Nano-hollow Spheres Research Articles

Tuning of structural, magnetic and dielectric properties of TFe2O4 (T = Mn, Fe, Co, Ni, Cu, and Zn) Nano-Hollow Spheres: Effect of cation substitution

Nano hollow sphere (NHS) is an emerging morphology among magnetic nanostructures and here, NHSs of spinel ferrites (TFe2O4, T = Mn, Fe, Co, Ni, Cu, and Zn) are synthesized in a facile solvothermal method and their structural, magnetic and dielectric properties are investigated in detail. These properties are found to largely depend on different divalent cation placements in the ferrite structures. Coercivity of TFe2O4 samples are observed to vary from ∼576 Oe (T = Co) to ∼ 116 Oe (T = Ni) and saturation magnetization, from ∼73.6 emu/g (T = Fe) to ∼ 53.6 emu/g (T = Mn), discussed in terms of anisotropy, super-exchange interaction and crystallite size of the materials. Variation of dielectric properties such as permittivity, dielectric loss and ac conductivity of these NHSs within frequency range 10 Hz −5.5 MHz at ∼300 K are explained on the basis of Maxwell-Wagner two layer model for space charge and polaron hopping from Fe3+ to Fe2+ as well as T2+ to T3+ ions at tetrahedral (A) and octahedral (B) sites. Analysis of dielectric relaxation mechanism ensures it as modified-Debye type and Jonscher’s power law displays ac conduction mechanism for TFe2O4 NHSs. Cole-Cole plots are fitted with equivalent circuit to understand the effect of resistive grain boundary and conductive grains with frequency. This study on tunable dielectric and magnetic properties with substitution of different cations provides a map to select an efficient material for applications from high-frequency devices to bio-medical field.

The novel p-Co3O4/n-I-Fe2O3 nano hollow spheres with the enhanced photocatalytic activity

The iodine doped α-Fe2O3 hollow spheres combined with Co3O4 were firstly prepared by a two-step method. The catalysts with the structure of p-Co3O4/n-I-Fe2O3 HS exhibited excellent photo-degradation activity under visible irradiation. More than 94% RhB was degraded within 10 min, the reaction rate constant was calculated to 0.303 min−1 which was 10.7 times higher than pure Fe2O3 particles. The iodine doping decreased the surface electron impedance and enhanced the separation of photo-induced carriers. The formation of hollow spheres increased the specific surface area of the catalysts as expected. The p-n junction further promoted carriers separation and the Fenton reaction.

Structure-related luminescent properties induced by doping in Sm-doped SnO2 hollow spheres

Despite the significant amount of research on the sensitization of positive trivalent lanthanide (Ln3+) ions doped into semiconductor nanocrystals, it is unclear how the local structure of doped ions affects luminescence. The difficulty is that an actual low-dimensional doping system is often a mixture of surface doping and bulk doping, and its distribution characteristics are sensitively dependent on external factors. The aim of this work on Sm3+ ion-doped SnO2 hollow spheres is to investigate the doping-related structural and luminescent properties, distinguish the luminescence mode characteristics subject to surface doping and bulk doping (or core doping), and depict the relative ratio change of the two doping sites caused by doping. Due to the synergistic or competitive interactions of quantum confinement effects, stress effects, and surface defects, it is found that the crystallite size, Raman mode, band gap, and luminescence properties exhibit specific changes with increasing doping. The optimal doping occurs at 4.5%, which corresponds to the best crystallization and maximized sensitized emission. The asymmetry ratio is used to determine the ratio of surface doping and bulk doping and its variation with doping concentration, which increases with decreasing doping, especially at low doping levels, indicating that the contribution of surface doping is significant at low doping level. This work provides a unique perspective to quantitatively study the sensitized luminescence characteristics of Sm3+ doped SnO2 nano-hollow spheres, which will provide a solution path for controlled sensitized emission.

