Liquid-phase exfoliation is one of the most promising routes for large scale
production of multilayer graphene dispersions. These dispersions, which may be
used in coatings, composites or paints, are believed to contain disorder-free
graphene multilayers. Here we address the nature of defects in such samples
obtained by liquid-phase exfoliation of graphite powder in
N-methyl--2--pyrrolidone. Our Raman spectroscopy data challenges the assumption
that these multilayers are free of bulk defects, revealing that defect
localization strongly depends on the sonication time. For short ultrasound
times, defects are located mainly at the layer edges but they turn out to build
up in the bulk for ultrasonic times above 2 h. This knowledge may help to
devise better strategies to achieve high-quality graphene dispersions.Comment: 5 pages, 4 figure
In the present paper, a systematic electrochemical investigation on thiourea (TU) electrooxidation was developed on polycrystalline and (111) single-crystal gold electrodes in 0.1 M perchloric acid. The combination of cyclic voltammetry with in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry techniques have allowed the nature of the species formed during the electroadsorption and electrooxidation of TU to be established. FTIRS experiments were performed in D2O to clean up the region of the H2O bending around 1600 cm(-1). It was concluded that TU adsorbs tilted on the surface in the 0.05-0.40 VRHE potential range. A dual-path reaction mechanism was evidenced in the oxidation process. The first pathway takes place from adsorbed TU at E > 0.40 VRHE and implies the formation of [Au(I)-(TU)2]+, which is oxidized to NH2CN and S0 at E > 0.80 VRHE. In a following oxidation step at E > 1.20 V, N2, CO2, and HSO4-/SO4(2-) were produced. The second parallel reaction occurs from TU in solution at E > 0.50 VRHE to form (TU)2(2+). All these species were characterized from the spectroscopic experiments. Similar results were obtained for both surfaces.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.