The influence exerted by addition of 3-(methacryloyloxy) propyltrimethoxysilane (MPTMOS) on the porosity and size of silica particles synthesized in a water-ethanol-ammonia-tetraethoxysilane (TEOS) ...mixture by the Stöber-Fink-Bohn method with the subsequent calcination in oxygen at 400 °C was studied. A set of particles was synthesized at the same relative amounts of the starting reagents and at the same temperature of the reaction mixture. It was shown that as the amount of MPTMOS in the TEOS + MPTMOS precursor is raised from 0 to 12.5 mol%, the final size of the resulting SiO2 particles decreases from ∼400 to ∼10 nm, which is presumably due to the increase in the number of nucleation centers by several orders of magnitude. It was found that the particles have micropores, which are presumably formed upon removal of methacryloyloxypropyl groups by calcination. As the MPTMOS:TEOS molar ratio is raised, the micropore volume and the apparent specific surface area of the particles first grow and reach values of 0.15 сm3 g−1 (350 m2 g−1), and then decrease to 0.05 сm3 g−1 (100 m2 g−1) because the particle size (∼10 nm) becomes comparable with the pore size (1–2 nm). Upon addition of one more porogen, cetyltrimethylammonium bromide (CTAB), to the reaction mixture, the micropore volume and the apparent specific surface area of the particles substantially increase to become 0.25 cm3 g−1 and 600 m2 g−1, correspondingly, and the particle size rises to 50 nm. Probably, mesopores formed upon oxidation of CTAB micelles and micropores are mutually connected and form a common network within the particles. The total pore volume and the specific surface area of the particles determined by BET reach values of 1.05 cm3 g−1 and 1200 m2 g−1, respectively.
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•The Stöber method was used to synthesize microporous SiO2 particles from TEOS and MPTMOS.•On replacing 12.5 mol% TEOS with MPTMOS, the size of SiO2 particles becomes 40 times smaller.•The SiO2 particles have a specific surface area determined by BET of up to 1200 m2 g−1.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Several series of new polymers were synthesized in this study: binary copolyesters of vanillic (VA) and 4′-hydroxybiphenyl-4-carboxylic (HBCA) acids, as well as ternary copolyesters additionally ...containing 4-hydroxybenzoic acid (HBA) and obtained via three different ways (in solution, in melt, and in solid state). The high values of logarithmic intrinsic viscosities and the insolubility of several samples proved their high molecular weights. It was found that the use of vanillic acid leads to the production of copolyesters with a relatively high glass transition temperature (~130 °C). Thermogravimetric analysis revealed that the onset of weight loss temperatures of ternary copolyesters occurred at 330–350 °C, and the temperature of 5% mass loss was in the range of 390–410 °C. Two-stage thermal destruction was observed for all aromatic copolyesters of vanillic acid: decomposition began with VA units at 420–480 °C, and then the decomposition of more heat-resistant units took place above 520 °C. The copolyesters were thermotropic and exhibited a typical nematic type of liquid crystalline order. The mechanical characteristics of the copolyesters were similar to those of semi-aromatic copolyesters, but they were much lower than the typical values for fully aromatic thermotropic polymers. Thus, vanillic acid is a mesogenic monomer suitable for the synthesis of thermotropic fully aromatic and semi-aromatic copolyesters, but the processing temperature must not exceed 280 °C.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Recently, nanodiamonds with negatively charged luminescent color centers based on atoms of the fourth group (SiV
, GeV
) have been proposed for use as biocompatible luminescent markers. Further ...improvement of the functionality of such systems by expanding the frequencies of the emission can be achieved by the additional formation of luminescent tungsten complexes in the diamond matrix. This paper reports the creation of diamond matrices by a hot filament chemical vapor deposition method, containing combinations of luminescing Si-V and Ge-V color centers and tungsten complexes. The possibility is demonstrated of creating a multicolor light source combining the luminescence of all embedded emitters. The emission properties of tungsten complexes and Si-V and Ge-V color centers in the diamond matrices were investigated, as well as differences in their luminescent properties and electron-phonon interaction at different temperatures.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Submicrometer spherical micro-mesoporous SiO2 particles have been synthesized with a Brunauer–Emmett–Teller specific surface area of up to 1600 m2 g−1, comparable with that of nanoporous carbon ...materials. The particles are constituted by densely packed SiO2 channels, similarly to materials of the MCM-41 type. The particles have two pore subsystems: monodisperse cylindrical mesopores with controllably varied average diameter (2.5–3.5 nm) and micropores supposedly situated within the walls of the SiO2 channels and between their outer surfaces. The particles with combined micro-mesoporous structure are obtained by hydrolysis of a mixture of tetraethoxysilane (TEOS) and 3-(methacryloyloxy)propyltrimethoxysilane (MPTMOS) with molar ratio 5:1 in an alcoholic–aqueous–ammonia medium containing surfactant (cetyltrimethylammonium bromide + 1,3,5-trimethylbenzene). Negatively charged products of hydrolysis of silica precursors (TEOS and MPTMOS) are condensed near the positively charged amino groups situated on the surface of the cylindrical micelles of surfactant forming SiO2 layer containing hydrophilic methacryloyloxypropyl (MP) groups in the interior. Due to the Van der Waals forces, these micelles coated with a SiO2 layer are organized into surfactant–silica clusters forming identical spherical aggregates. Removing of surfactant micelles and MP groups leads to formation of mesopores and micropores consequently.
