Pd-PVP colloid as catalyst for Heck and carbonylation reactions: TEM and XPS studies

Pd-PVP colloid (stabilized with polyvinylpyrrolidone) with a diameter of 19.8 nm in [Bu₄N]Br medium catalyzes Heck coupling of bromobenzene with butyl acrylate and methoxycarbonylation of iodobenzene reactions. Oxidative addition of PhI or PhBr to Pd-PVP as the first step of a catalytic reaction was confirmed by TEM and XPS measurements. TEM studies showed significant reduction of Pd nanoparticle size after their reaction with PhX (X = I, Br) and [Bu₄N]X (X = Cl, Br, I). The biggest shift of the center of nanoparticle size distribution, from 19.8 nm to 7.6 nm, was found when Pd-PVP reacted with PhI and [Bu₄N]Br. The formation of [Bu₄N]₂[Pd(Ph)Br₃]- and [Bu₄N]₂[PdBr₄]-type complexes in that system was evidenced by XPS and UV–vis spectra.     

Core–shell superparamagnetic iron oxide nanoparticle (SPION) clusters: TEM micrograph analysis,particle design and shape analysis

For the first time, particle shape analysis of silica coated iron oxide (maghemite/magnetite) nanoparticle clusters (core–shell nanostructures) is discussed using computational methods. We analyzed three samples of core–shell nanostructures synthesized with different thickness of the silica shell. A new computational method is presented and successfully applied to the segmentation of the core–shell nanoparticles, as one of the main problems in image analysis of the TEM micrographs. We have introduced the “circularity coefficient”, marked with k_circ and defined as the ratio of circularity measure C₂(S) of nanoparticles core and circularity measure core–shell nanoparticles in order to answer the question how the shell affects the overall shape of the final core–shell structure, with respect to circularity. More precisely, the “circularity coefficient” determines whether the circularity of the core–shell nanoparticle is higher, lower or equal to the circularity of the core. We have also determined the shell's share in the overall area of the core–shell nanoparticle. The core–shell nanoparticle clusters here investigated exhibit superparamagnetic properties at room temperature, thus emphasizing their potential for use in practical applications such as in biomedical and particle separation. We show that the saturation magnetization strength can be easily adjusted by controlling the thickness of the silica shell.     

Au anchored to (α-Fe2O3)-MCM-41-HS as a novel magnetic nanocatalyst for water-medium and solvent-free alkyne hydration

A novel catalytic system based on Au nanoparticle functionalized magnetic mesoporous silica was prepared as (α-Fe₂O₃)-MCM-41-HS-Au. This material was obtained through the reaction of ordered mesoporous silica-coated magnetic nanoparticles (α-Fe₂O₃)-MCM-41, (3-mercaptopropyl) trimethoxysilane (MPTMS) and HAuCl₄. This catalyst was extensively characterized by various techniques such as SEM, TEM, XRD, EDX, IR and N₂-sorption isotherm. Very uniform dispersion and ordered mesopores of (α-Fe₂O₃)-MCM-41-SH (about 2–3 nm) causes Au nanoparticles to be distributed very finely on the pore surfaces, resulting in a very useful and robust magnetically recyclable catalyst for water-medium and solvent-free alkyne hydration.     

Isothermal crystallization kinetics and morphology of PP/TiO2 nanocomposites using titanium n‐butoxide precursor

This study investigates the influence of the addition of TiO₂, obtained by hydrolysis–condensation reaction of titanium dioxide precursors, on the kinetics of polypropylene (PP) isothermal crystallization. The dispersion of nanoparticle and its relation to the degree of crystallinity by XRD was also investigated. The results indicated that the addition of the TiO₂ increased the degree of crystallinity of PP and its crystallization temperature. Likewise, the nucleation and crystal growth processes were also affected, as indicated by the TEM morphology, the Avrami kinetic model, and the optical microscopy, in which a nucleation effect was detected. POLYM. COMPOS. 36:517–526, 2015. © 2014 Society of Plastics Engineers     

