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

An impedimetric approach for determination of ammonium using silver/poly-1-aminoanthraquinone/carbon paste electrode

Here, we present the electrochemical determination of ammonium in water samples, emphasizing the importance of accurate and precise assessment of its concentration. The modified electrode used in this study was fabricated through the anodic polymerization of 1-aminoanthraquinone (1-AAQ) and deposition of silver particles into a carbon paste electrode. The fabrication process involved cyclic voltammetry in a 0.1 M HCl solution, followed by the application of a potential of 0.2 V for 75 s. The resulting Ag/poly-1-AAQ/CPE exhibited remarkable electrochemical properties, as confirmed by scanning electron spectroscopy (SEM), energy-dispersive X-ray analysis (EDX), and elemental mapping. The successful deposition of silver at percentages of 12.07% on Ag/CPE and 0.75% on Ag/poly-1-AAQ/CPE was observed. The Ag/poly-1-AAQ/CPE was employed for impedimetric determination of ammonium in a solution of 0.1 M Na2SO4. The charge transfer resistance) output from the fitting of the experimental impedimetric data of ammonium determination exhibited good linearity over a concentration range of 5 µM to 200 µM NH4+, with a detection limit of 3.3 µM NH4+. The precision of the modified electrode over ten replicate measurements were conducted at three concentration levels (a low of 5 µM NH4+, a medium of 50 µM NH4+, and a high of 200 µM NH4+). The obtained relative standard deviation (RSD) values of 18%, 12% and 7%, respectively, indicating good precision.

Aptamer and Electrochemical Aptasensor towards Selenate Ions (SeO42-)

Selenium is an essential inorganic compound in human and animal nutrition, involved in the proper functioning of the body. As a micronutrient, it actively contributes to the regulation of various metabolic activities, i.e., thyroid hormone, and protection against oxidative stress. However, Se exhibits a narrow concentration window between having a positive effect and exerting a toxic effect. In higher doses, it negatively affects living organisms and causes DNA damage through the formation of free radicals. Increased reactivity of Se anions can also disrupt the integrity and function of DNA-repairing proteins. As the permissible concentration of Se in drinking water is 10 µg/L, it is vital to develop sensitive and robust methods of Se detection in aqueous samples. In this study, for the first time, we proposed a selective aptamer for selenate ion detection, chosen following the SELEX process, and its application in the construction of an electrochemical aptasensor towards SeO42- ions. Measurement conditions such as the used redox marker and pH value of the measurement solution were chosen. The proposed aptasensor is characterized by good selectivity and an LOD of 1 nM. Conditions for biosensor regeneration and storage were also investigated in this research.

Recent advances in the modification of electrodes for trace metal analysis: a review

This review paper summarizes the research published in the last five years on using different compounds and/or materials as modifiers for electrodes employed in trace heavy metal analysis. The main groups of modifiers are identified, and their single or combined application on the surface of the electrodes is discussed. Nanomaterials, film-forming substances, and polymers are among the most used compounds employed mainly in the modification of glassy carbon, screen-printed, and carbon paste electrodes. Composites composed of several compounds and/or materials have also found growing interest in the development of modified electrodes. Environmentally friendly substances and natural products (mainly biopolymers and plant extracts) have continued to be included in the modification of electrodes for trace heavy metal analysis. The main analytical performance parameters of the modified electrodes as well as possible interferences affecting the determination of the target analytes, are discussed. Finally, a critical evaluation of the main findings from these studies and an outlook discussing possible improvements in this area of research are presented.

AutoGIS processing for site selection for solar pond development as efficient water treatment plants in Egypt

The increasing demand for renewable and environmentally friendly energy sources is a top priority for many countries around the world. It is obvious that renewable solar energy will help to meet most of the energy demand in the coming years. A solar pond is a huge Salt artificial Lake that serves as a solar energy collection system. However, site selection is a critical factor that affects the effectiveness and lifetime of a solar pond. Here, we present an innovative methodology for site selection based on three environmental factors, including direct solar irradiance (DNI), temperature, and wind speed. Our approach uses Python programming and clustering analysis with several libraries, including Pandas, Geopandas, Rasterio, Osgeo, and Sklearn, to analyse and process data collected over a 30-year period from NASA power. This method was applied to the geographic boundaries of Egypt, but the methods can be applied to any spatial context if the same dataset is available. The results show that Egypt has a potential land area of 500 km2 suitable for solar ponds construction along the border with Sudan throughout the year, including 2000 km2 in winter (between January and March), 800 km2 in spring (between April and June), 900 km2 in summer (between July and September), and the largest area of 3700 km2 (between October and December), most of which is located in the south of the Eastern Desert and around the Nile River. Notably, the northwestern region, close to the Mediterranean Sea on the border with Libya, exhibits suitability for solar pond development, with consistent performance throughout the year. Our results provide an efficient way for GIS and data processing and could be useful for implementing new software to find the best location for solar ponds development. This could be beneficial for those interested in investing in renewable energy and using solar ponds as an efficient water treatment plant.

