Detoxification of microcystins (cyanobacterial hepatotoxins) using TiO<sub>2sub> photocatalytic oxidation

TiO<sub>2sub> photocatalysis has been used to destroy microcystin-LR in aqueous solution. The destruction of this toxin was monitored by HPLC, and the disappearance was accompanied by the appearance of seven UV detectable compounds. Spectral analysis revealed that some of these compounds retained spectra similar to the parent compound suggesting that the Adda moiety, thought to be responsible for the characteristic spectrum, remained intact whereas the spectra of some of the other products was more radically altered. Six of the seven observed reaction products did not appear to undergo further degradation during prolonged photocatalysis (100 min). The degree to which microcystin-LR was mineralized by photocatalytic oxidation was determined. Results indicated that less than 10% mineralization occurred. Mass spectral analysis of the photocatalyzed microcystin-LR allowed tentative characterization of the reaction process and products. Reduction in toxicity due to the photocatalytic oxidation was evaluated using an invertebrate bioassay, which demonstrated that the disappearance of microcystin-LR was paralleled by a reduction in toxicity. These findings suggest that photocatalytic destruction of microcystins may be a suitable method for the removal of these potentially hazardous compounds from drinking water.

Processes influencing the destruction of microcystin-LR by TiO<sub>2sub> photocatalysis

We have previously reported the effectiveness of TiO<sub style="border: 0px; font-size: 0.75em; margin: 0px; padding: 0px; font-family: 'Arial Unicode MS', 'Arial Unicode', Arial, 'URW Gothic L', Helvetica, Tahoma, 'Cambria Math', sans-serif; line-height: 0; color: rgb(46, 46, 46); text-align: justify; word-spacing: -1.0356148481369px;">2sub> photocatalysis in the destruction of the cyanotoxin microcystin-LR [P.K.J. Robertson, L.A. Lawton, B. Münch, J. Rouzade, J. Chem. Soc., Chem. Commun., 4 (1997) 393; P.K.J. Robertson, L.A. Lawton, B. Münch, B.J.P.A. Cornish, J. Adv. Oxid. Technol., in press]. In this paper we report an investigation of factors which influence the rate of the toxin destruction at the catalyst surface. A primary kinetic isotope effect of approximately 3 was observed when the destruction was performed in a heavy water solvent. Hydroxylated compounds were observed as products of the destruction process. No destruction was observed when the process was investigated under a nitrogen atmosphere.

A continuous flow packed bed photocatalytic reactor for the destruction of 2-methylisoborneol and geosmin utilising pelletised TiO<sub>2sub>

Taste and odour compounds, especially geosmin (GSM) and 2-methylisoborneol (2-MIB), cause major problems in both drinking water and aquaculture industries world-wide. Aquaculture in particular has experienced significant financial losses due to the accumulation of taint compounds prior to harvest resulting in consumer rejection. UV-TiO2 photocatalysis has been demonstrated to remove GSM and 2-MIB at laboratory scale but the development of a continuous flow reactor suitable for use in water treatment has not been investigated. In this study, a pilot packed bed photocatalytic reactor was developed and evaluated for water treatment with both laboratory and naturally tainted samples. A significant reduction of both 2-MIB and GSM was achieved in both trials using the packed bed reactor unit. With the laboratory spiked water (100ngL-1 of each compound added prior to treatment), detectable levels were reduced by up to 97% after a single pass through the unit. When the reactor was used to treat water in a fish farm where both compounds were being produced in situ (2-MIB: 19ngL-1 and GSM: 14ngL-1) a reduction of almost 90% in taint compounds was achieved. These very encouraging promising results demonstrate the potential of this UV-TiO2 photocatalytic reactor for water treatment in fish rearing systems and other applications.

Exchange between sub-surface and surface oxygen vacancies on CeO2(111):a new surface diffusion mechanism

Using first principles calculations for O vacancy diffusion on CeO2(111), we locate a surface diffusion mechanism, the two-step O vacancy exchange one, which is more favored than the most common hopping mechanism. By analyzing the results, we identify quantitatively the physical origin of why the two-step exchange mechanism is preferred.

