Structural and functional properties of spinel oxide-based materials

U ovoj doktorskoj disertaciji detaljno je ispitan uticaj metoda sinteze, oblaganja sintetisanih čestica isinterovanja na magnetna i električna svojstva kako funkcionalizovanih spinelnih oksida, tako injihovih kompozita, a u cilju njihove primene, sa akcentom na biomedicinsku upotrebu. Jedan deoistraživanja posvećen je magnetnim svojstvima skrobom funkcionalizovanih kobalt-ferita (CoFe2O4)sintetisanih na pet različitih načina (metodom koprecipitacije, mehanohemijski, metodomkoprecipitacije potpomognute ultrazvukom, metodom mikroemulzije i mikrotalasno potpomognutimhidrotermalnim metodom). Dobijeni materijali su detaljno strukturno i morfološki okarakterisanistandardnim tehnikama. Utvrđeno je da metod sinteze kao i način oblaganja značajno utiče namagnetna svojstva. Prateći uspešnost oblaganja i efekat aglomeracije preko pokazanih magnetnihsvojstava, predloženi su najbolji materijali za primenu u magnetnoj rezonantnoj tomografiji. Drugideo istraživanja bio je posvećen magnetoelektričnim perovskit/spinel kompozitima. Detaljno jeispitan uticaj metoda sinteze, faznog sastava i temperature sinterovanja na električna svojstvaBaTiO3/CoFe2O4 i BaTiO3/NixZn1-xFe2O4 kompozita. Ispitana je struktura i morfologija materijalapre i posle sinterovanja. Odnos perovskit/ferit faza imao je presudan uticaj na električna svojstvasintetisanih kompozita. Ispitivanje električnih svojstava na ovim kompozitima može predstavljatidobar screening metod za odabir magnetoelektričnih materijala kao višefaznih multiferoika zasavremene primene u tehnologiji i/ili medicini.This doctoral dissertation deals with detailed investigation of synthesis methods, coating and sinteringeffects on magnetic and electrical properties of spinel oxide-based nanomaterials for the applicationsin biomedical field. Part of the investigations included magnetic properties study of starch-coatedcobalt-ferrite (CoFe2O4) nanoparticles prepared by five different routes (coprecipitation,mechanochemical, ultrasonically assisted coprecipitation, microemulsion, and microwave-assistedhydrothermal syntheses). The synthesized materials were thoroughly characterized by standardtechniques. The general conclusion was that the way of coating alongside with chosen preparationmethod had a crucial role for magnetic properties. The magnetic measurements served as a goodplatform to monitor agglomeration and coating effects, which helped to choose materials with bestperformances for applications in magnetic resonance imaging (MRI). Another part of theinvestigations was devoted to the influence of synthetic method, phase composition and sinteringtemperature on BaTiO3/CoFe2O4 and BaTiO3/NixZn1-xFe2O4 electrical properties. The structure andmorphology of as-prepared and sintered samples were examined in detail. The optimalperovskite/spinel phase ratio is a key factor for prominent electrical properties. The electricalmeasurements performed on this type of composites might be a good screening test for choosingmagnetoelectric material for further investigations including usage in technology and/or medicine

