http://hdl.handle.net/10197/2708 Fri, 24 May 2013 08:47:04 GMT 2013-05-24T08:47:04Z http://hdl.handle.net/10197/4309 The importance of laboratory water quality for studying initial bacterial adhesion during NF filtration processes Correia-Semiao, Andrea Joana; Habimana, O.; Cao, H.; Heffernan, R.; Safari, Ashkan; Casey, Eoin Biofouling of nanofiltration (NF) and reverse osmosis (RO) membranes for water treatment has been the subject of increased research effort in recent years. A prerequisite for undertaking fundamental experimental investigation on NF and RO processes is a procedure called compaction. This involves an initial phase of clean water permeation at high pressures until a stable permeate flux is reached. However water quality used during the compaction process may vary from one laboratory to another. The aim of this study was to investigate the impact of laboratory water quality during compaction of NF membranes. A second objective was to investigate if the water quality used during compaction influences initial bacterial adhesion. Experiments were undertaken with NF270 membranes at 15 bar for permeate volumes of 0.5L, 2L, and 5L using MilliQ, deionized or tap water. Membrane autopsies were performed at each permeation point for membrane surface characterisation by contact angle measurements, profilometry, and scanning electron microscopy. The biological content of compacted membranes was assessed by direct epi-fluorescence observation following nucleic acid staining. The compacted membranes were also employed as substrata for monitoring the initial adhesion of Ps. fluorescens under dynamic flow conditions for 30 minutes at 5 minutes intervals. Compared to MilliQ water, membrane compaction using deionized and tap water led to decreases in permeate flux, increase in surface hydrophobicity and led to significant buildup of a homogenous fouling layer composed of both living and dead organisms (>10⁶cells.cm−2). Subsequent measurements of bacterial adhesion resulted in cell loadings of 0.2×10⁵, 1.0×10⁵cells×cm−2 and 2.6×10⁵ cells.cm−2 for deionized, tap water and MilliQ water, respectively. These differences in initial cell adhesion rates demonstrate that choice of laboratory water can significantly impact the results of bacterial adhesion on NF membranes. Standardized protocols are therefore needed for the fundamental studies of bacterial adhesion and biofouling formation on NF and RO membrane. This can be implemented by first employing pure water during all membrane compaction proceduresand for the modelled feed solutions used in the experiment. Wed, 15 May 2013 00:00:00 GMT http://hdl.handle.net/10197/4309 2013-05-15T00:00:00Z http://hdl.handle.net/10197/4299 Functional Assessment for Predicting Charge-Transfer Excitations of Dyes in Complexed State: A Study of Triphenylamine-Donor Dyes on Titania for Dye-Sensitized Solar Cells Dev, Pratibha; Agrawal, Saurabh; English, Niall J. Time-dependent density functional theory (TD-DFT) was employed to calculate the UV/vis spectra for three of the triphenylamine (TPA)-donor dyes, TC1, L1, and LJ1, in isolation as well as when complexed with a titania nanoparticle. TPA-donor dyes are a class of promising organic dyes for use in dye-sensitized solar cells (DSSCs). The three dyes studied here are among the smallest of these molecules and provide important insight into the entire series of TPA dyes that are being explored as possible sensitizers in titania-based DSSCs. An attempt to calculate the optical spectra for these dyes within the B3LYP approximation to the exchange correlation functional produces erroneous results. However, Coulomb attenuated approximation (CAM-B3LYP) captures the correct photophysics of the dyes and produces more accurate charge-transfer excitation energies of their complexes with titania. This work shows that the extent to which a given approximation fails or succeeds to correctly predict the charge-transfer excitation energies in the isolated dyes is propagated in that it fails (or succeeds) to correctly predict the values of the excitation energies for the complexes. It is, therefore, important to determine the most appropriate functional for a dye before considering it in more complicated structures such as dye-titania complexes. Thu, 13 Dec 2012 00:00:00 GMT http://hdl.handle.net/10197/4299 2012-12-13T00:00:00Z http://hdl.handle.net/10197/4297 Comparative studies for evaluation of CO2 fixation in the cavity of the Rubisco enzyme using QM, QM/MM and linear-scaling DFT methods El-Hendawy, Morad M.; English, Niall J.; Mooney, Damian A. We evaluate the minimum energy configuration (MM) and binding free energy (QM/MM and QM) of CO2 to Rubisco, of fundamental importance to the carboxylation step of the reaction. Two structural motifs have been used to achieve this goal, one of which starts from the initial X-ray Protein Data Bank structure of Rubisco's active centre (671 atoms), and the other is a simplified, smaller model (77 atoms) which has been used most successfully, thus far, for study. The small model is subjected to quantum chemical density functional theory (DFT) studies, both in vacuo and using implicit solvation. The effects of the protein environment are also included by means of a hybrid quantum mechanical/molecular mechanical (QM/MM) approach, using PM6/AMBER and B3LYP/AMBER schemes. Finally, linear-scaling DFT methods have also been applied to evaluate energetic features of the large motif, and the result obtained for the binding free energy of the CO2 underlines the importance of the accurate modelling of the surrounding protein milieu using a full DFT description. Fri, 01 Feb 2013 00:00:00 GMT http://hdl.handle.net/10197/4297 2013-02-01T00:00:00Z http://hdl.handle.net/10197/4263 Comparative economic analysis of full scale MABR configurations Casey, Eoin; Syron, Eoin; Shanahan, John W.; Semmens, Michael J. The membrane-aerated biofilm reactor (MABR) is a technology that can deliver oxygen at high rates and transfer efficiencies. This paper provides a comparative cost analysis of the MABR compared to the activated sludge process. Membrane cost and electricity cost were found to be the critical parameters determining the relative feasibility of the conventional process to the membrane based process. The general downward trend in the market price of membranes and the steady increase in energy costs in recent years may prove to be a strong driver for the further development of this technology. 