Enhancement of the NH3-SCR property of Ce-Zr-Ti by surface and structure modification with P

The Px-Ce0.3-Zr-Ti catalysts were prepared by hydrothermal method and the effect of P modification on NH3-SCR property and structure was investigated. The P0.15-Ce0.3-Zr-Ti catalysts showed an excellent NH3-SCR activity in wide temperature range (Over 80% NOx conversion at 180–400 °C). Surprisingly, some nano-hollow spheres structures formed in P0.15-Ce0.3-Zr-Ti catalysts by introducing appropriate amount of H4P2O7, greatly increasing the specific surface area of catalysts and providing more reaction sites for active gases. And further characterizations indicated that there existed a new substance CePO4 in catalysts. With the increase of surface Ce3+, the redox ability of catalysts was greatly improved, resulting in a better catalytic activity at low temperature. Meanwhile, the catalysts modified by H4P2O7 produced more surface active oxygen species and other defects, as well as more surface acid sites, which played an important role in catalytic activity within a wide temperature window. DRIFTS results suggested that modification with P could promote the formation of NO2 and monodentate nitrates, thereby enhancing SCR reaction process (Langmuir-Hinshelwood reaction pathway). Besides, the presence of amide species (NH2) is an important marker for the catalyst to follow the E-R reaction mechanism.

Enhanced reversible hydrogen storage in nickel nano hollow spheres

Nickel is a good catalyst for the dissociation of molecular hydrogen to atomic form, but suffers from a negligible hydrogen storage capacity (∼10−4 wt% at 25 °C and 1 atm). The current investigation pertains to the enhancement in the reversible hydrogen storage capacity of Ni via storage in molecular form; thus utilizing a recently developed multi-mode storage philosophy. Ni nano hollow spheres (NiHS) have been synthesized using hydrothermal method (outer diameter of ∼300 nm and shell thickness ∼30 nm). Pressure-composition-isotherms and temperature programmed desorption curves have been used to characterize the hydrogen storage capacity and to establish the reversibility of the process. An enhancement in the reversible storage capacity by a factor of 7 × 103 (7,00,000%) is obtained at 25 °C and 150 bar pressure. The capacity is further enhanced to 0.91 wt% hydrogen by utilizing a pressure of 300 bar. Ni plays a dual catalytic role in the absorption and desorption process.

Electromagnetic wave trapping in NiFe2O4 nano-hollow spheres: An efficient microwave absorber

Abstract In search of lightweight, broadband and stable microwave absorbing material, here we have presented a morphology dependent study of microwave properties on Nickel Ferrite (NFO). A comparative study of permittivity (e), permeability (μ), Reflection Loss (RL) and Shielding efficiency (SE) on NFO nano hollow spheres (NHS) with its nano particles (NPs) and bulk counterpart has been performed for widely used X-Band (8–12 GHz) on composites filled (25 wt% and thickness of 2 mm) with each sample. Interestingly, NFO nano hollow spheres (NHS) are found to be highly efficient material towards microwave attenuation. An optimal RL of ∼−59.2 dB is obtained for frequency ∼11.7 GHz with a broad band-width (W) of ∼(9.18–12) GHz having RL 90%). Hollow cavity of NHS leads to a lower density (∼3.91 g/cc) as well as multiple internal reflections, which enhances wave absorption. Excellent impedance matching with free space, accompanied by proper dielectric and magnetic loss contributes towards maximization of RL for NHS. These properties enhance the potentiality of NFO NHS as an efficient microwave absorbing material suitable in various microwave devices.

Rheological response of magnetic fluid containing Fe3O4 nano structures

Abstract To understand the effect of particle size on magnetorheological effect two magnetorheological (MR) fluids, composed of nano-hollow spheres (NHSs), of diameters 250 nm (MRF250) and 700 nm (MRF700), are studied. The results are compared with their solid counterpart with Fe3O4 nanoparticles (NPs) based MR fluid of 100 nm diameter (MRF100). To understand the MR mechanism the flow curves (shear stress vs shear rate) are fitted with different established models and our samples are found to follow the Bingham Plastic model. The yielding behavior of the MR fluids is found to be morphology dependent. The MR fluid with larger particles show maximum yield stress ∼830 Pa at an applied field 0.4 T, due to the combined effect of larger surface area and higher magnetism. Hollow nano spheres show better stability than that of NPs due to compatible density with the carrier fluid.

