Observation of fast hydrogen atoms formed by ion bombarding of surfaces

We report on the observation of fast hydrogen atoms in a capacitively coupled RF reactor by optical emission spectroscopy. For the analysis we use the prominent H-alpha emission line of atomic hydrogen in combination with other lines from molecular hydrogen and argon. Several chaxacteristic emission structures can be identified. One of these structures is related to fast hydrogen atoms traveling from the surface of the powered electrode to the plasma bulk. From the appearance time within the RF period we conclude that this feature originates from ion bombardment of the electrode surface. Measured pressure dependencies and a simple model for the ion dynamics support this assumption.

Photocatalytic activity indicator inks for the probing a wide range of surfaces

Three photocatalyst inks based on the redox dyes, Resazurin (Rz), Basic Blue 66 (BB66) and Acid Violet 7 (AV7), are used to assess the photocatalytic activities of a variety of different materials, such as commercial paint, tiles and glass and laboratory made samples of sol–gel coated glass and paint, which collectively exhibit a wide range of activities that cannot currently be probed by any one of the existing ISO tests. Unlike the ISO tests, the ink tests are fast (typically <10 min), simple to employ and inexpensive. Previous work indicates that the Rz ink test at least correlates linearly with other photocatalytic tests such as the photomineralisation of stearic acid. The average time to bleach 90% of the key RGB colour component of the ink, red for Rz and BB66 inks and green for AV7 ink, is determined, ttb(90), for eight samples of each of the different materials tested. Five laboratories conducted the tests and the results revealed an average repeatability and reproducibility of: ca. 11% and ca 21%, respectively, which compare well with those reported for the current ISO tests. Additional work on commercial self-cleaning glass using an Rz ink showed that the change in the red component of the RGB image of the ink correlated linearly with that of the change of absorbance at 608 nm, as measured using UV/vis spectroscopy, and the change in the a* component of the Lab colour analysis of the ink, as measured using diffuse reflectance spectroscopy. As a consequence, all three methods generate the same ttb(90). The advantages of the RGB digital image analysis method are discussed briefly.

Measurement and modelling of perceived slant in surfaces represented by freely viewed line drawings

Simple pictures under everyday viewing conditions evoke impressions of surfaces oriented in depth. These impressions have been studied by measuring the slants of perceived surfaces, with probes (rotating arrowheads) designed to respect the distinctive character of depicted scenes. Converging arguments indicated that the perceived orientation of the probes was near theoretical values. A series of experiments showed that subjects formed well-defined impressions of depicted surface orientation. The literature suggests that perceived objects might be flattened', but that was not the general rule. Instead, both mean slant and uncertainty fitted models in which slant estimates are derived in a relatively straightforward way from local relations in the picture. Simplifying pictures tended to make orientation estimates less certain, particularly away from the natural anchor points (vertical and horizontal). The shape of the object affected all aspects of the observed-object/percept relationship. Individual differences were large, and suggest that different individuals used different relationships as a basis for their estimates. Overall, data suggest that everyday picture perception is strongly selective and weakly integrative. In particular, depicted slant is estimated by finding a picture feature which will be strongly related to it if the object contains a particular regularity, not by additive integration of evidence from multiple directly and indirectly relevant sources.

A density functional theory study of carbon monoxide oxidation on the Cu3Pt(111) alloy surface: Comparison with the reactions on Pt(111) and Cu(111)

Alloying metals is often used as an effective way to enhance the reactivity of surfaces. Aiming to shed light on the effect of alloying on reaction mechanisms, we carry out a comparative study of CO oxidation on Cu3Pt(111), Pt(111), and Cu(111) by means of density functional theory calculations. Alloying effects on the bonding sites and bonding energies of adsorbates, and the reaction pathways are investigated. It is shown that CO preferentially adsorbs on an atop site of Pt and O preferentially adsorbs on a fcc hollow site of three Cu atoms on Cu3Pt(111). It is also found that the adsorption energies of CO (or O-a) decreases on Pt (or Cu) on the alloy surface with respect to those on pure metals. More importantly, having identified the transition states for CO oxidation on those three surfaces, we found an interesting trend for the reaction barrier on the three surfaces. Similar to the adsorption energies, the reaction barrier on Cu3Pt possesses an intermediate value of those on pure Pt and Cu metals. The physical origin of these results has been analyzed in detail. (C) 2001 American Institute of Physics.

Heterogeneous mixed-layer clays from the Cretaceous greensand, Isle of Wight, southern England

The sea-cliffs of the Isle of Wight were deposited during a period of overall sea-level rise starting in the Barremian (Lower Cretaceous) and continuing into the Aptian and Albian. They consist of fluvial, coastal and lagoonal sediments including greensands and clays. Numerous episodes of erosion, deposition and faunal colonization reflect condensation and abandonment of surfaces with firmgrounds and hardgrounds. This study focused mainly on shallow marine cycles where variations in clay mineralogy would not be expected, because overall system composition, sediment source, and thermal history are similar for all the samples in the studied section. Instead we found a wide variety of clay assemblages even in single samples within a 200 in interval.

