Keith R Hallam

Photocatalytic oxidation of NOx gases using TiO2: a surface spectroscopic approach

The bandgap of solid-state TiO2 (3.2 eV) enables it to be a useful photocatalyst in the ultraviolet (lambda < 380 nm) region of the spectrum. A clean TiO2 surface in the presence of sunlight therefore enables the removal of harmful NOx gases from the atmosphere by oxidation to nitrates. These properties, in addition to the whiteness, relative cheapness and non-toxicity, make TiO2 ideal for the many de-NOX catalysts that are currently being commercially exploited both in the UK and Japan for concrete paving materials in inner cities. There is need, however, for further academic understanding of the surface reactions involved. Hence, we have used surface specific techniques, including X-ray photoelectron spectroscopy and Raman spectroscopy, to investigate the NOx adsorbate reaction at the TiO2 substrate surface.

XPS and laser Raman analysis of hydrogenated amorphous carbon films

Abstract Hydrogenated amorphous carbon films were deposited in an RF parallel plate plasma reactor using various values of process pressure (10–50 mTorr) and DC self-bias (0–300 V). The films were then analysed by laser Raman spectroscopy (LRS) at 514.5 nm and X-ray photoelectron spectroscopy (XPS). Values for the ratio of sp 2 :sp 3 bonded carbon in the various films were obtained by suitable fitting of the XPS carbon 1s energy peaks, using a three-curve fitting procedure, which recognises a portion of the peak attributable to CO surface bonding. The sp 3 content was found to depend upon the DC self bias (and hence the ion impact energy) during deposition, peaking at a value of 81% at approximately 150 V. The softer films grown at lower DC bias values still had an sp 3 content of approximately 70%. Microcombustion analysis showed that films deposited with low DC bias contained 7 at.% H compared to less than 2 at.% for films deposited at biases greater than 100 V. This high sp 3 content can be explained by H-termination of dangling bonds, suggesting that sp 3 content alone is not a reliable indication of film properties. Curve-fittings of LRS spectra of the films showed that the Breit–Wigner–Fano lineshape is inappropriate for use with hydrogen containing films. Fitting using a Gaussian profile gave precise values for the FWHM, intensity, and Stokes’ shift of the G and D-peaks. A linear relationship between the intensity ratio of the D to G peaks and the width of the G peak was found for films deposited at high DC bias (with low H content), but not for films deposited at low DC bias. This is consistent with the increased H content of the films causing a change in the elastic constants and/or affecting the stress levels within the films.

Banana peel: A green and economical sorbent for the selective removal of Cr(VI) from industrial wastewater

This study describes the use of banana peel, a commonly produced fruit waste, for the removal of Cr(VI) from industrial wastewater. The parameters pH, contact time, initial metal ion concentration, and temperature were investigated and the conditions resulting in rapid and efficient adsorption (95% within 10 min) were determined. The binding of metal ions was found to be pH dependent with the optimal sorption occurring at pH 2. The retained species were eluted with 5 mL of 2M H(2)SO(4). To elucidate the mechanism of the process, total amounts of chromium and Cr(VI) were analyzed using flame atomic absorption and ultraviolet-visible (UV-vis) spectroscopic techniques, respectively. The Langmuir and Dubinin-Radushkevich (D-R) isotherms were used to describe the partitioning behavior for the system at different temperatures. Kinetics and thermodynamics of Cr(VI) removal by banana peel were also studied. The influence of diverse ions on the sorption behavior revealed that only Fe(II) ions (of those tested) suppressed the sorption of Cr(VI) ions to some extent. The method was applied for the removal of Cr(VI) from industrial wastewater.

Visualisation of human plasma fibrinogen adsorbed on titanium implant surfaces with different roughness

Direct visualisation of adsorbed human plasma proteins on biomaterial surfaces may help the understanding of the performance of implants. The aim of this study was the visualisation of human plasma fibrinogen (HPF) adsorbed on different titanium implants with characterised surface properties. Seven types of titanium samples were used: mechanically polished (P); mechanically ground (G); sand blasted with alumina (B); sand blasted with alumina and etched in HF/HNO3 (BN); sand blasted with alumina and etched in HCl/H2SO4 (SLA); mechanically polished and etched in HCl/H2SO4 (PSLA); and plasma sprayed (TPS). The surface morphology and roughness of these surfaces were analysed by atomic force microscopy (AFM). The surface chemical composition of the implants was analysed by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). The seven processing methods influenced the roughness and produced distinct morphologies of the implant surfaces. The main chemical constituent of all surfaces was TiO2, with some samples showing the presence of other elements. HPF adsorbed on the titanium surfaces was visualised by AFM phase imaging. Visualisation of the adsorbed HPF was successfully achieved on samples P and G, but not on the other five samples. Differences in the dimensions and in the phase contrast of HPF molecules adsorbed on P and G surfaces were observed and discussed. No correlation between surface topography and morphology of the adsorbed proteins was observed on surfaces P and G. Possible reasons for not detecting HPF with AFM on five of the seven sample types were attributed to the surface physico-chemical properties of these samples.

