An evaluation of alternative media for pebble matrix filtration using clay balls and recycled crushed glass

Protecting slow sand filters (SSFs) from high-turbidity waters by pretreatment using pebble matrix filtration (PMF) has previously been studied in the laboratory at University College London, followed by pilot field trials in Papua New Guinea and Serbia. The first full-scale PMF plant was completed at a water-treatment plant in Sri Lanka in 2008, and during its construction, problems were encountered in sourcing the required size of pebbles and sand as filter media. Because sourcing of uniform-sized pebbles may be problematic in many countries, the performance of alternative media has been investigated for the sustainability of the PMF system. Hand-formed clay balls made at a 100-yearold brick factory in the United Kingdom appear to have satisfied the role of pebbles, and a laboratory filter column was operated by using these clay balls together with recycled crushed glass as an alternative to sand media in the PMF. Results showed that in countries where uniform-sized pebbles are difficult to obtain, clay balls are an effective and feasible alternative to natural pebbles. Also, recycled crushed glass performed as well as or better than silica sand as an alternative fine media in the clarification process, although cleaning by drainage was more effective with sand media. In the tested filtration velocity range of ð0:72–1:33Þ m=h and inlet turbidity range of (78–589) NTU, both sand and glass produced above 95% removal efficiencies. The head loss development during clogging was about 30% higher in sand than in glass media.

The relationship between building characteristics and the chemical composition of surface films found on glass windows in Brisbane, Australia

Films found on the windows of residential buildings have been studied. The main aim of the paper was to assess the roles of the films in the accumulation of potentially toxic chemicals in residential buildings. Thus the elemental and polycyclic aromatic hydrocarbon compositions of the surface films from the glass windows of eighteen residential buildings were examined. The presence of sample amounts of inorganic elements (4.0–1.2 × 106 μg m−2) and polycyclic aromatic hydrocarbons in the films (BDL - 620.1 ng m−2) has implications for human exposure and the fate of pollutants in the urban environment. To facilitate the interpretation of the results, data matrices consisting of the chemical composition of the films and the building characteristics were subjected to multivariate data analysis methods, and these revealed that the accumulation of the chemicals was strongly dependent on building characteristics such as the type of glass used for the window, the distance from a major road, age of the building, distance from an industrial activity, number of smokers in the building and frequency of cooking in the buildings. Thus, building characteristics which minimize the accumulation of pollutants on the surface films need to be encouraged.

Photocatalytic hydrogen production with iron oxide under solar irradiation

As solar hydrogen is a sustainable and environmental friendly energy carrier, it is considered to take the place of fossil fuels in the near future. Solar hydrogen can be generated by splitting of water under solar light illumination. In this study, the use of nanostructured hematite thin-film electrodes in photocatalytic water splitting was investigated. Hematite (á-Fe2O3) has a narrow band-gap of 2.2 eV, which is able to utilise approximately 40% of solar radiation. However, poor photoelectrochemical performance is observed for hematite due to low electrical conductivity and a high rate of electron-hole recombination. An extensive review of useful measures taken to overcoming the disadvantages of hematite so as to enhance its performance was presented including thin-film structure, nanostructuring, doping, etc. Since semiconductoring materials which exhibit an inverse opal structure are expected to have a high surface-volume ratio, unique optical characteristics and a shorter distance for photogenerated holes to travel to the electrode/electrolyte interface, inverse opals of hematite thin films deposited on FTO glass substrate were successfully prepared by doctor blading using PMMA as a template. However, due to the poor adhesion of the films, an acidic medium (i.e., 2 M HCl) was employed to significantly enhance the adhesion of the films, which completely destroyed the inverse opal structure. Therefore, undoped, Ti and Zn-doped hematite thin films deposied on FTO glass substrate without an inverse opal structure were prepared by doctor blading and spray pyrolysis and characterised using SEM, EDX, XRD, TGA, UV-Vis spectroscopy and photoelectrochemical measurements. Regarding the doped hematite thin films prepared by doctor blading, the photoelectrochemical activity of the hematite photoelectrodes was improved by incorporation of Ti, most likely owing to the increased electrical conductivity of the films, the stabilisation of oxygen vacancies by Ti4+ ions and the increased electric field of the space charge layer. A highest photoresponse was recorded in case of 2.5 at.% Ti which seemed to be an optimal concentration. The effect of doping content, thickness, and calcination temperature on the performance of the Ti-doped photoelectrodes was investigated. Also, the photoactivity of the 2.5 at.% Ti-doped samples was examined in two different types of electrochemical cells. Zn doping did not enhance the photoactivity of the hematite thin films though Zn seemed to enhance the hole transport due to the slow hole mobility of hematite which could not be overcome by the enhancement. The poor performance was also obtained for the Ti-doped samples prepared by spray pyrolysis, which appeared to be a result of introduction of impurities from the metallic parts of the spray gun in an acidic medium. Further characterisation of the thin-film electrodes is required to explain the mechanism by which enhanced performance was obtained for Ti-doped electrodes (doctor blading) and poor photoactivity for Zn and Ti-doped samples which were synthesised by doctor blading and spray pyrolysis, respectively. Ti-doped hematite thin films will be synthesised in another way, such as dip coating so as to maintain an inverse opal structure as well as well adhesion. Also, a comparative study of the films will be carried out.

Transition from n- to p-type of spray pyrolysis deposited Cu doped ZnO thin films for NO2 sensing

The structural, optical, and gas-sensing properties of spray pyrolysis deposited Cu doped ZnO thin films were investigated. Gas response of the undoped and doped films to N02 (oxidizing) gas shows an increase and decrease in resistance, respectively, indicating p-type conduction in doped samples. The UV-Vis spectra of the films show decrease in the bandgap with increasing Cu concentration in ZnO. The observed p-type conductivity is attributed to the holes generated by incorporated Cu atoms on Zn sites in ZnO thin films. The X-ray diffraction spectra showed that samples are polycrystalline with the hexagonal wurtzite structure and increasing the concentration of Cu caused a decrease in the intensity of the dominant (002) peak. The surface morphology of films was studied by scanning electron microscopy and the presence of Cu was also confirmed by X-ray photoelectron spectroscopy. Seebeck effect measurements were utilized to confirm the p-type conduction of Cu doped ZnO thin films. Copyright © 2009 American Scientific Publishers All rights reserved.

A Raman spectroscopic study of the mono-hydrogen phosphate mineral dorfmanite Na2(PO3OH)•2H2O – and in comparison with brushite

Aspects of the molecular structure of the mineral dorfmanite Na2(PO3OH)•2H2O were determined by Raman spectroscopy. The mineral originated from the Kedykverpakhk Mt., Lovozero, Kola Peninsula, Russia. Raman bands are assigned to the hydrogen phosphate units. The intense Raman band at 949 cm-1 and the less intense band at 866 cm-1 are assigned to the PO3 and POH stretching vibrations. Bands at 991, 1066 and 1141 cm-1 are assigned to the ν3 antisymmetric stretching modes. Raman bands at 393, 413 and 448 cm-1 and 514, 541 and 570 cm-1 are attributed to the ν2 and ν4 bending modes of the HPO4 units, respectively. Raman bands at 3373, 3443 and 3492 cm-1 are assigned to water stretching vibrations. POH stretching vibrations are identified by bands at 2904, 3080 and 3134 cm-1. Raman spectroscopy has proven very useful for the study of the structure of the mineral dorfmanite.