pH dependent electro-oxidation of arsenite on gold surface: Relative kinetics and sensitivity.

A detailed kinetic investigation of As(III) oxidation was performed on gold surface within pH between ∼3.0 and ∼9.0. It was found that the As(III) oxidation on the gold surface follows a purely adsorption-controlled process irrespective of pH. The evaluated adsorption equilibrium constant decreased from 3.21 × 105 to 1.61 × 105 mol L-1 for acidic to basic medium, which implies the strong affinity of the arsenic species in the acidic medium. Besides, the estimation of Gibbs free energy revealed that an acidic medium promotes arsenic oxidation on gold surface. In mechanistic aspect, the oxidation reaction adopts a stepwise pathway for acidic medium and a concerted pathway for neutral and basic medium. From the substantial kinetic evaluation, it is established that a conducive and compatible environment for the oxidation of arsenic was found in an acidic medium rather than a basic or neutral medium on gold surface. Besides, in sensitivity concern, neutral and highly acidic medium is quite favourable for the arsenite oxidation on gold surface.

Psidium guajava leaf extract mediated green synthesis of silver nanoparticles and its application in antibacterial coatings.

In this study, Psidium guajava (P. guajava) leaf extract-assisted silver nanoparticles (AgNPs) were synthesized and their antibacterial activities were investigated. The synthesized green AgNPs were characterized by various analytical techniques including UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, etc. From the UV-Vis spectroscopic analysis, the formation of nanoparticles has been confirmed by the color change from light yellow to reddish brown of the solution due to the excitation of the surface plasmon resonance peak at 430 nm. In addition, the FTIR study showed the reduction of Ag ions owing to the presence of biomolecules in the leaf extract, which acted as reducing as well as capping agents. Furthermore, XRD analysis reveals the identified 2θ peaks of AgNPs at ∼39° with cubic structure. The FE-SEM micrograph illustrated the material was formed in nano-dimensions, with an average particle size of ∼12 nm and almost spherical in shape. Moreover, P. guajava-mediated AgNPs demonstrated good antibacterial activity against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacterial strains. The synthesis was performed by a bio-reduction process where a bioactive agent is responsible for reducing metallic ions to metallic nanoparticles as an eco-friendly, cost-effective, non-toxic, one-step, and sustainable method. Therefore, this study may create an imperative synthetic route for the fabrication of green-AgNPs and their application in antibacterial coatings in cotton textiles.

Influence of Y3+ and La3+ ions on the structural, magnetic, electrical, and optical properties of cobalt ferrite nanoparticles.

In the current study, nanocrystalline CoY0.5xLa0.5xFe2-xO4 (where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) ferrites have been synthesized via a sol-gel auto combustion process. The synthesized powders were pressed into pellet forms and sintered at 900 °C for 4 h in the air. X-ray diffractometry (XRD) confirmed the single-phase cubic spinel structure of the synthesized samples having the mean crystallite domain sizes ranging from 122 and 54 nm. FTIR spectroscopic analyses revealed two strong bands within the range of 600 to 350 cm-1, further confirming the cubic inverse spinel structure of the prepared materials. The surface morphologies and composition were investigated by Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) Spectroscopy. The magnetic hysteresis curves recorded at room temperature exhibit ferrimagnetic behavior. The highest coercivity (Hc∼1276 Oe) was found at a high doping (x = 0.10) concentration of Y3+ and La3+ in cobalt ferrite. Dielectric constant increase with increased doping concentration whereas real-impedance and dielectric loss decrease with increased in doping concentration and applied frequency. The band gap energy increased from 1.48 to 1.53 eV with increasing Y3+ and La3+concentrations in the UV-Vis region. The elevated levels of magnetic and dielectric substances in the ferrite nanoparticles suggest that the material could be used for magnetic recording media and high-frequency devices.

Phytochemical-Assisted Synthesis of Fe3O4 Nanoparticles and Evaluation of Their Catalytic Activity.

In this study, magnetite nanoparticles (Fe3O4 NPs) were synthesized using Baccaurea ramiflora leaf extracts and characterized by visual observation, UV-Vis, FTIR, XRD, FESEM, and EDS. The UV-Vis spectrum showed continuous absorption at 300-500 nm, confirming the formation of Fe3O4 NPs. FTIR revealed that compounds containing the O-H group act as reducing agents during Fe3O4 NPs formation. Agglomerated spherical NPs were observed in the FESEM image. The prominent peak at ~6.4 keV in the EDS spectrum ascertained the existence of Fe, while the sharp peak at ~0.53 keV confirmed the presence of elemental oxygen. XRD patterns affirmed the crystalline nature. The size of as-synthesized NPs was observed to be 8.83 nm. The catalytic activity of Fe3O4 NPs for the reduction of methylene blue (MB) dye was monitored by UV-Vis. The maximum absorption peak of MB dye at 664 nm was almost diminished within 20 min, which revealed Fe3O4 NPs could be an excellent catalyst for wastewater treatment.

Effects of yttrium doping on structural, electrical and optical properties of barium titanate ceramics.

In this report, we study the Yttrium-doped Barium Titanate (Y-BT) Ba1 - xYxTiO3 (with x = 0.00, 0.01, 0.03, 0.05, 0.07 mmol) perovskite ceramics synthesized by sol-gel method. The as-made powder samples were pressed into a pellet shape and subsequently sintered at 1300 °C for 5 h in air. The structural, morphological, electrical, and optical properties of the synthesized samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), impedance analyzer, and UV-Vis-NIR Spectroscopy respectively. The XRD study revealed the formations of single phase tetragonal structure of Barium Titanate (BT) with ∼23-33 nm mean crystallite size. The crystallite size increases initially with Y-doping, found at about 33 nm for x = 0.01, and reduces for increase in Y3+ concentration further. The microstructural study from FESEM depicts the uniform distribution of compact and well-faceted grain growth for Y-BT in contrast with undoped barium titanate. The average grain size (∼0.29-0.78 µm) of the Y-BT decreases with increasing doping concentration. Frequency-dependent impedance analyses show enhanced dielectric properties like dielectric constant, quality factor, and conductivity with low dielectric loss in the presence of Yttrium. The optical bandgap energy (∼2.63-3.72 eV) estimated from UV-Vis-NIR diffuse reflection data shows an increasing trend with a higher concentration of yttrium doping.