Showing papers by "Lawrence B. Alemany published in 2012"
TL;DR: It is reported that during the acid treatment and chemical exfoliation of traditional pitch-based carbon fibers, that are both cheap and commercially available, the stacked graphitic submicrometer domains of the fibers are easily broken down, leading to the creation of GQDs with different size distribution in scalable amounts.
Abstract: Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating optical and electronic properties. These have been synthesized either by nanolithography or from starting materials such as graphene oxide (GO) by the chemical breakdown of their extended planar structure, both of which are multistep tedious processes. Here, we report that during the acid treatment and chemical exfoliation of traditional pitch-based carbon fibers, that are both cheap and commercially available, the stacked graphitic submicrometer domains of the fibers are easily broken down, leading to the creation of GQDs with different size distribution in scalable amounts. The as-produced GQDs, in the size range of 1–4 nm, show two-dimensional morphology, most of which present zigzag edge structure, and are 1–3 atomic layers thick. The photoluminescence of the GQDs can be tailored through varying the size of the GQDs by changing process parameters. Due to the luminescence stability, nanosecond lifetime, ...
1,980 citations
TL;DR: It is shown that the structure and properties of GO depend significantly on the quenching and purification procedures, rather than, as is commonly thought, on the type of graphite used or oxidation protocol, which allows us to add critical details to existing GO models.
Abstract: Graphite oxide (GO) is a lamellar substance with an ambiguous structure due to material complexity. Recently published GO-related studies employ only one out of several existing models to interpret the experimental data. Because the models are different, this leads to confusion in understanding the nature of the observed phenomena. Lessening the structural ambiguity would lead to further developments in functionalization and use of GO. Here, we show that the structure and properties of GO depend significantly on the quenching and purification procedures, rather than, as is commonly thought, on the type of graphite used or oxidation protocol. We introduce a new purification protocol that produces a product that we refer to as pristine GO (pGO) in contrast to the commonly known material that we will refer to as conventional GO (cGO). We explain the differences between pGO and cGO by transformations caused by reaction with water. We produce ultraviolet–visible spectroscopic, Fourier transform infrared spectr...
386 citations
TL;DR: The Birch reduction of graphite gives a highly reduced, exfoliated product that is free of lithium, and edge and interior hydrogenation were demonstrated by solid-state (13)C NMR spectroscopy.
Abstract: The Birch reduction (lithium in liquid ammonia) of graphite gives a highly reduced, exfoliated product that is free of lithium. Edge and interior hydrogenation were demonstrated by solid-state (13)C NMR spectroscopy. Elemental analysis of a carefully purified sample allows the chemical composition to be expressed as (C(1.3)H)(n). Atomic force microscopy images showed that the reduced graphene was highly exfoliated. Hydrogen mapping by electron energy loss spectroscopy showed that the entire surface of the reduced sample was covered by hydrogen, consistent with the NMR studies also indicating that hydrogen was added in interior positions of the graphene lattice as well as along the edge. A large band gap (4 eV) further establishes the high level of hydrogenation.
123 citations
TL;DR: A second generation motorized nanocar was designed, synthesized, and imaged to verify structural integrity, and all signals in (1)H NMR were unambiguously assigned, and the results were consistent with the helical structure of the motor.
Abstract: A second generation motorized nanocar was designed, synthesized, and imaged. To verify structural integrity, NMR-based COSY, NOESY, DEPT, HSQC, and HMBC experiments were conducted on the intermediate motor. All signals in 1H NMR were unambiguously assigned, and the results were consistent with the helical structure of the motor. The nanocar was deposited on a Cu(111) surface, and single intact molecules were imaged by scanning tunneling microscopy (STM) at 5.7 K, thereby paving the way for future single-molecule studies of this motorized nanocar atop planar substrates.
119 citations
TL;DR: A cost-effective and potentially industrially scalable, in situ functionalization procedure for preparation of soluble graphene nanoribbon (GNRs) from commercially available carbon nanotubes is presented.
Abstract: A cost-effective and potentially industrially scalable, in situ functionalization procedure for preparation of soluble graphene nanoribbon (GNRs) from commercially available carbon nanotubes is presented. The physical characteristics of the functionalized product were determined using SEM, evolved gas analysis, X-ray diffraction, solid-state 13C NMR, Raman spectroscopy, and GC–MS analytical techniques. A relatively high preservation of electrical properties in the bulk material was observed. Moreover, replacement of intercalated potassium with haloalkanes was obtained. While carbon nanotubes can be covalently functionalized, the conversion of the sp2-hybridized carbon atoms to sp3-hybridized atoms dramatically lowers their conductivity, but edge functionalized GNRs permit their heavy functionalization while leaving the basal planes intact.
117 citations
TL;DR: In this paper, the complex 13 C and 19 F spectra exhibited by two simple organofluorine compounds were studied, and the results showed that the resulting higher order effects are particularly noticeable in the spectra of perfluoro- t -butyl alcohol and hexafluoroethane-1-13 C.
5 citations