Browsing by Author "Ghosh, Saunab"

Now showing 1 - 6 of 6
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    Apparatus for Scalable Functionalization of Single-Walled Carbon Nanotubes via the Billups-Birch Reduction
    (MDPI, 2017) Pham, David; Zhang, Kevin S.; Lawal, Olawale; Ghosh, Saunab; Gangoli, Varun Shenoy; Ainscough, Thomas J.; Kellogg, Bernie; Hauge, Robert H.; Adams, W. Wade; Barron, Andrew R.
    A prototype design of a reactor for scalable functionalization of SWCNTs by the reaction of alkyl halides with Billups-Birch reduced SWCNTs is described. The Hauge apparatus is designed to allow for the safe handling of all the reagents and products under an inert atmosphere at controlled temperatures. The extent of reaction of Li/NH3 solution with the SWCNTs is measured in-situ by solution conduction, while homogenous mixing is ensured by the use of a homogenizer, and thermocouple are placed at different heights within the reactor flask. Addition of an alkyl halide yield alkyl-functionalized SWCNTs, which may be isolated by solvent extraction leaving a solid sample that is readily purified by hydrocarbon extraction. As an example, reaction of SWCNT/Li/NH3 with 1-iododecane yields dodecane-functionalized SWCNTs (C12-SWCNTs), which have been characterized by TG/DTA, XPS, and Raman spectroscopy. Sample extraction during the reaction allows for probing of the rate of the reaction in order to determine the end point of the reaction, which for C12-SWCNTs (at −78 °C) is 30 min.
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    Giant terahertz polarization rotation in ultrathin films of aligned carbon nanotubes
    (Optical Society of America, 2021) Baydin, Andrey; Baydin, Andrey; Komatsu, Natsumi; Tay, Fuyang; Ghosh, Saunab; Makihara, Takuma; Noe, G. Timothy; Kono, Junichiro; Kono, Junichiro; Kono, Junichiro; Kono, Junichiro
    For easy manipulation of polarization states of light for applications in communications, imaging, and information processing, an efficient mechanism is desired for rotating light polarization with a minimum interaction length. Here, we report giant polarization rotations for terahertz (THz) electromagnetic waves in ultrathin (∼45nm), high-density films of aligned carbon nanotubes. We observed polarization rotations of up to ∼20∘ and ∼110∘ for transmitted and reflected THz pulses, respectively. The amount of polarization rotation was a sensitive function of the angle between the incident THz polarization and the nanotube alignment direction, exhibiting a “magic” angle at which the total rotation through transmission and reflection becomes exactly 90°. Our model quantitatively explains these giant rotations as a result of extremely anisotropic optical constants, demonstrating that aligned carbon nanotubes promise ultrathin, broadband, and tunable THz polarization devices.
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    Method, synthesis, activation procedure and characterization of an oxygen rich activated porous carbon sorbent for selective removal of carbon dioxide with ultra high capacity
    (2019-08-13) Ghosh, Saunab; Barron, Andrew R.; Ho, Jason; Rice University; Apache Corporation; United States Patent and Trademark Office
    The present disclosure pertains to methods of capturing CO2 from an environment at pressures above 1 bar by associating the environment with a porous material that has a surface area of at least 2,800 m2/g, and a total pore volume of at least 1.35 cm3/g, where a majority of pores of the porous material have diameters of less than 2 nm. The present disclosure also pertains to methods for the separation of CO2 from natural gas in an environment at partial pressures of either component above 1 bar by associating the environment with a porous material that has a surface area of at least 2,200 m2/g, and a total pore volume of at least 1.00 cm3/g, where a majority of pores of the porous material have diameters of greater than 1 nm and less than 2 nm.
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    Method, synthesis, activation procedure and characterization of an oxygen rich activated porous carbon sorbent for selective removal of carbon dioxide with ultra high capacity
    (2019-03) Ghosh, Saunab; Barron, Andrew R.; Ho, Jason; Rice University; APACHE CORPORATION; United States Patent and Trademark Office
    The present disclosure pertains to materials for CO2 adsorption at pressures above 1 bar, where the materials include a porous material with a surface area of at least 2,800 m2/g, and a total pore volume of at least 1.35 cm3/g, where a majority of pores of the porous material have diameters of less than 2 nm as measured from N2 sorption isotherms using the BET (Brunauer-Emmett-Teller) method. The present disclosure also pertains to materials for separation of CO2 from natural gas at partial pressures of either component above 1 bar, where the materials include a porous material with a surface area of at least 2,200 m2/g, and a total pore volume of at least 1.00 cm3/g, where a majority of pores of the porous material have diameters of greater than 1 nm and less than 2 nm as measured from N2 sorption isotherms using the BET method.
