28 research outputs found
Small-angle neutron scattering and Molecular Dynamics structural study of gelling DNA nanostars
DNA oligomers with properly designed sequences self-assemble into well
defined constructs. Here, we exploit this methodology to produce bulk
quantities of tetravalent DNA nanostars (each one composed by 196 nucleotides)
and to explore the structural signatures of their aggregation process. We
report small-angle neutron scattering experiments focused on the evaluation of
both the form factor and the temperature evolution of the scattered intensity
at a nano star concentration where the system forms a tetravalent equilibrium
gel. We also perform molecular dynamics simulations of one isolated tetramer to
evaluate the form factor theoretically, without resorting to any approximate
shape. The numerical form factor is found to be in very good agreement with the
experimental one. Simulations predict an essentially temperature independent
form factor, offering the possibility to extract the effective structure factor
and its evolution during the equilibrium gelation.Comment: 9 pages, 5 figure
Epitaxial deposition of silver ultra-fine nano-clusters on defect-free surfaces of HOPG-derived few-layer graphene in a UHV multi-chamber by in situ STM, ex situ XPS, and ab initio calculations
The growth of three-dimensional ultra-fine spherical nano-particles of silver on few layers of graphene derived from highly oriented pyrolytic graphite in ultra-high vacuum were characterized using in situ scanning tunneling microscopy (STM) in conjunction with X-ray photoelectron spectroscopy. The energetics of the Ag clusters was determined by DFT simulations. The Ag clusters appeared spherical with size distribution averaging approximately 2 nm in diameter. STM revealed the preferred site for the position of the Ag atom in the C-benzene ring of graphene. Of the three sites, the C-C bridge, the C-hexagon hollow, and the direct top of the C atom, Ag prefers to stay on top of the C atom, contrary to expectation of the hexagon-close packing. Ab initio calculations confirm the lowest potential energy between Ag and the graphene structure to be at the exact site determined from STM imaging
Carbon nanotube-enhanced photoelectrochemical properties of metallo-octacarboxyphthalocyanines
The photoelectrochemistry of metallo-octacarboxyphthalocyanines (MOCPc, where M = Zn or Si(OH)2) integrated with MWCNTs for the development of dye-sensitized solar cells (DSSCs) is reported. The DSSC performance (obtained from the photo-chronoamperometric and photo-impedimetric data) decreased as ZnOCPc > (OH)2SiOCPc. The incorporation of the MWCNTs on the surface of the TiO2 film (MOCPc–MWCNT systems) gave higher photocurrent density than the bare MOCPc complexes. Also, from the EIS results, the MOCPc–MWCNT hybrids gave faster charge transport kinetics (approximately three times faster) compared to the bare MOCPc complexes. The electron lifetime was slightly longer (ca. 6 ms) at the ZnOCPc systems than at the (OH)2SiOCPc system (ca. 4 ms) meaning that the presence of the MWCNTs on the surface of the TiO2 film did not show any significant improvement on preventing charge recombination process
Mesoscopic organization in ionic liquids
We discuss some published results and provide new observations concerning the high level of structural complexity that lies behind the nanoscale correlations in ionic liquids (ILs) and their mixtures with molecular liquids. It turns out that this organization is a consequence of the hierarchical construction on both spatial (from \uc3\ua5ngstr\uc3\ub6m to several nanometer) and temporal (from fraction of picosecond to hundreds of nanosecond) scales, which requires joint use of experimental and computational tools
Microwave-assisted optimization of the manganese redox states for enhanced capacity and capacity retention of LiAlxMn2-xO4 (x = 0 and 0.3) spinel materials
Please read abstract in article.CSIR and the NRFhttp://www.rsc.org/advancesam2017Chemistr
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A high-rate aqueous symmetric pseudocapacitor based on highly graphitized onion-like carbon/ barnessite-type manganese oxide nanohybrids
We present a study on the pseudocapacitive properties of birnessite-type MnO2 grafted on highly graphitized onion-like carbon (OLC/MnO2). In a three-electrode setup, we evaluated two different substrates, namely a platinum disc and nickel foam. The OLC/MnO2 nanohybrid exhibited a large specific capacitance (Csp) of 295 and 323 F g−1 (at 1 A g−1) for the Pt disc and Ni foam, respectively. In addition, the Ni foam substrate exhibited much higher rate capability (power density) than the Pt disc. A symmetrical two-electrode device, fabricated with the Ni foam, showed a large Csp of 254 F g−1, a specific energy density of 5.6 W h kg−1, and a high power density of 74.8 kW kg−1. These values have been the highest for onion-based electrodes so far. The device showed excellent capacity retention when subjected to voltage-holding (floating) experiments for 50 h. In addition, the device showed a very short time constant (τ = 40 ms). This high rate handling ability of the OLC/MnO2 nanohybrid, compared to literature reports, promises new opportunities for the development of aqueous-based pseudocapacitors
