Cerium dioxide as a new reactive sorbent for fast degradation of parathion methyl and some other organophosphates

Cerium dioxide was used for the first time as reactive sorbent for the degradation of the organophosphate pesticides parathion methyl,chlorpyrifos,dichlofenthion,fenchlorphos,and prothiofos,as well as of some chemical warfare agents—nerve gases soman and O-ethyl S-[2-(diisopropylamino) ethyl] methylphosphonothioate(VX).CeO2 specimens were prepared by calcination of basic cerous carbonate obtained by precipitation from an aqueous solution.The CeO2 samples containing certain amounts(1 wt.%–5 wt.%) of the neighboring lanthanides(La,Pr,Nd) were prepared in a similar way from pure lanthanide salts.It was shown that ceria accelerated markedly the decomposition of parathion methyl causing the cleavage of the P-O-aryl bond in the pesticide molecule.A similar reaction mechanism was proposed for the degradation of other organophosphate pesticides and nerve agents.The degradation times(reaction half-times) were in an order of minutes in the presence of CeO2,compared to hours or days under common environmental conditions.The reaction in suitable organic solvents allowed conversions of about 90% for parathion methyl loading of 20 mg pesticide/g CeO2 within 2 h with a reactant half-life in the order of 0.1 min.The key parameter governing the degradation efficiency of CeO2 was the temperature during calcination.At optimum calcination temperature(about 773.15 K),the produced ceria retained a sufficiently high surface area,and attained an optimum degree of crystallinity(related to a number of crystal defects,and thus potential reactive sites).The presence of other lanthanides somewhat decreased the reaction rate,but this effect was not detrimental and permitted the possible use of chemically impure ceria as a reactive sorbent.A fast organophosphate degradation was demonstrated not only in non-polar solvents(such as heptane),but also in polar aprotic solvents(acetonitrile,acetone) that are miscible with water.This opens new possibilities for designing more versatile decontamination strategies.The cleavage of phosphate ester bonds is of a great importance not only for the degradation of dangerous chemicals(chemical weapons,pesticides),but also for interactions of ceria(especially the nano-sized one) in biologically relevant systems.     

Emerging risk of infestation and contamination of dried fruits by mites in the Czech Republic

The introduction of live insects into human food is rare in developed countries. However, we report, for the first time, an emerging risk that exists from dried fruit in Central Europe. Recently, massive and frequent infestation of dried fruit imported from the Mediterranean region by the mite, Carpoglpyhus lactis L. (Acarina: Carpoglyphidae), has been found. In 180 samples taken from supermarkets, 13% were contaminated; the contamination levels ranged from 0 to 660 mites per g of dried fruit. The contamination was found in dried apricots, figs, plums and raisins. To estimate the risks and food preferences of C. lactis, its growth rate was examined under laboratory conditions. Starting with a hypothetical population of 10 mites per g of dried fruit, the risk level of 1000 mites per g of dried fruit is reached at 42 days for dried figs, 49 days for dried pineapple and 63 days for dried apricots, dates and plums at 25 °C and 85% relative humidity. We found that mites are able to enter every dried fruit packing material tested, including polypropylene and aluminum foils. This indicates that mites can move from package to package in supermarkets. Mites are known as allergen producers and vectors of mycotoxin-producing fungi. These findings indicate that an increased risk of C. lactis contamination exists in dried fruit.     

Degradation of surfactant solutions by age and by a flow singularity

Four different surfactants were investigated in a closed hydraulic loop in order to find the influence of age of the solution on drag reducing effectiveness and on decrease of critical shear stress. It shows that aging of a particular surfactant is dependent on its concentration. Different sensitivity of solutions to flow disturbances is also shown.     

