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.

Strategically Designed Pd-Induced Changes in Alkaline Hydrogen Evolution Reaction and Oxygen Evolution Reaction Performances of Electrochemical Water Oxidation by the Galvanically Synthesized MoO2/MoO3 Composite Thin Film.

Electrochemical water oxidation is believed to be an effective pathway to produce clean, carbon-free, and environmentally sustainable green energy. In this work, we report a simple, easy-to-construct, facile, low-cost, and single-step galvanic technique to synthesize a Pd-supported temperature-assisted MoOx thin film nanocomposite for effective water oxidation. The most suitable nanocomposite exhibits very low overpotential at 10 mA/cm2 with smaller Tafel slope values for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) processes in an alkaline medium. The formation of a metal oxide-metal junction accelerates the growth of more active sites, promoting induced electronic synergism at the MoOx-Pd interface. This endows higher electrical conductivity and faster electron transfer kinetics, thus accelerating the faster water dissociation reaction following the Tafel-Volmer mechanism to boost the HER process in an alkaline medium. The excellent electrochemical HER and OER performances of our electrocatalyst even supersede the accomplishments of the benchmark catalysts Pt/C and RuO2. Moreover, neither of these two catalysts demonstrates both catalytic reactions, i.e., HER and OER at the same time, which have been observed for our synthesized catalyst. Our findings illustrate the potential of a thin-film MoOx-Pd nanocomposite to be an exceedingly effective electrocatalyst developed by interface engineering strategies. This also provides insight into designing several other semiconductor composite catalysts using simple synthesis techniques for highly efficient HER/OER processes that could be alternatives to benchmark electrocatalysts for water electrolysis.

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.

Modulation of Weak Interactions in Structural Isomers: Positional Isomeric Effects on Crystal Packing and Physical Properties and Solid-State Thin-Film Fabrication.

Selective formation of positional isomers and accordingly tuning the physicochemical properties of small conjugated organic molecules through structural isomers is an effective crystal engineering for a fascinating successful delivery of thermally stable and photophysically exciting compounds. By small structural skeleton changes, the single crystal of the naphthalenemaleonitrile isomers is found to exhibit a drastic change in crystal packing array, which in turn is found to tune the thermal and physicochemical properties. The α-isomer (A) forms the "herringbone packing" (HP) due to peri-interaction-sensitive C-H···(Ar)π (Ar = naphthalene ring) interactions, and the ß-isomer (B) forms the "bricklayer packing" (BP) due to π(C≡N)···π(Ar) stacking interactions. These two positional isomers have revealed insight of molecular packing-dependent structure-property relationship. In this report, we show that a simple modification of relatively less common weak interactions, such as C-H···π(Ar) ↔ π(C≡N)···π(Ar), through the preparation of isomers, can lead to a drastic change in crystal packing (HP ↔ BP). Also, this report demonstrates that by a small structural diversity, one can obtain significant changes in the physicochemical properties like melting behavior, enthalpy, entropy, and electrical properties in the solid state. Therefore, it transpires from this study that structural isomer provides a useful complement to intermolecular nonbonding interactions as a tool to design new promising materials.

Fluorescence enhancement via aggregation effect due to microenvironmental alterations in human hemoglobin protein in presence of carbon quantum dots (CQD): Comparative spectroscopic approach.

CQDs have emerged with outstanding properties as a star member of carbon nanomaterial family and in order to reveal its wide-range of application in biological microenvironment the interactions between human hemoglobin (HHb) and CQD and also with ethylenediamine-functionalized CQD (NCQD) are assessed using several techniques. Firstly, UV-vis absorption spectra of HHb reveal hyperchromic effect in the region of absorbance of tryptophan and tyrosine residues and also hypochromicity of Soret band in presence of CQD and NCQD. Interestingly, steady-state fluorescence spectroscopy reveal distinct fluorescence enhancement of HHb with significant red shift thereby indicating exposures of tryptophan and tyrosine residues to a more hydrophilic environment. However synchronous fluorescence spectra reveal that the microenvironment of tryptophan and tyrosine residues is altered in opposite manner, i.e. exposure of tryptophan residues to a more hydrophilic environment and the tyrosine residues to a more hydrophobic environment. Moreover the fluorescence enhancement is observed to be accompanied by increase in average fluorescence-lifetime and decrease in steady-state anisotropy thus signifying a decrease in restriction of rotational motion. Furthermore tryptophan residues within HHb appear to interact more with CQD compared to NCQD. Thermodynamic parameters as revealed by Isothermal Titration Calorimetry (ITC) demonstrate that electrostatic, hydrogen bonding and hydrophobic interactions are the predominant modes of interactions in presence of CQD. Whereas hydrophobic and hydrogen bonding interactions are the major interacting forces in presence of NCQD with five-site sequential binding as best-fit model in both the cases. Such interactions also appear to be associated with an increase in aggregation of HHb as evident from the measurements by atomic force microscopy (AFM) and dynamic light scattering (DLS) study. Although FT-IR spectra display alteration of amide I band, but the overall secondary structure of HHb seems to be nearly retained even in presence of CQDs, as evident in the CD spectra. These observations thus highlight the potential biomedical application of CQDs in biological microenvironment of human especially as drug-delivery system. Also bimolecular interaction of HHb as a model protein with other nanoparticles at the nano bio-interface has been outlined.

