B, N-co-doped graphene-supported Ir and Pt clusters for methane activation and C─C coupling: A density functional theory study.

Methane conversion by using transition metal catalysts plays in an important role in various usages of the industrial process. The mechanism of methane conversion on B, N-co-doped graphene supported Ir and Pt clusters, BNG-Ir4 and BNG-Pt4, have been investigated using density functional theory calculations. Methane was found to adsorb on BNG-Ir4 and BNG-Pt4 clusters via strong agostic interactions. The first step of methane dehydrogenation on BNG-Ir4 has a lower energy barrier, indicating a facile methane dissociation on BNG-Ir4. In addition, it shows that hydrogen molecule can form on the BNG-Ir4 and hydrogen can desorb from the surface. Besides, the C-C coupling reaction of CH3 to form ethane is a more thermodynamically favorable process than CH3 dehydrogenation on BNG-Ir4. Further, ethane is easier to desorb from the surface due to its low desorption energy. Therefore, the BNG-Ir4 cluster is a potential catalyst for activating methane to form ethane and to produce hydrogen. © 2019 Wiley Periodicals, Inc.

Two-dimensional gas chromatography coupled to isotope ratio mass spectrometry for determining high molecular weight polycyclic aromatic hydrocarbons in sediments.

The accuracy of compound-specific isotope analysis (CSIA) of trace-level pollutants in complex environmental samples has always been limited by two main challenges: poor chromatographic separation and insufficient amounts of analytes. In this study, a two-dimensional gas chromatography-isotope ratio mass spectrometry (2DGC-IRMS) system was constructed for compound-specific δ13C analysis of high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) in estuarine/marine sediments. This construction occurred through hyphenating an extra gas chromatography system (GC) to a conventional GC-IRMS using a commercially available multi-column switching-cryogenic trapping system (MCS-CTS). Compared with the previous 2DGC-IRMS strategy, which utilizes a Deans Switch device, the newly implemented 2DGC-IRMS scheme resulted in online purification of target analytes as well as enriched them online via duplicate injection and cryogenic trapping in CTS; this resultingly lowered the limits of detection (LOD) of CSIA. To improve the sample transfer efficiency to the IRMS, a broader-bore and longer fused-silica capillary was utilized to replace the original sample capillary running from the sample open split to the IRMS. A ẟ13C analysis of PAH standards showed accurate ẟ13C values, and high precisions (standard deviations 0.13-0.37%) were achieved, with the LOD of HMW-PAHs reduced to at least 1.0 mg/L (i.e., 0.07 to 0.09 nmol carbon per compound on-column). The successful application of this newly developed 2DGC-IRMS scheme provides a practical solution for the reliable CSIA of trace-level pollutants in complex environmental samples that cannot be measured using the conventional GC-IRMS system.

QuEChERS-based extraction and two-dimensional liquid chromatography-high resolution mass spectrometry for the determination of long chain chlorinated paraffins in sediments.

In this study, a method was established for the analysis of long-chain chlorinated paraffins (LCCPs) in sediment based on quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction and two-dimensional liquid chromatography-Orbitrap high resolution mass spectrometry (2DLCOrbitrap HRMS). Compared with other reported methods, this method greatly reduces sample preparation time (2 h) and solvent consumption. The QuEChERS extraction method presented satisfactory recoveries, 90.5-95.2, 84.7-86.6, and 81.4-83.4% of 5, 50, and 200 ng/g LCCPs with 49% Cl spiked into sediments. Meanwhile, no matrix effects were found in the LCCPs analysis after online purification by the 2DLC system. With the current commercial LCCP standards and a mixture of three chlorinated paraffins (CPs) industrial products, a suspect screening strategy was established and accurate identification of LCCPs (including vLCCPs, which carbon chain length greater than 20) under the plight that the reference standards for vLCCPs are currently unavailable. A total of 21 C18-20-LCCP and 22 vLCCP congeners were identified in sediment samples collected from Dongting Lake, China. The total concentrations of LCCPs in six sediment samples ranged from 1.69 to 18.0 ng/g (median 6.66 ng/g) and was dominated by C18 groups (mean, 28.8%), C19 groups (mean, 19.1%) and C21 groups (mean, 16.9%). Taken together, the successful application of this method to analyze sediment samples shows great potential for the analysis of LCCPs in environmental samples in future studies.

Facile synthesis of the crescent-like SnS nanocrystals capped by polyvinyl pyrrolidone and its performance of adsorbing dyes.

With using Sn2+ as tin source, l-cysteine as sulphur source and polyvinyl pyrrolidone (PVP, Mw = 1300000) as surfactant, a novel three-dimensional and crescent-like SnS nanocrystal (NCs) was successfully synthesized in a one-pot hydrothermal method. The as-prepared SnS NCs displayed uniform crescent-like morphological structure, and demonstrated excellent efficiency for the adsorption of cationic dyes such as rhodamine B (RhB) and methylene blue (MB). Kinetic analysis indicated that the adsorption process followed the pseudo second-order model, and the maximum capacity of the SnS NCs to adsorb MB was determined by Langmuir equation to be 252 mg⋅g-1 at 298 K. The pH dependence of SnS NCs on the adsorption of cationic dyes and the characterization of zeta potential jointly suggested the existence of electrostatic attraction in the process. Overall, this study showed that electrostatic field of functional groups and the capping of PVP could significantly enhance the adsorption performance of the SnS NCs, and also provides a novel insight into the development of highly efficient inorganic adsorbents for cationic dyes.