Synthesis and characterization of thermosensitive core–shell polymeric nanoparticles

Thermosensitive core–shell nanoparticles were synthesized by semicontinuous heterophase polymerization of styrene, followed by a seeded polymerization for forming a shell of poly(N-isopropyl acrylamide) (PNIPAM). Nanoparticles characterization by scanning transmission electronic microscopy showed core–shell morphology with average particle diameters around 40 nm. An inverse dependence of the particle size with temperature in the range 20–55 °C was identified by quasielastic light scattering measurements. As was expected for core–shell particles with PNIPAM as the shell, a volume phase transition near 32 °C was detected. In spite of thermosensitive properties of core–shell nanoparticles synthesized here, the volume percentage loss values were not so high, probably due to their relatively low content of PNIPAM.     

Facile synthesis of a Co–B nanoparticle catalyst for efficient hydrogen generation via borohydride hydrolysis

A Co–B nanoparticle catalyst was prepared by a modified polyol method. Borohydride served both as a reducing agent for Co²⁺ and as a boron source, and the solvent, ethylene glycol, served as the surfactant and stabilizer to assemble Co–B clusters into small and uniform particles. The as-prepared Co–B possessed high surface active metal area and highly unsaturated coordinated Co metal, resulting in lower activation energy and higher hydrogen generation rate for hydrolysis of alkaline NaBH₄ solution than the conventional Co–B catalyst synthesized from chemical reduction in water bath.     

Electrospun CdS–TiO2 doped carbon nanofibers for visible-light-induced photocatalytic hydrolysis of ammonia borane

CdS/TiO₂ NPs-decorated carbon nanofibers were introduced as a novel photocatalyst working under visible light radiation for the effective hydrolytic dehydrogenation of ammonia borane. Calcination of electrospun nanofiber mats composed of titanium tetraisopropoxide, poly (vinyl pyrrolidone) (PVP), and cadmium acetate dihydrate with a few drops of ammonium sulfide in argon atmosphere at 850 °C led to the production of CdS–TiO₂ decorated carbon nanofibers. As-synthesized nanocomposite exhibited a strong photocatalytic activity for catalytic hydrolysis of ammonia–borane. The favorable electrons-transfer properties, better dispersion, high surface area, and adsorption property are the main features of nanocomposites that exhibit high catalytic efficiency.     

Synthesis of superhydrophobic core–shell mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNPs) have been used in variety of applications due to their morphology and porous structure. This work reports the one-pot synthesis of ultrahydrophobic MSNPs using N-cetyl-n,n,n trimethyl ammonium bromide as a cationic surfactant template and ethanol (EtOH) as a cosolvent to form mesopores in the MSNPs. The effects of EtOH on the size and the pore structure of the MSNPs were studied by scanning electron microscopy and transmission electron microscopy. The results show that an addition of EtOH led to an enlargement of the MSNPs and a change in pore structure from a lamellar structure to a radially oriented structure. Co-condensation with two different types of fluoroalkyl silanes; trimethyl(fluoromethyl)silane, and trichloro(1H,1H,2H,2H-perfluorooctyl)silane provided low surface energy MSNPs with a core–shell structure. An assembly on the surface of these F-MSNPs generated nanostructure surface roughness rendering an improvement in surface wettability with water contact angle of 158.6°, which is a characteristic of oleophobic and ultrahydrophobic material.     

Enhanced electrocatalytic activity and stability of PdCo@Pt core–shell nanoparticles for oxygen reduction reaction

The carbon-supported PdCo@Pt core–shell nanoparticles for an oxygen reduction reaction (ORR) were prepared via a two-step process at room temperature. The as-prepared PdCo@Pt/C with an average particle size of ~3.5 nm exhibited a well-defined nanostructure consisting of Pd-rich core and Pt shell formed by displacing Co core with Pt. Compared to pure Pt, PdCo@Pt/C showed a higher current density in the kinetic controlled region and more positive half-wave potential for the ORR. In a cycling stability test of the PdCo@Pt/C electrocatalyst, no remarkable activity loss was seen.     

