se4+), a significant source of water pollution above the permissible limits, is considered a valuable metal by environmentalists. In this study, we described a novel electrochemical sensor that utilized a carbon paste electrode (CPE) that was modified using multiwall carbon nanotubes (MWCNTs) and poly(1-aminoanthraquinone) (p-AAQ) for finding Se4+ in water samples. Electrochemical quantification of Se4+ depends on the formation of a selective complex (piaselenol) with p-AAQ. In this work, we prepared a CPE modified by physical embedding of MWCNTs and 1-aminoanthraquione (AAQ), while the polymer film was formed by anodic polymerization of AAQ by applying a constant potential of 0.75 V in 0.1 M HCl for 20 s followed by cyclic voltammetry (CV) from -0.2 to 1.4 V for 20 cycles. The modified CPE was used for differential pulse voltammetry (DPV) of Se4+ in 0.1 M H2SO4 from 0 to 0.4 V with a characteristic peak at 0.27 V. Further, the proposed sensor was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electrochemical impedance spectroscopy (EIS). The analytical conditions regarding the electrode performance and voltammetric measurements were optimized, with the accumulation time and potential, supporting electrolyte, differential-pulse period/time, and amplitude. The EIS results indicated that the p-AAQ/MWCNTs-modified CPE sensor (p-AAQ/MWCNTs/CPE) that also exhibited low charge-transfer resistance (R ct) toward the anodic stripping of Se4+, exhibited good analytical performance toward different concentrations of Se4+ in a linear range of 5-50 μg L-1 Se4+ with a limit of determination (LOD) of 1.5 μg L-1 (3σ). Furthermore, differential-pulse voltammetry was employed to determine different concentrations of Se4+ in a linear range of 1-50 μg L-1 Se4+, and an LOD value of 0.289 μg L-1 was obtained. The proposed sensor demonstrated good precision (relative standard deviation = 4.02%) at a Se4+ concentration of 5 μg L-1. Moreover, the proposed sensor was applied to analyze Se4+ in wastewater samples that were spiked with Se, and it achieved good recovery values.

An electrochemical sensor for detecting selenium in biological fluids on an arenediazonium tosylate-modified metal electrode

This article presents the results on using a new electrochemical sensor modified with arenediazonium salts (MGE-Cu-COOH) to determine selenium in biological fluids (blood serum). It was shown that the sensitivity of the determination of selenite ions using this modified electrode is higher compared to that of the unmodified one (MGE-Cu). The effect of the concentration of arenediazonium tosylates on various substituents was studied, and the conditions for the production of the electrochemical sensor were developed. The surface of the modified electrode was investigated using SEM. The increase in the effective surface area of the electrode was found to be due to the formation of a system of ultramicroelectrodes. In biological samples, the LOD and LOQ of selenium were established at the levels of 0.057 and 0.166 μg l^-1, respectively. Finally, the correctness of the results on selenium determination in real samples by the "input-found" method, which correlates well with the known value, was verified.

Electroplating Kinetic of Nanostructured Selenium Films from Citrate Bath

In this work; Cyclic-Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were used to study the electrodeposition kinetic of selenium films in potentiostatic mode from aqueous solution containing selenium dioxide and sodium citrate at pH = 4.2. Semiconducting proprieties of obtained deposits were investigated by Mott-Schottky measurements whereas the optical ones were performed by UV–Visible spectrophotometry. The morphological characterization was carried out using the scanning electron microscopy (SEM). The obtained results showed that the electrodeposition process of selenium films in citrate bath occurred under diffusional regime as rate-limiting step. Deposition rate of selenium layers on platinum substrate is much superior than in the case of ITO substrate and up to a value of 0.65 μg/cm² s. The HSeO₃⁻/Se system becomes more rapid with the increase of the bath temperature. Obtained deposits are photoactive films that belong to p-type semiconductors with number of charge carriers in order of 10²¹/cm³ and energy band gap about 1.7 eV. The grains of electroplated films have spherical forms, nanometric sizes and strong adhesion on the substrate surface.

