Sinteza magneto-optičnih kompozitnih nanostruktur s spajanjem zlatih mikroploščic z magnetnimi heksaferitnimi nanoploščicami

magistrsko delo

Barbara Klun (Author), Darko Makovec (Mentor), Aleš Podgornik (Thesis defence commission member), Boštjan Genorio (Thesis defence commission member), Marjan Marinšek (Co-mentor)

Abstract

Magistrska naloga se osredotoča na sintezo magneto-optičnih kompozitnih delcev, ki so sestavljeni iz mikroploščic zlata in magnetnih nanoploščic barijevega heksaferita. Najprej sem sintetizirala obe vrsti delcev in jih nato spajala v kompozitne delce v etanolnih suspenzijah. Delce smo karakterizirali z različnimi metodami elektronske mikroskopije, merili magnetne lastnosti ter ovrednotili lastnosti suspenzij delcev (zeta potencial). Nanoploščice barijevega heksaferita sem sintetizirala po znani hidrotermalni metodi. Vodno suspenzijo Ba2+, Fe3+ in Sc3+ ionov, oborjenih ob velikem presežku hidroksilnih ionov, sem v zaprtem avtoklavu segrela do 240 °C. Sintetizirane nanoploščice (približno 50 nm široke in 3 nm debele) sem dispergirala v vodi s pomočjo adsorbirane citronske kisline in jih v suspenziji prevlekla z amorfnim silicijevim dioksidom s hidrolizo in polikondenzacijo tetraetoksi silana, ki sem mu dodala 3-merkaptopropiltrietoksisilan (približno 3 nm debela prevleka). S tem sem na površino magnetnih nanoploščic uvedla tiolne skupine, ki izkazujejo veliko afiniteto do površine zlata. Mikroploščice zlata sem sintetizirala z redukcijo tetrakloroaurične kisline v etilenglikolu z anilinom. Kot produkt sem v vzorcu poleg mikroploščic dobila tudi izotropne delce. Mikroploščice so bile široke več µm, a le nekaj deset nm debele. Izotropni delci so imeli obliko petkotne bipiramide velikosti okrog 1 μm. S sistematičnim spreminjanjem pogojev sinteze sem ovrednotila vpliv različnih parametrov, kot so temperatura, koncentracije reagentov in razmerje med reducentom anilinom in Au3+ delci, na morfologijo delcev produkta. Določila sem velikost obeh vrst delcev in ocenila volumsko razmerja med ploščatimi in izotropnimi delci. Za to sem razvila novo metodo, temelječo na računalniški obdelavi SEM slik. Rezultati analiz so pokazali, da tako mikroploščice kot izotropni delci nastanejo z mehanizmom pretirane rasti primarnih nanodelcev zlata, ki nastanejo ob hitri redukciji Au3+ pri povišani temperaturi. Pretirano rastejo nanodelci, ki vsebujejo ploskovne defekte – dvojčične meje (111). Kompozitne nanodelce sem sintetizirala z dodajanjem suspenzije zlatih mikroploščic v koloidno stabilno suspenzijo nanoploščic barijevega heksaferita v etanolu. Nanoploščice so se homogeno vezale na bazalne površine mikroploščic, predvidoma zaradi prevladujočih kemijskih interakcij med površinskimi tiolnimi skupinami na nanoploščicah in površino mikroploščic zlata. Zasedenost površine mikroploščic z nanoploščicami sem uravnavala s spreminjanjem koncentracije delcev v suspenzijah. Povezovanje med obema vrstama delcev je poteklo tudi elektrostatsko, brez predhodne funkcionalizacije silike na nanoploščicah s tiolini skupinami, vendar je bil nanos nanoploščic v tem primeru manj homogen. Kompozitne mikroploščice v suspenziji so se močno odzivale na zunanje magnetno polje. Zaradi prečnega permanentnega magnetnega momenta heksaferitnih nanoploščic so se kompozitne ploščice v suspenziji orientirale pravokotno na smer polja. To je omogočilo močan magneto-optični učinek v suspenziji kompozitnih nanoploščic – zlat odblesk suspenzije kompozitnih mikroploščic se močno spreminja glede na orientacijo magnetnega polja.