Refractive index of polymethylmethacrylate oriented by fluid temperature under electrical field

We prepared micron and submicron polymethylmethacrylate (PMMA) layers by the spin-coating method. We investigated the possibility to orientate polymer dipoles in electric field in the glass transition area (T _g) and the fluid temperature of PMMA with the aim to increase its refractive index (n) after the layer is cooled below T _g. We have studied the effect of electric field (up to 12 kV cm⁻¹) on change of surface morphology of the layer, dependence of n and contact angle (surface wettability) on the field and dependence of layers orientation on orientation of electric field. The surface morphology was examined using atomic force microscopy (AFM), contact angles were measured by goniometer, film thickness was measured by profilometer, refractive index of films was determined using refractometer. The change of refractive index as dependent on the PMMA layer orientation in electric field depends on temperature and electric field. The highest change in n was found for electric field 11 kV cm⁻¹. The change in contact angle (wettability) on surface of an orientated PMMA layer confirms the dipoles orientation in electric field unambiguously. The orientation of layers causes a “slight” change in their morphology and a “slight” increase of surface roughness only for one direction of field effect. Change in colour for oriented layers does not depend on orientation of electric field.     

A local implicit function theorem and application to systems of differential equations

A local implicit function theorem is proved which assumes certain injectivity rather than differentiability. Moreover, there is given a result on solvability of noncanonic systems of differential equations which arise in optimal control and network theory.     

Oxidation von Schweißverbindungen bei hohen Temperaturen

Oxidation behaviour of welds at high temperatures Experimental investigation into the behaviour of welds of 18 8 CrNi steel with CrNiMoMn 18 12 2 2 electrodes at temperatures Up to 900°C and test durations up 1000 h. The oxidation behaviour of the weld depends from its Cr and Si contents which must not be below definite values. At working temperatures exceeding 9OO°C it is necessary to use base metals of higher Cr and Si contents and electrodes containing 36% Ni and 18% Cr, in order to inhibit carbon diffusion and thus effectively to prevent the formation of decarburized and carburized zones.     

High-rate reactive deposition of transparent SiO2 films containing low amount of Zr from molten magnetron target

The paper reports on a reactive deposition of transparent SiO₂ films with a low amount (≤ 3 at.%) of Zr prepared from the molten target using the AC pulsed dual magnetron. It is shown that the deposition rate a_D of the transparent oxide film strongly increases at the critical target power density (W_t)_cr when the solid target starts to melt and the magnetron operates with a molten target. In this case, the evaporation of target material plays a dominant role in the reactive deposition of thin films. This process is called the ionized magnetron evaporation. Oxide films reactively deposited from the molten target are well transparent and highly elastic. The maximum deposition rate of the transparent oxide film achieved in our experiments is 814 nm/min.     

Energy utilisation of biowaste — Sunflower-seed hulls for co-firing with coal

Sunflower-seed hulls (SSH) represent a source of combustible biomass characterised by high contents of potassium and phosphorus and a low silica content. The relatively high net calorific value of 20 MJ/kg d.m. is mainly influenced by the lignin content. Potassium and phosphorus are very important elements in biomass combustion for fuel, influencing slagging and fouling problems. Mixtures with different ratios of brown coal and sunflower-seed hulls (0-22% SSH) were co-fired in the Olomouc power plant. The behaviour of elements in the fly ash and the bottom ash (SiO₂, Al₂O₃, K₂O, P₂O₅, Zn, Cu and Cd) varied in relation to the amount of SSH added to the coal. The fly ash from the co-firing of 20% SSH with coal had a high content of water-leachable sulphates and total dissolved solids. The utilisation of fly ash in civil engineering (land reclamation) should fulfil criteria established by the Council Decision 2003/33/EC for non-hazardous waste. To ensure that the required water-leachable sulphate concentrations are within regulatory limits the fuel may contain a maximum of 14% SSH.     

Two-Step Sintering of oxide ceramics with various crystal structures

The influence of Two-Step Sintering (TSS) process on the final microstructure of oxide ceramic materials with three different crystal structures was studied. Two kinds of alumina (particle size 100 nm resp. 240 nm) as well as tetragonal zirconia (stabilized with 3 mol% Y₂O₃, particle size 60 nm) and cubic zirconia (8 mol% Y₂O₃, 140 nm) powders were cold isostatically pressed and pressurelessly sintered with different heating schedules. The microstructures achieved with TSS method were compared with microstructures achieved with conventional Single-Step Sintering (SSS) schedule. The results showed that the efficiency of the TSS of these oxide ceramics was more dependent on their crystal structure than on their particle size and green body microstructure. The method of TSS brought only negligible improvement of the microstructure of tetragonal zirconia and hexagonal alumina ceramics. On the other hand, TSS was successful in the sintering of cubic zirconia ceramics; it led to a decrease in grain size by a factor of 2.