2008 IWA North American Membrane Research Conference, University of Massachusetts, Amherst, USA, August 10-13, 2008 Fri, 01 Aug 2008 00:00:00 GMT http://hdl.handle.net/10197/4263 2008-08-01T00:00:00Z http://hdl.handle.net/10197/4200 Dye sensitised solar cells with nickel oxide photocathodes prepared via scalable microwave sintering Gibson, Elizabeth A.; Awais, Muhammad; Dini, Danilo; Dowling, Denis P.; Pryce, Mary T.; Vos, Johannes G.; Boschloo, Gerrit; Hagfeldt, Anders Photoactive NiO electrodes for cathodic dye-sensitised solar cells (p-DSCs) have been prepared with thicknesses ranging between 0.4 and 3.0 mm by spray-depositing pre-formed NiO nanoparticles on fluorine-doped tin oxide (FTO) coated glass substrates. The larger thicknesses were obtained in sequential sintering steps using a conventional furnace (CS) and a newly developed rapid discharge sintering (RDS) method. The latter procedure is employed for the first time for the preparation of p-DSCs. In particular, RDS represents a scalable procedure that is based on microwave-assisted plasma formation that allows the production in series of mesoporous NiO electrodes with large surface areas for p-type cell photocathodes. RDS possesses the unique feature of transmitting heat from the bulk of the system towards its outer interfaces with controlled confinement of the heating zone. The use of RDS results in a drastic reduction of processing times with respect to other deposition methods that involve heating/calcination steps with associated reduced costs in terms of energy. P1-dye sensitized NiO electrodes obtained via the RDS procedure have been tested in DSC devices and their performances have been analysed and compared with those of cathodic DSCs derived from CS-deposited samples. The largest conversion efficiencies (0.12%) and incident photon-to-current conversion efficiencies, IPCEs (50%), were obtained with sintered NiO electrodes having thicknesses of B1.5–2.0 mm. In all the devices, the photogenerated holes in NiO live significantly longer (th B 1 s) than have previously been reported for P1-sensitized NiO photocathodes. In addition, P1-sensitised sintered electrodes give rise to relatively high photovoltages (up to 135 mV) when the triiodide–iodide redox couple is used. Thu, 06 Dec 2012 00:00:00 GMT http://hdl.handle.net/10197/4200 2012-12-06T00:00:00Z http://hdl.handle.net/10197/4199 Achieving enhanced DSSC performance by microwave plasma incorporation of carbon into TiO2 photoelectrodes Dang, Binh H.Q.; MacElroy, J. M. Don; Dowling, Denis P. The photoactivity of carbon-incorporated titanium dioxide (TiO2) has been widely reported. This study involves a novel approach to the incorporation of carbon into TiO2 through the use of microwave plasma processing. The process involved thermally treating printed TiO2 nanoparticle coatings in a microwave-induced argon-oxygen plasma containing low concentrations of methane. The resulting deposited carbon layer was characterized using XRD, XPS, Raman, UV–vis, ellipsometry, and optical profilometry. It was found that the methane gas was dissociated in the microwave plasma into its carbon species, which were then deposited as a nm-thick layer onto the TiO2 coatings, most likely in the form of graphite. The photovoltaic performances of both the TiO2 and the carbon-incorporated TiO2 were assessed through J-V and IPCE measurements of the N719-sensitized solar cells using the titania as their photoanodes. Up to a 72% improvement in the maximum power density (Pd-max) was observed for the carbon-incorporated TiO2 samples as compared to the TiO2, onto which no carbon was added. This improvement was found to be mainly associated with an increase in the short-circuit current density (Jsc), but independent from the open-circuit voltage (Voc), the filter factor (FF), and the level of dye adsorption. Possible contributory factors to the improved performance of the carbon-incorporated TiO2 were the enhanced electron conductivity and electron lifetime, both of which were elucidated through electrochemical impedance spectroscopy (EIS). When the surface layer was examined using XPS, the optimal carbon content on the TiO2 coating surface was found to be 8.4%, beyond which there was a reduction in the DSSC efficiency. Sat, 29 Dec 2012 00:00:00 GMT http://hdl.handle.net/10197/4199 2012-12-29T00:00:00Z http://hdl.handle.net/10197/4197 Spray deposited NiOx films on ITO substrates as photoactive electrodes for p-type dye-sensitized solar cells Awais, Muhammad; Dowling, Denis P.; Rahman, Mahfujur; Vos, Johannes G.; Decker, Franco; Dini, Danilo Spray deposition followed by sintering of nickel oxide (NiO x ) nanoparticles (average diameter: 40 nm) has been chosen as method of deposition of mesoporous NiO x coatings onto indium tin oxide (ITO) substrates. This procedure allows the scalable preparation of NiO x samples with large surface area (~103 times the geometrical area) and its potential for applications such as electrocatalysis or electrochemical solar energy conversion, which require high electroactivity in confined systems. The potential of these NiO x films as semiconducting cathodes for dye-sensitized solar cell (DSC) purposes has been evaluated for 0.3–3-μm-thick films of NiO x sensitized with erythrosine B (ERY). The electrochemical processes involving the NiO x coatings in the pristine and sensitized states were examined and indicated surface confinement as demonstrated by the linear dependence of the current densities with the scan rate of the cyclic voltammetry. Cathodic polarization of NiO x on ITO can also lead to the irreversible reduction of the underlying ITO substrate because of the mesoporous nature of the sintered NiO x film that allows the shunting of ITO to the electrolyte. ITO-based reduction processes alter irreversibly the properties of charge transfer through the ITO/NiOx interface and limit the range of potential to NiO x coatings sintered for DSC purposes. Fri, 01 Feb 2013 00:00:00 GMT http://hdl.handle.net/10197/4197 2013-02-01T00:00:00Z http://hdl.handle.net/10197/3744 Evaluation of microwave plasma oxidation treatments for the fabrication of photoactive un-doped and carbon-doped TiO2 coatings Dang, Binh H.Q.; Rahman, Mahfujur; MacElroy, J. M. Don; Dowling, Denis P. The photoactivity of both un-doped and carbon-doped titanium dioxide (TiO2) coatings has been widely reported. In this paper, the use of a microwave plasma as a novel oxidation treatment for the fabrication of these coatings is evaluated. The photoactivity performance of the microwave plasma-formed coatings is benchmarked against those fabricated through air furnace oxidation as well as those deposited using reactive magnetron sputtering. The un-doped and carbon-doped TiO2 coatings were prepared respectively by microwave plasma-oxidizing titanium metal sheets and sputter deposited titanium carbide thin films. The resulting oxides were characterized using XPS, XRD, FEG-SEM, and optical profilometry. The oxide layer thicknesses achieved over the 15 to 45 minute oxidation times were in the range of 0.15 to 3.44 µm. These coatings were considerably thicker than those obtained by air furnace oxidation. The microwave plasma-formed oxides also exhibited significantly higher surface roughness values compared with the magnetron-sputtered coatings. The photoactivity performance of both un-doped and carbon-doped coatings was assessed using photocurrent density measurements. Comparing the un-doped TiO2 coatings, it was observed that those obtained using the microwave plasma oxidation route yielded photocurrent density measurements that were 4.3 times higher than the TiO2 coatings of the same thickness that were deposited by sputtering. The microwave plasma-oxidized titanium carbide coatings did not perform as well as the un-doped TiO2 probably due to the presence of un-oxidized carbide in the coatings, which reduced their photoactivity. Fri, 25 May 2012 00:00:00 GMT http://hdl.handle.net/10197/3744 2012-05-25T00:00:00Z http://hdl.handle.net/10197/3625 Dynamical cage behaviour and hydrogen migration in hydrogen and hydrogen-tetrahydrofuran clathrate hydrates Gorman, Paul D.; English, Niall J.; MacElroy, J. M. Don Classical equilibrium molecular dynamics(MD) simulations have been performed to investigate dynamical properties of cage radial breathing modes and intra- and inter-cage hydrogen migration in both pure hydrogen and mixed hydrogen-tetrahydrofuran sII hydrates at 0.05 kbar and up to 250K. For the mixed H2-THF system in which