Viscoelasticity of shell-crosslinked core–shell nanoparticles filled polystyrene melt

Shell-crosslinked core–shell nanoparticles (SCCSN) of 63–104 nm in diameter and containing 79.1 wt% crosslinked polystyrene (PS) shell of 16.5–37.0 nm in thickness were prepared by miniemulsion polymerization of styrene in the presence of silane modified nanosilica. The PS shell was crosslinked using divinyl benzene in order to anchor the shell on the nanoparticle surface, to segregate the silica core from the matrix and to avoid entanglement between the shell PS and the matrix macromolecules in SCCSN filled PS composites. Steady and dynamic rheologies of SCCSN filled PS were compared with bare silica filled PS. The SCCSN filled PS composites exhibited exceedingly good rheological stability than silica filled ones during annealing. Both bare silica and SCCSN introduced a non-terminal dynamic rheology while they did not introduce additional mechanism responsible for origination of nonlinear steady flow except for macromolecular disentanglement of the PS matrix. The reinforcement of SCCSN to PS was related to the silica core even though the crosslinked shell could effectively eliminate filler aggregation as the case of silica filled PS.     

Waterborne polyurethane-acrylic copolymers crosslinked core–shell nanoparticles for humidity-sensitive coatings

A novel crosslinked core–shell emulsion of waterborne polyurethane-acrylic copolymers (PUA) was successfully synthesized by emulsion polymerization. The average particle size of the PUA particle was approximately 130 nm and its core–shell morphology was proved with transmission electron microscopy (TEM) and dynamic light scattering (DLS), whose structure was also confirmed by FT-IR and TGA. PUA was applied to prepare the humidity controlling coatings (PUA-C) by compositing with pigments and porous fillers. The structure and properties of humidity controlling coatings were investigated, with particular attention to the effects of the humidity controlling. The surface morphology of the PUA-C was observed by scanning electron microscope (SEM). The humidity controlling coatings showed excellent properties of humidity sensitivity and humidity retention.     

Conventional and microwave-assisted synthesis of hyperbranched and highly branched polylysine towards amphiphilic core–shell nanocontainers for metal nanoparticles

Hyperbranched amphiphilic polymeric systems with core–shell architecture can be used as versatile nanocontainers and templates with great potential in application fields ranging from medicine to organic coatings. In order to explore an alternative to the already widely used and established synthetic macromolecules, we synthesized new polymers based on hyperbranched polylysine. Polylysine was prepared with classical heating and microwave-assisted heating, respectively. While, the synthesis at 160 °C resulted in hyperbranched polylysine with degrees of branching (DB) between 0.50 and 0.54, the microwave-assisted heating at 200 °C resulted in highly branched polymers with DB values of 0.30–0.32. The molecular weight M_n could be controlled in a range of 5000–12,000 g/mol. The hyperbranched polylysine was hydrophobized via polymer-analogue reactions using a mixture of stearoyl/palmitoyl chloride and glycidyl hexadecyl ether, respectively. These reactions yielded in high degrees of modification (80% and 90%, respectively). The synthesized polymers are soluble in non-polar organic solvents, such as toluene and chloroform, and take up metal salts to up to 25 wt.%. They support the formation of Ag, Au, and Pd nanoparticles and nanocrystals in organic solvents and stabilize them. Thus, the here presented macromolecules are a promising readily achievable alternative to existing core–shell systems.     

Plasma-assisted ammonia decomposition over Fe–Ni alloy catalysts for CO x-Free hydrogen

On-site ammonia (NH₃) decomposition is considered as a potential path to supply CO _x-free hydrogen for fuel cell vehicles. In this article, monometallic catalysts (Fe, Co, Ni, and Mo) and bimetallic catalysts (Fe–Co, Mo–Co, Fe–Ni, and Mo–Ni) were prepared and tested in plasma-catalytic NH₃ decomposition, where 6Fe–4Ni catalyst exhibited the highest activity and synergistic capability with plasma. At 500°C, NH₃ were completely decomposed (>99.9% NH₃ conversion); the rate of H₂ production and the energy consumption of H₂ production reached 0.96 mol g⁻¹ h⁻¹ and 0.050 kW h (mol g⁻¹)⁻¹, respectively. The 200 h continuous operation results indicate an excellent durability of 6Fe–4Ni catalyst. The catalysts characterization and plasma diagnosis results indicate that NH₃ was pre-activated by plasma into excited-state species (NH₃, ˙NH₂, and ˙NH), and the 6Fe–4Ni catalyst exhibited the highest capability to adsorb excited NH₃, ˙NH₂, and ˙NH species, which could be the main reason why 6Fe–4Ni catalyst exhibited the highest activity. © 2018 American Institute of Chemical Engineers AIChE J, 65: 691–701, 2019     

