Granular Nanocomposites Research Articles

Copper oxide-incorporated pillared clay granular nanocomposite for efficient single and binary, batch and fixed bed column adsorption of levofloxacin and crystal violet

This study investigates single and binary removal of levofloxacin (LV) and crystal violet (CV) using granular CuO-silica pillared clay (G-CuO-SPC) in batch and continuous setups. Silica pillared clay (SPC) synthesized by sol–gel with SiO2 agents and cationic surfactants exhibited a 15-fold increase in surface area after column formation. CuO nanoparticles were incorporated into SPC by direct thermal decomposition, and alginate biopolymer facilitated granulation. Characterization techniques (XRD, N2 adsorption–desorption, FTIR, FESEM and EDS-mapping) confirmed uniformly-dispersed monoclinic CuO nanoparticles in G-CuO-SPC. LV adsorption peaked at pH:5–6, while CV adsorption was almost pH-independent. Sips isotherm modeling revealed maximum capacities for LV (705.2–731.1 mg/g) and CV (914.4–992.4 mg/g) at 25-55℃, with capacities decreasing in binary systems. LV and CV adsorption on G-CuO-SPC was spontaneous, exothermic, and occurred via mechanisms, including electrostatic interaction, van der Waals forces, hydrogen-bonding, and n-π interaction. Fixed-bed analysis favored the Yan model, indicating multilayer adsorption without a classical S-shaped profile.

Dielectric properties, polarization process, and charge transport in granular (FeCoZr)x(Pb(ZrTi)O3)(100−x) nanocomposites near the percolation threshold

This paper presents the research of dielectric properties of (FeCoZr)x(Pb(ZrTi)O3)(100−x) granular metal–dielectric nanocomposites below the percolation threshold. Tested materials have been prepared by using the ion beam sputtering technique in the atmosphere of argon and oxygen. The impedance spectroscopy method has been used to investigate the polarization processes and dielectric relaxation mechanism in the granular nanocomposites. AC measurements in the frequency region of 50 Hz to 1 MHz and measuring temperature range of 81–293 K have been performed. Interfacial, in the low frequency region, and dipolar, in intermediate and high frequency regions, types of polarization processes were observed. The interfacial relaxation process testifies to charge accumulation at the interfaces (grain boundaries) between conductive nanoparticles surrounding an insulative matrix, as well as the space charge region around the contact area between the measurement probes and tested sample. Dipolar polarization corresponds to electric dipole formation after applying to the material an external electric field. The conduction mechanism in the tested material is considered to be hopping carrier exchange and takes place between metallic phase nanograins. It corresponds to the exponential frequency dependence of conductivity. The relaxation mechanism in the (FeCoZr)x(Pb(ZrTi)O3)(100−x) layer has been estimated as a near-Debye process with relaxation time distribution. The nanocomposite exhibits dielectric type and capacitive characteristics in the whole measuring frequency range.

Granular metal-dielectric nanocomposites as an alternative to passive SMD

Granular metal-dielectric nanocomposites as an alternative to passive SMD

Resistive switching characteristics of Co2FeSi and Mn with Al2O3 granular nanocomposites

Materials containing high amounts of grain boundaries and crystal defects are promising candidates for the applications in memristor devices due to their intrinsic low manipulation energy. Here, we present memristive characteristics of granular composite samples containing Co2FeSi and Mn (CFS + M) for the first time. The structure is composed of an Mn oxide phase detected by x-ray diffraction (XRD) patterns which will role as an active layer. The bipolar memristance effect is seen in all samples which can be attributed to a valence change mechanism (VCM). Also, the composition of the granular material with different amounts of Al2O3 nano phases increased the RHRS/RLRS ratio through the reduction of the OFF current. Optimally, the RHRS/RLRS ratio of 1117 and a low threshold voltage of 0.88 V is obtained. Results can be considered for the development of memristors based on granular materials.

