Showing papers by "Vadim G. Kessler published in 2014"

The sol–gel synthesis of cotton/TiO2 composites and their antibacterial properties

Abstract: Presentwork is devoted to investigation of structure and functional properties of hybrid nanomaterials based on the TiO2-modified cellulose fibers of cotton. The titania hydrosol was successfully prepared using the titanium tetraisopropoxide as precursor and the nitric acid as peptizing agent via the low-temperature sol–gel synthesis in aqueous medium and applied to cotton fabric. For cross-linking of titania nanoparticles to cotton the 1,2,3,4-butanetetracarboxylic acid (BTCA) was used as a spacer. The morphology and composition of the surface pure and TiO2 modified cotton fibers were investigated by the scanning electron microscopy (SEM). The cotton/TiO2 composite was characterized by the dielectric permittivity. For the estimation of total titania concentration, all samples were calcined at 650 °C. The antimicrobial activity of the treated TiO2 cotton fibers was investigated against Escherichia coli as a model Gram-negative bacteria after exposure to UV-irradiation for 10 min

Precursor directed synthesis – “molecular” mechanisms in the Soft Chemistry approaches and their use for template-free synthesis of metal, metal oxide and metal chalcogenide nanoparticles and nanostructures

Abstract: This review provides an insight into the common reaction mechanisms in Soft Chemistry processes involved in nucleation, growth and aggregation of metal, metal oxide and chalcogenide nanoparticles starting from metal–organic precursors such as metal alkoxides, beta-diketonates, carboxylates and their chalcogene analogues and demonstrates how mastering the precursor chemistry permits us to control the chemical and phase composition, crystallinity, morphology, porosity and surface characteristics of produced nanomaterials.

Immobilization of urease on magnetic nanoparticles coated by polysiloxane layers bearing thiol- or thiol- and alkyl-functions

Abstract: Magnetically retrievable formulations of urease potentially promising for biomedical and environmental applications were constructed by immobilization of the enzyme on the surface of magnetite nanoparticles functionalized by siloxane layers with active thiol or thiol-and-alkyl moieties The latter were deposited using a hydrolytic polycondensation reaction of tetraethoxysilane with either 3-mercaptopropyltrimethoxysilane, or with 3-mercaptopropyltrimethoxysilane and methyltriethoxysilane, or alternatively n-propyltriethoxysilane Immobilization of urease was carried out in different ways for comparison: by adsorption, by entrapment during the hydrolytic polycondensation reaction, or by covalent bonding For entrapment the enzyme was introduced into solution before functionalization of the magnetite Entrapment bound high amounts of enzyme (more than 700 mg per g of carrier), but its activity was decreased compared to the native form to between 18 and 10% In the case of covalent binding of urease using Ellman's Reagent, binding of the enzyme was almost as efficient as in the case of entrapment but its residual activity was 75% The residual activity of urease immobilized by adsorption on the surface of thiol-functionalized particles was truly high as compared to that of the native enzyme (97%), but binding was significantly less efficient (46%) Introduction of alkyl functions permitted increase of the amounts of the adsorbed enzyme but its activity was somewhat decreased

Hybrid silica nanoparticles for sequestration and luminescence detection of trivalent rare-earth ions (Dy 3+ and Nd 3+ ) in solution

Abstract: New hybrid material-based adsorbents acting also as luminescent probes upon uptake of trivalent rare-earth (RE) ions Nd3+ and Dy3+ have been developed. SiO2 NPs functionalized by three different organic ligands, N-aminopropylen-amido-iminodiacetic acid (L1), pyridine-α,β-dicarboxylic acid bis(propylenamide) (L2), and N-propylen-iminodiacetic acid (L3), have been produced and fully characterized by 13C, 1H, and 29Si solid-state NMR, FTIR, TGA, XRD, TEM, nitrogen gas adsorption, and also by NTA and DLS in solution. The synthesized hybrid materials are well dispersible and stable in aqueous solutions according to NTA and consist of spheres with diameters less than 100 nm. Their affinities to the lanthanide ions Dy3+ and Nd3+ have been investigated in aqueous solution and characterized by SEM–EDS and complexometric titration, demonstrating that they can be successfully used as adsorbents for sequestration of trivalent RE ions. The adsorbed RE ions can efficiently be desorbed from saturated nanoadsorbents by addition of hydrochloric acid. The produced nanomaterials may also be used as luminescent probes for Dy3+ and Nd3+ ions in solution.

New product from old reaction: uniform magnetite nanoparticles from iron-mediated synthesis of alkali iodides and their protection from leaching in acidic media

Abstract: Iron-mediated synthesis of alkali metal iodides was quite unexpectedly demonstrated to be able to serve as a cost-efficient and reliable source of spherical single crystalline near-stoichiometric magnetite (Fe3O4) nanoparticles as revealed by TEM and XRD studies and also by XANES spectroscopic quantification of the Fe2+-content. Using the particles as nuclei for the Stoeber synthesis of silica nanoparticles, core-shell magnetic material has been produced. The nature of the magnetic component was probed by XANES spectroscopy. The size of the particles is dependent on the synthesis conditions and Si : Fe ratio but can be kept below 100 nm. It is the Si : Fe ratio that determines the stability of the particles in acidic medium. The latter was investigated spectrophotometrically as leaching of Fe3+-cations. Considerable stability was observed at Si : Fe > 10, while at Si : Fe >= 20 no measurable leaching could be observed in over 10 days. Magnetic nanoparticles with improved stability in acidic medium provide an attractive basis for creation of adsorbent materials for applications in harsh media.

