Sonochemical synthesis of solar-light-driven Ag@?-PbMoO₄ photocatalyst

Gyawali, G.,Adhikari, R.,Joshi, B.,Kim, T.H.,Rodriguez-Gonzalez, V.,Lee, S.W. Elsevier Scientific Pub. Co 2013 Journal of hazardous materials Vol.263 No.1

Ag@?-PbMoO<SUB>4</SUB> photocatalysts were synthesized by facile sonochemical method with different mol.% of Ag nanoparticles dispersed on the surface of PbMoO<SUB>4</SUB>. 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@?-PbMoO<SUB>4</SUB> samples were evaluated by the degradation of Indigo Carmine (IC) dye under simulated solar light irradiation. It has been observed that the sample containing 0.3mol.% 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 PbMoO<SUB>4</SUB> significantly enhances the photocatalytic activity of PbMoO<SUB>4</SUB>. Increase in photocatalytic activity of Ag@?-PbMoO<SUB>4</SUB> photocatalyst has been explained on the basis of surface plasmon resonance (SPR) effect caused by the silver nanoparticles present in the photocatalyst.

A Thermally Reduced Graphite Oxide and Carbon Nanotube Composite for Supercapacitor Applications

Gyawali GHANASHYAM,정혜경 한국물리학회 2018 New Physics: Sae Mulli Vol.68 No.2

A thermally reduced graphite oxide and carbon nanotube (TRGO-CNT) composite is synthesized for supercapacitor applications by using a simple chemical method. The TRGO-CNT composite shows higher capacitance then the precursors (TRGO and CNT), and its impedance is lower than that of CNT, meaning that TRGO of high surface area connected with a CNT could provide highly efficient surface area and good connection for supercapacitor electrodes. Different weight ratios of TRGO to CNT are investigated, and the results show that the composite with more TRGO has better performance in the electrochemical measurements. Based on these findings, the proper TRGO amount is necessary for a high-performance supercapacitor. Neither CNT nor TRGO by itself can give the highest electrochemical performance for the supercapacitor; thus, the synergistic effect of TRGO and CNT is important.

Pulse Electrodeposition and Characterization of Ni-Si₃N₄ Composite Coatings

Gyawali, Gobinda,Woo, Dong-Jin,Lee, Soo-Wohn The Korean Institute of Surface Engineering 2010 한국표면공학회지 Vol.43 No.5

$Ni-Si_3N_4$ nano-composite coatings were prepared by pulse current (PC) electrodeposition and direct current (DC) electrodeposition techniques. The micro-structure of the coatings was characterized by scanning electron microscopy (SEM), vickers microhardness, X-Ray Diffraction (XRD) and wear-friction tests. The results showed that the micro-structure and wear performance of the coatings were affected by the electrodeposition techniques. Pulse current electrodeposited $Ni-Si_3N_4$ composite coatings exhibited higher microhardness, smooth surface, and better wear resistance properties as compared to coatings prepared under DC condition. The $Ni-Si_3N_4$ composite coatings prepared at 50 Hz pulse frequency with 10% duty cycles has shown higher codeposition of nano-particles. Consequently, increased microhardness and less plastic deformations occurred in coatings during sliding wear test. The XRD patterns revealed that the increased pulse frequencies changed the preferred (100) nickel crystallite orientations into mixed (111) and (100) orientations.

Preparation of Ni-W-Si₃N₄ composite coatings and evaluation of their scratch resistance properties

Gyawali, G.,Joshi, B.,Tripathi, K.,Lee, S.W. Ceramurgica ; Elsevier Science Ltd 2016 CERAMICS INTERNATIONAL Vol.42 No.2

In this study, Ni-W-Si<SUB>3</SUB>N<SUB>4</SUB> nanocomposite coatings have been prepared by codeposition of Si<SUB>3</SUB>N<SUB>4</SUB> nanoparticles into Ni-W alloy coatings having different W contents. The surface morphology and elemental contents in the alloy composite coatings have been analyzed by scanning electron microscopy coupled with EDS. Structure and phase composition were evaluated by using X-ray diffraction (XRD). Progressive type of scratch test was carried out by the scratch tester using a diamond indenter. Results indicated that Vickers microhardness of the Ni-W-Si<SUB>3</SUB>N<SUB>4</SUB> composite coatings is found to be higher in comparison to the corresponding Ni-W coatings. In addition, a small increase in Vickers microhardness was observed in Ni-W coatings with higher content of tungsten. Apart from that, a significant influence had been found on scratch resistance properties with the codeposition of Si<SUB>3</SUB>N<SUB>4</SUB> and variation of W contents in Ni-W-Si<SUB>3</SUB>N<SUB>4</SUB> nanocomposite coatings. Ni-W-Si<SUB>3</SUB>N<SUB>4</SUB> nanocomposite with 12.7at% W and 2.1wt% Si<SUB>3</SUB>N<SUB>4</SUB> has shown improved scratch resistance among others.

