Density functional theory studies were performed to obtain the structures, rotational barriers, and potential energy curves of six selected polychlorinated biphenyls (PCBs):  3,3‘,4,4‘- and 2,2‘,5,5‘-tetrachlorobiphenyl; 3,3‘,4,4‘,5-, 2,2‘,4,5,5‘-, and 2,3‘,4,4‘,5-pentachlorobiphenyl; and 3,3‘,4,4‘,5,5‘-hexachlorobiphenyl. Becke's three-parameter hybrid density functional, B3LYP, combined with 6-31G(d), 6-311G(d,p), and 6-311+G(2d,2p) basis sets was utilized for this purpose. For the selected PCBs, we present optimized geometries at the B3LYP/6-311+G(2d,2p) level of theory; torsional barriers at 0° and 90° at the B3LYP/6-31G(d), B3LYP/6-311G(d,p), and B3LYP/6-311+G(2d,2p) levels of theory; and potential energy curves (relative energy vs torsional angle) at the B3LYP/6-311G(d,p) level of theory. The geometries, torsional barriers, and potential energy curves of the non-ortho-chlorinated PCBs mimicked those of their parent biphenyl, whereas the remaining selected PCBs showed different behaviors. The syn-like structures of the 2,2‘,5,5‘- and 2,2‘,4,5,5‘-PCBs were of particular interest. However, the energy difference between the near-syn-like and near-anti-like structures was very small. Both of these PCBs have large barriers near planarity.

Structural instability is the major obstacle in the Li2FeSiO4/C cathode during charge and discharge process, which can be improved by the substitution of cations in the host cage. In this study, the transition metal ions with different valence (Ag1+, Zn2+, Cr3+, and Ti4+) have been substituted in Li2FeSiO4/C via modified sol‐gel method and the impact on the structural, electrical, and electrochemical performances has been systematically explored. The Rietveld‐refined XRD pattern and HR‐TEM (SAED) result reveal that all the prepared samples maintain orthorhombic structure (S.G‐ Pmn21). The FE‐SEM and TEM micrographs of bare and doped Li2FeSiO4/C display nanoparticle formation with 20‐40 nm size. Among different cation‐substituted silicates, Li2Fe0.9Ti0.1SiO4/C sample exhibits an excellent total conductivity of 1.20 × 10−4 S cm−1 which is one order of magnitude higher than the bare Li2FeSiO4/C sample. The galvanostatic charge‐discharge curves and cyclic voltammetric analysis reveal that the Li2Fe0.9Ti0.1SiO4/C material provides an excellent initial specific capacity of 242 mAh g−1 and maintains a capacity of 226 mAh g−1 after 50 cycles with capacity retention of 93.38%. The Ti doping is a promising strategy to overcome the capacity fading issues, by preventing the structural collapse during Li‐ion intercalation/de‐intercalation processes in the Li2FeSiO4/C electrode through the strong hybridization between the 3d and 4s orbitals in titanium and 2p orbital in oxygen.

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Articles you may be interested inTransportable real-time single-particle ion trap mass spectrometer Rev. Sci. Instrum. 76, 064102 (2005); 10.1063/1.1938607 Corona discharge ion mobility spectrometry at reduced pressures Rev. Sci. Instrum. 75, 4656 (2004); 10.1063/1.1809301 Ion preparation systems for atomic isobar reduction in accelerator mass spectrometry AIP Conf. Development of an electrostatic ion guide in chemical ionization mass spectrometry Rev. Sci. Instrum. 69, 4002 (1998); 10.1063/1.1149223Fourier transform ion cyclotron resonance mass spectrometry AIP Conf.The design and construction of a lithium ion attachment mass spectrometer that is used to study the occurrence of free radical intermediates and molecular and atomic species ͑which are not found under ordinary conditions͒ on a real-time basis in the gas phase are described. The newly developed device exhibits several advantages over conventional mass spectrometers. The performance of this equipment was extensively tested and optimized, and experimental tests show that the efficiency and sensitivity of the instrument are moderately high. The main applications and possible future perspectives of this approach are briefly reviewed.

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