David A. Lewis

Sulfur-Limonene Polysulfide: A Material Synthesized Entirely from Industrial By-Products and Its Use in Removing Toxic Metals from Water and Soil.

Abstract A polysulfide material was synthesized by the direct reaction of sulfur and d‐limonene, by‐products of the petroleum and citrus industries, respectively. The resulting material was processed into functional coatings or molded into solid devices for the removal of palladium and mercury salts from water and soil. The binding of mercury(II) to the sulfur‐limonene polysulfide resulted in a color change. These properties motivate application in next‐generation environmental remediation and mercury sensing.

Highly conductive interwoven carbon nanotube and silver nanowire transparent electrodes

Abstract Electrodes fabricated using commercially available silver nanowires (AgNWs) and single walled carbon nanotubes (SWCNTs) produced sheet resistances in the range 4–24 Ω □−1 with specular transparencies up to 82 %. Increasing the aqueous dispersibility of SWCNTs decreased the bundle size present in the film resulting in improved SWCNT surface dispersion in the films without compromising transparency or sheet resistance. In addition to providing conduction pathways between the AgNW network, the SWCNTs also provide structural support, creating stable self-supporting films. Entanglement of the AgNWs and SWCNTs was demonstrated to occur in solution prior to deposition by monitoring the transverse plasmon resonance mode of the AgNWs during processing. The interwoven AgNW/SWCNT structures show potential for use in optoelectronic applications as transparent electrodes and as an ITO replacement.

Planar silver nanowire, carbon nanotube and PEDOT:PSS nanocomposite transparent electrodes

Abstract Highly conductive, transparent and flexible planar electrodes were fabricated using interwoven silver nanowires and single-walled carbon nanotubes (AgNW:SWCNT) in a PEDOT:PSS matrix via an epoxy transfer method from a silicon template. The planar electrodes achieved a sheet resistance of 6.6 ± 0.0 Ω/□ and an average transmission of 86% between 400 and 800 nm. A high figure of merit of 367 Ω−1 is reported for the electrodes, which is much higher than that measured for indium tin oxide and reported for other AgNW composites. The AgNW:SWCNT:PEDOT:PSS electrode was used to fabricate low temperature (annealing free) devices demonstrating their potential to function with a range of organic semiconducting polymer:fullerene bulk heterojunction blend systems.

Laying Waste to Mercury: Inexpensive Sorbents Made from Sulfur and Recycled Cooking Oils

Abstract Mercury pollution threatens the environment and human health across the globe. This neurotoxic substance is encountered in artisanal gold mining, coal combustion, oil and gas refining, waste incineration, chloralkali plant operation, metallurgy, and areas of agriculture in which mercury‐rich fungicides are used. Thousands of tonnes of mercury are emitted annually through these activities. With the Minamata Convention on Mercury entering force this year, increasing regulation of mercury pollution is imminent. It is therefore critical to provide inexpensive and scalable mercury sorbents. The research herein addresses this need by introducing low‐cost mercury sorbents made solely from sulfur and unsaturated cooking oils. A porous version of the polymer was prepared by simply synthesising the polymer in the presence of a sodium chloride porogen. The resulting material is a rubber that captures liquid mercury metal, mercury vapour, inorganic mercury bound to organic matter, and highly toxic alkylmercury compounds. Mercury removal from air, water and soil was demonstrated. Because sulfur is a by‐product of petroleum refining and spent cooking oils from the food industry are suitable starting materials, these mercury‐capturing polymers can be synthesised entirely from waste and supplied on multi‐kilogram scales. This study is therefore an advance in waste valorisation and environmental chemistry.

Poly(4-vinylpyridine): A New Interface Layer for Organic Solar Cells

Poly(4-vinylpyridine) (P4VP) was used as a cathode interface layer in inverted organic solar cells (OSCs) fabricated using poly[2,3-bis(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and PC71BM (phenyl C71 butyric acid methyl ester) as the donor and acceptor materials, respectively. We successfully demonstrate that the work function of underlying indium tin oxide (ITO) electrode can be significantly reduced by ∼0.7 eV, after modification of the surface with a thin film of P4VP. Photoconversion efficiency of 4.7% was achieved from OSCs incorporating P4VP interface layer between the ITO and bulk heterojunction (BHJ). Thin P4VP layer, when used to modify ZnO electron transport layer in inverted OSCs, reduced the ZnO work function from 3.7 to 3.4 eV, which resulted in a noteworthy increase in open-circuit voltage from 840 to 890 mV. On simultaneous modification of ZnO with P4VP and optimization of the BHJ morphology by using solvent additive chloronapthalene, photoconversion efficiency of OSCs was significantly increased from 4.6% to 6.3%. The enhanced device parameters are also attributed to an energetically favorable material stratification, as a result of an enrichment of PC71BM toward the P4VP interface.