Structural and functional properties of spinel oxide-based materials

U ovoj doktorskoj disertaciji detaljno je ispitan uticaj metoda sinteze, oblaganja sintetisanih čestica isinterovanja na magnetna i električna svojstva kako funkcionalizovanih spinelnih oksida, tako injihovih kompozita, a u cilju njihove primene, sa akcentom na biomedicinsku upotrebu. Jedan deoistraživanja posvećen je magnetnim svojstvima skrobom funkcionalizovanih kobalt-ferita (CoFe2O4)sintetisanih na pet različitih načina (metodom koprecipitacije, mehanohemijski, metodomkoprecipitacije potpomognute ultrazvukom, metodom mikroemulzije i mikrotalasno potpomognutimhidrotermalnim metodom). Dobijeni materijali su detaljno strukturno i morfološki okarakterisanistandardnim tehnikama. Utvrđeno je da metod sinteze kao i način oblaganja značajno utiče namagnetna svojstva. Prateći uspešnost oblaganja i efekat aglomeracije preko pokazanih magnetnihsvojstava, predloženi su najbolji materijali za primenu u magnetnoj rezonantnoj tomografiji. Drugideo istraživanja bio je posvećen magnetoelektričnim perovskit/spinel kompozitima. Detaljno jeispitan uticaj metoda sinteze, faznog sastava i temperature sinterovanja na električna svojstvaBaTiO3/CoFe2O4 i BaTiO3/NixZn1-xFe2O4 kompozita. Ispitana je struktura i morfologija materijalapre i posle sinterovanja. Odnos perovskit/ferit faza imao je presudan uticaj na električna svojstvasintetisanih kompozita. Ispitivanje električnih svojstava na ovim kompozitima može predstavljatidobar screening metod za odabir magnetoelektričnih materijala kao višefaznih multiferoika zasavremene primene u tehnologiji i/ili medicini.This doctoral dissertation deals with detailed investigation of synthesis methods, coating and sinteringeffects on magnetic and electrical properties of spinel oxide-based nanomaterials for the applicationsin biomedical field. Part of the investigations included magnetic properties study of starch-coatedcobalt-ferrite (CoFe2O4) nanoparticles prepared by five different routes (coprecipitation,mechanochemical, ultrasonically assisted coprecipitation, microemulsion, and microwave-assistedhydrothermal syntheses). The synthesized materials were thoroughly characterized by standardtechniques. The general conclusion was that the way of coating alongside with chosen preparationmethod had a crucial role for magnetic properties. The magnetic measurements served as a goodplatform to monitor agglomeration and coating effects, which helped to choose materials with bestperformances for applications in magnetic resonance imaging (MRI). Another part of theinvestigations was devoted to the influence of synthetic method, phase composition and sinteringtemperature on BaTiO3/CoFe2O4 and BaTiO3/NixZn1-xFe2O4 electrical properties. The structure andmorphology of as-prepared and sintered samples were examined in detail. The optimalperovskite/spinel phase ratio is a key factor for prominent electrical properties. The electricalmeasurements performed on this type of composites might be a good screening test for choosingmagnetoelectric material for further investigations including usage in technology and/or medicine

Ispitivanje ponašanja ferofluida pod uticajem spoljašnjeg magnetnog polja

Predstavljena su merenja transmitancije prilikom propuštanja bele svetlosti i laserskog snopa na 655 nm pod uticajem spoljašnjeg magnetnog polja kroz nanočestice CoFe2O4, FeFe2O4 i MgFe2O4 obložene citratom i oleatom. Za istraživanje ponašanja ferita u ferofluidu pod uticajem spoljašnjeg magnetnog polja jačine od 30 do 400 mT razvijeni su novi eksperimetalni uslovi. Spoljašnje magnetno polje izaziva promenu transmitancije i pojavu taloženja kod svih uzoraka. Nasuprot linearnim agregatima koji se stvaraju kod CoFe2O4 i FeFe2O4 u slučaju MgFe2O4 se stvaraju sferni agregati. Kod sva tri uzorka modifikacija feritne površine oblogom uzrokuje smanjenje dipol-dipol interakcija između feritnih jezgara, a samim tim su uočeni i manji agregati kod obloženih uzoraka. U poređenu sa uzorcima obloženim citratom, uzorci obloženi oleatom pokazuju manji efekat pod uticajem spoljašnjeg magnetnog polja. Agregacija nanočestica može potencijano povećati citotoksičnost. Pošto MgFe2O4 gradi sferne agregate može se zaključiti da njegovo izlučivanje iz organizma može biti lakše i brže kada se koristi u dijagnostici ili terapiji. Stoga bi trebalo više pažnje posvetiti primeni MgFe2O4 u biomedicinske svrhe.Light transmitting measurements of white light and consequentially chosen laser beam of 655 nm propagating through citrate and oleate coated CoFe2O4, FeFe2O4 and MgFe2O4 nanoparticles, under the influence of an external magnetic field, were presented. New experimental settings were developed for the study of behavior of ferrites in ferrofluid with the applied magnetic field strength in the range of 30-400 mT. Magnetic fieldinduced change of transmittance occurred and a precipitation of all studied samples was obtained. Contrary to the linear aggregates of colloidal CoFe2O4 and FeFe2O4, approximately spherical aggregates were observed in the case of MgFe2O4. In all three cases, the surface modification resulted in decreased dipole-dipole interactions between ferrite cores, and thus less precipitates were noticed. All oleate coated nanoparticles have shown weaker magnetic response in comparison to the citrate encapsulated samples. The aggregation of nanoparticles potentially increases cytotoxicity. Regarding non-linear clustering of MgFe2O4 suspensions, it can be concluded that its excretion from the organism could be likely easier and faster when used in diagnosis and/or therapy. Therefore, more attention should be paid to the low toxic MgFe2O4 for its medical application

