Core-shell Structured Nanocomposites Research Articles

Size effect of nanomagnetite on magnetoresistance of core-shell structured polyaniline nanocomposites

Size effect of nanomagnetite on magnetoresistance of core-shell structured polyaniline nanocomposites

An investigation of temperature and frequency-dependent dielectric response of paramagnetic Co3O4@SiO2 core–shell-structured nanocomposites

An investigation of temperature and frequency-dependent dielectric response of paramagnetic Co3O4@SiO2 core–shell-structured nanocomposites

Enhanced microwave absorption performances of onion-like carbon coated FeNiCoCuTi high-entropy alloys nanocapsules

High entropy alloys (HEAs), a new type of functional material, are rarely applied to prepare core-shell structured nanocomposites. In this work, FeCoNiCuTi@C nanocapsules have been prepared by arc discharging HEAs ingot under the atmosphere of methane, displaying the sphere shape with the average diameter of 72.1 nm and ~ 3 nm onion-like carbon shell and the single FCC phase. The melting points, crystal structure and electronegativity play the important role on determining the element composition and atomic percentage. Carbon facilitates protecting magnetic elements, improving EM parameters and enhancing resonance frequency. Good impedance matching, strong electromagnetic loss ability and large attenuation constant ensure the microwave can enter the nanocapsules to the largest extent and could be consumed. These advantages provide the basis for the excellent microwave absorption performance ( effective bandwidth of 5.52 GHz at 1.9 mm, maximal reflection loss of −37.78 dB and absorption efficiency of 52.41 dB·GHz/mm at 1.8 mm) of FeCoNiCuTi@C nanocapsules. • FeNiCoCuTi high-entropy alloys nanocapsules with onion-like carbon are prepared. • Core/shell structure leads to good impedance matching, strong attenuation and loss. • Effective bandwidth is 5.52 GHz at 1.9 mm and absorbing efficiency is 52.4 dB GHz/mm.

Core-shell structured nanocomposites formed by silicon coated carbon nanotubes with anti-oxidation and electromagnetic wave absorption

The silicon coated Carbon nanotubes (CNTs) nanocomposite (CNTs@Si) with a shell structure was successfully synthesized by a simple chemical vapor deposition (CVD) method. In this work, the CNTs@Si is not only introduced as a structural material providing oxidation performance, but also as an extremely effective electromagnetic wave (EMW) absorption nanocomposite. Dielectric characteristics EMW absorption properties within the frequency range of 2–18 GHz of CNTs@Si were studied, and the oxidation resistance of CNTs@Si was characterized. Due to the dense space conductive network formed by CNTs, the EMW absorbing properties of CNTs@Si nanocomposite features excellent electromagnetic wave absorption capacity at a filling amount of 1%. The maximum reflection loss (RL) reaches −61.57 dB at the thickness of 1.8 mm, and a wide effective absorption bandwidth (EAB, RL < −10 dB) of 2.88 GHz is achieved. The obtained CNTs@Si core-shell nanocomposites exhibit excellent antioxidant performance and absorbing performance due to silicon bridging. Efficient electromagnetic wave absorption and excellent oxidation resistance of CNTs@Si can be regarded as a brand-new competitive candidate for EMW absorption materials in harsh environment.

Decoupling of inter-particle polarization and intra-particle polarization in core-shell structured nanocomposites towards improved dielectric performance

Conductive-filler filled polymer composites have exhibited great potential due to the high dielectric constant that can be reached near the percolation threshold, yet the associated high dielectric loss prohibits wide use in practice. Recently, extensive efforts have been devoted to encapsulating conductive fillers with an insulating shell, with the aim to constrain the dielectric loss; but such efforts also significantly reduce dielectric constant. This dilemma raises the question of whether core-shell structured fillers are ultimately beneficial for the dielectric performance of composites, which is less explored. In this study, we investigate polymer nanocomposites containing a series of Al@Al2O3 nanofillers with different shell thicknesses. It shows that the high dielectric constant of percolative composites is contributed by a fast intra-particle polarization and a slow inter-particle polarization. Formation of an insulating shell enables the independent control of the two polarizations, which are otherwise coupled (increasing or decreasing together) in regular percolative composites. By promoting intra-particle polarization and suppressing inter-particle polarization, the core-shell structured nanocomposites can obtain a high dielectric constant and concurrently low dielectric loss, far surpassing the unmodified nanofiller composites. Moreover, the thermal conductivity and high field resistivity are also improved, resulting in a stable and low temperature during operation. This work offers a new paradigm for the design of percolative polymer composite with high dielectric constant and low dielectric loss as well as improved thermomechanical properties.

