A hybrid electrochemical–thermal method for the preparation of large ZnO nanoparticles

A simple and efficient two-step hybrid electrochemical–thermal route was developed for the synthesis of large quantity of ZnO nanoparticles using aqueous sodium bicarbonate electrolyte and sacrificial Zn anode and cathode in an undivided cell under galvanostatic mode at room temperature. The bath concentration and current density were varied from 30 to 120 mmol and 0.05 to 1.5 A/dm². The electrochemically generated precursor was calcined for an hour at different range of temperature from 140 to 600 °C. The calcined samples were characterized by XRD, SEM/EDX, TEM, TG-DTA, FT-IR, and UV–Vis spectral methods. Rietveld refinement of X-ray data indicates that the calcined compound exhibits hexagonal (Wurtzite) structure with space group of P63mc (No. 186). The crystallite sizes were in the range of 22–75 nm based on Debye–Scherrer equation. The TEM results reveal that the particle sizes were in the order of 30–40 nm. The blue shift was noticed in UV–Vis absorption spectra, the band gaps were found to be 5.40–5.11 eV. Scanning electron micrographs suggest that all the samples were randomly oriented granular morphology.     

Studies on electrodeposition of Zn–MoS<Subscript>2</Subscript> nanocomposite coatings on mild steel and its properties

Pure zinc and Zn–MoS₂ composite coatings were prepared by electrodeposition from zinc sulfate–chloride bath containing uniformly dispersed MoS₂ nanoparticles. The effect of MoS₂ on the deposition properties morphology, crystallographic orientation, and corrosion behavior were studied. The electrokinetic properties (zeta potential) and size distribution statistics in plating bath for the particles were evaluated using dynamic light scattering experiments. The Zn and Zn–MoS₂ deposition process was studied by linear polarization and cyclic voltammetry. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction analysis, and potentiodynamic polarization measurements were used to characterize the coatings. The addition of MoS₂ to the electrolyte significantly changed the microstructure and crystallographic orientation of the zinc deposits and enhanced the corrosion resistance of the coatings. The morphological and electrochemical properties of the zinc coatings were observed to be significantly affected by the incorporation of MoS₂ particles into the zinc matrix.     

Synthetic furocoumarins. Xanthotoxin and methylxanthotoxins

The synthesis of 4-methylxanthotoxin (X), 4,5′-dimethylxanthotoxin (XXIV) and the hitherto unknown 5′-methylxanthotoxin (XXIII) are described, using 6-allyl-7-hydroxy-8-methoxycoumarin (XV) and its 4-methyl derivative (XVII) as intermediates.     

Development of electroless Ni-Zn-P/nano-TiO2 composite coatings and their properties

Ni-Zn-P-TiO₂ composite coatings were successfully obtained on low carbon steel by electroless plating technique. Deposits were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis (EDS) studies. The hardness and microstructure of as plated and heat treated Ni-Zn-P and Ni-Zn-P-TiO₂ composite coatings were analyzed. The change in microstructure and higher hardness was noticed for heat treated composite. The corrosion resistance behavior of as plated and heat treated Ni-Zn-P and Ni-Zn-P-TiO₂ coatings was investigated by anodic polarization, Tafel plots and electrochemical impedance spectroscopic (EIS) studies in 3.5 wt% NaCl solution. The composite coating exhibited enhanced corrosion resistance property over Ni-Zn-P coating.     

Zn-ZrO2 nanocomposite coatings: Elecrodeposition and evaluation of corrosion resistance

The Zn and Zn-ZrO₂ composite coatings were produced by electrodeposition technique using sulphate bath. ZrO₂ particles were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The ZrO₂ particle size distribution in the plating bath and Zeta potential and the ZrO₂ were measured using dynamic light scattering technique (DLS). The corrosion resistance properties of Zn and Zn-ZrO₂ composite coatings were compared by examining the experimental data acquired through polarization, open circuit potential (OCP) and Tafel measurements. The corrosion environment was 3.5 wt% NaCl solution. The variation of amount of ZrO₂ in the solution on their % wt inclusion in the composite and on composite microhardness was investigated. XRD patterns were recorded for Zn and Zn-ZrO₂ coatings to compare their grain size. The SEM images of coatings before and after corrosion under chemical and electrochemical conditions were presented. The results were analyzed to establish the superiority of Zn-ZrO₂ composite over Zn coating.