Control of planktonic and sessile bacterial cells by essential oils

The antibacterial potential of essential oils (EOs) from Cinnamomum cassia bark and Melaleuca alternifolia and Cymbopogon flexuosus leaves was evaluated against planktonic and sessile cells of enteropathogenic Escherichia coli (EPEC) and Listeria monocytogenes. The EOs were tested singly and in different combinations of equal percentages: mixtures of two (1:1 in v/v) and three EOs (1:1:1 in v/v/v). The minimal inhibitory concentrations (MICs) were determined against planktonic cells and the anti-biofilm activity was verified against bacterial cells adhered in the wells of polystyrene microplates. These initial tests indicated the EO of C. cassia as a potential anti-biofilm agent, and their effect was studied against sessile cells of biofilms formed on stainless steel surface under agitation and static conditions. For both bacterial species, a solution containing 2% (v/v) of C. cassia EO was effective against the biofilm formed under static conditions, because the counts obtained were below the detection level of the plate count method employed. Although the biofilm of L. monocytogenes showed a decreased number of adhered cells after formation under agitating conditions (p < 0.05), it was surprisingly more resistant to the EO of C. cassia than the biofilm formed under static conditions (p < 0.05). All of the EOs and combinations tested presented antibacterial activity, almost against planktonic cells; however, the EO of C. cassia showed to be the most effective as a potential agent for the production of sanitizers for biofilm control in the food industries.     

Simulation of a composite cathode in solid oxide fuel cells

Incorporating the mechanistic model for oxygen reduction at YSZ/LSM interface, a complete micro-model for YSZ/LSM composite cathode considering all forms of polarization was developed which established the interrelationship among the transport phenomena, electrochemical processes and the microstructure of the composite cathode. The exchange current densities of the rate-limiting steps used in the simulation were obtained by fitting the proposed mechanistic model to the DC polarization curves. Simulation was conducted to predict the optimal design parameters, e.g. cathode thickness, particle size, particle size ratio and YSZ volume fraction, for a LSM/YSZ composite cathode. Except for the YSZ volume fraction beyond the percolation thresholds, the predicted results seem to be in good agreement with the experimental and literature data. Incorporating with reliable experimental data, the model can be used as a tool to guide the design of high performance cathodes.     

Preparation and properties of bacterial cellulose/graphene oxide composite films using dyeing method

In this study, bacterial cellulose (BC) hydrogels were cultured from a kombucha SCOBY starter. The scanning electron microscopy (SEM) results indicated that the dried BC exhibited an interpenetrating fibrous mat. The BC films harvested for 5, 10, and 15 days were 15–19, 14.4–24, and 30–31 μm thick, respectively. Then, BC/graphene oxide (GO) composite films were prepared via the exhaust dyeing method. GO sheets penetrated the BC matrix, resulting in the formation of a BC/GO composite, as revealed by the SEM analysis results. The mechanical properties of the composite films were investigated. Compared with virgin BC, the tensile strength of the composite films was higher, while the %E at break was lower, resulting in a significant increase in the Young's modulus. The X-ray diffraction results indicated that an increase in the dyeing time (0.5–2 h) gradually induced cellulose crystalline conformation, which in turn affected the swelling ability, mechanical properties, and electrical properties of the BC/GO composite films. After the reduction of GO to reduced GO (rGO), flexible conductive BC/rGO films were obtained, as confirmed by their resistivity values. Thus, flexible conductive composite films with excellent mechanical properties were successfully fabricated.     

Film percolation for composite electrodes of solid oxide fuel cells

A film percolation model is proposed for composite electrodes of solid oxide fuel cells (SOFCs). The model is developed to predict the percolation properties of 2D-infinite structures which represent the structural characteristics of composite electrodes of electrochemical devices such as SOFCs. The model can be used to estimate electrode properties, such as percolation probability, active three-phase boundary length and interfacial polarization resistance. Compared with the classic percolation theory, which is particularly applicable to 3D-infinite bulks, the model can explicitly capture the effects of thinly layered nature of composite electrodes, and describes a cross-over between 2D-infinite films and 3D-infinite bulks. It also permits the prediction within whole electrode composition range, and can be easily applied in SOFC modeling.     