Stable and efficient hybrid Ag-In-S/ZnS@SiO2-carbon quantum dots nanocomposites for white light-emitting diodes

• Overcome the aggregation-induced quenching effect of CDs in solid state. • A novel white light-emitting nanocomposite with a core–shell structure has been synthesized. • A UV-pumped WLED with a CRI up to 91 has been fabricated with the nanocomposite. • Controllable blue/yellow PL intensity ratios of the prepared nanocomposite. As a promising energy-saving technique, the eco-friendly and low-cost solid-state white light-emitting diodes (WLEDs) based on quantum dots (QDs) have been widely studied. Herein, a WLED device prepared by core–shell structure nanocomposites based on Ag-In-S/ZnS@SiO 2 quantum dots (AIS@SiO 2 ) and carbon quantum dots (CDs) was successfully constructed. CDs were combined onto the surface of AIS@SiO 2 QDs to synthesize Ag-In-S/ZnS@SiO 2 -Carbon quantum dots (AIS-CDs) nanocomposites with a white-light emission, which successfully overcome the quenching effect of CDs induced by conventional aggregation. The as-prepared AIS-CDs nanocomposites presented high stability and a photoluminescence quantum yield (PLQY) of 35%. Moreover, the corresponding AIS-CDs nanocomposites-based WLEDs demonstrated the color coordinate of (0.32, 0.33), which is comparable to the pure white light (0.33, 0.33); furthermore, the luminous efficiency of the as-prepared WLEDs showed 15.1 lm W −1 . These results reported herein may open up a new avenue for the development of high-performance, low-cost, and environmentally-friendly WLEDs.

Controlled synthesis and luminescence properties of core-shell-shell structured SiO2@AIPA-S-Si-Eu@SiO2 and SiO2@AIPA-S-Si-Eu-phen@SiO2 nanocomposites

Two novel core-shell structured SiO2@AIPA-S-Si-Eu and SiO2@AIPA-S-Si-Eu-phen nanocomposites have been synthesized by a bifunctional organic ligands ((HOOC)2C6H3NHCONH(CH2)3Si(OCH2CH3)3) (defined as AIPA-S-Si) connected with Eu3+ ions and silica via covalent bond. And the corresponding core-shell-shell structured SiO2@AIPA-S-Si-Eu@SiO2 and SiO2@AIPA-S-Si-Eu-phen@SiO2 nanocomposites with enhanced luminescence have been synthesized by tetraethyl orthosilicate (TEOS) hydrolysis co-deposition method. The composition and micromorphology of the nanocomposites were characterized by means of Fourier-transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS). The as-synthesized core-shell and core-shell-shell structured nanocomposites have excellent luminescence intensity and long lifetime. The nanocomposites show bright red light under ultraviolet lamp. However, the core-shell-shell structured nanocomposites have stronger luminescence intensity than the corresponding core-shell structured nanocomposites. Meanwhile, the core-shell-shell structured nanocomposites still exhibit good luminescence stability in aqueous solution. In addition, a large number of Si-OH on the surface of the core-shell-shell structured nanocomposites can be attached to many biomacromolecules. Therefore, they have potential applications in the fields of biology and luminescence.

