Filtern
Erscheinungsjahr
Dokumenttyp
Sprache
- Englisch (14)
Schlagworte
- Nanocomposite (5)
- Supercapacitor (3)
- Ellipsometry (2)
- Fractography (2)
- Interlaboratory study (2)
- Ionic liquid (2)
- Mechanical properties (2)
- Photocatalyst (2)
- XPS (2)
- Atom transfer radical polymerization (1)
Organisationseinheit der BAM
Metal oxide/graphene photocatalysts have been attracting considerable attention in solving environmental pollution problems because of the limitations of the semiconductor-based photocatalysts. In this study, highly efficient and inexpensive zinc oxide (ZnO) nanoparticles with three different morphologies, such as nanospheres, nanodisks, and nanorods, anchored on reduced graphene oxide (RGO) were synthesized in solvent mixtures with different ethanol to water ratios. Among the three morphologies, the nanospherical ZnO/RGO (sZG) Composite exhibited the highest methylene blue (MB) and rhodamine B removal efficiencies at 99% and 98%, respectively, after only 60 min under low-power (40 W) ultraviolet irradiation at a low catalyst loading of 0.1 g L−1. This nanocomposite also showed excellent photocatalytic stability under UV irradiation, retaining 96% Efficiency even after 15 cycles of MB degradation. Moreover, the sZG composite exhibited a high MB degradation Efficiency of approximately 99% after 100 min at a low catalyst loading of 0.2 g L−1 under solar light illumination. The
excellent photocatalytic performance and high stability of this low-cost nanospherical ZnO/RGO Composite exemplarily highlights the potential of sustainable next-generation photocatalysis for treating wastewater containing organic pollutants.
A hybrid nanocomposite of magnetic nanoparticles (Fe3O4) and poly(2-hydroxyethyl methacrylate)-blockpoly(methyl methacrylate) (PHEMA-b-PMMA) was synthesized successfully by the atom transfer radical polymerization (ATRP) in an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6). Fe3O4 nanoparticles were first surface-modified with the initiator, 2-bromoisobutyryl bromide (BiBBr), in dimethylformamide (DMF) solvent, which produced the macro-initiator, Fe3O4-BiB, to initiate the polymerization reactions for the synthesis of the block polymer, PHEMA-b-PMMA. After immobilizing the Initiator on the surface of Fe3O4, the block polymer chains were grafted successfully onto the Fe3O4 surface, causing the Formation of a core-shell nanostructure. The incorporation of Fe3O4 in the nanocomposite was confirmed by attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The thermal stability and magnetic properties increased with increasing amount of Fe3O4 in the nanocomposite.
This paper reports the results of an international interlaboratory study sponsored by the Versailles Project on Advanced Materials and Standards (VAMAS) and led by the National Institute of Standards and Technology (NIST) on the measurement of water vapor sorption isotherms at 25 °C on a pelletized nanoporous carbon (BAM-P109, a certified reference material). Thirteen laboratories participated in the study and contributed nine pure water vapor isotherms and four relative humidity isotherms, using nitrogen as the carrier gas. From these data, reference isotherms, along with the 95% uncertainty interval (Uk=2), were determined and are reported in a tabular format.
The use of a biocompatible and thermoresponsive polymer, poly (2-hydroxyethyl methacrylate) (PHEMA) grafted onto the surface of graphene oxide (GO) as an adsorbent for the removal of a cationic dye (methylene blue [MB]) from an aqueous solution is examined in this work. GO–PHEMA forms a hydrogel in water thus overcoming the problem faced by carbon-based adsorbent materials during post-treatment (i.e., separation of adsorbent from the aqueous phase). The GO–PHEMA composite was synthesized using a green approach through dispersion polymerization in supercritical CO2. The successful preparation of this composite was confirmed by a series of characterization techniques. The adsorption behavior of the composite toward MB, such as the effect of the adsorbent dosage, pH, contact time, dye concentration, and recyclability was observed. In addition, the adsorption isotherm, kinetics and thermodynamics were investigated. According to the experimental data, the adsorption parameters were found to fit well into the Freundlich adsorption isotherm with a correlation coefficient of 0.975 and a maximum predicted adsorption capacity of 39.41 mg g−1 at 25 °C. The adsorption kinetics studies showed that the adsorption behavior followed a pseudo-second-order reaction. On the other hand, the thermodynamics studies showed that the adsorption of MB on GO–PHEMA composite followed spontaneous and endothermic adsorption process with an efficient adsorption temperature at 45 °C. The experimental results also showed that the GO–PHEMA composite could remove 99.8 % of the dye in 45 min. Therefore, GO–PHEMA composite is a favorable green adsorbent for environmental applications.