Functionalization of nano-MgCr2O4 additives by silanol groups: a new approach to the development of magnesia-chrome refractories

This work describes a novel approach to improve the dispersion of a nanoparticle MgCr₂O₄ additive in the matrix of magnesia-chrome refractories by functionalizing the nanoparticle surfaces with silanol groups. The effect of the silanol groups on the nanoparticles within the refractory matrix was shown by FTIR spectroscopy, zeta potential measurements, UV–visible spectroscopy, Dynamic Light Scattering (DLS) and TEM to result in a decrease of the average particle size of the MgCr₂O₄ additive by about 50% due to de-agglomeration of the nano particles by the silanol groups. Silanol functionalization of the nano-additives in the magnesia-chrome refractories fired at 1600 °C resulted in a 65 Kgf/cm² increase in their compressive strength, while the hot modulus of rupture and corrosion resistance values of these refractories fired at 1400 °C were similar to those containing unfunctionalized nano-additives fired at 1600 °C. XRD and SEM results suggest the improvement in corrosion resistance is related to the formation of spinel phases in the refractories containing silanol-modified nano-additives.     

LDPE/Bi2O3 nanocomposites: Enhanced mechanical,dielectric, and optical properties

This study is focused on investigating the role of bismuth oxide (Bi₂O₃) nanoparticles to improve structural, optical, electrical, and mechanical properties of low-density polyethylene (LDPE). For this purpose, Bi₂O₃ nanoparticles were synthesized by using the solvothermal method and examined by transmission electron microscopes (TEM), x-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, and ultraviolet–visible (UV–Vis) light absorption methods. LDPE-based nanocomposites were prepared by changing the nanoparticle additive ratio in the composite from 0% to 2% by weight. The composites were analyzed in the context of their FTIR spectra, atomic force microscope (AFM) images, UV–Vis light absorption spectra, stress–strain curves, and energy storage abilities. While the AFM findings indicate a smoother surface for the composites, the optical band gap analysis reveals a slightly decreased direct optical band gap energy. The analyses based on dielectric spectroscopy also highlight the LDPE/0.5% n-Bi₂O₃ composite in terms of the best energy storage capability. Additionally, the highest Young's modulus, toughness, stress at break, and percentage of strain at break were also recorded for the LDPE/0.5% n-Bi₂O₃ composite. In this context, the LDPE/0.5% n-Bi₂O₃ composite with improved dielectric and mechanical properties can be suggested as a new promising LDPE-based nanocomposite with better properties for industrial purposes.     

Thermally Pretreated 46% Pt/Vulcan XC72: Characterisation by TGA/DSC/TEM and Cyclic Voltammetry

We report a study of thermal stability and impact of thermal pretreatment procedures for 46% Pt/Vulcan XC72 (Tanaka) fuel cell catalyst. Stability in air and in inert gas (nitrogen, argon, helium) has been investigated by thermal gravimetric analysis (TGA), TGA‐mass spectrometry (TGA‐MS) and differential scanning calorimetry (DSC). Two distinct low temperature mass loss processes (100–200 and 285–300 °C) were observed, each exhibiting unique pretreatment temperature dependencies. TGA‐MS data in helium show fragment ions that suggest the thermal degradation processes are associated with decomposition of materials such as processing aids. Transmission electron microscopy (TEM) reveals a modest increase in average Pt nanoparticle size upon thermal pretreatment. After a pretreatment protocol based on TEM and thermal characterisation (300 °C/15 min, N₂), the electrochemically active surface area did not increase. At the kinetically controlled potential region (E >0.8 V) there was a small drop in current density for treated 46% Pt/C in comparison with as‐received catalyst. The slowing in ORR kinetics is significant. Apparently, the removal of organic components, which would improve mass transport, is negated by increased nanoparticle size.     