Preparation of Zn0.5Cd0.5S@Ni-Glycerate composite for photocatalytic water reduction

Large specific surface is beneficial to improve the performance of catalyst in the application of water photolysis. In this work, we designed and successfully prepared the metal compound Ni-Glycerate with a large specific surface area, and combined it with Zn0.5Cd0.5S to form Zn0.5Cd0.5S@Ni-Glycerate core-shell structure nanocomposites. It was revealed that the introduction of nickel-glycerate can promote the separation of photoinduced charges and accelerate the photocatalytic water decomposition reaction. The optimized H2 production rate on Zn0.5Cd0.5S@Nickel-glycerate (3%) can reach 2800 μmol/h/0.1 g, about 6 times that of pure Zn0.5Cd0.5S. This work indicates that the sulfide-metal organic complex can play a synergistic role in the entire photocatalytic reaction.

Ultrafast synthesis of graphene nanosheets encapsulated Si nanoparticles via deflagration of energetic materials for lithium-ion batteries

Encapsulating silicon particles in conductive layers has proven to be an effective route to retain the high capacity of silicon during cycling. Here, through a core-shell structural design of silicon-polytetrafluoroethylene (PTFE) energetic materials, we demonstrate a large-scale top-down approach for directly obtaining graphene nanosheets encapsulated Si nanoparticles (GrSiNPs) using micrometer-sized PTFE and Si particles as low-cost starting materials. Upon deflagration, high temperature and high pressure of the exothermic reaction between PTFE and Si lead to the fragmentation of the Si core into nanoscale particles, during which the concomitant coating of the Si nanoparticles with graphene nanosheets is achieved. Repeated cycling at a current density of 400 mA g−1 for 6 months, the GrSiNPs demonstrate a high specific capacity of 1613 mAh g−1 after 800 cycles and the average Coulombic efficiency is 101 ± 2%. Our study provides a promising route to the mass production of core-shell structured graphene-Si nanocomposites for high-performance lithium-ion batteries.

Comparative Study on Photodynamic Activation of Ortho-Toluidine Blue and Methylene Blue Loaded Mesoporous Silica Nanoparticles Against Resistant Microorganisms

The number of pathogenic microorganisms has been increasing over the years, and so as resistance of these microorganisms are developing against various antibiotics. Antimicrobial photodynamic therapy (aPDT), also called photodynamic inactivation, is emerging as a promising alternative to treatments based on conventional antibiotics. Recent patents on structured silver mesoporous silica nanoparticles having antimicrobial activity (WO2010/071831 A2), photosensitiser modified core-shell structure nanocomposites (CN 103536935(A)), and Chitosan-coated magnetic mesoporous silica nanoparticles (MSN) (CN 104785214(A)) helped in selecting method of synthesis of MSN and photosensitizers. MSN were synthesised by Sol-Gel method and amino functionalised (APTES). Methylene blue (MB) and ortho-toluidine blue (O-TB) were used as photosensitisers. Different batches were synthesised. The final product was characterised by using FTIR, BET, SEM, time resolved fluorescence. The photosensitiser loaded MSN were illuminated by LED based lamp emitting red light at 620± 20nm for different time lengths viz 15 min and 30 mins. Fluorescence studies and antimicrobial assays were carried out as per 72 well plate method I.P, 2014 using, gram negative E. coli (ATCC no. 8739), S. aureus (ATCC no. 7447) and gram positive P. aeruginosa (ATCC no. 9027) pathogenic microorganisms. MB and O-TB were successfully adsorbed on APTES functionalised MSN. Different exposure time length of the photosensitisers to red light showed different zone of inhibition. MB and O-TB loaded MSN showed significant increase in zone of inhibition after irradiation as compared to MB and O-TB loaded on MSN without exposure to light. MB and O-TB adsorbed on APTES functionalized mesoporous silica nanoparticles were capable of efficiently inactivating E. coli, P. aeruginosa, S. aureus bacteria upon exposure to red light (620± 20nm wavelength) at a much lower concentration. Mesoporous silica nanoparticles played an important role in aPDT due to their high surface area and porous structure. Also, APTES functionalization resulted in the pore expansion of MSN, thereby increasing the loading capacity of the photosensitizer on MSN. From the results obtained it can be concluded that O-TB loaded MSN showed higher activity against gram negative and positive microorganisms microorganism as compared to that of MB.

