Shell Composites Research Articles

Activated carbons from coconut shell and NiO-based composites for energy storage systems

Activated carbons (ACs) are obtained from coconut shell (endocarp) through chemical activation using H3PO4 as activating agent. Ground coconut shell is impregnated with H3PO4 for 24 and 48 h; then pyrolyzed at 600 and 800 °C. Some ACs are additionally mixed with nickel oxide (NiO) for obtaining NiO/AC composites. The morphological characteristics are studied by scanning electron microscopy (SEM) and high-resolution transmission electron microscope (HRTEM). The chemical composition is analyzed by X-ray diffraction (XRD), infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). With both types of samples, ACs and NiO/AC, electrodes are processed as pellets. Electrochemical characterization of the electrodes is carried out in a three-electrode configuration, in which an aqueous 1 M KOH solution is the electrolyte. Two charge storage mechanisms are found: (i) supercapacitor response including double-layer capacitance and pseudocapacitance for the ACs and reaching specific capacitances up to 142 F g−1 at 6 mA g−1 and (ii) battery response, due to reversible redox reactions of NiO and reaching specific capacities up to 19 C g−1 at 7 mA g−1. The relative contribution of the AC and NiO components to the composites' specific capacity is also discussed. The specific energy and specific power are compared for the two types of samples, AC and NiO/AC.

Mechanical, dynamic and tribological characterization of HDPE/peanut shell composites

Polymer composites reinforced with natural fibres are more appealing than conventional materials due to their accessibility, renewability, low weight and price, low density, and biodegradability. There are a wide variety of different natural fibres, such as nutshells, flax, and palm, which can be applied as reinforcements or fillers, showing potential as replacements for inorganic fibres. Plastics are often somewhat economical when producing complex shapes, and the possibility of obtaining composite materials with reduced demoulding times, as no chemical reaction is required, makes them very interesting from an industrial point of view. Moreover, polymers are increasingly used for tribologically stressed components, whereby plastic components replace metallic bearings, gear wheels, or sliding elements. In this regard, this work's objective was to produce composites of high-density polyethylene (HDPE) with different proportions (2, 4, 6, 8. and 10 wt%) of peanut shell (PS) filler and evaluate the influence on the dynamic mechanical and tribological properties of the addition of different amounts of filler. The strain (%) increases with fibre contents of 2 and 4 wt%, but at higher fibre contents, a considerable reduction, approximately 4 times for a fibre content of 6 wt% and an even more substantial reduction for fibre contents of 8 wt% and 10 wt%, could be observed. From the Dynamic Mechanical Analysis (DMA) tests, it could be observed that E' is practically constant for composites for all fibre contents between −20 °C and ~50 °C at 1.5 Hz and 10 Hz, which is ~6 times higher than that of neat HDPE under the same conditions. The tribological assays were carried out by the reciprocating sliding wear test with loads of 10, 20, and 30 N. Although the wear rate (k) and wear volume (V) increased with increasing applied load, these values were similar for fibres with different wt% contents. Thus, the addition of fibre does not modify the tribological properties of HDPE. By Raman spectrum analysis, similar intensities and positions of the bands of the HDPE vibrational mode before and after wear tests could be observed.

Succulent-like core–shell composite: Synthesis of CdS coated with an ultrathin layer of TiO2 and enhanced photocatalytic performance in the degradation of crystal violet and hydrogen production

A core–shell composite CdS-APS@TiO2 (APS = 3-aminopropyltriethoxysilane) has been prepared by a temperature-programmed hydrothermal method combined with a simple and convenient chemical bath deposition. The form of the product resembles that of a succulent plant. Electrostatic interaction between the water-stable TiO2 precursor with negative charge and the amino-functionalized petal-like surfaces of CdS is evident. The as-prepared composite adopts the aforementioned succulent morphology with a petal-like structure, surface-coated with TiO2. Moreover, compared with the CdS precursor, the specific surface area of the as-prepared CdS-APS@TiO2 composite is increased, and its optical absorption extends into the visible region. The CdS-APS@TiO2 composite shows high activity in multiple photocatalytic processes, and some activity in photocatalytic hydrogen production (149.2 μmol/g, 8 h). To assess its mode of action, trapping experiments have been carried out by adding various radical scavengers. Possible mechanisms for the photocatalytic degradation of dyes and the photocatalytic splitting of water over the CdS-APS@TiO2 composite are proposed.

