Doped poly(<Emphasis Type="Italic">m</Emphasis>-phenylenediamine) (PmPDA): A new precursor for Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

Poly(m-phenylene diamine) has been synthesized and characterized by physical and spectral techniques. The effect of doping Cr, Co and Ni ions on the spectral, thermal and optical properties has been studied. Optical band gap measurements indicated that, doped polymers have wider optical band gap than the pure one. The effect of doping on the thermal stability differs according to the doped metal ion. The doped with Cr ions poly(m-phenylenediamine) has been used as a precursor of mesoporous Cr₂O₃ nanoparticles, which have been also characterized by XRD and HR-TEM.     

Electronic structure of Ti<Subscript>4</Subscript>Fe<Subscript>2</Subscript>O as determined from <Emphasis Type="Italic">ab initio</Emphasis> calculations and X-ray spectroscopy studies

The TiL _α, FeL _α and OK _α ultrasoft X-ray emission bands obtained in experiment reflect, respectively, the energy distribution of mainly the Ti3d, Fe3d and O2p electronic states in Ti₄Fe₂O compound, which is an efficient hydrogen absorber for energy cells. Full and partial densities of electronic states for all atoms constituting the indicated oxide were calculated by a modified method of associated plane waves (APW) using the WIEN2k software package. The APW calculation data for Ti₄Fe₂O compound as well as superposition of TiL _α, FeL _α and OK _α ultrasoft X-ray emission bands on a single energy scale indicate that O2p states in the oxide are localized mainly near the bottom of the valence band, the major contribution near the ceiling of the valence band belonging to Fe3d and Ti3d states. According to the APW calculation, the major contribution to the bottom of Ti₄Fe₂O conduction band is made by Fe3d* and Ti3d* states. The APW data for Ti₄Fe₂O are supported by the cluster calculation performed for this compound using a FEFF82 software package.     

Sulfonic acid-functionalized titanomagnetite nanoparticles as recyclable heterogeneous acid catalyst for one-pot solvent-free synthesis of 3,4-dihydropyrimidin-2(1<Emphasis Type="Italic">H</Emphasis>)-ones/thiones

Sulfonic acid-functionalized titanomagnetite (Fe_3?x Ti _x O₄@SO₃H) nanoparticles were prepared by grafting sulfonic acid groups on Fe_3?x Ti _x O₄ nanoparticles. This new heterogeneous acid nanocatalyst demonstrated an efficient catalytic performance in the one-pot synthesis of dihydropyrimidin-2(1H)-one/thione derivatives under solvent-free conditions with high yields. The nanocatalyst could easily be separated from the reaction mixture simply by using an external magnet, recycled and reused for several times with no significant loss of catalytic activity. These nanoparticles were characterized by different physicochemical techniques, such as Fourier transform infrared, scanning electron microscopy, energy-dispersive X-ray analysis, thermogravimetric and vibrating sample magnetometer (VSM) analyses.     

Structure and properties of solid solutions based on bismuth niobate Bi<Subscript>3</Subscript>NbO<Subscript>7</Subscript>

Solid solutions Bi₃Nb_1–yW_yO_{7 ± δ}, Bi₃Nb_1–yV_yO_{7 ± δ}, Bi₃Nb_1–yFe_yO_{7 ± δ} (y = 0.1–0.5; Δy = 0.1), and Bi_3–xY_xNb_1–yW_yO_{7 ± δ} (x = 0.05, 0.1; y = 0–0.3; Δy = 0.1) have been studied. The homogeneity ranges of the solid solutions and crystal-chemical parameters have been determined by means of X-ray powder diffraction. The electrical conductivity of sintered samples has been studied by impedance spectroscopy. The joint introduction of yttrium and tungsten into the niobium sublattice does not lead to an increase in the conductivity of solid solutions, and the change of the dopant type has no noticeable effect on this conductivity.     

Effects of base composition and dopants on the properties of hexagonal ferrites

The effects of the base composition and dopants on the saturation magnetization and coercivity of hexaferrites BaAl_xFe_12–xO₁₉, SrAl_xFe_12–xO₁₉, BaGa_xFe_12–xO₁₉, SrGa_xFe_12–xO₁₉, BaSc_xFe_12–xO₁₉ and SrSc_xFe_12–xO₁₉ have been studied. Isomorphic substitutions of Al₂O₃, Ga₂O₃, and Sc₂O₃ for Fe₂O₃ in barium and strontium ferrites are found to increase coercivity due to increasing crystallographic anisotropy constant and to reduce the saturation magnetization value. Processes controlling microstructure formation, specifically recrystallization processes, are shown to have a noticeable effect on the level of properties of the ferrites under study with the use of dopants. The most efficient dopants are boron, calcium, and silicon oxides, which provide the formation of relatively fine-grained structures. The increased coercivity upon doping with these dopants is also due to the formation of grain-boundary interlayers of a nonmagnetic glassy phase and the associated efficient retardation of moving domain walls.     

