Ageing of polysulfone membranes in contact with bleach solution: Role of radical oxidation and of some dissolved metal ions

In water production plants using membrane processes, contact with chemicals such as chlorine plays an important role in membrane ageing. This experimental study was aimed at gaining a better understanding of the effect of hypochlorite cleaning solutions on the properties of a polysulfone ultrafiltration membrane. Accelerated ageing of the membrane was simulated by soaking it in chlorine solutions and the mechanical properties of the membrane were monitored versus soaking time. An oxidation mechanism is validated which involves the catalytic effect of dissolved metal ions and the inhibitor effect of an antioxidant when these are present in soaking solutions

A combined NMR and DFT study of Narrow Gap Semiconductors: The case of PbTe

In this study we present an alternative approach to separating contributions to the NMR shift originating from the Knight shift and chemical shielding by a combination of experimental solid-state NMR results and ab initio calculations. The chemical and Knight shifts are normally distinguished through detailed studies of the resonance frequency as function of temperature and carrier concentration, followed by extrapolation of the shift to zero carrier concentration. This approach is time-consuming and requires studies of multiple samples. Here, we analyzed $^{207}$Pb and $^{125}$Te NMR spin-lattice relaxation rates and NMR shifts for bulk and nanoscale PbTe. The shifts are compared with calculations of the $^{207}$Pb and $^{125}$Te chemical shift resonances to determine the chemical shift at zero charge carrier concentration. The results are in good agreement with literature values from carrier concentration-dependent studies. The measurements are also compared to literature reports of the $^{207}$Pb and $^{125}$Te Knight shifts of $n$- and $p$-type PbTe semiconductors. The literature data have been converted to the currently accepted shift scale. We also provide possible evidence for the "self-cleaning effect" property of PbTe nanocrystals whereby defects are removed from the core of the particles, while preserving the crystal structure.Comment: 34 pages, 9 figure

De-pollution efficacy of photocatalytic roofing granules

Photocatalytic building surfaces can harness sunlight to reduce urban air pollution. The NOx abatement capacity of TiO2-coated granules used in roofing products was evaluated for commercial product development. A laboratory test chamber and ancillary setup were built following conditions prescribed by ISO Standard 22197-1. It was validated by exposing reference P25-coated aluminum plates to a 3 L min−1 air flow enriched in 1 ppm NO under UVA irradiation (360 nm, 11.5 W m−2). We characterized prototype granule-surfaced asphalt shingles and loose granules prepared with different TiO2 loadings and post-treatment formulations. Tests performed at surface temperatures of 25 and 60 °C showed that NOx abatement was more effective at the higher temperature. Preliminary tests explored the use of 1 ppm NO2 and of 1 ppm and 0.3 ppm NO/NO2 mixtures. Specimens were aged in a laboratory accelerated weathering apparatus, and by exposure to the outdoor environment over periods that included dry and rainy seasons. Laboratory aging led to higher NO removal and NO2 formation rates, and the same catalyst activation was observed after field exposure with frequent precipitation. However, exposure during the dry season reduced the performance. This inactivation was mitigated by cleaning the surface of field-exposed specimens. Doubling the TiO2 loading led to a 50–150% increase in NO removal and NOx deposition rates. Application of different post-treatment coatings decreased NO removal rates (21–35%) and NOx deposition rates (26–74%) with respect to untreated granules. The mass balance of nitrogenated species was assessed by extracting granules after UV exposure in a 1 ppm NO-enriched atmosphere

²¹⁰Pb- ²²⁶Ra chronology reveals rapid growth rate of Madrepora oculata and Lophelia pertusa on world's largest cold-water coral reef

Here we show the use of the 210Pb- 226Ra excess method to determine the growth rate of two corals from the world's largest known cold-water coral reef, Røst Reef, north of the Arctic circle off Norway. Colonies of each of the two species that build the reef, Lophelia pertusa and Madrepora oculata, were collected alive at 350 m depth using a submersible. Pb and Ra isotopes were measured along the major growth axis of both specimens using low level alpha and gamma spectrometry and trace element compositions were studied. 210Pb and 226Ra differ in the way they are incorporated into coral skeletons. Hence, to assess growth rates, we considered the exponential decrease of initially incorporated 210Pb, as well as the increase in 210Pb from the decay of 226Ra and contamination with 210Pb associated with Mn-Fe coatings that we were unable to remove completely from the oldest parts of the skeletons. 226Ra activity was similar in both coral species, so, assuming constant uptake of 210Pb through time, we used the 210Pb- 226Ra chronology to calculate growth rates. The 45.5 cm long branch of M. oculata was 31 yr with an average linear growth rate of 14.4 ± 1.1 mm yr -1 (2.6 polyps per year). Despite cleaning, a correction for Mn-Fe oxide contamination was required for the oldest part of the colony; this correction corroborated our radiocarbon date of 40 yr and a mean growth rate of 2 polyps yr -1. This rate is similar to the one obtained in aquarium experiments under optimal growth conditions. For the 80 cm-long L. pertusa colony, metal-oxide contamination remained in both the middle and basal part of the coral skeleton despite cleaning, inhibiting similar age and growth rate estimates. The youngest part of the colony was free of metal oxides and this 15 cm section had an estimated a growth rate of 8 mm yr -1, with high uncertainty (∼1 polyp every two to three years). We are less certain of this 210Pb growth rate estimate which is within the lowermost ranges of previous growth rate estimates. We show that 210Pb- 226Ra dating can be successfully applied to determine the age and growth rate of framework-forming cold-water corals if Mn-Fe oxide deposits can be removed. Where metal oxides can be removed, large M. oculata and L. pertusa skeletons provide archives for studies of intermediate water masses with an up to annual time resolution and spanning over many decades. © 2012 Author(s)