BaTiO3/NixZn1-xFe2O4 (x =0, 0.5, 1) composites synthesized by thermal decomposition: The influence of phase composition on their magnetic and electrical properties

To examine the influence of phase composition on the magnetic, dielectric, and ferroelectric properties of perovskite/spinel composites, NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4 were in situ prepared by thermal decomposition onto BaTiO3 surface. Acetylacetonate complexes were used as the precursors. The synthesized powders were compressed to pellets and additionally sintered at 1150 °C and 1300 °C. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS) were used for the comprehensive study of phase composition and morphology. The magnetic and electrical properties were performed in detail. The optimal phase composition was found in the BaTiO3/NiFe2O4 composite sintered at 1150 °C. This resulted in wide frequency range stability of relative dielectric constant. Furthermore, optimal phase composition in BaTiO3/NiFe2O4 led to suitable properties such as low conductivity and ideal-like hysteresis loop behavior. These functional properties of BaTiO3/NiFe2O4 make this composite a promising candidate for further studies on multiferroic properties

The influence of strontium content and sintering temperature on monazite stability

This paper shows a simple way to synthesize a series of Ce1-xSrxPO4 ceramic materials using acetate solutions of Ce and Sr instead of nitrate which were used so far. For synthesis, the preparation method was used by simple mixing of acetate solutions of Ceand Sr(, with NaH2PO4 at room temperature, and the studied compositions were Ce1-xSrxPO4 (where x = 0, 0.1, 0.2, 0.3, 0.4, 0.5). The disintegration of Sr in monazite structures in different sintering temperature ranges from 600°C to 1000°C was investigated. The X-ray diffraction was used to track the evolution of the phase composition with thermal treatment. The morphology of sintered ceramics was obtained by scanning electron microscopy and vibrational bands of selected spectra were observed using the FT-IR method. Relative geometric density of selected samples was evaluated. The most favorable conditions for obtaining high-temperature Ce, Sr phosphate-based ceramic material are reported.У овом раду је приказан једноставан начин да се синтетише серија Ce1-xSrxPO4 керамичких материјала коришћењем ацетатних раствора Ce и Sr уместо до сада коришћених нитрата. За синтезу је коришћен метод припреме једноставним мешањем раствора Ce(C2H3O2)3·xH2O), Sr(C2H3O2)2, и NaH2PO4 као прекурсора на собној температури, а испитивани састави су Ce1-xSrxPO4 (где је к = 0 , 0,1, 0,2, 0,3, 0,4, 0,5). Испитивана је дезинтеграција Sr у структурама моназита у различитим температурним распонима синтеровања од 600 °C до 1000 °C. Дифракција рендгенских зрака на праху (XRD) је коришћена за праћење еволуције фазног састава синтетисаних и синтерованих узорака. Морфологија синтероване керамике испитивана је скенирајућом електронском микроскопијом (СЕМ), а вибрациое траке одабраних спектра су испитане ФТИР методом. Згушњавање и еволуција микроструктуре су одређене коришћењем релативне геометријске густине одабраних узорака. Приказани су најповољнији услови за добијање високотемпературног керамичког материјала на бази Ce, Sr фосфата

Semiconducting Co3O4 Nanocatalyst Prepared by Eco-Friendly Thermal Decomposition

The cobalt oxide (Co3O4) is a very attractive material for optoelectronic applications due to the intense absorption of visible light and p-type semiconducting properties. On the other hand, conventional synthesis methods for its preparation could be either time- and energy-consuming or relying on toxic chemicals. To address this issue, spinel Co3O4 nanoparticles were prepared by a simple, facile, and eco-friendly method of synthesis. Such method is based on the thermal decomposition of hexaaquacobalt(II) D-camphor10-sulfonate at 900 °C. This synthesis route avoids the use of toxic organic solvents which overcomes the disadvantages of many combustion methods. In order to assess the potential use of synthesized powder, the characterization methods were performed in detail. The purity and semiconducting properties of the Co3O4 were confirmed by UV/Vis spectroscopy which indicated the presence of two band gaps (2.10 eV and 1.22 eV). A noteworthy improvement in the electron transfer kinetics with the addition of the prepared sample to the carbon-paste electrode led to an enhanced electrocatalytic performance. Such remarkable functional properties are suitable for a wide range of technological applications, open the way for the implementation of this preparation procedure for the synthesis of Co3O4 on a larger industrial scale

Mechanochemically synthesized cobalt-ferrite and starch-coated cobalt-ferrite nanoparticles as efficient adsorbents for hexavalent chromium removal