Au nanoparticles attached Ag@C core-shell nanocomposites for highly selective electrochemical detection of dopamine

Herein, a simple electrochemical sensor for dopamine (DA) detection was developed based on Ag@C core-shell structure and Au nanocomposites (Ag@C/Au). The Ag@C core-shell nanoparticles were synthesized by one-pot hydrothermal method, which were supported on Au nanoparticles in situ reduction process. The as-prepared nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and UV–vis absorption spectra. The electrochemical investigations indicated that Ag@C/Au nanocomposites possessed intriguing properties towards DA. These results could be attributed to the synergistic effect of Ag@C with enhanced substrate accessibility and conductivity, Au nanoparticles with surface of negative charges. Under the optimum experimental conditions, the liner range was 0.5 μM to 27.5 μM, 27.5 μM to 0.2775 mM and 0.2775 mM to 4.278 mM. The detection limit was 0.21 μM (S/N = 3). Furthermore, the electrochemical sensor showed favorable selectivity in the presence of interferents such as ascorbic acid (AA) and uric acid (UA). In general, the work could provide a promising possibility to develop excellent electrochemical sensors for DA detection.

Synthesis of BaTiO3@TiO2-sheet Core-Shell Structured Nanocomposites

Core-shell structure nanocomposites have been of interest, as they can exhibit unique properties arising from the combination of peculiar characteristics of each component. In this research, core-shell structured nanocomposites, comprising barium titanate (BaTiO3; BT) nanoparticles as the core and titanate (TiO2) nanosheets as the shell, were prepared. The surface of barium titanate (BT) nanoparticles was modified chemically by hydrogen peroxide (H2O2) to create hydroxyl groups. TiO2 nanosheets were deposited on the surface of the functionalized BT core, via alternate adsorption with oppositely charged polyelectrolyte poly(diallyl dimethylammonium) (PDDA) cations to produce an ultrathin TiO2 shell layer that encapsulates BaTiO3 nanoparticles. The structure of the core-shell particles was investigated in order to illustrate their formation mechanisms. Furthermore, this work reported the advance in utilizing a core-shell nanostructure to enhance relative permittivity and maintaining a low loss of polymer nanocomposites. A significant improvement in relative permittivity is attributed to the TiO2 shell, which acts as polarizable dipoles and consequently enhances interfacial polarization. The results indicated that the structure of core-shell nanocomposites is attractive as a novel structural building block for fabricating novel materials and electronic devices.

EMI shielding properties of laminated graphene and PbTiO3 reinforced poly(3,4-ethylenedioxythiophene) nanocomposites

In this paper, PEDOT/reduced graphene oxide (RGO)/PbTiO3 nanocomposites have been synthesized using facile insitu chemical oxidative polymerization method. The synthesis method leads to the formation of core-shell structured nanocomposites containing PbTiO3 as primary filler and RGO as secondary filler in PEDOT matrix. The core-shell morphology of the composites has been confirmed using transmission electron microscope with average particle size 20–30 nm observed for PbTiO3. The incorporation of RGO and PbTiO3 in the PEDOT matrix has been confirmed by X-ray diffraction. A systematic study on electromagnetic shielding properties and the effect of PbTiO3 concentration on different properties has been carried out. The ferro-electric PbTiO3 with RGO induced dielectric loss in the composites, whereas, PEDOT establish a conducting network over RGO layer and PbTiO3 nanoparticles that improve electromagnetic shielding properties by increasing the dielectric loss. As a result, an enhanced electromagnetic shielding effectiveness value of 51.94 dB (>99.999% attenuation) has been achieved in 12.4–18 GHz frequency range. The nanocomposites were further characterized using Fourier transmission infrared spectroscopy and thermal gravimetric analysis.