Palladium nanocatalysts protected by polyacids

Several colloidal palladium nanocatalysts prepared by the in situ reduction of palladium chloride PdCl₂, ammonium tetrachloropalladate (NH₄)₂PdCl₄, and palladium acetate Pd(CH₃COO)₂ were protected by various water-soluble polymers, with special emphasis on polyacids. The particle sizes, morphologies, and size distributions of the palladium nanoparticles were determined by transmission electron microscopy (TEM), and their catalytic activities were qualitatively tested by the hydrogenation of cyclohexene. The type of the polymer (for example, polyacid versus a nonionic, water-soluble polymer) can influence the nanoparticle sizes and morphologies, as well as colloidal stabilities. For the catalytic activities of these metal–polymer systems, the choice of the protective polymer can be equally important. Lower catalytic activities have been mostly found if polyacids were used as protective matrices for these palladium nanocatalysts. It was found to be important to consider several influences, such as the particle size and morphology, as well as the interaction between the polymer and the catalyst nanoparticle. Thus, the selection of the protective polymer is crucial for the development of tailored metal–polymer catalyst systems. Additional influences may stem from the presence of ions, for example, those from the metal precursor, or the counterions of the polymer side groups. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1209–1219, 1998     

Change of phase composition and morphology of sonochemically synthesised hydroxyapatite nanoparticles with glycosaminoglycans during thermal treatment

Abstract

Based on the preparation of glycosaminoglycans (GAGs) stabilised hydroxyapatite (HAP) nanoparticle suspension via sonochemical synthesis, the change of phase composition and morphology of freeze dried HAP nanoparticles with GAGs was investigated from 500 to 1200°C by TEM, X-ray diffraction, Fourier transform infrared spectroscopy and SEM. Results show that thermal treatment brought the phase transformation and the morphology change of HAP nanoparticles. In the low temperature stage (～650°C), the samples were mainly composed of HAP as main crystalline phase and β-NaCaPO₄ as minor crystalline phase. This phase transformation was mainly attributed to the residues containing sodium derived from combustion of GAGs. The particles were near spherical, and the nanocrystalline nature was retained. In the high temperature stage (650–1200°C), the samples were glass ceramic powders composed of HAP, β-tricalcium phosphate, Na₃Ca₆(PO₄)₅, β-NaCaPO₄ and Na–Ca–P–O glass phase. The grains rapidly grew into larger particles with morphology transformation from rodlike shape to irregular shape and the size increase from (0·1–0·15) × (0·3–0·5) μm to 1·5–10 μm.     

Electrohydrodynamic instabilities of polymer thin films: Filler effect

The influence of various nanoparticles with different dimension, density, dielectric constant, and surface property on electrohydrodynamic (EHD) instabilities of polymer/nanoparticle nanocomposite thin films was examined as a function of nanoparticle concentration. Transmission electron microscopy (TEM) images of polystyrene (PS)/nanoparticles (NPs) thin films demonstrated that all the nanoparticles were uniformly distributed in polymer matrix and the homogeneous dispersions of nanoparticles were not affected by thermal annealing above glass transition temperature. Optical microscopy (OM) observations indicated that thin films of polystyrene containing silica (SiO₂), gold (Au), cadmium selenide (CdSe), and titania (TiO₂) nanoparticles showed electrohydrodynamic instability patterns similar to those seen in pure polystyrene, up to 3 vol% nanoparticles. The presence of nanoparticles changed the dielectric constant of the thin films, which led to systematic variations in the wavelengths of the surface instabilities, which were consistent with calculated values. Cross-sectional transmission electron microscopy (TEM) images showed that migration or aggregation of the nanoparticles occurred only for silica contrary to other nanoparticles. This work points to a simple route to reduce the scale of final well-ordered columnar structures.     

Polymethacrylic acid/Na-montmorillonite/SiO<Subscript>2</Subscript> nanoparticle composites structures and thermal properties

In this article, polymethacrylic acid/Na-montmorillonite/SiO₂ nanoparticle (PMAA/Na-MMT/SiO₂) composites were prepared via in situ polymerization. Fourier transform infrared spectroscopy (FTIR) indicated that the polymerization of SiO₂ nanoparticle and MAA have been taken place. X-ray diffraction (XRD) results suggest that Na-MMT layers are exfoliated during the polymerization process. As evidenced by the transmission electron microscopy (TEM), the Na-MMT layers and SiO₂ nanoparticles exhibit good dispersion in the polymer matrix. It was found that the PMAA/Na-MMT/SiO₂ composite exhibit considerably enhanced thermal properties compared with the PMAA/Na-MMT.     

