Advanced Photocatalysts: Pinning Single Atom Co-Catalysts on Titania Nanotubes

Single atom (SA) catalysis, over the last 10 years, has become a forefront in heterogeneous catalysis, electrocatalysis, and most recently also in photocatalysis. Most crucial when engineering a SA catalyst/support system is the creation of defined anchoring points on the support surface to stabilize reactive SA sites. Here, a so far unexplored but evidently very effective approach to trap and stabilize SAs on a broadly used photocatalyst platform is introduced. In self-organized anodic TiO₂ nanotubes, a high degree of stress is incorporated in the amorphous oxide during nanotube growth. During crystallization (by thermal annealing), this leads to a high density of Ti³⁺-O_v surface defects that are hardly present in other common titania nanostructures (as nanoparticles). These defects are highly effective for SA iridium trapping. Thus a SA-Ir photocatalyst with a higher photocatalytic activity than for any classic co-catalyst arrangement on the semiconductive substrate is obtained. Hence, a tool for SA trapping on titania-based back-contacted platforms is provided for wide application in electrochemistry and photoelectrochemistry. Moreover, it is shown that stably trapped SAs provide virtually all photocatalytic reactivity, with turnover frequencies in the order of 4 × 10⁶ h⁻¹ in spite of representing only a small fraction of the initially loaded SAs.     

The presence of nanostructured Al2O3 in PMMA-based gel electrolytes

Gel polymer electrolytes (GPEs)-based on poly(methyl methacrylate) PMMA and propylene carbonate (PC) with LiClO₄ or NaClO₄ salt are prepared using either the commercial product Superacryl^® or directly from the monomer and AIBN (2,2′-azobis(isobutyronitrile)) initiator. The nanostructured aluminum oxide is added to the mentioned systems in various ratios. Solutions of liquid PC–perchlorate and polymer electrolytes are compared with focus on ionic conductivity. The ionic conductivity of polymer-based electrolytes is significantly influenced (of almost by one half order of magnitude at room temperature) by the addition of nanosized Al₂O₃. On the contrary, the conductivity of liquid electrolytes is decreased by the addition of alumina in the blend. A slight enhancement of mechanical properties is observed.     

Drying activity of oxovanadium(IV) 2-ethylhexanoate in solvent-borne alkyd paints

Oxovanadium(IV) 2-ethylhexanoate was established as a new primary drier for alkyd-based paints. A series of experiments has demonstrated an excellent drying activity toward solvent-borne alkyd resins of different oil length at considerably lower metal concentration than optimal for commercial cobalt(II) 2-ethylhexanoate. The behavior in real paint was simulated on formulations bearing inhibitor of autooxidation. The detailed studies of the drying process have shown that the relatively slow initial step of autooxidation reaction, when compared with cobalt compounds, is compensated for by the absence of the induction times. Furthermore, the active oxovanadium(IV) species are not consumed during the drying processes as evidenced by EPR spectroscopic measurements.     

Collective polyelectrolyte diffusion as a function of counterion size and dielectric constant

We report studies of the effect of counterions on the properties of solutions of a strong polyelectrolyte for a wide range of solvent dielectric constant. For this purpose we investigated the dynamic properties of polystyrene sulfonate in N‐methylformamide whose dielectric constant changes significantly with temperature. By means of dynamic light scattering and NMR spectroscopy, polymers of different molecular weights and various counterions were investigated, including large phosphazene counterions P₁, P₂ and P₄ measured for the first time. It was found that the order of counterion binding of ionomers in the solvent changed with an increase of dielectric constant. The order for low dielectric constant (high temperature) was Na < Rb < Cs < P₁ < P₂ < P₄, whereas for a solvent with high dielectric constant no influence of counterion nature was observed. The solvation–desolvation effect together with electrostatic interactions are responsible for the observed phenomenon. © 2012 Society of Chemical Industry     