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•Micro-mesoporous SiO2 particles are obtained by single-step soft-template synthesis.•Porous SiO2 particles have a Brunauer-Emmett-Teller specific surface area of up to 1600 m2 g−1.•Submicrometer porous SiO2 particles have a spherical shape and a narrow size distribution.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An approach has been developed that allows the synthesis of submicron spherical silica particles with a controlled micro-mesoporous structure possessing a large specific surface area (up to 1300 m
g
...). Particle synthesis is carried out by the hydrolysis of a mixture of various organosilanes mostly associated either with CTAB or with each other. A change in the concentration of CTAB in the reaction mixture apparently leads to a change in the formation mechanism of nuclei for the silica particle growth, which allows for varying the diameter of the synthesized particles in the range from 40-450 nm. The effect of the composition of the silica precursor (3-(methacryloyloxy)propyltrimethoxysilane, (3-aminopropyl)triethoxysilane and tetraethoxysilane) on the formation process and porosity of the resulting particles is studied. It was shown that by simply varying the ratio of organosilanes in the composition of the precursor, one can control the pore diameter of the particles in a wide range from 0.6-15 nm. The large-pore (up to 15 nm) silica particles are used as a matrix for the spatial distribution of luminescent carbon dots. The incorporation of carbon dots into SiO
particles prevents their aggregation leading to emission quenching after drying, thus allowing us to obtain highly luminescent composite particles. LEDs based on the obtained composite material show bright visible luminescence with spectral characteristics similar to that of a commercial cold white LED.
The rheological properties, spinnability, and thermal-oxidative stabilization of high-molecular-weight linear polyacrylonitrile (PAN) homopolymers (molecular weights
= 90-500 kg/mol), synthesized via ...a novel metal-free anionic polymerization method, were investigated to reduce coagulant use, enable solvent recycling, and increase the carbon yield of the resulting carbon fibers. This approach enabled the application of the mechanotropic (non-coagulating) spinning method for homopolymer PAN solutions in a wide range of molecular weights and demonstrated the possibility of achieving a high degree of fiber orientation and reasonable mechanical properties. Rheological analysis revealed a significant increase in solution elasticity (G') with increasing molecular weight, facilitating the choice of optimal deformation rates for effective chain stretching prior to strain-induced phase separation during the eco-friendly spinning of concentrated solutions without using coagulation baths. The possibility of collecting ~80 wt% of the solvent at the first stage of spinning from the as-spun fibers was shown. Transparent, defect-free fibers with a tensile strength of up to 800 MPa and elongation at break of about 20% were spun. Thermal treatment up to 1500 °C yielded carbon fibers with a carbon residue of ~50 wt%, in contrast to ~35 wt% for industrial radically polymerized PAN carbonized under the same conditions.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The investigation of the hot filament chemical vapor deposition nanodiamonds with simultaneously embedded luminescent GeV
and SiV
color centers from solid sources showed that both the absolute and ...relative intensities of their zero-phonon lines (at 602 and 738 nm) depend on nanodiamond growth conditions (a methane concentration in the CH
/H
gas mixture, growth temperature, and time). It is shown that a controlled choice of parameters of hot filament chemical vapor deposition synthesis makes it possible to select the optimal synthesis conditions for tailoring bicolor fluorescence nanodiamond labels for imaging biological systems.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Search for new types of efficient magnetoplasmonic structures that combine high transparency with strong magneto-optical (MO) activity is an actual problem. Here, we demonstrate that composite ...heterostructures based on thin perfectly-arranged opal films and a perforated cobalt nanolayer meet these requirements. Anomalous transmission appears due to periodic perforation of Co consistent with the regular set of voids between opal spheres, while resonantly enhanced MO response involves the effects of surface plasmon-polariton (SPP) excitation at opal/Co interface or those associated with photonic band gap (PBG) in opal photonic crrystals. We observed the enhancement of the MO effect of up to 0.6% in the spectral vicinity of the SPP excitation, and several times less strong effect close to the PBG, while the combined appearance of PBG and SPP decreases the resultant MO response. Observed resonant magneto-optical properties of opal/Co heterostructures show that they can be treated as functional self-assembled magnetoplasmonic crystals with resonantly enhanced and controllable MO effect.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Nanodiamonds with the 'diamond' 1332.5 cm−1 Raman line as narrow as 1.8 cm−1 have been produced by reactive ion etching in oxygen plasma of heteroepitaxial diamond particles grown by microwave plasma ...enhanced chemical vapour deposition (MWPECVD) on silicon. After the etching, a doublet is recorded in the zero-phonon line photoluminescence spectra of an ensemble of silicon-vacancy (SiV) centres at 10 K. Each line of the doublet is split into two lines corresponding to the optical transitions between the split excited and ground energy levels of the SiV centres. These Raman and photoluminescent features have been observed previously only in low-strain homoepitaxial diamond films and single-crystal diamond.
Nonlinear absorption of metal–halide perovskite nanocrystals (NCs) makes them an ideal candidate for applications which require multiphoton-excited photoluminescence. By doping perovskite NCs with ...lanthanides, their emission can be extended into the near-infrared (NIR) spectral region. We demonstrate how the combination of Yb3+ doping and bandgap engineering of cesium lead halide perovskite NCs performed by anion exchange (from Cl− to Br−) leads to efficient and tunable emitters that operate under two-photon excitation in the NIR spectral region. By optimizing the anion composition, Yb3+-doped CsPbClxBr3−x NCs exhibited high values of two-photon absorption cross-section reaching 2.3 × 105 GM, and displayed dual-band emission located both in the visible (407–493 nm) and NIR (985 nm). With a view of practical applications of bio-visualisation in the NIR spectral range, these NCs were embedded into silica microspheres which were further wrapped with amphiphilic polymer shells to ensure their water-compatibility. The resulting microspheres with embedded NCs could be easily dispersed in both toluene and water, while still exhibiting a dual-band emission in visible and NIR under both one- and two-photon excitation conditions.
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