Carbon Materials Supported Metal Nanostructures for Efficient Catalytic Organic Transformations （金属ナノ粒子および炭素材料を用いた触媒による有機化学反応の高効率化）

信州大学(Shinshu university)博士（学術）この博士論文は、次の学術雑誌論文を一部に使用しています。JOURNAL OF PHYSICAL CHEMISTRY C. 117(45):23582-23596 (2013); doi:10.1021/jp402978q. © 2013 American Chemical Society.CARBON. 62:135-148 (2013); doi:10.1016/j.carbon.2013.06.005. © 2013 Elsevier Ltd.CATALYSIS SCIENCE & TECHNOLOGY. 3(6):1485-1489 (2013); doi:10.1039/c3cy20735h. © 2013 Royal Society of Chemistry.ThesisMAYAKRISHNAN GOPIRAMAN. Carbon Materials Supported Metal Nanostructures for Efficient Catalytic Organic Transformations （金属ナノ粒子および炭素材料を用いた触媒による有機化学反応の高効率化）. 信州大学, 2014, 博士論文. 博士（学術）, 甲第81号, 平成26年3月20日授与.doctoral thesi

Preparation, Characterization, and Applications of Electrospun Carbon Nanofibers and Its Composites

Carbon nanofibers (CNFs) and its composites have gained vast attention due to its exceptional chemical and textural properties. So far, various multifunctional carbon nanofibers and its composites are developed with highly unique and tunable morphology. In this chapter, we reviewed unique fabrication methods that are recently reported and its characterization techniques such as SEM, FE-SEM, TEM, WAXD, XPS, AFM, and Raman. In addition, catalytic, energy, and environmental applications of carbon nanofiber composites (metals and/or metal oxide nanoparticles incorporated and/or decorated hybrid carbon nanofibers) are discussed. Preparation and characterization of electrospun carbon nanofiber composites and its applications in catalysis and energy storage are the main focus of this chapter

Carbon Nanocomposites: Preparation and Its Application in Catalytic Organic Transformations

Carbon nanocomposites have gained huge interest in catalysis due to their small size and shape-dependent physicochemical properties. Particularly, metal nanostructures/carbon materials (mainly graphene and carbon nanotubes) based nanocomposites demonstrated extraordinary catalytic activity in organic reactions. The catalytic products prepared by using carbon nanocomposites are found to be highly valuable in various fields including pharmaceutical, biomedical, agricultural, and material sciences. Hence, the demand of carbon nanocomposites has been increasing rapidly, and the development of novel preparation methods also deserve a special concern. In this chapter, we discuss the main advances in the field over the last few years and explore the novel preparation methods of carbon nanocomposites (metal nanostructures/carbon materials) and their applications in various catalytic organic transformations

Catalytic N-oxidation of tertiary amines on RuO(2)NPs anchored graphene nanoplatelets

Ultrafine ruthenium oxide nanoparticles (RuO2NPs) with an average diameter of 1.3 nm were anchored on graphene nanoplatelets (GNPs) using a Ru(acac)3 precursor by a very simple dry synthesis method. The resultant material (GNPs–RuO2NPs) was used as a heterogeneous catalyst for the N-oxidation of tertiary amines for the first time. The transmission electron microscopy (TEM) images of the GNPs–RuO2NPs showed the excellent attachment of RuO2NPs on GNPs. The loading of Ru in GNPs–RuO2NPs was 2.68 wt%, as confirmed by scanning electron microscope-energy dispersive spectroscopy (SEM-EDS). The X-ray photoelectron spectrum (XPS) and the X-ray diffraction pattern (XRD) of GNPs–RuO2NPs revealed that the chemical state of Ru on GNPs was +4. After the optimization of reaction conditions for N-oxidation of triethylamine, the scope of the reaction was extended to various aliphatic, alicyclic and aromatic tertiary amines. The GNPs–RuO2NPs showed excellent catalytic activity in terms of yields even at a very low amount of Ru catalyst (0.13 mol%). The GNPs–RuO2NPs was heterogeneous in nature, chemically as well as physically, very stable and could be reused up to 5 times.ArticleCATALYSIS SCIENCE & TECHNOLOGY. 4(7):2099-2106 (2014)journal articl

Photodegradation of dyes by a novel TiO2/u-RuO2/GNS nanocatalyst derived from Ru/GNS after its use as catalyst in aerial oxidation of primary alcohols (GNS = Graphene NanoSheets)

