Proučavanje procesa sinteze i svojstava višefaznih oksidnih prahova dobijenih hidrotermalnim procesiranjem

Abstract

Doktorska disertacija obuhvata istraživanja fundamentalnih aspekata i strategija sinteze koloidnih nanokristala, nanostruktura i submikronskih kristala nekoliko neorganskih oksidnih materijala i zlata, hidrotermalnim i solvotermalnim procesima. Motivacija za istraživanja je opšti naučni interes za poznavanjem mehanizama sinteze koloidnih nanokristala i rasta kristala u hidrotermalnim i solvotermalnim uslovima u cilju uspostavljanja metoda kontrolisane sinteze homogenih i heterogenih funkcionalnih nanostruktura. Dalja istraživanja su vođena u dva pravca, formiranje različitih struktura višeg reda supramolekulskim interakcijama i potencijalna implementacija sintetisanih materijala u praksi. Materijal koji je po obimu najviše bio zastupljen u istraživanjima koja su obuhvaćena doktorskom disertacijom je kalcijum hidroksiapatit (HAp) i njegovi parcijalno supstituisani derivati sa jonima Co2+ (CoHAp) i Zr4+/ZrO2 (ZrHAp). Ispitana je sinteza HAp, CoHAp i ZrHAp u hidrotermalnom sistemu bez prisustva organskih supstanci. Uračena je detaljna karakterizacija uzoraka metodama kao što su rendgenska difrakcija na prahu (XRD), laserska difrakcija (LD), atomska spektroskopija (ICP AS) i skanirajuća elektronska mikroskopija (SEM). U nastavku istraživanja, ekstenzivno su ispitani HAp i CoHAp sa različitim udelima supstituisanog kobalta u strukturi u in vitro i in vivo biološkim uslovima kao funkcionalnog materijala za reparaciju oštećenog koštanog tkiva mandibule pacova. Dobijeni rezultati pokazuju da sinergistiĉki efekti u biološkim sistemima prilikom implantacije CoHAp materijala, omogućavaju iznenađujuće brzu regeneraciju i povećanje gustine koštanog tkiva. Ispitana je mogućnost sinteze ambifilnih nanočestica HAp u kombinovanom dvofaznom hidrotermalnom sistemu uz pomoć trietanolamina i oleinske kiseline. Karakterizacija uzoraka LD, SEM i infracrvenom spektroskopijom sa Furijeovom transformacijom (FTIR), kao i makroskopska svojstva, potvrdila su da sintetisane ĉestice HAp imaju dvostruku polarnost, što je pokazano stabilizacijom Pikeringovih emulzija za primenu u nanobiotehnologiji. Drugi, veći deo istraživanja, se odnosi na okside gvožđa. Detaljno je istražena kombinovana jednofazna i dvofazna solvotermalna hidrolitiĉka metoda u smeši rastvaraĉa za sintezu koloidnih nanokristala magnetita. U zavisnosti od prekursora i odnosa rastvaraĉa, dobijeni su monodisperzni alkil – terminisani superparamagnetni nanokristali oksida gvožđa (SPION's) veličine od 5 nm do 20 nm. Ovo je potvrđeno metodama kao što su XRD, FTIR, transmisiona elektronska mikroskopija (TEM), elektronska difrakcija (ED), dinamičko rasejanje svetlosti (DLS) i magnetometrija sa vibrirajućim uzorkom (VSM). Nanokristali veličine 5 nm imaju magnetizaciju saturacije 40 emu/g. Alkil – terminisani SPION's su