Fatty Acid Binding Domain Mediated Conjugation of Ultrafine Magnetic Nanoparticles with Albumin Protein

A novel bioconjugate of stearic acid capped maghemite nanoparticle (γ-Fe₂O₃) with bovine serum albumin (BSA) was developed by taking recourse to the fatty acid binding property of the protein. From FT-IR study, it was found that conjugation took place covalently between the amine group of protein molecule and carboxyl group of stearic acid capped maghemite nanoparticle. TEM study further signified the morphology of the proposed nanobioconjuagte. The binding constant of nanoparticle with protein molecule was evaluated from the optical property studies. Also, magnetic measurement (M–H) showed retaining of magnetic property by significant values of saturation magnetization and other hysteretic parameters.     

Graft Gum Ghatti Caped Cu<Subscript>2</Subscript>O Nanocomposite for Photocatalytic Degradation of Naphthol Blue Black Dye

Photodecolorization of naphthol blue black dye through the use of Cu₂O nanoparticles capped with a biopolymer matrix containing gum ghatti (Gg) grafted with acrylic acid (AA) and acrylamide (AAm) (Cu₂O/Gg–AAm–AA) has been studied. While the homogeneous co-precipitation method was adopted for the synthesis of the Cu₂O nanoparticle, its incorporation into the biopolymer matrix (Gg–AAm–AA) was performed through the graft copolymerization method. The synthesized Cu₂O and Cu₂O/Gg–AAm–AA were characterized using SEM, TEM, XRD, EDX and UV–Vis spectroscopies, and BET surface area analysis. The photodecolorization experiment was performed using simulated ultraviolet and visible light irradiations, and these results compared with that of adsorption studies. The influence of pH, catalyst dose and dye concentration on the decolorization efficiency were also taken into consideration. The results revealed the Cu₂O/Gg–AAm–AA to be an excellent photocatalyst for effective elimination of naphthol blue black dye from water. The process was observed to be pH dependent, with pH 6 being the optimum value. The photodecolorization process increased with increasing catalyst concentration but decreased beyond the optimum value of 0.3 g L^?1. The process also decreased with increasing dye concentration. The result of the recyclability study indicates that the Cu₂O/Gg–AAm–AA nanocomposite can be effectively recycled and re-used over a number cycles.     

Electrochemical synthesis and In situ spectroelectrochemistry of conducting NMPy‐TiO2 and ZnO polymer nanocomposites for Li secondary battery applications

Poly(N‐methylpyrrole) (PNMPy), poly(N‐methylpyrrole‐TiO₂) (PNMPy‐TiO₂), and poly (N‐methylpyrrole‐ZnO) (PNMPy‐ZnO) nanocomposites were synthesized by in situ electropolymerization for cathode active material of lithium secondary batteries. The charge–discharging behavior of a Li/LiClO₄/PNMPy battery was studied and compared with Li/LiClO₄/PNMPy‐nanocomposite batteries. The nanocomposites and PNMPy films were characterized by cyclic voltammetry, in situ resistivity measurements, in situ UV–visible, and Fourier transform infra‐red (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The differences between redox couples (ΔE) were obtained for polymer nanocomposites and PNMPy films. During redox scan, a negative shift of potential was observed for polymer nanocomposite films. Significant differences from in situ resistivity of nanocomposites and PNMPy films were obtained. The in situ UV–visible spectra for PNMPy and polymer nanocomposite films show the intermediate spectroscopic behavior between polymer nanocomposites and PNMPy films. The FTIR peaks of polymer nanocomposite films were found to shift to higher wavelengths in PNMPy films. The SEM and TEM micrographs of nanocomposite films show the presence of nanoparticle in PNMPy backbone clearly. The result suggests that the inorganic semiconductor particles were incorporated in organic conducting PNMPy, which consequently modifies the properties and morphology of the film significantly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41526.     