Temperature- and pH-sensitive core–shell nanogels as efficient carriers of doxorubicin with potential application in lung cancer treatment

Temperature- and pH-sensitive core–shell nanogels were prepared by one-pot soapless emulsion polymerization of N-isopropylacrylamide and 2-methacryloyloxy benzoic acid with the aid of a crosslinker (core) using poly(ethylene glycol) methyl ether methacrylate as stabilizer (shell). The size of nanogels depended on the crosslinker used, being considerable smaller (around 100?nm) with the use of the acid-labile crosslinker 9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane (DVA). Doxorubicine (DOX) was loaded in nanogels with good efficiency. The empty nanogels were biocompatible for a lung cancer cell line (NCI-H1437), while the DOX-loaded, DVA-crosslinked nanogels resulted with efficient cytotoxicity for that cell line.     

pH-responsive polymer in a core–shell magnetic structure as an efficient carrier for delivery of doxorubicin to tumor cells

A pH-responsive polymer derived from polyethyleneimine with zwitterionic function was used as a shell around super paramagnetic iron oxide nanoparticles (SPIONs), to introduce an efficient drug carrier for cancer drug delivery and imaging. Core–shell magnetic Fe₃O₄@FA-PEI-SUC (SUC: Succinate conjugated) nanoparticles were attained and characterized. Right chemical attachments, 61.34% modification of primary amino groups of poly(ethyleneimine) (PEI) in PEI–SUC, spherical shape, core–shell structure, crystal structure of SPIONs, 18.23% polymer coating of NPs, 8% decrease in magnetization following polymer coating around SPIONs, doxorubicin loading efficiency 85.19%, two times more released amount in acidic pH, and proper toxicity results were obtained by different analysis methods.     

Preparation of superparamagnetic β-cyclodextrin-functionalized composite nanoparticles with core–shell structures

In this article, we report an original and feasible protocol for the preparation of superparamagnetic β-cyclodextrin-functionalized composite nanoparticles with core–shell structures via cross linking reaction on the surface of carboxymethyl β-cyclodextrin-modified magnetite (Fe₃O₄) nanoparticles by using epichlorohydrin as a crosslinking agent. The structure and morphology of the prepared composite nanoparticles were studied by Fourier transform infrared spectrometry, X-ray diffraction measurement, transmission electron microscopy and the thermogravimetric analysis. The results show that the prepared roughly spherical composite nanoparticles (diameter about 10–20 nm) with core–shell structures turned out to be magnetite nanoparticles surface-surrounded by a layer of cross-linked CM-β-cyclodextrin polymer. Results of vibrating sample magnetometry testing and inclusive behaviour studying confirmed the superparamagnetism with saturation magnetization value of 52.0 emu/g in an external applied magnetic field of 20000 Oe and inclusion functionality of the composite nanoparticles consisting of magnetite cores and β-cyclodextrin moiety, which implies very important applications in targeting drug delivery technology and separation for specific substances.     

Optimization of conditions for preparation of ZSM-5@silicalite-1 core–shell catalysts via hydrothermal synthesis

Although the preparation of ZSM-5@silicalite-1 (ZS) core-shell catalysts has been reported in the literature, their selectivity to para-xylene (PX) in the toluene alkylation with methanol is difficult to control. Here we present the effects of water and ZSM-5 adding amounts in the synthesis solution, the hydrothermal synthesis time, and the Si/Al ratio of core ZSM-5 on the catalytic performance of ZS core-shell catalysts. The ZS core-shell catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption, and NH₃ temperature-programmed desorption (NH₃-TPD) techniques. The highest PX selectivity of 95.5% was obtained for the ZS (Si/Al=140) catalyst prepared in the synthesis solution with a molar ratio of 0.2TPAOH:1TEOS:250H₂O at 175℃ and 10 r·min^-1 for only 2 h and the corresponding toluene conversion is as high as 22.8% for the alkylation of toluene with methanol.     