Carbon nanotubes-polyethylene oxide composite electrolyte for solid-state dye-sensitized solar cells

Novel carbon nanotubes (CNTs)-polyethylene oxide (PEO) composite electrolyte for dye-sensitized solar cell (DSSC) was prepared and characterized for the first time. The strong bonding and interaction between CNTs and PEO in CNTs-PEO composites was observed by the characterization of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectra. The introduction of CNTs into PEO matrix significantly improved the electrolyte properties of DSSC such as roughness, amorphicity and ionic conductivity. The solid-state DSSC fabricated with the optimum composite electrolyte (added 1% CNTs in PEO matrix, 1%CNT-PEO) achieved maximum conversion efficiency of 3.5%, an open circuit voltage (V_OC) of 0.589 V, short circuit current density (J_SC) of 10.64 mA/cm² and fill factor (FF) of 56%. The highest IPCE in the DSSC fabricated with 1%CNT-PEO electrolyte is ascribed to the improved ionic conductivity of composite electrolytes and enhanced interfacial contact between electrode and electrolyte.     

Thermal,mechanical, and electrical properties of LSCo/mullite composite contact materials for solid oxide fuel cells

Lanthanum strontium cobaltite (LSCo) is considered as a good candidate cathode contact material for solid oxide fuel cells, due to high electrical conductivity. However, LSCo has a very large coefficient of thermal expansion (CTE) than the cells and metallic interconnects. As a result, poor mechanical stability is expected during thermal cycling. To minimize the CTE mismatch, we investigate a composite approach involving mixing LSCo with an inert material of low CTE, such as mullite at volume fractions from 0.1 to 0.4. Composite's CTE shows a decreasing trend with increasing mullite volume fractions and is consistent with model predictions. X-ray powder diffraction analysis of sintered LSCo/mullite composites exhibits no presence of other phases for samples aged for 500 hours at 800°C, indicating chemical compatibility. Electrical conductivity by a 4-pt method shows a decreasing trend with increasing mullite content. Contact strength of as-sintered and thermally cycled samples show that only the composite with 0.4 volume fraction has a measurable strength; the other composites have no strength. Overall, the composite approach is demonstrated in the LSCo/mullite system to lower the CTE and hence achieve thermal cycle stability. The addition of the inert phase to the LSCo matrix, however, also reduces the electrical conductivity.     

Optimization of laser-patterned YSZ-LSM composite cathode-electrolyte interfaces for solid oxide fuel cells

Patterned cathode/electrolyte interfaces formed by a hexagonal array of ～22 μm deep wells with 24 μm lattice parameter have been prepared by pulsed laser machining to enlarge the contact surface and, consequently, to reduce the cathode polarization of Solid Oxide Fuel Cells. These new interfaces have been tested in YSZ-LSM/YSZ/YSZ-LSM symmetrical cells, where the cathode is deposited by dip-coating. Appropriate ceramic suspensions have been formulated to penetrate into deep wells without presenting interfacial delamination after sintering. We analyse their applicability by comparing their rheology with the microstructure and electrochemical performance of the cells. The activation component of the polarization resistance is reduced by ～50% using ethanol-based suspensions with 20 wt% solids loading, although the gas diffusion component increases due to excessive densification. Alternative ceramic suspensions with 17.5 wt% solids loading provide optimum electrode gas diffusion but lower activation components, resulting in an overall decrease of ～20% in polarization resistance.     

Processing and properties of oxide matrix/oxide fibre composite

Abstract

An all-oxide composite was fabricated. Single crystal alumina fibres were coated with a carbon/zirconia slurry, dried, and uniaxially aligned by winding. Matrix material, alumina with 5 vol.-% unstabilised zirconia added, was tape cast on top of the fibres. Pre-pregs were cut, stacked, and laminated to cross-ply material. Final sintering was done by hot isostatic pressing. A heat treatment was added to remove the carbon and create a porous zirconia interphase. Flexure strengths around 200 MPa were obtained for composites at room temperature while a strength of 124 MPa was recorded at 1200°C. The mechanical properties and non-brittle behaviour was sustained after aging at 1400°C for 1000 h in air.     