Large tunneling magneto-dielectric enhancement in Co(Fe)−MgF2 granular films by minor addition of Si

We report a large enhancement of the tunneling magneto-dielectric (TMD) effect in Co−MgF2 granular films induced by doping using a small amount of Si. This minor addition of Si is dispersed uniformly in the MgF2 matrix and acts by inhibiting the interdiffusion between the Co and MgF2 phases, thus enhancing the magnetization when compared with the case of the corresponding undoped Co−MgF2 films; this consequently results in a greatly enhanced peak dielectric variation (TMD ratio, Δε′/ε′), as indicated by theoretical fittings. Extension of this Si doping effect to CoFe−MgF2 films led to a record-high Δε′/ε′ of 4.3% at 10 kHz and 8.5% at 200 kHz under the application of a magnetic field (H) of 10 kOe, while remaining as high as 2.1% even under H = 1 kOe. This study presents a simple but highly effective approach to enhance the TMD effect in granular nanocomposites, thus opening up the prospect of development of high-performance magnetoelectric devices.

Synthesis in a High-Energy Planetary Mill of Granules Based Onaluminum Alloy Containing Nanocrystalline Graphite

Bulk nanocomposite granules based on AlMg2 alloy, containing nanocrystalline graphite, are prepared by mechanical synthesis using a high-energy ball mill. Structural and phase compositions are studied by optical metallography, computer-aided X-ray tomography, Raman spectroscopy and transmission electron spectroscopy methods. A model of the structural formation is proposed for the granules produced at rotation rates of 660 and 815 min–1. Granule structure consists of slightly-misorientated aluminum solid solution sub-grains with sizes from tens to hundreds nanometers. It is proposed that the initial micro- size graphite particles are subjected to mechanical splitting during mechanical milling. Nanocrystalline graphite particles are located between aluminum grains, as well as at several grain junctions. These nanocomposite granules have high micro-hardness. The granular aluminum-matrix nano-composites may find application during component manufacture by pressure forming and as the precursors for preparing composite alloys by liquid-phase methods.

Tailored tunneling magneto-dielectric effects in Co–MgF2 granular nanostructures by in-situ insertion of thin MgF2 layers

We report a Co–MgF/MgF heterostructure that comprises periodic layers of super-paramagnetic Co0.23–(MgF)0.77 and thin crystalline MgF, to tailor the frequency response of tunneling magneto-dielectric (TMD) effect. The results indicate that increasing MgF interlayer thickness (t) from 0 to 4 nm causes the position of peak dielectric change (Δε′/ε′0) at a specific frequency fTMD, to shift from 300 to 3 kHz, while also retaining a slight decrease in Δε′/ε′0 from 2.9% to 2.4%. The magnitude of Δε′/ε′0 can be controlled by varying the Co content in the granular layers. Theoretical curve fittings predict that the TMD effect in the heterostructure arises from both the granular layers and interlayers, and a change in inter-granular distance within the interlayers leads to a shift in the position of fTMD. This study may prove helpful for tailoring the magneto-dielectric response of granular nanocomposites to a particular frequency, with potential magnetoelectric applications over a wide frequency range.

Dielectric properties of metallic alloy FeCoZr-dielectric ceramic PZT nanostructures prepared by ion sputtering in vacuum conditions

The main objective of the research was investigation of dielectric properties of (FeCoZr)x(PZT)(100-x) granular nanocomposites and determination the influence of isochronous annealing in temperatures of 398 K-573 K on them. The impedance spectroscopy methodology was used. The measurements of electrical parameters, such as: phase shift angle φ, dielectric loss factor tgδ, capacity C and conductivity σ of (FeCoZr)x(PZT)(100-x) nanocomposites have been performed. Frequency dependencies of these parameters were obtained for the ambient temperature range 98 K-373 K for the frequencies ranging from 50 Hz to 105 Hz. It was established, that the conductivity σ of the tested materials before the percolation threshold demonstrates non-linear dependence on frequency. Furthermore, it increases when the ambient temperature is increasing, which indicates a dielectric type of the material. The two types of electrical conduction: capacitive (phase shift angle φ takes negative values) and inductive (φ takes positive values) have been observed. It was concluded that the hopping conductivity dominated in the nanocomposites. Voltage and current resonances phenomena are observed in the materials. The isochronous annealing intensifies the dielectric properties of (FeCoZr)x(PZT)(100-x) nanocomposites.

