Papers by Keyword: Core-Shell Structure

Abstract: The present work focuses on the fabrication of novel hybrid materials for toxic dye removal from an aqueous environment. Nanocarbon template (20-30 nm) was coated with tri-ethyl-orthosilicate (TEOS). The core-shell structure developed was further air pyrolyzed at 600 °C to produce mesoporous silica shells. The pore structures and characteristics of the material were evaluated using XRD, nitrogen adsorption studies, SEM, and TEM. Owing to the hierarchical porosity in range of 1-4 nm and 10-20 nm their adsorption studies were investigated for Phenol-Red. Dye adsorption studies performed revealed 98% removal efficiency with only 20 mg of adsorbent dose within 15 minutes.

Abstract: This study is mainly focused on the fabrication of SiO₂ as an inorganic shell material encapsulated an organic thermochromic (TC) core material comprises of either the (i) three-component as-synthesized blue dyes [BDTCM@SiO₂] or (ii) off-the-shelf (commercial) black dyes [CDTCM@SiO₂]. Both the SiO₂ encapsulated thermochromic systems have successfully demonstrated the color transition at around 31 °C. For the three-component thermochromic microcapsules, we have used the crystal violet lactone (CVL) as a leuco dye, bisphenol-A (BPA) as a color developer, and 1-tetradecanol (TD) as a solvent. Different ratios of the thermochromic dye and the metal oxide were prepared to examine the effect of the core@shell ratio on the microstructural and thermal properties of the encapsulated microcapsules. The mean particles sizes of the BDTCM@SiO₂ are below 100 nm, whereas, the CDTCM@SiO₂ samples exhibited the mean particle sizes varied in a range of 100-1000 nm. The endothermic phase transition due to melting and in general, the thermal stabilities of these SiO₂ encapsulated TCMs have been explored for the purpose of deploying these systems for thermal energy savings or storage applications.

Abstract: Stable electronic configuration between the interface of an n-type oxide semiconductor core and a p-type polymer shell is necessary in order to guarantee a consistent functioning core-shell structure. This research aims to use silane-aniline to link between an n-type Titanium (IV) oxide (TiO₂) core and p-type polyaniline emeraldine salt (PANI-ES) shell. Core-shell structure was created by functionalizing TiO₂ powders with silane aniline molecules using simple soaking technique and then polymerizing the attached aniline molecules using an oxidative technique. Infrared spectroscopy reveals the presence of Si-O bonds signifying the presence of linkage between the inorganic core and polymeric shell. Polymerization of the attached aniline molecules may have led to coupling of aromatic rings to form long polymeric structures which caused widening and shifting of aromatic rings’ IR peak to lower wavenumber. In conclusion, silane-aniline was successfully utilized to connect the n-type TiO₂ core and p-type PANI-ES shell.

Abstract: In this work, the insulating SiO₂ was coated successfully on the surface of reduced iron particles by a sol-gel method to decrease the core loss at low frequency. The scanning electron microscope images and elements analysis confirm that the surface of iron powders particles were covered by a thin insulating layer in the form of uniform core-shell structure. The samples were annealed at 400 °C in N₂ atmosphere to obtain better magnetic properties. The annealed SMCs with 10 mL/h dropping rate of TEOS have optimum magnetic properties with low core loss P_s of 280.89 W/kg and high saturation magnetic flux density B_s of 1.038 T at 1000 Hz.

Abstract: In order to explore the supercapacitor electrode material with high energy density, a composite material that nickel-cobalt sulfide loaded in graphene (NiCo₂S₄@rGO) with core-shell structure was successfully prepared by hydrothermal, room temperature vulcanization and annealing. The core-shell structure of the material greatly increased the contact area between the material and the electrolyte and improved the electrochemical performance. In addition, the energy density has been significantly improved. NiCo₂S₄@rGO was characterized by field emission scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectrometer. The electrochemical properties of the material were evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The results show that the capacitance can reach 1100 F/g at the current density of 0.5 A/g. Furthermore, the NiCo₂S₄@rGO as positive electrode and reduced graphene oxide (rGO) as negative electrode were assembled into an asymmetric supercapacitor (ASC). The device exhibits a high energy density of 74.78 Wh/Kg at a power density of 400 W/Kg, as well as excellent cycling stability of 88.9% after 3 000 cycles, which reflects the excellent electrochemical performance of the material.

