Conversion of methane to C2 and C3 hydrocarbons over TiO2/ZSM-5 core–shell particles in an electric field

Catalytic conversion of methane (CH₄) to light olefins is motivated by increasing recoverable reserves of methane resources, abundantly available in natural gas, shale gas, and gas hydrates. The development of effective processes for conversion of CH₄ to light olefins is still a great challenge. The interface of ZSM-5 zeolite and TiO₂ nanoparticles is successfully constructed in their core–shell particles via mechanochemical treatment with high shear stress. The oxidative coupling of methane at a low temperature under application of an electric field may be induced by the O₂ activation via electrons running through the surface of TiO₂ located at the interface of TiO₂ and zeolite particles. Moreover, C₃H₆ was also produced by the ethylene to propylene (ETP) reaction catalyzed by Brønsted acid sites in the ZSM-5 zeolite within core–shell particles.

A TiO₂/ZSM-5 composite catalyst efficiently works for the oxidative coupling of methane and the subsequent ethylene-to-propylene reactions in an electric field.     

SiO2@MnOx@Na2WO4@SiO2 core–shell-derived catalyst for oxidative coupling of methane

SiO₂@MnO_x@Na₂WO₄@SiO₂ core–shell catalysts were prepared and their fabrication was confirmed using transmission electron microscopy. The formation of Mn-based nanosheets on the silica spheres is important for the deposition of nanoscopic Na₂WO₄. The SiO₂@MnO_x@Na₂WO₄@SiO₂ core–shell catalysts were used for the oxidative coupling of methane at a temperature of 700–800 °C at which the nanostructures were completely destroyed. Although the core–shell structures did not survive the high-temperature oxidative coupling of methane, the selective production of olefins and paraffins can be attributed to highly dispersed Na₂WO₄ derived from confined core–shell structures.

SiO₂@MnO_x@Na₂WO₄@SiO₂ core–shell catalysts were prepared for the oxidative coupling of methane.     

Synthesis of TiO2–ZnS nanocomposites via sacrificial template sulfidation and their ethanol gas-sensing performance

TiO₂–ZnS core–shell composite nanorods were synthesized by using ZnO as a sacrificial shell layer in a hydrothermal reaction. ZnO thin films of different thicknesses were sputter-deposited onto the surfaces of TiO₂ nanorods as templates for hydrothermally synthesizing TiO₂–ZnS core–shell nanorods. Structural analysis revealed that crystalline TiO₂–ZnS composite nanorods were formed without any residual ZnO phase after hydrothermal sulfidation in the composite nanorods. The thickness of the ZnO sacrificial shell layer affected the surface morphology and sulfur-related surface defect density in hydrothermally grown ZnS crystallites of TiO₂–ZnS composite nanorods. Due to the distinctive core–shell heterostructure and the heterojunction between the TiO₂ core and the ZnS shell, TiO₂–ZnS core–shell nanorods exhibited ethanol gas-sensing performance superior to that of pristine TiO₂ nanorods. An optimal ZnO sacrificial shell layer thickness of approximately 60 nm was found to enable the synthesis of TiO₂–ZnS composite nanorods with satisfactory gas-sensing performance through sulfidation. The results demonstrated that hydrothermally derived TiO₂–ZnS core–shell composite nanorods with a sputter-deposited ZnO sacrificial shell layer are promising for applications in gas sensors.

TiO₂–ZnS core–shell composite nanorods were synthesized by using ZnO as a sacrificial shell layer in a hydrothermal reaction.     

Preparation of MoS2-based polydopamine-modified core–shell nanocomposites with elevated adsorption performances

New molybdenum disulfide (MoS₂)-based core–shell nanocomposite materials were successfully prepared through the self-assembly of mussel-inspired chemistry. Characterization by Fourier transform infrared, thermogravimetric analysis, scanning electron microscope and transmission electron microscopy revealed that the surface of the flaked MoS₂ was homogeneously coated with a thin layer of polydopamine (PDA). Dye adsorption performances of the synthesized MoS₂–PDA nanocomposites were investigated at different pH values and reaction times. Compared with pure MoS₂ nanosheets, the obtained core–shell nanocomposites showed elevated adsorption performances and high stability, indicating their potential applications in wastewater treatment and composite materials.

