Low-temperature positron annihilation study of B⁺-ion implanted PMMA

Temperature dependent positron annihilation lifetime spectroscopy (PALS) measurements in the range of 50–300 K are carried out to study positronium formation in 40 keV B+-ion implanted polymethylmethacrylate (B:PMMA) with two ion doses of 3.13·10¹⁵ and 3.75·10¹⁶ ions/cm². The investigated samples show the various temperature trends of ortho-positronium (o-Ps) lifetime τ3 and intensity I3 in PMMA before and after ion implantation. Two transitions in the vicinity of ∼150 and ∼250 K, ascribed to γ and β transitions, respectively, are observed in the PMMA and B:PMMA samples in consistent with reference data for pristine sample. The obtained results are compared with room temperature PALS study of PMMA with different molecular weight (Mw) which known from literature. It is found that B⁺-ion implantation leads to decreasing Mw in PMMA at lower ion dose. At higher ion dose the local destruction of polymeric structure follows to broadening of lifetime distribution (hole size distribution)

Self-assembled fractal hybrid dendrites from water-soluble anionic (Thia)calix[4] arenes and Ag+

Novel water-soluble anionic p-tertbutylthiacalix[ 4]arene with propanesulfonate fragments has been synthesized. Alkylation of the lower rim of thiacalix[4]arene in the presence of NaH/THF led to cone conformation instead of the expected 1,3-alternate conformer due to metal template effect. The presence of supramolecular associates at the critical micelle concentration of 1.65 · 10−5 M were investigated in aqueous solutions by a combination of different techniques (DLS and conductivity). It was observed that the macrocyclic platform decreases the CMC by tenfold as compared with non-macrocycle analogs. A simple approach for the design of stable monodisperse Ag-based nanoaggregates (near 95 nm) containing ionic Ag and organic ligand-thiacalix[4]arene sulfo derivative in water has been developed. Self-assembled fractal hybrid nanodendrites consisting of water-soluble anionic (thia)calix[4]arenes and Ag+ have been obtained in a single step under mild conditions. © Springer Science+Business Media Dordrecht 2017

Two-Step Mediated Electrosynthesis and Catalytic Activity of Au/Cu<inf>2</inf>O@poly(N-vinylpyrrolidone) Nanocomposite

© 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. Efficient two-step methylviologen (MV2+) - mediated electrosynthesis of a nanocomposite of gold nanoparticles with copper(I) oxide stabilized by a shell of poly(N-vinylpyrrolidone) (Au/Cu2O@PVP) was performed in DMF at room temperature at the potentials of MV.+ radical cation generation. At the first step, the mediated reduction of Cu2+ ions, generated in situ by dissolution of the copper anode, in the presence of dissolved oxygen or with subsequent oxidation with oxygen, leads to Cu2O@PVP composite containing Cu(0) and Cu2O in a different ratio. In the latter case, the resulting composite is in the form of stable nanoroses. When AuCl is added into the resulting solutions of Cu2O@PVP, the partial chemical reduction of AuCl by Cu(0) occurs to form Au(0) and CuCl. At the second step, the electrochemical reduction of AuCl leads to Au/Cu2O@PVP nanocomposite not containing Cu(0), but nanoroses are preserved. Cu2O@PVP nanoparticles are catalytically inactive in the reduction reaction of p-nitrophenol with sodium borohydride in water, and Au/Cu2O@PVP nanocomposites exhibit catalytic activity. In the presence of cetyltrimethylammonium chloride, the catalytic activity of both types of particles sharply increases; in the case of Cu2O@PVP, the increase is so high that the catalytic activity becomes the same as for Au/Cu2O@PVP

Two-step electrosynthesis and catalytic activity of CoO−CoO • xH<inf>2</inf>O-supported Ag, Au, and Pd nanoparticles

