Publications

Journal article

Perni S, Piccirillo C, Kafizas A, Uppal MA, Pratten J, Wilson M, Parkin IPet al., 2010,

Antibacterial Activity of Light-Activated Silicone Containing Methylene Blue and Gold Nanoparticles of Different Sizes

, Journal of Cluster Science, Vol: 21, Pages: 427-427, ISSN: 1040-7278

Methylene Blue and methylene blue-gold nanoparticle mixtures were encapsulated in a silicone polymer using a swell-encapsulation-shrink technique. The antibacterial properties of the materials, when tested against Escherichia coli and Staphylococcus epidermidis, and exposed to laser light (660 nm), were sig- nificantly affected by both the presence and size of Au nanoparticles. Bacterial inactivation data were analysed using the Weibull inactivation model. For both E. coli and S. epidermidis the value of the parameter, indicating the time required to achieve the first log10 reduction in the viable count, decreased when Au nanopar- ticles of ca 2 nm diameter were present. Larger Au nanoparticles (diameters of 5 and 20 nm) in combination with methylene blue were also embedded in silicone. The values of these materials increased with nanoparticle diameter, indicating a reduction in antibacterial activity. In all cases E. coli had higher values than S. epidermidis.

Journal article

Kafizas A, Mills A, Parkin IP, 2010,

A comprehensive aerosol spray method for the rapid photocatalytic grid area analysis of semiconductor photocatalyst thin films.

, Analytica Chimica Acta, Vol: 663, Pages: 69-69, ISSN: 1873-4324

Indicator inks, previously shown to be capable of rapidly assessing photocatalytic activity via a novel photo-reductive mechanism, were simply applied via an aerosol spray onto commercially available pieces of Activ self-cleaning glass. Ink layers could be applied with high evenness of spread, with as little deviation as 5% upon UV-visible spectroscopic assessment of 25 equally distributed positions over a 10cmx10cm glass cut. The inks were comprised of either a resazurin (Rz) or dichloroindophenol (DCIP) redox dye with a glycerol sacrificial electron donor in an aqueous hydroxyethyl cellulose (HEC) polymer media. The photo-reduction reaction under UVA light of a single spot was monitored by UV-vis spectroscopy and digital images attained from a flat-bed scanner in tandem for both inks. The photo-reduction of Rz ink underwent a two-step kinetic process, whereby the blue redox dye was initially reduced to a pink intermediate resorufin (Rf) and subsequently reduced to a bleached form of the dye. In contrast, a simple one-step kinetic process was observed for the reduction of the light blue redox dye DCIP to its bleached intermediates. Changes in red-green-blue colour extracted from digital images of the inks were inversely proportional to the changes seen at corresponding wavelengths via UV-visible absorption spectroscopy and wholly indicative of the reaction kinetics. The photocatalytic activity areas of cuts of Activ glass, 10cmx10cm in size, were assessed using both Rz and DCIP indicator inks evenly sprayed over the films; firstly using UVA lamp light to activate the underlying Activ film (1.75mWcm(-2)) and secondly under solar conditions (2.06+/-0.14mWcm(-2)). The photo-reduction reactions were monitored solely by flat-bed digital scanning. Red-green-blue values of a generated 14x14 grid (196 positions) that covered the entire area of each film image were extracted using a custom-built program entitled RGB Extractor(C). A homogenous degradation over the 196 positi

Journal article

Uppal MA, Kafizas A, Ewing MB, Parkin IPet al., 2010,

The effect of initiation method on the size, monodispersity and shape of gold nanoparticles formed by the Turkevich method