Abstract: Zirconium oxide was obtained via traditional precipitation from a ZrOCl₂ solution with ammonia followed by drying at 110 °C. The carbon-coated samples were synthesized by calcination of the pristine zirconia mixed with polyvinylalcohol. The obtained ZrO₂@C samples of core-shell structure as well as the reference samples of pristine zirconia were calcined at different temperatures from 500 to 1400 °C. All the materials were examined by a set of physicochemical methods (a low-temperature argon adsorption, transmission electron microscopy, X-ray diffraction analysis, photoluminescence spectroscopy). It was found that the carbon coating prevents the sintering of the oxide nanoparticles, which allows one to maintain the specific surface area, the size of the oxide core and, finally, stabilize its phase composition. Transformation of the cubic phase into monoclinic phase becomes significantly complicated. Thus, 40% of the cubic phase was detected even after calcination of the ZrO₂@C sample at 1400 °C. Moreover, the carbon-coated samples treated at elevated temperatures with subsequent removal of the carbon shell were found to possess the highest concentration of the defects related to a presence of the anion vacancies in zirconia.

Abstract: Carbon-coated hematite α-Fe₂O₃ core-shell structure had been synthesized by a facile method of pulsed high-voltage discharge. The structure, morphology, and phase composition of the material were characterized by SEM, TEM, and XRD methods. When carbon-coated α-Fe₂O₃ was galvanostatically cycled at 100 mA g^–1 in the voltage range of 3.0–0.005 V, it exhibits a reversible capacity of 479 mAh g^–1, assuming about three Li⁺ ions retrieval.

Abstract: Multilayer ceramic capacitor (MLCC) chips have been successfully prepared through tape-casting and screen-printing. Conventional sintering method and two-step sintering method with different sintering temperature and holding time are used to obtain the MLCC chips. The scanning electron microscopes show that MLCC chips sintered by two-step sintering at T₁=1200°C and T₂=1130°C for 3h have a highly dense dielectric layer. The temperature coefficient of capacitance (TCC) of the MLCC chip is less than ±15% from-60°C to 235 °C that satisfactorily meets the requirement of X9R. The average capacitance and the dielectric loss of the MLCC chip are 88nF and 1.8% at the room temperature, respectively.

Abstract: In this paper, the liquid phase separation and solidification process of the Al₇₅Bi₉Sn₁₆ immiscible alloy were studied with calorimetric and resistivity methods to make the melt superheated treatment process. The impact of melt overheating treatment (MOT) on the phase constitution and solidification microstructures were investigated using X-Ray diffraction (XRD) and field emission scanning electron microscope (FESEM) to determine the structural sensitivity to the melt superheated degree, and find a new strategy for improving the forming ability of the core-shell structure of the Al₇₅Bi₉Sn₁₆ alloy. The results show that: the liquid phase separation and precipitation of primary (Sn) phase occur in 1039K-880K and 460K-403K; the core-shell structure with Sn-Bi-rich core and Al-rich shell can be formed under conventional casting conditions; the melt overheating treatment (MOT) can promote the formation of core-shell structure by increasing solidification time t₀ and decreasing the average solidification rate v.

Abstract: The positron annihilation lifetime spectroscopy (PALS) was applied to investigate the properties of capsules composed of n-alkanes (filling material) and polymer (shell) in the broad range of pressures up to 450 MPa. These microcapsules aggregate into the grains having about 200 μm in diameter. Their properties were investigated as a function of pressure (p) at several selected temperatures: when the filling material is in liquid, rotator and solid phase. Pressure experiments were performed without gas access to the sample and in an argon atmosphere. Two o-Ps components were found, the longer-lived correspond to the filler material, and the shorter-lived one – to the shell. These components change with p; even a small pressure (6 MPa) reduces considerably the o-Ps lifetimes (τ). At 303 K the o-Ps lifetime in the core changes non-monotonically, and at 60 MPa τ is higher than at 20 MPa. The increase of pressure induces the phase changes in the filling material, and also produces the deformation of microcapsule aggregates and crash of small capsules at the grain boundary region. Internal structure of the microcapsules was observed by SEM.