Electrodeposition of Co–Pd alloys from ammonia solutions and their catalytic activity for hydrogen evolution reaction

Investigations of the influence of electrolysis parameters such as the concentration of metal ammonia complexes, working electrode potential and temperature on the composition, structure and catalytic activity of synthesized alloys for water molecule reduction reaction in 2 M NaOH (T = 25 °C) were conducted. The alloys were deposited under potentiostatic conditions within potential range from ?0.7 to ?1.1 V in electrolytes of pH 9.5, containing ammonia complexes of cobalt(III) and palladium(II), [Co(NH₃)₆]³⁺ and [Pd(NH₃)₄]²⁺, of different concentration ratio. Structural changes in electrodeposited alloys were discussed based on results of X-ray diffraction measurements. An elemental analysis was performed using the energy-dispersive X-ray spectroscopy technique. Finally, based on results of galvanostatic measurements, the Tafel slope within the range of activation control for hydrogen evolution reaction was determined and mechanism of the process was discussed. The alloys presented low Tafel slope value, from 25.4 to 88.7 mV dec^?1. The alloy of the highest activity for hydrogen evolution reaction contained 31.2 at.% of Pd.     

Ionic liquid supported on magnetic nanoparticles as highly efficient and recyclable catalyst for the synthesis of β-keto enol ethers

A magnetically ionic liquid supported on γ-Fe₂O₃ nanocatalyst (Al_xCl_y-IL-SiO₂@γ-Fe₂O₃) was synthesized and evaluated as a recoverable catalyst for the synthesis of β-keto enol ethers. The immobilized catalyst proved to be effective and provided the products in high to excellent yield at room temperature. Moreover, the catalyst could be easily recovered by magnetic separation and recycled for six times without significant loss of its catalytic activity.     

Comparison of film properties for crosslinked core–shell latexes

Thermosetting acrylic latexes were synthesized using butyl acrylate (BA), methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA) via seeded two-stage process. A 2-level factorial experimental design was employed to investigate the effect of hydroxyl (core phase), carboxylate (shell phase) groups, and type of surfactant (Triton X200, Tergitol XJ) on the mechanical properties of thermosetting latexes. Eight latexes with varying concentration of HEMA, MAA and two types of surfactants were synthesized and crosslinked with three crosslinkers. Latex functionality for crosslinking was located in the core only, the shell only, and both the core–shell with varying concentrations. Melamine-formaldehyde (hexamethoxymethyl melamine) resin was employed to crosslink hydroxyl functionalities in the core. Carboxylic acid groups in the shell were crosslinked with zinc ammonium carbonate. HDI isocyanurate (Desmodur N3300A) were used to crosslink with hydroxyl or carboxyl functional groups in core and shell. The mechanical properties of coatings were evaluated in terms of tensile properties, cross-hatch adhesion, pencil hardness, and impact resistance. Design of experiment (DOE) was utilized to investigate the effect of variables on mechanical properties of crosslinked thermoset films.     

Ruthenium promoted cobalt–alumina catalysts for the synthesis of high-molecular-weight solid hydrocarbons from CO and hydrogen

The effect of the ruthenium promotion of Fischer–Tropsch (FT) cobalt–alumina catalysts on the temperature of catalyst activation reduction and catalytic properties in the FT process is studied. The addition of 0.2–1 wt % of ruthenium reduces the temperature of reduction activation from 500 to 330–350°C while preserving the catalytic activity and selectivity toward C₅₊ products in FT synthesis. FT ruthenium-promoted Co–Al catalysts are more selective toward higher hydrocarbons; the experimental value of parameter α_ASF of the distribution of paraffinic products for ruthenium-promoted catalysts is 0.93–0.94, allowing us to estimate the selectivity toward C₂₀₊ synthetic waxes to be 48 wt %, and the selectivity toward C₃₅₊ waxes to be 23 wt %. Ruthenium-promoted catalysts also exhibit high selectivity toward olefins.