Composites Based on Polytetrafluoroethylene and Detonation Nanodiamonds: Filler–Matrix Chemical Interaction and Its Effect on a Composite’s Properties

Specific properties of PTFE composites filled with ultradisperse detonation diamonds (UDDs) with different surface chemistries are studied. It is found for the first time that filler in the form of UDDs affects not only the rate of PTFE thermal decomposition in vacuum pyrolysis, but also the chemical composition of the products of degradation. The wear resistance of UDD/PTFE composites is shown to depend strongly on the UDD surface chemistry. The presence of UDDs in a PTFE composite is found to result in perfluorocarbon telomeres, released as a readily condensable fraction upon composite pyrolysis. The chemical interaction between PTFE and UDDs, characterized by an increase in the rate of gas evolution and a change in the desorbed gas’s composition, is found to occur at temperature as low as 380°C. It is shown that the intensity of this interaction depends on the concentration of oxygen-containing surface groups, the efficiency of UDDs in terms of the composite’s wear resistance being reduced due to the presence of these groups. Based on the experimental data, a conclusion is reached about the chemical interaction between UDDs and a PTFE matrix, its dependence on the nanodiamond surface chemistry, and its effect on a composite’s tribology.     

Blend Composites Based on Polystyrene–CdSe Quantum Dots and Polystyrene–Gold Nanoparticles Hybrid Systems

Polystyrenes of different molecular masses are synthesized by controlled radical polymerization via the reversible addition fragmentation chain transfer mechanism. The resulting polymers are used for designing nanocomposites based on cadmium selenide quantum dots and gold nanoparticles. It is demonstrated that the photoluminescence of quantum dots in the sol grows appreciably during continuous irradiation for 5–6 h but is reduced during the “light switching off–switching on” process. It is shown that, upon the addition of gold nanoparticles, the photoluminescence of quantum dots in the sols changes insignificantly.     

A General Catalyst Based on Cobalt Core–Shell Nanoparticles for the Hydrogenation of N-Heteroarenes Including Pyridines

Herein, we report the synthesis of specific silica-supported Co/Co₃O₄ core–shell based nanoparticles prepared by template synthesis of cobalt-pyromellitic acid on silica and subsequent pyrolysis. The optimal catalyst material allows for general and selective hydrogenation of pyridines, quinolines, and other heteroarenes including acridine, phenanthroline, naphthyridine, quinoxaline, imidazo[1,2-a]pyridine, and indole under comparably mild reaction conditions. In addition, recycling of these Co nanoparticles and their ability for dehydrogenation catalysis are showcased.     

Synthesis of CuInS2@CdS Core‐Shell Nanocrystals

CuInS₂@CdS core‐shell nanocrystals were prepared in a wet chemical process. Transmission electron microscope (TEM), x‐ray energy dispersive spectroscopy (EDAX), x‐ray diffraction (XRD), absorption, and photoluminescence (PL) spectra were used to confirm the formation of the CuInS₂@CdS core‐shell structure. The growth of CdS shell not only increased the PL intensity, but also restrained the transformation of CuInS₂ from nanoparticles to nanorods after annealing, which was attributed to an effective chemical passivation of the CuInS₂ core by the CdS shell.     

Synthesis and Optical Properties of Fe@Au,Ni@Au Bimetallic Core–Shell Nanoparticles

Fe@Au and Ni@Au core–shell nanoparticles (NPs) were synthesized by liquid-phase reduction of iron and nickel compounds by sodium borohydride in an aqueous medium. Transmission electron microscopy, X-ray powder diffraction, and spectrophotometry were used to confirm the structure of the NPs and to determine their shape and the average core and shell size.     

Microwave-Assisted Synthesis of ZnO–rGO Core–Shell Nanorod Hybrids with Photo- and Electro-Catalytic Activity

The unique two-dimensional structure and surface chemistry of reduced graphene oxide (rGO) along with its high electrical conductivity can be exploited to modify the electrochemical properties of ZnO nanoparticles (NPs). ZnO–rGO nanohybrids can be engineered in a simple new two-step synthesis, which is both fast and energy-efficient. The resulting hybrid materials show excellent electrocatalytic and photocatalytic activity. The structure and composition of the as-prepared bare ZnO nanorods (NRs) and the ZnO–rGO hybrids have been extensively characterised and the optical properties subsequently studied by UV/Vis spectroscopy and photoluminescence (PL) spectroscopy (including decay lifetime measurements). The photocatalytic degradation of Rhodamine B (RhB) dye is enhanced using the ZnO–rGO hybrids as compared to bare ZnO NRs. Furthermore, potentiometry comparing ZnO and ZnO–rGO electrodes reveals a featureless capacitive background for an Ar-saturated solution whereas for an O₂-saturated solution a well-defined redox peak was observed using both electrodes. The change in reduction potential and significant increase in current density demonstrates that the hybrid core–shell NRs possess remarkable electrocatalytic activity for the oxygen reduction reaction (ORR) as compared to NRs of ZnO alone.     