there is single H2 occupation of the small cage (labelled ‘1SC 1LC’), we find that no H2 migration occurs, and this is also the case for pure H2 hydrate with single small-cavity occupation and quadruple occupancy for large cages (dubbed ‘1SC 4LC’). However, for the more densely-filled H2-THF and pure- H2 systems, in which there is double H2 occupation in the small cage (dubbed ‘2SC 1LC’ and ‘2SC 4LC’, respectively), there is an onset of inter-cage H2 migration events from the small cages to neighbouring cavities at around 200 K, with an approximate Arrhenius temperature-dependence for the migration rate from 200 to 250 K. It was found that these ‘cage hopping’ events are facilitated by temporary openings of pentagonal small-cage faces with the relaxation and reformation of key stabilising hydrogen bonds during and following passage. The cages remain essentially intact up to 250 K, save for transient hydrogen bond weakening and reformation during and after inter-cage hydrogen diffusion events in the 200 to 250 K range. The ‘breathing modes’, or underlying frequencies governing the variation in the cavities’ radii, exhibit a certain overlap with THF rattling motion in the case of large cavities, while a there is some overlap of small cages’ radial breathing modes with lattice acoustic modes. Tue, 24 Jan 2012 00:00:00 GMT http://hdl.handle.net/10197/3625 2012-01-24T00:00:00Z http://hdl.handle.net/10197/3495 Mechanisms for thermal conduction in hydrogen hydrate English, Niall J.; Gorman, Paul D.; MacElroy, J. M. Don Extensive equilibrium molecular dynamics (MD) simulations have been performed to investigate thermal conduction mechanisms via the Green-Kubo approach for (type II) hydrogen hydrate, at 0.05 kbar and between 30 and 250 K, for both lightly-filled H2 hydrates (1s4l) and for more densely-filled H2 systems (2s4l), in which four H2 molecules are present in the large cavities, with respective single- and double-occupation of the small cages. The TIP4P water model was used in conjunction with a fully atomistic hydrogen potential along with long-range Ewald electrostatics. It was found that substantially less damping in guest-host energy transfer is present in hydrogen hydrate as is observed in common type I clathrates (e.g., methane hydrate), but more akin in to previous results for type II and H methane hydrate polymorphs. This gives rise to larger thermal conductivities relative to common type I hydrates, and also larger than type II and H methane hydrate polymorphs, and a more crystal-like temperature dependence of the thermal conductivity. Mon, 23 Jan 2012 00:00:00 GMT http://hdl.handle.net/10197/3495 2012-01-23T00:00:00Z http://hdl.handle.net/10197/3438 A TD-DFT study of the effects of structural variations on the photochemistry of polyene dyes Agrawal, Saurabh; Dev, Pratibha; English, Niall J.; Thampi, Ravindranathan; MacElroy, J. M. Don We report a TD-DFT study of three polyene dyes namely: NKX-2553, NKX-2554 and NKX-2569 in isolation as well as upon their adsorption on TiO2 nanoparticles. By choosing closely related dyes we wish to focus on the effects of structural variations on the absorption and charge-transfer properties of these systems. These three dyes show a non-intuitive trend in their respective efficiencies and therefore, were chosen to shed light on the structural components that contribute to this behaviour. Although, NKX-2554 has an additional donor group, it is less efficient compared to the simpler NKX-2553 dye that contains only one donor group. When NKX-2554 structure is slightly modified by lengthening the linker-group, one obtains the most efficient dye among this set, namely, NKX-2569. In this work, we show that the changes in the donor moiety has very little or no effect on the efficiency of these dyes as can be seen in the case of NKX-2553 and NKX-2554. On the other hand, the improved performance of NKX-2569-titania complex can be understood to be a result of the longer linker group. A better understanding of these properties within different dye-titania complexes is important for the continual improvement of DSSCs. In this regards, this study will serve to provide guidelines to improve efficiencies of novel organic dyes. Thu, 06 Oct 2011 00:00:00 GMT http://hdl.handle.net/10197/3438 2011-10-06T00:00:00Z http://hdl.handle.net/10197/3386 Electrophoretic deposition of poly(3-decylthiophene) onto gold-mounted cadmium selenide nanorods Garate, Jose-Antonio; English, Niall J.; Singh, Ajay; Ryan, Kevin M.; Mooney, Damian A.; MacElroy, J. M. Don Molecular mechanisms of electrophoretic deposition (EPD) of poly(3-decylthiophene) (P3DT) molecules onto vertically aligned cadmium selenide arrays have been studied using large-scale, nonequilibrium molecular dynamics (MD), in the absence and presence of static external electric fields. The field application and larger polymer charges accelerated EPD. Placement of multiple polymers at the same lateral displacement from the surface reduced average deposition times due to “crowding”, giving monolayer coverage. These findings were used to develop and validate Brownian dynamics simulations of multilayer polymer EPD in scaled-up systems with larger inter-rod spacings, presenting a generalized picture in qualitative agreement with random sequential adsorption. Wed, 21 Sep 2011 00:00:00 GMT http://hdl.handle.net/10197/3386 2011-09-21T00:00:00Z http://hdl.handle.net/10197/3385 Dynamical and energetic properties of hydrogen and hydrogen–tetrahydrofuran clathrate hydrates Gorman, Paul D.; English, Niall J.; MacElroy, J. M. Don Classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the dynamical and energetic properties in hydrogen and mixed hydrogen-tetrahydrofuran sII hydrates at 30 and 200K and 0.05 kbar, and also at intermediate temperatures, using SPC/E and TIP4P-2005 water models. The potential model is found to have a large impact on overall density, with the TIP4P-2005 systems being on average 1 % more dense than their SPC/E counterparts, due to the greater guest-host interaction energy. For the lightly-filled mixed H2-THF system, in which there is single H2 occupation of the small cage (1s1l), we find that the largest contribution to the interaction energy of both types of guest is the van der Waals component with the surrounding water molecules in the constituent cavities. For the more densely-filled mixed H2-THF system, in which there is double H2 occupation in the small cage (2s1l), we find that there is no dominant component (i.e., van der Waals or Coulombic) in the H2 interaction energy with the rest of the system, but for the THF molecules, the dominant contribution is again the van der Waals interaction with the surrounding cage-water molecules; again, the Coulombic component increases in importance with increasing temperature. The lightly-filled pure H2 hydrate (1s4l) system exhibits a similar pattern vis-à-vis the H2 interaction energy as for the lightly-filled mixed H2-THF system, and for the more densely-filled pure H2 system (2s4l), there is no dominant component of interaction energy, due to the multiple occupancy of the cavities. By consideration of Kubic harmonics, there is some evidence of preferential alignment of the THF molecules, particularly at 200 K; this was found to arise at higher temperatures due to transient hydrogen bonding of the oxygen atom in THF molecules with the surrounding cage-water molecules. Mon, 03 Oct 2011 00:00:00 GMT http://hdl.handle.net/10197/3385 2011-10-03T00:00:00Z