Academic literature on the topic 'Bi-metallic core-shell'

<p>Core-shell type magnetic nanoparticles are finding attractive applications in biomedicine, from diagnostic to cancer therapy. Both for targeted drug delivery and hyperthermia, as well as a contrast agent used for external biomedical imaging systems, small (&lt; 20 nm) superparamagnetic nanoparticles are desired. Some iron oxide nanoparticle formulations are already approved for human administration as contrast agent for magnetic resonance imaging. However, search continues for nanoparticles with higher saturation magnetisation. Metallic, bi-metallic and intermetallic magnetic nanoparticles are finding attention. Biocompatibility and optimal clearance are important criteria for the medical applications and therefore core-shell type particles are favored, where a biocompatible shell (e.g. polymer, Silica) can prevent inadvertent host reaction with the magnetic core. A recently developed novel synthesis method (electrochemical selective phase dissolution - ESPD), which can produce core-shell magnetic nanoparticles, is reviewed in this paper. ESPD, as the name suggests, uses electro-chemical separation of a phase from metallic alloys to synthesize nanoparticles. It is a versatile method and can be adopted to produce a wide range of nanostructures in addition to the core-shell magnetic nanoparticles.</p>

This study investigates the synthesis of mono metallic (copper and silver) and bi-metallic (copper/silver core/shell) conductive nanopigments for inkjet printing. Polyethylene glycol (PEG) was used as a main reducing agent followed by polyvinylpyrrolidone (PVP) as a capping and dispersing agent. From the XRD, TEM, and SEM analyses, the synthesized mono and bi metallic particles were con?rmed to be in a nano scale with particle size 7, 8.5 and 15.5 nm for copper, silver and copper/silver core/shell, respectively. The prepared nanopigments were included in inkjet ink formulation and printed on flexible polyethylene terephthalate (PET) films. The printed ink films were sintered at various temperatures (110, 150, 200). The results revealed that the resistivity of these particles was reduced by sintering and the resistivity of Cu, Ag and Cu/Ag patterns sintered in air at 200 ºC for 30 min were 3.1, 2.99 and 4.14 µ?-cm, respectively. The obtained results were in a good agreement with the published ones and insured the promising using of our products in metal-based inkjet printed circuit boards (PCB).

Metal nanoparticles encapsulated by silicate sol-gel matrix find numerous applications particularly in electrocatalysis and sensors. In our previous reports, we have reported the mono- and bi-metal gold, silver, and core/shell gold/silver nanoparticles embedded in functionalized silicate sol-gel matrices. Modified electrodes were fabricated using mono- and bi-metallic gold, silver, and core/shell gold/silver nanoparticles embedded in silicate sol-gel, and they were used for the electrocatalysis and sensing of H2O2 and simultaneous detection of hydrazine, sulfite, and nitrite. We have prepared the gold nanoparticles encapsulated by amine-functionalized silicate sol-gel matrix in a single step without using any external reducing agents. The gold nanoparticles were also synthesized by using amine-functionalized silane monomer in the presence of β-cyclodextrin (β-CD), resulting in metal/polymer core/shell nanostructures. This nanocomposite material showed a synergistic stabilizing effect when compared to either silicate sol-gel matrix or β-CD alone as stabilizer. The synthesized gold nanoparticles were characterized using UV–vis spectroscopy and high-resolution transmission electron microscopy. Modified electrodes were prepared by using the gold nanoparticles embedded in silicate sol-gel matrix, and their electrochemical characteristics were studied.

Classical molecular dynamics (MD) simulations were used to investigate how free surfaces, as well as supporting substrates, affect phase separation in a NiAg alloy. Bulk samples, droplets, and droplets deposited on a graphene substrate were investigated at temperatures that spanned regions of interest in the bulk NiAg phase diagram, i.e., miscible and immiscible liquid, liquid-crystal, and crystal-crystal regions. Using MD simulations to cool down a bulk sample from 3000 K to 800 K, it was found that phase separation below 2400 K takes place in agreement with the phase diagram. When free surface effects were introduced, phase separation was accompanied by a core-shell transformation: spherical droplets created from the bulk samples became core-shell nanoparticles with a shell made mostly of Ag atoms and a core made of Ni atoms. When such droplets were deposited on a graphene substrate, the phase separation was accompanied by Ni layering at the graphene interface and Ag at the vacuum interface. Thus, it should be possible to create NiAg core-shell and layer-like nanostructures by quenching liquid NiAg samples on tailored substrates. Furthermore, interesting bimetallic nanoparticle morphologies might be tuned via control of the surface and interface energies and chemical instabilities of the system.