Cathodic selenium recovery in bioelectrochemical system: Regulatory influence on anodic electrogenic activity

Metal(loid)s are used in various industrial activities and widely spread across the environmental settings in various forms and concentrations. Extended releases of metal(loid)s above the regulatory levels cause environmental and health hazards disturbing the ecological balance. Innovative processes for treating the metal(loid)-contaminated sites and recovery of metal(loid)s from disposed waste streams employing biotechnological routes provide a sustainable way forward. Conventional metal recovery technologies demand high energy and/or resource inputs, which are either uneconomic or unsustainable. Microbial electrochemical systems are promising for removal and recovery of metal(loid)s from metal(loid)-laden wastewaters. In this communication, a bioelectrochemical system (BES) was designed and operated with selenium (Se) oxyanion at varied concentrations as terminal electron acceptor (TEA) for reduction of selenite (Se⁴⁺) to elemental selenium (Se⁰) in the abiotic cathode chamber. The influence of varied concentrations of Se⁴⁺ towards Se⁰ recovery at the cathode was also evaluated for its regulatory role on the electrometabolism of anode-respiring bacteria. This study observed 26.4% Se⁰ recovery (cathode; selenite removal efficiency: 73.6%) along with organic substrate degradation of 74% (anode). With increase in the initial selenite concentration, there was a proportional increase in the dehydrogenase activity. Bioelectrochemical characterization depicted increased anodic electrogenic performance with the influence of varied Se⁴⁺ concentrations as TEA and resulted in a maximum power density of 0.034 W/m². The selenite reduction (cathode) was evaluated through spectroscopic, compositional and structural analysis. X-ray diffraction and Raman spectroscopy showed the amorphous nature, while Energy Dispersive X-ray spectroscopy confirmed precipitates of the deposited Se⁰ recovered from the cathode chamber. Scanning electron microscopic images clearly depicted the Se⁰ depositions (spherical shaped; sized approximately 200 nm in diameter) on the electrode and cathode chamber. This study showed the potential of BES in converting soluble Se⁴⁺ to insoluble Se⁰ at the abiotic cathode for metal recovery.

Electrochemical, Spectroscopic, and Computational Investigations on Redox Reactions of Selenium Species on Galena Surfaces

Despite previous studies investigating selenium (Se) redox reactions in the presence of semiconducting minerals, Se redox reactions mediated by galena (PbS) are poorly understood. In this study, the redox chemistry of Se on galena is investigated over a range of environmentally relevant Eh and pH conditions (+0.3 to −0.6 V vs. standard hydrogen electrode, SHE; pH 4.6) using a combination of electrochemical, spectroscopic, and computational approaches. Cyclic voltammetry (CV) measurements reveal one anodic/cathodic peak pair at a midpoint potential of +30 mV (vs. SHE) that represents reduction and oxidation between HSeO3− and H2Se/HSe−. Two peak pairs with midpoint potentials of −400 and −520 mV represent the redox transformation from Se(0) to HSe− and H2Se species, respectively. The changes in Gibbs free energies of adsorption of Se species on galena surfaces as a function of Se oxidation state were modeled using quantum-mechanical calculations and the resulting electrochemical peak shifts are (−0.17 eV for HSeO3−/H2Se, −0.07 eV for HSeO3−/HSe−, 0.15 eV for Se(0)/HSe−, and −0.15 eV for Se(0)/H2Se). These shifts explain deviation between Nernstian equilibrium redox potentials and observed midpoint potentials. X-ray photoelectron spectroscopy (XPS) analysis reveals the formation of Se(0) potentials below −100 mV and Se(0) and Se(−II) species at potentials below −400 mV.

Nucleation and growth mechanism of a nanosheet-structured NiCoSe2 layer prepared by electrodeposition

Ni-Co-Se layers have attracted a great deal of attention in the field of solar cells, electrocatalyst water splitting and supercapacitors. Electrodeposition is a simple, convenient and low-cost way to obtain Ni-Co-Se layers. However, until now, the electrochemical kinetics of the Ni-Co-Se system, including its growth and nucleation mechanisms, are still unclear. In present work a NiCoSe₂ layer with a nanosheet structure was electrodeposited in a chloride bath. The electrochemical mechanisms of the Ni-Co-Se system were also studied. It is noted that the electrochemical kinetics of Ni-Co-Se electrodeposition can be influenced by both temperature and electrode material; however, temperature does not change the progressive nucleation process and mixed controlled growth mechanism of Ni-Co-Se. The diffusion coefficient D and charge-transfer coefficient α of the Ni-Co-Se system were calculated. The values of D obtained by cyclic voltammogram and chromoamperometry are close to each other at both 20 and 50 °C, respectively, and increase with the increase of temperature. Moreover, the activation energy E _a was also calculated. Specially, a uniform 3D network-structure NiCoSe₂ layer was electrodeposited on ITO glass at -0.9 V and 40 ∼ 60 °C. The increased overpotential during deposition makes the NiCoSe₂ layer more easily gather together; however, there is no significant effect on the surface morphology of the NiCoSe₂ layer when the temperature is between 40 and 60 °C.