One-Step Realization of Layered/Spinel Heterostructures and Na Doping by Sodium Dodecyl Sulfate-Assisted Sol-Gel Method for Li-Ion Batteries.

Li-rich layered oxide cathodes have attracted extensive attention due to their high energy density. However, due to the low initial Coulombic efficiency and the capacity fading and voltage fading during cycling, its practical application is still a great challenge. Here, we report the one-step realization of layered/spinel heterostructures and Na doping by the sodium dodecyl sulfate (SDS)-assisted sol-gel method. The spinel phase provides 3D diffusion channels for Li-ions, and sodium doping changes the layered lattice constant and expands the layer spacing. Therefore, the designed Li1.15Mn0.54Ni0.13Co0.13Na0.05O2 (SDS-2) cathode possesses excellent electrochemical performance such as higher initial Coulombic efficiency and rate capacity and also alleviates voltage decay. The initial discharge-specific capacity of SDS-2 is 298.8 mAh g-1 at 0.1 C, and the discharge-specific capacity can reach 111.7 mAh g-1 at 10 C. This strategy can provide new insights into the design and synthesis of high-performance Li-rich layered oxide cathode materials.

Efficient Structural Regulation Platform for the Controlled Synthesis of LiFePO4 Cathodes with Shorter Li-Ion Diffusion Paths.

The rate performance of lithium iron phosphate (LiFePO4) is mainly limited by its poor electronic conductivity and slow Li-ion diffusion rate. Graphene-based materials are often compounded with LiFePO4 (LFP) to improve their rate performance, mainly because of their excellent electrical conductivity. Unlike most past composite work focusing on the conductive network between LFP and graphene, in this work, we further developed the functionality of graphene-based materials as nanoparticle carriers, where the nitrogen-doping strategy endows graphene with properties that make it an efficient structural regulation platform during the solvothermal process. Compared to reduced graphene oxide, not only does the nitrogen-doped sites confer more nucleation growth sites for LFP on the graphene surface during the solvothermal process, but also the localized formation of an EG-enriched microenvironment helps to further inhibit the in situ growth of LFP along [010]. The efficient structural regulation platform assisted the synthesis of (010)-oriented LFP with a smaller particle size, which further shortens the Li-ion diffusion paths. The optimized LFP composite electrode materials exhibit a discharge-specific capacity of 133.1 mA·h/g at 10C, which exceeds/is comparable to that of previously reported LFP compounded with graphene-based materials. This work broadens the functionality of graphene-based carriers and provides new ideas for the controllable synthesis of nanoparticles.

A Promising Solid-State Synthesis of LiMn1- yFeyPO4 Cathode for Lithium-ion Batteries.

LiMn1-yFeyPO4 (LMFP) is a significant and cost-effective cathode material for Li-ion batteries, with a higher working voltage than LiFePO4 (LFP) and improved safety features compared to layered oxide cathodes. However, its commercial application faces challenges due to a need for a synthesis process to overcome the low Li-ion diffusion kinetics and complex phase transitions. Herein, a solid-state synthesis process using LFP and nano LiMn0.7Fe0.3PO4 (MF73) is proposed. The larger LFP acts as a structural framework fused with nano-MF73, preserving the morphology and high performance of LFP. These results demonstrate that the solid-state reaction occurs quickly, even at a low sintering temperature of 500 °C, and completes at 700 °C. However, contrary to the expectations, the larger LFP particles disappeared and fused into the nano-MF73 particles, revealing that Fe ions diffuse more easily than Mn ions in the olivine framework. This discovery provides valuable insights into understanding ion diffusion in LMFP. Notably, the obtained LMFP can still deliver an initial capacity of 142.3 mAh g-1, and the phase separation during the electrochemical process is significantly suppressed, resulting in good cycling stability (91.1% capacity retention after 300 cycles). These findings offer a promising approach for synthesizing LMFP with improved performance and stability.

Study on thermal behavior and kinetics of Al/MnO2 poly(vinylidene fluorine) energetic nanocomposite assembled by electrospray.

To explore the effect of the addition of poly(vinylidene fluorine) (PVDF) to a nanothermite system, an Al/MnO2/PVDF energetic nanocomposite was prepared using an electrospray method, Al/MnO2 nanothermite was prepared as a control group. Then, the energetic nanocomposite and nanothermite were tested and analyzed by XRD, FE-SEM and TG-DSC, and the reaction products were collected. The results show that energetic nanocomposite would have three obvious exothermic peaks in the range of room temperature to 800 °C with a total more than 1700 J g-1 heat release while the control experiment, Al/MnO2 nanothermite, could be found one exothermic peak with a 1100 J g-1 heat release. The residues are mainly MnAl2O4, MnF2 and AlF3 which indicates that Al/MnO2/PVDF energetic nanocomposite could make full use of manganese oxide. Finally, thermal analysis experiments were carried out under different heating rates to calculate the activation energy. The calculation results show that the addition of PVDF could significantly reduce the activation energy, which would help spark the thermite at comparatively low energy and temperature.