Treatment of crude oil polluted water using stearic acid grafted mango seed shell (Mangifera indica) composite

This work focuses on the treatment of crude oil polluted water using indigenous adsorbent prepared using mango seed shell. Esterification of mango seed shell (MSS) as a novel composite with high surface area and well-ordered framework of porosity was prepared and kinetic and isotherm modelling of crude oil removal considered. Batch adsorption studies were carried out with the function of oil water ratio, pH and temperature. Material characterization was carried out to ascertain the nature of the composite prepared and its affinity to oil sorption. Surface morphology was investigated with scan electron microscope (SEM). Chemical composition of compounds was investigated using X-ray fluorescent machine while the X-ray diffraction machine (XRD) examined the crystallographic nature of the pretreated mango seed shell (MSS). Salt addition techniques was employed for point zero charge analysis at ionic strengths 0.05 and 0.1 ​mol/dm3. The influence of pH, temperature and oil/water ratio was found to be highly significant and strongly influences oil removal by the composite. SEM analysis showed several changes on the surface of the composite after acid treatment. XRF and XRD revealed that the raw MSS were highly composed of quartz. The point zero charge revealed that the surface of esterified MSS was predominately positive charge at pH ranging between 4.06±0.1 and 4.04±0.1. However, the composite exhibited high adsorption efficiency at a very low pH of 5 with 90.69% of crude oil removal. Isotherm modelling revealed that the composite material was highly matched to Temkin isotherm model with maximum adsorption capacity of 50.80 ​mg/g. The kinetic data fitted well with Bahattacharya-Venkobachor model. The regenerated biomass exhibited high performance and functionality and used successively in different adsorption activities. Therefore, esterified MSS composite is an efficient, economic viable and sustainable adsorbent materials suitable in remediation of crude oil polluted water.

Preparation of TiO2@Sn(Sb)O2 core–shell composites and their applications for electrocatalytic degradation of methylene blue

Preparation of TiO2@Sn(Sb)O2 core–shell composites and their applications for electrocatalytic degradation of methylene blue

Yolk–shell magnetic composite Fe3O4@Co/Zn-ZIF for MR imaging-guided chemotherapy of tumors in vivo

The yolk–shell composites Fe3O4@Co/Zn-ZIF exhibited high doxorubicin loading capacity, pH-responsive release characteristics, and strong T2-weighted MR imaging contrast enhancement, and were used for MR imaging-guided chemotherapy of tumors in vivo.

Vanadium-substituted heteropolyacids (H3+mPW12−mVmO40) encapsulated in Fe3O4@UiO-66 magnetic core–shell microspheres as excellent catalysts for oxidative desulfurization under oxygen

In this study, the novel magnetic core–shell composites Fe3O4@UiO-66-HPA, consisting of magnetic Fe3O4@UiO-66 and vanadium-substituted Keggin-type heteropolyacid active species supported by Zr-MOF, were preparedvia a one-pot method and fully characterized.

Preparation of Palm Oil Industry’s Biomass-Based Graphene Composite for the Adsorptive Removal of Methylene Blue

The ability of POME-based graphene shell composite (P-GSC), an adsorbent generated from oil palm wastes abundantly available in Malaysia such as POME and PKS, was examined in removing methylene blue (MB) dye by adsorption. Adsorption experiments, involving a batch column study and a batch equilibrium study, were conducted to investigate the efficiency of synthesized P-GSC from PKS as a base material in the removal of MB dye. The batch column study demonstrated that small-sized synthesized P-GSC from PKS as a base material could remove up to 98.5% for concentration. Therefore, the following batch equilibrium study was carried out on small-sized P-GSC only. Adsorption isotherms and kinetic isotherms were studied, from which the experimental data showed that the adsorption exhibited a good fit with the Freundlich model ([Formula: see text]) and followed the pseudo-second order model ([Formula: see text]). FESEM, XPS, and XRD morphological and elemental analysis indicated the successful graphinization of POME on the P-GSC surface. The concept of deploying POME as the carbonaceous source to produce P-GSC, and then, deploying the resultant P-GSC as the adsorbent for MB dye removal has presented promising practical potential. Such cost-effective and environmentally friendly reuse of waste materials is envisioned to promote a ‘zero-waste industry.’

Immobilizing Polysulfide by In Situ Topochemical Oxidation Derivative TiC@Carbon-Included TiO2 Core-Shell Sulfur Hosts for Advanced Lithium-Sulfur Batteries.

