Marappan Sathish

Solvent Engineering for Shape-Shifter Pure Fullerene (C60)

As a highly anticipated technique for bottom-up nanotechnology, i.e., shape control of pure functional molecules, we here report controlled formation of two-dimensional (2D) objects such as hexagons and rhombi and their selective shape shifting into one-dimensional (1D) rods through solvent-dependent changes of crystal lattice, all from pure C(60). Uniformly shaped rhombi and hexagons were obtained at tert-butyl alcohol/toluene and i-propyl alcohol/CCl(4) interfaces, respectively. In addition, exposure of these 2D nanosheets to water induced selective transformation into 1D nanorods. Nanorhombi were converted to short nanorods upon exposure to water. This shape shift is accompanied by changes in crystalline structures from a mixed fcc/hexagonal to pure fcc lattice, the latter of which is almost identical with morphologically similar C(60) nanowhiskers. Metastable nanorhombi which possess a strained mixed crystalline structure metamorphosize into the more stable short nanowhisker (nanorods). In contrast, the stable nanohexagon of a single lattice (and so less strain) does not undergo shape shifting. These results clearly demonstrate controlled formation of 2D nanosheets with various shapes (hexagons, rhombi, etc.) and selective shape shifting to nanorods (short nanowhiskers) all from pure C(60) molecules by very simple solvent treatments.

Superhydrophilic Graphene-Loaded TiO2 Thin Film for Self-Cleaning Applications

We develop a simple approach to fabricate graphene-loaded TiO(2) thin films on glass substrates by the spin-coating technique. Our graphene-loaded TiO(2) films were highly conductive and transparent and showed enhanced photocatalytic activities. More significantly, graphene/TiO(2) films displayed superhydrophilicity within a short time even under a white fluorescent light bulb, as compared to a pure TiO(2) film. The enhanced photocatalytic activity of graphene/TiO(2) films is attributed to its efficient charge separation, owing to electrons injection from the conduction band of TiO(2) to graphene. The electroconductivity of the graphene-loaded TiO(2) thin film also contributes to the self-cleaning function by its antifouling effect against particulate contaminants. The present study reveals the ability of graphene as a low cost cocatalyst instead of expensive noble metals (Pt, Pd), and further shows its capability for the application of self-cleaning coatings with transparency. The promising characteristics of (inexpensive, transparent, conductive, superhydrophilic, and highly photocatalytically active) graphene-loaded TiO(2) films may have the potential use in various indoor applications.

Open-Mouthed Metallic Microcapsules: Exploring Performance Improvements at Agglomeration-Free Interiors

Although artificial capsule structures have been thoroughly investigated, functionality at the surfaces of their interiors has been surprisingly overlooked. In order to exploit this aspect of capsular structure, we here report the breakthrough fabrication of metallic (platinum) microcapsules with sufficient accessibility and electroactivity at both interior and exterior surfaces (open-mouthed platinum microcapsules), and also we demonstrate improvements in electrochemical and catalytic functions to emphasize the practical importance of our concept. The open-mouthed platinum microcapsules were prepared by template synthesis using polystyrene spheres, where surface-fused crystalline nanoparticles formed a capsule shell. Subsequent removal of the polystyrene spheres induced formation of mouth-like openings. The open-mouthed platinum microcapsules exhibit a substantial increase of their electrode capability for methanol oxidation and catalytic activities for carbon monoxide (CO) oxidation. Notably, activity loss during CO oxidation due to undesirable particle agglomeration can be drastically suppressed using the open-mouthed microcapsules.

Preparation and Optical Properties of Fullerene/Ferrocene Hybrid Hexagonal Nanosheets and Large-Scale Production of Fullerene Hexagonal Nanosheets

The supramolecular nanoarchitectures, C(60)/ferrocene nanosheets, were prepared by a simple liquid-liquid interfacial precipitation method and fully characterized by means of SEM, STEM, HRTEM, XRD, Raman and UV-vis-NIR spectra. The highly crystallized C(60)/ferrocene hexagonal nanosheets had a size of ca. 9 microm and the formulation C(60)(ferrocene)(2). A strong charge-transfer (CT) band between ferrocene and C(60) was observed at 782 nm, indicating the presence of donor-acceptor interaction in the nanosheets. Upon heating the nanosheets to 150 degrees C, the CT band disappeared due to the sublimation of ferrocene from the C(60)/ferrocene hybrid, and C(60) nanosheets with an fcc crystal structure and the same shape and size as the C(60)/ferrocene nanosheets were obtained.

MnO2 assisted oxidative polymerization of aniline on graphene sheets: Superior nanocomposite electrodes for electrochemical supercapacitors

Graphene-polyaniline nanocomposite electrodes have been developed via oxidative polymerization of aniline by MnO2 on a graphene surface for electrochemical supercapacitor applications. The formation mechanism of the above nanocomposite indicates that the MnO2 undergoes oxidative disintegration and results in porous polyaniline (PANI) nanofibers formation on the graphene surface. The electron microscopic (SEM and TEM) images clearly showed the presence of porous PANI nanofiber formation on the graphene-PANI nanocomposites. The XRD, SEM-EDX and TG analysis confirmed the complete removal/degradation of MnO2 during the oxidative polymerization of aniline. For comparison, graphene-PANI nanocomposites have also been prepared via conventional polymerization using (NH4)2S2O8 as oxidant in acidic medium and the effect of carbon nanotube (CNT) addition has been studied. The electrochemical properties of different graphene-PANI nanocomposites have been investigated using galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy measurements. A superior supercapacitive performance (∼15 to 40% more than the reported capacitance) has been observed for the graphene-PANI nanocomposite electrode obtained via oxidative polymerization of aniline by MnO2. Addition of CNT into the graphene-PANI nanocomposite prepared via the conventional polymerization method showed improved specific capacitance and stability. Carbon nanofibers and graphite have been used as the carbon source and the effect of the carbon source on the specific capacitance has been investigated.