Porous Si-Cu3Si-Cu Microsphere@C Core–Shell Composites with Enhanced Electrochemical Lithium Storage

Low-cost Si-based anode materials with excellent electrochemical lithium storage present attractive prospects for lithium-ion batteries (LIBs). Herein, porous Si-Cu₃Si-Cu microsphere@C composites are designed and prepared by means of an etching/electroless deposition and subsequent carbon coating. The composites show a core–shell structure, with a porous Si/Cu microsphere core surrounded by the N-doped carbon shell. The Cu and Cu₃Si nanoparticles are embedded inside porous silicon microspheres, forming the porous Si/Cu microsphere core. The microstructure and lithium storage performance of porous Si-Cu₃Si-Cu microsphere@C composites can be effectively tuned by changing electroless deposition time. The Si-Cu₃Si-Cu microsphere@C composite prepared with 12 min electroless deposition delivers a reversible capacity of 627 mAh g⁻¹ after 200 cycles at 2 A g⁻¹, showing an enhanced lithium storage ability. The superior lithium storage performance of the Si-Cu₃Si-Cu microsphere@C composite can be ascribed to the improved electronic conductivity, enhanced mechanical stability, and better buffering against the large volume change in the repeated lithiation/delithiation processes.     

Synthesis of Cu@Ag Nanoparticles with a Core–Shell Structure Stabilized with Oxyethylated Carboxylic Acid

Russian Journal of General Chemistry - Bimetallic Cu@Ag nanoparticles with a core–shell structure were synthesized by reduction of copper 2-[2-(2-methoxyethoxy)ethoxy]acetate with hydrazine...     

Electrochemical Synthesis of Fe–Cu Composites Based on Copper(II) Ferrite and Their Electrocatalytic Properties

Russian Journal of Electrochemistry - Copper(II) ferrite is synthesized by the co-precipitation method in the absence and in the presence of polyvinyl alcohol which is followed by thermally...     

Surface Atomic Regulation of Core–Shell Noble Metal Catalysts

Core–shell noble metal catalysts have gained significant attention in the past few decades, as they not only reduce the use of noble metals effectively but also exhibit unique properties derived from the synergistic effect between core and shell metals. In particular, regulating the surface structure of shells to maximize the atomic utilization efficiency of noble metals is critically important. Controlling the shell thickness of noble metal catalysts at the atomic level as an efficient approach to realize this goal has been attracting growing attention; this approach involves the formation of ultrathin shells (typically 2–6 atomic layers), monolayers, or even atomically dispersed noble metals embedded in the host metal. These strategies drive the core/support metals to improve the number of active sites and the intrinsic activity of the deposited noble metals remarkably, meanwhile minimizing the usage of noble metals. Herein, recent advances regarding atomic control of the core–shell noble metal catalysts is reviewed, with focus on the surface regulation. First, synthesis methods and surface structures are summarized, and then catalytic applications of these architectures are highlighted.     

One-Step Photochemical Green Synthesis of Water-Dispersible Ag,Au, and Au@Ag Core–Shell Nanoparticles

A simple and green synthetic protocol for the rapid and effective preparation of Ag, Au and Au@Ag core–shell nanoparticles (NPs) is reported based on the light irradiation of a biocompatible, water-soluble dextran functionalized with benzophenone (BP) in the presence of AgNO₃, HAuCl₄, or both. Photoactivation of the BP moiety produces the highly reducing ketyl radicals through fast (<50 ns) intramolecular H-abstraction from the dextran scaffold, which, in turn, ensures excellent dispersibility of the obtained metal NPs in water. The antibacterial activity of the AgNPs and the photothermal action of the Au@Ag core–shell are also shown.     

Photoinduced Electron Transfer from the Inorganic Core to the Organic Shell of Hybrid Core–Shell Nanoparticles: Impedance Spectroscopy

In hybrid core–shell nanoparticles with inorganic nanocrystals in the core and organic molecules in the shell, photoinduced electron transfer occurs from the core to the shell. This leads to exciton dissociation through an ultrafast electron-transfer process that results in charge separation and finally photocurrent in the external circuit in devices based on such core–shell nanoparticles. In this work, we have fabricated and characterized sandwiched devices based on a series of core–shell systems. From impedance spectroscopy, we have observed that photoinduced charge separation in core–shell systems is associated with a decrease in the device resistance and an increase in the dielectric constant of the active material. In the series of core–shell systems, we have observed a one-to-one correlation between the photoinduced electron-transfer process and the changes in resistive and dielectric parameters upon illumination.     

Synthesis of Symmetrical Polyamide–Sulfonimides Based on Bis-saccharin Dicarboxylic Acid Dichlorides

Russian Journal of General Chemistry - Polycondensation of ethylene-bridged bis(saccharincarbonyl chlorides) with aliphatic diamines afforded soluble polyamide–sulfonimides. The effects of...     