© 2020, Springer Science+Business Media LLC. Two-step electrosynthesis of CoO-CoO•xH2O-supported metal nanoparticles (MNPs, M = Au, Ag, Pd) was carried out in N,N-dimethylformamide in the absence and in presence of poly(N-vinylpyrrolidone) (PVP) using atmospheric oxygen as both a reagent and a mediator at potentials of its reduction to a superoxide radical anion. In the first step, oxygen reduction in the presence of Co2+ ions added to the solution as a salt or generated by dissolving the Co-anode during electrolysis produces a mixture of cobalt oxide CoO and its hydrated form CoO-CoO • xH2O (CoOxHy). When Ag+, Au+, Pd2+ ions are added to the obtained solution of CoOx H y, a redox reaction between CoO and the metal ion gives the MNPs and CoO+. In the second step, oxygen-mediated electroreduction of CoO+ serving as the second mediator is carried out, and the redox reaction is completely shifted towards the formation of MNPs. In the absence of PVP, AgNPs (18±4 nm) bind and stabilize completely in the CoOxHy matrix, PdNPs (6±1 nm) stabilize only partially, and AuNPs (21±10 nm) do not bind and, therefore, only their agglomerates are obtained (~200 nm). In the presence of PVP, individual AgNPs (5±2 nm), AuNPs (13±5 nm), PdNPs (3±1 nm) are stabilized in the PVP shell and are bound by the matrix. The obtained nanocomposites M/CoOx H y and M@PVP/CoOxHy catalyze the reduction of p-nitrophenol with sodium borohydride in an aqueous medium. Their catalytic activity is due to MNPs; CoOx H y acts as an inert matrix

Self-assembled fractal hybrid dendrites from water-soluble anionic (Thia)calix[4] arenes and Ag+

Novel water-soluble anionic p-tertbutylthiacalix[ 4]arene with propanesulfonate fragments has been synthesized. Alkylation of the lower rim of thiacalix[4]arene in the presence of NaH/THF led to cone conformation instead of the expected 1,3-alternate conformer due to metal template effect. The presence of supramolecular associates at the critical micelle concentration of 1.65 · 10−5 M were investigated in aqueous solutions by a combination of different techniques (DLS and conductivity). It was observed that the macrocyclic platform decreases the CMC by tenfold as compared with non-macrocycle analogs. A simple approach for the design of stable monodisperse Ag-based nanoaggregates (near 95 nm) containing ionic Ag and organic ligand-thiacalix[4]arene sulfo derivative in water has been developed. Self-assembled fractal hybrid nanodendrites consisting of water-soluble anionic (thia)calix[4]arenes and Ag+ have been obtained in a single step under mild conditions. © Springer Science+Business Media Dordrecht 2017

CoO–xCo(OH)<inf>2</inf> supported silver nanoparticles: electrosynthesis in acetonitrile and catalytic activity

© 2020 The two-step electrosynthesis of the nanocomposites of silver nanoparticles supported on CoO–xCoO(OH)2 was carried out in acetonitrile using dissolved oxygen as a reagent in the first step (support synthesis) and a mediator in the second step (silver nanoparticle synthesis). The support and nanocomposite catalyzed the reduction of p-nitrophenol with sodium borohydride in an aqueous medium, and poly(N-vinylpyrrolidone) decreased their catalytic activity

Benzimidazo[1',2':1,2]Quinolino[4,3-b][1,2,5]Oxodiazolo[3,4-f]Quinoxaline—New Mediator for Electrosynthesizing Metal Nanoparticles

