An effective rhodium catalyst system on the synthesis of acetic acid from methyl formate

Rh/Lil/SnR₄ is an effective catalyst system for the conversion of methyl formate to acetic acid under carbon monoxide pressure. The effects of solvent and initial CO partial pressure on the turnover rate of the reaction were investigated. The possibility of replacing some of the iodide promoters by tin compounds has been probed.     

Iodide mediated electrolysis of acidic coke/coal suspension

Hydrogen is among the emerging energy vectors that are being developed to replace nonrenewable hydrocarbon energy sources. The preferred method to produce hydrogen without generating greenhouse gases is the electrolysis of water using renewable energy. The reduction of energy during the water electrolysis process is a desirable goal regardless of the source of electric power. Similar to ferrous/ferric mediation, iodide can be used as a mediator in the electrolysis of an acidic suspension of coke or coal. The iodide ion is oxidized at a far lower anodic potential than the alternative oxygen evolution reaction. This reduces the cell electrolysis voltage and, consequently, reduces electricity use. The iodide consumed at the anode is continuously regenerated by chemical reaction with the coke/coal in suspension.     

测定银的新催化分光光度法研究──藏红T－碘化钾指示反应体系

根据银对藏红Ｔ与碘离子氧化还原反应的催化作用，建立了一种测定微量银的动力学光度法。方法的线性范围为０．５～４．０μｇ／ｍｌ，检测限为０．０２μｇ／ｍｌ。除Ｈｇ２＋严重干扰，Ｆｅ３＋、Ｃｒ６＋有轻度干扰外，其余常见的离子不影响测定。与常见测定银的动力学法相比，本法反应速度很快，且所有测定均可在室温下进行。     

结晶锆棒的碘化制备技术

碘化法制备结晶锆是提纯金属锆的有效方法之一,制备的结晶锆具有纯度高、气体杂质含量低、加工性能好等优点。以海绵锆为原料,通过碘化提纯,制备的金属锆纯度可达到99.9%。本文简述了碘化法生产锆晶棒的原理,并重点对碘化设备和碘化提纯影响因素的研究进展进行了综述。     

碘化铅多晶合成与单晶体生长研究

碘化铅 (PbI2 )的平均原子序数较大 ,碘化铅晶体有较宽的禁带宽度 ,作为一种新型的室温核辐射探测器材料有广泛的前景。本文对碘化铅原料的合成与晶体生长工艺进行了初步研究 ,用垂直布里奇曼法生长出了直径达 2 0mm、长约 3 0mm的完整半透明的碘化铅单晶体     

Determination of iodide,iodate and organo-iodine in waters with a new total organic iodine measurement approach

The dissolved iodine species that dominate aquatic systems are iodide, iodate and organo-iodine. These species may undergo transformation to one another and thus affect the formation of iodinated disinfection byproducts during disinfection of drinking waters or wastewater effluents. In this study, a fast, sensitive and accurate method for determining these iodine species in waters was developed by derivatizing iodide and iodate to organic iodine and measuring organic iodine with a total organic iodine (TOI) measurement approach. Within this method, organo-iodine was determined directly by TOI measurement; iodide was oxidized by monochloramine to hypoiodous acid and then hypoiodous acid reacted with phenol to form organic iodine, which was determined by TOI measurement; iodate was reduced by ascorbic acid to iodide and then determined as iodide. The quantitation limit of organo-iodine or sum of organo-iodine and iodide or sum of organo-iodine, iodide and iodate was 5 μg/L as I for a 40 mL water sample (or 2.5 μg/L as I for an 80 mL water sample, or 1.25 μg/L as I for a 160 mL water sample). This method was successfully applied to the determination of iodide, iodate and organo-iodine in a variety of water samples, including tap water, seawater, urine and wastewater. The recoveries of iodide, iodate and organo-iodine were 91–109%, 90–108% and 91–108%, respectively. The concentrations and distributions of iodine species in different water samples were obtained and compared.     

A channel flow cell system specifically designed to test the efficiency of redox shuttles in dye sensitized solar cells

The construction and use of a thin layer flow cell test system employing a TiO₂ working electrode, a platinum quasi-reference electrode and the ruthenium dye (H₂-dcbpy)Ru(NCS)₂ (H₂-dcbpy=2,2′-bipyridine-4,4′-dicarboxylic acid) is described. The efficient design enables significant advantages to be gained over presently available procedures for the measurement of photocurrents of dye-sensitized solar cells. The widely used iodide/triiodide redox shuttle system has been investigated over a wide range of conditions. A linear dependence of photocurrent on cation radius was revealed. Under certain conditions, the photocurrent measured in the presence of the Li⁺ cation is five times larger than when the (C₄H₉)₄N⁺ cation is used. Additionally, the addition of low concentrations of cations with small diameters has a significant catalytic enhancement effect on the photocurrent. Other redox shuttles, based on ferrocene, thiocyanate, triiodide and bromide, were tested for their performance in the flow cell and compared to iodide. However, despite some apparent thermodynamic advantages, the photocurrents obtained with these redox shuttles were more than two orders of magnitude lower than those measured with iodide. This finding implies that the efficiency of redox shuttles is limited by kinetic restraints rather than their thermodynamic properties and confirms that the iodide/triiodide system is the dominant redox shuttle.     