, New Journal of Chemistry, Vol: 34, Pages: 2906-2906, ISSN: 1144-0546

The growth of gold nanoparticle (Au NP) colloids was initiated either thermally, by sonolysis, microwave (MWA) or hard ultra-violet (UVC; 254 nm) irradiation. The solutions were formulated analogous to Turkevich et al. and contained an auric acid gold source and different amounts of sodium tri-citrate reductant and stabiliser. A comparison of the initiation methods, using reagent solutions of equal concentration, was used to make gold nanoparticles. This showed marked differences in the final colloid, with variance in the monodispersity, size and shape of particles with initiation method. The physical size, shape and monodispersity of colloids formed were ascertained from transition electron microscopy (TEM) imaging. Properties such as average particle size and shape were directly related to changes in the surface plasmon resonance (SPR) band from UV-visible spectra. We demonstrate how a variety of simple initiation methods can be used to synthesise near monodisperse gold nanoparticles. More importantly, it is shown how the initiation method is fundamental to the eventual particle size of the resulting colloids; with sizes ranging from 11.0–11.9 nm in thermal reactions, 16.9–18.0 nm in sonolysis reactions, 11.3–17.2 nm in MWA reactions and 8.0–11.2 nm in UVC initiated reactions. Possible reaction pathways and mechanisms are put forward to explain these marked differences

Journal article

Kafizas A, Parkin IP, 2010,

The combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) of a gradating N-doped mixed phase titania thin film

, Journal of Materials Chemistry, Vol: 20, Pages: 2157-2157, ISSN: 0959-9428

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) was used to synthesise a film with gradating nitrogen dopant and phase from anatase to anatase–rutile mixtures on a single film. This is the first time such a mixed graduating system has been reported. The film was characterised via X-ray diffraction (XRD), Raman, wavelength dispersive X-ray (WDX) and X-ray photoelectron spectroscopy (XPS) mapping. Film thicknesses were determined by Swanepoel method manipulations of UV-visible reflectance spectra and side-on scanning electron microscopy (SEM). Electrical resistivities were derived from conductivities measured on a two-point probe and the photocatalytic activity assessed using a novel high-throughput digital image colour analysis method. This allowed for the systematic investigation on the effect of phase composition and nitrogen content on the films’ functional properties; indicating the effect of substitutional nitrogen doping and/or increased rutile content on the photocatalytic activity under UVA light and the benefit of substitutional nitrogen doping on the films electrical conductivity. Novel WDX, Raman and photocatalysis mapping tools are presented for derivation of a films Ti :Natomic ratio, anatase : rutile ratio and photocatalytic activity, respectively. Films synthesised by the cAPCVD route analysed in conjunction with mapping analysis tools provide a shortcut to identifying numerous phases and compositions and their functional property relationships on a single film, offering a rapid method for analysis of phase space.

Journal article

Uppal MA, Kafizas A, Lim TH, Parkin IPet al., 2010,

The extended time evolution size decrease of gold nanoparticles formed by the Turkevich method

, New Journal of Chemistry, Vol: 34, Pages: 1401-1401, ISSN: 1144-0546

Gold nanoparticle (Au NP) solutions were synthesised by the Turkevich reduction method and stored in either the light or dark. All solutions were monitored daily using UV-visible absorption spectroscopy and displayed surface plasmon resonance (SPR), typical of Au nanoparticle colloids. An increase in SPR intensity, a narrowing of the SPR peak as well as a gradual shift towards lower wavenumbers over time indicated a decrease in average nanoparticle diameter and a more mono-dispersed particle size. After two weeks no further changes were observable by UV-visible absorption spectroscopy. A series of high resolution transmission electron micrographs (HRTEM) taken over the evolution period confirmed that the plasmon resonance shifts correlated to a decrease in nanoparticle size. A systematic size decrease in nanoparticle size was also observed for solutions even after centrifugation to remove the excess un-reacted citrate and auric acid. This indicated that the size evolution was independent of further excess reactant chemistries and charge stabilities. The gold nanoparticle evolution followed an inverse Ostwald type growth, by which the size of the NPs decreases, in effect a digestive ripening. The aging process provides a reliable route to fairly mono-dispersed gold nanoparticles of ca. 11.5–12.5 nm in size via the Turkevich method.