Mechanical and tribological properties of Ni-W-TiB₂ composite coatings

Gyawali, Gobinda,Tripathi, Khagendra,Joshi, Bhupendra,Lee, Soo Wohn ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.721 No.-

<P><B>Abstract</B></P> <P>Pure Ni, Ni-W alloy, and Ni–W–TiB<SUB>2</SUB> composite coatings were prepared on the copper substrate by electrodeposition technique. Surface morphology and elemental composition of as prepared samples were observed and analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). X-ray diffraction (XRD) technique was used to analyze the crystallinity and phase composition of the samples. XRD patterns show a typical FCC Ni-W alloy phase of the Ni-W-TiB<SUB>2</SUB> composite coating. Vickers microhardness of Ni-W-TiB<SUB>2</SUB> composite coating is significantly improved as compared to pure Ni and Ni-W alloy coatings. Wear and coefficient of friction of the Ni-W-TiB<SUB>2</SUB> composite coating are found to be improved. Adhesive wear is found to be predominant in pure Ni, and Ni-W coating whereas abrasive nature of wear is obtained in Ni-W-TiB<SUB>2</SUB> composite coating. The Ni-W-TiB<SUB>2</SUB> composite coating exhibited improved scratch resistance over pure nickel and Ni-W coatings. The scratch resistance of the composite coating is influenced by W alloying and TiB<SUB>2</SUB> incorporation to the nickel matrix.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ni-W-TiB<SUB>2</SUB> composites were prepared by electrochemical co-deposition method. </LI> <LI> Microstructure, scratch, friction and wear behaviors of the composites were studied. </LI> <LI> Enhanced scratch resistance of the Ni-W-TiB<SUB>2</SUB> were observed. </LI> <LI> Tribological properties of Ni-W-TiB<SUB>2</SUB> composites were significantly improved. </LI> </UL> </P>

Synthesis of TiO2 nanotubes using different alkaline media and their applications in photocatalysis and DSSCs

Gyawali, G.,Son, J.,Hao, N. H.,Cho, S. H.,Kim, T. H.,Lee, S. W. Elsevier 2017 Research on chemical intermediates Vol.43 No.9

Microstructural and electrochemical analysis of Ni-SiC composite coatings prepared in presence of additives

Gyawali, G.,Hamal, K.,Joshi, B.,Rajbhandari , A.,Wohn Lee, S. North-Holland 2014 Materials letters Vol.126 No.-

Ni-SiC composite coatings have been successfully prepared by pulse electrodeposition technique by dispersing SiC nanoparticles into the sulfamate electrolytic bath. Different contents of cetyltrimethyl ammonium bromide (CTAB) and saccharin (SAC) have been used to evaluate the effect of additives concentration on the final properties of deposits. The composite coatings exhibited refined matrix grains and increased microhardness as compared to pure nickel coating. The results revealed that microstructural changes and codeposition of SiC nanoparticles in nickel deposit are influenced by presence of additives. Findings revealed that despite of nickel crystallite grain refinement and increase in vickers microhardness of composite coatings by application of saccharin, electrochemical corrosion property is found to be affected.

Effect of Ultrasound on the Mechanical Properties of Electrodeposited Ni-SiC Nano Composite

Gyawali, Gobinda,Cho, Sung-Hun,Woo, Dong-Jin,Lee, Soo-Wohn Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.8

Nano sized SiC particles (270 nm) are easily agglomerated in nickel sulfamate electrolytic bath during a composite electrodeposition process. The agglomeration of nano particles in composite coatings can significantly reduce the mechanical properties of the composite coatings. In this study, Ni-SiC nano composite coatings were fabricated using a conventional electrodeposition process with the aid of ultrasound. Nano particles were found to be distributed homogeneously with reduced agglomeration in the ultrasonicated samples. Substantial improvements in mechanical properties were observed in the composite coatings prepared in presence of ultrasound over those without ultrasound. Ni-SiC composite coatings were prepared with variable ultrasonic frequencies ranging from 24 kHz to 78 kHz and ultrasonic powers up to 300 watts. The ultrasonic frequency of 38 kHz with ultrasonic power of 200 watt was revealed to be the best ultrasonic conditions for homogeneous dispersion of nano SiC particles with improved mechanical properties in the composite coatings. The microstructures, phase compositions, and mechanical properties of the composite coatings were observed and evaluated using SEM, XRD, Vickers microhardness, and wear test. The Vickers microhardness of composite coatings under ultrasonic condition was significantly improved as compared to the coatings without ultrasound. The friction coefficient of the composite coating prepared with an ultrasonic condition was also smaller than the pure nickel coatings. A synergistic combination of superior wear resistance and improved microhardness was found in the Ni-SiC composite coatings prepared with ultrasonic conditions.

Carbon Nanofiber on Nickel Foam for Flexible Supercapacitors

Gyawali GHANASHYAM,Hae Kyung JEONG 한국물리학회 2023 새물리 Vol.73 No.5

Nitrogen-doped Molybdenum Disulfide to Catalyze Hydrogen and Oxygen Evolution Reactions

Gyawali Ghanashyam,Hae Kyung Jeong 한국물리학회 2022 새물리 Vol.72 No.4

Nitrogen-doped molybdenum disulfide (N-MoS2) was synthesized using melamine as the nitrogen source to be used as a catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as-synthesized N-MoS₂ had an atomic nitrogen composition of 13%, and it exhibited a low overpotential of −0.20 V at −10 mA/c㎠ for HER and 1.43 V at 10 mA/㎠ for OER, with small Tafel slope values of 97 and 117 mV/dec for HER and OER, respectively. The enhanced HER and OER performances observed as a result of the nitrogen doping of MoS₂ is attributed to N-MoS₂ being characterized by a higher electrochemical active surface area (9.1 × 10<SUP>−4</SUP> ㎠) and lower charge transfer resistance (8.1 Ω) than its precursor.