Azide photochemistry for facile modification of graphitic surfaces : preparation of DNA-coated carbon nanotubes for biosensing

A facile, two-step method for chemically attaching single-stranded DNA to graphitic surfaces, represented here by carbon nanotubes, is reported. In the first step, an azide-containing compound, N-5-azido-nitrobenzoyloxy succinimide (ANB-NOS), is used to form photo-adducts on the graphitic surfaces in a solid-state photochemical reaction, resulting in active ester groups being oriented for the subsequent reactions. In the second step, pre-synthesized DNA strands bearing a terminal amine group are coupled in an aqueous solution with the active esters on the photo-adducts. The versatility of the method is demonstrated by attaching pre-synthesized DNA to surfaces of carbon nanotubes in two platforms—as vertically-aligned multi-walled carbon nanotubes on a solid support and as tangled single-walled carbon nanotubes in mats. The reaction products at various stages were characterized by x-ray photoelectron spectroscopy. Two different assays were used to check that the DNA strands attached to the carbon nanotubes were able to bind their partner strands with complementary base sequences. The first assay, using partner DNA strands tethered to gold nanoparticles, enabled the sites of DNA attachment to the carbon nanotubes to be identified in TEM images. The second assay, using radioactively labelled partner DNA strands, quantified the density of functional DNA strands attached to the carbon nanotubes. The diversity of potential applications for these DNA-modified carbon-nanotube platforms is exemplified here by the successful use of a DNA-modified single-walled carbon-nanotube mat as an electrode for the specific detection of metal ions.

Carbon dioxide corrosion inhibition : an overview of recent research on new inhibitor development

Since the introduction of inhibitors to the oil and gas industry in the 1940’s, corrosion inhibition has played a key role in carbon dioxide (CO2) corrosion control. Major inhibitor discoveries occurred from the late 1940's to the late 1960's, followed by the refinement of formulations and the development of improved application methods. Over the past two to three decades, although some new derivatives of existing inhibitors such as amide, amine and imidazoline have been reported, there have been few if any discoveries of new CO2 corrosion inhibitors. In recent years, the development of environmentally friendly inhibitors and the inhibition of localised corrosion have become driving forces behind new advances in corrosion inhibitor technology. Recently a rare earth metal organic compound, lanthanum 4-hydroxy cinnamate has been found to be an efficient corrosion inhibitor for mild steel in CO2 containing aqueous media. A resorcinarene acid has been found to provide effective localised corrosion inhibition by promoting a random distribution of insignificant anodic currents. The advent of advanced scanning probe techniques and an electrochemical integrated multi-electrode array have facilitated the discovery of corrosion inhibitors. This paper provides a brief overview of recent progress in this field.

Review of critical issues in carbon dioxide corrosion testing and monitoring techniques

This paper presents a brief review of major techniques applied in carbon dioxide corrosion testing and monitoring. The focus is on the advantages and disadvantages of variously designed testing apparatus and monitoring devices for localized corrosion detection and assessment. Critical factors affecting the reliability and accuracy of major corrosion testing techniques are briefly discussed. It is concluded that major reasons that lead to reporting of inaccurate corrosion rates and patterns include: (i) limitations in conventional electrochemical and nonelectrochemical methods for localized corrosion measurements, and difficulties in data interpretation; (ii) challenges in simulating localized corrosion mechanisms and their changes with the extension of corrosion testing. Underdeposit corrosion testing is presented as a case to illustrate challenges in simulating localized corrosion processes and mechanisms. Experiment data have been presented to show potential difficulties of the artificial pit electrode method in evaluating underdeposit corrosion and its inhibitors. The wire beam electrode method has been used to study underdeposit corrosion with and without inhibitor present. Several interesting corrosion mechanisms have been revealed at different stages of underdeposit corrosion processes.

Carbon Nanotube – Reduced Graphene Oxide Composites for Thermal Energy Harvesting Applications

By controlling the SWNT-rGO electrode composition and thickness to attain the appropriate porosity and tortuosity, the electroactive surface area is maximized while rapid diffusion of the electrolyte through the electrode is maintained. This leads to an increase in exchange current density between the electrode and electrolyte which results in enhanced thermocell performance.

Carbon Nanotube Nanoweb–Bioelectrode for Highly Selective Dopamine Sensing

A highly sensitive and selective dopamine sensor was fabricated with the unique 3D carbon nanotube nanoweb (CNT-N) electrode. The as-synthesised CNT-N was modified by oxygen plasma to graft functional groups in order to increase selective electroactive sites at the CNT sidewalls. This electrode was characterized physically and electrochemically using HRSEM, Raman, FT-IR, and cyclic voltammetry (CV). Our investigations indicated that the O2-plasma treated CNT-N electrode could serve as a highly sensitive biosensor for the selective sensing of dopamine (DA, 1 μM to 20 μM) in the presence of ascorbic acid (AA, 1000 μM).