复合介孔氧化镍的合成、表征及催化性能

以十二烷基苯磺酸钠(LAS)为模板剂,硝酸镍为镍源,在n(Ni)∶n(LAS)∶n(H2NCH2CH2NH2)∶n(H2O)=1.0∶1.0∶1.0∶200,反应温度80℃、反应2 h条件下,通过水热法合成了氧化镍/十二烷基苯磺酸钠复合介孔氧化物(NiOS),并利用XRD、FTIR、N2吸附脱附和Hammett等方法对材料的晶体结构和表面物性进行了表征。研究结果表明,合成的NiOS具有介孔结构特征,平均孔径为2.2 nm,比表面积为170 m2.g-1。将NiOS用于催化正辛醇乙氧基化反应,当NiOS占正辛醇质量的10%,反应温度150℃,初始反应压力0.5 MPa,环氧乙烷(EO)平均加合数为3时,EO平均反应速率为1.8 mol.h-1.mol-1,与NaOH催化体系相比,所得产品的相对分子质量分布较窄。     

Synthesis and screening of an oroidin library against Pseudomonas aeruginosa biofilms

A 50-compound library based on the marine natural product oroidin was synthesized and assayed for anti-biofilm activity against PAO1 and PA14, two strains of the medically relevant gamma-proteobacterium Pseudomonas aeruginosa. Through structure-activity relationship (SAR) analysis of analogues based on the oroidin template, several conclusions can be drawn as to what structural properties of the synthetic derivatives are necessary to elicit a biological response. Notably, the most active analogues identified were those that contained a 2-aminoimidazole (2-AI) motif and a dibrominated pyrrolecarboxamide subunit. Here we disclose the synthesis and subsequently determined biological activity of this unique class of compounds as inhibitors of biofilm formation that have no direct antibiotic effect.     

Optimization of the microstructure of porous composite cathodes in solid oxide fuel cells

A comprehensive micromodel to predict the electrochemical performance of porous composite LSM‐YSZ cathodes in solid oxide fuel cells (SOFCs) is developed. The random packing sphere model is used to estimate the cathode microstructural properties required for the micromodel. The micromodel developed takes into account the complex interdependency among the mass transport, electron and ion transports, and the electrochemical reaction, and can be used for optimization of the microstructure of porous LSM‐YSZ composite cathodes. It is shown that the electrochemical performance of these cathodes depends on the microstructural variables of the cathode porosity, thickness, particle size ratio, and size and volume fraction of LSM particles. The effect of these microstructural variables on the cathode total resistance, as the objective function to achieve the optimum microstructure for the cathode, is studied through computer simulation. The results indicated that for a LSM‐YSZ cathode operated at the average temperature of 1073.15 K, bulk oxygen partial pressure of 0.21 atm, and total current density of 5000 Am^?2, and constrained to the minimum value of 1 μm for the size of LSM particles and 0.25 for the cathode porosity, the optimum microstructure is obtained at the particle size ratio of unity, LSM particle size of 1 μm and volume fraction of 0.413, porosity of 0.25, and thickness of 60 μm. The cathode total resistance corresponding to the cathode optimized is estimated to be 0.291 Ω cm². © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Development of LSM/YSZ composite cathode for anode-supported solid oxide fuel cells

This paper presents the effect of (La,Sr)MnO₃ (LSM) stoichiometry on the polarization behaviour of LSM/Y₂O₃-ZrO₂ (YSZ) composite cathodes. The composite cathode made of A-site deficient (La_0.85Sr_0.15)_0.9MnO₃ (LSM-B) showed much lower electrode interfacial resistance and overpotential losses than that made of stoichiometric (La_0.85Sr_0.15)_1.0MnO₃ (LSM-A). The much poorer performance of the latter is believed to be due to the formation of resistive substances such as La₂Zr₂O₇/SrZrO₃ between LSM and YSZ phases in the composite electrode. A slight A-site deficiency (∼0.1) was effective in inhibiting the formation of these resistive substances. A power density of ∼1 W cm⁻² at 800 °C was achieved with an anode-supported cell using an LSM-B/YSZ composite cathode. In addition, the effects of cathodic current treatment and electrolyte surface grinding on the performance of composite cathodes were also studied.     