Synthesis and characterization of poly(ɛ-caprolactone)/Fe3o4 nanocomposites by in situ polymerization

A series of magnetic nanocomposites based on poly(?-caprolactone) (PCL) and Fe₃O₄ nanoparticles were prepared using a facile in situ polymerization method. The chemical structures of the PCL/Fe₃O₄ nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy. Results of wide-angle X-ray diffraction (WAXD) showed that the incorporation of the Fe₃O₄ nanoparticles did not affect the crystallization structure of the PCL. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and dispersion of the Fe₃O₄ nanoparticles within the as-synthesized nanocomposites. Results of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) showed that the crystallization temperature was raised and the spherulites size decreased by the presence of Fe₃O₄ nanoparticles in the nanocomposites due to the heterogeneous nucleation effect. The thermal stability of the PCL was depressed by incorporation of Fe₃O₄ nanoparticles from thermogravimetric analysis (TGA). The superparamagnetic behavior of the PCL/Fe₃O₄ nanocomposites was testified by the superconducting quantum interference device (SQUID) magnetometer analysis. The obtained biodegradable nanocomposites will have a great potential in magnetic resonance imaging contrast and targeted drug delivery.     

Preparation of antibacterial polyimide films containing silver nanoparticles

Polyimide/silver composite films were successfully prepared by in situ polymerization. A precursor, AgNO₃ was used as the source of the silver nanoparticles. The structure and morphology of resulting films were characterized by FTIR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Consequently, the silver nanoparticles were well dispersed in polyimide matrix. Meanwhile, thermal properties from thermal gravimetric analyses (TGA) and mechanical properties from tensile test which confirmed composites were kept good performance as compared to pure polyimide. In addition, the antimicrobial activity of polyimide/silver composite films against three different bacteria, B. subtilis, S. aureus, and E. coil, illustrated excellent activity. This composite is potential useful as antimicrobial material with good thermal performance in a wide variety of biomedical and general use applications.     

Investigation of structural,rheological and thermal properties of PMMA/ONi-Al LDH nanocomposites synthesized <Emphasis Type="Italic">via</Emphasis> solvent blending method: Effect of LDH loading

This article addresses the synthesis of organically tailored Ni-Al layered double hydroxide (ONi-Al LDH) and its use in the fabrication of exfoliated poly(methyl methacrylate) (PMMA) nanocomposites. The pristine Ni-Al LDH was initially synthesized by co-precipitation method and subsequently modified using sodium dodecyl sulfate to obtain ONi-Al LDH. Nanocomposites of PMMA containing various amounts of modified Ni-Al LDH (3 wt%-7 wt%) were synthesized via solvent blending method to investigate the influence of LDH content on the properties of PMMA matrix. Several characterization methods such as X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), rheological analysis, differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA), were employed to examine the structural, viscoelastic and thermal properties of PMMA/OLDH nanocomposites. The results of XRD and TEM examination confirm the formation of partially exfoliated PMMA/OLDH nanocomposites. The FTIR results elucidate that the characteristic bands for both pure PMMA and modified LDH are present in the spectra of PMMA/OLDH nanocomposites. Rheological analyses were carried out to examine the adhesion between polymer matrix and fillers present in the nanocomposite sample. The TGA data indicate that the PMMA nanocomposites exhibit higher thermal stability when compared to pure PMMA. The thermal decomposition temperature of PMMA/OLDH nanocomposites increases by 28 K compared to that of pure PMMA at 15% weight loss as a point of reference. In comparison with pure PMMA, the PMMA nanocomposite containing 7 wt% LDH demonstrates improved glass transition temperature (T _g) of around 3 K. The activation energy (E _a), reaction orders (n) and reaction mechanism of thermal degradation of PMMA/OLDH nanocomposites were evaluated using different kinetic models. Water uptake capacity of the PMMA/OLDH nanocomposites is less than that of the pure PMMA.     