A turn-on fluorogenic chemosensor for Fe3+ and a Schottky barrier diode with frequency-switching device applications.

A novel highly sensitive and selective fluorescent chemosensor L has been synthesized and characterized by various physicochemical techniques. In 3 : 7 water : MeCN (v/v) at pH 7.2 (10 mM HEPES buffer, µ = 0.05 M LiCl), it selectively recognizes Fe3+ through 1 : 1 complexation resulting in a 106-fold fluorescence enhancement and a binding constant of 8.10 × 104 M-1. The otherwise non-fluorescent spirolactam form of the probe results a dual-channel (absorbance and fluorescence) recognition of Fe3+via CHEF (chelation enhanced fluorescence) through the opening of the spirolactam ring. We have also carried out fluorescence titration and anisotropy (r) studies in pure water in the presence of SDS (sodium dodecyl sulphate). Based on the dependence of FI (fluorescence intensity) and r on [SDS] it was proposed that the probe is trapped between two SDS monolayers which again interact among themselves by ππ stacking. As a result, there is an increase in FI up to [SDS] ∼ 7 mM - a phenomenon reminiscent of aggregation-induced enhancement of emission (AIEE). Beyond this concentration of SDS (7 mM), micelle formation takes place and the ππ stacked polymer now becomes a monomer and is trapped inside the micellar cavity. As a result, there is a decrease in FI at [SDS] > 7 mM. But for anisotropy, it increases with [SDS] beyond 7 mM. Ligand, metal, and SDS interactions are well established through different optical and morphological studies. [L-Fe(NO3)]2+ thin films on FTO (Fluorine-doped Tin Oxide) glass substrates have been designed with the help of the spin-coating deposition technique. The deposited film of thickness 1.6 × 10-5 cm is well characterized by optical band gap calculation with a direct band gap, εg ∼ 1.6 eV. FESEM was also performed for the [L-Fe(NO3)]2+/FTO film. The current-voltage characteristics were measured by the two-probe technique. Light-dependent exciton generation was carried out by taking the top and bottom contacts with graphite paste on FTO and on the [L-Fe(NO3)]2+ films for the measurement of switching behavior. The response ratio curve for the light-induced frequency-switching phenomena has been obtained. The frequency taped here is the oscillation frequency of the photo-generated electron and the hole in an exiton. Thus, the light-induced frequency-switching behavior and Schottky barrier diode characteristics of the material were established.

Design of a Pyrene Scaffold Multifunctional Material: Real-Time Turn-On Chemosensor for Nitric Oxide, AIEE Behavior, and Detection of TNP Explosive.

A dual-emission pyrene-based new fluorescent probe (N-(4-nitro-phenyl)-N'-pyren-1-ylmethyl-ene-ethane-1,2-diamine (PyDA-NP)) displays green fluorescence for nitric oxide (NO) sensing, whereas it exhibits blue emission in the aggregated state. The mechanism of nitric oxide (NO/NO+) sensing is based on N-nitrosation of aromatic secondary amine, which was not interfered by reactive oxygen species and reactive nitrogen species. The aggregation-induced enhancement of emission (AIEE) behaviors of the PyDA-NP could be attributed to the restriction of intramolecular rotation and vibration, resulting in rigidity enhancement of the molecules. The AIEE behavior of the probe was well established from fluorescence, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, optical fluorescence microscopy, and time-resolved photoluminescence studies. In a H2O/CH3CN binary mixture (8:2 v/v), the probe showed maximum aggregation with extensive (833-fold) increases in fluorescence intensity and high quantum yield (0.79). The aggregated state of the probe was further applied for the detection of nitroexplosives. It displayed efficient sensing of 2,4,6-trinitrophenol (TNP), corroborating mainly the charge-transfer process from pyrene to a highly electron-deficient TNP moiety. Furthermore, for the on-site practical application of the proposed analytical system, a contact-mode analysis was performed.