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    Structural Sorting and Oxygen Doping of Semiconducting Single-Walled Carbon Nanotubes
    (2012) Ghosh, Saunab; Weisman, R. Bruce
    Existing growth methods produce single-walled carbon nanotubes (SWCNTs) with a range of structures and electronic properties, but many potential applications require pure nanotube samples. Density gradient ultracentrifugation (DGU) has recently emerged as a technique for sorting as-grown mixtures of single-walled nanotubes into their distinct ( n,m ) structural forms, but this approach has been limited to samples containing only a small number of nanotube structures, and has often required repeated DGU processing. For the first time, it has been shown that the use of tailored nonlinear density gradient ultracentrifugation (NDGU) can significantly improve DGU separations. This new sorting process readily separated highly polydisperse samples of SWCNTs grown by the HiPco method in a single step to give fractions enriched in any of ten different ( n,m ) species. In addition, minor variants of the method allowed separation of the minor-image isomers (enantiomers) of seven ( n,m ) species. Optimization of this new approach was aided by the development of instrumentation that spectroscopically mapped nanotube contents inside undisturbed centrifuge tubes. Besides, sorted nanotube samples enabled the discovery of novel oxygen-doped SWCNTs with remarkable photophysical properties. Modified nanotube samples were produced using mild oxidation of SWCNTs with ozone followed by a photochemical conversion step that induced well-defined changes in emissive properties. As demonstrated for a set of ten separated SWCNT ( n,m ) structures, chemically altered nanotubes possess slightly lower band gap energies with correspondingly longer photoluminescence wavelengths. Treated samples showed distinct, structure-specific near-infrared fluorescence at wavelengths 10 to 15% longer than the pristine semiconducting SWCNTs. Quantum chemical modeling suggests that dopant sites harvest light energy absorbed in undoped nanotube regions by trapping mobile excitons. The oxygen-doped SWCNTs are much easier to detect and image in biological specimen than pristine SWCNTs because they give stronger near-IR emission and do not absorb at the shifted emission wavelength. This novel modification of SWCNT properties may lead to new optical and electronic applications, as it provides a way to change optical band gaps in whole nanotubes or in selected sections.
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    Structure-Dependent Thermal Defunctionalization of Single-Walled Carbon Nanotubes
    (American Chemical Society, 2015) Ghosh, Saunab; Wei, Fang; Bachilo, Sergei M.; Hauge, Robert H.; Billups, W.E.; Weisman, R. Bruce; Smalley Institute for Nanoscale Science and Technology
    Covalent sidewall functionalization of single-walled carbon nanotubes (SWCNTs) is an important tool for tailoring their properties for research purposes and applications. In this study, SWCNT samples were first functionalized by reductive alkylation using metallic lithium and 1-iodododecane in liquid ammonia. Samples of the alkyl-functionalized SWCNTs were then pyrolyzed under an inert atmosphere at selected temperatures between 100 and 500 °C to remove the addends. The extent of defunctionalization was assessed using a combination of thermogravimetric analysis, Raman measurements of the D, G, and radial breathing bands, absorption spectroscopy of the first- and second-order van Hove peaks, and near-IR fluorescence spectroscopy of (n,m)-specific emission bands. These measurements all indicate a substantial dependence of defunctionalization rate on nanotube diameter, with larger diameter nanotubes showing more facile loss of addends. The effective activation energy for defunctionalization is estimated to be a factor of ∼1.44 greater for 0.76 nm diameter nanotubes as compared to those with 1.24 nm diameter. The experimental findings also reveal the quantitative variation with functionalization density of the Raman D/G intensity ratio and the relative near-IR fluorescence intensity. Pyrolyzed samples show spectroscopic properties that are equivalent to those of SWCNTs prior to functionalization. The strong structure dependence of the defunctionalization rate suggests an approach for scalable diameter sorting of mixed SWCNT samples.