Understanding Complex Electrochemical Impedance Spectroscopy in Corrosion Systems Using in‐situ Synchrotron Radiation Grazing Incidence X‐ray Diffraction

The difficulty in interpreting electrochemical impedance spectroscopy (EIS) data has limited the potential of the method despite its utility as an electrochemical method for studies of electrode reactions and interfacial structures. Taking the test case of the carbon dioxide corrosion of carbon steel, in‐situ synchrotron radiation grazing incidence X‐ray diffraction (SR‐GIXRD) has been demonstrated to be a powerful technique for validating and understanding the interfacial structures associated with complex EIS data. Carbon dioxide corrosion was found to occur in several steps, which may only be surmised by EIS, but the use of SR‐GIXRD in conjunction with EIS has enabled the establishment of a link between EIS time constants and structural changes associated with the evolution of corrosion products with time. By comparison to previous studies by the authors and others in this field, this communication provides the first direct experimental evidence linking SR‐GIXRD surface compositional data to otherwise indistinctive EIS time constants.     

Structure, microstructure, and size dependent catalytic properties of nanostructured ruthenium dioxide

Nanostructured powders of ruthenium dioxide RuO₂ were synthesized via a sol gel route involving acidic solutions with pH varying between 0.4 and 4.5. The RuO₂ nanopowders were characterized by X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM). Rietveld refinement of mean crystal structure was performed on RuO₂ nanopowders and crystallized standard RuO₂ sample. Crystallite sizes measured from X-ray diffraction profiles and TEM analysis varied in the range of 4-10 nm, with a minimum of crystallite dimension for pH=1.5. A good agreement between crystallite sizes calculated from Williamson Hall approach of X-ray data and from direct TEM observations was obtained. The tetragonal crystal cell parameter (a) and cell volumes of nanostructured samples were characterized by values greater than the values of standard RuO₂ sample. In addition, the [Ru-O₆] oxygen octahedrons of rutile structure also depended on crystal size. Catalytic conversion of methane by these RuO₂ nanostructured catalysts was studied as a function of pH, catalytic interaction time, air methane composition, and catalysis temperature, by the way of Fourier transform infrared (FTIR) spectroscopy coupled to homemade catalytic cell. The catalytic efficiency defined as FTIR absorption band intensities I(CO₂) was maximum for sample prepared at pH=1.5, and mainly correlated to crystallite dimensions. No significant catalytic effect was observed from sintered RuO₂ samples.     

An improved colorimetric method for chlorine dioxide and chlorite ion in drinking water using lissamine green B and horseradish peroxidase

Lissamine Green B (LGB) was carefully selected as a potential candidate for the development of a new U.S. Environmental Protection Agency (EPA) method that is intended for use at water utilities to determine chlorine dioxide (ClO₂) in drinking water. Chlorine dioxide reacts with LGB in aqueous solution to decrease the absorbance of LGB in direct proportion to the ClO₂ concentration. LGB was confirmed to have adequate sensitivity, and to suffer less interference than other dyes reported in the literature. The stoichiometry for the reaction between LGB and ClO₂ was found not to be 1:1 and is dependent on the LGB concentration. This required calibration of each LGB stock solution and prompted the investigation of alternate means of calibration, which utilized a horseradish peroxidase (HRP)-catalyzed conversion of chlorite ion (ClO₂⁻) to ClO₂. This approach allowed the simultaneous determination of ClO₂⁻ concentration, which is also required each day at water plants that use ClO₂. Studies were conducted to characterize and carefully optimize the HRP-conversion of ClO₂⁻ to ClO₂ in order to yield reaction conditions that could be accomplished in less than 30 min at modest cost, yet meet EPA's sensitivity and robustness requirements for routine monitoring. An assessment of method detection limit, linearity and slope (or sensitivity), precision, and accuracy in finished drinking water matrices indicated that this approach was suitable for publication as EPA Method 327.0.     