http://hdl.handle.net/10197/3016 First-principles study of the excited-state properties of coumarin-derived dyes in dye-sensitized solar cells Agrawal, Saurabh; Dev, Pratibha; English, Niall J.; Thampi, Ravindranathan; MacElroy, J. M. Don Using Time-Dependent Density Functional Theory (TD-DFT), we have investigated the optical properties of dye-sensitized solar cells (DSSCs) comprised of TiO2 nanoparticle sensitized with two coumarins, namely, NKX-2311 and NKX-2593. The two sensitizers (dyes) differ only in their linker moieties and are shown to have different absorption spectra when adsorbed on to the TiO2 surface. Knowledge of different light absorption and charge transfer (CT) behavior within these complexes is useful for further improving the photo-dynamics of newer organic dyes presently being designed and investigated worldwide. Moreover, we have also investigated the effect of deprotonation of the sensitizers' carboxylic groups during adsorption on the titania surface and the excited state electronic properties of the resulting species. Thu, 23 Jun 2011 00:00:00 GMT http://hdl.handle.net/10197/3016 2011-06-23T00:00:00Z http://hdl.handle.net/10197/2972 Disinfection of meticillin-resistant Staphylococcus aureus and Staphylococcus epidermidis biofilms using a remote non-thermal gas plasma Cotter, John J.; Maguire, Paul; Soberon, Felipe; Daniels, Stephen; O'Gara, James P.; Casey, Eoin The effective disinfection of hospital surfaces is recognised as an important factor in preventing hospital-acquired infections. The purpose of this study was to quantify the disinfection rate of a novel gas plasma system on clinically relevant biofilms. Clinical isolates of Staphylococcus epidermidis and methicillin-resistant Staphylococcus aureus (MRSA) were grown as biofilms on glass surfaces and tested in a disinfection container remote from the plasma source. The strains used in this study were known to produce substantial quantities of biofilm and average log10 counts were 9.0 and 9.1 cfu/cm2 for S. epidermidis and MRSA respectively. Counts were reduced by between 4 and 4.5 log10 after 1 h of exposure for MRSA and S. epidermidis respectively. More prolonged treatment in the case of MRSA biofilms resulted in a 5.5 log10 reduction after 90 min. Biofilm samples were also placed in medical device packaging bags and similar rates of disinfection were observed. Sun, 01 May 2011 00:00:00 GMT http://hdl.handle.net/10197/2972 2011-05-01T00:00:00Z http://hdl.handle.net/10197/2960 Factors influencing 4-fluorobenzoate degradation in biofilm cultures of Pseudomonas knackmussii B13 Misiak, Katarzyna; Casey, Eoin; Murphy, Cormac D. Membrane aerated biofilm reactors (MABRs) have potential in wastewater treatment as they permit simultaneous COD minimisation, nitrification and denitrification. Here we report on the application of the MABR to the removal of fluorinated xenobiotics from wastewater, employing a Pseudomonas knackmussii monoculture to degrade the model compound 4-fluorobenzoate. Growth of biofilm in the MABR using the fluorinated compound as the sole carbon source occurred in two distinct phases, with early rapid growth (up to 0.007 h−1) followed by ten-fold slower growth after 200 h operation. Furthermore, the specific 4-fluorobenzoate degradation rate decreased from 1.2 g g−1 h−1 to 0.2 g g−1 h−1, indicating a diminishing effectiveness of the biofilm as thickness increased. In planktonic cultures stoichiometric conversion of substrate to the fluoride ion was observed, however in the MABR, approximately 85% of the fluorine added was recovered as fluoride, suggesting accumulation of ‘fluorine’ in the biofilm might account for the decreasing efficiency. This was investigated by culturing the bacterium in a tubular biofilm reactor (TBR), revealing that there was significant fluoride accumulation within the biofilm (0.25 M), which might be responsible for inhibition of 4-fluorobenzoate degradation. This contention was supported by the observation of the inhibition of biofilm accumulation on glass cover slips in the presence of 40 mM fluoride. These experiments highlight the importance of fluoride ion accumulation on biofilm performance when applied to organofluorine remediation. Sun, 01 May 2011 00:00:00 GMT http://hdl.handle.net/10197/2960 2011-05-01T00:00:00Z http://hdl.handle.net/10197/2896 Conversion of amorphous TiO2 coatings into their crystalline form using a novel microwave plasma treatment Dang, Binh H.Q.; Rahman, Mahfujur; MacElroy, J. M. Don; Dowling, Denis P. Crystalline titanium dioxide (TiO2) coatings have been widely used in photo-electrochemical solar cell applications. In this study, TiO2 and carbon-doped TiO2 coatings were deposited onto unheated titanium and silicon wafer substrates using a DC closed-field magnetron sputtering system. The resultant coatings had an amorphous structure and a post-deposition heat treatment is required to convert this amorphous structure into the photoactive crystalline phase(s) of TiO2. This study investigates the use of a microwave plasma heat treatment as a means of achieving this crystalline conversion. The treatment involved placing the sputtered coatings into a 2.45 GHz microwave-induced nitrogen plasma where they were heated to approximately 550°C. It was observed that for treatment times as short as 1 minute, the 0.25-µm thick coatings were converted into the anatase crystalline phase of TiO2. The coatings were further transformed into the rutile crystalline phase after treatments at higher temperatures. The doping of TiO2 with carbon was found to result in a reduction in this phase transformation temperature, with higher level of doping (up to 5.8% in this study) leading to lower anatase-to-rutile transition temperature. The photoactivity performance of both doped and un-doped coatings heat-treated using both furnace and microwave plasma was compared. The carbon-doped TiO2 exhibited a 29% increase in photocurrent density compared to that observed for the un-doped coating. Comparing carbon-doped coatings heat-treated using the furnace and microwave plasma, it was observed that the latter yielded a 19% increase in photocurrent density. This enhanced performance may be correlated to the differences in the coatings’ surface morphology and band gap energy, both of which influence the coatings’ photoabsorption efficiency. Mon, 25 Jul 2011 00:00:00 GMT http://hdl.handle.net/10197/2896 2011-07-25T00:00:00Z http://hdl.handle.net/10197/2886 Activation of hematite nanorod arrays for photoelectrochemical water splitting Morrish, Rachel; Rahman, Mahfujur; MacElroy, J. M. Don; Wolden, Colin Andrew Hematite nanorod arrays were activated through proper control of annealing conditions. The 100-fold improvement in photocurrent was correlated with increased absorption and Sn doping from the tin oxide coated glass substrate. The low onset potential is attributed to a reduction in surface defects, while the morphology is credited for promoting tin diffusion and facilitating electron transport. Mon, 18 Apr 2011 00:00:00 GMT http://hdl.handle.net/10197/2886 2011-04-18T00:00:00Z http://hdl.handle.net/10197/2877 A theoretical thermodynamic investigation of cascade reactions in dinuclear octa-azacryptates involving carbon dioxide English, Niall J.; Mooney, Damian A. This paper investigates the thermodynamics of gas-phase CO2 cascade uptake-reactions in the form of carbonate or methoxycarbonate anions in the host cavity of various dinuclear octa-azacryptates of m-CH2C6H4CH2 and 2,5-furano-spaced hosts, L1 and L2 cryptands, using density functional theory (DFT). The cascade process involves two stages, namely the formation of dinuclear cryptate complexes and the subsequent formation of either μ-carbonato cryptate complexes or μ-monomethylcarbonato cryptates. The geometric and electronic structures are also investigated to determine the parameters which affect the stability of the complexes. Natural bond orbital (NBO) analysis has been used to investigate the interactions between the trapped anion and its host. The ion selectivity has been studied in terms of the formation of dinuclear crypate complexes, while the basicity and nucleophilicity of cryptands towards Lewis acids have also been studied, and good agreement was found vis-à-vis available experimental data. Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/10197/2877 2011-01-01T00:00:00Z http://hdl.handle.net/10197/2792 Electronic structure and origin of visible-light activity of C-doped cubic In2O3 from first-principles calculations Long, Run; English, Niall J. The origin of the experimentally observed band gap narrowing and red-shift of the adsorption edge of cubic In2O3 induced by C doping has been investigated using density functional theory calculations. We have compared the stability of all these doped systems based on the calculated formation energy as a function of the oxygen chemical potential. The calculated electronic structures show that: (I) at low C concentration, substitutional replacement of O by C could lead to small gap narrowing, owing to C 2p states below the conduction band minimum while interstitial C doping does not induce band gap narrowing; and (II) at high C concentration, C2p states mix well with O 2p states above the valence band, which may account for the experimentally observed red-shift of the absorption edge. Thu, 19 Aug 2010 00:00:00 GMT http://hdl.handle.net/10197/2792 2010-08-19T00:00:00Z http://hdl.handle.net/10197/2790 First-principles calculation of electronic structure of V-doped anatase TiO2 Long, Run; English, Niall J. The energetic and electronic structures of V-doped anatase TiO2 have been investigated systematically by the GGA+U approach, including replacement of Ti by V in the absence and presence of oxygen vacancies and the presence of an interstitial site. It was found that V should exist as a V4+ ion in the replacement of Ti in the anatase lattice, the electron transitions of which to the conduction band from V 3d states are responsible for the experimentally observed visible-light absorption. The influence of V dopant concentration on the electronic and magnetic properties is also discussed, such as the influence of the U value in systems containing oxygen vacancies and spin flip phenomena for interstitial V-doping. Mon, 23 Aug 2010 00:00:00 GMT http://hdl.handle.net/10197/2790 2010-08-23T00:00:00Z http://hdl.handle.net/10197/2789 Electronic properties of F/Zr co-doped anatase TiO2 photocatalysts from GGA + U calculations Long, Run; English, Niall J. The energetic and electronic properties of F and/or Zr-doped anatase TiO2 are investigated by first-principles calculations. For F-doping, reduced Ti3+ ions are formed and Ti orbitals lie slightly below the conduction band, leading to band gap narrowing. For Zr-doping, Zr 4d orbitals reside well into the conduction band, with essentially no band gap change. For F/Zr–codoping, the electronic structure is similar to that for F–monodoping, where Ti3+ gap states are induced by both the oxygen vacancy and F dopant. The influence of oxygen vacancies indicates that interplay between dopants and oxygen vacancies is key for improvement of photocatalytic activity. The theoretical findings present a reasonable explanation of recent experimental results. Fri, 08 Oct 2010 00:00:00 GMT http://hdl.handle.net/10197/2789 2010-10-08T00:00:00Z http://hdl.handle.net/10197/2759 Model-based comparative performance analysis of membrane aerated biofilm reactor configurations Syron, Eoin; Casey, Eoin The potential of the membrane aerated biofilm reactor (MABR) for high-rate bio-oxidation was investigated. A reaction-diffusion model was combined with a preliminary hollow-fiber MABR process model to investigate reaction rate-limiting regime and to perform comparative analysis on prospective designs and operational parameters. High oxidation fluxes can be attained in the MABR if the intra-membrane oxygen pressure is sufficiently high, however the volumetric oxidation rate is highly dependent on the membrane specific surface area and therefore the maximum performance, in volumetric terms, was achieved in MABRs with relatively thin fibers. The results show that unless the carbon substrate concentration is particularly high, there does not appear to be an advantage to be gained by designing MABRs on the basis of thick biofilms even if oxygen limitations can be overcome. Tue, 15 Apr 2008 00:00:00 GMT http://hdl.handle.net/10197/2759 2008-04-15T00:00:00Z http://hdl.handle.net/10197/2758 Studies on the effect of concentration of a self-inhibitory substrate on biofilm reaction rate under co-diffusion and counter diffusion configurations Syron, Eoin; Kelly, Hugh; Casey, Eoin A simple mathematical model was developed to investigate the utilization rate of a self-inhibitory substrate in idealised biofilm reactors operating with either counter-diffusion or co-diffusion of oxygen and phenol. This study has implications for the development of membrane-supported biofilm technologies, such as the membrane-aerated biofilm reactor. An unsteady-state formulation of the model was used to investigate the effect of shock loads of phenol on biofilm performance. It was found that the counter-diffusion configuration may be advantageous under high phenol concentrations provided the biofilm thickness is above a critical value. The performance advantage of the counter-diffusion configuration is gained by the presence of an oxygen depleted layer, adjacent to the liquid–biofilm interface which acts as a diffusive barrier to phenol transport to the region of respiratory activity. Mon, 15 Jun 2009 00:00:00 GMT http://hdl.handle.net/10197/2758 2009-06-15T00:00:00Z http://hdl.handle.net/10197/2757 Membrane aerated biofilms for high rate biotreatment : performance appraisal, engineering principles, scale-up and development requirements Syron, Eoin; Casey, Eoin Diffusion of the electron acceptor is the rate controlling step in virtually all biofilm reactors employed for aerobic wastewater treatment. The membrane-aerated biofilm reactor (MABR) is a technology that can deliver oxygen at high rates and transfer efficiencies, thereby enhancing the biofilm activity. This paper provides a comparative performance rate analysis of the MABR in terms of its application for carbonaceous pollutant removal, nitrification/denitrification and xenobiotic biotreatment. We also describe the mechanisms influencing process performance in the MABR and the inter-relationships between these factors. The challenges involved in scaling-up the process are discussed with recommendations for prioritization of research needs. Sat, 15 Mar 2008 00:00:00 GMT http://hdl.handle.net/10197/2757 2008-03-15T00:00:00Z http://hdl.handle.net/10197/2746 Tracer measurements reveal experimental evidence of biofilm consolidation Casey, Eoin The ability to simultaneously measure both biofilm thickness and the mass transfer coefficient of an inert tracer through it provides a powerful method to study biofilm