Integrated High-Efficiency Pt/Carbon Nanotube Arrays for PEM Fuel Cells

A facile strategy to deposit Pt nanoparticles with various metal-loading densities on vertically aligned carbon nanotube (ACNT) arrays as electrocatalysts for proton exchange membrane (PEM) fuel cells is described. The deposition is achieved by electrostatic adsorption of the Pt precursor on the positively charged polyelectrolyte functionalized ACNT arrays and subsequent reduction by L-ascorbic acid. The application of the aligned electrocatalysts in fuel cells is realized by transferring from a quartz substrate to nafion membrane using a hot-press procedure to fabricate the membrane electrode assembly (MEA). It is shown that the MEA with vertically aligned structured electrocatalysts provides better Pt utilization than that with Pt on conventional carbon nanotubes or carbon black, resulting in higher fuel cell performance.

Carbon nanotube architectures as catalyst supports for proton exchange membrane fuel cells

Catalyst support materials exhibit great influence on the performance and durability of proton exchange membrane (PEM) fuel cells. This minireview article summarises recent developments into carbon nanotube-based support materials for PEM fuel cells, including the membrane electrode assembly (MEA). The advantages of using CNTs to promote catalyst performance and stability, a perspective on research directions and strategies to improve fuel cell performance and durability are discussed. It is hoped that this minireview will act as a conduit for future developments in catalyst supports and MEA design for PEM fuel cells.

Nanostructured carbon electrodes

In its conducting form, carbon has proven to be a versatile, robust and high performing electrode material in areas such as energy conversion, energy storage and even medical bionics. In our laboratories we have been interested in the fabrication and utilization of nanostructured electrodes based on more recently discovered forms of carbon. These include carbon nanotubes and graphene.

Porous carbon nanotube/polyvinylidene fluoride composite material: Superhydrophobicity/superoleophilicity and tunability of electrical conductivity

Porous carbon nanotube/polyvinylidene fluoride (CNT/PVDF) composite material can be fabricated via formation and freeze-drying of a gel. The field emission scanning electron microscopy, nitrogen adsorption-desorption and pore size distribution analysis reveal that the introduction of a small amount of carbon nanotubes (CNTs) can effectively increase the surface roughness and porosity of polyvinylidene fluoride (PVDF). Contact angle measurements of water and oil indicate that the as-obtained composite material is superhydrophobic and superoleophilic. Further experiments demonstrate that these composite material can be efficiently used to separate/absorb the insoluble oil from oil polluted water as membrane/absorbent. Most importantly, the electrical conductivity of such porous CNT/PVDF composite material can be tuned by adjusting the mass ratio of CNT to PVDF without obviously changing the superhydrophobicity or superoleophilicity. The unique properties of the porous CNT/PVDF composite material make it a promising candidate for oil-polluted water treatment as well as water-repellent catalyst-supporting electrode material.

Sulfur-doped porous reduced graphene oxide hollow nanosphere frameworks as metal-free electrocatalysts for oxygen reduction reaction and as supercapacitor electrode materials.

Chemical doping with foreign atoms is an effective approach to significantly enhance the electrochemical performance of the carbon materials. Herein, sulfur-doped three-dimensional (3D) porous reduced graphene oxide (RGO) hollow nanosphere frameworks (S-PGHS) are fabricated by directly annealing graphene oxide (GO)-encapsulated amino-modified SiO2 nanoparticles with dibenzyl disulfide (DBDS), followed by hydrofluoric acid etching. The XPS and Raman spectra confirmed that sulfur atoms were successfully introduced into the PGHS framework via covalent bonds. The as-prepared S-PGHS has been demonstrated to be an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR) with the activity comparable to that of commercial Pt/C (40%) and much better methanol tolerance and durability, and to be a supercapacitor electrode material with a high specific capacitance of 343 F g(-1), good rate capability and excellent cycling stability in aqueous electrolytes. The impressive performance for ORR and supercapacitors is believed to be due to the synergistic effect caused by sulfur-doping enhancing the electrochemical activity and 3D porous hollow nanosphere framework structures facilitating ion diffusion and electronic transfer.

