Influence Of Alkali Ions Research Articles

Influence of Alkali Metal Ions on the Structural and Spectroscopic Properties of Sm3+-Doped Silicate Glasses

In the present work, the influence of alkali ions (Li, Na, K) on the structural and spectroscopic properties of silica glasses doped with Sm3+ was investigated. Infrared and Raman spectroscopy techniques were used to investigate the structural properties of the alkali silicate glasses. The optical absorption showed bands characteristic of Sm3+ ions in alkali silicate glasses, and this was investigated. The Judd–Ofelt theory was applied to evaluate the phenomenological intensity parameters (Ω2, Ω4, and Ω6) of the optical absorption measurements. The multi-channel visible and near infrared emission transitions originating from the 4G5/2-emitting state of the Sm3+ in alkali silicate glasses with a maximum phonon energy of ~1050 cm−1 were investigated. From the evaluated Judd–Ofelt parameters, radiative parameters such as spontaneous emission probabilities, radiative lifetimes, branching ratios, and stimulated emission cross-sections were calculated. The recorded luminescence spectra regions revealed intense green, orange, red, and near-infrared emission bands, providing new traces for developing tunable laser and optoelectronic devices.

Density functional theory study on the adsorption of alkali metal ions with pristine and defected graphene sheet

ABSTRACTThe graphene-based materials along with the adsorption of alkali metal ions are suitable for energy conversion and storage applications. Hence in the present work, we have investigated the structural and electronic properties of pristine and defected graphene sheet upon the adsorption of alkali metal ions (Li+, Na+, and K+) using density functional theory (DFT) calculations. The presence of vacancies or vacancy defects enhances the adsorption of alkali ions than the pristine sheet. From the obtained results, it is found that the adsorption energy of Li+ on the vacancies defected graphene sheet is higher (3.05 eV) than the pristine (2.41 eV) and Stone–Wales (2.50 eV) defected sheets. Moreover, the pore radius of the pristine and defected graphene sheets are less affected by metal ions adsorption. The increase in energy gap upon the adsorption of metal ions is found to be high in the vacancy defected graphene than that of other sheets. The metal ions adsorption in the defective vacancy sheets has high charge transfer from metal ions to the graphene sheet. The bonding characteristic between the metal ions and graphene sheet are analysed using QTAIM analysis. The influence of alkali ions on the electronic properties of the graphene sheet is examined from the Total Density of States (TDOS) and Partial Density of States (PDOS).

Influence of alkali ions on the efficiency of shrinkage reduction by polypropylene glycol in alkali activated systems

Alkali-activated materials, especially when activated by water glass, exhibit substantial drying shrinkage that hinders their broader industrial application. The effect of shrinkage-reducing admixtures (SRA), based on polypropylene glycol, on drying shrinkage of alkali-activated blast furnace slag (BFS) mortars was examined. The determination of SRA efficiency and the influence of potassium alkali activators with varying silicate modulus on drying shrinkage characteristics were studied. It was observed that a high amount of alkalis positively affected the effect of SRA. The higher the amount of alkalis was, the lower was the drying shrinkage. The paper further discusses and underlines the role of the amount of alkali ions on the properties of alkali-activated BFS systems.

Influence of Alkali Ions on Tribological Properties of Silicon Surface

Tribological properties of surfaces (friction, adhesion and wear) provide challenging limitations to the design of reliable machines on the micro- and nanometer scale as the surface to volume area increases and volume, mass and inertia of the mobile parts decrease. This study reports on the reduction in the friction force of silicon surfaces after the alkali metal ion exposure in the form of aqueous solutions. A scanning force microscope equipped with a liquid cell was used to investigate the friction force and the pull-off force of a flat silicon surface immersed in water and in different alkali metal chlorides solutions: LiCl, NaCl and CsCl. The concentration ranged from 0.1 up to 1000 µmol/l. The changes in the free surface energy of the initial surface and of the modified surfaces after drying were determined from contact angle measurements and from the acid–base adhesion theory. In both cases, in the liquid environment and after drying of the exposed silicon substrates in air, the friction force is reduced by approximately 50 %. Our results provide new, fundamental insight into the exchange of surface termination layers in particular for tribology. Also it is suggested to use the procedure as a low-cost alternative to improve the tribological properties of the silicon surface in particular in applications where lubricating fluids are not appropriate, e.g., in nanomachines and devices.