Sandwich nanoarchitecture of LiV<sub>3sub>O<sub>8sub>/graphene multilayer nanomembranes via layer-by-layer self-assembly for long-cycle-life lithium-ion battery cathodes

A lack of suitable high-performance cathode materials has become the major barrier to their applications in future advanced communication equipment and electric vehicle power systems. In this paper, we have developed a layer-by-layer self-assembly approach for fabricating a novel sandwich nanoarchitecture of multilayered LiV<sub>3sub>O<sub>8sub> nanoparticle/graphene nanosheet (M-nLVO/GN) hybrid electrodes for potential use in high performance lithium ion batteries by using a porous Ni foam as a substrate. The prepared sandwich nanoarchitecture of M-nLVO/GN hybrid electrodes exhibited high performance as a cathode material for lithium-ion batteries, such as high reversible specific capacity (235 mA h g^-1 at a current density of 0.3 A g^-1), high coulombic efficiency (over 98%), fast rate capability (up to a current density of 10 A g^-1), and superior capacity retention during cycling (90% capacity retention with a current density of 0.3 A g^-1 after 300 cycles). Very significantly, this novel insight into the design and synthesis of sandwich nanoarchitecture would extend their application to various electrochemical energy storage devices, such as fuel cells and supercapacitors.

An effective three-dimensional ordered mesoporous ZnCo<sub>2sub>O<sub>4sub> as electrocatalyst for Li-O<sub>2sub> batteries

Three-dimensional ordered mesoporous (3DOM) ZnCo<sub>2sub>O<sub>4sub> materials have been synthesized via a hard template and used as bifunctional electrocatalysts for rechargeable Li-O<sub>2sub> batteries. The as-prepared ZnCo<sub>2sub>O<sub>4sub> nanoparticles possess a high specific surface area of 127.2 m² g^-1 and a spinel crystalline structure. The Li-O<sub>2 sub>battery utilizing 3DOM ZnCo<sub>2sub>O<sub>4sub> shows a higher specific capacity of 6024 mAh g^-1 than that with pure Ketjen black (KB). Moreover, the ZnCo<sub>2sub>O<sub>4sub>-based electrode enables much enhanced cyclability with a smaller discharge-recharge voltage gap than that of the carbon-only cathode. Such excellent catalytic performance of ZnCo<sub>2sub>O<sub>4sub> could be associated with its larger surface area and 3D ordered mesoporous structure

Co-tape casting fabrication, field assistant sintering and evaluation of a coke resistant La<sub>0.2sub>Sr<sub>0.7sub>TiO<sub>3sub>-Ni/YSZ functional gradient anode supported solid oxide fuel cell

The ability to directly utilize hydrocarbons and other renewable liquid fuels is one of the most important issues affecting the large scale deployment of solid oxide fuel cells (SOFCs). Herein we designed La<sub>0.2sub>Sr<sub>0.7sub>TiO<sub>3sub>-Ni/YSZ functional gradient anode (FGA) supported SOFCs, prepared with a co-tape casting method and sintered using the field assisted sintering technique (FAST). Through SEM observations, it was confirmed that the FGA structure was achieved and well maintained after the FAST process. Distortion and delamination which usually results after conventional sintering was successfully avoided. The La<sub>0.2sub>Sr<sub>0.7sub>TiO<sub>3sub>-Ni/YSZ FGA supported SOFCs showed a maximum power density of 600mWcm^-2 at 750°C, and was stable for 70h in CH<sub>4sub>. No carbon deposition was detected using Raman spectroscopy. These results confirm the potential coke resistance of La<sub>0.2sub>Sr<sub>0.7sub>TiO<sub>3sub>-Ni/YSZ FGA supported SOFCs.

Preparation of La<sub>2sub>NiO<sub>4+δsub> powders as a cathode material for SOFC via a PVP-assisted hydrothermal route

Uniform submicron La<sub>2sub>NiO<sub>4+δsub> (sm-LNO) powders have been synthesized by a facile polyvinylpyrrolidone (PVP)-assisted hydrothermal route. In the presence of PVP, sm-LNO of pure phase has been obtained by calcination at the relatively low temperature of 900 °C for 8 h. Compared micron-sized LNO (m-LNO) particles obtained at 1,000 °C by hydrothermal synthesis route without PVP assisted, the sm-LNO-PVP displays regularly shaped and well-distributed particles in the range of 0.3–0.5 μm. The scanning electron microscopy (SEM) results showed that the sm-LNO sample is submicronic and that the m-LNO sample shows agglomerates with a broad size distribution. The electrochemical performance of m-LNO and sm-LNO-PVP has been investigated by electrochemical impedance spectroscopy. The polarization resistance of the sm-LNO-PVP cathode reaches a value of 0.40 Ω cm² at 750 °C, which is lower than that of m-LNO (0.62 Ω cm²). This result indicates that a fine electrode microstructure with submicron particles can help to increase the active sites, accelerate oxygen diffusion, and reduce polarization resistance. An anode-supported single cell with sm-LNO cathode has been fabricated and tested over a temperature range from 650 to 800 °C. The maximum power density of the cell has achieved 834 mW cm⁻² at 750 °C. These results therefore show that this PVP-assisted hydrothermal method is an effective approach to construct submicron-structured cathode and enhance the performance of intermediate temperature solid oxide fuel cell.