development. In this communication previously published data has been collated to interpret global trends in biofilm structure during the transition towards steady-state. It appears that sudden changes in biofilm structure (directly related to the rate of change of biofilm mass transfer resistance) may occur following transitions in rate of biomass production. These observations are consistent with the concept of consolidation, recently introduced into spatially structured biofilm mathematical models to account for structural realignment of the biofilm under dynamic conditions. Thu, 01 Nov 2007 00:00:00 GMT http://hdl.handle.net/10197/2746 2007-11-01T00:00:00Z http://hdl.handle.net/10197/2745 Characterisation of a modified rotating disk reactor for the cultivation of Staphylococcus epidermidis biofilm Cotter, John J.; O'Gara, James P.; Stewart, Philip S.; Pitts, Betsey; Casey, Eoin Aims:  The purpose of this study was to develop a system that would allow biofilms to be cultivated under strictly defined conditions in terms of dissolved oxygen, fluid shear and to assess whether the method was suitable for the detection of respiratory activity stratification in biofilm samples. Methods:  The system is a modified version a commercially available laboratory biofilm reactor and incorporates a number of features such as the provision of defined levels of dissolved oxygen, constant average shear, enhanced gas–liquid mass transfer, aseptic operation and the ability to remove biofilm for ex situ analysis during or after continuous cultivation. Conclusions:  The system was shown to be effective for the characterization of the effects of dissolved oxygen on a pure culture of Staphylococcus epidermidis. The versatility of the system offers the potential for cultivating pure culture biofilm in defined, controlled conditions and facilitates a range of analyses that can be performed ex situ. Significance and Impact of the Study:  The ability to provide strict regulation of environmental conditions and enhanced transfer of oxygen to the biofilm during cultivation are important, first because oxygen is known to regulate biofilm development in several micro-organisms and second because many conventional biofilm cultivation systems may not provide adequate oxygen supply to the biofilm. Wed, 01 Dec 2010 00:00:00 GMT http://hdl.handle.net/10197/2745 2010-12-01T00:00:00Z http://hdl.handle.net/10197/2744 Oxygen-mediated regulation of biofilm development is controlled by the alternative sigma factor sigma(B) in Staphylococcus epidermidis Cotter, John J.; O'Gara, James P.; Mack, Dietrich; Casey, Eoin Using a modified rotating-disk reactor to sparge oxygen to Staphylococcus epidermidis cultures, we found that oxygen negatively regulates biofilm development by influencing the activity of {sigma}B. Under anaerobic conditions, increased {sigma}B activity activates icaADBC, which encodes enzymes responsible for polysaccharide intercellular adhesin synthesis, by repressing transcription of the negative regulator icaR. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/10197/2744 2009-01-01T00:00:00Z http://hdl.handle.net/10197/2743 Treatment of fluoroacetate by a Pseudomonas fluorescens biofilm grown in membrane aerated biofilm reactor Heffernan, Barry; Murphy, Cormac D.; Syron, Eoin; Casey, Eoin Fluorinated organic compounds have widespread applications, and their accumulation in the environment is a concern. Biofilm reactors are an effective technology for the treatment of contaminated wastewater, yet almost no research has been conducted on the effectiveness of biofilms for the biodegradation of fluorinated aliphatic compounds. In this paper we describe experiments undertaken to investigate the degradation of fluoroacetate using a membrane aerated biofilm reactor (MABR) by Pseudomonas fluorescens DSM8341. The concentration of fluoroacetate in the medium influenced biofilm structure, with less dense biofilm observed at lower fluoroacetate loading rates. As biofilm thickness increased, oxygen utilization decreased, probably as a consequence of increased resistance to oxygen transfer. Furthermore, most of the biofilm was anaerobic, since oxygen penetration depth was less than 1000 μm. Biofilm performance, in terms of fluoroacetate removal efficiency, was improved by decreasing the fluoroacetate loading rate, however increasing the intramembrane oxygen pressure had little effect on biofilm performance. A mathematical model showed that while fluoroacetate does not penetrate the entire biofilm, the defluorination intermediate metabolite glycolate does, and consequently the biofilm was not carbon limited at the biofilm−membrane interface where oxygen concentrations were highest. The model also showed the accumulation of the free fluoride ion within the biofilm. Overflow metabolism of glycolate was identified to be most likely a result of a combination of oxygen limitation and free fluoride ion inhibition. The study demonstrated the potential of MABR for treating wastewater streams contaminated with organofluorine compounds. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/10197/2743 2009-01-01T00:00:00Z http://hdl.handle.net/10197/2742 Comparison of planktonic and biofilm cultures of Pseudomonas fluorescens DSM 8341 cells grown on fluoroacetate Heffernan, Barry; Murphy, Cormac D.; Casey, Eoin Comparisons between the physiological properties of Pseudomonas fluorescens biofilm cells grown in a tubular biofilm reactor and planktonic cells grown in a chemostat were performed. Fluoroacetate was the sole carbon source for all experiments. The performance of cells was assessed using cell cycle kinetics and by determining specific fluoroacetate utilization rates. Cell cycle kinetics were studied by flow cytometry in conjunction with the fluorescent stain propidium iodide. Determination of the DNA content of planktonic and biofilm cultures showed little difference between the two modes of growth. Cultures with comparable specific glycolate utilization rates had similar percentages of cells in the B phase of the cell cycle, indicating similar growth rates. Specific fluoroacetate utilization rates showed the performance of planktonic cells to be superior to that of biofilm cells, with more fluoroacetate utilized per cell at similar specific fluoroacetate loading rates. A consequence of this decreased biofilm performance was the accumulation of glycolate in the effluent of biofilm cultures. This accumulation of glycolate was not observed in the effluent of planktonic cultures. Spatial stratification of oxygen within the biofilm was identified as a possible explanation for the overflow metabolism of glycolate and the decreased performance of the biofilm cells. Fri, 01 May 2009 00:00:00 GMT http://hdl.handle.net/10197/2742 2009-05-01T00:00:00Z http://hdl.handle.net/10197/2730 Application of a novel microwave plasma treatment for the sintering of nickel oxide coatings for use in dye-sensitized solar cells Awais, Muhammad; Rahman, Mahfujur; MacElroy, J. M. Don; Dini, Danilo; Vos, Johannes G.; Dowling, Denis P. In this study the use of microwave plasma sintering of nickel oxide (NiOx) particles for use as p-type photoelectrode coatings in dye-sensitized solar cells (DSSCs) is investigated. NiOx was chosen as the photocathode for this application due to its stability, wide band gap and p-type nature. For high light conversion efficiency DSSCs require a mesoporous structure exhibiting a high surface area. This can be achieved by sintering