Synthesis and thermal conversions of unsaturated nickel(II) dicarboxylates as precursors of metallopolymer nanocomposites

Nickel(II) dicarboxylates of unsaturated carboxylic acids (maleic (MalA), itaconic (ItA), acetylenedicarboxylic (ADCA), allylmalonic (AlMalA), glutaconic (GlutA), cis,cis-muconic (MucA) acids) were synthesized and characterized by thermal analysis and IR spectroscopy. The synthesized dicarboxylates were subjected to thermolysis, and the obtained nanocomposites were studied by transmission and scanning electron microscopy and X-ray diffraction. The synthesized metallopolymer nanocomposites were NiO and metallic Ni nanoparticles distributed over a stabilizing matrix. The formation enthalpy of dicarboxylates (ΔН_r^°) was calculated by the PM3 semi-empirical quantum-chemical method. The nanoparticle size was determined, and a relationship between the average nanoparticle diameter (d_avg) and ΔН_r^° was established. The microstructure and magnetic characteristics of the obtained nanocomposites, namely, the maximum and residual magnetization and the coercive force, were studied.     

Surface structure of semicrystalline polyimide films

The surface structure of thin films based on poly[4,4′-bis(4″-N-phenoxy)diphenyl]amic acid of 1,3-bis(3′,4-dicarboxyphenoxy)benzene and the product of its thermal imidization—a semicrystalline polyimide—poly[4,4′-bis(4″-N-phenoxy)diphenyl]imide of 1,3-bis(3′,4-dicarboxyphenoxy)benzene—at various stges of thermal imidization and after melting and subsequent annealing has been studied by methods of transmission, scanning electron, and atomic force microscopies. The topological structure of the film surface has been described in terms of the discrete cluster model. Under heating to 200 and 280°C, a continuous network of the infinite cluster appears; subsequent annealing leads to disintegration of the network to discrete fragments that practically correspond to clusters in the starting poly(amic acid) film. The polyimide film heated to 280°C crystallizes in the form of needle crystals stable to the argon plasma. The surface morphology of polyimide films recrystallized from melt is of the spherulite character.     

Synthesis of Graft Copolyimides with Poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylamino-2-ethyl methacrylate) Side Chains and Hybrid Nanocomposites with Silver Nanoparticles

The controlled radical polymerization of N,N-dimethylamino-2-ethyl methacrylate on polyimide multicenter macroinitiators under the action of the activating complex of Cu(I) with nitrogen-containing ligands is studied. The complex investigation of the kinetics of copolymerization and the molecular-mass characteristics of the products is performed. The polarity of a medium and the nature of the nitrogen-containing ligand used to prepare the catalytic complex considerably affect the rate of polymerization and the composition and molecular-mass characteristics of the product. Process conditions that enable the synthesis of regularly graft copolyimides with poly(N,N-dimethylamino-2-ethyl methacrylate) side chains are determined. It is shown that the products of grafting copolymerization may be used as a nanoreactor and a stabilizing agent for the template synthesis of composite structures containing silver nanoparticles in the absence of additional reducing agents.     

A green synthesis of biaryls in water catalyzed by palladium nanoparticles immobilized on <Emphasis Type="Italic">N</Emphasis>-amidinoglycine-functionalized iron oxide nanoparticles

Fe₃O₄ nanoparticles were prepared by co-precipitation and coated with SiO₂ following the Stöber process. N-Amidinoglycine amino acid was then covalently connected to provide an excellent ligand for the immobilization of Pd nanoparticles. The resulting material was characterized by FE-SEM, TEM, EDX, XRD, VSM and ICP-AES analysis. The Fe₃O₄@SiO₂@N-amidinoglycine@Pd⁰ proved to be a highly active catalyst for the Suzuki coupling reactions of various aryl halides with substituted phenylboronic acids in water, giving the desired products in excellent yields for short reaction times. Moreover, this catalyst can be easily recovered by using an external magnet and directly reused for several times without significant loss of activity.     

