ß-MnO2 as a cathode material for lithium ion batteries from first principles calculations.

The search for excellent cathodes for lithium batteries is the main topic in order to meet the requirements of low cost, high safety, and high capacity in many real applications. ß-MnO2, as a potential candidate, has attracted great attention because of its high stability and potential high capacity among all the phases. Because of the complexity of ß-MnO2, some fundamental questions at the atomic level during the charge-discharge process, remain unclear. The lithiation process of ß-MnO2 has been systematically examined by first-principles calculations along with cluster expansion techniques. Five stable configurations during the lithium intercalation process are firstly determined, and the electrochemical voltages are from 3.47 to 2.77 eV, indicating the strongly correlated effects of the ß-MnO2-LiMnO2 system. During the lithiation process, the changes in the lattice parameters are not symmetric. The analysis of electronic structures shows that Mn ions are in the mixed valence states of Mn(3+) and Mn(4+) during the lithiation process, which results in Jahn-Teller distortion in Mn(3+)O6 octahedra. Such results uncover the intrinsic origin of the asymmetric deformation during the charge-discharge process, resulting in the irreversible capacity fading during cycling. From the analysis of the thermal reduction of delithiated LixMnO2, the formation of oxygen is thermodynamically infeasible in the whole extraction process. Our results indicate that ß-MnO2 has great potential as a cathode material for high capacity Li-ion batteries.

Facile synthesis of 3D hierarchical foldaway-lantern-like LiMnPO4 by nanoplate self-assembly, and electrochemical performance for Li-ion batteries.

Olivine-structured LiMnPO(4) with 3D foldaway-lantern-like hierarchical structures have been prepared via a one-step, template-free, solvothermal approach in ethylene glycol. The foldaway-lantern-like LiMnPO(4) microstructures are composed of numerous nanoplates with thickness of about 20 nm. A series of electron microscopy characterization results indicate that the obtained primary LiMnPO(4) nanoplates are single crystalline in nature, growing along the [010] direction in the (100) plane. Time-dependent morphology evolution suggests that ethylene glycol plays dual roles in oriented growth and self-assembly of such unique structures. After carbon coating, the as-prepared LiMnPO(4) cathode demonstrated a flat potential at 4.1 V versus Li/Li(+) with a specific capacity close to 130 mA h g(-1) at 0.1 C, along with excellent cycling stability.

In situ identification of the adsorption of 4,4'-thiobisbenzenethiol on silver nanoparticles surface: a combined investigation of surface-enhanced Raman scattering and density functional theory study.

We investigated the configuration characteristic and adsorption behavior of 4,4'-thiobisbenzenethiol (TBBT) on the surface of silver nanoparticles (NPs). Under different conditions and preparation processes, several possible surface species were produced including single-end adsorption on a silicon wafer, double-end adsorption and bridge-like adsorption. Although consisting of the same molecule and nano material, different adsorption systems exhibited different spectral characteristics in the surface-enhanced Raman spectroscopy (SERS). A density functional theory (DFT) study further verified the corresponding adsorption states. The combined SERS-DFT study provided a framework towards investigating and designing adsorption systems at a molecular level, indicating the potential use in applications such as nano-sensors.

Chemical effects in SERS of pyrazine adsorbed on Au-Pd bimetallic nanoparticles: a theoretical investigation.

Chemical enhancement in surface-enhanced Raman scattering (SERS) of pyrazine adsorbed on Au-Pd nanoclusters is investigated by using density functional theory. Changing Pd content in the bimetallic clusters enables modulation of the direct chemical interactions between the pyrazine and the clusters. The magnitude of chemical enhancement is correlated well with the induced polarizability for the complexes with low Pd content, which fails for the complexes with high Pd content. Furthermore, the dependence of chemical enhancement on cluster size and coupling is also described by the induced polarizability. Additionally, the chemical enhancement in the cluster-molecule-cluster junction is found to account for as much as 10(3), which suggests that a chemical mechanism might be more important than previously believed, in particular for Au-Pd bimetallic nanoparticle aggregates.

A DFT investigation of surface-enhanced Raman scattering of adenine and 2'-deoxyadenosine 5'-monophosphate on Ag20 nanoclusters.

We present a detailed analysis of the surface-enhanced Raman scattering (SERS) of adenine and 2'-deoxyadenosine 5'-monophosphate (dAMP) adsorbed on an Ag(20) cluster by using density functional theory. Calculated Raman spectra show that spectral features of all complexes depend greatly on adsorption sites of adenine and dAMP. The complexes consisting of adenine adsorbed on the Ag(20) cluster through N3 reproduce the measured SERS spectra in silver colloids, and thus demonstrated that adenine interacts with the silver surface via N3. We also investigate the SERS spectrum of adenine at the junction between two Ag(20) clusters and demonstrate that adenine can bind to the clusters through N3 and the external amino group, while dAMP can be adsorbed on the cluster in an end-on orientation with the ribose and phosphate groups near to or away from the silver cluster. In contrast to the adenine-Ag(20) complexes, the dAMP-Ag(20) complexes produce new and strong bands in the low- or high-wavenumber region of the Raman spectra, due to vibrations of the ribose and phosphate groups. Furthermore, the spectrum of dAMP bound to the Ag(20) cluster via N7 approaches the experimental SERS spectra on silver colloids.

Quantitative analysis of mononucleotides by isotopic labeling surface-enhanced Raman scattering spectroscopy.

A novel surface-enhanced Raman scattering (SERS) approach for accurate quantification of mononucleotides of deoxyribonucleic acid (DNA) is described. Reproducible SERS measurement was achieved by using isotopically labeled internal standard. By measuring the SERS spectra of mononucleotides and its isotope internal standard in combination with multivariate data analysis, the method was successfully applied to quantify mononucleotides. The independent validation of analyte concentrations gave a standard deviation of within 2%, which is comparable to HPLC result. Finally, a mixture of four mononucleotides of DNA was prepared to explore the possibility of quantifying the concentration of label-free, sequence-specific DNA strands by this approach. As compared to liquid chromatography/mass spectrometry (LC/MS), our method can be similarly precise but the SERS measurement is simple, rapid and potentially cheap.