Nano-scale hollow structure carbon-coated LiFePO4 as cathode material for lithium ion battery

In this paper, carbon-coated LiFePO4 nano-hollow spheres (LFP@C HSs) were successfully synthesized using lithium phosphate (Li3PO4) nano-spheres as templates and precursors. The X-ray diffractometer (XRD) demonstrated the crystal structure of LFP@C HSs. The morphology of LFP@C HSs was determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compared with LiFePO4 nano-hollow spheres without carbon coating (LFP HSs) and commercial LiFePO4 (commercial LFP), the rate performance of LFP@C HSs has been evidently improved by carbon coating and hollow structure. At the highest rate of 5 C, LFP@C HSs still maintains a capacity of 101.4 mA h−1 g−1. LFP@C HSs show excellent cycling performance at a current density of 1 C, maintaining 92.5% of the initial capacity after 500 cycles.

NiFe2O4 nano-hollow spheres with improved magnetic and dielectric properties

From the detail morphology dependent studies, nano-hollow spheres (NHS) of NiFe2O4 (NFO) are found to exhibit better magnetic and dielectric properties compared to their nanoparticles and bulk counterparts. Prepared by solvothermal method, these NHS with diameter of ∼228 nm and much lower tap density of ∼3.91 g/cc, show excellent magnetic properties with MS and HC, 63.5 emu/g and 122 Oe respectively. Variation of dielectric properties such as permittivity (ε), dielectric loss (tanδ) and ac conductivity (σac) of these NHS with frequency and temperature is explained on the basis of Maxwell-Wagner two layer model for space charge and hopping of charges from Fe3+ to Fe2+ as well as Ni2+ to Ni3+ ions at B (octahedral)-sites. The complex impedance spectroscopy study indicates the presence of grain and grain boundary effects in NHS and the conduction mechanism is explained by Jonscher's power law. A comparatively low value of the activation energy (E = 0.325 eV) is found for these NHS. High value of magnetic and dielectric properties of NFO NHS enhance their potential applications for microwave devices in the form of isolators, circulators etc.

Enhanced magnetic properties of Zn doped Fe3O4 nano hollow spheres for better bio-medical applications

Abstract We synthesized ZnxFe3−xO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 1.0) nano-hollow spheres (NHSs), a promising functional magnetic material for bio-medical applications. Detailed temperature dependent magnetic studies indicate an increase in saturation magnetization (MS) with Zn doping, attaining a maximum at x = 0.2 (MS = 92.52 emu/g at room temperature), due to the replacement of antiferromagnetically coupled FeA3+ ion on the A site by Zn2+ and transformation of FeB2+ to FeB3+ on B site for maintaining the charge neutrality. The dynamic magnetic properties of the powdered ZnxFe3−xO4 samples were investigated using frequency dependent real and imaginary parts of ac susceptibility. The data obtained by fitting Vogel Fulcher law indicates reduced dipolar interaction in our systems due to Zn doping. Applications of Fe3O4 nanostructures can be improved by doping Zn and making hollow spheres.

Synthesis, characterization and adsorption studies of amino functionalized silica nano hollow sphere as an efficient adsorbent for removal of imidacloprid pesticide

In the present research, silica nano hollow sphere (SNHS) and amino functionalized silica nano hollow sphere (SNHS-NH2) adsorbents have been used to remove imidacloprid as a high consumption pesticides from aqueous solutions. SNHS and SNHS-NH2 have been synthesized based on our previously reported methods. FT-IR and SEM techniques have been employed to analyze physicochemical characteristics of produced adsorbents. The adsorption of imidacloprid has been evaluated in terms of kinetic and equilibrium on used different synthesized adsorbents. The adsorption tests were performed in various conditions, in addition to assess the effects of pH, temperature and adsorbent dosage. Equilibrium empirical data have been fitted by Langmuir, Sips, Freundlich, Toth, Khan, Tempkin and Redlich-Peterson isotherms. Correlation coefficients demonstrated that equilibrium data were better matched with the Redlich-Peterson (R-P) isotherm. On the other hand, experiments showed that the amount of adsorbate per unit mass of adsorbent is decreased by increasing of the pH, and the maximum value of qe is obtained in acidic pH. In addition, the amount of adsorbate per unit mass of adsorbent is reduced by rising temperature and the equilibrium adsorption is dropped by increasing the amount of silica adsorbent. Kinetic data have been fitted with Elovich, pseudo-first-order and pseudo-second-order models; according to the obtained correlation coefficients. It can be stated that the pseudo-first-order model is more suited to the kinetic data related to pesticide adsorption on silica adsorbent. Kinetics of imidacloprid adsorption has been investigated at the concentrations of 7.2 mg/L and 10 mg/L. The results demonstrated that the equilibrium rate slope become much steeper in the initial times by increasing concentrations of imidacloprid.