The Preparation of Core–Shell P(St-MMA)–SiO2 Hybrid Nanoparticles and Filling in the Styrene/n-butyl Acrylate Adhesive

In this study, core–shell poly(styrene-methyl methacrylate) (P(St-MMA))–SiO₂ hybrid nanoparticles were prepared successfully by emulsion polymerization. Firstly, nanosilica particles were modified by oleic acid (OA) in order to introduce the polymerization active vinyl groups and hydrophobic groups onto the nanosilica. This was followed by graft copolymerization onto the modified nanosilica particles to obtain P(St-MMA)–SiO₂ hybrid nanoparticles. The hybrid nanoparticles were characterized by: transmission electron microscope (TEM); Fourier transform infrared spectroscopy (FT-IR); dynamic light scattering (DLS); and thermal gravimetric analysis (TGA). The results indicate that the hybrid particles had a regular spherical morphology with a diameter ranging from 50 to 80 nm. A reasonable mechanism for the preparation of the core–shell hybrid nanocomposites was presented. The obtained hybrid nanoparticles were subsequently (incorporated into) filled in the poly(styrene-n-butyl acrylate) (PSBA) latex. The effect of (hybrid nanoparticle concentration) filling content on the physicochemical properties of PSBA latex and the resulting node strength per monofilanment of the fibre glass gridding cloth was investigated. The results indicated that the node strength/monofilanment of the fibre glass gridding cloth coated with the PBSA latex filled with 1.0 wt% hybrid nanoparticles demonstrated greatest improvement among all the investigated PSBA latex. This result is related to the rheological properties of the latex. Moreover, the water-resistance property of PSBA composite film was found to be enhanced when compared with that of unfilled PSBA film.     

A convenient approach to synthesize stable silver nanoparticles and silver/polystyrene nanocomposite particles

In this study, silver nanoparticles were prepared by the reduction of silver nitrate in SDS+ isopentanol/styrene/H₂O reverse microemulsion system using sodium citrate as reducing agent. The Ag/PS nanocomposite particles were prepared by in situ emulsion polymerization of the styrene system containing silver nanoparticles that did not separate from the reaction solution. The polymerization dynamic characteristic was studied, at the same time, silver nanparticles and the encapsulation of composite particles were characterized by Fourier‐transform‐infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X‐ray diffraction (XRD) measurement, UV–vis diffuse reflectance spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The results of TEM and UV–vis absorption spectra showed that well‐dispersed silver nanoparticles have a narrow size distribution. XRD showed that Ag and Ag/PS nanocomposite particles were less than 10 and 20 nm in size, which is similar to those observed by TEM. The results of XPS spectra revealed that the microemulsion system can stabilize the silver nanoparticles from aggregation and provided supporting evidence for the polystyrene encapsulated silver nanoparticle structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Tribological properties of SiO2 nanoparticle filled–phthalazine ether sulfone/phthalazine ether ketone (50/50 mol %) copolymer composites

SiO₂ nanoparticle filled–poly(phthalazine ether sulfone ketone) (PPESK) composites with various filler volume fractions were made by heating compression molding. The tribological behavior of the PPESK composites was investigated using a block‐on‐ring test rig by sliding PPESK‐based composite blocks against a mild carbon steel ring. The morphologies of the worn composite surfaces, wear debris, and the transferred films formed on the counterpart steel surface were examined with a scanning electron microscope, whereas the chemical state of the Fe element in the transfer film was analyzed with X‐ray photoelectron spectroscopy. In addition, IR spectra were taken to characterize the structure of wear debris and PPESK composites. It was found that SiO₂ nanoparticle filled–PPESK composites exhibit good wear resistance and friction‐reduction behavior. The friction and wear behavior of the composites was improved at a volume fraction between 4.2 and 14.5 vol % of the filler SiO₂. The results based on combined SEM, XPS, and IR techniques indicate that SiO₂ nanoparticle filled–PPESK composite is characterized by slight scuffing in dry sliding against steel and polishing action between composite surface and that of the countpart ring, whereas unfilled PPESK is characterized by severe plastic deformation and adhesion wear. In the former case a thin, but not complete, transfer film was formed on the surface of the counterpart steel, whereas in the latter case, a thick and lumpy transfer film was formed on the counterpart steel surface. This accounts for the different friction and wear behavior of unfilled PPESK and SiO₂ nanoparticle filled–PPESK composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2136–2144, 2002     