The performance of lithium-sulfur (Li-S) batteries is greatly hindered by the notorious shuttle effect of lithium polysulfides (LiPSs). To address this issue, in situ topochemical oxidation derivative TiC@carbon-included TiO2 (TiC@C-TiO2 ) core-shell composite is designed and proposed as a multifunctional sulfur host, which integrates the merits of conductive TiC core to facilitate the redox reaction kinetics of sulfur species, and porous C-TiO2 shell to suppress the dissolution and shuttling of LiPSs through chemisorption. A unique dual chemical mediation mechanism is demonstrated for the proposed TiC@C-TiO2 composite that synergistically entraps LiPSs through thiosulfate/polythionate conversion coupled with strong polar-polar interaction. The morphological characterization reveals that the TiC@C-TiO2 -based cathode can well regulate the distribution of electrode materials to retard their accumulation inside the electrode, ensuring effective contact between the active materials and electrolyte. Based on its unique function and structure, the cathode delivers an improved capacity of 1256 mAh g-1 at 0.2C, a remarkable rate capability of 643 mAh g-1 , and an ultralow capacity decay rate of 0.065% per cycle at 2C over 900 cycles. This work not only demonstrates a dual chemical mediation mechanism to immobilize LiPSs, but also provides a universal strategy to construct multifunctional sulfur hosts for advanced Li-S batteries.

NiMoO4@Ni3S2 core–shell composites grown in situ on nickel foam for applications in supercapacitors

A binder-free Ni3S2 nanosheets wrapped NiMoO4 nanorods hybrid electrode (NiMoO4@Ni3S2) was prepared on conductive Ni-foam via a simple two-step hydrothermal process. The microstructure and chemical composition of as-prepared NiMoO4@Ni3S2 core–shell hybrid electrode was confirmed by means of SEM, TEM, XRD, and XPS. The SEM analysis results demonstrated that the NiMoO4@Ni3S2 composites consisted of NiMoO4 nanorods in the core, which were surrounded by a myriad of Ni3S2 nanosheets in the shell. Electrochemical characterization revealed that the integrated structure of the NiMoO4@Ni3S2 electrode exhibited a high areal capacitance (2.3 F cm−2 at areal current density of 1 mA cm−2), which was 1.8 times than the NiMoO4 nanorods, excellent rate performance and outstanding cycling performance (84.4% retention at 30 mA cm−2 after 6000 cycles). An asymmetric capacitor assembled with NiMoO4@Ni3S2 core–shell composites and AC as the positive and negative electrodes, respectively, delivered a maximum area energy density of 158.4mWhcm−2 at an area power density of 2.199 W cm−2, and exceptional capacitance retention of 93.1% after 20k cycles. With such outstanding electrochemical performance, this NiMoO4@Ni3S2 electrode material will have a potential application value in the field of portable and flexible energy storage equipment.

Over All Water Splitting By Anti-Photocorrosive Core-Shell Composite Sulfide Photocatalyst Synthesized Via Acid Dissolution Process