Study of iodide sorption to the argillite of Tournemire in alkaline media

Argillaceous rocks are considered potential host rocks for radioactive waste repositories. The concrete matrix that could be used as a barrier could react with the groundwater of the geological site, inducing a drastic change in its chemical composition and its pH (10–13). Consequently, the physicochemical properties of the rock in contact with this alkaline solution may be modified and, in turn, may induce modification on the behaviour of radioelements. This study, applied to the argillite of Tournemire, involves characterizing I⁻ sorption to an argillaceous rock in alkaline media in batch experiments under N₂-controlled conditions. I⁻ was added as a ¹²⁵I radiotracer and measured by γ spectrometry.Preliminary experiments were conducted with different solution/solid ratios (v/m=2.5, 5 and 20 ml g⁻¹) and contact times (1–14 days) in order to determine the optimal experimental conditions. The chosen v/m ratio was 5 ml g⁻¹ as the best compromise between a high K_d value and a low error of the measure. The chosen experiment duration was 1 day because I⁻ sorption was highest and to limit the effects of pyrite oxidation. One of the experiments, performed with a radio-sterilized sample to test possible effects from microorganisms, showed that they could enhance iodide retention, particularly during the first 2 contact days.The influence of pH on I⁻ sorption was tested using solutions between values of 8.3 and 12.8. The K_d values were independent of pH and very low (0.3 ml g⁻¹).Finally, the influence of the chemical composition of concrete fluids was also tested. Three solution compositions corresponding to different steps in the evolution of fluids in contact with altering concrete were used: fluid in contact with fresh concrete (pH 13.2), with moderately degraded concrete (pH 12.1) and with strongly degraded concrete (pH 11.5). Each solution contained variable amounts of sodium, potassium, calcium, silica and sulphate. I⁻ sorption was also very low (K_d0.2 ml g⁻¹). Additional experiments were conducted with alkaline solutions containing different amounts of SO₄²⁻ ions (10⁻³–10⁻² M) to test sulphate–iodide sorption competition. I⁻ retention was independent of the sulphate concentration.     

DI-B experiment: planning, design and performance of an in situ diffusion experiment in the Opalinus Clay formation

The DI-B experiment is a long-term, natural-scale, in situ diffusion experiment, which is being performed in the Opalinus Clay formation at the Mont Terri Underground Rock Laboratory (URL), in Switzerland, employing nonradioactive tracers. One of the key aspects to be addressed for nuclear waste repository safety assessment purposes is the understanding of the transport mechanisms of the radionuclides contained in the radioactive waste. Consolidated clay formations display very low water hydraulic conductivities, so it is expected that the predominant transport process will be diffusion.The experimental set-up has been designed to withstand the site conditions and for monitoring and recording several physicochemical parameters (pH, conductivity, oxidation–reduction potential), as well as the pressures in the circuit and for the long-distance monitoring of the data acquisition system.The tracer selection has been made based on previous investigations carried out at CIEMAT, including a literature survey, laboratory sorption experiments and hydrogeochemical modeling for determining tracer stability under the physicochemical conditions to be expected in the site. The final selection includes ⁶Li, ⁸⁷Rb, D (as D₂O) and I (as I⁻). Hydrogeochemical modeling confirmed the stability of all the tracers selected. Batch sorption experiments showed that no sorption in the rock occurred in the case of ⁶Li, D and I (conservative tracers), whereas ⁸⁷Rb was 100% sorbed. However, ⁸⁷Rb was chosen because of its analogy with Cs, a relevant radionuclide commonly present in the nuclear spent fuel.Diffusion experiments have been carried out at laboratory scale with Opalinus Clay samples to provide diffusion parameters for modeling purposes. Effective diffusion coefficients, perpendicular and parallel to the bedding planes of the rock, respectively, were (1.68± 0.42)×10⁻¹¹ and (4.02± 0.30)×10⁻¹¹ m²/s for tritium, and (2.70± 0.27)×10⁻¹² and (1.38± 0.49)×10⁻¹¹ m²/s for iodide. Additional through-diffusion experiments (parallel to the bedding) were performed with the nonsorbing tracer ³⁶Cl⁻, in order to check the results obtained for iodide. The effective diffusion coefficient measured for chloride ions was (1.18± 0.27)×10⁻¹¹ m²/s, which is practically equal to the value obtained for iodide.Preliminary diffusion calculations have been carried out using two transport codes: GIMRT and CORE^2D, with conservative and nonconservative tracers, using effective diffusion coefficients (D_e) obtained experimentally in the laboratory (through-diffusion experiments) or selected from the literature. The diffusion profiles obtained from the calculations showed slight variations, which were consistent with the different modeling approaches employed. The predictive modeling results have been used to determine the initial tracer concentration that should be added to the circuit to assure well-defined profiles at the end of the experiment.This long-term in situ diffusion experiment will also provide useful data for the interpretation of previous diffusion experiments performed at the Mont Terri URL.     

Characterizations of tungsten carbide as a non-Pt counter electrode in dye-sensitized solar cells

Tungsten carbide particles as a counter electrode for dye-sensitized solar cells are prepared by heating layered tungsten oxides at 700, 800, and 900 °C. In particular, the sample heated at 800 °C reveals dominant WC structure and relatively high specific surface area. The improved photoelectrochemical properties of the sample prepared at 800 °C may be due to both catalytic activity of WC phase and high active sites for iodide reduction in comparison with other electrodes.