Ruthenium nanoparticles (RuNPs) supported on graphene nanosheets (GNS), a composite (Ru/GNS), were prepared by a dry synthesis method and were used as nanocatalysts for the aerial oxidation of various primary alcohols. Ru/GNS was highly efficient, selective, stable and heterogeneous in nature. Owing to the high stability of the used catalyst (u-Ru/GNS), it was further applied in a different catalytic system viz photocatalytic degradation, after suitable modifications. We have obtained a novel TiO2/u-RuO2/GNS catalyst from u-Ru/GNS by the sol-gel method. The catalytic activity of TiO2/u-RuO2/GNS toward the photodegradation of methyl orange (MO) and acridine orange (AO) was found to be excellent. Overall, the sustainable use of these recyclable materials (Ru/GNS and TiO2/u-RuO2/GNS) could lead to economic and environmental benefits.Reaction Kinetics, Mechanisms and Catalysis. 115(2):759-772 (2015)journal articl

Handspinning Enabled Highly Concentrated Carbon Nanotubes with Controlled Orientation in Nanofibers

The novel method, handspinning (HS), was invented by mimicking commonly observed methods in our daily lives. The use of HS allows us to fabricate carbon nanotube-reinforced nanofibers (CNT-reinforced nanofibers) by addressing three significant challenges: (i) the difficulty of forming nanofibers at high concentrations of CNTs, (ii) aggregation of the CNTs, and (iii) control of the orientation of the CNTs. The handspun nanofibers showed better physical properties than fibers fabricated by conventional methods, such as electrospinning. Handspun nanofibers retain a larger amount of CNTs than electrospun nanofibers, and the CNTs are easily aligned uniaxially. We attributed these improvements provided by the HS process to simple mechanical stretching force, which allows for orienting the nanofillers along with the force direction without agglomeration, leading to increased contact area between the CNTs and the polymer matrix, thereby providing enhanced interactions. HS is a simple and straightforward method as it does not require an electric field, and, hence, any kinds of polymers and solvents can be applicable. Furthermore, it is feasible to retain a large amount of various nanofillers in the fibers to enhance their physical and chemical properties. Therefore, HS provides an effective pathway to create new types of reinforced nanofibers with outstanding properties.ArticleSCIENTIFIC REPORTS. 6:37590 (2016)journal articl

A highly hydrophilic water-insoluble nanofiber composite as an efficient and easily-handleable adsorbent for the rapid adsorption of cesium from radioactive wastewater

Herein, we report a new Prussian blue nanoparticle (PBNPs) incorporated polyvinyl alcohol (PVA) composite nanofiber (c-PBNPs/PVA) for the rapid adsorption of cesium (Cs) from radioactive wastewater. Initially, various electrospinning parameters such as solvent, PVA wt%, PBNPs wt% and glutaraldehyde (GA) wt% were extensively optimized to obtain a better physicochemical property of the c-PBNPs/PVA. In order to improve the water insoluble nature of the PVA, post cross-linking was carried out for the c-PBNPs/PVA using glutaraldehyde (GA) and HCl vapor as the cross-linker and catalyst, respectively. SEM images revealed the smooth and continuous morphology of the c-PBNPs/PVA composite nanofibers with diameters of 200–300 nm and lengths up to several millimeters. TEM images confirmed homogeneous dispersion and good incorporation of PBNPs into the PVA matrix. The amorphous nature of the c-PBNPs/PVA was confirmed by the XRD analysis. FT-IR spectra showed successful cross-linking of PVA with GA. It was found that the prepared composite nanofiber is highly hydrophilic and water-insoluble. The c-PBNPs/PVA showed an excellent and faster Cs adsorption rate of 96% after only 100 min. These results are comparable to those previously reported. After the Cs adsorption test, the c-PBNPs/PVA composite nanofiber can be easily separated from the wastewater.ArticleRSC ADVANCES. 4(103):59571-59578 (2014)journal articl

Facile Mechanochemical Synthesis of Nickel/Graphene Oxide Nanocomposites with Unique and Tunable Morphology: Applications in Heterogeneous Catalysis and Supercapacitors