Device for Increasing the Magnetic Flux Pinning in Granular Nanocomposites Based on the High-Temperature Superconducting Ceramic

A device for modifying the granular high-temperature superconducting ceramics in the plasma of a low-pressure arc discharge has been considered. The particular features of the design and operational principle of this device have been described. The device made it possible to combine the synthesis of that play a role of additional pinning centers and simultaneous deposition of these nanoparticles on microgranules in a single processing cycle. The experimental results on the effect of additional pinning centers on an increase in the critical current thanks to the formation of self-assembled structures in the form of whiskers have been considered.

Enhanced spin-dependent charge transport of Co-(Al-fluoride) granular nanocomposite by co-separate sputtering

Spin-dependent charge transport behavior involving the recently discovered tunnel-type magneto-dielectric (TMD) and magnetoresistance (TMR) effects was studied in Co-(Al-fluoride) granular nanocomposites. By setting a changeable partition height (t = 1–4 cm) on a substrate holder in a conventional co-sputtering (CS) deposition system, we developed a co-separate sputtering (CSS) method to fabricate Co-(Al-F) granular nanocomposites. XPS analysis shows that the Al content remains balanced between the Al metal and Al-F compounds by controlling t. This phenomenon can be attributed to the magnetron plasma interference from the two target sources. Fittings between TMR and normalized magnetization suggest that the CSS films with clear granular structures may have high spin polarization. Compared with the CS samples (t = 0 cm), the CSS films with t = 4 cm show enhanced charge transport properties with a maximum TMD ratio (0.5%) and TMR ratio (7.2%) under a magnetic field of H = 10 kOe. This study demonstrates that the Al-F tunnel barrier between Co granules plays an essential role in controlling the charge transport behavior and will be of significance for applications in field sensors and impedance-tunable devices with large magnetic-field response.

Computational modeling of interfacial behaviors in nanocomposite materials

Towards understanding the bulk material response in nanocomposites, an interfacial zone model was proposed to define a variety of material interface behaviors (e.g. brittle, ductile, rubber-like, elastic-perfectly plastic behavior etc.). It also has the capability to predict bulk material response though independently control of the interface properties (e.g. stiffness, strength, toughness). The mechanical response of granular nanocomposite (i.e. nacre) was investigated through modeling the “relatively soft” organic interface as an interfacial zone among “hard” mineral tablets and simulation results were compared with experimental measurements of stress-strain curves in tension and compression tests. Through modeling varies material interfaces, we found out that the bulk material response of granular nanocomposite was regulated by the interfacial behaviors. This interfacial zone model provides a possible numerical tool for qualitatively understanding of structure-property relationships through material interface design.

Influence of oxide matrix on electron transport in (FeCoZr)x(Al2O3)1-x nanocomposite films

Electron transport in (Fe0.45Co0.45Zr0.10)x(Al2O3)1-x granular nanocomposites (NCs) produced by the ion-beam sputtering of compound target was studied in the temperature range of 2–300 K. Conductivity of the films synthesized in the inert (Ar) atmosphere is determined below percolation threshold by the thermally activated electron tunneling over metallic granules at low temperatures and replaced by the Mott variable range hopping (VRH) with increasing temperature. Introduction of oxygen to the sputtering chamber suppresses VRH leading to retention of the thermally activated tunneling in the whole studied temperature range for the metallic phase atomic concentrations up to х = 0.62. The model of thermally activated tunneling over metallic granules gives an excellent agreement with experimental data when alumina matrix permittivity is considered as increasing with concentration of the metallic phase fraction in the films, which is due to increase in number of localized electronic states. The established influence of the sputtering atmosphere on the electron transport in nanocomposites is explained by reduction of concentration of the defects in matrix when oxygen is added to the sputtering atmosphere.