Synthesis and Characterization of SnO2-TiO2 Nanocomposite with Rutile-phase via Hydrothermal Method at Low Temperature

With Ti(SO₄)₂, SnCl₄·5H₂O and urea as raw materials, SnO₂-TiO₂ nanocomposites were synthesized via low temperature hydrothermal method at 80―100 ℃ in aqueous solutions. The morphologies of the products were altered systematically by varying the Ti/Sn molar ratio of the reactants, and rutile-phase particles were obtained with an average diameter of about 52.2 nm at a molar ratio of Ti/Sn=7.5. The surface composition of the composite was revealed by X-ray photoelectron spectroscopy(XPS) and X-ray diffraction(XRD) to be solely TiO₂ with a rutile structure. This new composite material exhibits a high ultraviolet absorption capacity, and its photocatalytic activity for phenol oxidation is much lower than that of the commercial titania nanoparticles(P25).     

Inactivation of Chironomid Larvae with Chlorine Dioxide and Chlorine

Chironomid larvae propagate prolifically in eutrophic water body and they cannot be exterminated by conventional disinfection process. The inactivation effects of chlorine and chlorine dioxide on Chironomid larvae were investigated and some bourdary values in practice were determined under .conditions of various oxidaat dosage, organic precursor concentmtion and pH value. In addition, removal effect of different pre-oxidation cambined with coagulation process on Chironomid larvae in raw water was evaluated. It was found that chlorine dioxide possessed better inactivation effect than chlorine. Complete inactivation of Chironomid larvae in raw water was resulted by 1.5 mg/L of chlorine dioxide with 30 min of contact ＇time. Additionally, the organic precursor concentration, pH value had little influence on the inactivation effect. The coagulation jar test showed that Chironomid larvae in the raw water could be completely removed by chlorine dioxide pre-oxidation in combination with the coagulation process at chlorine dioxide dosage of 0.8 mg/L.     

超临界CO2介质中反胶团的形成与热力学

以甲基橙为溶剂化探针，根据其在超临界CO2／表面活性剂／助表面活性剂多元体系中的增溶情况，推断在正丁醇作用下，二辛酯琥珀酸磺酸钠（AOT）与辛基酚聚氧乙烯醚（TX-10）在超临界CO2介质中形成了反胶团．反胶团的形成是一个热力学自发过程：对于非离子表面活性剂TX-10，形成反胶团的主要动力来源于体系熵增加．对于阴离子型表面活性剂AOT，在低温下，熵增加是反胶团形成的主要动力；温度较高时，焓变成为反胶团形成的主要推动力．     

Neon matrix isolation spectroscopy of CO2 isotopologues

The solid neon matrix isolated spectrum of CO₂ are recorded in the 2–5 μm region. Natural and ¹³C or ¹⁸O enriched CO₂ samples were used and the nν₁ + ν₃ (n = 0, 1, 2) series bands of different CO₂ isotopologues have been observed. The solid neon matrix shift due to Fermi-resonance of bands within the same vibrational polyad is analyzed.     

采用TiO2光催化剂对河水中污染物进行光催化降解

用光催化剂TiO2对西清河废水进行了废水处理研究.实验结果表明,随着催化剂用量的增加,COD、色度的去除率逐渐增大, 但当其用量超过0.5g时,COD、色度的去除率增加缓慢,超过0.6g时开始下降;当pH<6.5时,随着pH值降低,当pH>6.5时,随着pH值升高,COD、色度去除率均降低;随着光照时间延长,COD、色度去除率逐渐升高,但当光照时间超过 10h 后, COD、色度去除率升高幅度非常缓慢.当催化剂用量为0.6g、 pH =6.5、光照12 h时,西清河废水的COD、色度去除率分别达到75.0%、78.5%.     

NH3/CO2低温制冷系统研究

研究了一种NH3/CO2 复叠式低温制冷系统 ,其中高温部分采用NH3做工质 ,低温部分利用CO2 为工质 .通过对NH3/CO2 复叠式制冷系统的性能进行的热力学模拟计算 ,分析了该循环的运行参数和性能系数在中间温度和冷凝温度改变时的变化规律 ,结果表明 :在同一冷凝温度下 ,复叠式两级低温制冷系统存在一个最佳中间温度 ,使系统性能系数最大 ,在最佳中间温度的± 5K范围内 ,性能系数降低很少 ;高温级冷凝温度改变时 ,循环性能系数也要随之变化 ,随冷凝温度增加 ,系统达到最大性能系数时的最大中间温度也增加 .研究结果为该复叠式制冷系统的优化设计和实际运行提供了理论基础