Tracing the impact of stack configuration on interface resistances in reverse electrodialysis by in situ electrochemical impedance spectroscopy

• RED performance and stack resistance were studied by EIS and LSV. • Interface resistance were discriminated from Ohmic resistance by EIS. • Impacts of spacer shadow effect and concentration polarization were analyzed. • Ionic short current reduced the power density for more cell pairs. • The results enabled to predict RED performance with different configurations. Reverse electrodialysis (RED) is an emerging membrane-based technology for the production of renewable energy from mixing waters with different salinities. Herein, the impact of the stack configuration on the Ohmic and non-Ohmic resistances as well as the performance of RED were systematically studied by using in situ electrochemical impedance spectroscopy (EIS). Three different parameters (membrane type, number of cell pairs and spacer design) were controlled. The Ohmic and non-Ohmic resistances were evaluated for RED stacks equipped with two types of commercial membranes (Type I and Type II) supplied by Fujifilm Manufacturing Europe B.V: Type I Fuji membranes displayed higher Ohmic and non-Ohmic resistances than Type II membranes, which was mainly attributed to the difference in fixed charge density. The output power of the stack was observed to decrease with the increasing number of cell pairs mainly due to the increase in ionic shortcut currents. With the reduction in spacer thickness from 750 to 200 µm, the permselectivity of membranes in the stack decreased from 0.86 to 0.79 whereas the energy efficiency losses increased from 31% to 49%. Overall, the output of the present study provides a basis for understanding the impact of stack design on internal losses during the scaling-up of RED.     

气相分子吸收光谱法测定水中氨氮干扰因素的研究

气相分子吸收光谱法测定成分复杂氨氮实际样品时,干扰因素造成测定结果不准确,而现有的标准方法和文献对干扰物质的研究不全面,制约了仪器的应用。该文系统地开展干扰因素的研究,提出干扰因素的消除方法,用加标回收率验证消除的有效性。结果表明,亚硫酸盐、硫化物等还原性物质对测定产生负干扰;石油烃、N,N-二甲基甲酰胺(DMF)等挥发性有机物、有机胺类以及亚硝酸盐对测定产生正干扰。根据不同干扰类型,通过加入适量酸性重铬酸钾溶液、在酸性条件下加热煮沸、预蒸馏等方法可消除干扰,消除干扰后加标回收率为84%~120%。生活污水、石化企业废水等6种典型水样消除干扰后,气相分子吸收光谱法和纳氏试剂分光光度法测定氨氮有较好的可比性,干扰消除方式有效。     

Spectroscopic characterization and photochemistry of the Criegee intermediate CF3C(H)OO

Criegee intermediates (CIs), also known as carbonyl oxide, are reactive intermediates that play an important role in the atmospheric chemistry. Investigation on the structures and reactivity of CIs is of fundamental importance in understanding the underlying mechanism of their atmospheric reactions. In sharp contrast to the intensively studied parent molecule (CH₂OO) and the alkyl-substituted derivatives, the knowledge about the fluorinated analogue CF₃C(H)OO is scarce. By carefully heating the triplet carbene CF₃CH in an O₂-doped Ar-matrix to 35 K, the elusive carbonyl oxide CF₃C(H)OO in syn- and anti-conformations has been generated and characterized with infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy. The spectroscopic identification is supported by ¹⁸O-labeling experiments and quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) and MP2/6-311++G(2d,2p) levels. Upon the long-wavelength irradiation (λ > 680 nm), both conformers of CF₃C(H)OO decompose to give trifluoroacetaldehyde CF₃C(H)O and simultaneously rearrange to the isomeric dioxirane, cyclic-CF₃CH(OO), which undergoes isomerization to the lowest-energy carboxylic acid CF₃C(O)OH upon UV-light excitation at 365 nm. The O₂-oxidation of CF₃CH via the intermediacy of CF₃C(H)OO and cyclic-CF₃CH(OO) might provide new insight into the mechanism for the degradation of hydro-chlorofluorocarbon CF₃CHCl₂ (HCFC-123) in the atmosphere.