Oyster Pearl-Shaped Ternary Iron Chalcogenide, FeSe0.5Te0.5, Films on FTO through Electrochemical Growth from the Exchange of Chalcogens Boosted the Enzyme-Free Urea-Sensing Ability toward Real Analytes.

Here, iron chalcogenide thin films were developed for the first time by using the less hazardous electrodeposition technique at optimized conditions on an FTO glass substrate. The chalcogenides have different surface, morphological, structural, and optical properties, as well as an enzyme-free sensing behavior toward urea. Numerous small crystallites of about ∼20 to 25 nm for FeSe, ∼18 to 25 nm for FeTe, and ∼18 to 22 nm in diameter for FeSeTe are observed with partial agglomeration under an electron microscope, having a mixed phase of tetragonal and orthorhombic structures of FeSe, FeTe, and, FeSeTe, respectively. Profilometry, XRD, FE-SEM, HR-TEM, XPS, EDX, UV-vis spectroscopy, and FT-IR spectroscopy were used for the analysis of binary and ternary composite semiconductors, FeSe, FeTe, and FeSeTe, respectively. Electrochemical experiments were conducted with the chalcogenide thin films and urea as the analyte in phosphate-buffered media at a pH of ∼ 7.4 in the concentration range of 3-413 µM. Cyclic voltammetry was performed to determine the sensitivity of the prepared electrode at an optimized scan rate of 50 mV s-1. The electrodeposited chalcogenide films appeared with a low detection limit and satisfactory sensitivity, of which the ternary chalcogenide film has the lowest LOD of 1.16 µM and the maximum sensitivity of 74.22 µA µM-1 cm-2. The transition metal electrode has a very wide range of detection limit of 1.25-2400 µM with a short response time of 4 s. This fabricated biosensor is capable of exhibiting almost 75% of its starting activity after 2 weeks of storage in the freezer at 4 °C. Simple methods of preparation, a cost-effective process, and adequate electrochemical sensing of urea confirm that the prepared sensor is suitable as an enzyme-free urea sensor and can be utilized for future studies.

ß-Bi2O3-Bi2WO6 Nanocomposite Ornated with meso-Tetraphenylporphyrin: Interfacial Electrochemistry and Photoresponsive Detection of Nanomolar Hexavalent Cr.

Hexavalent chromium exposure via inhalation, ingestion, or both has been proven to adversely affect internal organs, induce toxic effects, cause allergies, and contribute to the development of cancer. It requires a substantial and challenging effort to detect several heavy metal ions conveniently, sensitively, and reliably by using materials that are easy to synthesize and have a high yield. The impact of light on the electrocatalytic oxidation/reduction process proves an environmentally friendly methodology with numerous applications in pollution control. The extensive use of photoactive materials in photoelectrochemical (PEC) sensors necessitates the development of stable and highly effective photoactive materials. Hence, the solvothermal synthesis of the organic-inorganic hybrid nanocomposite ß-Bi2O3-Bi2WO6/H2TPP with varying weight percentages of meso-tetraphenylporphyrin (H2TPP) resulted in a selective electrode for electrocatalytic and photoelectrocatalytic reduction of Cr6+ on fluorine-doped tin oxide (FTO) by an adsorption-reduction mechanism. H2TPP increases the active site density and provides an effective surface area for efficient adsorption by providing both pyridinic- and pyrrolic-N atoms to ß-Bi2O3-Bi2WO6/H2TPP. H2TPP could effectively adsorb Cr6+ in the ß-Bi2O3-Bi2WO6/H2TPP composite system through electrostatic interaction, and the adsorbed Cr6+ ions were reduced to trivalent chromium Cr3+, resulting in promising Cr6+ sensing. The projected density of states and Bader charge calculations result in the electrostatic attraction among the N-2p orbital of H2TPP and the 3d and 4s orbitals of the Cr atom, resulting in the adsorption of the hexavalent Cr atom onto the active center of H2TPP. Moreover, the addition of H2TPP results in the development of a mesoporous surface that offers strong electrical conductivity, a substantial surface area, improved charge-mass transport, intimate contact between the electrolyte and catalyst, an extended fluorescence lifetime, and increased stability. The role of pH values was thoroughly investigated. All electrochemical and photoelectrochemical studies were carried out on 5 wt % H2TPP-ornated ß-Bi2O3-Bi2WO6. Nanocomposite ß-Bi2O3-Bi2WO6/5 wt % H2TPP demonstrated reliable cyclic stability, reproducibility, good sensitivity (8.005 µA mM cm-2), and a low limit of detection (LOD) (8.0 nM) toward photoelectrocatalytic reduction of Cr6+. The interference study in the presence of a few inorganic entities exhibited excellent selectivity. This tale amplification approach for developing a ß-Bi2O3-Bi2WO6/5 wt % H2TPP nanocomposite system suggests a deeper understanding of the application of photoelectrocatalytic reduction of Cr6+ in environmental remediation with real samples under light irradiation.

Tetraphenylporphyrin Decorated Bi2MoO6 Nanocomposite: Its Twin Affinity of Oxygen Reduction Reaction and Electrochemical Detection of 4-Nitrophenol.

A selective electrode for oxygen reduction reaction (ORR) and electrocatalytic reduction of 4-nitrophenol (p-NP) was fabricated on a glassy carbon electrode using organic-inorganic Bi2MoO6/H2TPP nanocomposites with different weight percentages of tetraphenylporphyrin, synthesized by the solvothermal process. Materials thus synthesized were characterized through UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analysis. The electrocatalytic performance of the modified electrode toward ORR in the 0.1 M KOH solution, the onset potential Eonset (0.942 V), E1/2 (0.704 V) vs RHE, Jd (-5.545 mA cm-2), and n = 4 physicochemical parameters were well appreciable. It exhibits good catalytic activity toward ORR through a four-electron pathway with excellent stability and high active site density, and thus, the in situ Porphy-decorated metal oxide system facilitates the electron transport process. High selectivity and efficacy for the oxygen reduction reaction (ORR) are a significant measure for several energy-converting applications. The decorated electrode, glassy carbon electrode (GCE)/Bi2MoO6/3 wt % Porphy, serves as an electrochemical sensor that exhibited good sensitivity (0.4683 µAµM-1 cm-2), good reproducibility, a low detection limit (0.0940 µM), and long-term stability in the aqueous phase without any appreciable effect in the presence of some common organic and inorganic interferences for the detection of p-NP in a linear concentration range of 0.5-350 µM. Therefore, the material performs as an effective electrode for both the ORR and the electrocatalytic reduction of p-NP with real matrix samples at room conditions.