Sensing Abilities of Crown Ether Functionalized Polythiophenes

Tuning sensing abilities! The affinity of three different [15]crown-5 ether functionalized polythiophenes for alkali ions has been explored (see figure). Ab initio and DFT quantum mechanical calculations show that the binding energy between neutral conducting polymers and metallic ions, which interact attractively, decreases as the size of the ion increases. Oxidation of these polythiophene derivatives significantly reduces their affinity towards alkali ions, becoming low or even nonexistent.This work reports a theoretical study of the affinity of three different [15]crown-5 ether functionalized polythiophenes for alkali ions. Ab initio and DFT quantum mechanical calculations have evidenced that the binding energy between neutral conducting polymers and metallic ions, which interact attractively, decreases as the size of the ion increases. However, the preferences of these polythiophene derivatives have been found to be influenced by the entropic contribution, which favors binding with Na(+) in preference to Li(+). Molecular dynamics simulations have shown that this behavior can be accounted for on the basis of the large fluctuations that Li(+) undergoes when it is contained in the cavity of the [15]crown-5 ether macrocycle. In contrast, the fluctuations detected for complexes with Na(+) and K(+) were particularly low, even though only the former ion fits into the center of the macrocyclic cavity. Oxidation of these polythiophene derivatives produces a drastic change in their sensing abilities, their affinities towards alkali ions becoming low or even nonexistent. Moreover, calculations indicate that the presence of unsubstituted thiophene rings directly attached to a functionalized thiophene modulates the strength of the binding in the oxidized state by reducing the repulsive interaction between the metallic cation and the pi-conjugated system. On the other hand, the influence of alkali ions on the electronic properties, in particular, on the ionization potentials and the lowest pi-pi* transitions, of both the neutral and oxidized polythiophenes is discussed.

Profiling of external metabolites during production of hantavirus nucleocapsid protein with recombinant Saccharomyces cerevisiae

Recombinant strains of Saccharomyces cerevisiae, producing hantavirus Puumala nucleocapsid protein for diagnostics and as a candidate vaccine were analyzed for uptake and excretion of intermediary metabolites during process optimization studies of fed-batch bioreactor cultures. Concentrations of glucose, maltose, galactose, pyruvate, acetaldehyde, ethanol, acetate, succinate and formaldehyde (used as a selection agent) were measured in the culture medium in order to find a metabolite pattern, indicative for the physiological state of the producer culture. When the inducer galactose was employed as a growth substrate, the metabolite profile of recombinant yeast cells was different from those of the non-recombinant original strain which excreted considerable amounts of metabolites with this substrate. In contrast, galactose-induced heterologous gene expression was indicated by the absence of excreted intermediary metabolites, except succinate. A model strain expressing a GFP fusion of hantavirus nucleocapsid protein differed in the excretion of metabolites from strains without GFP. In addition, the influence of alkali ions, employed for pH control is also demonstrated.

Effects of alkali ions on the circadian leaf movements of Oxalis regnellii

The influence of alkali ions on the circadian leaf movements of Oxalis regnellii Mig. was investigated. Ions were given to the oscillating system via the transpiration stream of cut stalks in nutrient medium. Chloride solutions of Rb+, Cs+, Na+ and K+ were tested and the results compared to previously published LiCl‐results.The period of the circadian leaf movements was unaffected by a continual addition of Na+ or K+ to the nutrient medium (at least up to 40 mM). Rb+, in the concentration of 2.5 or 5 mM, caused a shortening of the period when applied continuously. Rb+ concentrations up to 60 mM were tested. Cs+ ions caused only lengthenings of the circadian period. Cs+ concentrations up to 40 mM were tested. Cs+ resembled Li+ in producing period lengthenings, but was not as effective as Li+ when compared on a concentration basis. Toxicity of the effective ions was in the following order: Li+Cs+Rb+, Rb+ pulses (50 mM, 4 h) phase‐shifted the rhythm and caused advances. A phase response curve was determined and the maximum steady state advances were of the order of 1 h. The dual effect of the Rb+ ions is discussed and is assumed to be due to two counteracting processes, exemplified by Rb+‐sensitive ATPase‐controlled pumping processes and protein synthesis. For comparison, the effects of Rb+ and Li+ in human depressive disorders is also discussed in relation to their influence on circadian systems. It is emphasized that Rb+ and K+ behave differently and are not interchangeable in their action on circadian systems.

Precipitation from supersaturated aluminate solutions. III. Influence of alkali ions with special reference to Li +

The precipitation of Al(OH) 3 from supersaturated aluminate solutions ( C Al = 4 × 10 −3 M) in the presence of Li +, Na +, and K + is compared. In the presence of Na + and K + at 25°C the same precipitation behavior is observed. The precipitation sequence, amorphous phase → pseudo-boehmite → bayerite, is dictated by the supersaturation (pH + pAl) and the growth rate of bayerite is found to depend on the available surface area and on the square of the supersaturation. In the presence of Li + ions a selective and drastic acceleration of the precipitation rate of bayerite is observed at 25 and 50°C. Pseudo-boehmite plays a minor role in the overall precipitation process because lithium not only selectively accelerate bayerite formation but also increase the rate of transformation of pseudoboehmite to bayerite. The discontinuous nature of the acceleration of bayerite formation strongly suggests that a fast nucleating lithium aluminate phase acts as a precursor for the precipitation and growth of bayerite. From an analysis of the measured relaxation times a variable composition of the precursor phase is deduced with a Li Al ratio ranging from 0.2 to 0.4. At high solution Li Al ratios and low supersaturations a distinct phase of composition LiA1 2(OH) 7 · 2H 2O is observed.