New core–shell MoS₂–PDA nanocomposites are prepared via mussel-inspired chemistry and a simple interfacial self-assembly process, demonstrating potential applications in wastewater treatment and self-assembled core–shell composite materials.     

A core–shell structured polyacrylonitrile@poly(vinylidene fluoride-hexafluoro propylene) microfiber complex membrane as a separator by co-axial electrospinning

A novel and facile core–shell structured polyacrylonitrile@poly (vinylidene fluoride-hexafluoro propylene) (PAN@PVDF-HFP) microfiber complex membrane was designed and fabricated via co-axial electrospinning, which was used as a separator in lithium-ion batteries. Poly(vinylidene fluoride-co-hexafluoro propene) (PVDF-HFP) and polyacrylonitrile (PAN) were used as the shell (outer) layer and core (inner), respectively. Structure, surface morphology, porosity, and thermal properties of the core–shell structured microfiber membranes were investigated. Compared with the traditional commercial porous polyethylene (PE) separator, the PAN@PVDF-HFP microfiber complex membranes exhibited higher porosity, superior thermal stability, better electrolyte wettability and higher ionic conductivity. As a consequence, batteries assembled with the PAN@PVDF-HFP microfiber complex membrane display better cycling stability and superior rate performance compared to those with the PE separator.

A novel and facile core–shell structured polyacrylonitrile@poly (vinylidene fluoride-hexafluoro propylene) (PAN@PVDF-HFP) microfiber complex membrane was designed and fabricated via co-axial electrospinning.     

In situ synthesis of copper nanoparticles encapsulated by nitrogen-doped graphene at room temperature via solution plasma

Metal–carbon core–shell nanostructures have gained research interest due to their better performances in not only stability but also other properties, such as catalytic, optical, and electrical properties. However, they are limited by complicated synthesis approaches. Therefore, the development of a simple method for the synthesis of metal–carbon core–shell nanostructures is of great significance. In this work, a novel Cu–core encapsulated by a N-doped few-layer graphene shell was successfully synthesized in a one-pot in-liquid plasma discharge, so-called solution plasma (SP), to our knowledge for the first time. The synthesis was conducted at room temperature and atmospheric pressure by using a pair of copper electrodes submerged in a DMF solution as the precursor. The core–shell structure of the obtained products was confirmed by HR-TEM, while further insight information was explained from the results of XRD, Raman, and XPS measurements. The obtained Cu-core encapsulated by the N-doped few-layer graphene shell demonstrated relatively high stability in acid media, compared to the commercial bare Cu particles. Moreover, the stability was found to depend on the thickness of the N-doped few-layer graphene shell which can be tuned by adjusting the SP operating conditions.

An excellent corrosion protection for copper nanoparticles by nitrogen-doped few-layer graphene via solution plasma process.     

Symmetric and asymmetric overgrowth of a Ag shell onto gold nanorods assisted by Pt pre-deposition

The plasmonic properties of noble metallic nanoparticles could be tuned by morphology and composition, enabling opportunities for applications in sensors, photocatalysis, biomedicine, and energy conversion. Here, we report a method of the symmetric and asymmetric overgrowth of a Ag shell onto gold nanorods assisted by Pt pre-deposition via a 2-step approach. Firstly, gold nanorods (AuNRs), synthesized via a seed-mediated method, were used as seeds to form a AuNR–Pt structure, by using K₂PtCl₄ as the precursor. In this step, most of the Pt material was selectively deposited on the tips of the AuNR. Secondly, by using AgNO₃ as the precursor, a Ag shell was overgrown on the surface of the AuNRs–Pt nanoparticles, resulting in a (AuNR–Pt)–Ag core–shell tri-metallic nanostructure. Due to the surface energy and lattice matching between Au and Ag, the Ag shell preferred to be epitaxially overgrown on the side of AuNR. The Ag shell thickness and symmetry of the (AuNR–Pt)–Ag could be tuned by changing the amounts of AgNO₃ precursor. With the increase of the Ag shell thickness, the (AuNR–Pt)–Ag nanostructures changed from symmetric to asymmetric. The obtained (AuNR–Pt)–Ag nanostructures were studied using UV-vis-NIR spectroscopy, transmission electron microscopy, EDS mapping, DLS, and ICP-MS. The growth mechanism was discussed.