imobilisani u polimernu matricu poli-L-laktida:polietilenimina i dobijene su stabilne disperzije hibridnih magnetnih nanočestica u vodi, sa česticama veličine oko 200 nm. Sve ovo je takoće potvrđeno TEM, ED i LD tehnikama. Sintetisani SPION's su takoĊe upotrebljeni za sintezu hetero nanodimera zlato – magnetit. Dimer je karakterisan TEM i UV – VIS spektroskopijom. Submikronski kristali hematita α – Fe2O3 oblika pločica sintetisani su hidrotermalnom metodom. Kristalografska analiza je pokazala da pločice imaju preferentni rast duž [012] kristalografskog pravca. Usmereni rast pločica je postignut dodavanjem male koliĉine oleatnog liganda u sistem. Pomoću magnetnih merenja ustanovljeno je da je vrednost koerecitivnosti ovih pločica veća u poređenju sa kompaktnim hematitom. Magnetna svojstva ovih struktura su u jakoj korelaciji sa njihovom morfologijom, što je bilo predmet daljih istraživanja. Sledeće, ispitana je hidroliza molekulskog prekursora Fe(III) – oleata u dvofaznom sistemu i taloženje nanostrukturnog litijum gvožđe fosfata LiFePO4 u hidrotermalnim uslovima. Taloženje je omogućeno mehanizmom redukcionog rastvaranja produkta hidrolize u enkapsuliranoj vodenoj fazi. Uspostavljena metoda je pokazala sofisticiranost, ekonomičnost potrošnje litijuma i visok stepen reproducibilnosti. Cikliranjem materijala bez dodatnog tretmana u bateriji pri strujama od C/20 na 55 °C, ustanovljeno je da je njegov kapacitet 80 % teorijskog. Predložena je modifikacija metode koja će se dalje ispitati. Ispitane su mogućnosti sinteze plazmonskih nanokristala, konkretno, nanokristala zlata u jednostavnom solvotermalnom sistemu sa oleilaminom u funkciji liganda, rastvarača, reducenta i vodom kao reaktantom. Rasvetljen je mehanizam redukcije i izvedeni su bitni zaključci. Metoda se pokazala efektivnom za sintezu monodisperznih hidrofobnih nanokristala zlata veličine 7 nm, što je potvrđeno TEM, ED, DLS i UV – VIS tehnikama. Nanokristali Au su solubilizovani lipidima MHCP, DPPE – PEG2k i DGS – NTA(Ni) i konjugovani putem specifičnog vezivanja za inženjerisane nanokaveze feritina. Ovo je takođe potvrđeno TEM i DLS metodama. I na kraju, dodatno je ispitana mogućnost katalitiĉkog i fotokatalitičkog nagrizanja Si za dobijanje poroznog fotoluminiscentnog (PL) silicijuma. Ovo je postignuto impregnacijom površine hidrofobnim nanokristalima Au. Dobijene su porozne strukture i 1D nanostrukture Si,ultraduge nano – žice debljine između 40 i 60 nm, što je potvrđeno SEM analizom. Nanostrukture Si imaju ogroman potencijal u biomedicinskim i drugim tehnološkim primenama. Istraživanja hidrotermalnih i solovtermalnih postupaka za sintezu nanostrukturnih materijala koji su prikazani u disertaciji pokazuju relativnu sloţenost ovih metoda, ali i njihovu veliku mogućnost i superiornost u odnosu na druge metode dizajniranja ovakvih struktura na molekulskom nivou sa ciljanim morfološkim, fizičkim i hemijskim svojstvima.