Some of the most significant challenges of the 21st century are related to energy exhaustion and global warming. In order to overcome these issues, it is necessary to produce sustainable energy without carbon dioxide emissions. Since the discovery of the Honda-Fujishima effect (H2O + 2h ν → 1/2 O2 + H2) in 1972, photocatalytic water splitting has attracted considerable attention as a solution to energy exhaustion. Since hydrogen is a clean source of energy that does not generate carbon dioxide when employed, water splitting has been considered an effective measure against global warming. The most commonly studied photocatalyst is TiO2. However, hydrogen production from water using TiO2 requires ultraviolet light, which deems it inefficient. In order to achieve a high conversion efficiency, which is considered suitable for practical applications, it is necessary to achieve a minimal absorption of visible light. To satisfy this requirement, a visible-light-responsive photocatalyst should be employed in the water splitting process. However, many of the photocatalysts with high visible light responsiveness, such as sulfide semiconductors and nitride semiconductors, have photocorrosive issues. This is an issue where hole carriers generated by photo-excitation cause the oxidative decomposition of the photocatalyst itself. To date, two approaches have been reported to suppress photocorrosion. The first is to transfer photocorrosive holes to different photocatalysts. The transfer of holes to the valence band of another photocatalyst has been reported. (H. Nagakawa et al., ACS Omega, 2018, 3, 10, 12770-12777.) In the previous study, the hydrogen generation efficiency was increased by transporting the excited electrons and holes from CdS to SiC. This approach successfully suppressed the photocorrosion of CdS. The second photocorrosion suppression method is to protect the photocorrosion-susceptible photocatalyst with different stable photocatalysts, thereby reducing exposure to the solution and preventing elution. The current authors reported that this method promoted the water splitting reaction in a CdS composite photocatalyst. (H. Nagakawa et al., ACS Applied Energy Materials, 2018, 1, 12, 6730-6735.) In the study, we achieved an overall water splitting under visible light using a home-synthesized tri-composite, in which CdS was covered with a photocatalyst on both the oxidation and reduction sides. Previously, the use of CdS/SiC/TiO2 tri-composite photocatalysts was found to promote the consumption of holes on CdS and reduce the exposure of CdS to the solution, thereby suppressing photocorrosion. However, since oxidation of water cannot be achieved with the oxidizing power of SiC, in this study, we employed WO3 instead of SiC and realized stronger oxidizing power by constructing a Z-scheme. In addition, we employed CdWO4 as a photocatalyst on the reduction side in order to enable the transport of electrons excited on CdS to the conduction band of CdWO4. A highly controlled CdS/CdWO4 core–shell composite was synthesized by a simple method via the dissolution of CdS under acidic conditions. The eluted Cd2+ reacted with the dissolved WO4 2- in solution in situ, allowing selective deposition on the CdS surface for uniform shell synthesis. (H. Nagakawa et al., RSC Advances, 2020, 10, 1, 105-111.) As a result, recombination was suppressed and the hydrogen production ability was improved compared to that of the dispersion system of CdS and WO3. Furthermore, water splitting was achieved by reducing the CdS exposure and suppressing photocorrosion. Hydrogen evolution experiments were conducted in vial bottles under Ar flow. First, 1 wt % Pt was deposited on the prepared photocatalyst using H2PtCl6·6H2O through photo-deposition under visible light (λ > 420 nm) in 30 vol% methanol aqueous solution. The synthesized CdS/WO3/CdWO4-Pt composite photocatalyst (0.03 g) and pure water (15 mL) were prepared in the reaction cell. A Xe lamp with a UV cutoff filter (λ > 420 nm) was used as a visible-light source. A 0.1 mL aliquot of the evolved gas was collected using a gastight syringe, and the sampled gas was injected into the gas chromatograph to determine the amounts of evolved hydrogen and oxygen. As a result, hydrogen and oxygen were constantly produced at a ratio of 2 : 1 while suppressing photocorrosion. This is the first report of water splitting by a powder-based photocatalyst using CdS under visible light. Figure 1

Crystallization- and morphology-tunable Fe3O4@C core–shell composites decorated on carbon nanotube skeleton with tailorable electromagnetic wave absorption behavior

Herein, a scalable method is developed to fabricate carbon nanotube (CNT)/Fe3O4@C composites, in which the crystallization and morphology of the carbon shell on the surface of Fe3O4 nanoparticles can be controlled by manipulating the synthesis conditions of chemical vapor deposition technology. Owing to the synergic dissipation effect of the core–shell structure, as well as the excellent conductive loss induced by the CNT skeleton, the CNT/Fe3O4@C composite shows a minimum reflection loss of −50.1 dB at 9.7 GHz and an effective bandwidth of 4.6 GHz. This study provides new insight into preparing core–shell-structured microwave absorbers with excellent performance.

Kinetic simulation of the viscosity of rarefied gas nanosuspensions with composite particles

The viscosity of rarefied gas suspensions with composite nanoparticles was studied using the previously developed kinetic theory. The interaction of carrier gas molecules is described by the Lennard-Jones potential, the interaction of the gas molecules with a nanoparticle does by Rudyak–Krasnolutskii (RK) potential, and the interaction of the nanoparticles with each other does by the Rudyak–Krasnolutskii–Ivanov potential (RKI). Nitrogen-based gas suspensions with carbon (graphite) nanoparticles in a 1 nm thick uranium shell and with solid carbon and uranium nanoparticles at a temperature of 300 K and atmospheric pressure are considered. The diameter of the nanoparticles varied from 2 to 100 nm. It is shown that the viscosity of gas suspension with composite nanoparticles with a core of less dense material than the material of the shell is always lower than the viscosity of the gas suspension with solid nanoparticles of the same material as the shell composite. The decrease in the viscosity of the above-mentioned gas suspension with composite nanoparticles can be explained on the basis of the kinetic theory by the smaller mass of such nanoparticles compared to solid ones.