Micro‐modeling of porous composite anodes for solid oxide fuel cells

A new anode micromodel for solid oxide fuel cells to predict the electrochemical performance of hydrocarbon‐fuelled porous composite anodes with various microstructures is developed. In this model, the random packing sphere method is used to estimate the anode microstructural properties, and the complex interdependency among the multicomponent mass transport, electron and ion transports, and electrochemical and chemical reactions is taken into account. As a case study, a porous Ni–YSZ composite anode operated with biogas fuel is simulated numerically and distributions of the current density, polarization, and mole fraction and rate of flux of the fuel components along the thickness of the anode are determined. The effect of the anode microstructural variables including the porosity, thickness, particle‐size ratio, and particle size and volume fraction of Ni particles on the anode electrochemical performance is also studied. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1893–1906, 2012     

Cycling of lithium/metal oxide cells using composite electrolytes containing fumed silicas

The effect on cycle capacity is reported of cathode material (metal oxide, carbon, and current collector) in lithium/metal oxide cells cycled with fumed silica-based composite electrolytes. Three types of electrolytes are compared: filler-free electrolyte consisting of methyl-terminated poly(ethylene glycol) oligomer (PEGdm, M_w=250)+lithium bis(trifluromethylsufonyl)imide (LiTFSI) (Li:O=1:20), and two composite systems of the above baseline liquid electrolyte containing 10-wt% A200 (hydrophilic fumed silica) or R805 (hydrophobic fumed silica with octyl surface group). The composite electrolytes are solid-like gels. Three cathode active materials (LiCoO₂, V₆O₁₃, and Li_xMnO₂), four conducting carbons (graphite Timrex® SFG 15, SFG 44, carbon black Vulcan XC72R, and Ketjenblack EC-600JD), and three current collector materials (Al, Ni, and carbon fiber) were studied. Cells with composite electrolytes show higher capacity, reduced capacity fade, and less cell polarization than those with filler-free electrolyte. Among the three active materials studied, V₆O₁₃ cathodes deliver the highest capacity and Li_xMnO₂ cathodes render the best capacity retention. Discharge capacity of Li/LiCoO₂ cells is affected greatly by cathode carbon type, and the capacity decreases in the order of Ketjenblack>SFG 15>SFG 44>Vulcan. Current collector material also plays a significant role in cell cycling performance. Lithium/vanadium oxide (V₆O₁₃) cells deliver increased capacity using Ni foil and carbon fiber current collectors in comparison to an Al foil current collector.     

溴虫腈的杀虫活性及作用方式研究

室内测定研究了溴虫腈的生物活性和作用方式。结果表明,溴虫腈对多种农业害虫和害螨具有优异的毒杀活性,作用方式以胃毒活性为主,兼有触杀和杀卵活性,但无明显的根内吸活性。     

Novel and high-performance (La,Sr)MnO3 based composite cathodes for intermediate-temperature solid oxide fuel cells

The rapid decrease of the electrocatalytic activity at low temperature (<700 ℃) limits the popularization and application of the classical cathode material LSM (Sr doped LaMnO₃) in SOFC. Herein, we report that the introduction of CBO (CuBi₂O₄) oxide could not only reduce the sintering temperature of LSM-based cathode, but also significantly improves its electrochemical performance at intermediate temperature range of 500–700 ℃. The polarization resistance (R_p) of LSM-CBO20 (including 20 wt. % CBO) composite cathode on GDC electrolyte is only 0.13 Ω cm² at 700 ℃, which is significantly lower than the LSM cathode. The study found that the quite promoted oxygen surface exchange kinetics and catalytic activity of CBO, and the much reduced sintering temperature of the composite cathode contribute to the dramatic decrease of R_p. In addition, when Gd_0.1Ce_0.9O_1.95 (GDC) is introduced, the polarization resistance is further reduced to 0.11 Ω cm² at 700 ℃. The maximum power density of the single cell with LSMGDC-CBO20 triadic phase cathode reaches to 1460 mW cm^-2 at 700 ℃. The present study demonstrates that introducing CBO is an effective and promising approach to improve the electrochemical performance of conventional LSM-based cathode at reduced temperatures.     