Tolerance of Pseudomonas aeruginosa in in vitro biofilms to high level peracetic acid disinfection

Biofilm has been suggested as a cause of disinfection failures in flexible endoscopes where no lapses in the decontamination procedure can be identified. To test this theory, the activity of peracetic acid (PAA), one of the commonly used disinfectants in the reprocessing of flexible endoscopes, was evaluated against both planktonic and sessile communities of Pseudomonas aeruginosa. To investigate the ability of P. aeruginosa biofilm to survive high level PAA disinfection. The susceptibility of planktonic cells of P. aeruginosa and biofilms 24, 48, 96 and 192 h old to PAA was evaluated by estimating their viability using resazurin viability and plate count methods. The biomass of the P. aeruginosa biofilms was also quantified using crystal violet assay. Planktonic cells of P. aeruginosa were treated with 5 - 30 ppm concentration of PAA in the presence of 3.0 g/L of Bovine serum albumin (BSA) for 5 min. Biofilms of P. aeruginosa were also treated with various PAA concentrations (100 - 3000 ppm) for 5 min. Planktonic cells of P. aeruginosa were eradicated by 20 ppm of PAA, whereas biofilms showed an age dependent tolerance to PAA, and 96 h old biofilm was only eradicated at PAA concentration of 2500 ppm. 96 h old P. aeruginosa biofilm survives 5 min treatment with 2000 ppm of PAA, which is the working concentration used in some endoscope washer disinfectors. This implies that disinfection failure of flexible endoscopes could occur when biofilms are allowed to build up in the lumens of endoscopes

Robustness of fossil fish teeth for seawater neodymium isotope reconstructions under variable redox conditions in an ancient shallow marine setting

Fossil fish teeth from pelagic open ocean settings are considered a robust archive for preserving the neodymium (Nd) isotopic composition of ancient seawater. However, using fossil fish teeth as an archive to reconstruct seawater Nd isotopic compositions in different sedimentary redox environments and in terrigenous‐dominated, shallow marine settings is less proven. To address these uncertainties, fish tooth and sediment samples from a middle Eocene section deposited proximal to the East Antarctic margin at Integrated Ocean Drilling Program Site U1356 were analyzed for major and trace element geochemistry, and Nd isotopes. Major and trace element analyses of the sediments reveal changing redox conditions throughout deposition in a shallow marine environment. However, variations in the Nd isotopic composition and rare earth element (REE) patterns of the associated fish teeth do not correspond to redox changes in the sediments. REE patterns in fish teeth at Site U1356 carry a typical mid‐REE‐enriched signature. However, a consistently positive Ce anomaly marks a deviation from a pure authigenic origin of REEs to the fish tooth. Neodymium isotopic compositions of cleaned and uncleaned fish teeth fall between modern seawater and local sediments and hence could be authigenic in nature, but could also be influenced by sedimentary fluxes. We conclude that the fossil fish tooth Nd isotope proxy is not sensitive to moderate changes in pore water oxygenation. However, combined studies on sediments, pore waters, fish teeth, and seawater are needed to fully understand processes driving the reconstructed signature from shallow marine sections in proximity to continental sources

A conceptual approach to determine optimal indoor air quality: A mixture experiment method

Achieving good air quality in large residential and commercial buildings continues to be a top priority for owners, designers, building managers and occupants. The challenge is even greater today. There are many new materials, furnishing, products and processes used in these buildings that are potential source of contaminations and pollutants. A common problem to the indoor and outdoor environments is that of exposure to mixtures of air pollutants. Researchers and practitioners tend to focus on single pollutants (e.g. CO2, PM2.5) ignoring the mixtures combined effect. Fashion dictates to study the pollutant most thoroughly talked about. Distinguishing the effects of such co-pollutants is difficult. The conclusions about which component of a mixture is actually producing a given effect are sometimes less soundly based than could be wished. It is especially important in considering the indoor mixture of air pollutants as this mixture may be entirely different from those found outside. Exposures to raised levels of air pollutants can damage health, for example carbon monoxide can cause death and significant lasting disability. Controlling levels of indoor air pollutants is therefore important, as good indoor air quality is essential to health. There are three strategies for achieving acceptable indoor air quality: ventilation, source control and cleaning/filtration. Depending on the building and the specific characteristics of the location, these strategies can be used singly or in combination. However, mixture experiment would throw more light and understanding into indoor air composition and interaction properties and the combine effects it has on human health. Mixture experiments have been used extensively in other industries, for example the pharmaceutical industry and the agrochemical industry, for the production of tablets and the control of plant diseases and pests. Developing a mixture model for the internal microclimate for a particular building type and/or location may help us in developing better indicators, standards and policy document in the near future, when the levels of pollutants concentration can be successfully predicted