Characterisation of crystalline C-S-H phases by X-ray photoelectron spectroscopy

Abstract We have prepared a number of crystalline calcium-silicate-hydrate (C-S-H) phases hydrothermally, with calcium–silicon ratios varying from approximately 0.5 (K-phase) to 2.0 (hillebrandite and α-dicalcium silicate hydrate). The phases were then analysed using X-ray photoelectron spectroscopy (XPS). Increasing calcium–silicon ratios resulted in decreased silicon binding energies. Additionally, changes in the O 1s spectra could be explained in terms of bridging (BO) and nonbridging oxygen (NBO) moieties. Finally, the modified Auger parameter has proved particularly useful in determining the extent of silicate anion polymerisation. Of note also are the apparently unusual spectra for 11 A tobermorite. The silicon and oxygen photoelectron spectra indicate a phase with a lower degree of silicate polymerisation than predicted from its composition. The main contributing factor is the intrinsic disorder within the tobermorite structure. This study has shown how XPS may be used to obtain valuable structural information from C-S-H phases, and our analysis of the crystalline phases is the first step towards the analysis of real C-S-H-based cement systems.

Characterisation of the Spinels MxCo1-xFe2O4(M=Mn,Fe or Ni) using X-ray Photoelectron Spectroscopy

Abstract X-ray photoelectron spectra have been recorded from a series of characterised cobalt-iron containing spinels M x Co 1− x Fe 2 O 4 where M = Mn, Fe or Ni and 0 ≤ x ≤ 1. The binding energies of photoelectron peaks observed for the transition metal ions were recorded. Changes in their relative positions were noted and the measured intensities used to determine the surface composition. The observed surface segregation of certain elements were interpreted in terms of kinetic and thermodynamic factors.

Deposition and properties of amorphous carbon phosphide films

a Abstract Radio frequency plasma deposition has been used to deposit phosphorus doped diamond-like carbon (DLC) films on Si and quartz substrates, using a gas mixture consisting of CH with additions of 0-90% PH . XPS studies reveal that the films contain 43

X-ray photoelectron spectroscopy of the cement clinker phases tricalcium silicate and β-dicalcium silicate

Abstract We have used X-ray photoelectron spectroscopy (XPS) to investigate both tricalcium silicate (Ca3SiO5, C3S) and β-dicalcium silicate (Ca2SiO4, β-C2S), the principal components of cement clinkers. In addition to showing how the two phases may be characterised and differentiated, we show how the sensitivity of these phases to atmospheric carbon dioxide and moisture may, as a result of improper sample preparation, lead to erroneous results. The observed alteration processes of the clinker minerals shed light upon the aging process of cement clinker during storage.

THE EFFECT OF DIAMOND SURFACE TERMINATION SPECIES UPON FIELD EMISSION PROPERTIES

Abstract Undoped CVD diamond films on Si substrates have been chemically treated in order to change the surface termination species. Treatments used include hydrodrogenation, deuteration, oxidation, hydrolysis, amination, chlorination, fluorination, and metallisation, using Na, K and Cs layers. The effect of these treatments upon field emission characteristics has been measured. In general, it is found that emission currents increase and threshold voltages decrease as the electronegativity of the surface species decreases. The best field emission properties were observed for the films with metal layers, with threshold voltages of ∼15 V/μm.

Residual stresses in a multi-pass CrMoV low alloy ferritic steel repair weld

Abstract A trial part through-section excavation manual metal arc repair weld, designed to minimise residual stresses was prepared using a critical combination of weld metal strength, bead size and deposition pattern. The repair was in a low alloy ferritic CrMoV steel plate, and the weldment was made using a lower strength C–Mn steel weld metal. Residual stresses have been measured to a high spatial resolution across the weldment using the X-ray diffraction technique with CrKα X-radiation. Peak tensile stresses have been identified in the heat affected zone in the parent plate adjacent to the weld metal. Further measurements have been made using the rosette strain gauge centre hole relaxation and deep hole drilling techniques. The measured residual stress profiles are discussed with respect to comparisons between techniques, the range of microstructures within the weldment and predictions of a finite element model for this particular multi-pass repair weld.