Demonstrating asymmetric (AuNR–Pt)–Ag tri-metallic nanostructures by a two-step seed-mediated method. The shell thickness was controlled by the amount of AgNO₃.     

Non-photochemical catalytic hydrolysis of methyl parathion using core–shell Ag@TiO2 nanoparticles

Highly water-dispersible core–shell Ag@TiO₂ nanoparticles were prepared and shown to be catalytically active for the rapid degradation of the organothiophosphate pesticide methyl parathion (MeP). Formation of the hydrolysis product, p-nitrophenolate was monitored at pH 7.5 and 8.0, using UV-Vis spectroscopy. ³¹P NMR spectroscopy confirmed that hydrolysis is the predominant pathway for substrate breakdown under non-photocatalytic conditions. We have demonstrated that the unique combination of TiO₂ with silver nanoparticles is required for catalytic hydrolysis with good recyclability. This work represents the first example of MeP degradation using TiO₂ doped with AgNPs under mild and ambient conditions. Analysis of catalytic data and a proposed dark mechanism for MeP hydrolysis using core–shell Ag@TiO₂ nanoparticles are described.

Ag@TiO₂ non-photochemical catalyzed degradation of organophosphosphates.     

High-sensitivity refractive index of Au@Cu2−xS core–shell nanorods

A high refractive index sensitivity of Au@Cu_2−xS core–shell nanorods working in the near-infrared is theoretically demonstrated. The sensitivity of our sensor reaches 1200 nm per Refractive Index Unit (RIU), which is higher than that of other metal–metal core–shell nanorods. The reason is that the new materials and structure of Au@Cu_2−xS core–shell nanorods lead to a unique sensing principle. It is noteworthy that the refractive index (RI) sensitivity is more susceptible to the effects of the shell-thickness to core-radius ratio than to the aspect ratio. These results show that the excellent sensitivity performance of Au@Cu_2−xS core–shell nanorods working in the near-infrared can be treated as a new tool to detect the minute variations in refractive index for small amounts of chemicals and biomolecules.

A high refractive index sensitivity of Au@Cu_2−xS core–shell nanorods working in the near-infrared is theoretically demonstrated.     

An ultrasonic method for the synthesis,control and optimization of CdS/TiO2 core–shell nanocomposites

In this study, an ultrasonic method was utilized in combination with microemulsion to synthesize CdS/TiO₂ core–shell nanoparticles and control their particle size and ultimately optimize the influential parameters. Moreover, response surface methodology (RSM) was used to optimize the thickness of the shell. Herein, four parameters, i.e. temperature (67–79 °C), synthesis retention time (45–105 min), TiO₂ : CdS ratio (1.5–7.5) and the power of ultrasound waves (37–53 watt), were optimized to synthesize nanoparticles with an average size of up to 10 nm. A correlation equation was introduced for the size range of 10–90 nm, which was then proven to have excellent predictions. To verify the proposed model, two different sets of combinations were selected to synthesize 10 nm composites, and consequently, nanocomposites with the sizes of 10.4 and 10.9 nm were successfully synthesized. The power of ultrasound waves and retention time had the most influence on the size of the particles. Further experiments proved that the optical absorption spectrum of the composite particles was extended to the visible region. Furthermore, the formation of CdS/TiO₂ core–shell nanocomposites was confirmed by different characterization techniques including XRD, TEM, EDAX, UV-vis, FTIR and DLS.

In this study, an ultrasonic method was utilized in combination with microemulsion to synthesize CdS/TiO₂ core–shell nanoparticles and control their particle size and ultimately optimize the influential parameters.     

