PHOTOCATALYTIC HYDROGEN EVOLUTION FROM WATER SPLITTING UNDER VISIBLE LIGHT IRRADIATION ON NOVEL PHOTOCATALYST FULLENES-PVP-ZN0.999NI0.001S

Fullerenes (C60/C70) linked up to Ni-doped ZnS through the medium of an amphalic polymer polyvinyl pyrrolidone (PVP) to form a new kind of photocatalyst for hydrogen evolution from aqueous Na2S/Na2SO3 solution under visible light irradiation, the photocatalytic activities of this novel photocatalyst C60/C70-PVP-Zn0.999Ni0.001S are 3-5 fold higher compared with that of precurse catalyst Zn0.999Ni0.001S. This result could be attributed to Schottky barrier layer built between C60/C70 and Zn0.999Ni0.001S due to the electro-negativity of C60 and characteristic of being used as a multiple electron acceptor. C60 or C60/C70, its moiety, with its low energy first excited singlet state, is a good energy acceptor and in addition readily accepts multiple electrons, making it a potential electron accumulate as we know, which could protect the separation between electrons and holes against combination. This is an important reason for the marked increase of amount of H2 evolution during the photocatalytic process for the composite system C60/C70-PVP-Zn0.999Ni0.001S.     

Sample enrichment by using monolithic precolumns in microcolumn liquid chromatography

An on-line sample enrichment system was designed using monolithic precolumns in microcolumn LC. The monolithic ODS capillary columns were prepared via in situ sol-gel processes. The enrichment efficiency of the monolithic columns was tested by using phthalates as the analytes. The relative standard deviations (n = 6) for the retention time, peak area and peak height were between 0.4 and 1.2%, 0.9 and 5.5% and 0.4 and 3.9%, respectively. The system was linear (R2 > 0.99) within the working sample concentration and sample volume ranges. Comparing to 0.2 microl injection with a typical sample injector, the theoretical plate number of a same separation column was increased by 3-6-fold when the precolumn unit was used for sample injection. The recoveries of the analytes were between 88 and 120%, and the sample volume that could be injected into the system was increased up to 5000-fold. The limits of detection were improved by more than 2000-fold and were between 0.21 and 0.87 ng ml(-1) even with a UV absorbance detector. This system was applied to the determination of phthalates contained in laboratory distilled water and tap water samples.     

In situ sensing of the middle atmosphere with balloonborne near-infrared laser diodes

Since 1997, two near-infrared laser diode sensors have been developed with the support of the CNES, the French space agency, to provide in situ data of H(2)O, CH(4) and CO(2) in the middle atmosphere. The realized instruments were flown from stratospheric balloons within the framework of European campaigns for the study of stratospheric ozone and water vapor and were involved in the validation of the ODIN and ENVISAT satellites. In this paper, we describe the developed laser probing technique, we report atmospheric measurements and finally we discuss future perspectives, particularly the in situ laser sensing of the lower atmosphere of Mars and the implication of the laser hygrometers in balloon campaigns at mid-latitudes and tropical regions to investigate the sources and sinks of stratospheric H(2)O.     

Sensitive trace enrichment of environmental andiandrogen vinclozolin from natural waters and sediment samples using hollow-fiber liquid-phase microextraction

The presence of vinclozolin in the environment as far as the endocrine disruption effects in biota are concerned has raised interest in the environmental fate of this compound. In this respect, the present study attempts to investigate the feasibility of applying a novel quantitative method, liquid-phase microextraction (LPME), so as to determine this environmental andiandrogen in environmental samples such as water and sediment samples. The technique involved the use of a small amount (3 microL) of organic solvent impregnated in a hollow fiber membrane, which was attached to the needle of a conventional GC syringe. The extracted samples were analyzed by gas chromatography coupled with electron-capture detection. Experimental LPME conditions such as extraction solvent, stirring rate, content of NaCl and pH were tested. Once LPME was optimized, the performance of the proposed technique was evaluated for the determination of vinclozolin in different types of natural water samples. The recovery of spiked water samples was from 80 to 99%. The procedure was adequate for quantification of vinclozolin in waters at levels of 0.010 to 50 microg/L (r> 0.994) with a detection limit of 0.001 microg/L (S/N= 3). Natural sediment samples from the Aliakmonas River area (Macedonia, Greece) spiked with the target andiandrogen compound were liquid-liquid extracted and analyzed by the methodology developed in this work. No significant interferences from the samples matrix were noticed, indicating that the reported methodology is an innovative tactic for sample preparation in sediment analysis, with a considerable improvement in the achieved detection limits. The results demonstrated that apart from analyte enrichment, the proposed LPME procedure also serves as clean-up method and could be successfully performed to determine trace amounts of vinclozolin in water and sediment samples.     