Preparation,characterization, and properties of graphene oxide/urushiol-formaldehyde polymer composite coating

Graphene oxide (GO) was modified by 3-methacryloxypropyltrimethoxysilane (MPS) to obtain modified graphene oxide (MGO). MGO was dispersed in urushiol-formaldehyde polymer by mechanical mixing and ultrasonic dispersion, and MGO/urushiol-formaldehyde polymer (UFP) coatings with different MGO contents were fabricated. The microstructure, physico-mechanical properties, and electrochemical properties of the MGO/UFP composite coatings were investigated. The results indicated that the hardness, adhesion, and corrosion resistance of the MGO/UFP composite coatings were obviously enhanced compared with the pure UFP coatings. The hardness and the adhesion grade of the MGO/UFP composite coatings with 3.5 wt% MGO (GO, 1.5 wt%, and MPS, 2.0 wt%) reached 6H and 2, respectively. Additionally, GO connected with MPS by chemical bond and the well-dispersed MGO in UFP could significantly enhance the anticorrosion performance of the UFP coatings, which could result from bending the diffusion pathway of penetrant species in the UFP coating matrix.     

Mechanical properties and biomedical applications of a nanotube hydroxyapatite-reduced graphene oxide composite

As a result of the growing interest in the biological and mechanical performance of hydroxyapatite (HA)–graphene nano-sheets (GNs) composite systems, reduced graphene oxide (rGO) reinforced hydroxyapatite nano-tube (nHA) composites were synthesized in situ using a simple hydrothermal method in a mixed solvent system of ethylene glycol (EG), N,N-dimethylformamide (DMF) and water, without using any of the typical reducing agents. The consolidation process was performed by hot isostatic pressing (HIP) at 1150 °C and 160 MPa. The composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, enabling confirmation of the synthesis and reduction of the nHA and rGO, respectively. The structure of the synthesized powder and cell attachment on the sintered sample was confirmed by field emission scanning electron microscopy (FESEM). The effects of the rGO on the mechanical properties and the in vitro biocompatibility of the nHA based ceramic composites were investigated. The elastic modulus and fracture toughness of the sintered samples increased with the increase of the rGO content when compared to the pure nHA by 86% and 40%, respectively. Cell culture and viability test results showed that the addition of the rGO promotes osteoblast adhesion and proliferation, thereby increasing the biocompatibility of the nHA–rGO composite.     

Microstructure and mechanical properties of three-dimensional oxide/oxide composite fabricated by a slurry infiltration and sintering process

Oxide/oxide composites reinforced by two-dimensional fiber fabrics are important structural materials at high temperatures but exhibit low delamination resistance. This study developed a simple slurry infiltration and sintering (SIS) process to fabricate three-dimensional oxide/oxide composites. The results showed that a homogeneous microstructure in three directions was obtained. This composite possessed a weak matrix, which had a porous structure and low elastic modulus. Typical mechanical properties of the composite were not lower than those of two-dimensional oxide/oxide composites since the flexural strength and fracture toughness were 332.4 MPa and 11.6 MPa·m^1/2, respectively. Particularly, the composite had a good interlaminar shear strength of 25.4 MPa and a superior transthickness tensile strength of 5.6 MPa. X-ray computed tomography showed that fiber yarns in the through-thickness direction effectively impeded crack propagation and enhanced delamination resistance. Therefore, the reported SIS process is a very promising method for manufacturing three-dimensional oxide/oxide composites.     

介孔铈锆氧化物的制备及表征

为了探讨催化剂的活性氧储量与催化剂组成和结构的关系,以Ce~(4+)、Zr~(4+)混合液为基本原料,NaOH溶液为沉淀剂,CTAB为模板剂,制备了Ce~(4+)与Zr~(4+)比例不同的系列铈锆复合氧化物,通过BET、H_2-TPR和XRD对制备的铈锆复合氧化物进行了表征。结果表明,Ce/Zr≤2/3的铈锆复合氧化物具有四方相结构特征,Ce/Zr=1的铈锆复合氧化物具有立方相结构特征;都是典型的介孔材料,有高的比表面积,最大值达到185.7 m~2/g;程序升温测试表明,铈锆复合氧化物在450℃和650℃附近有两个耗氢还原峰,分别对应于表面Ce~(4+)的还原和体相Ce~(4+)的还原;活性氧储量0.148～0.84 molO_2/mol(Ce+Zr),具有良好的可逆吸氧和释氧性质;活性氧储量不仅与材料的组成有关,也与材料的晶体结构有关,与材料的比表面积成正比。