Andrew I. Minett

Large-scale exfoliation of inorganic layered compounds in aqueous surfactant solutions.

Ronan J. Smith , Paul J. King , Mustafa Lotya , Christian Wirtz , Umar Khan , Sukanta De , Arlene O’Neill , Georg S. Duesberg , Jaime C. Grunlan , Gregory Moriarty , Jun Chen , Jiazhao Wang , Andrew I. Minett , Valeria Nicolosi , and Jonathan N. Coleman *

Edge-enriched graphene quantum dots for enhanced photo-luminescence and supercapacitance

Graphene quantum dots (GQDs) with their edge-bound nanometer-size present distinctive properties owing to quantum confinement and edge effects. We report a facile ultrasonic approach with chemical activation using KOH to prepare activated GQDs or aGQDs enriched with both free and bound edges. Compared to GQDs, the aGQDs we synthesized had enhanced BET surface area by a factor of about six, the photoluminescence intensity by about four and half times and electro-capacitance by a factor of about two. Unlike their non-activated counterparts, the aGQDs having enhanced edge states emit enhanced intense blue luminescence and exhibit electrochemical double layer capacitance greater than that of graphene, activated or not. Apart from their use as part of electrodes in a supercapacitor, the superior luminescence of aGQDs holds potential for use in biomedical imaging and related optoelectronic applications.

High-yield aqueous phase exfoliation of graphene for facile nanocomposite synthesis via emulsion polymerization

Aqueous phase exfoliation was developed for producing high-yield graphene nanosheets from expanded graphite (EG). The process included ultrasonication with sodium dodecyl sulfate (SDS) emulsion in aqueous phase. The high throughput exfoliation process was characterized by UV-vis spectroscopy, transmission electron microscopy (TEM) and electrical impedance spectroscopy (EIS). Controlled sonication experiments revealed that optimum exfoliation corresponds to maxima in UV-vis spectra. TEM results showed that the exfoliated graphene comprised nanoflakes having ≤5 layers (~60%) and ≤10 layers for 90% of the product. The potential use of this highly dispersed graphene was demonstrated by one-pot synthesis of graphene/polymer composite via in situ emulsion polymerization with styrene. The integrated role of SDS included adsorption and exfoliation of graphite, dispersion of graphene produced and assisting with micelle formation in emulsion. The high surface area graphene nanosheets as dispersed phase in polymeric nanocomposites showed significant improvement in thermal stability and electrical conductivity.

BiVO4/CeO2 nanocomposites with high visible-light-induced photocatalytic activity

Preparation of bismuth vanadate and cerium dioxide (BiVO4/CeO2) nanocomposites as visible-light photocatalysts was successfully obtained by coupling a homogeneous precipitation method with hydrothermal techniques. The BiVO4/CeO2 nanocomposites with different mole ratios were synthesized and characterized by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). Absorption range and band gap energy, which are responsible for the observed photocatalyst behavior, were investigated by UV-vis diffuse reflectance (UV-vis DR) spectroscopy. Photocatalytic activities of the prepared samples were examined by studying the degradation of model dyes Methylene Blue, Methyl Orange, and a mixture of Methylene Blue and Methyl Orange solutions under visible-light irradiation (>400 nm). Results clearly show that the BiVO4/CeO2 nanocomposite in a 0.6:0.4 mol ratio exhibited the highest photocatalytic activity in dye wastewater treatment.

High-Performance Multifunctional Graphene Yarns: Toward Wearable All-Carbon Energy Storage Textiles

The successful commercialization of smart wearable garments is hindered by the lack of fully integrated carbon-based energy storage devices into smart wearables. Since electrodes are the active components that determine the performance of energy storage systems, it is important to rationally design and engineer hierarchical architectures atboth the nano- and macroscale that can enjoy all of the necessary requirements for a perfect electrode. Here we demonstrate a large-scale flexible fabrication of highly porous high-performance multifunctional graphene oxide (GO) and rGO fibers and yarns by taking advantage of the intrinsic soft self-assembly behavior of ultralarge graphene oxide liquid crystalline dispersions. The produced yarns, which are the only practical form of these architectures for real-life device applications, were found to be mechanically robust (Youngs modulus in excess of 29 GPa) and exhibited high native electrical conductivity (2508 ± 632 S m(-1)) and exceptionally high specific surface area (2605 m(2) g(-1) before reduction and 2210 m(2) g(-1) after reduction). Furthermore, the highly porous nature of these architectures enabled us to translate the superior electrochemical properties of individual graphene sheets into practical everyday use devices with complex geometrical architectures. The as-prepared final architectures exhibited an open network structure with a continuous ion transport network, resulting in unrivaled charge storage capacity (409 F g(-1) at 1 A g(-1)) and rate capability (56 F g(-1) at 100 A g(-1)) while maintaining their strong flexible nature.