The present study investigated decoration of Cu(OH)₂ with different morphologies by copper precursors on 3D nickel foam. The Cu(OH)₂-A (nano flower)electrode showed an excellent capacitance of 1332 Fg⁻¹ at current density of 2 Ag⁻¹ compared to the Cu(OH)₂-C (nano ribbon, 1100 Fg⁻¹) and Cu(OH)₂-S (nano Long leaf, 1013 Fg⁻¹) electrodes. An asymmetric supercapacitor (ASC) was fabricated and showed a Maximum capacitance of 165 Fg⁻¹ at current density of 2 Ag⁻¹ with high energy density of 66.7 Wh kg⁻¹ and power density of 5698 W kg⁻¹ with excellent stability of 80 % after 10,000 cycles.
With the vast exploration of the applications of graphene, researchers are assessing different methods for fabricating graphene-based electrode material with high capacitance but low material and energy costs. In this study, reduced graphene oxide/nickel oxide (RGO/NiO) nanocomposites were prepared using a non-aqueous solvent-based method followed by calcination. Nickel acetate tetrahydrate and tert-butanol were used as the precursor and solvent, respectively. Ultrasmall nickel oxide nanoparticles, ca. 8.0 nm in size, were deposited on the surface of the graphene sheets simultaneously with the partial reduction of graphene oxide. The resulting RGO/NiO electrode exhibited a high capacitance of 689 F g⁻1 at a current density of 0.8 A g⁻1. After 1500 cycles, the specific retention and the coulombic efficiency yielded to 86.34% and 96.39%, respectively, which supports the viability of this composite as an alternative activated material with high electrochemical performance.
A simple and efficient method of preparing composites of carbon nanotubes and titania (CNT-TiO2) is reported via a microwave-assisted synthesis in an ionic liquid, [bmim][BF4]. CNT-TiO2 nanocomposites were formed by the thermal decomposition of titanium (IV) isopropoxide (Ti(OPri)4) in the presence of CNTs under microwave irradiation. The obtained product was characterized by BET surface area, XRD, SEM, and TEM. TiO2 particles with average size of 9 nm were as anatase. The surface area of the Composites increased with an increase of CNT content. Moreover, the catalytic efficiency of the composite was investigated through the photoelectrodegradation of methylene blue.
The continual increase in energy demand and inconsistent supply have attracted attention towards sustainable energy storage/conversion devices, such as electrochemical capacitors with high energy densities and power densities. Perovskite oxides have received significant attention as anion-intercalation electrode materials for electrochemical capacitors. In this study, hollow nanospheres of nonstoichiometric cubic perovskite fluorides, KNi1-xCoxF3-delta (x = 0.2; delta = 0.33) (KNCF-0.2) have been synthesized using a localized Ostwald ripening. The electrochemical performance of the non-stoichiometric perovskite has been studied in an aqueous 3 M KOH electrolyte to categorically investigate the fluorine-vacancy-mediated charge storage capabilities. High capacities up to 198.55 mA h g-1 or 714.8 C g-1 (equivalent to 1435 F g-1) have been obtained through oxygen anion-intercalation mechanism (peroxide pathway, O-). The results have been validated using ICP (inductively coupled Plasma mass spectrometry) analysis and cyclic voltammetry. An asymmetric supercapacitor device has been fabricated by coupling KNCF-0.2 with activated carbon to deliver a high energy density of 40 W h kg-1 as well as excellent cycling stability of 98 % for 10,000 cycles. The special attributes of hollow-spherical, non-stoichiometric perovskite (KNCF-0.2) have exhibited immense promise for their usability as anion-intercalation type electrodes in supercapacitors.
Zinc ferrite and graphene composites have attracted considerable attention in wastewater treatment. In this work, a magnetically separable mesoporous composite of ZnFe2O4 nanoparticles (NPs) and reduced graphene oxide (rGO) was prepared through a simple and eco-friendly method with pure water as solvent and without the need for subsequent thermal treatment. Uniformly dispersed ZnFe2O4 NPs on the surface of rGO sheets exhibited good crystallinity and a large BET specific surface area. These factors contributed to good photocatalytic performance of the composite for the degradation of methylene blue (MB) under simulated solar-light radiation, increased adsorptivity, increased separation efficiency of the photo-excited charges on the surface of the catalyst, and broadened light-absorption range of the composite. Efficient interfacial interaction between the ZnFe2O4 NPs and rGO sheets resulted in synergistic effects. The magnetically separable ZnFe2O4@rGO nanocomposite proved an efficient and stable catalyst in three consecutive photodegradation cycles for MB dye in aqueous solution under solar radiation. In addition, the synthesis method proposed in this study could be scaled-up easily due to the simplicity of the process, the lack of a toxic reagent, and the use of low temperatures.