Electrochemical sensor using graphene/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanosheets functionalized with garlic extract for the detection of lead ion

Based on the modulated electronic properties of Fe₃O₄-graphene (Fe₃O₄/GN composite) as well as the outstanding complexation between Pb²⁺ and natural substances garlic extract (GE), a novel electrochemical sensor for the determination of Pb²⁺ in wastewater was prepared by immobilization of Fe₃O₄/GN composite integrated with GE onto the surface of glassy carbon electrode (GCE). Fe₃O₄/GN composite was employed as an electrochemical active probe for enhancing electrical response by facilitating charge transfer while GE was used to improve the selectivity and sensitivity of the proposed sensor to Pb²⁺ assay. The electrochemical sensing performance toward Pb²⁺ was appraised by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and square wave voltammetry (SWV). Under the optimized condition, the sensor exhibited two dynamic linear ranges (LDR) including 0.001 to 0.5 nM and 0.5 to 1000 nM with excellent low detection limit (LOD) of 0.0123 pM (S/N =?3) and quantification limit (LOQ) of 0.41 pM (S/N =?10). Meanwhile, it displayed remarkable stability, reproducibility (RSD of 3.61%, n =?3), and selectivity toward the assay for the 100-fold higher concentration of other heavy metal ions. Furthermore, the novel sensor has been successfully employed to detect Pb²⁺ from real water samples with satisfactory results.     

Preparation and characterization of polyimide/mesoporous silica hybrid nanocomposites based on water-soluble poly(amic acid) ammonium salt

Recently, mesoporous silica was blended with polyimide to develop low dielectric constant (k) materials with improving mechanical and thermal properties of polyimide by utilizing both the nanoporous structure and silica framework. However, even the use of mesoporous silica did not show a significant decrease of k due to the phase segregation in between polyimide and the mesoporous silica materials. In this work, we attempted to prepare polyimide/mesoporous silica hybrid nanocomposites having relatively good phase mixing behavior by utilizing polyimide synthesized from a water soluble poly(amic acid) ammonium salt, which lead to low k up to 2.45. The thermal properties of polyimide were improved by adding mesoporous silicas. For this work, we have fabricated mesoporous silicas through surfactant-templated condensation of tetraethyl orthosilicate (TEOS). Pyromellitic dianhydride (PMDA)-4,4′-oxydianiline (ODA) polyimide was prepared from poly(amic acid) ammonium salt, which had been obtained by incorporating triethylamine (TEA) into PMDA-ODA poly(amic acid) in dimethylacetamide (DMAc), followed by thermal imidization.     

Synthesis and Thermal Conversions of Unsaturated Cobalt(II) Monocarboxylates: Precursors for Metal Polymer Nanocomposites

Cobalt(II) salts of unsaturated monocarboxylic acids (acrylic acid, methacrylic acid, sorbic acid, 4-pentynoic acid, crotonic acid, linoleic acid, and oleic acid) are prepared. The prepared compounds are characterized by elemental analysis, IR spectroscopy, thermogravimetry, and differential scanning calorimetry. Cobalt-containing nanocomposites are produced by the thermal decomposition of the prepared carboxylates and characterized by elemental analysis, IR spectroscopy, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray powder diffraction. The enthalpies of reaction (ΔH_r°) for the formation of cobalt(II) salts of unsaturated monocarboxylic acids are calculated by the PM3 semiempirical quantum-chemical method. A correlation is found between the mean diameter (d_mean) of nanoparticles in nanocomposites and ΔH_r°.     

Graphene oxide wrapped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@Au nanostructures as substrates for aptamer-based detection of <Emphasis Type="Italic">Vibrio parahaemolyticus</Emphasis> by surface-enhanced Raman spectroscopy

The authors describe a sensitive surface-enhanced Raman scattering (SERS)-based aptasensor for the detection of the food pathogen Vibrio parahaemolyticus. Nanostructures consisting of Fe₃O₄@Au particles wrapped with graphene oxide (GO) were used both as SERS substrates and separation tools. A first aptamer (apt 1) was immobilized on the Fe₃O₄@Au/GO nanostructures to act as a capture probe via the affinity binding of aptamer and V. parahaemolyticus. A second aptamer (apt-2) was modified with the Raman reporter molecule TAMRA to act as a SERS sensing probes that binds to the target the same way as the Fe₃O₄@Au/GO-apt 1. The sandwich formed between Fe₃O₄@Au/GO-apt 1/V. parahaemolyticus and apt 2-TAMRA can be separated with the aid of a magnet. The concentration of V. parahaemolyticus can be quantified by measurement of the SERS intensity of TAMRA. Under optimal conditions, the signal is linearly related to the V. parahaemolyticus concentration in the range between 1.4 × 10² to 1.4 × 10⁶ cfu·mL^?1, with a detection limit of 14 cfu·mL^?1. Recoveries ranging from 98.5% to 105% are found when analyzing spiked salmon samples. In our perception, the assay described here is a useful tool for quantitation of V. parahaemolyticus in real samples.