particles of NiOx onto a conductive substrate. In this study the use of both 2.45 GHz microwave plasma and conventional furnace sintering were compared for the sintering of the NiOx particles. Coatings 1 to 2.5 μm thick were obtained from the sintered particles (mean particle size of 50 nm) on 3 mm thick fluorine-doped tin oxide (FTO) coated glass substrates. Both the furnace and microwave plasma sintering treatments were carried out at ~ 450 °C over a 5 minute period. Dye sensitization was carried out using Erythrosin B and the UV-vis absorption spectra of the NiOx coatings were compared. A 44% increase in the level of dye adsorption was obtained for the microwave plasma sintered samples as compared to that obtained through furnace treatments. While the photovoltaic performance of the DSSC fabricated using the microwave plasma treated NiOx coatings exhibited a tenfold increase in the conversion efficiency in comparison to the furnace treated samples. This enhanced performance was associated with the difference in the mesoporous structure of the sintered NiOx coatings. Mon, 25 Jul 2011 00:00:00 GMT http://hdl.handle.net/10197/2730 2011-07-25T00:00:00Z http://hdl.handle.net/10197/2729 Rapid depletion of dissolved oxygen in 96 well microtitre plate Staphylococcus epidermidis biofilm assays promotes biofilm development and is influenced by inoculum cell concentration Cotter, John J.; O'Gara, James P.; Casey, Eoin Biofilm-related research using 96-well microtiter plates involves static incubation of plates indiscriminate of environmental conditions, making oxygen availability an important variable which has not been considered to date. By directly measuring dissolved oxygen concentration over time we report here that dissolved oxygen is rapidly consumed in Staphylococcus epidermidis biofilm cultures grown in 96-well plates irrespective of the oxygen concentration in the gaseous environment in which the plates are incubated. These data indicate that depletion of dissolved oxygen during growth of bacterial biofilm cultures in 96-well plates may significantly influence biofilm production. Furthermore higher inoculum cell concentrations are associated with more rapid consumption of dissolved oxygen and higher levels of S. epidermidis biofilm production. Our data reveal that oxygen depletion during bacterial growth in 96-well plates may significantly influence biofilm production and should be considered in the interpretation of experimental data using this biofilm model. Sat, 01 Aug 2009 00:00:00 GMT http://hdl.handle.net/10197/2729 2009-08-01T00:00:00Z http://hdl.handle.net/10197/2724 Energetic and electronic properties of P Doping at the rutile TiO2 (110) Surface from First Principles Long, Run; English, Niall J. The energetic and electronic properties of various P doping configurations at the rutile TiO2 (110) surface are investigated by first-principles density functional theory (DFT) calculations. Several substitution and adsorption configurations for P impurities at the surface and the subsurface are considered. The stability of the P-doped systems is compared on the basis of the calculated formation energy and adsorption energy. Our calculated results indicate that the P impurities replace surface Ti atoms preferentially under O-rich growth conditions，and surface O atoms under Ti-rich conditions. In addition, it was found that the creation of oxygen vacancies favors P incorporation at substitution sites but not at adsorption sites. Doping with a single P atom into an O site may lead to either anionic or cationic states in the dopant. This causes either band-to-band transitions or introduces gap states to band transitions, with the former corresponding to a small band gap narrowing or broadening and the latter resulting in obvious reductions of photon transition energy. Substitutional replacement of Ti atoms by P atoms and adsorption on the surface (P-cation doping) results in either a small band reduction or a slight band gap enlargement, depending on the doping sites. It is speculated that the interaction between P impurities and surface oxygen vacancies will lead to further enhanced photocatalytic activity in the visible light region. Mon, 20 Apr 2009 00:00:00 GMT http://hdl.handle.net/10197/2724 2009-04-20T00:00:00Z http://hdl.handle.net/10197/2723 First-principles study of S doping at the rutile TiO2 (110) surface Long, Run; English, Niall J.; Dai, Ying The structural, energetic and electronic properties of various S doping configurations by substitution and adsorption at the rutile TiO2 (110) surface have been investigated by first-principles density functional theory (DFT) calculations. The stability of these configurations has been compared on the basis of the calculated formation and adsorption energies. Our results indicate that S dopants replace surface O atoms or bind to Ti atoms preferentially. Moreover, implantation of S dopants into the rutile lattice favored the formation of oxygen vacancies, which promotes further S incorporation. Doping of single S atoms into Ti sites (S-cation doping) led to relatively small reductions of the photon transition energy, while S-substitution of O atoms (S-anion doping) and adsorption on the surface (S-cation/anion doping) resulted in significant red-shifts of the optical absorption edge. Our results suggest that the interplay between S impurities and oxygen vacancies does not enhance visible light absorption in an obvious way, and helps to rationalise recent experimental studies. Tue, 15 Sep 2009 00:00:00 GMT http://hdl.handle.net/10197/2723 2009-09-15T00:00:00Z http://hdl.handle.net/10197/2722 First-principles calculation of nitrogen-tungsten codoping effects on the band structure of anatase-titania Long, Run; English, Niall J. The electronic properties and photocatalytic activity of nitrogen (N) and/or tungsten (W)-doped anatase are calculated using density functional theory. For N-doping, isolated N 2p states above the top of the valence band are responsible for experimentally observed redshifts in the optical absorption edge. For W-doping, W 5d states below the conduction band lead to band gap narrowing; the transition energy is reduced by 0.2 eV. Addition of W to the N-doped system yields significant band gap narrowing gap by 0.5 eV. This rationalizes recent experimental data which showed that N/W-doped titania exhibits higher visible-light photocatalytic efficiency than either N- or W-doping alone. Thu, 02 Apr 2009 00:00:00 GMT http://hdl.handle.net/10197/2722 2009-04-02T00:00:00Z http://hdl.handle.net/10197/2720 Synergistic effects on band gap-narrowing in titania by codoping from first-principles calculations Long, Run; English, Niall J. The large intrinsic band gap in TiO2 has hindered severely its potential application for visible-light irradiation. In this study, we have used a passivated approach to modify the band edges of anatase-TiO2 by codoping of X (N, C) with transition metals (TM=W, Re, Os) to extend the absorption edge to longer visible-light wavelengths. It was found that all the codoped systems can narrow the band gap significantly; in particular, (N+W)-codoped systems could serve as remarkably better photocatalysts with both narrowing of the band gap and relatively smaller formation energies and larger binding energies than those of (C+TM) and (N+TM)-codoped systems. Our theoretical calculations provide meaningful guides for experiments to develop more powerful visible-light photocatalysts. Fri, 12 Feb 2010 