Synthesis of Novel Carbosilane Dendrimers Based on Pentaerythritol

Novel pentaerythritol-based carbosilane dendrimers centered at carbon have been synthesised. Starting from tetraallyl ether based upon pentaerythritol as the core molecule, a succession of alternate Pt-catalyzed hydrosilylation of allyl groups with HSiC13 and allylations of SiC1 groups thus introduced with CH2=CHCH2MgBr in THF provided a divergent synthesis of three generations of carbosilane dendrimers in which the Si atoms are linked by CH2CH2CH2 groups. The reaction conditions for hydrosilylation must be well controlled. After purification by chromatography on silica gel pure products for each generation were obtained. The IR, ^1H and ^13C NMR spectra and elemental analysis data are consistent with the proposed structures. The molecular weights of the resulting carbosilne dendrimers have been determined by vapor pressure osmometry.     

Bayesian Optimization-guided Discovery of High-performance Methane Combustion Catalysts based on Multi-component PtPd@CeZrOx Core–Shell Nanospheres

Formula regulation of multi-component catalysts by manual search is undoubtedly a time-consuming task, which has severely impeded the development efficiency of high-performance catalysts. In this work, PtPd@CeZrO_x core–shell nanospheres, as a successful case study, is explicitly demonstrated how Bayesian optimization (BO) accelerates the discovery of methane combustion catalysts with the optimal formula ratio (the Pt/Pd mole ratio ranges from 1/2.33–1/9.09, and Ce/Zr from 1/0.22–1/0.35), which directly results in a lower conversion temperature (T₅₀ approaching to 330 °C) than ones reported hitherto. Consequently, the best sample obtained could be efficiently developed after two rounds of iterations, containing only 18 experiments in all that is far less than the common human workload via the traditional trial-and-error search for optimal compositions. Further, this BO-based machine learning strategy can be straightforward extended to serve the autonomous discovery in multi-component material systems, for other desired properties, showing promising opportunities to practical applications in future.     

Synthesis of New Sulfonamides Based on β-Pinene

Russian Journal of Organic Chemistry - Reactions of pinane-10-sulfonyl chlorides with alkyl-, aryl-, and hetarylamines afforded up to 92% of new chiral sulfonamides that are potentially...     

Utility of Core–Shell Nanomaterials in the Catalytic Transformations of Renewable Substrates

In recent years, core–shell nano-catalysts have received increasing attention due to their tunable properties and broad applications in catalysis. Control of the two components of these materials allows their catalytic properties to be tuned to various sustainable processes in synthetic and energy-related applications. This Concept article describes recent state-of-the-art core–shell materials and their application as heterogeneous catalysts for a range of sustainable catalytic transformations, focusing on two important classes of renewable substrates, CO₂ and biomass. In the discussion, emphasis is directed to the role of the constituent parts of the core–shell structure and how they can be manipulated to enhance activity.     

Magnetism and Afterglow United: Synthesis of Novel Double Core–Shell Eu2+-Doped Bifunctional Nanoparticles

Afterglow–magnetic nanoparticles (NPs) offer enormous potential for bioimaging applications, as they can be manipulated by a magnetic field, as well as emitting light after irradiation with an excitation source, thus distinguishing themselves from fluorescent living cells. In this work, a novel double core–shell strategy is presented, uniting co-precipitation with combustion synthesis routes to combine an Fe₃O₄ magnetic core (≈15 nm) with an afterglow SrAl₂O₄:Eu²⁺,Dy³⁺ outer coat (≈10 nm), and applying a SiO₂ protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe₃O₄@SiO₂@SrAl₂O₄:Eu²⁺,Dy³⁺ NPs emit green light attributed to the 4f⁶5d¹→4f⁷(⁸S_7/2) transition of Eu²⁺ under UV radiation and for a few seconds afterwards. This bifunctional nanocomposite can potentially be applied for the detection and separation of cells or diagnostically relevant molecules.     

Preparation and Chromatographic Features of Fibrous Core–Shell HPLC Packing Material

In this study, fibrous core–shell silica particles were successfully synthesized via a one-step oil–water biphase stratification coating strategy. The core–shell silica particles were composed of 3-µm non-pore silica cores and thin shells (50–100 nm), which have radial-like direct channels and a large pore size (19.89 nm). The fibrous core–shell silica particles were further modified by n-octadecyltrichlorosilane and used as stationary-phase media in high-performance liquid chromatography (HPLC). The chromatographic properties of the particles were systematically studied in small-molecule and protein separation processes. The results showed that the back pressure was as low as 8.5 MPa under the 1.0-mL min^?1 flow velocity. Furthermore, fibrous core–shell silica particles with an 80-nm shell were used for separating seven small molecules within 10 min and six proteins within 6 min. This work demonstrates that the fibrous core–shell silica particles could be used as an HPLC stationary phase with good performance and low back pressure, and that they have great potential for application to HPLC separation in the future.     

Heat Resistance and Electrophysical Characteristics of Polyheteroarylenes and Ferroelectric–Polymer Film Composites Based on Them

Russian Journal of Applied Chemistry - Structurally related poly(amido-o-hydroxy amides) derived from 5,5-methylenebis(2-aminophenol) with tetramethylsiloxane and heteroaromatic (benzoxazole and...