Facile synthesis of porous LiMn2O4 micro-/nano-hollow spheres with extremely excellent cycle stability as cathode of lithium-ion batteries

In present work, the porous LiMn2O4 micro-/nano-hollow spheres are directly prepared from the globe precursor MnCO3 obtained via a facile precipitation route without any intermediate and ethanol. X-ray diffraction and scanning electron microscopy results indicate that the as-synthesized porous LiMn2O4 micro-/nano-hollow spheres are composed of nanometer-sized primary particles. Charge–discharge tests, cyclic voltammetry, and electrochemical impedance spectra show that the obtained LiMn2O4 delivered higher reversible capacity, extremely excellent cycle stability, superior kinetic properties, and rate capacities. Specially, there are nearly no any capacity loss after 200 cycles, and the coulombic efficient is nearly close to 100%, which are attributed the unique porous micro-/nano-hollow structure and a better crystallinity.

在酸碱性介质中具有增强的表面微观结构敏感性的氧析出催化活性的铱-钯纳米合金研究

Ir-based electrocatalysts have been systematically studied for a variety of applications, among which the electrocatalysis for oxygen evolution reaction (OER) is one of the most prominent. The investigation on surface-microstructure- sensitive catalytic activity in different pH media is of great significance for developing efficient electrocatalysts and corresponding mechanism research. Herein, shape-tunable Ir-Pd alloy nanocrystals, including nano-hollow-spheres (NHSs), nanowires (NWs), and nanotetrahedrons (NTs), are synthesized via a facile one-pot solvothermal method. Electrochemical studies show that the OER activity of the Ir-Pd alloy nanocatalysts exhibits surface-microstructure-sensitive enhancement in acidic and alkaline media. Ir-Pd NWs and NTs show more than five times higher mass activity than commercial Ir/C catalyst at an overpotential of 0.25 V in acidic and alkaline media. Post-XPS analyses reveal that surface Ir(VI) oxide generated at surface defective sites of Ir-Pd nanocatalysts is a possible key intermediate for OER. In acidic medium, the specific activity of Ir-Pd nanocatalysts has a positive correlation with the surface roughness of NWs > NHSs > NTs. However, the strong dissociation of surface Ir(VI) species (IrO42-) at surface defective sites is a possible obstacle for the formation of Ir(VI) oxide, which reverses the activity sequence for OER in alkaline medium.

Multiferroic properties of bilayered BiFeO3/CoFe2O4 nano-hollowspheres

Here, we reported the synthesis of bilayered BiFeO3/CoFe2O4 nano-hollow spheres (NHSs) by depositing a BiFeO3 (BFO) layer of thickness ∼20nm on CoFe2O4 (CFO) nano-hollow spheres surface of diameter ∼250nm and investigated their electric, magnetic and magnetoelectric properties in view of their applications in electronic and magnetic devices. The nano-composites exhibit better properties compared to their individual counterpart. The maximum polarization in CFO/BFO NHSs is found to be 2.1µC/cm2 at a frequency 50Hz. Magnetic measurements show the saturation magnetization to be 30.1emu/g with high value of remnant magnetization (17.9emu/g), and coercivity (1320Oe). Its magnetoelectric coefficient, αME at 1kHz is estimated to be ∼8.6mV/cmOe.

Synthesis and functionalization of MnFe2O4 nano−hollow spheres for novel optical and catalytic properties

Herein, we synthesize MnFe2O4 nano−hollow spheres (NHSs) of average diameter 100nm through a facile template free solvothermal process and carry out a time dependent morphological study to investigate their process of core excavation. Further, a surface engineering of as−synthesized MnFe2O4 NHSs has been executed with organic disodium tartrate dihydrate ligand and interestingly, the surface modified MnFe2O4 NHSs are found to capable of emerging multicolor fluorescence starting from blue, green to red. The magnetic measurements through vibrating sample magnetometer demonstrate that room temperature superparamagnetic nature of MnFe2O4 NHSs remains unaltered after surface modification. Moreover, functionalized MnFe2O4 NHSs are found to exhibit excellent reusable photocatalytic efficiency in the degradation of cationic dye, methylene blue with rate constant of 2.64×10−2min.

