Gobinda Gyawali

Sonochemical synthesis of solar-light-driven Ag̊-PbMoO4 photocatalyst

Ag°-PbMoO4 photocatalysts were synthesized by facile sonochemical method with different mol.% of Ag nanoparticles dispersed on the surface of PbMoO4. The synthesized powders were characterized by X-ray Diffraction (XRD) Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), and Diffuse Reflectance Spectroscopy (UV-vis DRS) to investigate the crystal structure, morphology, chemical composition, and optical properties of the photocatalyst. Photocatalytic activities of the Ag°-PbMoO4 samples were evaluated by the degradation of Indigo Carmine (IC) dye under simulated solar light irradiation. It has been observed that the sample containing 0.3 mol.% of Ag showed the best photocatalytic activity as compared to other samples. The results suggest that the dispersion of Ag nanoparticles on the surface of PbMoO4 significantly enhances the photocatalytic activity of PbMoO4. Increase in photocatalytic activity of Ag°-PbMoO4 photocatalyst has been explained on the basis of surface plasmon resonance (SPR) effect caused by the silver nanoparticles present in the photocatalyst.

Electrodeposition and characterization of Ni-TiB2 composite coatings

Nickel-titanium diboride (Ni-TiB2) composite coatings were successfully fabricated by pulse electrodeposition techniques from nickel sulfamate bath containing dispersed submicron TiB2 particles. The effect of TiB2 codeposition on the morphological, microstructural, microhardness and anti-corrosive properties of the composite coatings have been investigated by using scanning electron microscopy coupled with energy dispersive spectroscopy system, X-ray diffraction (XRD), vickers microhardness, and electrochemical impedance spectroscopy (EIS) techniques. Incorporation of TiB2 particles into the nickel matrix has modified the regular crystal growth of nickel. The XRD patterns revealed that the preferred (100) crystallite orientation of pure nickel has been modified into mixed orientations by the enhancement of (111) and attenuation of (200) diffraction intensities by the incorporation of TiB2 particles into the nickel matrix. Vickers microhardness of the Ni-TiB2 composite coating is found to be increased which is nearly 3 times higher than pure nickel coating. The results obtained by polarization curves and EIS analysis in 3.5 wt% NaCl solution have shown the improved corrosion resistance properties of Ni-TiB2 composite coating over pure nickel electrodeposit.

Synergy Effect of Ultrasonic Nanocrystalline Surface Modification and Laser Surface Texturing on Friction and Wear Behavior of Graphite Cast Iron

ABSTRACT Laser surface texturing (LST) followed by an ultrasonic nanocrystalline surface modification (UNSM) process was applied to graphite cast iron to improve the friction and wear behavior. The surface hardness of the UNSM-treated and UNSM + LST-treated specimens was increased significantly compared to the polished and LST-treated specimens. The friction and wear behavior of the specimens was assessed using a ball-on-disk friction tester at an applied load of 10 N and a speed of 5 cm/s in both dry and lubrication conditions. The friction coefficient of the UNSM-, LST-, and UNSM + LST-treated specimens reduced in both dry and lubrication conditions compared to the polished specimen by 64, 30, and 64% and 63, 67, and 75%, respectively. In lubrication condition, the friction coefficient of the UNSM- and LST-treated specimens was further reduced by about 30 and 25% by UNSM + LST processes. In dry condition, the UNSM + LST-treated specimen exhibited a reduction in the friction coefficient of 46% compared to the LST-treated specimen, whereas no reduction in friction coefficient was found compared to the UNSM-treated specimen. The wear resistance of the UNSM-, LST-, and the UNSM + LST-treated specimens was enhanced by 22, 11, and 37% in the dry condition, respectively, whereas minuscule wear was observed in the lubrication condition that was difficult to quantify in our experiment. UNSM and LST processes were effectively combined to improve the friction and wear behavior of graphite cast iron.

Effect of calcination environments and plasma treatment on structural, optical and electrical properties of FTO transparent thin films

The dependence of the structural, optical and electrical properties of the FTO thin films on the film thickness (276 nm - 546 nm), calcination environment, and low temperature plasma treatment were examined. The FTO thin films, prepared by spray pyrolysis, were calcinated under air followed by either further heat treatment under N2 gas or treatment in low temperature atmospheric plasma. The samples before and after calcination under N2, and plasma treatment will be represented by Sair, SN2 and SPl, respectively, hereafter. The thin films were characterized by measuring the XRD spectra, SEM images, optical transmittance and reflectance, and sheet resistance of the films before and after calcination in N2 environment or plasma treatment. The presence of sharp and narrow multiple peaks in XRD spectra hint us that the films were highly crystalline (polycrystalline). The samples Sair with the thickness of 471 nm showed as high as 92 % transmittance in the visible range. Moreover, from the tauc plot, the optica...