Probabilistic risk assessment of highway tunnels

Many approaches to risk analysis in tunnels have been proposed by both international and national authorities over the last few years. Many safety problems have been discussed and a large number of important risk factors and hazards in tunnels have been identified. The concept of risk analysis in the scope of tunnel risks is, however, still under development; particularly an overall idea about the risk management concept is still missing. The paper introduces the concept of risk analysis in the scope of risk management and employs methods well-known in aeronautics and aircraft industry, yet, still unused in tunnels. The proposed methodology enables building and refurbishing costs minimization subject to preservation of satisfactory safety level. The outcomes of the proposed method have clear technical and economic interpretation and create a strong support tool for the decision making process. The paper also includes a case study of the Strahov tunnel in Prague, Czech Republic.     

In vivo optical detection of pH in microscopic tissue samples of Arabidopsis thaliana

Minimally invasive in vivo measurement of pH in microscopic biological samples of μm or μl size, e.g. plant cells, tissues and saps, may help to explain complex biological processes. Consequently, techniques to achieve such measurements are a focus of interest for botanists. This paper describes a technique for the in vivo measurement of pH in the range pH 5.0 to pH 7.8 in microscopic plant tissue samples of Arabidopsis thaliana based on a ratiometric fluorescence method using low-loss robust tapered fiber probes. For this purpose tapered fiber probes were prepared and coated with a detection layer containing ion-paired fluorescent pH-transducer 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (c-HPTS). A fluorescence ratiometric approach was employed based on excitation at 415 nm and 450 nm and on the comparison of the fluorescence response at 515 nm. The suitability of tapered fiber probes for local detection of pH between 5.0 and 7.8 was demonstrated. A pH sensitivity of 0.15 pH units was achieved within the pH ranges 5.0–5.9 and 7.1–7.8, and this was improved to 0.04 pH units within the pH range 5.9–7.1. Spatial resolution of the probes was better than 20 μm and a time response within 15–20 s was achieved. Despite the minute dimensions of the tapered fiber probes the setup developed was relatively robust and compact in construction and performed reliably. It has been successfully employed for the in vivo local determination of pH of mechanically resistant plant tissues of A. thaliana of microscopic scale. The detection of momentary pH gradients across the intact plant seems to be a good tool for the determination of changes in pH in response to experimental treatments affecting for example enzyme activities, availability of mineral nutrients, hormonal control of plant development and plant responses to environmental cues.     

Polypyrrole thin films for gas sensors prepared by Matrix-Assisted Pulsed Laser Evaporation technology: Effect of deposition parameters on material properties

Thin films of polypyrrole (PPY) were prepared by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technology from two matrices: water and dimethylsulfoxide (DMSO). The deposition was carried out using a KrF excimer laser (laser fluence F ranged from 0.1 to 0.6 J cm^− 2). This work deals with optimization of two deposition parameters - laser fluence and number of pulses - for both matrices. From the deposition curves, the fluence thresholds, F_th, and maximum growth rates were subsequently determined (water matrix: F_th ~ 0.40-0.45 J cm^− 2, maximum growth rate 0.16 nm pulse^− 1; DMSO matrix: F_th ~ 0.25-0.30 J cm^− 2; maximum growth rate 0.20 nm pulse^− 1). The changes in chemical composition of deposited layers were studied by Attenuated Total Reflection Fourier Transform Infrared spectroscopy. Surface morphology was characterized by Atomic Force Microscopy. A discussion is also presented concerning relationships between laser fluence and chemical composition of deposited layers with respect to their potential application in gas sensors. Finally, the response of a sensor with a MAPLE deposited PPY active layer to air humidity is presented.     

Space Tourism: Waiting for Ignition

Space tourism is in its infancy, having been launched a little over a decade ago by billionaire businessman Dennis Tito's venture into Space. Ondřej Doule , Assistant Professor of Human-Centered Design and Aerospace Engineering at the Florida Institute of Technology, and Chair of the Space Architecture Technical Committee at the AIAA, considers the shift that will have to be made in designing Space Architecture as space shuttles and stations transition from being ostensibly high-security labs into floating hotels.