One-dimensional porous La<sub>0.5sub>Sr<sub>0.5sub>CoO<sub>2.91sub> nanotubes as a highly efficient electrocatalyst for rechargeable lithium-oxygen batteries

The electrochemical performance of one-dimensional porous La<sub>0.5sub>Sr<sub>0.5sub>CoO<sub>2.91sub> nanotubes as a cathode catalyst for rechargeable nonaqueous lithium-oxygen (Li-O<sub>2sub>) batteries is reported here for the first time. In this study, one-dimensional porous La<sub>0.5sub>Sr<sub>0.5sub>CoO<sub>2.91sub> nanotubes were prepared by a simple and efficient electrospinning technique. These materials displayed an initial discharge capacity of 7205 mAh g^-1 with a plateau at around 2.66 V at a current density of 100 mA g^-1. It was found that the La<sub>0.5sub>Sr<sub>0.5sub>CoO<sub>2.91sub> nanotubes promoted both oxygen reduction and oxygen evolution reactions in alkaline media and a nonaqueous electrolyte, thereby improving the energy and coulombic efficiency of the Li-O<sub>2sub> batteries. The cyclability was maintained for 85 cycles without any sharp decay under a limited discharge depth of 1000 mAh g^-1, suggesting that such a bifunctional electrocatalyst is a promising candidate for the oxygen electrode in Li-O<sub>2sub> batteries.

Three-dimensional graphene-Co<sub>3sub>O<sub>4sub> cathodes for rechargeable Li-O<sub>2sub> batteries

A three-dimensional (3D) graphene-Co<sub>3sub>O<sub>4sub> electrode was prepared by a two-step method in which graphene was initially deposited on a Ni foam with Co<sub>3sub>O<sub>4sub> then grown on the resulting graphene structure. Cross-linked Co<sub>3sub>O<sub>4sub> nanosheets with an open pore structure were fully and vertically distributed throughout the graphene skeleton. The free-standing and binder-free monolithic electrode was used directly as a cathode in a Li-O<sub>2sub> battery. This composite structure exhibited enhanced performance with a specific capacity of 2453 mA h g^-1 at 0.1 mA cm^-2 and 62 stable cycles with 583 mA h g^-1 (1000 mA h g<sub>carbonsub>^-1). The excellent electrochemical performance is associated with the unique architecture and superior catalytic activity of the 3D electrode. 

Investigation into the effect of molybdenum-site substitution on the performance of Sr<sub>2sub>Fe<sub>1.5sub>Mo<sub>0.5sub>O<sub>6-δ sub>for intermediate temperature solid oxide fuel cells

In this paper, niobium doping is evaluated as a means of enhancing the electrochemical performance of a Sr<sub>2sub>Fe<sub>1.5sub>Mo<sub>0.5sub>O<sub>6-δsub> (SFM) perovskite structure cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) applications. As the radius of Nb approximates that of Mo and exhibits +4/+5 mixed valences, its substitution is expected to improve material performance. A series of Sr<sub>2sub>Fe<sub>1.5sub>Mo<sub>0.5-xsub>Nb<sub>xsub>O<sub>6-δsub> (x = 0.05, 0.10, 0.15, 0.20) cathode materials are prepared and the phase structure, chemical compatibility, microstructure, electrical conductivity, polarization resistance and power generation are systematically characterized. Among the series of samples, Sr<sub>2sub>Fe<sub>1.5sub>Mo<sub>0.4sub>Nb<sub>0.10sub>O<sub>6-δsub> (SFMNb<sub>0.10sub>) exhibits the highest conductivity value of 30 S cm^-1 at 550°C, and the lowest area specific resistance of 0.068 Ω cm² at 800°C. Furthermore, an anode-supported single cell incorporating a SFMNb<sub>0.10sub> cathode presents a maximum power density of 1102 mW cm^-2 at 800°C. Furthermore no obvious performance degradation is observed over 15 h at 750°C with wet H<sub>2sub>(3% H<sub>2sub>O) as fuel and ambient air as the oxidant. These results demonstrate that SFMNb shows great promise as a novel cathode material for IT-SOFCs.