Thermal behavior and combustion of Al nanoparticles/ MnO2-nanorods nanothermites with addition of potassium perchlorate.

To explore the effect of potassium perchlorate (KClO4) on Al nanoparticles/MnO2-nanorods nanothermite systems, in this paper, Al/MnO2 nanothermites with different mass fraction of KClO4 were prepared by electrospray. The samples were characterized by XRD, SEM, TG-DSC analysis. According to the results of TG-DSC, the addition of KClO4 seemed to cause no direct improvement on their exothermic reactions. But the results of activation energy calculations showed that KClO4 could remarkably reduce the activation energy of nanothermite systems by up to 48.8%. The XRD results indicated that residues consisted mainly of Mn3O4. The reasons why KClO4 has little effect on thermal properties but makes a great difference on kinetics were analyzed and discussed. Finally, onset combustion tests were carried out. The results and findings provide a useful approach to decrease the activation energy and combustion rate of nanothermites, which may facilitate practical and combustible applications.

A completely controlled sphere-to-bilayer micellar transition: the molecular mechanism and application on the growth of nanosheets.

The combination of a simple modification of the sample addition method to generate a sort of continuously accumulated external stimulation with only minute increments in amplitude and the introduction of probe molecules (herein aniline) within the micelle allow the direct continuous in situ spectroscopic monitoring of possible micellar transitions. In this way, a sphere-to-ellipsoid and further an ellipsoid-to-bilayer micellar transition of sodium dodecyl sulfate (SDS) induced by camphor sulfuric acid (CSA) is observed to experience four stages in the time sequence: (i) the accumulated protons released from CSA in the hydration layer of the micelle stimulate the rearrangement of SDS micelles; (ii) the micelles transform into ellipsoidal shapes as evidenced by the characteristic chemical shift anisotropy and the corresponding molecular dynamic properties from probe molecules; (iii) further protonation of aniline induces the micelle to turn into lamellar structures; (iv) aniline is freed from the micelle while leaving the SDS bilayers undistorted. Moreover, polyaniline nanosheets incorporating SDS bilayers in sandwich structures, which can display excellent capacitive behavior at relatively high current densities for the fabricated supercapacitors, are prepared from the aniline oriented by the bending energy of the SDS bilayers.

Nucleation of polyaniline nano-/macrotubes from anilinium composed micelles.

A mechanistic study on the nucleation of polyaniline nanotubes (PANI-NT) through template-free method is explored by in situ solution-state (1)H NMR experiments via a careful analysis of the spectral evolution of the major species in the course of the reaction. Before polymerization, aniline and salicylic acid have assembled into loosely packed micelles due to electrostatic interactions and the proton exchange reaction between aniline and anilinium. A three-stage polymerization with a formation, accumulation of aniline dimers, as well as a generation of phenazine-like oligomers is observed, which can be attributed to the monomer transformation from neutral aniline molecules to anilinium cations and the significantly lowered pH in the reaction. Strong π-π stacking interactions from the phenazine-like oligomers facilitate the intermolecular aggregation which initiates the formation of PANI-NT. At first, such aggregates, locating at the outermost layer of anilinium composed micelles, shield in situ formed protons from releasing into the aqueous bulk but into the micelle instead. Due to the continuously increased charge in the micelle, a sphere-to-rod structural transition occurs which leads the oligomer aggregates to be sheathed at the exterior of the rod. Further consumption of anilinium in the micelle leaves the internal cavity while the fusion between the micelles elongates the length of the tubes. Our work demonstrates that (i) loosely packed anilinium composed micelles, highly mobile monomers within the micelle, and efficient blockage of the proton-releasing to the aqueous bulk are three key factors for the generation of tubular structures; and (ii) dynamic NMR line shape analysis provides a new perspective for resolving the formation profile of nanostructured polymers.

Room-temperature synthesis of self-assembled Sb2S3 films and nanorings via a two-phase approach.

The freestanding Sb(2)S(3) films were easily synthesized at the interface of water and toluene at room temperature, where Na(2)S and (C(2)H(5)OCS(2))(3)Sb (xanthate, O-ethyldithiocarbonate) acted as sulfur and antimony source, respectively. After 3 h of aging, the Sb(2)S(3) films with a flat surface toward organic side and rough surface toward aqueous side were assembled by sheaflike Sb(2)S(3) nanowires. The Sb(2)S(3) nanorings formed by end-to-end connection of the bundled nanowires appeared in the water layer when the reaction time reached 24 h. The Sb(2)S(3) nanorings showed higher photocatalytic activity for methyl orange degradation under visible light than the Sb(2)S(3) films owing to broader spectrum response and better aqueous dispersion.