Dichotomous adsorption behaviour of dyes on an amino-functionalised metal–organic framework, amino-MIL-101(Al)

An amino-functionalised metal–organic framework (MOF), aluminium aminoterephthalate (amino-MIL-101(Al)), has been applied to the adsorptive removal of dyes (cationic methylene blue, MB, and anionic methyl orange, MO) from aqueous solutions in order to examine the effect of the amino group on sorption behaviour. Adsorption isotherms and thermodynamic studies indicated the spontaneous adsorption of MB with a maximum adsorption capacity at 30 °C (762 ± 12 mg gMOF−1) higher than those observed for MB on other MOFs and most other materials. In contrast, lower adsorption capacities were observed in the adsorption of the same dye on the analogous non-amino-functionalised framework (MIL-101(Al), 195 mg g−1) and in the adsorption of MO by amino-MIL-101(Al) (188 ± 9 mg g−1), suggesting that an electrostatic interaction between the amino groups of the MOF and the cationic dye MB may have contributed to the high adsorption capacity. The adsorptions of both dyes on amino-MIL-101(Al) were spontaneous, endothermic, and entropy-driven, as is common for dye adsorptions. However, the ΔS value obtained for the adsorption of MB (346 J mol−1 K−1) was extreme. Further analysis demonstrated that after exposure to MB, the ordered amino-MIL-101(Al) structure was absent, ∼30% of the Al3+ was lost to solution, and significant changes occurred in the X-ray photoelectron spectrum of the MOF. On the other hand, the MOF structure was intact following the adsorption of MO. Several groups have exploited electrostatic interactions to improve dye adsorption; however, these proved excessive in the case of MB (but not MO) adsorption on amino-MIL-101(Al).

A review of techno-economic models for the retrofitting of conventional pulverised-coal power plants for post-combustion capture (PCC) of CO2

In this paper, we compare and contrast the four most promising (i.e. commercially viable in the near future) technologies for the post-combustion capture (PCC) of CO2 that can be retrofitted to a conventional pulverised-coal power plant. These are CO2 capture using: (i) chilled ammonia, (ii) alkali-metal carbonates, (iii) membranes and (iv) calcium looping. These four technologies are compared to the benchmark monoethanolamine (MEA) scrubbing process in terms of efficiency penalty and cost indicators. We first review the relevant CO2 capture chemistry and typical process flow schematics, and then discuss energy- and mass-balance considerations. We consider 18 published techno-economic studies on these technologies and highlight the key measures, including net CO2 capture rate, net power output, net plant efficiency, capital costs, cost of electricity and cost of CO2 avoided. Calcium looping technology results in the lowest efficiency penalty (4.6%-points) and cost of PCC (36.3% increase in levelised cost of electricity). In addition, the cost of CO2 avoided by employing calcium looping for PCC can be as low as 29 USD2010 per tCO2. On all three of these criteria, calcium looping performs more than twice as well as the benchmark MEA PCC process.

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.

Compositional effects of PEDOT-PSS/single walled carbon nanotube films on supercapacitor device performance

Supercapacitors are promising energy storage and power output technologies due to their improved energy density, rapid charge-discharge cycle, high cycle efficiency and long cycle life. Free standing poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate)/single walled nanotube films have been characterised by scanning electron microscopy, Raman spectroscopy and thermo-gravimetric analysis to understand the physical properties of the films. Films with varying compositions of poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) and single walled nanotubes were compared by electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge/discharge to understand their electrochemical properties. A comparison of the results shows that having single walled nanotubes dispersed throughout the polymer matrix increase the capacitance by 65% and the energy density by a factor of 3 whilst achieving good capacity retention over 1000 cycles.

Carbon nanotube network modified carbon fibre paper for Li-ion batteries

Here we report on the direct deposition of large quantities of highly porous carbon nanotube networks onto a carbon fibre paper support; subsequently utilised as the anode in a Li-ion battery application showing improved long-term performance and chemical stability with a significant fully reversible capacity of 546 mAh g−1.