© 2020, Pleiades Publishing, Ltd. Abstract: Spherical silver nanoparticles (NP-Ag) stabilized in shells of poly(N-vinylpyrrolidone) (PVP) are synthesized electrochemically by the benzimidazo[1',2':1,2]quinolino[4,3-b][1,2,5]oxodiazolo[3,4-f]quinoxaline (BIQOQ)-mediated reduction of Ag+ ions in the presence of PVP and cellulose nanofibers (NC) at the potential controlled at the BIQOQ– generation in the DMF/0.1 M Bu4NBF4 medium at room temperature. The mediator is not consumed in this process, the generated metal is not deposited on the cathode, being formed in solution volume in the quantitative yield corresponding to the theoretical quantity of electricity passed. The synthesized products represent cellulose nanofibers decorated most compactly with silver nanoparticles covered by PVP shells Ag@PVP/NC. The size of NP-Ag in Ag@PVP/NC (11 ± 3 nm) is much lower as compared with the Ag@PVP nanocomposite synthesized by the methyl-viologen‑mediated reduction of Ag+ ions under similar conditions in the absence of NC (20 ± 7 nm). The synthesized nanocomposite exhibits catalytic activity in the reactions of reduction of nitroaromatic compounds by sodium borohydride in aqueous media

Two-step one-pot electrosynthesis and catalytic activity of xCoO–yCo(OH)<inf>2</inf>-supported silver nanoparticles

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. Efficient two-step electrosynthesis of xCoO–yCo(OH)2 (CoOxHy)-supported silver nanoparticles (AgNPs) is carried out in N,N-dimethylformamide (DMF) using atmospheric oxygen as a reagent and mediator at the potentials of its reduction to the superoxide ion. In the first step, the reduction of oxygen in the presence of Co (II) ions added to the solution as a salt or generated upon dissolution of a Co anode by means of electrolysis results in a mixture of amorphous cobalt oxide CoO and its hydrated form Co (OH)2. The addition of Ag+ ions to the resulting solution of CoOxHy by similar methods results in two parallel reactions of Ag+ reduction to give AgNPs: reversible reduction by CoO and irreversible reduction by DMF. In the second step, oxygen-mediated electroreduction of CoO+ and residual quantities of Ag+ occurs, as well as regeneration of CoOxHy. The resulting spherical AgNPs are bound and stabilized by the CoOxHy matrix. Both steps occur quantitatively and consume the theoretical amount of electricity (2 F with respect to Co2+ in the first step and 1 F with respect to Ag+ in the second step). Depending on the production method, the size of the AgNPs varies in a range from 7±2 to 27±10 nm. The Ag/CoOxHy nanocomposites obtained exhibit catalytic activity in the p-nitrophenol reduction with sodium borohydride in an aqueous medium. Their activity caused by AgNPs significantly increases in the presence of cetyltrimethylammonium chloride (CTAC), a micelle-forming cationic surfactant

Nanoparticles based on the zwitterionic pillar[5]arene and Ag⁺: Synthesis, self-assembly and cytotoxicity in the human lung cancer cell line A549

© 2020 Shurpik et al. For the first time, stable pillar[5]arene/Ag+ nanoparticles, consisting of water-soluble pillar[5]arene containing γ-sulfobetaine fragments and Ag+ ions without Ag-Ag bonds, were synthesized and characterized. The pillar[5]arene/Ag+ (ratio 1:10) nanoparticles obtained were cubic with a rib length of 100 nm and are less cytotoxic than Ag+ ions. The survival of the A549 model cells in the presence of pillar[5]arene/Ag+ (1:10) nanoparticles at a concentration of 30 and 40 μM was 76% and 55%, while in the absence of pillar[5]arene, the cell survival for free Ag+ ions at the same concentration was 30% and 10%, respectively. The results can be used to create new antibacterial materials and 2D biomedical coatings

Iminodiacetic derivatives of p-tert-butylthiacalix[4]arene: Synthesis and influence of conformation on the aggregation with bismarck brown Y

Three conformers (cone, partial cone and 1,3-alternate) of tetrasubstituted at the lower rim p-tert-butylthiacalix[4] arene derivatives with iminodiacetic fragments were synthesized and characterized. It was shown by spectral methods (UV-Vis,1H NMR and DOSY spectroscopy, DLS) and TEM that the monodisperse nano-sized particles are formed by self-assembly of synthetic octaacids in water with azo dye Bismarck brown Y in the case of the partial cone and 1,3-alternate conformations. It was found that the dye associates with the acid binding sites of the macrocycle. © ISUCT Publishing