Cobalt-ferrite (CoFe2O4) and starch-coated CoFe2O4 nanoparticles were prepared by the mechanochemical method and carefully chosen as adsorbents for Cr(VI) removal from wastewater. The kinetic study, adsorption isotherms and influence of pH, contact time and interfering ions were investigated to have deeper insight into adsorbent quality. UV/Vis spectroscopy confirmed that the dominant adsorption mechanism is the electrostatic attraction at lower pH values. The study showed there was no significant change in adsorption efficiency for starch-coated nanoparticles. However, starch as a natural and biocompatible compound can enhance nanoparticles water dispersibility. The advantage of such materials is that saturation time does not exceed 20 minutes. Therefore, the as-prepared and starch-coated CoFe2O4 presents very efficient material for application in the field of water remediation

Spectral analysis of external magnetic field influence on magnetic oxide nano-particles in ferrofluid

Light transmitting measurements of white light and laser beam propagating through FeFe2O4, CoFe2O4 and MgFe2O4 nanoparticles coated with starch, citric and oleic acid, under the influence of an external magnetic field in the range of 30-400 mT, were presented. The unexpected and unusually large changes of transmitted light occurred. This can be explained by the model based on ordering of magnetic moments of nano-particles along the lines of magnetic field into magnetic chains and organization of magnetic chains into spatial structure - a quasi-lattice. Under the influence of external magnetic field, a precipitation of all studied samples was obtained. To the best of our knowledge, the field-induced precipitation effect of ferrites in ferrofluid was not analysed so far and its significance and influence on the further laser treatment of patients previously exposed to ferrite-based MRI agents is not well recognized. This should be of great importance, since neglecting of the precipitation effect would lead to inappropriate response when patients are exposed to diagnostic and/or therapy procedures

Mechanochemically synthesized cobalt-ferrite and starch-coated cobalt-ferrite nanoparticles as efficient adsorbents for hexavalent chromium removal

Cobalt-ferrite (CoFe2O4) and starch-coated CoFe2O4 nanoparticles were prepared by the mechanochemical method and carefully chosen as adsorbents for Cr(VI) removal from wastewater. The kinetic study, adsorption isotherms and influence of pH, contact time and interfering ions were investigated to have deeper insight into adsorbent quality. UV/Vis spectroscopy confirmed that the dominant adsorption mechanism is the electrostatic attraction at lower pH values. The study showed there was no significant change in adsorption efficiency for starch-coated nanoparticles. However, starch as a natural and biocompatible compound can enhance nanoparticles water dispersibility. The advantage of such materials is that saturation time does not exceed 20 minutes. Therefore, the as-prepared and starch-coated CoFe2O4 presents very efficient material for application in the field of water remediation

Crystal chirality – cobalt complexes with thiazole based derivatives

Hiralnost je izraženo svojstvo biološkog sveta. Mnogi organski molekuli su hiralni, uključujući većinu bioloških aminokiselina. Takođe, dvostruki heliks DNK u svom kanonskom obliku ima formu desnog zavrtnja. Međutim, značaj hiralnosti sagledan je tek nakon tragedije sa talidomidom [1]. S druge strane, postoje mnogi nebiološki hiralni kristali kojima nije razmatrana hiralnost, a oni uključuju važne enantioselektivne katalizatore i senzorske materijale, kao i enantioselektivne hromatografke materijale. Kada se radi o hiralnosti u kristalnim strukturama, važno je razlikovati tri različite grupe objekata koji mogu biti ili hiralni ili ahiralni: 1) molekulske komponente kristala, 2) same kristalne strukture, 3) simetrijske grupe kristalnih struktura. Hiralnost kristala će biti razmatrana na primerima kompleksa kobalta sa tiazolskim ligandima.Chirality is a striking property of the biological world. Many organic molecules, including the most biological amino acids are chiral and the DNA double helix in its standard form twists like a right-handed screw. The importance of chirality in biological systems was brought to light by the thalidomide tragedy [1]. On the other hand, there are many non-biological chiral crystals which have not been treated in terms of chirality, which include important enantioselective catalysts and sensing materials, as well as enenatioselective chromatographic materials. In dealing with chirality in relation to crystal structures it is essential to distinguish between three different objects that may be either chiral or achiral: 1) the molecular components of the crystal, 2) the crystal structure itself and 3) the symmetry group of the crystal structure. Chirality of crystals will be discussed taking cobalt complexes with thiazole based ligands as examples