Thermoelektrische Phänomene können in Nanomaterialien im Vergleich zum Volumenmaterial stark modifiziert werden. Die Bestimmung der elektrischen Leitfähigkeit, des absoluten Seebeck-Koeffizienten (S) und der Wärmeleitfähigkeit ist eine wesentliche Herausforderung für die Messtechnik in Hinblick auf Mikro- und Nanostrukturen aufgrund dessen, dass die Transporteigenschaften vom Volumenmaterial sich durch Oberflächen- und Einschränkungseffekte verändern können. Im Rahmen dieser Abschlussarbeit wird der Einfluss von Größeneffekten auf die thermoelektrischen Eigenschaften von dünnen Platinschichten untersucht und mit dem Volumenmaterial verglichen. Dafür wurde eine Messplattform als standardisierte Methode entwickelt, um S einer dünnen Schicht zu bestimmen. Strukturelle Eigenschaften wie Schichtdicke und Korngröße werden variiert. Grenz- und Oberflächenstreuung reduzieren S der dünnen Schichten im Vergleich zum Volumenmaterial. Außerdem wird eine Methode demonstriert um S von einzelnen metallischen Nanodrähten zu bestimmen. Für hochreine und einkristalline Silber-Nanodrähte wird der Einfluss von Nanostrukturierung auf die Temperaturabhängigkeit von S gezeigt. Ein Modell ermöglicht die eindeutige Zerlegung des temperaturabhängigen S von Platin und Silber in einen Thermodiffusions- und Phononen-Drag-Anteil. Des Weiteren werden die thermoelektrischen Transporteigenschaften von einzelnen auf Bismut-basierenden Kern/Hülle-Nanodrähten untersucht. Der Einfluss des Hüllenmaterials (Tellur oder Titandioxid) und der räumlichen Dimension des Nanodrahts auf die Transporteigenschaften wird diskutiert. Streuung an Oberflächen, Einkerbungen und Grenzflächen zwischen dem Kern und der Hülle reduzieren die elektrische und thermische Leitfähigkeit. Eine Druckverformung induziert durch die Hülle kann zu einer Bandöffnung bei Bismut führen, sodass S gesteigert werden kann. Das Kern/Hülle-System zeigt in eine Richtung, um die thermoelektrischen Eigenschaften von Bismut erfolgreich anzupassen.
Thermoelectric phenomena can be strongly modified in nanomaterials compared to the bulk. The determination of the electrical conductivity, the absolute Seebeck coefficient (S) and the thermal conductivity is a major challenge for metrology with respect to micro- and nanostructures because the transport properties of the bulk may change due to surface and confinement effects. Within the scope of this thesis, the influence of size effects on the thermoelectric properties of thin platinum films is investigated and compared to the bulk. For this reason, a measurement platform was developed as a standardized method to determine S of a thin film. Structural properties, like film thickness and grain size, are varied. Boundary and surface scattering reduce S of the thin films compared to the bulk. In addition, a method is demonstrated to determine S of individual metallic nanowires. For highly pure and single crystalline silver nanowires, the influence of nanopatterning on the temperature dependence of S is shown. A model allows the distinct decomposition of the temperature-dependent S of platinum and silver into a thermodiffusion and phonon drag contribution. Furthermore, the thermoelectric transport properties of individual bismuth-based core/shell nanowires are investigated. The influence of the shell material (tellurium or titanium dioxide) and spatial dimension of the nanowire on the transport properties are discussed. Scattering at surfaces, indentations and interfaces between the core and the shell reduces the electrical and the thermal conductivity. A compressive strain induced by the shell can lead to a band opening of bismuth increasing S. The core/shell system points towards a route to successfully tailor the thermoelectric properties of bismuth.