Photocatalytic hydrogen production and storage in carbon nanotubes: a first-principles study

As it is a promising clean energy source, the production and storage of hydrogen are crucial techniques. Here, based on first-principles calculations, we proposed an integral strategy for the production and storage of hydrogen in carbon nanotubes via photocatalytic processes. We considered a core–shell structure formed by placing a carbon nitride nanowire inside a carbon nanotube to achieve this goal. Photo-generated holes on the carbon nanotube surface promote water splitting. Driven by intrinsic electrostatic field in the core–shell structures, protons produced by water splitting penetrate the carbon nanotube and react with photo-generated electrons on the carbon nitride nanowire to produce hydrogen molecules in the carbon nanotube. Because carbon nanotubes have high hydrogen storage capacity, this core–shell structure can serve as a candidate system for photocatalytic water splitting and safe hydrogen storage.

The production and storage of hydrogen in CNNW/CNT core–shell structures via photocatalytic processes.     

RAFT polymerization mediated core–shell supramolecular assembly of PEGMA-co-stearic acid block co-polymer for efficient anticancer drug delivery

In this work, core–shell supramolecular assembly polymeric nano-architectures containing hydrophilic and hydrophobic segments were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. Herein, polyethylene glycol methyl ether methacrylate (PEGMA), and stearic acid were used to synthesize the poly(PEGMA) homopolymer and stearyl ethyl methacrylate (SEMA), respectively. Then, PEGMA and SEMA were polymerized through controlled RAFT polymerization to obtain the final diblock copolymer, poly(PEGMA-co-SEMA) (BCP). Model anticancer drug, doxorubicin (DOX) was loaded on BCPs. Interestingly, efficient DOX release was observed at acidic pH, similar to the cancerous environment pH level. Significant cellular uptake of DOX loaded BCP50 (BCP50-DOX) was observed in MDA-MB-231 triple negative breast cancer cells and resulted in a 35 fold increase in anticancer activity against MDA MB-231 cells compared to free DOX. Scanning electron microscopy (SEM) imaging confirmed the apoptosis mediated cellular death. These core–shell supramolecular assembly polymeric nano-architectures may be an efficient anti-cancer drug delivery system in the future.

In this work, core–shell supramolecular assembly polymeric nano-architectures containing hydrophilic and hydrophobic segments were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization.     

Understanding metal-enhanced fluorescence and structural properties in Au@Ag core–shell nanocubes

Au@Ag core–shell structures have received particular interest due to their localized surface plasmon resonance properties and great potential as oxygen reduction reaction catalysts and building blocks for self-assembly. In this study, Au@Ag core–shell nanocubes (Au@AgNCs) were fabricated in a facile manner via stepwise Ag reduction on Au nanoparticles (AuNPs). The size of the Au@AgNCs and their optical properties can be simply modulated by changing the Ag shell thickness. Structural characterization has been carried out by TEM, SAED, and XRD. The metal-induced fluorescence properties of probe molecules near the Au@AgNCs were measured during sedimentation of the Au@AgNCs. The unique ring-like building block of Au@AgNCs has dual optical functions as a fluorescence quencher or fluorescence enhancement medium depending on the assembled regions.

The unique ring-like building block of Au@AgNCs has dual optical functions as a fluorescence quencher and fluorescence enhancement medium.     

Synthesis of core–shell Ce-modified mixed metal oxides derived from P123-templated layered double hydroxides

Layered double hydroxides are a promising platform material which can be combined with a variety of active species based on their characteristic features. Silicon@P123-templated Ce-doped layered double hydroxide (SiO₂@CeMgAl-LDH(P123)) composites were synthesized via a facile in situ co-precipitation method, and characterized by TEM, X-ray diffraction, FTIR, XPS, CO₂-, etc. in detail. Meanwhile, the calcined powder (SiO₂@CeMgAl-LDO(P123)) possessed an excellent core–shell structure and a high surface area inherited from the LDH structure, which led to an outstanding catalytic activity (99.7% conversion of propylene oxide, 92.4% selectivity of propylene glycol methyl ether) under mild reaction conditions (120 °C). Cerium oxide provides a large number of oxygen vacancies and significantly improves the medium basic strength of the material, which facilitates the selective ring-opening of PO. Furthermore, the introduction and removal of P123 make the cerium oxide uniformly dispersed on the LDH layers, providing more reaction sites for the reaction of methanol and propylene oxide. The core–shell structure prepared by the in situ co-precipitation method could solve the shortcomings of agglomeration of layered double hydroxides and prolong the catalytic life evidently.