Application of nickel foam in electrochemical systems : a review
The effectiveness of electrochemical systems in various applications (e.g., energy storage and conversion, wastewater treatment, ammonia synthesis) is, in essence, dependent on the electrode materials employed in such systems. The emphasis of research on electrochemical systems is given to developing electrode materials that would offer cost-effectiveness, stability, and reliable results that can be practical for commercial scaling. However, the operation of these systems also relies on other various components that include electrode fabrication, electrolytes, system architecture, the durability of the systems, and supporting components (i.e., substrate/current collector). On the choice of the current collector, nickel foam (NF) has enjoyed widespread attention as a favourable substrate in various electrochemical systems. This growing trend is attributed to its unique interlinked three-dimensional structure that offers advantages such as light weight, high porosity, great mechanical strength, chemical stability, and promising electrical and thermal conductivity. These traits are favourable for maximized contact areas between the current collector, the active materials, and charged species, resulting in the reduction of charge transport pathways, which is a vital step for improving the electrochemical performance. This review aims at highlighting the use of NF as a substrate of choice in developing effective electrodes for various electrochemical systems and can serve as a navigational tool for the literature involving the use of NF as the current collector. It also shows, to a certain extent, the impact of NF on electrochemical performance as compared with other current collectors.Gauteng City-Region Academy (GCRA); the Learning Academy of the Department of
Water and Sanitation; the National Research Foundation, South Africa, under the
Thuthuka programme and the Competitive Support for Unrated Researchers.https://link.springer.com/journal/116642024-02-11hj2023Physic
Reduced Graphene Oxide Aerogels with Functionalization-Mediated Disordered Stacking for Sodium-Ion Batteries
Surface modified reduced graphene oxide (rGO) aerogels were synthesized using the hydrothermal method. Ethylene diamine (EDA) and α-cyclodextrin (CD) were used to functionalize the surface of the graphene oxide layers. The oxygen reduction and surface modification occurred in-situ during the hydrothermal self-assembly process. The chemical functionality and structure of the resulting ethylene diamine modified (rGO-EDA) and cyclodextrin modified (rGO-CD) aerogels as well as of the pristine unmodified rGO aerogel were studied using XPS, SEM, XRD, and SANS techniques. The overall surface composition showed a significant decrease in the oxygen content for all synthesized aerogels. The surface modified aerogels were characterized by a disordered stacking of the assembled rGO layers. The surface functionalities resulted in a broad distribution of the interlayer spacing and introduced structural heterogeneities. Such disordered structures can enable a better adsorption mechanism of the sodium ions. Coin cells based on the synthesized aerogels and sodium metal were assembled and tested at several charge and discharge rates. The correlation between the surface functionality of the rGO, the induced structural heterogeneities due to the disordered stacking, and the electrochemical performance of sodium-ion batteries were investigated. Operando XRD measurements were carried out during the battery cycling to investigate the adsorption or intercalation nature of the sodiation mechanism
Microwave-Assisted Synthesis of High-Voltage Nanostructured LiMn<sub>1.5</sub>Ni<sub>0.5</sub>O<sub>4</sub> Spinel: Tuning the Mn<sup>3+</sup> Content and Electrochemical Performance
The
LiMn<sub>1.5</sub>Ni<sub>0.5</sub>O<sub>4</sub> spinel is an important
lithium ion battery cathode material that has continued to receive
major research attention because of its high operating voltage (∼4.8
V). This study interrogates the impact of microwave irradiation on
the Mn<sup>3+</sup> concentration and electrochemistry of the LiMn<sub>1.5</sub>Ni<sub>0.5</sub>O<sub>4</sub> spinel. It is shown that microwave
is capable of tuning the Mn<sup>3+</sup> content of the spinel for
enhanced electrochemical performance (high capacity, high capacity
retention, excellent rate capability, and fast Li<sup>+</sup> insertion/extraction
kinetics). This finding promises to revolutionize the application
of microwave irradiation for improved performance of the LiMn<sub>1.5</sub>Ni<sub>0.5</sub>O<sub>4</sub> spinel, especially in high
rate applications