Lanthanum molybdate nanoparticles from the Bradley reaction: factors influencing their composition, structure, and functional characteristics as potential matrixes for luminescent phosphors.

Abstract: Interaction of lanthanum isopropoxide with molybdenum(VI) alkoxides in La/Mo ratios varying from 3:1 to 1:1 in acetophenon or allyl alcohol as solvents offers nanosized poorly crystalline products of complex composition, where the precipitation of Mo-rich ones is followed by the formation of La-rich ones with conservation of the reaction stoichiometry in total. Thermal treatment of the precipitates at temperatures over 700 °C leads to the formation of stoichiometric phases of the α- and β-La2Mo2O9 compositions. Introduction of smaller Re3+ cations such as Sm3+ by doping favors stabilization of the La2–xRExMo2O9 phase with improved crystallinity even after lower-temperature thermal treatment. The doping is successful only when the Re3+ (Sm3+, Eu3+, and Tb3+) is introduced as an alkoxide: application of Re3+(acac)3 as Re3+ sources leads to materials free from Re3+. The produced samples were characterized by XPD, TGA, SEM, and TEM studies as well as the luminescent properties for the Sm3+-doped phases.

General facile approach to transition-metal oxides with highly uniform mesoporosity and their application as adsorbents for heavy-metal-ion sequestration.

Abstract: Mesoporous powders of transition-metal oxides, TiO2, ZrO2, HfO2, Nb2O5, and Ta2O5, pure from organic impurities were produced by a rapid single-step thermohydrolytic approach. The obtained materials display an impressively large active surface area and sharp pore-size distribution, being composed of partially coalesced uniform nanoparticles with crystalline cores and amorphous shells. They reveal extremely high adsorption capacity in removal of CrVI anions from solutions (25.8 for TiO2, 73.0 for ZrO2, and 74.7 mg g−1 for Nb2O5 in relation to the Cr2O72− anion), making them very attractive as adsorbents in water remediation applications. The difference in adsorption capacities for the studied oxides may be explained by variation in surface hydration and surface-charge distribution.

A family of hexanuclear Mn(III) single-molecule magnets

Abstract: In an attempt to employ salicylic acid (HOsalH), 2,6-dihydroxy benzoic acid {(HO)2PhCO2H}, and naphthalene-1,8-dicarboxylic acid {1,8-naph(CO2H)2} in Mn(III) salicylaldoximate chemistry as a means to alter the structural identity of the hexanucluear clusters usually obtained from this reaction system, we have isolated a family of hexanuclear Mn(III) complexes based on salicyladloxime (saoH2) and 2-hydroxy-1-naphthaldehyde oxime (naphthsaoH2). Five hexanuclear clusters, [Mn6O2(sao)6(HOsal)2(EtOH)4]·EtOH (1·EtOH), [Mn6O2(sao)6{1,8-naph(CO2Me)(CO2)}2(MeOH)6]·3MeOH (2·3MeOH), [Mn6O2(naphthsao)6{1,8-naph(CO2Et)(CO2)}2(EtOH)6] (3·2MeOH), [Mn6O2(naphthsao)6(MeCO2)2(EtOH)4]·2H2O (4·2H2O), and [Mn6O2(naphthsao)6{(HO)2PhCO2}2(EtOH)4]·4EtOH (5·4EtOH), have been synthesized and characterized by single-crystal X-ray crystallography. The magnetic properties of 3, 4, and 5 are discussed.

A family of [Ni8] cages templated by μ6-peroxide from dioxygen activation

Abstract: A family of exceptionally thermally stable [Ni8] cages is reported, each being templated by a rare η3:η3:μ6-O22− species produced by dioxygen activation, where the reducing agent for the O2 reduction appears to be the ligand used in the reaction mixtures, which was found within the nickel cages in its oxidized form.

Study of the curing mechanism of metal alkoxide liquid threads for the synthesis of metal oxide fibers or microtubes

Abstract: Curing processes enabling transformation of liquid threads into solid material have gained technological importance. Our study is focusing on the comparison of curing mechanisms for metal alkoxide-derived liquid threads. We studied the mechanisms of the formation of fine metal oxide fibers or hollow microtubes by comparing the solidification of propoxide and butoxide precursors.

Novel solvothermal approach to hydrophilic nanoparticles of late transition elements and its evaluation by nanoparticle tracking analysis

Abstract: Solvothermal treatment of late transition metal acetylacetonates in a novel medium composed either of pure acetophenone or acetophenone mixtures with amino alcohols offers a general approach to uniform hydrophilic metal nanoparticles with high crystallinity and low degree of aggregation. Both pure metal and mixed-metal particles can be accesses by this approach. The produced materials have been characterized by SEM-EDS, TEM, FTIR in the solid state and by Nanoparticle Tracking Analysis in solutions. The chemical mechanisms of the reactions producing nanoparticles has been followed by NMR. Carrying out the process in pure acetophenone produces palladium metal, copper metal with minor impurity of Cu2O, and NiO. The synthesis starting from the mixtures of Pd and Ni acetylacetonates with up to 20 mol% of Pd, renders in minor yield the palladium-based metal alloy along with nickel oxide as the major phase. Even the synthesis starting from a mixed solution of Cu(acac)2 and Ni(acac)2 produces oxides as major products. The situation is improved when aminoalcohols such as 2-aminoethanol or 2-dimethylamino propanol are added to the synthesis medium. The particles in this case contain metallic elements and pairs of individual metals (not metal alloys) when produced from mixed precursor solutions.