Progress on microwave absorption materials with core-shell structure

Microwave absorber is a kind of functional material, which can absorb electromagnetic (EM) wave effectively and then convert EM energy into thermal energy or make EM wave dissipate by interference. The researches of microwave absorbers are important to satisfy the need of electromagnetic interference in daily life and industrial production, also meet the application requirements of stealth technology in military. Nowadays, the rapid increase in the use of telecommunications equipment, digital systems, and fast processors result in the increasing demand for the development of novel high-efficient microwave absorbers with light weight, thin thickness, wide absorption frequency, and strong absorption characteristics. The structures of microwave absorber are found closely related to the absorption properties. In recent years, many research institutions including our research group, found that the core-shell structure has good absorption performance. The core-shell structured nanocomposites, which combined functionalities of cores and shells, show great potential for significant effect on broadening the absorption spectrum and increasing the absorption intensity because of the complex impedance material matching, interface polarization and multi structure interface scattering. For example, the combination of magnetic materials (e.g., Fe3O4, Co, Ni) and dielectric materials (e.g., TiO2, SnO2, carbon nanotubes) in one entity may take advantages of both the magnetic and dielectric materials, which then can be used as high-performance microwave absorbers. It is well known that Fe3O4, which have been widely used as microwave absorbers because of low cost and strong absorption characteristics usually suffer from ease of oxidation at high-tempera- ture and relatively narrow absorption frequency bandwidth at applied frequency range. While, the magnetic nanoparticles encapsulated within carbon-nanotube composites and Fe3O4/TiO2 core/shell nanotubes were found with lower reflection loss and wider absorption frequency range than single-component absorbers. Meanwhile, remarkable progress has been made in the study of the absorbing mechanism of core-shell structure absorbing materials, which is a great contribution to the design of new structures to meet the new demands of absorbing materials. For example, the particle shapes and grain sizes of magnetic absorbents are of importance for high performance microwave absorbing materials, which are well known. However, research into the relationships among microstructure, electromagnetic property, and microwave absorption performance is rarely reported, especially from the influence of microcosmic magnetism distribution on microwave absorption performance is still lacking previously. While, based on the micro-magnetic investigation via electron holography and Lorentz microscopy, the micromagnetic analysis of the absorber provides a series of direct evidences regarding the effect of grain size on the microcosmic magnetic property, which was important for the further comprehension of the microwave absorption mechanism and new insight into the microstructure design strategy. Other researches, which focus on the influence of cores or shells to absorption performance, are also meaningful to absorption mechanism explanation. The development of science and technology has never stopped the demand for high performance microwave absorbing materials. It is still a difficult but meaningful task for absorbers practical applications to design microwave absorption materials with minimal coating thickness, even light weight, ultra-wide bandwidth, stronger absorption and higher heat-resistance characteristics

Construction of magnetic-targeted and NIR irradiation-controlled drug delivery platform with Fe3O4@Au@SiO2 nanospheres

Near-infrared (NIR) light has great potential in biomedical applications due to its advantages of deep penetration depth and low photodamage to biological tissues. In this paper, we constructed a novel core-shell structured drug nanocarrier, Fe3O4@Au@SiO2, for the controlled delivery of etoposide (VP16), a chemotherapeutic drug for cancer patients. The novel core-shell structured drug delivery platform is composed of a mesoporous silica shell and a magnetic Fe3O4 core using Au nanoparticles (AuNPs) as the interlayer, which is characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, N2 adsorption/desorption isotherms and the magnetic measurements with vibrating-sample magnetometer (VSM). The synergistic effects of AuNPs, mesoporous silica and Fe3O4 make the core-shell structured nanocomposites an excellent candidate for targeted and NIR light irradiation-controlled drug delivery. For the proposed nanocarrier of VP16, the mesopores in silica can enhance the encapsulation capacity of the nanocarrier and the AuNPs can effectively convert the NIR light into heat to speed up the drug deliver; meanwhile, the incorporation of Fe3O4 with high magnetization to the drug delivery platform realize drug targeting under an applied external magnetic field.