Pathway to high throughput, low cost indium-free transparent electrodes

A roll-to-roll compatible, high throughput process is reported for the production of highly conductive, transparent planar electrode comprising an interwoven network of silver nanowires and single walled carbon nanotubes imbedded into poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The planar electrode has a sheet resistance of between 4 and 7 Ω □−1 and a transmission of >86% between 800 and 400 nm with a figure of merit of between 344 and 400 Ω−1. The nanocomposite electrode is highly flexible and retains a low sheet resistance after bending at a radius of 5 mm for up to 500 times without loss. Organic photovoltaic devices containing the planar nanocomposite electrodes had efficiencies of ∼90% of control devices that used indium tin oxide as the transparent conducting electrode.

Investigation of Roughness Periodicity on the Hydrophobic Properties of Surfaces

Hydrophobic films were synthesized with a variety of silica particle sizes ranging from 58 to 1428 nm to investigate the effect of particle size on the contact and sliding angles. While the surface roughness created by varying the particle size did not appear to affect water contact angles, the sliding angles showed a significant monotonic decrease, reducing from 90° to 20°.

A simple method for the quantification of molecular decorations on silica particles

Abstract A simple, rapid quantitative approach to determining attachment density on silica nanoparticles has been demonstrated using attenuated total reflectance Fourier transform infrared spectroscopy and verified by thermogravimetric analysis. A very high attachment of approximately 5 attachments per nm2 has been achieved through photoinduced thiol–ene click reaction of 11-bromo-1-undecene with a thiol functionalized silica nanoparticle formed from mercaptopropyltrimethoxysilane as the sole precursor. Attachment density with concentration of alkene and reaction time is shown to be highly nonlinear and appears to be limited by accessability of thiols on the surface of the particle. This method opens the opportunity to form nanoparticles with controlled functionality including multifunctional particles, which have been produced in this work.

Carbon nanotube modified probes for stable and high sensitivity conductive atomic force microscopy

Conductive atomic force microscopy (C-AFM) is used to characterise the nanoscale electrical properties of many conducting and semiconducting materials. We investigate the effect of single walled carbon nanotube (SWCNT) modification of commercial Pt/Ir cantilevers on the sensitivity and image stability during C-AFM imaging. Pt/Ir cantilevers were modified with small bundles of SWCNTs via a manual attachment procedure and secured with a conductive platinum pad. AFM images of topography and current were collected from heterogeneous polymer and nanomaterial samples using both standard and SWCNT modified cantilevers. Typically, achieving a good current image comes at the cost of reduced feedback stability. In part, this is due to electrostatic interaction and increased tip wear upon applying a bias between the tip and the sample. The SWCNT modified tips displayed superior current sensitivity and feedback stability which, combined with superior wear resistance of SWCNTs, is a significant advancement for C-AFM.

Synthesis and Characterisation of High Fullerene Content Polymers and Their Use in Organic Photovoltaic Devices

Narrow dispersity polymers with a high tethered fullerene content were synthesised by first polymerising poly(chloromethyl styrene) using reversible addition–fragmentation chain transfer (RAFT) polymerisation and subsequently functionalising them with pristine fullerene. The polymers comprised 52 % by weight fullerene, corresponding to approximately one fullerene per monomer in the polymer with a different morphology to poly(3-hexyl thiophene) (P3HT) : phenyl-C61-butyric acid methyl ester (PCBM) systems. Bulk heterojunctions formed from the polymer tethered fullerene (PTF) with P3HT yielded functioning organic photovoltaic devices with power conversion efficiencies ranging from 0.0030 to 0.22 % as the PTF was increased from 1 : 0.8 to 1 : 1.3. Process optimisation resulted in a maximum efficiency of 0.4 %.