Excellent electrochemical performance of LiFe0.4Mn0.6PO4 microspheres produced using a double carbon coating process

Composite LiFe0.4Mn0.6PO4/C microspheres are considered advanced cathode materials for electric vehicles and other high-energy density applications due to their advantages of high energy density and excellent cycling stability. LiFe0.4Mn0.6PO4/C microspheres have been produced using a double carbon coating process employing traditional industrial techniques (ball milling, spray-drying and annealing). The obtained LiFe0.4Mn0.6PO4 microspheres exhibit a high discharge capacity of around 166 mA h g-1 at 0.1 C and excellent rate capabilities of 132, 103, and 72 mA h g-1 at 5, 10, and 20 C, respectively. A reversible capacity of about 152 mA h g-1 after 500 cycles at a current density of 1 C indicates an outstanding cycling stability. The excellent electrochemical performance is attributed to the micrometer-sized spheres of double carbon-coated LiFe0.4Mn0.6PO4 nanoparticles with improved electric conductivity and higher Li ion diffusion coefficients, ensuring full redox reactions of all nanoparticles. The results show that the advanced high-energy density cathode materials can be produced using existing industry techniques.

Carbon coated Na7Fe7(PO4)6F3: A novel intercalation cathode for sodium-ion batteries

Electrode materials are being developed to realise sodium-ion batteries that can provide energy storage solutions. Here, we develop amorphous carbon coated Na₇Fe₇(PO₄)₆F₃, prepared by combining hydrothermal and solid state reaction methods, as an insertion electrode for sodium-ion batteries applications. Na₇Fe₇(PO₄)₆F₃ particles are surrounded by a thin layer (∼1.5–2 nm) of amorphous carbon. The Na₇Fe₇(PO₄)₆F₃/C composite cathode undergoes reversible sodium intercalation/de-intercalation with an average operational potential of ∼3.0 V (vs Na⁺/Na). This cathode has a capacity of 65 mA h g⁻¹ at 100 mA g⁻¹ current after 60 cycles and features twice higher capacity than that of an uncoated Na₇Fe₇(PO₄)₆F₃ sample. Therefore, the carbon-coated Na₇Fe₇(PO₄)₆F₃ composite presents feasible sodium intercalation/de-intercalation capacity, offering possibilities for developing a low cost, high performance sodium-ion battery positive electrode.

Gamma-irradiated carbon nanotube yarn as substrate for high-performance fiber supercapacitors

As an electrical double layer capacitor, dry-spun carbon nanotube yarn possesses relatively low specific capacitance. This can be significantly increased as a result of the pseudocapacitance of functional groups on the carbon nanotubes developed by oxidation using a gamma irradiation treatment in the presence of air. When coated with high-performance polyaniline nanowires, the gamma-irradiated carbon nanotube yarn acts as a high-strength reinforcement and a high-efficiency current collector in two-ply yarn supercapacitors for transporting charges generated along the long electrodes. The resulting supercapacitors demonstrate excellent electrochemical performance, cycle stability, and resistance to folding-unfolding that are required in wearable electronic textiles.

Novel ultrathin nanoflake assembled porous MnO2/carbon strip microspheres for superior pseudocapacitors

A novel hierarchical MnO2/carbon strip (MnO2/C) microsphere is synthesized via galvanostatic charge-discharge of a MnO@C matrix precursor where the carbon is from a low-cost citric acid. This hierarchical structure is composed of manganese oxides nanoflakes and inlaid carbon strips. The ultrathin nanoflakes assemble to form porous microspheres with a rippled surface superstructure. Due to its improved conductivity and remarkable increased phase contact area, this novel structure exhibits an excellent electrochemical performance with a specific capacitance of 485.6 F g -1 at a current density of 0.5 A g-1 and an area capacitance as high as 4.23 F cm-2 at a mass loading of 8.7 mg cm-2. It also shows an excellent cycling stability with 88.9% capacity retention after 1000 cycles. It is speculated that the present low-cost novel hierarchical porous microspheres can serve as a promising electrode material for pseudocapacitors. © 2014 American Chemical Society.

Large-scale production of h-In2O3/carbon nanocomposites with enhanced lithium storage properties

h-In2O3/carbon nanocomposites were obtained via a facile ball milling process from a mixture of h-In2O3 nanoparticles and Super P carbon. Compared to pure h-In2O3 nanoparticles, the nanocomposites exhibited an initial discharge capacity of 1360 mAh g-1, a stable reversible capacity of 867 mAh g-1 after 100 cycles as well as a high coulombic efficiency of 99%. The superior lithium-ion battery performance can be attributed to the specific structure of h-In2O3 and the uniform and continuous nano-carbon coating layers. The nano-carbon coating could protect the inner active materials from fragmentation and increase the electronic conductivity. This study not only provides a promising electrode material for high-performance lithium-ion batteries, but also further demonstrates a straightforward, effective and environmental friendly process for synthesizing nanocomposites. © 2014 Elsevier Ltd.