Investigation into the effect of Fe-site substitution on the performance of Sr<sub>2sub>Fe<sub>1.5sub>Mo<sub>0.5sub>O<sub>6-δ sub>anodes for SOFCs

Ni-substituted Sr<sub>2sub>Fe<sub>1.5-xsub>Ni<sub>xsub>Mo<sub>0.5sub>O<sub>6-δsub> (SFNM) materials have been investigated as anode catalysts for intermediate temperature solid oxide fuel cells. Reduced samples (x = 0.05 and 0.1) maintained the initial perovskite structure after reduction in H<sub>2sub>, while metallic nickel particles were detected on the grain surface for x = 0.2 and 0.3 using transmission electron microscopy. Temperature programmed reduction results indicate that the stable temperature for SFNM samples under reduction conditions decreases with Ni content. In addition, X-ray photoelectron spectroscopy analysis suggests that the incorporation of Ni affects the conductivity of SFNM through changing the ratios of Fe³⁺/Fe²⁺ and Mo⁶⁺/Mo⁵⁺. Sr<sub>2sub>Fe<sub>1.4sub>Ni<sub>0.1sub>Mo<sub>0.5sub>O<sub>6-δsub> shows the highest electrical conductivity of 20.6 S cm^-1 at 800 °C in H<sub>2sub>. The performance of this anode was further tested with electrolyte-supported cells, giving 380 mW cm^-2 at 750 °C in H<sub>2sub>, hence demonstrating that Ni doping in the B-site is beneficial for Sr<sub>2sub>Fe<sub>1.5sub>Mo<sub>0.5sub>O<sub>6-δsub> anode performance. 

Surface modification of LiV<sub>3sub>O<sub>8sub> nanosheets via layer-by-layer self-assembly for high-performance rechargeable lithium batteries

In this work, an economical route based on hydrothermal and layer-by-layer (LBL) self-assembly processes has been developed to synthesize unique Al <sub>2sub>O<sub>3sub>-modified LiV<sub>3sub>O<sub>8sub> nanosheets, comprising a core of LiV<sub>3sub>O<sub>8sub> nanosheets and a thin Al <sub>2sub>O<sub>3sub> nanolayer. The thickness of the Al<sub>2sub>O <sub>3sub> nanolayer can be tuned by altering the LBL cycles. When evaluated for their lithium-storage properties, the 1 LBL Al<sub>2sub>O <sub>3sub>-modified LiV<sub>3sub>O<sub>8sub> nanosheets exhibit a high discharge capacity of 191 mA h g^-1 at 300 mA g^-1 (1C) over 200 cycles and excellent rate capability, demonstrating that enhanced physical and/or chemical properties can be achieved through proper surface modification. © 2014 Elsevier B.V. All rights reserved.

Extracellular DNA impedes the transport of vancomycin in Staphylococcus epidermidis biofilms pre-exposed to sub-inhibitory concentrations of vancomycin

Staphylococcus epidermidis biofilm formation is responsible for the persistence of orthopedic implant infections. Previous studies have shown that exposure of S. epidermidis biofilms to sub-MICs of antibiotics induced an increased level of biofilm persistence. BODIPY FL-vancomycin (a fluorescent vancomycin conjugate) and confocal microscopy were used to show that the penetration of vancomycin through sub-MIC-vancomycin-treated S. epidermidis biofilms was impeded compared to that of control, untreated biofilms. Further experiments showed an increase in the extracellular DNA (eDNA) concentration in biofilms preexposed to sub-MIC vancomycin, suggesting a potential role for eDNA in the hindrance of vancomycin activity. Exogenously added, S. epidermidis DNA increased the planktonic vancomycin MIC and protected biofilm cells from lethal vancomycin concentrations. Finally, isothermal titration calorimetry (ITC) revealed that the binding constant of DNA and vancomycin was 100-fold higher than the previously reported binding constant of vancomycin and its intended cellular D-Ala-D-Ala peptide target. This study provides an explanation of the eDNA-based mechanism of antibiotic tolerance in sub-MIC-vancomycin-treated S. epidermidis biofilms, which might be an important factor for the persistence of biofilm infections.