Electroanalysis of selenium in water on an electrodeposited gold-nanoparticle modified glassy carbon electrode

Microelectrode Voltammetric Analysis of Low Concentrations of Se(IV) Ions in Environmental Waters

The current research is an attempt to analyze on-site selenium(IV) ions in environmental water samples using an eco-friendly miniaturized sensor developed by deposition of a very thin amount of metallic bismuth in a solid Bi electrode tightly closed in miniaturized housing. Numerous experimental variables are optimized, including the composition of the supporting electrolyte and its pH, as well as activation and accumulation conditions. Under optimized measurement conditions, the method shows high sensitivity, permitting a very low limit of detection equal to 7 × 10-10 mol L-1 to be achieved in a short accumulation time of 50 s. The performance of this microsensor was investigated against numerous interference factors and its good anti-interference capability was demonstrated. A series of voltammetric experiments by differential pulse cathodic stripping voltammetry (DPCSV) were carried out and they proved that the miniaturized sensor is characterized by very good accuracy and precision as well as long-term stability. The solid bismuth microelectrode displays a good voltammetric response in the analysis of diverse samples with a complex matrix and demonstrates a good recovery rate.

Electrochemical detection of selected heavy metals in water: a case study of African experiences

The safety of water resources throughout the globe has been compromised by various human activities and climate change over the last decades. Consequently, the world is currently confronted with a severe shortage of water supply and a water safety crisis, amidst a growing population. With poor environmental regulations, indiscriminate budding of urban slums, poverty, and a lack of basic knowledge of hygiene and sanitation, the African water supply has been critically threatened by different organic and inorganic contaminants, which results in several health issues. Inorganic pollutants such as heavy metals are particularly of interest because they are mostly stable and non-biodegradable. Therefore, they are not easily removed from water. In different parts of the continent, the concentration of heavy metals in drinking water far exceeds the permissible level recommended by the World Health Organization (WHO). Worse still, this problem is expected to increase with growing population, industrialization, urbanization, and, of course, corruption of government and local officials. Most of the African population is ignorant of the standards of safe water. In addition, the populace lack access to affordable and reliable technologies and tools that could be used in the quantification of these pollutants. This problem is not only applicable to domestic, but also to commercial, communal, and industrial water sources. Hence, a global campaign has been launched to ensure constant assessment of the presence of these metals in the environment and to promote awareness of dangers associated with unsafe exposure to them. Various conventional spectroscopic heavy metal detection techniques have been used with great success across the world. However, such techniques suffer from some obvious setbacks, such as the cost of procurement and professionalism required to operate them, which have limited their applications. This paper, therefore, reviews the condition of African water sources, health implications of exposure to heavy metals, and the approaches explored by various indigenous electrochemists, to provide a fast, affordable, sensitive, selective, and stable electrochemical sensors for the quantification of the most significant heavy metals in our water bodies.

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.

Materials interacting with inorganic selenium from the perspective of electrochemical sensing

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(VI) to detectable Se(IV). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials…) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

New Strategies for the Simple and Sensitive Voltammetric Direct Quantification of Se(IV) in Environmental Waters Employing Bismuth Film Modified Glassy Carbon Electrode and Amberlite Resin

An analytical procedure regarding the determination of selenium(IV) by anodic stripping voltammetry exploiting the in situ plated bismuth film electrode is described. Since organics are commonly present in untreated natural water samples, the use of Amberlite XAD-7 resin turns out to be quite important to avoid problems such as the adsorption of these compounds on the working electrode. The optimum circumstances for the detection of selenium in water using differential pulse voltammetry techniques were found to be as follows: 0.1 mol L-1 acetic acid, 1.9 × 10-5 mol L-1 Bi(III), 0.1 g Amberlite XAD-7 resin, and successive potentials of -1.6 V for 5 s and -0.4 V for 60 s, during which the in situ formation of the bismuth film on glassy carbon and the accumulation of selenium took place. The current of the anodic peak varies linearly with the selenium concentration ranging from 3 × 10-9 mol L-1 to 3 × 10-6 mol L-1 (r = 0.9995), with a detection limit of 8 × 10-10 mol L-1. The proposed procedure was used for Se(IV) determination in certified reference materials and natural water samples, and acceptable results and recoveries were obtained.

Graphitic Carbon Nitride: A Highly Electroactive Nanomaterial for Environmental and Clinical Sensing

Graphitic carbon nitride (g-C3N4) is a two-dimensional conjugated polymer that has attracted the interest of researchers and industrial communities owing to its outstanding analytical merits such as low-cost synthesis, high stability, unique electronic properties, catalytic ability, high quantum yield, nontoxicity, metal-free, low bandgap energy, and electron-rich properties. Notably, graphitic carbon nitride (g-C3N4) is the most stable allotrope of carbon nitrides. It has been explored in various analytical fields due to its excellent biocompatibility properties, including ease of surface functionalization and hydrogen-bonding. Graphitic carbon nitride (g-C3N4) acts as a nanomediator and serves as an immobilization layer to detect various biomolecules. Numerous reports have been presented in the literature on applying graphitic carbon nitride (g-C3N4) for the construction of electrochemical sensors and biosensors. Different electrochemical techniques such as cyclic voltammetry, electrochemiluminescence, electrochemical impedance spectroscopy, square wave anodic stripping voltammetry, and amperometry techniques have been extensively used for the detection of biologic molecules and heavy metals, with high sensitivity and good selectivity. For this reason, the leading drive of this review is to stress the importance of employing graphitic carbon nitride (g-C3N4) for the fabrication of electrochemical sensors and biosensors.

Determination of trace Se(IV) by anodic stripping voltammetry following double deposition and stripping steps

A procedure of Se(IV) determination by anodic stripping voltammetry using two deposition and stripping steps at gold electrodes was proposed. A well-defined stripping peak of selenium was obtained at potential 0.9 V. The optimization of parameters influencing the selenium peak current including both deposition and stripping steps was performed. A linear relationship was observed between the Se(IV) peak current and its concentration in the range from 5×10^-9 to 1×10^-7mol L^-1. The limit of detection was found to be 8.5×10^-10mol L^-1. Repeatability of the method determined as RSD % for Se(IV) concentration of 5×10^-8mol L^-1 was 4.3% (n=7). The proposed procedure was used for Se(IV) determination in certified reference material and natural water samples and acceptable results and recoveries were obtained.