Keywords

magneto-optični nanodelci;kompozitni nanodelci;plazmonski nanodelci;magnetne lastnosti;nanoploščice barijevega heksaferita;zlate mikroploščice;magistrska dela;

Data

Language:	Slovenian
Year of publishing:	2020
Typology:	2.09 - Master's Thesis
Organization:	UL FKKT - Faculty of Chemistry and Chemical Technology
Publisher:	[B. Klun]
UDC:	620.3(043.2)
COBISS:	34138371
Views:	455
Downloads:	93
Average score:	0 (0 votes)
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Other data

Secondary language:	English
Secondary title:	Assembling gold microplatelets with hexaferrite magnetic nanoplatelets into magneto-optical composite nanostructures
Secondary abstract:	The work focuses on synthesis of magneto-optical composite particles combining gold microplatelets and barium-hexaferrite magnetic nanoplatelets. First, both types of particles were synthesized and subsequently assembled into the composite particles in ethanol suspensions. The particles were characterized by various methods of electron microscopy and with magnetic measurements. The colloidal properties of particles suspensions (e.g., zeta potential) were also evaluated. The barium-hexaferrite nanoplatelets were synthesized using a hydrothermal method. The Ba2+, Fe3+ and Sc3+ ions in the aqueous suspension were precipitated with a large excess of hydroxyl ions and heated to 240 °C in a closed autoclave. The synthesized nanoplatelets (approximately 50 nm wide and 3 nm thick) were dispersed in water using adsorbed citric acid and coated with a thin (approximately 3 nm thick) silica layer using hydrolysis and polycondensation of tetraethoxysilane (TEOS) in the suspension. A mixture of 3-mercaptopropyltriethoxysilane and the TEOS was used to introduce thiol groups on the surfaces of nanoplatelets. The thiol groups exhibit a high affinity towards a gold surface. Gold microplatelets were synthesized by reduction of tetrachloroauric acid with aniline in ethylene glycol. The product contained a mixture of microplatelets and isotropic particles. The microplatelets were several µm wide, but only a few tens of nm thick. The isotropic particles, approximately 1 μm in size, were of a pentagonal-bipyramidal shape. The size of both types of particles was measured from images acquired with a scanning electron microscope (SEM). A new method was developed for estimation of a volume ratio between the microplatelets and the isotropic particles based on digital processing of the SEM images. The influence of various parameters, e.g., the temperature, the concentrations of reagents and the aniline–to-Au3+ ratio, on the morphology of the particles was systematically evaluated. The analysis showed that both, the microplatelets and the isotropic particles were formed by a mechanism of exaggerated growth of primary gold nanoparticles, which were formed by rapid reduction of Au3+ at the elevated temperature. During the exaggerated growth the nanoparticles, which contained planar defects - (111) twin boundaries, grew on the expense of other nanoparticles. Composite nanoparticles were synthesized by mixing a suspension of the gold microplatelets into a colloidal suspension of the barium-hexaferrite nanoplatelets in ethanol. The nanoplatelets bonded homogeneously onto the basal surfaces of microplatelets, presumably with chemical interactions between the surface thiol groups on the nanoplatelets and the surfaces of gold microplatelets. The surface concentration of the nanoplatelets bonded on the microplatelets was controlled by changing the concentration of particles in the suspensions. Bonding between the two types of particles can also occur as the result of electrostatic interactions, i.e. without prior functionalization of the silica on the nanoplatelets with the thiol groups. However, the layer of nanoplatelets was less homogeneous in this case. The suspended composite microplatelets efficiently responded to the external magnetic field. Due to permanent magnetic moments of the hexaferrite nanoplatelets, which points perpendicular to the plate, the suspended composite platelets orient perpendicular to the direction of an applied magnetic field resulting in a strong magneto-optical effect. A golden glare of the suspension of composite microplatelets depends strongly on the strength and the orientation of magnetic field.
Secondary keywords:	magneto-optical composite nanoparticles;barium hexaferrite nanoplatelets;gold microplatelets;
Type (COBISS):	Master's thesis/paper
Study programme:	1000376
Embargo end date (OpenAIRE):	1970-01-01
Thesis comment:	Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo, smer Kemijsko inženirstvo
Pages:	63 str.
ID:	12044658