Effect of Carbon Nanotube Aqueous Dispersion Quality on Mechanical Properties of Cement Composite

An effect of the quality of carbon nanotube (CNT) dispersions added to cement on paste mechanical properties has been studied. High-quality dispersions of few-walled CNT (FWCNTs) were produced in two steps. First, FWCNTs were functionalized in a mixture of nitric and sulfuric acids (70 wt.% and 96 wt.%, resp.) at 80 ∘C . Second, functionalized FWCNTs were washed out by acetone to remove carboxylated carbonaceous fragments (CCFs) formed during CNT oxidation. Mechanical test results showed 2-fold increase in the compressive strength of the cement paste prepared from the dispersion of acetone-washed functionalized FWCNTs, which is believed to occur due to the chemical interaction between cement matrix and functional groups (–COOH and –OH). Utilisation of unwashed FWCNTs led to a marginal improvement of mechanical properties of the cement pastes, whereas surfactant-treated functionalized FWCNT dispersions only worsened the mechanical properties.Peer reviewe

Carbon Nanotube/Nanofibers and Graphite Hybrids for Li-Ion Battery Application

To improve the electrical conductivity of negative electrodes of lithium ion batteries, we applied a direct CVD synthesis of carbon nanomaterials on the surface of graphite particles. To prepare a catalyst, two alternative approaches were utilized: colloidal nanoparticles (NPs) and metal (Ni and Co) nitrate salt precursors deposited on the graphite surface. Both colloidal and precursor systems allowed us to produce carbon nanofibers (CNFs) on the graphite surface with high coverage under the optimum CVD conditions. Electrical measurements revealed that the resistivity of the actual electrodes fabricated from CNFs coated graphite particles was about 40% lower compared to the original pristine graphite electrodes.Peer reviewe

Single-Walled Carbon Nanotube Network Field Effect Transistor as a Humidity Sensor

Single-walled carbon nanotube network field effect transistors were fabricated and studied as humidity sensors. Sensing responses were altered by changing the gate voltage. At the open channel state (negative gate voltage), humidity pulse resulted in the decrease of the source-drain current, and, vice versa, the increase in the source-drain current was observed at the positive gate voltage. This effect was explained by the electron-donating nature of water molecules. The operation speed and signal intensity was found to be dependent on the gate voltage polarity. The positive or negative change in current with humidity pulse at zero-gate voltage was found to depend on the previous state of the gate electrode (positive or negative voltage, respectively). Those characteristics were explained by the charge traps in the gate dielectric altering the effective gate voltage, which influenced the operation of field effect transistor.Peer reviewe

Simple immobilization of pyrroloquinoline quinone on few-walled carbon nanotubes

Pyrroloquinoline quinone (PQQ) was immobilized on glassy-carbon electrodes (GCE) modified with single-walled carbon nanotubes (SWCNT), few-walled carbon nanotubes (FWCNT) and carbon black (Vulcan XC72R). Modified electrodes were prepared by drop-casting. Immobilization was achieved with an extremely simple dipping procedure and without any further modification to the electrodes. Electrochemical performance of the electrodes was studied by cyclic voltammetry and spectroelectrochemistry. FWCNT adsorbed 30 times more PQQ than the other carbon materials. Compared to more complicated immobilization methods, PQQ/FWCNT/GCE showed well-defined electrochemistry in a considerably wide pH area from 2 to 12. The dipping process is affected by pH and electrostatic forces. At dipping pH 9.5, where both FWCNTs and PQQ have strong negative charge, the adsorption was halved compared to dipping pH 2, where the charges are smaller.Peer reviewe

Electrical behaviour of native cellulose nanofibril/carbon nanotube hybrid aerogels under cyclic compression

Hybrid aerogels consisting of cellulose nanofibers (CNF) and modified few-walled carbon nanotubes (FWCNT) are investigated under cyclic mechanical compression to explore "electrical fatigue". For this purpose the FWCNTs were hydrophilized, thus promoting their aqueous dispersibility to allow FWCNT/CNF hybrid hydrogels, followed by freeze-drying to obtain hybrid aerogels. The optimized composition consisting of FWCNT/CNF 20/80 wt/wt showed conductivity of 10-5 S cm-1 as promoted due to double percolation, and showed only small changes in electrical and mechanical behaviour upon cycling 100 times. The electrical behaviour under cycled compression shows good stability and reversibility.Peer reviewe

Enhanced performance of a silicon microfabricated direct methanol fuel cell with PtRu catalysts supported on few-walled carbon nanotubes

Silicon micro fuel cells (Si-MFCs) are promising power supplies for microelectronic applications, however their development is still at early stages compared to the conventional proton exchange membrane fuel cells (PEMFCs). There are not many published reports on the durability of Si-MFCs and those available only projected the life-time of standard Vulcan based catalysts. However, the limited durability resulting from carbon corrosion is one of the crucial issues in fuel cells. In this study, Si-MFC with an integrated silicon nanograss diffusion layer is used for the direct methanol fuel cell investigations. The long-term (3-day) performance of PtRu catalysts supported on different carbon supports, namely Vulcan, Graphitized carbon nanofibers (GNFs) and Few-walled carbon nanotubes (FWCNTs), was studied. PtRu-FWCNTs and PtRu-GNFs exhibited respectively 471% (20.0 mW cm-2) and 274% (13.1 mW cm-2) power density enhancements compared to PtRu-Vulcan (3.5 mW cm-2). After 3-day durability measurements, power densitystayed at 72, 68 and 91% of the initial value, respectively for PtRu-FWCNTs, PtRu-GNFs and PtRu-Vulcan. To evaluate the influence of carbon supports as well as the distribution and the size of the nanoparticles on the overall performance of Si-MFCs, further characterizations with Raman, BET, XRD, SEM and TEM were performed.Peer reviewe

Optical Properties of Graphene Nanoribbons Encapsulated in Single-Walled Carbon Nanotubes

We report the photoluminescence (PL) from graphene nanoribbons (GNRs) encapsulated in single-walled carbon nanotubes (SWCNTs). New PL spectral features originating from GNRs have been detected in the visible spectral range. PL peaks from GNRs have resonant character, and their positions depend on the ribbon geometrical structure in accordance with the theoretical predictions. GNRs were synthesized using confined polymerization and fusion of coronene molecules. GNR@SWCNTs material demonstrates a bright photoluminescence both in infrared (IR) and visible regions. The photoluminescence excitation mapping in the near-IR spectral range has revealed the geometry-dependent shifts of the SWCNT peaks (up to 11 meV in excitation and emission) after the process of polymerization of coronene molecules inside the nanotubes. This behavior has been attributed to the strain of SWCNTs induced by insertion of the coronene molecules