EDA-steered in situ staged reduction–etching synthesis of hollow CuxNi1−x/Ni core–shell composites with broad bands and strong microwave absorption

Despite the progress in the synthesis of hollow nanomaterials, the one-pot fabrication of magnetic bimetallic hollow core–shell composites remains a major challenge. Herein, we first reported a novel, simple, and one-pot strategy to facilely prepare CuxNi1−x/Ni core–shell composites, whose morphologies evolve from solid nanorods to hollow microspheres and novel nanotubes in the absence of any surfactant or template. The morphological evolution is related to the selective adsorption of ethylenediamine (EDA) on the Cu (111) surface, which steers the anisotropy growth and the final morphology. The CuxNi1−x/Ni composites have excellent ferromagnetic behavior, and the solid nanorods and hollow microspheres exhibit the largest Ms and Hc, respectively. Here, the wax-based composites containing 22 wt% CuxNi1−x/Ni nanotubes possess remarkably enhanced absorption capability with a maximum absorption of −64.69 dB at 11.97 GHz and an effective bandwidth (90% attenuation) of 5.54 GHz. The superior microwave absorption performance is associated with the cooperation of multiple polarizations, double magnetic resonances, large attenuation, and proper impedance match resulting from the 1D, core–shell, and hollow nanostructures. Our work develops a new strategy with greater value for the construction of bimetallic core–shell hollow structures in electromagnetic wave absorbing materials, catalysis, sensors, as well as microreactors.

Synthesis of core–shell activated carbon/CaO composite from Ficus Nitida leaves, as an efficient adsorbent for removal of methylene blue

In this work, activated carbon is prepared from Ficus Nitida leaves using CaCO3 as an activation agent (AC/CaO core–shell composite). The properties of produced activated carbon were characterized by Fourier transform infrared spectroscopy (FT-IR), N2 adsorption Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM). According to the results, the external surface area, total surface area, and mesoporous area of AC/CaO core–shell composite were found to be (153.8 m2/g), (1255.5 m2/g), and (1101.7), respectively. On the other hand, the adsorption capacity is expressed by the iodine numbers. The adsorptive property of the AC/CaO core–shell composite was tested using methylene blue dye. Subsequently, equilibrium data were best fitted by the Freundlich isotherm model, showing a maximum adsorption capacity of 356 mg/g. To determine the kinetic data, the pseudo-first kinetic model and the second kinetic model were studied, and the rate constants also were estimated. Adsorption of the methylene blue dye obeyed pseudo-second-order kinetics. Thermodynamic parameters for instance free energy change, enthalpy change, and entropy change of dye adsorption were obtained. Different thermodynamic parameters such as free energy change, enthalpy change, and entropy change of dye adsorption have also been evaluated, and it has been found that the adsorption was favorable, spontaneous, and exothermic in nature. The results indicate that the AC/CaO core–shell composite could be used to effectively adsorb the methylene blue dye from the contaminated solutions.

Synthesis of core/shell-structured CaCu3Ti4O12/SiO2 composites for effective degradation of rhodamine B under ultraviolet light

The rapid growth of industrialization has driven the development of wastewater treatment technologies to overcome the environmental pollution that comes with it. Organic-based pollutants such as dyes and petroleum-based hydrocarbons are known to be the major pollutants from industries. Advanced photocatalysts is an alternative solution for organic pollutants clean up without the generation of toxic by-products. In this paper, a forthright dye removal technique by CCTO/SiO2 core–shell composites produced via chemical precipitation was introduced. The core–shell CCTO/SiO2 composites were produced from a silica precursor, i.e. TEOS. The effects of TEOS content (x = 0.5 and 1 ml) on the morphology, structure, and photocatalytic activities of core–shell CCTO/SiO2 composites were studied. The phase compositions and structural properties of core–shell CCTO/SiO2 composites were analyzed by TEM-EDAX, XRD, FTIR, and BET. The particle and crystallite sizes of core–shell CCTO/SiO2 composite produced with higher TEOS content (x = 1 ml) were smaller, i.e. 380 ± 57 nm and 42 nm respectively. However, higher surface area (8.23 m2g−1) was observed. The photodegradation efficiency (η%) of core–shell CCTO/SiO2 composite prepared using 1 ml of TEOS was 76.5% after 40 min exposure to UV light; better than product from the system with 0.5 ml TEOS. The C1S photocatalyst was very stable with a high photodegradation efficiency of 73.5% even after 4 cycles of RhB degradation.