One of the key challenges in nanoparticle synthesis is the quality control on scaling up the operation from bench to plant scale, which is constrained by conventionally adopted batch operation. Translation from batch operation to continuous green synthesis (metal, bi-metallic core-shell, and alloy nanoparticles (NPs)) with low polydispersity index (PDI) could unlock potential applications of metallic nanostructures with a projected market of $40.6 Billion and more by 20271. However, the continuous large-scale production suffers from high polydispersity due to lack of process optimization. We attempt to address such scale-up challenges while using the green synthesis of metallic nanoparticles in this work. The objective of this thesis is to optimize continuous processing of metal nanoparticle synthesis and demonstrate application of metallic nanostructure printed of flexible substrate using inkjet printing technology. The first part of the thesis is motivated by the desire to translate the batch protocol for NPs synthesis (developed in our group earlier)2,3 to a continuous process, and hence increase the affordability of NPs for end users. In this work, nanoparticle colloids are synthesized using different designs of CFRs and steady-state synthesis of nanoparticles is achieved with insignificant variation in particle size. Our results further showed that a balance between engineering and chemical parameters are required to obtain desired particle size distribution (PSD) and morphology during green synthesis of NPs. We improved our reactor design from channel to pool-based to address poor reagent mixing and our results show that the pool reactors could produce uniform particles of sizeii 7.2±1.0 nm with the production rate of 7.1 mg/h. We later moved to a CSTR-based reactor to address variations in the particles’ morphology while changing the flow rate of precursor salt. We found that the CSTR-based reactor can synthesise colloids (Gold, Silver, bimetallic gold-silver core-shell, and gold-silver alloy) at higher (10 times) flow rates and offers a better and affordable route for continuous nanoparticles synthesis within numerous applications in the healthcare and energy sectors. For the first time, to the best of my knowledge, the steady-state synthesis of metal nanoparticles is demonstrated here. After attaining steady state, the particle size distribution does not vary significantly. Investigations are performed to find out the effect of engineering parameters as well as chemical parameters. Particle size distribution is more sensitive to chemical parameters in comparison to engineering parameters. Although, engineering parameters like reactor design, mixing, temperature are important parameters to tailor nanoparticle size in a controlled fashion. Hence, there must be a balance between both to get desired particle size and morphology. In the second part of the thesis, we demonstrated the application of in-situ fabricated silver nanowires on copier paper for non-enzymatic glucose, using a form of inkjet printing technology. The inkjet printing technique is another avenue of fabrication of nanostructure-based flexible substrates that can be scaled using roll to roll printing techniques. Using this technique, we could fabricate, and customize electroadhesive pads based on interdigitated electrode designs with an interelectrode distance of 1 mm on paper. It was observed that, if left as a residue, lateral silver ion migration on applying high voltage leads to lowering of the gaps between electrodes, which resultsiii in increased load capacity. Further electromigration can be controlled by chemical fixing of the sample, i.e., by immersing printed samples in 0.5 M Sodium thiosulphate. The advantage of this process is that different designs of electrodes can be easily fabricated depending upon the required application. The in-situ fabricated silver nanowires incorporated with CuO/Cu2O nanoparticles are used for non-enzymatic glucose detection. Non-enzymatic sensors (4th generation) can replace the enzymatic detectors (3rd generation)4, but major challenge associated with 4th generation detectors is that it requires alkaline pH for reaction to be initiated. Paper based standard electrode (Ag/AgCl); silver nanowire incorporated with CuO/Cu2O nanoparticles (synthesised by wet chemical method) are used as working electrode. Ag nanowires modified with CuO nanoparticles show a linear increment in current with increase in glucose concentration. Glucose detection is performed in the concentration range of normal sugar level in human body in the range from 2.2 – 6.6 mM.iv References: 1 Metal Nanoparticles - Global Market Trajectory & Analytics 2021, (19/09/2021). 2 Sivaraman, S. K., Kumar, S. Santhanam, V. Room-temperature synthesis of gold nanoparticles; Size-control by slow addition. Gold Bulletin 43, 275-286 (2010). 3 Sivaraman, S. K., Kumar, S. Santhanam, V. Monodisperse sub-10nm gold nanoparticles by reversing the order of addition in Turkevich method – The role of chloroauric acid. Journal of Colloid and Interface Science 361, 543-547 (2011). 4 Toghill, K. E. & Compton, R. G. Electrochemical non-enzymatic glucose sensors: a perspective and an evaluation. Int. J. Electrochem. Sci 5, 1246-1301 (2010).