Graphene Coating via Chemical Vapor Deposition for Improving Friction and Wear of Gray Cast Iron at Interfaces

This study reports the influence of CVD-graphene on the tribological performance of gray cast iron (GCI) from the internal combustion engine (ICE) cylinder liners by performing a ball-on-disk friction tests. The graphene-coated specimen exhibited a significant reduction (∼53%) of friction as compared to that of the uncoated specimen, whereas wear resistance increased by 2- and 5-fold regarding the wear of specimen and ball, respectively. Extremely low shear strength and highly lubricating nature of graphene contribute to the formation of a lubricative film between the sliding surfaces and decreases the interaction between surfaces in the dry environment. Under the applied load, a uniform film of iron oxides such as Fe2O3, Fe3O4, and FeOOH is found to be formed between the surfaces. It is proposed that the graphene encapsulation with the metal debris and oxides formed between the specimens increases the lubricity and decreases the shear force. The transformation of graphene/graphite into nanocrystalline graphites across the contact interfaces following the amorphization trajectory further increases the lubricity of the film that ultimately reduces friction and wear of the material.

Electrodeposition of Ni-SiC Nano Composite in Presence of Ultrasound

Ni-SiC nano composite coatings were fabricated using electrodeposition technique with the aid of ultrasound. The properties of the nano composite were investigated using SEM and Vicker’s microhardness tester. The results demonstrated that the microhardness of composite coatings under ultrasonic vibrations was improved significantly as compared to conventional electrodeposition techniques without ultrasound. The nano particles were found to be distributed homogeneously with reduced agglomeration due to the ultrasonic vibration.

Understanding Mechanism of Photocatalytic Microbial Decontamination of Environmental Wastewater

Several photocatalytic nanoparticles are synthesized and studied for potential application for the degradation of organic and biological wastes. Although these materials degrade organic compounds by advance oxidation process, the exact mechanisms of microbial decontamination remains partially known. Understanding the real mechanisms of these materials for microbial cell death and growth inhibition helps to fabricate more efficient semiconductor photocatalyst for large-scale decontamination of environmental wastewater or industries and hospitals/biomedical labs generating highly pathogenic bacteria and toxic molecules containing liquid waste by designing a reactor. Recent studies on microbial decontamination by photocatalytic nanoparticles and their possible mechanisms of action is highlighted with examples in this mini review.

Synthesis of TiO 2 nanotubes using different alkaline media and their applications in photocatalysis and DSSCs

TiO2 nanotubes (TNTs) were successfully synthesized from different alkaline media (i.e., NaOH and KOH) by using a microwave hydrothermal process. The effects of different alkaline media on the formation of TiO2 nanotubes and their physicochemical properties were investigated. The phases of different TiO2 nanostructures were studied by using X-ray diffraction patterns. Morphologies of the nanostructures were observed with a transmission electron microscope. The optical properties of the nanostructures were evaluated through the absorption behavior using UV–Vis diffuse reflectance spectroscopy. The photocatalytic activities of the TiO2 nanostructures were evaluated by the degradation of methylene blue aqueous dye solution under the simulated solar light irradiation. Similarly, the photovoltaic efficiencies of the prepared samples were investigated by making photo-anode layers in the Dye Sensitized Solar Cells (DSSCs). The results revealed that in comparison to the single layered TiO2 nanostructures in the DSSC, creation of a double layer structure significantly enhanced the efficiency of DSSC.

Improved Tribological Behavior of Grey Cast Iron Under Low and High Viscous Lubricants by Laser Surface Texturing

The main objective of this paper was to investigate the effect of laser surface texturing (LST) on the friction and wear behavior of gray cast iron in lubricated conditions. The dimples with a diameter of 54 μm and depth of about 10 μm were produced with various dimple densities in the range from 5 to 35 %. Ball-on-disc friction tests were carried out for all the specimens in low and high viscous oils. The friction coefficient was reduced by about 35 % after the LST compared with the untextured specimen at a load of 5 N and speed of 5 cm/s. The textured specimen with a dimple density of 10 % possessed the lowest friction coefficient of all the dimpled specimens in both low and high viscous oils. However, the high viscous oil was found to be more effective to achieve a lower friction coefficient compared to the low viscous oil. The friction coefficient reduced by about 46 % in high viscous oil compared to the low viscous oil. Similarly, the lower wear was noticed for the specimen with a dimple density of 10 % and 5 % among all the specimens in both low and high viscous oils. The resistance to wear of the specimens was also found to be enhanced in high viscous oil compared to those in low viscous oil.

Effect of Plating Parameters on the Electrodeposition of Ni-alumina Nanocomposite

Ni-Al₂O₃ nanocomposite coatings were fabricated by conventional electrodeposition technique using nickel sulfamate bath. Effect of plating parameters on electrodeposition of Ni-Al₂O₃ nanocomposite were studied. The properties of the nano composite were investigated by using SEM, XRD, and Vicker’s microhardness test. The results demonstrated that Al₂O₃ incorporation in the composite coatings was found to be increased by increasing stir rate and Al₂O₃ content in plating bath. Microhardness of the composite coatings was also increased with increasing content of the nano particles in the plating bath. The surface morphologies of the nanocomposite coatings were found to be varied with varying pH, current densities as well as alumina content in the plating bath.