Swelling of physically cross-linked copolymers in water vapour

A general thermodynamic equation for the swelling of a cross-linked polymer system in the vapour of a swelling agent has been derived under isothermal and isobaric conditions. The equation is used to describe the equilibrium uptake of water by elastomers Arnitel^® (DSM), which are hard-soft-segment block copolymers in which the hard segments poly(butylene terephthalate) crystallise and are responsible for a physical cross-linking. The gravimetrically determined degrees of swelling of different elastomers in water vapour of various partial pressures are analysed and discussed by the application of an extended semi-empirical swelling equation of Flory-Huggins-Staverman-van Santen.     

A flow injection-ETAAS system for the on-line determination of total and dissolved silica in waters

In this work total (Si-tot) and ‘soluble’ or reactive (Si-sol) concentrations of silicon in natural and tap waters were sequentially determined by electrothermal atomic absorption spectrometry (ETAAS). First, samples were on-line diluted based on the merging-zone principle in order to allow the determination of Si-tot within the 300–1000 μgSi l⁻¹ range. After the dilution process, a sub-sample was collected in the capillary of a sampling arm assembly (SAA). Thereafter, samples were subject to a precipitation/dissolution process in order to allow the determination of Si-sol within the 280–850 μgSi l⁻¹. Si-sol was precipitated with ammonium chloride and collected on the walls of a knotted coil. The precipitate was dissolved with ammonium molybdate in an acidic medium (HNO₃) and a sub-sample was then collected in the SAA. In both cases, 10 μl volumes of the sub-sample were injected into the atomizer with the previous introduction of 20 ng of Eu as chemical modifier (10 μl) by the spectrometer autosampler. The recovery values obtained with natural waters spiked samples were over 46% and the agreement between observed and certified samples values was good. The proportion of Si-sol in comparison with the Si-tot was high (85–95%) in most natural waters. The precision of the method was 2.4–3.5 and 4.5–6.2% (n=10) for the determination of Si-tot and Si-sol, respectively.     

Developing a sequential injection-square wave voltammetry (SI-SWV) method for determination of atrazine using a hanging mercury drop electrode

This paper describes the development of a sequential injection analysis method to automate the determination of atrazine by square wave voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. To perform these tasks, an 800 μL monosegment is formed, composed by 400 μL of sample and 400 μL of buffer/standard solution. To obtain an efficient homogenization, the sample solution is divided in five zones intercalated by four zones of the Britton-Robinson buffer (pH 2.0) in presence of appropriate concentration of NaNO₃ and varying atrazine standard concentrations. This mixture zone is isolated from the carrier solution by two 100 μL air bubbles. After homogenization in an auxiliary reaction coil the mixture zone is injected toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode, at a flow rate of 50 μL s⁻¹. After a suitable delay time, the potential is scanned from −0.5 to −1.2 V versus Ag/AgCl using a frequency of 300 Hz and pulse height of 25 mV. The linear dynamic range is observed for atrazine concentrations between 1.16 × 10⁻⁷ and 2.32 × 10⁻⁶ mol L⁻¹, obeying the linear equation i_p = (−6.91 ± 0.07) × 10⁸[atrazine] + (4 ± 8), with r² = 0.9996, for which the slope is given in nA L mol⁻¹. The detection and quantification limits of the method are 2.1 × 10⁻⁸ and 7.0 × 10⁻⁸ mol L⁻¹, respectively. The sampling frequency is 37 h⁻¹, when the standard addition protocol is followed. This frequency can be increased to 42 h⁻¹ if the protocol to obtain in-line calibration curve is used for quantification. The method was applied for determination of atrazine in spiked river water samples and its accuracy was evaluated by comparison with the batch standard addition approach, which revealed that there is no evidence of statistically significant differences between the two methods.     

一种新的库仑微水滴定仪的设计方法

在传统微库仑滴定仪原理的基础上，利用８７５１单片机和微机，采用对电解电流时间调制的方法以及测量精度为准则判断滴定终点，从而大大地提高了仪器的测量精度和重复性。     

Polarisabilites moléculaires et effet diélectrique de milieu à l'état liquide. Étude théorique de la molécule d'eau et de ses diméres

The model of Onsager in which a polar molecule undergoes a reaction field due to the polarization of the molecular surroundings is used to evaluate by a S.C.F. calculation (CNDO/2 approximation) the modifications of a molecular structure in the liquid state.Application to water molecule and to three polar dimers for values of the dielectric constant varying between 3 and 78, shows that most of geometric parameters and dipoles moments vary of few per cent when the molecule is inserted in a liquid. In the liquid state dipole moments do not depend very much on the dielectric constant but energies and relative stabilities of isomers are strongly dependent on the medium.[/p]