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.

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.

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.

Microwave Hydrothermal Synthesis and Characterization of Ag₃PO₄/MoS₂ Composite Photocatalyst

Gyawali, Gobinda,Lee, Soo Wohn American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.11

<P>Ag3PO4/MoS2 composite photocatalysts with 1 to 10 wt% of MoS2 have been synthesized by the microwave assisted hydrothermal process. Prepared Ag3PO4/MoS2 composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). It was found that the as prepared Ag3PO4 revealed micron-sized particles, whereas Ag3PO4/MoS2 composites have shown a significantly reduced size of Ag3PO4 particles which were found to be deposited on the surface of MoS2. The Ag3PO4/MoS2 composites exhibited enhanced photocatalytic activity for the photocatalytic degradation of methyl orange (MO) under a simulated solar light condition. The photocatalytic reaction rate of Ag3PO4/3 wt% MoS2 composite is found to be the highest among all other samples. Furthermore, the photocatalytic stability of Ag3PO4/3 wt% MoS2 composite is significantly enhanced in comparison to bare Ag(3)PO4 photocatalyst.</P>

Electrodeposition and Characterization of Ni-TiB2 Composite Coatings

GYAWALI GOBINDA,조성훈,이수완 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.1

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.

Electrodeposition and characterization of Ni-W-TiB2 composite coatings

Gyawali Gobinda,Dhakal Dhani Ram,Bin Humam, Sami,Choi Jin-Hyuk,Lee Soo Wohn 한국표면공학회 2019 한국표면공학회 학술발표회 초록집 Vol.2019 No.11

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.

Essential Oil Constituents of Swertia chirata Buch.-Ham.

Gyawali, Rajendra,Ryu, Keun-Young,Shim, Sung-Lye,Kim, Jun-Hyoung,Seo, Hye-Young,Han, Kyu-Jae,Kim, Kyong-Su The Korean Society of Food Science and Nutrition 2006 Preventive Nutrition and Food Science Vol.11 No.3

The essential oil of Swertia chirata Buch.-Ham. was extracted by solvent extraction (n-pentane:diethylether, 1:1) method using simultaneous distillation-extraction (SDE) apparatus and analyzed by gas chromatography-mass spectrometry (GC/MS). The yield of essential oil obtained from S. chirata was 236.47 mg/kg. Seventy seven compounds of the essential oil belonging to chemical classes of acid (4), alcohol (21), aldehyde (15), ester (3), furan (3), hydrocarbon (7), ketone (17) and miscellaneous (7) were tentatively identified. The major volatile compounds ranged in content order were as follows: undecanoic acid (28.63%), 2-buten-2-one (20.42%), camphor (18.40%), 2-heptadecanone (14.72%), and cedrol (13.07%).

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>

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.