On the exact crystal structure of exchange-biased Fe3O4–CoO nanoaggregates produced by seed-mediated growth in polyol

The nucleation and growth mechanism of exchange-biased magnetically contrasted highly crystallized and perfectly epitaxied Fe3O4–CoO nanoaggregates was investigated using local probe analysis, namely 57Fe Mossbauer and L2,3 Co XMCD spectroscopies, and advanced magnetometry. The granular nanocomposites were produced by a two-step chemical route. Spinel iron oxide nanoparticles were first synthesised by forced hydrolysis of iron acetate in a polyol and then used as seeds for rock-salt cobalt monoxide nanocrystalline growth. In one case, this crystallochemical step is carried out by separating the seeds, washing and drying them before mixing them in a fresh polyol solution of cobalt precursors. In another case, it is conducted by introducing, directly in the seed reaction solution, the cobalt precursors in the same Fe/Co nominal atomic ratio. It appears that the composite formation proceeds differently in the two cases. It is driven, in the ex situ route, by Co2+ cation diffusion into the spinel lattice leading to the formation of CoxFe3−xO4 core single crystals around which CoO nanocrystals start growing. Conversely, in the in situ route, it is driven by Co2+ cation reactivity with unreacted dissolved Fe3+, conducted to the coating of the preformed Fe3O4 cores by a CoFe2O4-like thin interlayer, itself decorated by outer CoO nanocrystals. These reaction schemes are well confirmed by magnetometry experiments. The low-temperature magnetic properties of the produced composites are consistent with the establishment of an exchange-bias feature into hard-magnet@antiferromagnet and soft-magnet@hard-magnet@antiferromagnet structures, respectively.

Sorption-membrane system for deep deoxygenation of water

We have studied the redox sorption of oxygen from flowing distilled water in a multistage sorptionmembrane cell with a metal (Cu)–sulfo cation exchanger (KU-23 in the H+ form) granular nanocomposite in the cathode compartment and a sulfo cation exchanger (KU-23 in the H+ form) in the anode compartments separated by a cation-exchange membrane (MC-40 in the H+ form). It is shown that the redox sorption of oxygen on the granular nanocomposite bed polarized with a current which is less than the limiting external diffusion one is complicated by internal steps (oxygen diffusion in the polymer matrix pores and the chemical oxidation of metal nanoparticles) and proceeds with a mixed diffusion-kinetic control. In the mode of limiting diffusion current polarization, the contribution of internal stages decreases and the process becomes steady due to the transition into the external diffusion region. A theoretical calculation shows that the process performed in series-connected multistage cells with polarization of each stage in the mode of limiting external diffusion current allows obtaining water with a dissolved oxygen content of <10 ppb.

Coexistence of superconductivity and ferromagnetism in cluster-assembled Sn–Co nanocomposites

The coexistence of superconductivity and ferromagnetism is investigated in granular Sn–Co nanocomposites. The nanocomposites have been prepared by co-deposition of Sn atoms and Co clusters, the morphology and composition of which can be tuned by varying the deposition rate of Co clusters relative to Sn atoms. Flat isolated Sn islands are obtained at zero or low Co cluster flux, while granular nanocomposites are formed with increasing Co cluster flux, reaching Co concentrations up to 44vol.%. Interfaces with a low electronic transparency between superconductor and ferromagnet are obtained by a combination of the granular nature of the nanocomposites and the formation of Sn–Co alloys at the Sn/Co interfaces. The structure and composition of the nanocomposites have been thoroughly characterized by atomic force microscopy, X-ray diffraction and conversion electron Mössbauer spectroscopy. Over the entire Co concentration range, the hybrids show a ferromagnetic response. The superconducting phase boundary and the Meissner response depend on the morphology and composition of the nanocomposites. In particular, the superconducting critical temperature decreases with increasing Co concentration, while the Meissner response varies from a reversible to a strongly hysteretic behaviour depending on the morphology of the samples with different Co content. The persistence of superconductivity at high Co concentrations is attributed to a suppression of the superconducting proximity effect in these nanocomposites, which is ascribed to the low interface transparency between the Sn and Co components that make up these hybrid systems.

Granular and layered ferroelectric–ferromagnetic thin-film nanocomposites as promising materials with high magnetotransmission effect

Epitaxial thin films of granular and layered nanocomposites consisting of ferromagnetic perovskite Pr1–xSrxMnO3 and ferroelectric hexagonal LuMnO3 were grown on ZrO2(Y2O3) substrates using metal-organic chemical vapor deposition (MOCVD). A self-organized growth of the granular composite took place in situ as a result of phase separation of the Pr–Sr–Lu–Mn–O system into the perovskite and hexagonal phases. Optical transmission measurements revealed a large negative magnetotransmission effect in the layered nanocomposite over a wide spectral and temperature range. The granular nanocomposite unexpectedly showed an even larger, but positive, magnetotransmission effect at room temperature.