A shell of P123-templated CeMgAl-LDO was distributed in transverse and longitudinal directions on spheres of SiO₂. The composites displayed high catalytic activity in the synthesis of propylene glycol methyl ether.     

Eco-friendly synthesis of CuInS2 and CuInS2@ZnS quantum dots and their effect on enzyme activity of lysozyme

We report on the green and facile aqueous microwave synthesis of glutathione (GSH) stabilized luminescent CuInS₂ (CIS, size = 2.9 nm) and CuInS₂@ZnS core–shell (CIS@ZnS, size = 3.5 nm) quantum dots (QDs). The core–shell nanostructures exhibited excellent photo- and water/buffer stability, a long photoluminescence (PL) lifetime (463 ns) and high PL quantum yield (PLQY = 26%). We have evaluated the comparative enzyme kinetics of these hydrophilic QDs by interacting them with the model enzyme lysozyme, which was probed by static and synchronous fluorescence spectroscopy. The quantification of the QD–lysozyme binding isotherm, exchange rate, and critical flocculation concentration was carried out. The core–shell QDs exhibited higher binding with lysozyme yielding a binding constant of K = 5.04 × 10⁹ L mol⁻¹ compared to the core-only structures (K = 6.16 × 10⁷ L mol⁻¹), and the main cause of binding was identified as being due to hydrophobic forces. In addition to the enzyme activity being dose dependent, it was also found that core–shell structures caused an enhancement in activity. Since binary QDs like CdSe also show a change in the lysozyme enzyme activity, therefore, a clear differential between binary and ternary QDs was required to be established which clearly revealed the relevance of surface chemistry on the QD–lysozyme interaction.

Eco-friendly synthesis of CIS and CIS@ZnS quantum dots was carried out, and their interaction with lysozyme revealed spontaneous and hydrophobic binding. Lysozyme helicity and enzymatic activity increased upon complexation.     

Counterion coupled (COCO) gemini surfactant capped Ag/Au alloy and Ag@Au core–shell nanoparticles for cancer therapy

Hybrid silver (Ag)–gold (Au) nanoparticles (NPs) with different sizes and compositions were synthesized. Ag/Au alloy and Ag@Au core–shell type NPs were prepared from Ag and Au with various ratios using the COCO gemini surfactant, 1,6-bis (N,N-hexadecyldimethylammonium) adipate (COCOGS), 16-6-16 as a stabilizer. The formation of the Ag/Au alloy and Ag@Au core–shell was confirmed by UV-visible absorption spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX) and selected area electron diffraction (SAED) patterns. Depending on the composition of the Ag/Au alloy NPs, the λ_max values varied from 408 nm to 525 nm. FTIR measurements were used to evaluate the adsorption of the COCO gemini surfactant (16-6-16) on the Ag/Au alloy and Ag@Au core–shell surface. In this present work, we study how to achieve the stability and activity of the COCO gemini surfactant (16-6-16) capped Ag/Au alloy and Ag@Au core–shell NPs for developing novel anti-cancer agents by evaluating their potentials in the Hep-2 cell line model. Thus the developed core–shell NPs were possibly involved in inducing cytotoxicity followed by inhibition of cell proliferation to the cancer cells with apoptosis induction. The developed core–shell NPs might serve as highly applicable agents in the development of next-generation cancer chemotherapeutic agents.

In this work hybrid silver (Ag)–gold (Au) nanoparticles (NPs) with different sizes and compositions were synthesized and applied for anticancer evaluations and which is effectively involved in cancer cell apoptosis through DNA damage.     

Epitaxial growth of ultrathin layers on the surface of sub-10 nm nanoparticles: the case of β-NaGdF4:Yb/Er@NaDyF4 nanoparticles

Upconversion core–shell nanoparticles have attracted a large amount of attention due to their multifunctionality and specific applications. In this work, based on a NaGdF₄ sub-10 nm ultrasmall nanocore, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process. NaDyF₄ coated upconversion luminescent nanoparticles showed an obvious fluorescence quenching under excitation at 980 nm as a result of energy resonance transfer between Yb³⁺, Er³⁺ and Dy³⁺. NaGdF₄:Yb,Er@NaDyF₄ core–shell nanoparticles with ultrathin layer shells exhibited a better T₁-weighted MR contrast.