Hybrid poly(ethylene terephthalate)/silica nanocomposites prepared by in‐situ polymerization

The nanocomposites, based on hybrid poly(ethylene terephthalate) (PET)/silica nanoparticles, were prepared via in‐situ condensation polymerization of terephthalic acid and ethylene glycol in the presence of silica nanoparticles pretreated with a silane coupling agent. Such a polymerization process ensured that the silica nanoparticles were well dispersed in PET matrix with the size ranging from 40 to 60 nm, which was confirmed by transmission electron microscope (TEM) observation. Attributed to the unique bonding between SiO₂ nanoparticle and PET, the crystallization behavior of PET was improved significantly, at a low temperature in particular. To further explore the effects of silica nanoparticles on crystallization, extensive differential scanning calorimeter (DSC) measurements were performed in an attempt to reveal the impact of the morphology of the dispersed silica nanoparticle (i.e., sphere or gel‐like) on the peak temperature during melting as well as the amount of heat involved in crystallization. The influences of the structure of polyether glycol (PEG) used for PET preparation as well as the addition of glass fibres (GF) were also investigated using DSC. It was concluded that the synergy among silica nanoparticles, modified PEG, and GFs lowers both T_g and T_m of PET, thus facilitating the injection processes in application. POLYM. COMPOS. 28:42–46, 2007. © 2007 Society of Plastics Engineers     

Effects of the Template Composition and Coating on the Photoluminescence Properties of ZnS:Mn Nanoparticles

Mn-doped ZnS nanocrystals based on low dopant concentrations (0–2%) and coated with a shell of Zn(OH)₂ have been prepared via soft template and precipitation reaction. The results indicate that the ZnS:Mn nanocrystal is cubic zinc blende structure and its diameter is 3.02 nm as demonstrated by XRD. Measured by TEM, the morphology of nanocrystals is a spherical shape, and their particle size (3–5 nm) is similar to that of XRD results. Photoluminescence spectra under ultraviolet region shows that the volume ratio of alcohol to water in the template has a great effect on the luminescence properties of ZnS:Mn particles. Compared with unpassivated ZnS:Mn nanocrystals, ZnS:Mn/Zn(OH)₂ core/shell nanocrystal exhibits much improved luminescence and higher absolute quantum efficiency. Meanwhile, we simply explore the formation mechanism of ZnS:Mn nanocrystals in alcohol and water system and analyze the reason why alcohol and water cluster structures can affect the luminescent properties of nanoparticle.     

A molecular level model for the nucleation of a single-wall carbon nanotube cap over a transition metal catalytic particle

Recent in-situ video rate TEM studies have revealed that the base growth of single-wall carbon nanotubes (SWCNT) in thermal chemical vapour deposition (CVD) is accompanied by a considerable deformation of the Ni catalyst nanoparticle and the creation of a subsurface carbon layer. In this paper we argue that these effects may be produced by the adsorption – on the catalyst nanoparticle – of cyclopentadienyl ions formed in gas phase during C₂H₂ pyrolysis. These ions can, at the same time, facilitate the nucleation of a SWCNT cap by the provision of “ready made” pentagons. To this end we have performed semi-empirical quantum mechanical calculations with the ZINDO method. The results support the above proposed mechanism. We also suggest that this mechanism could also explain the increased rate of SWCNT production in plasma enhanced CVD, where these ions are expected to be present in higher concentrations during C₂H₂ pyrolysis.