Influence of sputtering atmosphere on hopping conductance in granular nanocomposite (FeCoZr)x(Al2O3)1−x films

The present paper investigates conductivity σ for a wide temperature range of 2K<T<300K in the nanocomposite (FeCoZr)x(Al2O3)1−x films (1–6μm thicknesses, 0.30<x<1.00) which were sputtered on glass–ceramic substrates from the compound target in vacuum chamber filled with Ar (set 1 films) or Ar+O2 gas mixture (set 2 films). TEM and HRTEM images revealed that granular films of set 1 containing nanosized crystalline metallic bcc α-FeCo-based nanoparticles embedded in the amorphous Al2O3 matrix. In case of Ar+O atmosphere of deposited α-FeCo-based crystalline “cores” with stabilized sizes were covered with an amorphous FeCo-based oxide “shells”. The σ(T) dependences were found to be in agreement with this phase structure. They show transition of the set 1 films σ(T) curves with x from tunneling (hopping) behavior below the percolation threshold x<xC≈0.46 to metallic one for x>xC. Moreover, as opposed to such behavior, for the set 2 films hopping mechanism of σ(T) was revealed far beyond xC due to the formation of semiconducting FeCo-based oxide “shells” separating electrically contacting FeCoZr cores.

Biopolymer-reinforced synthetic granular nanocomposites for affordable point-of-use water purification

Creation of affordable materials for constant release of silver ions in water is one of the most promising ways to provide microbially safe drinking water for all. Combining the capacity of diverse nanocomposites to scavenge toxic species such as arsenic, lead, and other contaminants along with the above capability can result in affordable, all-inclusive drinking water purifiers that can function without electricity. The critical problem in achieving this is the synthesis of stable materials that can release silver ions continuously in the presence of complex species usually present in drinking water that deposit and cause scaling on nanomaterial surfaces. Here we show that such constant release materials can be synthesized in a simple and effective fashion in water itself without the use of electrical power. The nanocomposite exhibits river sand-like properties, such as higher shear strength in loose and wet forms. These materials have been used to develop an affordable water purifier to deliver clean drinking water at US $2.5/y per family. The ability to prepare nanostructured compositions at near ambient temperature has wide relevance for adsorption-based water purification.

Granular polymer composites

To advance our understanding of molecular packing in glassy nanocomposites, we adopt a macroscopic granular model—comprising spherical inclusions dispersed in ball-chain polymers—and ascertain from measurements of the bulk density the partial molar sphere volume at small but finite sphere volume fractions. By systematically varying the chain length, sphere size, and mixture composition, the ratio of the sphere radius to the chain loop size was found to be the primary dimensionless parameter that bridges solvent (small inclusion size) and continuum (large inclusion) scaling regimes. In the intermediate regime, where the inclusion and chain loop radius are comparable, the primary sphere–chain interaction increases free volume—up to twice the intrinsic inclusion volume per particle—and the primary sphere–sphere interaction decreases free volume. The results gleaned from these ‘granular nanocomposites’ may help to understand how geometrical constraints influence packing in dense granular systems and glassy molecular nanocomposites.

Effect of oxygen pressure on phase composition and magnetic structure of FeCoZr-Pb(ZrTi)O3 nanocomposites

The elemental and phase compositions and the magnetic state of metal particles in FeCoZr-Pb(ZrTi)O3 granular nanocomposites (GNCs) synthesized by ion-beam sputtering of composite targets in oxygen-containing media at different oxygen partial pressures have been studied. The phase transformations in GNCs have been monitored by the Raman and Mossbauer spectroscopy techniques. Correlation between the oxygen pressure during GNC synthesis and the valence state of iron ions in metal granules has been established. It has been confirmed that (i) the degree of metal oxidation increases with increasing oxygen pressure and (ii) the degree of crystallinity of oxides increases as a result of annealing. It has been established that the percolation threshold in GNCs can also be varied by changing the oxygen pressure during GNC synthesis.