Geoffrey Will

Efficient microwave hydrothermal preparation of nanocrystalline anatase TiO2 colloids

Titanium dioxide nanocrystals are an important commercial product used primarily in white pigments and abrasives, however, more recently the anatase form of TiO2 has become a major component in electrochemical and photoelectrochemical devices. An important property of titanium dioxide nanocrystals for electrical applications is the degree of crystallinity. Numerous preparation methods exist for the production of highly crystalline TiO2 particles. The majority of these processes require long reaction times, high pressures and temperatures (450–1400 °C). Recently, hydrothermal treatment of colloidal TiO2 suspensions has been shown to produce quality crystalline products at low temperatures (<250 °C). In this paper we extend this idea utilising a direct microwave heating source. A comparison between convection and microwave hydrothermal treatment of colloidal TiO2 is presented. The resulting highly crystalline TiO2 colloids were characterised using Raman spectroscopy, XRD, TEM, and electron diffraction. The results show that the microwave treatment of colloidal TiO2 gives comparable increases in crystallinity with respect to normal hydrothermal treatments while requiring significantly less time and energy than the hydrothermal convection treatment.

Experimental and Theoretical Studies of the Redox Potentials of Cyclic Nitroxides

The redox potentials of 25 cyclic nitroxides from four different structural classes (pyrrolidine, piperidine, isoindoline, and azaphenalene) were determined experimentally by cyclic voltammetry in acetonitrile, and also via high-level ab initio molecular orbital calculations. It is shown that the potentials are influenced by the type of ring system, ring substituents and/or groups surrounding the radical moiety. For the pyrrolidine, piperidine, and isoindolines there is excellent agreement (mean absolute deviation of 0.05 V) between the calculated and experimental oxidation potentials; for the azaphenalenes, however, there is an extraordinary discrepancy (mean absolute deviation of 0.60 V), implying that their one-electron oxidation might involve additional processes not considered in the theoretical calculations. This recently developed azaphenalene class of nitroxide represents a new variant of a nitroxide ring fused to an aromatic system and details of the synthesis of five derivatives involving differing aryl substitution are also presented.

Electrochemically exfoliated graphene for electrode films : effect of graphene flake thickness on the sheet resistance and capacitive properties

We present an electrochemical exfoliation method to produce controlled thickness graphene flakes by ultrasound assistance. Bilayer graphene flakes are dominant in the final product by using sonication during the electrochemical exfoliation process, while without sonication the product contains a larger percentage of four-layer graphene flakes. Graphene sheets prepared by using the two procedures are processed into films to measure their respective sheet resistance and optical transmittance. Solid-state electrolyte supercapacitors are made using the two types of graphene films. Our study reveals that films with a higher content of multilayer graphene flakes are more conductive, and their resistance is more easily reduced by thermal annealing, making them suitable as transparent conducting films. The film with higher content of bilayer graphene flakes shows instead higher capacitance when used as electrode in a supercapacitor.

Photoelectrochemical measurement of phthalic acid adsorption on porous TiO2 film electrodes

A new adsorption measurement method based on photoelectrochemical oxidation principles has been developed. The method can be used to directly quantify the amount of adsorbates at a TiO2 electrode surface in a sensitive and accurate manner. The adsorption of phthalic acid was studied as a test case. The relationship between the amount of adsorbate at the TiO2 surface and the concentration of phthalic acid in the solution was obtained. The adsorption of phthalic acid on TiO2 surface was shown to follow a Langmuir type adsorption model. For the first time, the adsorption equilibrium constant of an adsorbate at TiO2 surface has been photoelectrochemically measured. The adsorption equilibrium constant of phthalate on TiO2 porous film at pH 4.0, K=4.0×104 M−1, was obtained using our method, which was close to that obtained by conventional methods. The effect of solution pH on the amount of adsorbate at TiO2 surface was also investigated. The results indicate the adsorption of phthalic acid is mainly of chemical bonding nature.

Photoelectrochromic heterosupramolecular assemblies

Heterosupramolecular assemblies based on modified transparent nanostructured TiO2 (anatase) membranes are described. Exposure of these heterosupramolecular assemblies to visible light causes them to turn blue. Furthermore, if a negative potential is applied to the nanostructured TiO2 membrane this blue color persists for hours. Because only those areas which have been irradiated are blue, and because the lifetime of the blue colored state depends on the potential applied to the nanostructured TiO2 membrane, applications are foreseen for these photoelectrochromic materials.

