Purification of Single-Wall carbon nanotubes by heat treatment and supercritical extraction

Arc discharge is the most practical method for the synthesis of single wall carbon nanotubes (SWCNT). However, the production of SWCNT by this technique has low selectivity and yield, requiring further purification steps. This work is a study of purification of SWCNT by heat treatment in an inert atmosphere followed by supercritical fluid extraction. The raw arc discharge material was first heat-treated at 1250 °C under argon. The nanotubes were further submitted to an extraction process using supercritical CO2 as solvent. A surfactant (tributylphosphate, TBP) and a chelating agent (hexafluoroacetylacetone, HFA) were used together to eliminate metallic impurities from the remaining arc discharge catalysts. Analysis of Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) showed an efficient removal of iron and cobalt (>80%). The purified nanotubes were further analyzed by TGA and Raman spectroscopy

Chemical Vapor Deposition Synthesis of N-, P-, and Si-D Carbon Nanotubesoped Single-Walled

7 p. : il.ABSTRACT - Here we report the synthesis of single-walled carbon nanotube bundles by chemical vapor deposition in the presence of electron donor elements (N, P, and Si). In order to introduce each dopant into the graphitic carbon lattice, different precursors containing the doping elements (benzylamine, pyrazine, triphenylphosphine, and methoxytrimethylsilane) were added at various concentrations into ethanol/ferrocene solutions. The synthesized nanotubes and byproduct were characterized by electron microscopy and Raman spectroscopy. Our results reveal intrinsic structural and electronic differences for the N-, P-, and Si- doped nanotubes. These tubes can now be tested for the fabrication of electronic nanodevices, and their performance can be observed

Origin of optical bandgap fluctuations in graphene oxide

In this work, we explore the electrical, optical and spectroscopic properties of different Graphene Oxide (GO) samples focusing on new oxidative strategies to tune their physicochemical properties. Three types of GO samples were prepared by changing the oxidative conditions resulting in carbonyl-, epoxy- or hydroxyl-rich GO. These materials were characterized by UV-VIS absorption, Raman spectroscopy and X-ray diffraction. The experimental results indicate that all samples exhibit oxidation and exfoliation degrees typical of graphene oxides obtained by using the modified Hummers’ method. The optical bandgap values were measured using the Tauc’s plot from UV-VIS data and showed that the stoichiometry of GO impacts the width of the bandgap. The carbonyl-rich sample presented the lowest gap around 3.20 ± 0.02 eV, while epoxy- and hydroxyl-rich GOs showed out gaps of about 3.48 ± 0.07 and 3.72 ± 0.05 eV, respectively. These experimental results are consistent with theoretical calculations of bandgaps obtained with coronene and circumcoronene GO models. The calculations were obtained using different theoretical approaches, such as: Huckel, PM3, AM1 and DFT. The present work suggests that a precise tuning of the optical bandgap of GOs can be achieved by only changing their stoichiometry thus allowing their use in a large range of electronic applications

New Class of Organic Hole-Transporting Materials Based on Xanthene Derivatives for Organic Electronic Applications

In this work, we investigate the influence of three novel 14-aril-14<i>H</i>-dibenzo­[<i>a</i>,<i>j</i>]­xanthene derivatives (XDs) modified with different functional groups as very promising hole-transporting materials for organic optoelectronic devices. Optical, electronic, and structural properties were analyzed by UV–vis absorption spectrum, cyclic voltammetry, and powder X-ray powder diffraction (XRPD). We investigated the influence of these XD as hole-transporting layers (HTL) on the performance of a simple stack bilayer OLED built with commercial aluminum tris­(8-hydroxyquinoline) Alq₃ acting as an electron-transporting and emissive layer (EML). As a proof-of-principle the XD devices were compared to reference devices fabricated with one of the most common hole-transporting materials, the <i>N</i>,<i>N</i>′-bis­(naphthalen-1-yl)-<i>N</i>,<i>N</i>′-bis­(phenyl)-2,2′-dimethylbenzidine (α-NPD). The structure of the devices was ITO/HTL (50 nm)/Alq₃ (50 nm)/Al (120 nm) without encapsulation. Under the same conditions, the devices using XD as HTL exhibited high performance and significant durability when compared to the reference ones. These results are also supported by a theoretical study using density functional theory (DFT) showing that this set of XD presents a higher hole mobility than α-NPD. Thus, we demonstrated that this class of molecules are very promising when used as hole-transport material in organic electronic devices

3D conductive monolithic carbons from pyrolyzed bamboo for microfluidic self-heating system

Bamboo, like wood, is a promising natural template for biobased devices that takes advantage of its hierarchical architecture, microarray channels, anisotropic mechanical and electrical properties. Herein we report a low heat thermal treatment (HTT, 700-1000 °C) of natural bamboo specimens to obtain bamboo-based graphitic devices with thermoelectric and electrochemical properties. The preservation of the highly anisotropic architecture of three-dimensional carbon material (3D-CM) allowed adding specific thermoelectric and electrochemical properties depending on the HTT of the pristine specimens. High electric conductivity (σ, 839 S/m) was observed at 1000 °C showing a remarkable potential application as a bamboo-based working electrode. The bamboo annealed to 700 °C showed higher resistivity (ρ, 0.15 Ω m, and σ, 6.6 S/m), thermal conductivity (1.77 W/m K), and thermal heating rate (1.0 °C/s). The pyrolyzed biomass (B-700) was used as a 3D microfluidic heater to heat polar solvents (H2O and ethylene glycol) in flow mode up to their boiling points. A 2D carbon hotplate heater was built-up to warm solvent in batch mode. A complete chemical and physical characterization of the samples allowed us to determine structural and chemical compositions, cellulose crystalline structure phase transition to graphitic/turbostratic carbon, thermal and electrical conductivity of unprecedented bambootronics bio-devices