In this study, a very simple and highly effective mechanochemical preparation method was developed for the preparation of Ni nanoparticles supported graphene oxide (GO) nanocomposites (Ni/GO, where Ni is a composition of Ni(OH)2, NiOOH, NiO, Ni2O3 and NiO2), 3 wt% NiO/GO (Ni/GO-1) and 8 wt% NiO/GO(Ni/GO-2). The developed method is not only very simple and efficient, but also, the morphology of Ni/GO nanocomposites can be tuned by simply varying the metal loading. Morphology and specific surface area of the resultant Ni/GO nanocomposites were investigated by mean of AFM, HR-TEM and BET. Chemical sate and factual content of Ni in Ni/GO-1 and Ni/GO-2, and the presence of defective sites in Ni-nanocomposites were investigated in detail. To our delight, the prepared Ni/GO-2 demonstrated superior catalytic activity toward the reduction of 2- and 4-nitrophenol in water with high rate constant (kapp) of 35.4 × 10−3 s−1. To the best of our knowledge, this is the best efficient Ni-based graphene nanocomposites for the reduction of 2- and 4-NP reported to date. The Ni/GO-1 and Ni/GO-2 demonstrated an excellent reusability; no loss in its catalytic activity was noticed, even after 10th cycle. Surprisingly the Ni/GO-2 as electrode material exhibited an excellent specific capacitance of 461 F/g in 6 M KOH at a scan rate of 5 mV. Moreover, the Ni/GO nanocomposites were found to possess poor electrical resistance and high stability (no significant change in the specific capacitance even after 1000 cycles)

Stepwise Construction of Ru(II)Center Containing Chiral Thiourea Ligand on Graphene Oxide: First Efficient, Reusable, and Stable Catalyst for Asymmetric Transfer Hydrogenation of Ketones

Heterogenization of homogenous catalysts on solid support has attracted tremendous attention in organic synthesis due to the key benefits of heterogenized catalysts such as easy recovery and reusability. Although a considerable number of heterogenized catalysts are available, to the best of our knowledge, there is no efficient and reusable heterogenized catalyst reported for asymmetric reactions to date. Herein, we prepared a [RuCl2(η6-p-cymene)]/chiralthiourea ligand covalently bonded to graphene nanosheets (G-CLRu(II), where G represents graphene oxide (GO), CL denotes chiral N-((1-phenylethyl)carbamothioyl)acetamide and Ru(II) symbolizes [RuCl2(η6-p-cymene)]), for the asymmetric transfer hydrogenation of ketones. Five simple steps were involved in the preparation of the G-CLRu(II) catalyst. The structure of G-CLRu(II) was investigated by means of various spectroscopic and microscopic techniques. Coordination mode and covalent bonding involved in the G-CLRu(II) structure we reconfirmed. G-CLRu(II) demonstrated good catalytic performance towards the asymmetric transfer hydrogenation of ketones (conversion of up to 95%, enantiomeric excesses (ee) of up to 99%, and turnover number (TON) and turnover frequency (TOF) values of 535.9 and 22.3 h−1, respectively). A possible mechanism is proposed for the G-CLRu(II)-catalyzed asymmetric transfer hydrogenation of ketones. Recovery (~95%), reusability (fifth cycle, yield of 89% and ee of 81%), and stability of G-CLRu(II) were found to be good. We believe that the present stepwise preparation of G-CLRu(II) opens a new door for designing various metal-centered heterogenized chiral catalysts for asymmetric synthesis

Highly Active, Selective, and Reusable RuO₂/SWCNT Catalyst for Heck Olefination of Aryl Halides

Very fine RuO₂ nanoparticles (RuO₂NPs) with a mean diameter of about 0.9 nm were decorated on single-walled carbon nanotubes (SWCNTs) by a straightforward “dry synthesis” method. TEM images and the Raman spectrum of the resultant material (RuO₂/SWCNT) revealed excellent adhesion and homogeneous dispersion of the RuO₂NPs on anchoring sites of the SWCNTs. The surface area of RuO₂/SWCNT was found to be 416 m² g^–1. The SEM–EDS results showed that the weight percentage of Ru in RuO₂/SWCNT was 13.8%. The oxidation state of Ru in RuO₂/SWCNT was +4, as confirmed by XPS and XRD analyses. After the complete characterization, a 0.9 mol % loading of RuO₂/SWCNT was used as a nanocatalyst for the Heck olefination of a wide range of aryl halides to yield products in excellent yields with good turnover numbers and turnover frequencies. Less reactive bromo- and chloroarenes were also used for the formation of coupled products in good yields. RuO₂/SWCNT is regioselective, chemoselective, heterogeneous in nature, and reusable. The stability of RuO₂/SWCNT was also studied by means of TEM, ICP-MS, SEM–EDS, and XPS analyses