Oxygen vacancies induced self-assembling synthesis of V4+-BiVO4/rGO core-shell nanorods with enhanced water splitting efficiency and superior sewage purification capability

Graphene sheets fully wrapped core-shell structured nanocomposites are receiving increasingly more attention in photocatalysis owing to their amazing charge carriers transporting characteristics. However, the preparation of this interesting and valuable architecture remains a big challenge. Herein, we successfully prepared high-quality V4+-BiVO4/rGO core-shell structured composite nanorods using a facile solution-processed method. Positively charged oxygen vacancies on V4+ self-doped BiVO4 nanorods play a key role in rGO wrapping because they can strongly attract and finally anchor COO anions on them, which finally enables the self-assembling formation of V4+-BVO/rGO core-shell nanocomposite. The optimal photocatalytic O2 evolution rate can reach up to 119.5umolh−1 after wrapping rGO, which is 1.36 times higher than that of bare V4+-BiVO4. Significantly, when treating natural waste water from Huangpu River, 2wt.% V4+-BiVO4/rGO is capable of eliminating 92.6% of TOC and 84.6% of TN under visible light irradiation within 8h indicating its huge practical value. The enhanced photoactivities of V4+-BiVO4/rGO are primarily owing to the fact that rGO shell around the composite nanorods can provide a fast channel for photogenerated electrons migrating and subsequently facilitate e−/h+ separation efficiency. This work provides deep insights into the forming mechanism and properties of high-quality V4+-BiVO4/rGO core-shell structure, and will facilitate the design of other rGO fully wrapped nanocomposites.

Ultrasonic-induced nanocomposites with anatase@amorphous TiO2 core–shell structure and their photocatalytic activity

Anatase@amorphous TiO2 core–shell structure nanocomposites were obtained through ultrasonic irradiation on hydrothermally synthesized anatase nanocrystals. The optimized research of the phase proportion revealed the effects of disorder phase.

Facile synthesis of CdS@TiO2 core–shell nanorods with controllable shell thickness and enhanced photocatalytic activity under visible light irradiation

Amorphous TiO2 layers with a controllable thickness from 3.5 to 40nm were coated on the one-dimensional CdS nanorods surface under mild conditions. Compared to the bare CdS nanorods, the as-prepared CdS@TiO2 nanorods exhibit enhanced photocatalytic activities for phenol photodecomposition under visible light irradiation. The improved photoactivity is ascribed to the efficient separation of photogenerated electron and hole charge carriers between CdS cores and TiO2 shells. This study promises a simple approach to fabricating CdS@TiO2 core–shell structure nanocomposites, and can be applied for other semiconductor cores with TiO2 shells.

Preparation and characterization of ZnSe/CdSe core-shell microspheres

The preparation of ZnSe/CdSe core-shell structure nanocomposites by using the re-prepared ZnSe microspheres as the template under the hydrothermal condition was presented. The influence of different mole ratios of ZnSe to Cd(NO3)2 on the morphology and structure of the final product was investigated. And the performances of ZnSe/CdSe core-shell structure nanocomposites were characterized by the means of X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The results indicate that the core-shell structure product can be prepared, when the mole ratio of ZnSe to Cd(NO3)2 is larger than 1:1; and the product will be ball solid structure, when the mole ratio of ZnSe to Cd(NO3)2 is equal to 1:1. The photo luminescence results show that ZnSe/CdSe core-shell structures have high photo luminescence emission properties, and the product with mole ratio of ZnSe to Cd(NO3)2 being 1:0.5 has the best luminescence properties.

Synthesis and Microwave Absorption Properties of Core-Shell Structured Co3O4-PANI Nanocomposites

The core-shell structured Co3O4-PANI nanocomposites have been successfully prepared using an in situ polymerization method, while the core Co3O4 nanoparticles were synthesized by carbon-assisted method using degreasing cotton as a template. The obtained samples were characterized by XRD, TEM, FTIR, and XPS. The results indicated that the amorphous PANI was well covered on the surface of the spinel Co3O4 and the Co3O4-PANI with core-shell structure was formed with particle size of about 100 nm. The interfacial interaction of the core-shell nanocomposite greatly enhances the microwave absorption properties. The maximum reflection loss of Co3O4-PANI is up to −45.8 dB at 11.7 GHz with a thickness of 2.5 mm and the adsorption bandwidth with the reflection loss below −10 dB reaches 14.1 GHz ranging from 3.9 to 18 GHz when the thickness is between 2 and 5.5 mm. Therefore, the facilely synthesized and low-cost Co3O4-PANI nanocomposite with superior microwave absorption properties can be a promising nanomaterial for high efficient microwave absorption.