Capacitive and Charge Transfer Effects of Single-Walled Carbon Nanotubes in TiO2 Electrodes

The transfer of nanoscale properties from single-walled carbon nanotubes (SWCNTs) to macroscopic systems is a topic of intense research. In particular, inorganic composites of SWCNTs and metal oxide semiconductors are being investigated for applications in electronics, energy devices, photocatalysis, and electroanalysis. In this work, a commercial SWCNT material is separated into fractions containing different conformations. The liquid fractions show clear variations in their optical absorbance spectra, indicating differences in the metallic/semiconducting character and the diameter of the SWCNTs. Also, changes in the surface chemistry and the electrical resistance are evidenced in SWCNT solid films. The starting SWCNT sample and the fractions as well are used to prepare hybrid electrodes with titanium dioxide (SWCNT/TiO₂ ). Raman spectroscopy reflects the optoelectronic properties of SWCNTs in the SWCNT/TiO₂ electrodes, while the electrochemical behavior is studied by cyclic voltammetry. A selective development of charge transfer characteristics and double-layer behavior is achieved through the suitable choice of SWCNT fractions.

High ion adsorption densities of site-selective nitrogen doped carbon sheets prepared from natural lignin

Carbon fibers and sheets were prepared from jet-milled natural chitin and cellulose samples, and from natural lignin sample using ice-templating technique, respectively. Nitrogen doping treatments using melamine were also performed for the carbon fibers and sheets. Electric double layer capacitor (EDLC) electrode properties of the prepared carbon fibers and sheets including the nitrogen doped samples were investigated with aqueous (sulfuric acid) and organic (tetraethylammonium tetrafluoroborate in propylene carbonate) electrolytes. It was found that the nitrogen doped lignin carbon sheets having very small specific surface area of 66 m² g⁻¹ show very high EDLC capacitances of 227 F g⁻¹ and 80 F g⁻¹ determined by charge–discharge measurements at current density of 50 mA g⁻¹ for aqueous and organic electrolytes, respectively. X-ray photoelectron spectroscopy (XPS) measurements revealed that nitrogen atoms of the nitrogen doped lignin carbon sheets exist dominantly in pyridinic sites unlike other chitin and cellulose carbon fibers. We discussed that this site-selective nitrogen doping gives exceptionally high ion adsorption density per unit surface area of the nitrogen doped lignin carbon sheets.

Carbon fibers and sheets were prepared from jet-milled natural chitin and cellulose samples, and from natural lignin sample using ice-templating technique, respectively.

Nanoscaled Surface Modification of Poly(dimethylsiloxane) Using Carbon Nanotubes for Enhanced Oil and Organic Solvent Absorption

This article demonstrates a novel nanoscale surface modification method to enhance the selectivity of porous poly(dimethylsiloxane) (PDMS) in removing oil from water. The surface modification method is simple and low cost by using sugar as a sacrificial template for temporal adhering of carbon nanotubes (CNT) before addition of PDMS prepolymer to encapsulate the CNT on its surface once polymerized. The PDMS-CNT demonstrated a tremendous increase in absorption capacity up to 3-fold compared to previously reported absorbents composed solely of PDMS. Besides showcasing excellent absorption capacity, the PDMS-CNT also shows a faster absorption rate (25 s) as compared to that of pure PDMS (40 s). The enhanced absorption rate is due to the incorporation of CNT, which roughens the surface of the polymer at the nanoscale and lowers the surface energy of porous PDMS while at the same time increasing the absorbent hydrophobicity and oleophilicity. This property makes the absorbent unique in absorbing only oil but repelling water at the same time. The PDMS-CNT is an excellent absorbent material with outstanding recyclability and selectivity for removing oil from water.

Quinone molecules encapsulated in SWCNTs for low-temperature Na ion batteries

We have performed Li and Na ion charge-discharge experiments of 9,10-phenanthrene quinone (PhQ) molecules encapsulated in single-walled carbon nanotubes (SWCNTs) with mean tube diameters of 1.5 and 2.5 nm at room temperature and also at low temperatures. The Na ion reversible capacity of PhQ encapsulated in the larger diameter SWCNTs, measured at a low temperature of 0 °C, remained as high as that measured at room temperature (RT), while the capacity of PhQ in the smaller diameter SWCNTs at 0 °C was about a half of that at RT. The diameter dependence of the capacity should be attributed to the difference in the interactions between the encapsulated PhQ molecules and the host SWCNTs, which was revealed by Raman peak profile analysis. Charge-transfer reaction from metallic tubes to PhQ molecules encapsulated in the smaller diameter SWCNTs was detected by Raman measurements. The electrostatic interaction between charged SWCNTs and PhQ molecules, induced by the charge-transfer reaction, would partly contribute to the stabilization of PhQ molecules in the smaller diameter SWCNTs, while only van der Waals interaction stabilizes PhQ molecules in the larger diameter SWCNTs. The difference in stability was confirmed by thermogravimetric, x-ray photoelectron spectroscopy, and Raman measurements. Charge-discharge curves of PhQ encapsulated in SWCNTs were also discussed based on the stability difference.

Electrochemical lithium-ion storage properties of quinone molecules encapsulated in single-walled carbon nanotubes

We investigated the electrochemical lithium-ion storage properties of 9,10-anthraquinone (AQ) and 9,10-phenanthrenequinone (PhQ) molecules encapsulated in the inner hollow core of single-walled carbon nanotubes (SWCNTs).