Interfacing colloidal graphene oxide sheets with gold nanoparticles.

Aqueous solutions of graphene oxide (GO) and citrate-stabilised gold nanoparticles (AuNPs) are two classic, negatively charged colloids. Using the surface plasmon resonance spectra of AuNPs as a probe, we illustrate how the two like-charged colloids interact with each other and in so doing, reveal the unique solution behaviour of GO. We demonstrate that the electrical double layer of the GO sheets in water plays a key role in controlling the interaction between GO and AuNPs, which displays a one-way gate effect. It is shown that GO can capture and disperse AuNPs in water in a controllable fashion, without the need for additional chemical linkers. This discovery allows the successful synthesis of uncapped, yet solution-dispersible metal-nanoparticle assemblies. Such metal nanostructures have long been pursued for nano-plasmonics and sensing applications, but have remained difficult to prepare using conventional polymer dispersants. This work also makes clear that the combination of the two-dimensional conformation of GO along with its large molecular size and self-contained functional groups allows it to act as a unique soluble nanocarrier/substrate (the thinnest, functionalised flat substrate possible in nature) for the synthesis of new, soluble functional materials.

Discussion on microcosmic derivation of biological golden section phenomena from DNA geometric structure and snow flower generation.

As a mysterious and most universal mathematical constant, the ratio of golden section exists in biological organism widely either from microstructure to macrostructure or from anatomical structure to functional features, and the DNA is the most universal germ plasm throughout all life world. In this paper, by analyzing the DNA microstructure and generating process of snow flowers, such a fact is disclosed that biological golden section phenomena derives from the DNA structure at the molecular layer based on the complex nonlinear interaction with the inner environments.

Excitation profile of surface-enhanced Raman scattering in graphene-metal nanoparticle based derivatives.

Understanding energy transfer mechanisms in graphene derivatives is strongly motivated by the unusually interesting electronic properties of graphene, which can provide a template for the creation of novel nanostructured derivatives. From a synthetic point of view, it is highly attractive to envision being able to synthesize pristine graphene from precursors such as graphene oxide (GO). While this goal may be challenging over large length-scales, it is possible to generate regions of graphene at the nanoscale, confirmed by Raman spectroscopy or other methods. We describe an in situ method of nucleating gold or palladium nanoparticles in the presence of ethylene glycol as a reducing agent, while simultaneously reducing GO to graphene. The Au nanoparticles aid in spectroscopic characterization by both quenching fluorescence, allowing the graphene D and G bands to be quantified, and yielding a surface enhancement of about two orders of magnitude. We observe the excitation profile (488-785 nm) of the surface enhanced Raman spectrum (SERS) of graphene with Au nanoparticles adsorbed on the surface. Both the D and G bands display a resonance at approximately 593 nm (2.09 eV). This resonance may be interpreted as a combination of the plasmon resonance at 548 nm and a likely contribution from charge transfer as well. In addition, we observe a stiffening of the G band compared with that of graphene. The mechanism of the SERS, whether plasmonic or charge transfer-based, enables insight into the electronic pathways available to the graphene-nanoparticle system. We discuss our results in the context of several existing studies of graphene-based nanostructure derivatives.

Substituent effects on heats of formation, group interactions, and detonation properties of polyazidocubanes.

We have calculated the heats of formation (HOFs) for a series of polyazidocubanes by using the density functional theory (DFT), Hartree-Fock, and MP2 methods with 6-31G* basis set as well as semiempirical methods. The cubane skeleton was chosen for a reference compound, that is, the cubane skeleton was not broken in the process of designing isodesmic reactions. There exists group additivity for the HOF with respect to the azido group. The semiempirical AM1 method also produced reliable results for the HOFs of the title compounds, but the semiempirical MINDO3 did not. The relationship between HOFs and molecular structures was discussed. It was found that the HOF increases 330-360 kJ/mol for each additional number of the azido group being added to the cubane skeleton. The distance between azido groups slightly influences the values of HOFs. The interacting energies of neighbor azido groups in polyazidocubanes are in the range of 2.3 approximately 6.6 kJ/mol, which are so small and less related to the substituent numbers. The average interaction energy between nearest neighbor --N3 groups in the most stable conformer of octaazidocubane is 2.29 kJ/mol at the B3LYP/6-31G* level. The relative stability related to the number of azido groups of the title compounds was assessed based on the calculated HOFs, the energy gaps between the frontier orbitals, and the bond orders of the C--N3 and C--C bonds. The predicted detonation velocity of hepta- and octa-derivatives is over 9 km/s, and the detonation pressure of them is ca. 40 GPa or over.