00:00:00 GMT http://hdl.handle.net/10197/2720 2010-02-12T00:00:00Z http://hdl.handle.net/10197/2719 Band gap engineering of (N, Ta)-codoped TiO2 : a first-principles calculation Long, Run; English, Niall J. The electronic properties and photocatalytic activity of X (N, C) / transition metal (TM=Ta, Hf, Fe) – codoped anatase TiO2 have been investigated using density functional theory. It was found that only the (N, Ta)-codoping case narrows the band gap significantly by about 0.48 eV, driven by the continuum-like p-d hybridized states above the top of valence band and d states at the bottom of conduction band. The calculated energy results suggest that codoping of Ta with N can increase the N concentration in N-doped TiO2 based on energy results. Wed, 29 Jul 2009 00:00:00 GMT http://hdl.handle.net/10197/2719 2009-07-29T00:00:00Z http://hdl.handle.net/10197/2718 Magnetic properties of first-row element-doped ZnS semiconductors : a density functional theory investigation Long, Run; English, Niall J. Based on first-principles calculations, we have investigated the magnetic properties of the first-row element-doped ZnS semiconductors. Calculations reveal that Be, B, and C dopants can induce magnetic, while N cannot lead to spin polarization in ZnS. A possible explanation was rationalized from the elements’ electronegativity and interaction between dopant atoms and host atoms. The total magnetic moments are 2.00, 3.16, and 2.38 μB per 2 x 2 x 2 supercell for Be, B, and C doping, respectively, and ferromagnetic coupling is generally observed in these cases. The ferromagnetism of Be-, B-, and C-doped ZnS can be explained by hole-mediated s-p or p-p interactions’ coupling mechanisms. However, the clustering effect was found to be in Be-, B-, and C-doped ZnS but the degree is more obvious in the former two cases than in latter case. Analysis revealed that C-doped ZnS displays better potential ferromagnetic behavior than Be- and B-doped ZnS due to its half-metallic characteristic. Tue, 22 Sep 2009 00:00:00 GMT http://hdl.handle.net/10197/2718 2009-09-22T00:00:00Z http://hdl.handle.net/10197/2717 Electronic structures of N- and C-doped NiO from first-principles calculations Long, Run; English, Niall J.; Mooney, Damian A. The large intrinsic band gap of NiO has hindered severely its potential application under visible-light irradiation. In this study, we have performed first-principles calculations on the electronic properties of N- and C-doped NiO to ascertain if its band gap may be narrowed theoretically. It was found that impurity bands driven by N 2p or C 2p states appear in the band gap of NiO and that some of these locate at the conduction band minimum, which leads to a significant band gap narrowing. Our results show that N-doped NiO may serve as a potential photocatalyst relative to C-doped NiO, due to the presence of some recombination centres in C-doped NiO. Mon, 15 Feb 2010 00:00:00 GMT http://hdl.handle.net/10197/2717 2010-02-15T00:00:00Z http://hdl.handle.net/10197/2713 Synergistic effects of Bi/S codoping on visible light-activated anatase TiO2 photocatalysts from first principles Long, Run; English, Niall J. The electronic properties and photocatalytic activity of S and/or Bi-doped anatase TiO2 are investigated by first-principles density functional theory calculations. For S-doped TiO2, S 3p states locate above the top of the valence band and mix with O 2p states, leading to band gap narrowing. For Bi-doped anatase, the energy levels of the impurity Bi 6s states lie below the bottom of the conduction band while the Fermi level EF lies above the gap states, indicating the gap states are fully occupied. The transition from Bi 6s to Ti 3d states is responsible for a red-shift of the visible light absorption edge. In Bi/S–doped TiO2, both S 3p acceptor states and partially occupied Bi 6s donor states hybridized with S 3p appear simultaneously; this observation suggests that photocatalytic efficiency would be improved significantly due to greater separation of electron-hole pairs. These findings present a reasonable explanation of recent experimental results. Mon, 20 Apr 2009 00:00:00 GMT http://hdl.handle.net/10197/2713 2009-04-20T00:00:00Z http://hdl.handle.net/10197/2712 Density functional theory studies of doping in Titania Long, Run; English, Niall J. The structural and electronic properties of rutile and anatase, and the influence of both mono- and co-doping, have been studied using Density Functional Theory. Ge-doped anatase and rutile exhibit different band gap-narrowing mechanisms; in particular, host Ti 3d states move to lower energy regions in anatase and Ge 4s impurities states locate below the conduction band of rutile. For S-doping, S 3p states locate above the top of the valence band and mix with O 2p states, leading to band gap narrowing. For Bi-doping, the energy levels of the Bi 6s states lie below the bottom of the conduction band while the Fermi level EF lies above the gap states, indicating the gap states are fully occupied. For Bi/S–codoping, both S 3p acceptor states and partially occupied Bi 6s donor states hybridised with S 3p appear simultaneously. For N- and W-monodoping, isolated N 2p states above the top of the valence band and W 5d states below the conduction band lead to band gap narrowing. N/W codoping yields significant band gap narrowing. Both studies for Bi/S and N/W codoping rationalise recent experimental data which show that these doped anatase systems exhibit higher visible-light photocatalytic efficiency than respective monodoping. Tue, 01 Jun 2010 00:00:00 GMT http://hdl.handle.net/10197/2712 2010-06-01T00:00:00Z http://hdl.handle.net/10197/2711 Density functional theory description of the mechanism of ferromagnetism in nitrogen-doped SnO2 Long, Run; English, Niall J. Based on first-principles calculations, we have studied the occurrence of spin polarization in the magnetic metal oxide SnO2 doped with nonmagnetic nitrogen (N) impurities. It was found that the local magnetic moments are localized mainly on the N dopant, causing a total moment of 0.95μB per cell. The long-range magnetic coupling of N-doped SnO2 may be attributed to a p-p coupling interaction between the N impurity and host valence states. Mon, 28 Dec 2009 00:00:00 GMT http://hdl.handle.net/10197/2711 2009-12-28T00:00:00Z http://hdl.handle.net/10197/2533 Estimation of zeta potentials of titania nanoparticles by molecular simulation English, Niall J.; Long, William F. Non-equilibrium molecular dynamics (NEMD) simulations have been performed for static electric fields for a range of positively charged spherical rutile–titania nanoparticles with radii of 1.5 to 2.9 nm for two different salt concentrations in water, in order to simulate electrophoresis directly. Using the observed limiting drag velocities, Helmholtz–Smoluchowski (HS) theory was used to estimate their ζ potentials. These estimates were compared to values from numerical solution of the non-linear Poisson–Boltzmann (PB) equation for representative configurations of the nanoparticles, in addition to idealised analytic and Debye–Hückel (DH) solutions about spherical particles of the same geometry and charge state, for the given salt concentrations. It was found that reasonable agreement was obtained between the various approaches, with the NEMD-HS results some 15%–15% smaller than the numerical PB results for more highly charged nanoparticles. Thu, 01 Oct 2009 00:00:00 GMT http://hdl.handle.net/10197/2533 2009-10-01T00:00:00Z