Surface modification of Cobalt ferrite nano-hollowspheres for inherent multiple photoluminescence and enhanced photocatalytic activities

Nano-hollow spheres (NHSs) are the new drift in magnetic nanostructures as they provide more surface area at nano length scale with enhanced magnetic properties compared to their nanoparticle counterpart. Here we reported the synthesis of biocompatible CoFe2O4 NHSs of diameter around 250nm and emergence of intrinsic multiple photoluminescence from blue, green to red on modifying their surface with small organic ligands like tartrate. The surface modified NHSs also showed notable photocatalytic activity towards the degradation of environmentally malefic dyes like Methylene Blue and Rhodamine B. The surface modified NHSs are found to exhibit superior magnetic properties.

Boosted adsorption–photocatalytic activities and potential lithium intercalation applications of layered potassium hexaniobate nano-family

We demonstrated that the KN nano-family (including KN nanolaminas and nano hollow spheres) can be derived from the same Nb2O5-based hydrothermal reaction.

Influence of functional group of dye on the adsorption behaviour of CoFe2O4nano-hollow spheres

Excellent preferential dye adsorption of CoFe2O4nano-hollow spheres.

THz conductivity of semi-insulating and magnetic CoFe2O4 nano-hollow structures through thermally activated polaron

Herein, terahertz (THz) time domain spectroscopy is used to measure the complex conductivity of semi-insulating CoFe2O4 nanoparticles (NPs) and nano-hollow spheres (NHSs) with different diameters ranging from 100 to 350 nm having a nanocrystalline shell thickness of 19 to 90 nm, respectively. Interestingly, the magnitude of conductivity for CoFe2O4 NPs and NHSs of same average diameter (∼100 nm) for a given frequency of 0.3 THz is found to be 0.33 S/m and 9.08 S/m, respectively, indicating that the hollow structure exhibits greater THz conduction in comparison to its solid counterpart. Moreover, THz conductivity can be tailored by varying the nano-shell thickness of NHSs, and a maximum conductivity of 15.61 S/m is observed at 0.3 THz for NHSs of average diameter 250 nm. A detailed study reveals that thermally activated polaronic hopping plays the key role in determining the electrical transport property of CoFe2O4 nanostructures, which is found to solely depend on their magnitude of THz absorptivity. The non-Drude conductivity of all CoFe2O4 nanostructures is well described by the Polaron model instead of the Drude-Smith model, which is relevant for backscattering of free electrons in a nanostructured material. The Polaron model includes intra-particle and interparticle polaronic conductivities for closely spaced magnetic nanostructures and provides a mean free path of 29 nm for CoFe2O4 NPs of diameter 100 nm, which is comparable with its average crystallite size, indicating the applicability of the developed model for nanomaterials where charge transport is determined by polaronic hopping. Finally, we have demonstrated the morphology and size dependent magnetic measurements of ferrimagnetically aligned CoFe2O4 nanostructures through a vibrating sample magnetometer in the temperature range of 80–250 K, revealing that the disordered surface spin layer of nanostructures significantly controls their magnetism.

Synthesis of Micelles Guided Magnetite (Fe3O4) Hollow Spheres and their application for AC Magnetic Field Responsive Drug Release.

This paper reports on synthesis of hollow spheres of magnetite, guided by micelles and their application in drug release by the stimulus responsive technique. Here oleyelamine micelles are used as the core substance for the formation of magnetite nano hollow spheres (NHS). Diameter and shell thickness of NHS have been changed by changing concentration of the micelles. Mechanism of NHS formation has been established by investigating the aliquot collected at different time during the synthesis of NHS. It has been observed that oleyelamine as micelles play an important role to generate hollow-sphere particles of different diameter and thickness just by varying its amount. Structural analysis was done by XRD measurement and morphological measurements, SEM and TEM were performed to confirm the shape and size of the NHS. FTIR measurement support the formation of magnetite phase too. Frequency dependent AC magnetic measurements and AC magnetic field stimulated drug release event by these particles provide a direction of the promising application of these NHS for better cancer treatment in near future. Being hollow & porous in structure and magnetic in nature, such materials will also be useful in other applications such as in removal of toxic materials, magnetic separation etc.