In this work, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process.     

Surface plasmon-driven photocatalytic activity of Ni@NiO/NiCO3 core–shell nanostructures

Ni@NiO/NiCO₃ core–shell nanostructures have been investigated for surface plasmon driven photocatalytic solar H₂ generation without any co-catalyst. Huge variation in the photocatalytic activity has been observed in the pristine vs. post-vacuum annealed samples with the maximum H₂ yield (∼110 μmol g⁻¹ h⁻¹) for the vacuum annealed sample (N70-100/2 h) compared to ∼92 μmol g⁻¹ h⁻¹ for the pristine (N70) photocatalyst. Thorough structural (X-ray diffraction) and spectroscopic (X-ray photoelectron spectroscopy and transmission electron microscopy coupled electron energy loss spectroscopy) investigations reveal the core Ni nanoparticle decorated with the shell, a composite of crystalline NiO and amorphous NiCO₃. Significant visible light absorption at ∼475 nm in the UV-vis region along with the absence of a peak/edge corresponding to NiO suggest the role of surface plasmons in the observed catalytic activity. As per the proposed mechanism, amorphous NiCO₃ in the shell has been suggested to serve as the dielectric medium/interface, which enhances the surface plasmon resonance and boosts the HER activity.

Surface plasmonic resonance enabled Ni@NiO/NiCO₃ core–shell nanostructures as promising photocatalysts for hydrogen evolution under visible light.     

Synthesis of hollow core–shell ZnFe2O4@C nanospheres with excellent microwave absorption properties

The special hollow core–shell structure and excellent dielectric-magnetic loss synergy of composite materials are two crucial factors that have an important influence on the microwave absorption properties. In this study, hollow ZnFe₂O₄ nanospheres were successfully synthesized by a solvothermal precipitation method firstly; based on this, a C shell precursor phenolic resin was coated on the ZnFe₂O₄ hollow nanospheres'' surface by an in situ oxidative polymerization method, and then ZnFe₂O₄@C was obtained by high-temperature calcination. Samples were characterized by SEM, TEM, XRD, XPS, BET, VSM, VNA. The results show that the maximum reflection loss (RL_max) reaches −50.97 dB at 8.0 GHz, and the effective bandwidth (EAB) of hollow core–shell structure ZnFe₂O₄@C is 3.2 GHz (6.16–9.36 GHz) with a coating thickness of 3.5 mm. This work provides a useful method for the design of lightweight and high-efficiency microwave absorbers.

The hollow core–shell structure ZnFe₂O₄@C in this work has excellent EM absorption performance.     

Elevated electrochemical performances enabled by a core–shell titanium hydride coated separator in lithium–sulphur batteries

To date, the lithium–sulphur battery is still suffering from fast capacity fade and poor rate performance due to its special electrochemical mechanism. The interlayer or separator with conductive coatings is considered effective in inhibiting the shuttle effect. Here, we proposed a novel metal hydride with high conductivity and preferably chose TiH₂ as the conductive coating because of its low cost, high conductivity, and good stability in air. The TiH₂ powder was prepared by a simple ball-milling method, and the effect of the atmosphere was also investigated. A core–shell heterostructure formed, in which the TiH₂ core acted as an electron transfer pathway, and the titanium oxide nano-shell functioned as the absorber for polysulfides. Thus, with the combination of fast electronic transfer and strong absorption ability, the TiH₂ coated separator could improve the cycling stability, the rate performances, and the self-discharge rate. The TiH₂ separator could increase the capacity of the lower plateau and delay the oversaturation points at high rates, promoting the liquid–solid conversion. It is believed that the promotion resulted from the high conductivity and polysulfide absorption of the TiH₂ separator. Although the preparation process still needs further optimization, the core–shell metal hydride provided a novel strategy for designing the heterostructure, which could provide high conductivity and strong absorption ability toward polysulfides simultaneously.

A TiO_2−x@TiH₂ core–shell microstructure formed spontaneously, in which the TiH₂ core acts as an electron transfer pathway and the shell functioned as the polysulfide absorber.