Journal article

Kafizas A, Dunnill CW, Hyett G, Parkin IPet al., 2010,

Combinatorial CVD: New Oxynitride Photocatalysts

, ECS Transactions, Vol: 25, Pages: 139-139

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) was used to synthesise a film with mixed gradating phases from pure orthorhombic pseudo-brookite Ti3-δO4N (0.06 < δ < 0.25) to interstitial N-doped anatase TiO2 on a single film. This is the first time such a mixed graduating system has been reported. The film was characterized via Raman mapping and X-ray photocatalytic photoelectron spectroscopy (XPS). Film thicknesses were determined by Swanepoel method manipulations of UV-visible reflectance spectra and side-on scanning electron microscopy (SEM). Using a novel flat-bed digital scanning technique, the activity of the film to dichloroindophenol (DCIP) degradation under 365 nm light was also mapped. This allowed for the systematic investigation on the effect of pseudo-brookite: interstitial N-doped anatase phase composition, indicating pseudo-brookite to be the more photocatalytically active material. Films synthesized by the cAPCVD route analysed in conjunction with mapping analysis tools is a shortcut to identifying numerous phases and compositions and their functional property relationships on a single film, offering a rapid method for analysis of phase-space. Introduction

Journal article

Kafizas A, Dunnill CW, Parkin IP, 2010,

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) of niobium doped anatase; effect of niobium on the conductivity and photocatalytic activity

, Journal of Materials Chemistry, Vol: 20, Pages: 8336-8336, ISSN: 0959-9428

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) was used to synthesise anatase thin-films with gradating substitutionally doped niobium content on a single film. This is the first time such a combinatorial system has been formed by CVD or other means. The film was characterised via X-ray diffraction (XRD) mapping, Raman spectroscopy, atomic force microscopy (AFM), wavelength dispersive X-ray analysis (WDX) and X-ray photoelectron spectroscopy (XPS) analysis. Film thicknesses and band-gap energies were derived from Swanepoel thickness analysis and Tauc plots of transmittance spectra. Water droplet contact angle measurements displayed a UVC induced movement to super hydrophilic behaviour by a photo-induced superhydrophilicity (PSH) mechanism, irrespective of niobium levels. The film’s conductivity and photocatalytic activity to different light sources were mapped using a four-point probe and novel flat-bed digital scanning technique. This allowed for the systematic investigation on the effect of niobium doping. It was found that film growth rate in addition to niobium concentration directly influenced photocatalytic activity and electrical conductivity. Adirect relationship between conductivity of these Nb-doped anatase thin- films and photocatalytic activity to bothUVAand indoor lighting was also observed. Films synthesized by the cAPCVD route analysed in conjunction with mapping analysis tools provide a shortcut to investigating the effect of metal dopant on the functional properties for a wide range of phase space on a single film, enabling rapid analysis.

Journal article

Kafizas A, Adriaens D, Mills A, Parkin IPet al., 2009,

Simple method for the rapid simultaneous screening of photocatalytic activity over multiple positions of self-cleaning films.

, Physical Chemistry Chemical Physics, Vol: 11, Pages: 8367-8367, ISSN: 1463-9076

An intelligent ink, previously shown to be capable of rapidly assessing photocatalytic activity, was simply applied via a felt-pen onto a commercially available piece of Activ self-cleaning glass. The ink, comprising of redox dye resazurin and the sacrificial electron donor glycerol within an aqueous hydroxy ethyl cellulose (HEC) polymer media, was photocatalytically degraded in a two-step process. The key initial stage was the photo-reductive conversion of resazurin to resorufin, whereby a colour change from blue to pink occurred. The latter stage was the subsequent photo-reduction of the resorufin, where a slower change from pink to colourless was seen. Red and green components of red-green-blue colour extracted from flat-bed scanner digital images of resazurin ink coated photocatalytic films at intervals during the photocatalysis reaction were inversely proportional to the changes seen via UV-visible absorption spectroscopy and indicative of reaction kinetics. A 3 x 3 grid of intelligent ink was drawn onto a piece of Activ and a glass blank. The photocatalysis reaction was monitored solely by flat-bed digital scanning. Red-green-blue values of respective positions on the grid were extracted using a custom-built program entitled RGB Extractor. The program was capable of extracting a number of 5 x 5 pixel averages of red-green-blue components simultaneously. Allocation of merely three coordinates allowed for the automatic generation of a grid, with scroll-bars controlling the number of positions to be extracted on the grid formed. No significant change in red and green components for any position on the glass blank was observed; however, the Activ film displayed a homogenous photo-reduction of the dye, reaching maxima in red and minima in green components in 23 +/- 3 and 14 +/- 2 min, respectively. A compositionally graded N-doped titania film synthesised in house via a combinatorial APCVD reaction was also photocatalytically tested by this method where 247 positio

