D. Jason Riley

Templated electrosynthesis of nanomaterials and porous structures

Templated electrosynthesis is a simple and versatile method that has been widely used to form nanomaterials and porous structures in materials science. The technique permits dimension-controlled materials synthesis. A variety of templates have been employed to define the morphology of conductive materials in electrodeposition. The formation of those materials has triggered intensive study and development of various novel properties and potential applications. This review presents recent advances in templated electrosynthesis as a method to fabricate nanomaterials and porous structures.

Photoelectrochemical properties of chemically exfoliated MoS2

Group 6 transition metal dichalcogenides (TMD) such as MoS2 are promising candidates for photocatalysis and photoelectrochemical applications. Despite their promise, scalable deposition of thin films remains a challenge for TMD-based photoanodes. Here we investigate the photoelectrochemical properties of ultra-thin films of chemically exfoliated MoS2 and its composites with TiO2 nanoparticles. We show that MoS2 monolayer films exhibit photoelectrochemical properties similar to bulk materials, generating photocurrent at excitation wavelengths above the direct band gap edge at ∼660 nm (∼1.9 eV). We also demonstrate that MoS2 monolayers adsorbed on TiO2 behave as effective photosensitizers. We find that in TiO2–MoS2 composite photoanodes, photoexcited hot electrons in MoS2 are able inject into TiO2 whilst holes are removed by the electrolyte so as to generate electrical current from incident light. Our results demonstrate the potential of solution-processed MoS2 monolayers for photoelectrochemical applications.

Voltammetry at C60-modified electrodes

Abstract The reduction of electrodes coated with C 60 -fullerene is examined in acetonitrile solution containing a wide variety of supporting electrolytes (MClO 4 ; M = Li, Na, Ba 0.5 , NR 4 ). Electrochemical intercalation is observed with the formation of fulleride salts. Intercalation is typically irreversible except for the case of R = n -butyl where stable coats of fullerides may be formed into which charge can be passed with near chemical reversibility. Electron-transfer reactions at electrodes modified with C 60 coatings were investigated for diverse substrates. With unreduced coats impeded diffusion to the metal surface was seen, whereas with films reduced in the presence of tetrabutylammonium perchlorate coat-mediated electron transfer to the substrate was possible.

Nanoscale control of Ag nanostructures for plasmonic fluorescence enhancement of near-infrared dyes

AbstractPotential utilization of proteins for early detection and diagnosis of various diseases has drawn considerable interest in the development of protein-based detection techniques. Metal induced fluorescence enhancement offers the possibility of increasing the sensitivity of protein detection in clinical applications. We report the use of tunable plasmonic silver nanostructures for the fluorescence enhancement of a near-infrared (NIR) dye (Alexa Fluor 790). Extensive fluorescence enhancement of ∼2 orders of magnitude is obtained by the nanoscale control of the Ag nanostructure dimensions and interparticle distance. These Ag nanostructures also enhanced fluorescence from a dye with very high quantum yield (7.8 fold for Alexa Fluor 488, quantum efficiency (Qy) = 0.92). A combination of greatly enhanced excitation and an increased radiative decay rate, leading to an associated enhancement of the quantum efficiency leads to the large enhancement. These results show the potential of Ag nanostructures as metal induced fluorescence enhancement (MIFE) substrates for dyes in the NIR “biological window” as well as the visible region. Ag nanostructured arrays fabricated by colloidal lithography thus show great potential for NIR dye-based biosensing applications.

Impedance studies of boron-doped CVD diamond electrodes

The mechanism of electron transfer across the boron-doped diamond electrode/electrolyte interface is investigated using impedance spectroscopy. At an oxygenated electrode surface, two time constants are observed in the impedance plots. The results are discussed in terms of surface-state-mediated electron transfer.

Colloidal bismuth sulfide nanoparticles: a photoelectrochemical study of the relationship between bandgap and particle size

A method of preparing Bi2S3 nanoparticles by arrested precipitation is described. It is shown that varying the amount of stabiliser employed in the preparation controls the size of the particles. The as-prepared nanoparticles may be self-assembled on a tin oxide substrate. Photocurrent studies of the Bi2S3 modified electrode indicate that the presence of an oxidisable surface trap at approximately −0.15 V vs. Ag|AgCl|3.0 mol dm−3 NaCl. Photocurrent spectra indicate that the band edge of the Bi2S3 particles is only weakly dependent on particle size, consistent with a high effective mass of electrons in this material.

Preparation of tin dioxide nanotubes via electrosynthesis in a template

A gold electrode modified with a porous polycarbonate membrane was immersed in an aqueous tin chloride solution. Electrochemistry was employed to control the local pH within the pores and drive a precipitation reaction. Removal of the gold and dissolution of the polymer yielded 1-dimensional polycrystalline tin oxide particles, the crystallinity of the material was enhanced by annealing at 650 °C in ambient. Scanning electron microscopy indicated that the diameter of the as-prepared 1-dimensional tin oxide nanoparticles matched the diameter of the pores in the membrane, 100 nm, and the length, between 0.4 and 1.4 µm, was dependent on the charge passed. High resolution transmission electron microscopy indicates that the particles were hollow, with a wall thickness of approximately 10 nm. The formation of nanotubes results from continuous side-wall precipitation along a reaction front.

Electrochemical studies of moderately boron doped polycrystalline diamond in non-aqueous solvent

Abstract The electrochemistry of boron doped diamond is currently an active field of research. In the majority of studies of diamond electrodes it has been reported that the material acts as a semi-metallic electrode. This paper is concerned with studies of moderately doped diamond electrodes in non-aqueous solvent. The results of Mott–Schottky analysis and the cyclic voltammetry of both ferrocene and bis(pentamethylcyclopentadienyl)iron are reported. The influence of surface bond termination, either hydrogen or oxygen, is also considered. It is shown that a response characteristic of a semiconductor can be attained at diamond electrodes immersed in acetonitrile provided that the redox couple does not have a similar energy to the graphitic surface states. The results obtained are discussed in terms of the Gerischer–Marcus model of charge transfer at semiconductor electrodes.

Au nanostructures by colloidal lithography: from quenching to extensive fluorescence enhancement

Enhanced local electric fields are created by nanoparticles when pumped at wavelengths corresponding to Localised Surface Plasmon Resonance (LSPR) modes, leading to Metal Induced Fluorescence Enhancement (MIFE). This paper describes the fluorescent enhancement due to reproducible and tuneable Au nanostructures on glass substrates fabricated over large areas by colloidal lithography. Interparticle separation, particle resonance, and the fluorescent dye properties (quantum yield and emission/excitation wavelengths) are all important factors influencing the fluorescent enhancement. A maximum fluorescence enhancement of 69 times from near infra-red (NIR) dye Alexa Fluor® 790 was observed.

Intensity modulated photocurrent spectroscopy studies of CdS nanoparticle modified electrodes

The dynamics of charge separation at tin oxide electrodes modified with CdS nanoparticles is investigated using intensity modulated photocurrent spectroscopy. Analytical expressions for the frequency dependent photocurrent, which results from small amplitude modulation of the illumination intensity, are derived. The influence of the applied potential on the rates of charge carrier transfer and recombination is discussed. The experimental data is fitted and rate constants for electron transfer from the nanoparticle to the substrate, hole capture, recombination and back electron transfer are determined. The photocarrier dynamics indicate that the electron remains in the conduction band and that the hole is rapidly trapped. The energy of the trap-state is reported.