Results are reported from a pilot study under the Consultative Committee for Amount of Substance (CCQM) to compare measurements of and resolve any relevant measurement issues in, the amount of thermal SiO2 oxide on (100) and (111) orientation Si wafer substrates in the thickness range 1.5 - 8 nm. As a result of the invitation to participate in this activity, 45 sets of measurements have been made in different laboratories using 10 analytical methods: medium-energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), XPS, SIMS, ellipsometry, grazing-incidence x-ray reflectrometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM). The measurements are made on separate sets of 10 carefully prepared samples, all of which have been characterised by a combination of ellipsometry and XPS using carefully established reference conditions and reference parameters.
The results have been assessed against the National Physical Laboratory (NPL) data and all show excellent linearity. The remaining data sets correlate with the NPL data with average root-mean-square scatters of 0.15 nm, half being better than 0.1 nm and a few at or better than 0.05 nm. Each set of data allows a relative scaling constant and a zero thickness offset to be determined. Each method has an inherent zero thickness offset between 0 nm and 1 nm and it is these offsets, measured here for the first time, that have caused many problems in the past. There are three basic classes of offset: water and carbonadeous contamination equivalent to ~1 nm as seen by ellipsometry; adsorbed oxygen mainly from water at an equivalent thickness of 0.5 nm as seen by MEIS, NRA, RBS and possibly GIXRR; and no offset as seen by XPS using the Si 2p peaks. Each technique has a different uncertainty for the scaling constant and consistent results have been achieved. X-Ray photoelectron spectroscopy has large uncertainties for the scaling constant but a high precision and, critically, if used correctly, has zero offset. Thus, a combination of XPS and the other methods allows the XPS scaling constant to be determined with low uncertainty, traceable via the other methods. XPS laboratories returning results early were invited to test a new reference procedure. All showed very significant improvements. The reference attenuation lengths thus need scaling by 0.986 ± 0.009 (at an expansion factor of 2) deduced from the data for the other methods. Several other methods have small offsets and, to the extent that these can be shown to be constant or measurable, then these methods will also show low uncertainty. Recommendations are provided for parameters for XPS, MEIS, RBS and NRA to improve their accuracy.
Mechanical and microstructural characterisation of multifunctional structural power composites
(2013)
Although the inherent anisotropy of polymer composites has presented daunting technical challenges, these materials now offer engineers considerable opportunities for efficient structural design. More recently, the advent of multifunctional composites which can fulfill more than one role within a system has attracted considerable interest, providing designers with exciting opportunities to innovate. Of particular interest here are structural power composites, which simultaneously carry mechanical load whilst storing/delivering electrical energy. Although the development of these composites is highly challenging, often with conflicting constituent requirements, the STORAGE consortium has had considerable success in the development of these materials for automotive applications.
The focus of this paper is structural supercapacitors, the basic architecture of a single cell of which is shown in Fig. 1. This entails two carbon fibre woven lamina (electrodes) which sandwich a glass fibre woven lamina (separator), all of which is embedded within a multifunctional matrix (electrolyte). This architecture has been the focus of the research to date, leading to components such as that shown in Fig.1 having been fabricated. This paper reports on the mechanical properties and microstructures of the different reinforcement and matrix combinations for structural supercapacitors.
Multifunctional composites which can fulfil more than one role within a system have attracted considerable interest. This work focusses on structural supercapacitors which simultaneously carry mechanical load whilst storing/delivering electrical energy. Critical mechanical properties (in-plane shear and in-plane compression performance) of two monofunctional and four multifunctional materials were characterised, which gave an insight into the relationships between these properties, the microstructures and fracture processes. The reinforcements included baseline T300 fabric, which was then either grafted or sized with carbon nanotubes, whilst the baseline matrix was MTM57, which was blended with ionic liquid and lithium salt (two concentrations) to imbue multifunctionality. The resulting composites exhibited a high degree of matrix heterogeneity, with the ionic liquid phase preferentially forming at the fibres, resulting in poor matrix-dominated properties. However, fibre-dominated properties were not depressed. Thus, it was demonstrated that these materials can now offer weight savings over conventional monofunctional systems when under modest loading.
Poly(p-phenylenediamine) (PpPD)/carboxylic acid-functionalized multiwalled carbon nanotubes (c-MWCNTs) nanocomposites were prepared by chemical oxidative polymerization using potassium persulfate (K2S2O8) as an oxidant. Field-emission scanning electron microscopy (FE–SEM) and field-emission Transmission electron microscopy (FE–TEM) showed that a tubular layer of PpPD was coated on the surface of carbon nanotubes with a thickness of 10–20 nm. FT–IR analysis provided an evidence for the formation of nanocomposites. The thermal stability of nanocomposites was improved by addition of c-MWCNTs as confirmed by thermogravimetric analysis (TGA). XRD spectra showed that the crystalline nature of PpPD was not affected much by the addition of c-MWCNTs. As the content of c-MWCNTs was increased, the electrical conductivity of the nanocomposites increased due to the interaction between polymer and nanotubes that enhances electron delocalization.