Synthesis of novel bio-composite by powder processing: an assessment

ABSTRACT This experimental study presents the development of a novel bio-composite with a process of utilization of waste chicken egg shells. The objective of work is to identify the effect of processing of coconut jute fiber, gelatin and chicken egg shells relating its influence on mechanical and micro structural properties bio-composite created. Cold powder processing was used to establish the effect of gelatin in gel form on coconut jute-egg shell bio-composite. Coconut jute fiber reinforced egg shell composites were analyzed using Field Emission Scanning Electron Microscopy with Energy Dispersive X-ray, X-ray diffraction, Fourier Transform Infrared Spectroscopy and physical properties for density, Shore-D hardness, water, and steam absorption rate. Obtained results suggest a possibility to utilize waste chicken egg shells as an environment friendly composite which exhibits valuable characteristics.

Controlled synthesis of α-Fe2O3@rGO core–shell nanocomposites as anode for lithium ion batteries

The fine shape control of metal oxides nanocrystal and component are the key for the preparation of high-performance metal oxides/graphene nanocomposites. Herein, a simpler and practicable in situ one-pot approach was used to synthetize α-Fe2O3@reduced graphene oxide (rGO) core–shell nanocomposites. By controlling the amount of hydrazine hydrate and GO in reaction system, the shape of α-Fe2O3 nanocrystals can be tailored from spindle gradually to ellipsoid and quasi-sphere, and the thickness of enwrapped rGO can also be finely controlled. The as-prepared α-Fe2O3@rGO core–shell composites showed much better lithium storage performance than bare α-Fe2O3 nanocrystals. Owing to the core–shell structure and the high conductivity and stability of rGO nanosheet, the quasi-sphere-α-Fe2O3@rGO composites delivered a high reversible specific capacity up to 971 mAh g−1 at the current density of 0.2 A g−1, retaining 530 mA h g−1 at 2 A g−1 and 361 mA h g−1 at 5 A g−1 after 800 cycles with only 0.05% decay per-cycle. Moreover, the facile approach can provide a new strategy for the fabrication of other shape-size dependent, functional, and multicomponent graphene-based composites.

Preparation, characterization, and functionality of bio-based polyhydroxyalkanoate and renewable natural fiber with waste oyster shell composites

This paper reports the fabrication process for a new composite of modified polyhydroxyalkanoate (MPHA), treated renewable pineapple leaf fiber (PLF), and waste oyster shell powder (OSP), with antibacterial, cytocompatibility, and biodegradability properties. PLF and OSP were thermally processed in a solar energy tube as a filler for MPHA-based green composites. The compositions and structures of composites were characterized using Fourier transform-infrared spectroscopy and X-ray diffraction. Tensile and morphological analyses revealed enhanced adhesion and improved compatibility between OSP/PLF and MPHA in composites, compared with polyhydroxyalkanoate (PHA)/OSP/PLF composites. MTT assay and cell adhesion tests revealed that the relative growth rate of human foreskin fibroblasts cells increased with OSP/PLF content, indicating that the composites were not cytotoxic. OSP enhanced the antimicrobial properties of MPHA/OSP/PLF composites. PHA/OSP/PLF composites absorbed more water than MPHA/OSP/PLF composites. The weight loss of composites after being buried in soil compost indicated that both were biodegradable, especially at high levels of OSP/PLF substitution.

Broadband dielectric spectroscopy of La0.65Sr0.35MnO3@TiO2 core–shell nanocomposites

Core–shell composites of ferromagnetic conducting nanoparticles La0.65Sr0.35MnO3 (LSMO) embedded in an insulating matrix of TiO2 (LSMO@TiO2) have been processed, structurally and magnetically characterized, and their DC magnetoresistivity and complex dielectric response measured and fitted from Hz up to the infrared (IR) range (1014 Hz). XRD indicates that the TiO2 shells are amorphous. Modelling of the IR spectra using standard models based on the effective medium approximation has it confirmed and has characterized the effective phonon modes of the LSMO nanoceramics and LSMO@TiO2 composite. Modelling of the lower-frequency spectra has shown that TiO2 shell thicknesses are rather non-uniform down to thin nm values, which leads to giant low-frequency permittivity values and non-negligible free-carrier tunnelling among the LSMO cores. Two main dielectric dispersion regions were observed and shown to be due to the inhomogeneous conductivity—the one occuring in the 1011–1012 Hz range relates to nonmagnetic less-conducting dead layers on the surface of LSMO nanocrystallites and the broad second one below the 1010 Hz range is due to the non-uniform thicknesses of the dielectric TiO2 shells. In the IR range, effective phonon modes of the LSMO nanoceramics and LSMO@TiO2 composite were characterized from the reflectivity spectra.