Stephen R. McEvoy

Bio: Stephen R. McEvoy is an academic researcher from Commonwealth Scientific and Industrial Research Organisation. The author has contributed to research in topics: Photocatalysis & Titanium dioxide. The author has an hindex of 12, co-authored 15 publications receiving 2496 citations.

Role of Nanoparticles in Photocatalysis

Abstract: The aim of this review paper is to give an overview of the development and implications of nanotechnology in photocatalysis. The topics covered include a detailed look at the unique properties of nanoparticles and their relation to photocatalytic properties. Current applications of and research into the use of nanoparticles as photocatalysts has also been reviewed. Also covered is the utilization of nanoparticles in doped, coupled, capped, sensitized and organic–inorganic nanocomposite semiconductor systems, with an effort to enhance photocatalytic and/or optical properties of commonly used semiconductor materials. The use of nanocrystalline thin films in electrochemically assisted photocatalytic processes has been included. Finally, the use of nanoparticles has made a significant contribution in providing definitive mechanistic information regarding the photocatalytic process.

Novel Photocatalyst: Titania-Coated Magnetite. Activity and Photodissolution

Abstract: Magnetic photocatalysts were synthesized by coating titanium dioxide particles onto colloidal magnetite and nano-magnetite particles. The photoactivity of the prepared coated particles was lower than that of single-phase TiO2 and was found to decrease with an increase in the heat treatment. These observations were explained in terms of an unfavorable heterojunction between the titanium dioxide and the iron oxide core, leading to an increase in electron−hole recombination. Interactions between the iron oxide core and the titanium dioxide matrix upon heat treatment were also seen as a possible cause of the observed low activities of these samples. Other issues considered include the physical and chemical characteristics of the samples, such as surface area and the presence of surface hydroxyl groups. Depending on the calcination conditions, these photocatalysts were found to suffer from varying degrees of photodissolution. Photodissolution tests revealed the greater the extent of the heat treatment, the low...

Photocatalytic oxidation of organics in water using pure and silver-modified titanium dioxide particles

Abstract: The simultaneous photocatalytic degradation of organic compounds and reduction of silver ions in titanium dioxide suspensions at pH 3.0-3.5 has been studied. The organic compounds of interest were sucrose and salicylic acid. The presence of silver ions in TiO 2 suspensions was found to enhance the photooxidation of high loadings (2001) μgC) of sucrose. However, for low sucrose loadings (100 μg C), pure TiO 2 particles performed as well as modified TiO 2 particles. An optimum silver ion loading of 2.0 at.% Ag + was observed for the mineralisation of 2000 μg C sucrose. At this silver ion loading, the mineralisation of 2000 μg C sucrose was enhanced by a factor of approximately 4.0 (based on 90% overall oxidation rates). In contrast, the addition of silver ions to TiO 2 suspensions did not have any significant effect on the photocatalytic mineralisation of salicylic acid to carbon dioxide, for both low and high loadings of salicylic acid in the suspension. It was also observed that pure TiO 2 particles performed as well as silver-modified TiO 2 particles for the degradation of 2000 μg C salicylic acid. The higher activity of silver ion-modified titanium dioxide suspensions for sucrose mineralisation is predominantly due to the presence of small silver particles on the titania surface, rather than due to the trapping of electrons during the reduction of silver ions. Approximately 50% of the initial mass of silver ions added to TiO 2 suspensions were reduced to metallic silver deposits in the presence of sucrose and salicylic acid mineralisation at the 2.0 at.% Ag + loading. Nanosize silver deposits on TiO 2 particles act as sites of electron accumulation where the reduction of adsorbed species such as oxygen occur. The enhanced reduction of oxygen through better electron-hole separation in Ag/TiO 2 particles compared to pure TiO 2 particles increases the rate of sucrose mineralisation. Therefore, it is proposed that the rate-limiting step in the sucrose photooxidation reaction is the transfer of electrons to dissolved oxygen molecules, whereas in the case of salicylic acid degradation and mineralisation, the rate-limiting step is the attack of salicylic acid molecules and its degradation intermediate products by holes and hydroxyl radicals. Hence silver deposits on TiO 2 particles are not beneficial for the photocatalytic degradation and mineralisation of salicylic acid but are advantageous for the mineralisation of sucrose.

Formation of nitrate and ammonium ions in titanium dioxide mediated photocatalytic degradation of organic compounds containing nitrogen atoms

Abstract: The photocatalytic oxidation of a related series of primary, secondary, and tertiary amines and other nitrogen- and sulfur-containing organic compounds over a UV-illuminated film of TiO{sub 2} has been studied. The compounds were as follows: n-pentylamine, piperidine, pyridine, phenylalanine, desipramine, thioridazine, penicillamine, isosorbide dinitrate, 4-nitrocatechol, 2,4-dinitrophenol, cyclophosphamide, 5-fluorouracil, atrazine, ethylenediaminetetracetic acid, and tetrabutylammonium phosphate. Both ammonium and nitrate ions were formed. The relative concentration of the two ions depended on the nature of the nitrogen in a compound, but was also influenced by the illumination time and concentration of the solute. It was found that for n-pentylamine, piperidine and pyridine, the rate of formation of ammonium ions was n-pentylamine {much gt} pyridine > piperidine. The order of rates of nitrate formation was pyridine = piperidine {much gt} pentylamine. For n-pentylamine the rate of formation of ammonium ions was {approximately}100 times that of nitrate.

Photocatalytic degradation of phenol in the presence of near-UV illuminated titanium dioxide

Abstract: The photocatalytic oxidation of aqueous phenol solutions in the presence of near-UV illuminated titanium dioxide has been studied at concentrations of 1–100 μM. The titanium dioxide was used as a free suspension and attached to sand. Under identical illumination conditions the degradation rate with the free suspension was approximately 2.6 times faster than with the immobilized catalyst. The quantum yield for the disappearance of phenol from a 100 μM solution in 0.1% TiO2 suspension illuminated with ‘Blacklight Blue’ 360–370 nm maximum emission radiation was approximately 0.6%. Direct solar illumination gave degradation rates comparable with that achieved with a 100 W medium pressure mercury lamp. In less than 1 h the midday summer sun degraded 90% of a 100 μM phenol solution, of volume 0.5 l in a 145 mm diameter open dish. The disappearance of phenol and the formation of carbon dioxide with illumination time was quantitatively accounted for by numerical integration of simultaneous differential equations based on Langmuir-Hinshelwood kinetics. An unexpected observation emerging from this analysis was a dependence of the adsorption equilibrium constant on the reciprocal of the initial phenol concentration. This dependence occurred at each solution pH studied. A possible explanation for the observation is given in terms of phenol reformation reactions competing with irreversible phenol degrading reactions and free diffusion of OH radicals from the catalyst surface at low solute concentrations.

A review on the visible light active titanium dioxide photocatalysts for environmental applications

Abstract: Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.

An overview of semiconductor photocatalysis

Abstract: The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .