Compound-specific online chlorine isotope analysis of chlorinated hydrocarbons was evaluated and validated using gas chromatography coupled to a regular quadrupole mass spectrometer (GC-qMS). This technique avoids tedious off-line sample pretreatments, but requires mathematical data analysis to derive chlorine isotope ratios from mass spectra. We compared existing evaluation schemes to calculate chlorine isotope ratios with those that we modified or newly proposed. We also tested systematically important experimental procedures such as external vs. internal referencing schemes, and instrumental settings including split ratio, ionization energy, and dwell times. To this end, headspace samples of tetrachloroethene (PCE), trichloroethene (TCE), and cis-dichloroethene (cDCE) at aqueous concentrations in the range of 20-500 μg/L (amount on-column range: 3.2-115 pmol) were analyzed using GC-qMS. The results (³⁷Cl/³⁵Cl ratios) showed satisfying to good precisions with relative standard deviations (n = 5) between 0.4‰ and 2.1‰. However, we found that the achievable precision considerably varies depending on the applied data evaluation scheme, the instrumental settings, and the analyte. A systematic evaluation of these factors allowed us to optimize the GC-qMS technique to determine chlorine isotope ratios of chlorinated organic contaminants.

No abstract

The present work demonstrates the self-organized formation of anodic molybdenum oxide nanotube arrays. The amorphous tubes can be crystallized to MoO2 or MoO3 and be converted fully or partially into molybdenum sulfide. Vertically aligned MoOx /MoS2 nanotubes can be formed when, under optimized conditions, defined MoS2 sheets form in a layer by layer arrangement that provide a high density of reactive stacking misalignments (defects). These core-shell nanotube arrays consist of a conductive suboxide core and a functional high defect density MoS2 coating. Such structures are highly promising for applications in electrocatalysis (hydrogen evolution) or ion insertion devices.

No abstract

No abstract

Olivine LiMPO 4 (M = Fe and Mn) cathode materials are already present in commercial batteries for diverse applications ranging from tools to electric vehicles due to their excellent thermal stability, compared to LiCoO 2 . [1][2][3][4][5][6][7][8][9][10][11] LiMnPO 4 (LMP) offers a higher energy density than LiFePO 4 due to its higher redox potential (4.1 V vs. Li/Li + ). However, LMP ( > 10 − 10 Scm − 1 ) suffers from lower intrinsic electrical and ionic conductivities than LiFePO 4 ( > 10 − 8 Scm − 1 ), resulting in much poorer electrochemical performance. In response, strategies including carbon coating on LMP, minimizing particle size, and Mn-site substitution have been applied in efforts to improve the electrochemical performance. [12][13][14][15] Several reports have also noted that the electrochemical performance of LMP is not dramatically enhanced, even when the particle size is decreased to the nanoscale ( ∼ 30 nm) and after carbon coating ( > 20 wt%). [16][17][18][19][20][21][22][23][24][25][26][27] Martha et al. [ 17 ] synthesized platelet-like carbon-coated LMP by a polyol method. After ball-milling of the LMP plate with carbon, core-shell composites consisting of < 5 nm carbon coating layer and ∼ 10 nm LMP were obtained. The results showed a practical capacity of 140 mAhg − 1 and 120 mAh g − 1 at 0.1 C; however, this rather rapidly decreased to 70 mAg − 1 at a 5C charge rate at 30 ° C. In general, cathode materials with poor electrical conductivity tend to increase in specifi c capacity with increasing temperature; however, cycling data including rate capability need to show results at 21 ° C.Considering all these factors, a 3D microporous (3DM) structure in which nanoparticles are well dispersed in the carbon matrix is the best choice to maximize the capacity of an LMP cathode. The advantage of 3D electrodes [ 28 , 29 ] are: 1) the solidstate diffusion length of lithium ions is on the order of a few tens of nanometers; 2) there are a large number of active sites for charge-transfer reactions because of the material's high surface area; and 3) reasonable electrical conductivity of the 3DM carbon matrix. These factors lead to signifi cantly improved rate performance compared to other nanoparticles.In this paper, we describe a method for fl exible construction of 3DM-LMP balls and fl akes using a polymethylmethacrylate (PMMA) template. PMMA colloidal crystals provide a fi rm scaffolding onto the dried LMP precursor solution; once removed during calcination, LiMnPO 4 particles feature pores with a diameter of about 250 nm and porewall thickness of about 40 nm. Depending on the impregnation step of the LMP precursor solution, 3DM balls and fl akes with similar porewall size and porewall thickness were obtained. Both samples demonstrated excellent rate capability and capacity retention both at 21 ° C and 60 ° C. Figure 1 shows the schematic view of the preparation procedure for 3DM-LMP balls and fl akes on a Si substrate. A dilute PMMA solution was fi rst poured onto a Si substrate and dried. This was fo...

Anyone can freely access the full text of works made available as "Open Access". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law.

Transport of multicomponent electrolyte solutions in saturated porous media is affected by the electrostatic interactions between charged species. Such Coulombic interactions couple the displacement of the different ions in the pore water and remarkably impact mass transfer not only under diffusion, but also under advection‐dominated flow regimes. To accurately describe charge effects in flow‐through systems, we propose a multidimensional modeling approach based on the Nernst‐Planck formulation of diffusive/dispersive fluxes. The approach is implemented with a COMSOL‐PhreeqcRM coupling allowing us to solve multicomponent ionic conservative and reactive transport problems, in domains with different dimensionality (1‐D, 2‐D, and 3‐D), and in homogeneous and heterogeneous media. The Nernst‐Planck‐based coupling has been benchmarked with analytical solutions, numerical simulations with another code, and high‐resolution experimental data sets. The latter include flow‐through experiments that have been carried out in this study to explore the effects of electrostatic interactions in fully three‐dimensional setups. The results of the simulations show excellent agreement for all the benchmarks problems, which were selected to illustrate the capabilities and the distinct features of the Nernst‐Planck‐based reactive transport code. The outcomes of this study illustrate the importance of Coulombic interactions during conservative and reactive transport of charged species in porous media and allow the quantification and visualization of the specific contributions to the diffusive/dispersive Nernst‐Planck fluxes, including the Fickian component, the term arising from the activity coefficient gradients, and the contribution due to electromigration.