Vortex-Aligned Fullerene Nanowhiskers as a Scaffold for Orienting Cell Growth

A versatile method for the rapid fabrication of aligned fullerene C60 nanowhiskers (C60NWs) at the air-water interface is presented. This method is based on the vortex motion of a subphase (water), which directs floating C60NWs to align on the water surface according to the direction of rotational flow. Aligned C60NWs could be transferred onto many different flat substrates, and, in this case, aligned C60NWs on glass substrates were employed as a scaffold for cell culture. Bone forming human osteoblast MG63 cells adhered well to the C60NWs, and their growth was found to be oriented with the axis of the aligned C60NWs. Cells grown on aligned C60NWs were more highly oriented with the axis of alignment than when grown on randomly oriented nanowhiskers. A study of cell proliferation on the C60NWs revealed their low toxicity, indicating their potential for use in biomedical applications.

Nanocrystalline tin compounds/graphene nanocomposite electrodes as anode for lithium-ion battery

Nanocrystalline tin (Sn) compounds such as SnO2, SnS2, SnS, and graphene nanocomposites were prepared using hydrothermal method. The X-ray diffraction (XRD) pattern of the prepared nanocomposite reveals the presence of tetragonal SnO2, hexagonal SnS2, and orthorhombic SnS crystalline structure in the SnO2/graphene nanosheets (GNS), SnS2/GNS, and SnS/GNS nanocomposites, respectively. Raman spectroscopic studies of the nanocomposites confirm the existence of graphene in the nanocomposites. The transmission electron microscopy (TEM) images of the nanocomposites revealed the formation of homogeneous nanocrystalline SnO2, SnS2, and SnS particle. The weight ratio of graphene and Sn compound in the nanocomposite was estimated using thermogravimetric (TG) analysis. The cyclic voltammetry experiment shows the irreversible formation of Li2O and Li2S, and reversible lithium-ion (Li-ion) storage in Sn and GNS. The charge–discharge profile of the nanocomposite electrodes indicates the high capacity for the Li-ion storage, and the cycling study indicates the fast capacity fading due to the poor electrical conductivity of the nanocomposite electrodes. Hence, the ratio of Sn compounds (SnO2) and GNS have been altered. Among the examined SnO2:GNS nanocomposites ratios (35:65, 50:50, and 80:20), the nanocomposite 50:50wt% shows high Li-ion storage capacity (400xa0mAh/g after 25 cycles) and good cyclability. Thus, it is necessary to modify GNS and Sn compound composition in the nanocomposite to achieve good cyclability.

Alcohol-induced decomposition of Olmstead's crystalline Ag(I)–fullerene heteronanostructure yields ‘bucky cubes’

Olmsteads crystalline C60-fullerene–Ag(I) organometallic heteronanostructure [C60{AgNO3}5] undergoes an apparently irreversible structural rearrangement upon exposure to low molecular weight aliphatic alcohols leading to a uniquely structured formation of well-oriented fullerene nano/microcrystals (‘bucky cubes’). The mechanism of rearrangement represents a supramolecular analogue of topotactic processes more commonly associated with some purely inorganic materials, such as maghemite, where chemical changes can occur with addition or loss of materials. Hence C60{AgNO3}5, whose rearrangement occurs at the nano/molecular level (i.e. not atomic scale), undergoes a transformation from a crystalline organometallic complex to well ordered cube-shaped arrays of needle-like fullerene microcrystals which reflect the original cubic crystal morphology and internal structure. Processing of bucky cubes by reduction with hydrazine results in a Ag nanoparticle–C60 crystal nanocomposite with potential for SERS analyses.

Synthesis and Characterization of Fullerene Nanowhiskers by Liquid-Liquid Interfacial Precipitation: Influence of C60 Solubility

Fullerene nanowhiskers (FNWs) composed of C60 fullerene molecules were prepared using the liquid–liquid interfacial precipitation (LLIP) method in the carbon-disulfide (CS2) and isopropyl alcohol (IPA) system. The electron microscopic images reveal the formation of non-tubular FNWs. The X-ray diffraction (XRD) pattern studies indicate the presence of fcc crystalline structure and unusual triclinic structure in the FNWs. The selected area electron diffraction pattern (SAED) analysis demonstrates the existence of triclinic and electron beam assisted fcc to tetragonal crystalline phase transformation. The formation of triclinic structure might be validated due to the partial polymerization of FNWs at C60 saturated CS2-IPA interface. The high solubility of C60 in CS2 solvent system results in partial polymerization of FNWs. The polymerization of fullerene molecules in the FNWs has been further confirmed using Raman spectroscopy.

Supercritical Fluid Facilitated Disintegration of Hexagonal Boron Nitride Nanosheets to Quantum Dots and Its Application in Cells Imaging

Preparation of quantum dots (QDs) and exfoliation of two-dimensional layered materials have gathered significant attention in recent days. Though, there are number of attempts have been reported, facile and efficient methodology is yet to be explored. Here, we demonstrate supercritical fluid processing approach for rapid and facile synthesis of blue luminescent BN QDs from layered bulk material via in situ exfoliation followed by disintegration. The microscopic and AFM analysis confirmed the few layer BN QDs formation. The strong luminescent behavior of BN QDs is utilized to stain Gram-negative bacterial cells specifically in the presence of Gram-positive bacterial cells.