Journal article

Kafizas A, Kellici S, Darr JA, Parkin IPet al., 2009,

Titanium dioxide and composite metal/metal oxide titania thin films on glass: A comparative study of photocatalytic activity

, Journal of Photochemistry and Photobiology A: Chemistry, Vol: 204, Pages: 183-183, ISSN: 1010-6030

Titania and composite (Ag, Au, W) titania coatingswere prepared on glass microscope slides via a sol–gel dip-coating method. The resulting coatings were characterised by X-ray diffraction, Raman, scanning electron microscopy (SEM),wavelength dispersive X-ray (WDX), Brunauer–Emmett–Teller (BET) surface area analysis, atomic force microscopy (AFM) and UV–visible absorption techniques. Photocatalytic activ- ity of the coatings was determined by photomineralisation of stearic acid under 254, 365nm and white light sources monitored by FT-IR spectroscopy. These activities at 254 and 365nmlightwere represented as formal quantum efficiencies (FQEs) after determination of photon flux. Water contact angle mea- surements were made before and after irradiation with monochromatic 254 or 365nm light; all films demonstrated photo-assisted super hydrophilicity (PSH). A Ag:Au titania composite coatingwas found to be the most significant photoactive film. The mode of improved photocatalytic activitywas postulated in terms of a charge separation model. The Ag:Au TiO2 coating showed potential as a useful coating for hard self-cleaning surfaces due to its robustness, stability to cleaning and reuse and its photoactive response to indoor lighting conditions. ©

Conference paper

Kafizas A, Dunnill CW, Hyett G, Parkin IPet al., 2009,

Combinatorial CVD: New Oxynitride Photocatalysts

, Joint Conference on EuroCVD / 17th International Chemical Vapor Deposition Symposium (CVD) held jointly at the 216th Meeting of the Electrochemical-Society, Publisher: ELECTROCHEMICAL SOC INC, Pages: 1239-1250, ISSN: 1938-5862

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Citations: 6

Journal article

Dunnill CW, Aiken ZA, Kafizas A, Pratten J, Wilson M, Morgan DJ, Parkin IPet al., 2009,

White light induced photocatalytic activity of sulfur-doped TiO2 thin films and their potential for antibacterial application

, Journal of Materials Chemistry, Vol: 19, Pages: 8747-8747, ISSN: 0959-9428

Journal article

Kafizas A, Hyett G, Parkin IP, 2009,

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) of a mixed vanadium oxide and vanadium oxynitride thin film

, Journal of Materials Chemistry, Vol: 19, Pages: 1399-1399, ISSN: 0959-9428

A novel combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) technique was used to synthesise numerous vanadium oxide and vanadium oxynitride phases on a single film. This is the first example of cAPCVD having been used to synthesise a gradating mixed anion system. The film was characterised by X-ray diffraction (XRD) mapping, Raman, wavelength dispersive X-ray analysis (WDX) and X-ray photoelectron spectroscopy (XPS) analysis of positions along the film’s front edge allowed the chemical composition to be determined and correlated with XRD data. Film thicknesses were determined using side-on scanning electron microscopy (SEM). Functional property mapping of the optical transmittance/reflectance and electrical resistance allowed systematic investigation on the effects of oxygen content within a vanadium oxynitride film. cAPCVD used in conjunction with mapping analysis tools is a shortcut for identifying numerous, phases, compositions and properties and their relationships on a single film, and offers a rapid method for analysis of phase-space.

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