Synthesis and characterization magnetic nanoparticles for self-regulated magnetic hypertermia

Povzetek Doktorska disertacija prikazuje sintezne metode in karakterizacijo magnetnih nanodelcev Mg1+xFe2-2xTixO4, ki se lahko uporabljajo v samoregulativni magnetni hipertermiji. Mg1+xFe2-2xTixO4 je eden izmed redkih materialov, kateremu lahko s spreminjanjem sestave, spreminjamo Curie-jevo temperaturo in je glede na svojo sestavo biokompatibilen. V doktorski disertaciji so bile izbrane tiste sintezne metode, ki so ekonomično najcenejše in v industrijskem pogledu najenostavnejše, kot so soobarjanje, Pechini-jeva metoda, sinteza gorenja s samovžigom iz raztopin (glicin + nitrati) in hidrotermalna sinteza. Uporabljene so bile tudi nekatere nove metode oz. izpeljanke obstoječih, ki se do sedaj še niso uporabljale oz. o njih še ni nihče poročal. Pri vseh metodah, je bilo potrebno delce kalcinirat/sintrat, saj nastane material z zahtevanimi lastnostmi šele pri 900 °C. Hidrotermalna sinteza se ni izkazala za uspešno, kajti nastanejo hidroksidi in tudi amorfni magnetni nanodelci (eden od feritov), s čimer se poruši celotna sestava Mg1+xFe2-2xTixO4. Pri tako nizkih temperaturah (do 220 °C) ni možno ustvariti ferita s sestavo Mg1+xFe2-2xTixO4, kajti iz reaktantov delno nastane amorfni magnetni material (ferit), preostali reaktanti pa tvorijo najrazličnejše hidrokside. Tudi pogosto uporabljena sintezna metoda po Pechini-ju se pri mojih nanodelcih ni izkazala za uspešno, saj ne glede na razmerje med citronsko kislino in nitrati in pH raztopine, ne dobimo transparentnega gela, temveč se oborijo delci prekurzorjev. S tem je porušeno bistvo tega procesa, saj tako kovinski kationi niso enakomerno porazdeljeni po matrici/gelu. Kot uspešna metoda se je pokazala sinteza gorenja s samovžigom iz raztopin, kjer sem raztopino glicina in nitratov segreval do samovžiga. S spreminjanjem razmerja med glicinom in nitrati sem kontroliral temperaturo gorenja mešanice, kar se je videlo kot burno ali manj burno gorenje. Nekateri nanodelci so že po prvi stopnji izkazovali magnetizacijo, nekatere je bilo potrebno še dodatno sintrat. Pri tej metodi sem opazoval tudi vpliv mletja delcev pred sintranjem. Metoda soobarjanja je dala najboljše rezultate. Pri soobarjanju sem uporabil soli nitratov ali sulfatov in iz dobljenih rezultatov spoznali, da so sulfati bolj ugodni za sintezo prekurzorja, saj po kalciniranju in pregledu posnetkov s TEM-a dobimo homogenejše delce velikosti od 50 - 100 nm, medtem ko je pri sintezi z nitrati njihova velikost 100 - 200 nm. Pri soobarjanju sem preveril parameter vpliva izbrane baze (NaOH ali KOH), pri čemer sem s TEM posnetkov videl, da s KOH nastanejo nekoliko večji nanodelci. Uspešno sintetizirane nanodelce sem karakteriziral s pomočjo praškovnega difraktograma XRD, Curie-jevo temperaturo (TC) sem pomeril z modificirano termogravimetrično metodo (mTGA). Temperaturni odziv nanodelcev v zunanjem izmeničnem magnetnem polju sem izmeril v sestavljenem merilnem sistemu. Magnetne lastnosti sem pomeril z magnetometrom z vibrirajočim vzorcem (VSM) in SQUID magnetometrom (ZFC/FC meritve). Velikost magnetnih nanodelcev v raztopini sem pomeril z uporabo dinamičnega sipanja svetlobe (DLS).This doctoral dissertation shows the synthesis and characterization of magnetic nanoparticles of Mg1+xFe2-2xTixO4, which can be used as magnetic materials in self-regulating magnetic hyperthermia. Mg1+xFe2-2xTixO4 is one of the few materials with the abiliy to change the Curie temperature with changing material stoichiometry and it is composed of biocompatible elements. In this doctoral thesis I selected the economically most relevant synthetic methods that are feasible for large-scale (industrial) production, i.e. coprecipitation, Pechini method, solution combustion synthesis (SCS) (glycine + nitrates) and hydrothermal synthesis. In the frame of this work, novel methods or their related methods were applied in combination with calcination or sintering, since the desired properties of Mg1+xFe2-2xTixO4 are generated at 900 °C or higher. High temperature hydrothermal treatment favored the formation of metal hydroxides and magnesium ferrite nanoparticles, while it was imposible to obtain the desired Mg1+xFe2-2xTixO4 composition at low hydrothermal temperature (220 °C). Furthermore, the Pechini method did not produce transparent gels due to precipitation of the precursor, leading to nonuniform distribution throughout the organic matrix. The new method was solution combustion syntheses using a mixture of glycine as fuel with dissolved metal nitrates as a source of oxygen that was heated up until self ignition occurs. Through variation of the ratio of glycine and nitrates I was able to control the combustion temperature of the mixture. Nanoparticles produced during violent combustion already showed good magnetization and nanoparticles with less treatment still needed additional sintering. In some cases I also grinded nanoparticles prior to sintering to follow the effect on particle size. In this respect, the coprecipitation method provided the best results using the nitrate or sulfate salts as reactants. I observed that sulfates are more beneficial for the synthesis of the precursor, yielding homogeneous nanoparticles with sizes ranging from 50 to 100 nm after calcination, while the synthesis of nitrates allowed production of nanoparticles with sizes ranging from 100 to 200 nm. With coprecipitation I followed the influence of the base (NaOH or KOH) on nanoparticles and from TEM images I saw that KOH produces slightly larger nanoparticles. Successfully synthesized nanoparticles were characterized by X-Ray powder diffraction and the Curie temperature was measured by a modified thermogravimetrc analysis (mTGA). Temperature response of nanoparticles in an external alternating magnetic field was measured in the assembled measuring system. Magnetic properties were determined with a magnetometer with vibrating model (VSM) and the SQUID magnetometer (ZFC/FC measurements). The size (hydrodynamic diameter) of the magnetic nanoparticles in the solution was measured using a dynamic light scattering (DLS)