Modified electrode decorated with silver as a novel non-enzymatic sensor for the determination of ammonium in water

Ammonium is an essential component of the nitrogen cycle, which is essential for nitrogen cycling in ecosystems. On the other hand, ammonium pollution in water poses a great threat to the ecosystem and human health. Accurate and timely determination of ammonium content is of great importance for environmental management and ensuring the safety of water supply. Here we report a highly sensitive electrochemical sensor for ammonium in water samples. The modified electrode is based on the incorporation of silver nitrate (AgNO3) into a carbon paste embedded with 1-aminoanthraquinone and supported by multi-walled carbon nanotubes, which are commercially available. A potential of 0.75 V is applied to the modified electrode, followed by activation in hydrochloric acid. The modified electrode was used for square wave voltammetry of ammonium in water in the potential range of - 0.4-0.2 V. The performance of ammonium analysis was determined in terms of square wave frequency, square wave amplitude and concentration of electrolyte solution (sodium sulphate). The calculation of the surface area according to the Randles-Sevcik equation resulted in the largest surface area for the Ag/pAAQ/MWCNTs/CPE. The modified electrode exhibited a linear range of 5-100 µM NH4+ in 0.1 M Na2SO4 with a detection limit of 0.03 µM NH4+ (3σ). In addition, the modified electrode showed high precision with an RSD value of 9.93% for 10 repeated measurements. No interfering effect was observed at twofold and tenfold additive concentrations of foreign ions. Good recoveries were obtained in the analysis of tap and mineral water after spiking with a concentration of ammonium ions.

A new approach for determination of orthophosphate based on mixed valent molybdenum oxide/poly 1,2-diaminoanthraquinone in seawater

Orthophosphate is an essential macronutrient in natural water that controls primary production and strongly influences the global ocean carbon cycle. Electrochemical determination of orthophosphate is highly recommended because electrochemistry provides the simplest means of determination. Here the determination of orthophosphate based on the formation of a phosphomolybdate complex is reported. Mixed-valent molybdenum oxide (MoxOy) was prepared by cyclic voltammetry on poly-1,2-diaminoanthraquinone (1,2-DAAQ), which was performed by cyclic voltammetry on the surface of a glassy carbon electrode under pre-optimized conditions for the thickness of the modified electrode layers. The proposed modified electrode was used for square-wave voltammetry of orthophosphate ions under pre-optimized square-wave parameters (i.e., frequency and amplitude) in strongly acidic medium (pH < 1). The linear range was 0.05-4 µM with a limit of quantification (LOD) of 0.0093 µM with no effect on two peaks due to cross interference from silicate. Furthermore, MoxOy/PDAAQ shows good reproducibility with a relative standard deviation (RSD) of 2.17% for the peak at 0.035 V and 3.56% for the peak at 0.2 V. Real seawater samples were also analyzed for PO43- analysis by UV spectrophotometry and the results were compared with the measurement results of our proposed electrode, with good recoveries obtained.

Biosynthesized silver nanoparticles for electrochemical detection of bromocresol green in river water

In this study, silver nanoparticles (AgNPs)-based electrochemical sensor has been reported for assessing bromocresol green (BG) in river water. Firstly, AgNPs were greenly produced using the aqueous extract of Ficus sycomorus leaves. Then, the AgNP-modified glassy carbon (GC) electrode was prepared using the sticking method. AgNPs were characterized using transmission electron microscope (TEM), X-ray diffraction (XRD), square wave voltammetry (SWV) and scanning electron microscope (SEM). TEM and SEM were used for determining the size of AgNPs before and after adsorption, respectively. The results show that there was an increase in AgNP size from 20 to 30 nm. Additionally, XRD was used for characterizing the crystal nature of AgNPs, while SWV exhibited a characteristic oxidation peak of AgNPs at 0.06 V. Moreover, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for characterizing the catalytic effect of AgNPs. BG as a targeted pollutant was detected at AgNPs/GC based on its oxidation through proton and electron transfer. Two peaks corresponding to the monomer and polymer oxidation were detected. The monomer- and polymer-based sensors have revealed a linear range of 2.9 × 10-5 to 2.1 × 10-4 mole l-1 and low detection limits (LODs) of 1.5 × 10-5 and 1.3 × 10-5 mole l-1, respectively.

Highly sensitive electrochemical detection of myricetin in food samples based on the enhancement effect of Al-MOFs

Microporous aluminum-based metal-organic frameworks (CAU-1) are used to develop a simple and sensitive electrochemical sensor for myricetin (MYR) based on a modified carbon paste electrode (CPE) for the first time. The morphologies and electrochemical properties of the as-synthesized CAU-1 are studied utilizing various analytical methods including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, N₂ adsorption-desorption, and electrochemical impedance spectroscopy. In terms of electrochemical oxidation of MYR, CAU-1/CPE with its large number of active micropores and rapid electron transfer demonstrates superior performance compared to the bare CPE. Under optimized conditions, the calibration curve for MYR exhibits a linear range of 1.0-10 μg L^-1 and 10-1000 μg L^-1 with a detection limit of 0.50 μg L^-1. The developed CAU-1/CPE exhibits superior analytical characteristics, compared to previously reported electrochemical sensors for MYR detection. Furthermore, CAU-1/CPE is employed to determine MYR in Myrica bark samples, and the results are consistent with those obtained by high-performance liquid chromatography, demonstrating the excellent potential of CAU-1/CPE for the rapid analysis of MYR in complicated real samples.