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Graphical abstract GO wrapped Fe₃O₄@Au nanostructures were synthesized as the substrate and modified with with a first aptamer (apt 1) to capture V. parahaemolyticus. TAMRA labelled aptamer 2 was then used as signal probe. The V. parahaemolyticus concentrations are closely related to the Raman intensity of TAMRA.

     

Magnetic,Electrical and Thermal Studies of Polypyrrole-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocomposites

This research paper comprises of the synthesis of polypyrrole (PPy)-Fe₂O₃ nanocomposites by employing the in situ chemical oxidative polymerization method. The concentration of the filler material was adjusted between 10–50 wt % of PPy. The synthesized nanocomposites were characterized by using X-ray diffraction (XRD). Magnetic analysis and DC electrical conductivity of the samples were carried out using vibrating sample magnetometer (VSM) and two probe DC conductivity method, point towards magnetically active and electrically conductive samples. The magnetic parameters under applied magnetic field demonstrated that the values of coercivity (H _c ), saturation magnetization (M _s ) and remanence (M _r ) can be tailored by carefully controlling the amount of dopant material into the nanocomposites indicating their suitability for controllable switching devices and microwave absorption applications. The DC electrical conductivity showed an increase up to 20 wt % of filler material and thereafter a decrease in the conductivity of nanocomposites with increase in filler content is observed. Thermogravimetric analysis (TGA) showed an increase in thermal stability with an increase in ferrite content in nanocomposites.     

Adsorption properties of aluminium oxide modified with palladium,gold, and cerium oxide nanoparticles

The adsorption properties of nanocomposites based on γ-Al₂O₃ modified with CeO_x, Au/CeO_x, and Pd/CeO_x nanoparticles with contents of deposited metals ranging from 0.07 to 1.71 wt % are investigated by means of dynamic sorption method. n-Alkanes (C₆–C₈), acetonitrile, diethyl ether, tetrahydrofuran, and dioxane are used as test adsorbates. Adsorption isotherms are measured, and the isosteric heats of adsorption of a number of test adsorbates are calculated. Electron-donor and electron-acceptor characteristics of the surfaces of γ-Al₂O₃-based nanocomposites are estimated. It is shown that Au(0.1%)/CeO_x(0.07%)/γ-Al₂O₃ nanocomposite, which has the lowest content of nanoparticles of the deposited metals, has the highest adsorption activity.     

Preparation of polyimide/BaTiO3/Ag nanocomposite films via in situ technique and study of their dielectric behavior

Triphase polyimide nanocomposite films were fabricated using barium titanate （BaTiO3） with high dielectric constant and silver （Ag） with high conductivity as fillers. In situ method was utilized to obtain the homogeneous dispersion of nanoparticles. The in situ polymerization of polyimide precursor-poly（amic acid） was performed in the presence of BaTiO3 particles. Silver compound 1,1,1-trifluoro-2,4-pentadionato silver（I） was added into the BaTiO3 containing poly（amic acid） solution to achieve silver nanoparticles via in situ self metallization technique. The thermally induced reduction converted silver （I） to metallic silver with concomitant imidization of poly（amic acid） to polyimide. Both BaTiO3 and silver nanoparticles were uniformly dispersed in the polyimide substrate. The dependence of dielectric behavior on the BaTiO3 and Ag contents was studied. The incorporation of small amount of silver nanoparticles greatly increased dielectric constant of composite films.     

Mass spectrometric and thermal analyses of the salt system Zn<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>CO<Subscript>3</Subscript> · <Emphasis Type="Italic">x</Emphasis>H<Subscript>2</Subscript>O-NaCl

The gas phase over nanocomposites consisting of zinc carbonate hydroxide (ZCH) Zn₂(OH)₂CO₃ · xH₂O(x = 1, 3) dispersed in a NaCl matrix has been characterized by high-temperature mass spectrometry and on-line FTIR spectroscopy coupled with thermal analysis. Volatile zinc-sodium chloro complexes are in equilibrium with ZCH-rich nanocomposites at 20–700°C under mass spectrometric conditions. This is evidence that sodium chloride reacts readily with zinc oxide nanoparticles. The thermal events in the ZCH-NaCl (Li₂CO₃) system have been investigated by differential scanning calorimetry.