The PhD thesis includes research of the fundamental aspects and the synthetic strategies of colloidal nanocrystals, nanostructures and submicron crystals of several inorganic oxide materials and gold element obtained by hydrothermal and solvothermal processes. The motivation for the research was the general scientific interest for understanding the mechanisms of the colloidal nanocrystals synthesis and the crystal growth in hydrothermal and solvothermal conditions, in order to establish controlled synthesis of homogeneous and heterogeneous functional nanostructures. The following investigations were conducted in two directions, the first one was the formation of various structures of higher orders by supramolecular interactions, and the other was the potential implementation of the synthesized materials in practice. The most used materials in the research included in this thesis were calcium hydroxyapatite (HAp) and its derivates, the partial substituent with Co2+ (CoHAp) and Zr4+/ZrO2 (ZrHAp). The synthesis of HAp, CoHAp and ZrHAp were investigated in hydrothermal system without any presence of organic compounds. The detailed characterization of samples was performed using methods such as X – ray powder diffraction (XRD), the laser diffraction (LD), atomic spectroscopy (ICP AS) and scanning electron microscopy (SEM). In addition, the extensive study of HAp and CoHAp was conducted in vitro and in vivo in the biological environment to examine functional properties of these materials for bone damage reparation in rat’s mandible. Obtained results shows that synergistic effects in biological systems, when implanting CoHAp material, enable unexpectedly fast regeneration and improve density of bone tissue. The possibility of ambiphilic HAp nanoparticle synthesis was investigated in combined two phase hydrothermal system using triethanolamine and oleic acid. The characterization of dispersions by SEM and LD, using Fourier transformed infrared spectroscopy, as well as macroscopic properties confirmed that synthesized HAp nanoparticles have hydrophilic as well as hydrophobic properties. Also it was demonstrated by stabilization of Pickering emulsion for nanobiotechnology application. The second larger part of the research was related to iron oxides. The combined one and two phase solvothermal hydrolitic method for synthesis of colloidal magnetite nanocrystals in mixtured solvent was detaily examined. Regarding of precursor and solvents ratio, different sizes, from 5 nm up to 20 nm, of monodispersed alkyl – terminated superparamagnetic iron oxide nanocrystals (SPION's) were produced. This was confirmed by means of methods such as XRD, FTIR, transmision electron microscopy (TEM), electron diffraction (ED), dinamic light scattering (DLS) and vibrating sample magnetometry (VSM). The 5 nm sized nanocrystals have saturation magnetization of ~ 40 emu/g. The alkyl – terminated SPION’s were immobilized in polymeric matrix of poly-Llactide: polyethylenimine. The stabile dispersions of hybrid magnetic nanoparticles in water were obtained, contaning of 200 nm sized particles. All of this was confirmed also by TEM, ED and LD techniques. The synthesized SPION’s were also used for hetero nanodimmer gold – magnetite synthesis. The dimmer was characterized using TEM and UV – VIS spectroscopy. Plate–like shaped submicron crystals of hematite α – Fe2O3 were synthesized by hydrothermal method. Crystallographic analysis revealed that growth of platelets was oriented in [012] crystallographic direction. Oriented growth was achieved by adding small amounts of oleate ligand in system. Measurements established that coercivity value of these platelets is higher than for bulk hematite. Magnetic properties of these structures are strongly, correlated with morphology which, was the subject of further research. Furthermore, hydrolysis of molecular precursor Fe(III) – oleate in two phase system and precipitation of nanostructured lithium iron phosphate LiFePO4 in hydrothermal conditions were examined. The precipitation was enabled by mechanism of reductive dissolution of hydrolysis product in encapsulated water phase. The established method demonstrated sophistication, chemical efficiency of lithium consumption and high degree of reproducibility. Galvanostatic cycling of battery made out of ―as prepared‖ material on 55 oC, showed capacity of 80% of theoretical at rate of C/20. Modification of the method was also proposed and will be examined. The plasmonic nanocrystals was also investigated, specifically, gold nanocrystals in simple solvothermal system using oleylamine as ligand, solvent, reducing agent and water as reactant. The reduction mechanism was elucidated and some important remarks were made. The method was proven to be effective for synthesis of monodispersed hydrophobic Au nanocrystals (7 nm in sizes), which was confirmed by TEM, ED, DLS and UV – VIS techniques. Au nanocrystals were solubilized by MHCP, DPPE – PEG2k and DGS – NTA(Ni) lipids, and conjugated by specific binding to engineered ferritin nanocages. This is also confirmed using TEM and DLS methods. Finnaly, possibility of catalitic and photocatalitic etching of Si wafers to obtain porous photoluminescent (PL) silicon were examined. This is achieved by impregnation of wafer surface with hydrophobic Au nanocrystals. Porous structures and 1D nanostructures of Si, ultra –long nanowires from 40 nm to 60 nm ticknes, were obtained, which was confirmed by SEM analysis. Silicon nanostructures have great potential in biomedical and other technological applications. The study of hydrothermal and solvothermal synthesis processes of nanostructured materials presented in the thesis, demonstrated relative complexity of these methods and their great ability and superiority over other methods of designing such structures at molecular level with controllable morphological, physical and chemical properties.