Rositsa Kukeva

From kröhnkite- to alluaudite-type of structure: novel method of synthesis of sodium manganese sulfates with electrochemical properties in alkali-metal ion batteries

The alluaudite-type of structure is of huge research interest as an open matrix ensuring fast alkali-metal ion mobility, a property that could contribute to the development of novel electrode materials for rechargeable alkali-metal ion batteries. In this contribution, we provide new data on the formation of well-crystallized sodium manganese sulfates Na2+δMn2−δ/2(SO4)3 with an alluaudite-type of structure by simple dehydratation of the corresponding dihydrate Na2Mn(SO4)3·2H2O with a krohnkite-type of structure. The structure of Na2+δMn2−δ/2(SO4)3 is determined on the basis of Rietveld refinement of powder XRD patterns, infrared (IR) and Raman spectroscopy and electron paramagnetic resonance at X- and Q-band frequencies (EPR). From a structural point of view, the release of two H2O molecule from the krohnkite phase takes place by a transformation of the infinite [Mn(SO4)2(H2O)2] chains into Mn2O10 dimers bounded by distorted Na(1)O-polyhedra. The anhydrous sulfates are able to participate in the electrochemical reaction delivering a reversible capacity of 135 mA h g−1, when they are used as cathode materials in lithium ion cells. The stability of the alluaudite phase Na2+δMn2−δ/2(SO4)3 in the lithium electrolyte solution and the mechanism of the electrochemical reaction are discussed on the basis of ex situ EPR, IR and Raman spectroscopy. This is a first report on electrochemical activity of manganese-based sulfate with an alluaudite-type of structure.

Layered P3-NaxCo1/3Ni1/3Mn1/3O2 versus Spinel Li4Ti5O12 as a Positive and a Negative Electrode in a Full Sodium–Lithium Cell

The development of lithium and sodium ion batteries without using lithium and sodium metal as anodes gives the impetus for elaboration of low-cost and environmentally friendly energy storage devices. In this contribution we demonstrate the design and construction of a new type of hybrid sodium-lithium ion cell by using unique electrode combination (Li4Ti5O12 spinel as a negative electrode and layered Na3/4Co1/3Ni1/3Mn1/3O2 as a positive electrode) and conventional lithium electrolyte (LiPF6 salt dissolved in EC/DMC). The cell operates at an average potential of 2.35 V by delivering a reversible capacity of about 100 mAh/g. The mechanism of the electrochemical reaction in the full sodium-lithium ion cell is studied by means of postmortem analysis, as well as ex situ X-ray diffraction analysis, HR-TEM, and electron paramagnetic resonance spectroscopy (EPR). The changes in the surface composition of electrodes are examined by ex situ X-ray photoelectron spectroscopy (XPS).

Impact of Cu(II) and Zn(II) ions on the functional properties of new PAMAM metallodendrimers

In this study, the synthesis, spectral characterization and in vitro antimicrobial activity of two new metallodendrimers based on the PAMAM dendrimer modified with four 1,8-naphthalimide units are described. The chemical structure of metallodendrimers has been analyzed by FT-IR, UV-Vis, fluorescence, NMR spectroscopy, MS and SEM analysis. The antimicrobial activity of the new compounds has been tested in vitro against different model pathogenic microorganisms. The results showed good inhibitory activity of the compounds better expressed against the tested Gram-positive bacteria and yeasts. Cotton fabrics were treated with each of the dendrimers, and their morphology, antimicrobial activity and biofilm inhibiting potential were investigated. Both metallodendrimers showed stronger antimicrobial and biofilm inhibiting abilities compared to the initial dendrimer ligand.

Synthesis, spectral characterization, and in vitro antimicrobial activity in liquid medium and applied on cotton fabric of a new PAMAM metallodendrimer

ABSTRACT A new polyamidoamine metallodendrimer modified with eight 1,8-naphthalimide units was synthesized. The Cu(II) complex has been investigated by EPR spectroscopy and it has shown that 17 copper ions have involved in the dendrimer complex. To confirm the presence of metallodendrimers on the cotton surface, scanning electron microscopy characterization has been used. In vitro antimicrobial activity of the metallodendrimer against different pathogens was investigated and compared to the dendrimer ligand free of copper ions. Both dendrimers were deposited on a cotton fabric and antibacterial activity of the treated cotton samples was investigated against model Gram-positive and Gram-negative bacteria. It has been shown that the studied dendrimers reduce bacterial growth and prevent the formation of biofilms. The metallodendrimer showed stronger antimicrobial and biofilm inhibiting abilities than those of the free of Cu(II) ions ligand.