Experimental validation of the performance of a microreactor for the high-throughput screening of catalytic coatings

In this paper, the results of computational fluid dynamics simulations of flow, temperature, and concentration distributions used in the design of a microreactor for the high-throughput screening of catalytic coatings (Mies et al., Chem. Eng. J. 2004, 101, 225) are compared with experimental data, and good agreement is obtained in all cases. The experimental results on flow distribution were obtained from laser Doppler anemometry measurements in the range of Reynolds numbers from 6 to 113. The measured flow nonuniformity in the separate reactor compartments was below 2%. The temperature distribution was obtained from thermocouple measurements. The temperature nonuniformity between the reactor compartments was below 3 K at a maximum heat production rate of 1.3 W in ethylene oxidation at 425 degrees C over CuO/Al2O3/Al coatings. With respect to concentration gradients, a deviation from the average rate of reaction of only 2.3% was obtained at realistic process conditions in the ethylene ammoxidation process over identical Co-ZSM-5 coatings in all reactor compartments. The cross talking noise between separate compartments does not exceed 0.1% when the reactor parts have a smooth surface finish. This illustrates the importance of ultraprecision machining of surfaces in microtechnology, when interfaces cannot be avoided.

Application of atmospheric pressure nonthermal plasma for the in vitro eradication of bacterial biofilms

The use of atmospheric pressure nonthermal plasma represents an interesting and novel approach for the decontamination of surfaces colonized with microbial biofilms that exhibit enhanced tolerance to antimicrobial challenge. In this study, the influence of an atmospheric pressure nonthermal plasma jet, operated in a helium and oxygen gas mixture under ambient pressure, was evaluated against biofilms of Bacillus cereus,Staphylococcus aureus,Escherichia coli and Pseudomonas aeruginosa. Within <4 min of plasma exposure, complete eradication of the two Gram-positive bacterial biofilms was achieved. Although Gram-negative biofilms required longer treatment time, their complete eradication was still possible with 10 min of exposure. Whilst this study provides useful proof of concept data on the use of atmospheric pressure plasmas for the eradication of bacterial biofilms in vitro, it also demonstrates the critical need for improved understanding of the mechanisms and kinetics related to such a potentially significant approach. © 2012 Federation of European Microbiological Societies.

Photocatalytic destruction of geosmin using novel pelleted titanium dioxide

Geosmin is produced by cyanobacteria and actinomycetes in surface waters. It causes undesirable earthy off-flavours in freshwater fish and is a major concern for the drinking water industry. This paper presents the first published study on the use of the novel pelleted Ti0₂ photocatalyst, Hombikat K01/C, for the removal of geosmin from water. Ti0₂ in pelleted form eliminates the requirement for the separation of the catalyst from the water following treatment which is normally the case with the widely used powdered catalysts. A laboratory reactor was designed to limit system loss since the compound adsorbs to a wide range of surfaces. Initial concentration, aeration rate and irradiation were evaluated. It was found that degradation of geosmin followed the Langmuir-Hinshelwood model. Elevated aeration had no effect on the photocatalytic removal of geosmin, but increasing irradiation was found to increase degradation rates. The catalyst proved effective within 10 min under optimum conditions. 

General rules for predicting where a catalytic reaction should occur on metal surfaces: A density functional theory study of C-H and C-O bond breaking/making on flat, stepped, and kinked metal surfaces

To predict where a catalytic reaction should occur is a fundamental issue scientifically. Technologically, it is also important because it can facilitate the catalyst's design. However, to date, the understanding of this issue is rather limited. In this work, two types of reactions, CH4 CH3 + H and CO C + 0 on two transition metal surfaces, were chosen as model systems aiming to address in general where a catalytic reaction should occur. The dissociations of CH4 - CH3 + H and CO --> C + O and their reverse reactions on flat, stepped, and kinked Rh and Pd surfaces were studied in detail. We find the following: First, for the CH4 Ch(3) + H reaction, the dissociation barrier is reduced by similar to0.3 eV on steps and kinks as compared to that on flat surfaces. On the other hand, there is essentially no difference in barrier for the association reaction of CH3 + H on the flat surfaces and the defects. Second, for the CO C + 0 reaction, the dissociation barrier decreases dramatically (more than 0.8 eV on Rh and Pd) on steps and kinks as compared to that on flat surfaces. In contrast to the CH3 + H reaction, the C + 0 association reaction also preferentially occurs on steps and kinks. We also present a detailed analysis of the reaction barriers in which each barrier is decomposed quantitatively into a local electronic effect and a geometrical effect. Our DFT calculations show that surface defects such as steps and kinks can largely facilitate bond breaking, while whether the surface defects could promote bond formation depends on the individual reaction as well as the particular metal. The physical origin of these trends is identified and discussed. On the basis of our results, we arrive at some simple rules with respect to where a reaction should occur: (i) defects such as steps are always favored for dissociation reactions as compared to flat surfaces; and (ii) the reaction site of the association reactions is largely related to the magnitude of the bonding competition effect, which is determined by the reactant and metal valency. Reactions with high valency reactants are more likely to occur on defects (more structure-sensitive), as compared to reactions with low valency reactants. Moreover, the reactions on late transition metals are more likely to proceed on defects than those on the early transition metals.