Heterosupramolecular optical write–read–erase device

A covalently linked ruthenium tris(bipyridyl) complex and viologen have been chemisorbed at the surface of the constituent nanocrystals of a transparent nanostructured TiO 2 film supported on conducting glass. This resulting heterosupramolecular assembly, when incorporated as the working electrode in a sealed two-electrode cell, yields a device which can be written to using blue–green light, read using red light and erased by applying a voltage.

Photocatalytic Disinfection of Bacterial Pollutants Using Suspended and Immobilized TiO2 Powders

The photocatalytic disinfection of Enterobacter cloacae and Enterobacter coli using microwave (MW), convection hydrothermal (HT) and Degussa P25 titania was investigated in suspension and immobilized reactors. In suspension reactors, MW‐treated TiO2 was the most efficient catalyst (per unit weight of catalyst) for the disinfection of E. cloacae. However, HT‐treated TiO2 was approximately 10 times more efficient than MW or P25 titania for the disinfection of E. coli suspensions in surface water using the immobilized reactor. In immobilized experiments, using surface water a significant amount of photolysis was observed using the MW‐ and HT‐treated films; however, disinfection on P25 films was primarily attributed to photocatalysis. Competitive action of inorganic ions and humic substances for hydroxyl radicals during photocatalytic experiments, as well as humic substances physically screening the cells from UV and hydroxyl radical attack resulted in low rates of disinfection. A decrease in colony size (from 1.5 to 0.3 mm) was noted during photocatalytic experiments. The smaller than average colonies were thought to occur during sublethal •OH and O2•− attack. Catalyst fouling was observed following experiments in surface water and the ability to regenerate the surface was demonstrated using photocatalytic degradation of oxalic acid as a model test system.

Phosphorus as a limiting factor on sustainable greywater irrigation.

Water reuse through greywater irrigation has been adopted worldwide and has been proposed as a potential sustainable solution to increased water demands. Despite widespread adoption, there is limited domestic knowledge of greywater reuse. There is no pressure to produce low-level phosphorus products and current guidelines and legislation, such as those in Australia, may be inadequate due to the lack of long-term data to provide a sound scientific basis. Research has clearly identified phosphorus as a potential environmental risk to waterways from many forms of irrigation. To assess the sustainability of greywater irrigation, this study compared four residential lots that had been irrigated with greywater for four years and adjacent non-irrigated lots that acted as controls. Each lot was monitored for the volume of greywater applied and selected physic-chemical water quality parameters and soil chemistry profiles were analysed. The non-irrigated soil profiles showed low levels of phosphorus and were used as controls. The Mechlich3 Phosphorus ratio (M3PSR) and Phosphate Environmental Risk Index (PERI) were used to determine the environmental risk of phosphorus leaching from the irrigated soils. Soil phosphorus concentrations were compared to theoretical greywater irrigation loadings. The measured phosphorus soil concentrations and the estimated greywater loadings were of similar magnitude. Sustainable greywater reuse is possible; however incorrect use and/or lack of understanding of how household products affect greywater can result in phosphorus posing a significant risk to the environment.

Characterization of a commercial dye-sensitised titania solar cell electrode

We have characterised a dye-sensitised nanoporous nanocrystalline titania film used in prototype photoelectrochemical solar cell production. From transmission electron microscopy the particles were seen as mixtures of tetrahedral and rhombohedral geometries with size distribution in the range between 10 and 25 nm. These particles were identified by X-ray diffraction as nanocrystals of anatase and brookite phases. The film was sensitised with a ruthenium (II) based chromophore for different times (between 0.5 and 24 h) and the penetration and coverage of the dye was studied using secondary ion mass spectroscopy. The dye was found to percolate through the whole of the titania film and was distributed uniformly. Using Rutherford backscattering, the composition of the film was determined and found to be 1 wt% Ru on maximum sensitisation. The optical properties of the dye-sensitised films were also measured which resulted in an increase of absorbance and a decrease of transmittance for dyeing times up to 8 h. Beyond this time the values remained unchanged and thus a semi-transparent film with luminous transmittance between 0.12 and 0.60 were obtained.

Electropolymerization of Pyrrole on Cotton Fabrics

Polypyrrole was electrochemically deposited onto cotton fabrics with the aid of a water-soluble adhesive. The conductivity and surface structure of the resultant polymer were studied, showing a templated dendritic growth on the surface of the cotton fabric. The mechanism for templated growth is discussed.