Yüzeyi polimer kaplı magnetit nano taneciklerin yeni bir yöntemle tek basamakta elde edilmesi
A new method for preparing polymer capsulated magnetic nanoparticles in one pot
- Tez No: 350644
- Danışmanlar: PROF. DR. OKAN SİRKECİOĞLU
- Tez Türü: Yüksek Lisans
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2013
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Kimya Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 89
Özet
Magnetit Fe3O4 kimyasal yapısına sahip doğada doğal olarak bulunan bir demiroksittir. Kendiliğinden mıknatıslanma özelliğine sahip olması ve laboratuvar ortamında sentezinin oldukça kolay hale gelmesi nedeni ile son yıllarda uygulama alanları oldukça artmıştır ve araştırıcılar tarafından oldukça ilgi görmeye başlamıştır. Manyetit nanopartiküller hipertermi tedavisi, hedefli ilaç taşınması, manyetik rezonans görüntüleme, biyoseparasyon gibi biyomedikal uygulamalar başta olmak üzere mühendislik alanlarında ve teknolojik sistemlerde kullanılmaktadır. Özellikle son yıllarda manyetit nanopartiküllerin ıslak kimyasal yöntemlerle sentezlenmeye başlaması ile bu partiküllerin uygulama alanları giderek artmıştır. Manyetit nanopartiküllerin istenilen yapıda ve boyutta sentezinin gerçekleştirilebilmesi bir çok yöntem geliştirilmiştir. Bunlardan ilki Fe(II) ve Fe(III) tuzlarının yüksek alkoller varlığında muamelesi sayılabilir. Bu yöntemle magnetit nanopartiküllerin 10-20 nm aralığında sentezlenebileceği söylenmiştir. Ancak bu yöntem ortamdaki hidroksil iyonlarının ve demir oksitin dengelenmemiş stokiyometrisine oldukça bağlıdır. İkinci yöntem olarak yüksek sıcaklıkta Fe(III)?ün Fe(II)?ye indirgenmesi söylenebilir. Bu yönteminin ortaya koyduğu mekanizma henüz tam olarak anlaşılamamış olmakla beraber literatürde bu yöntemle yapılmış bir çok manyetit nanopartikül yer almaktadır. Bunların yanı sıra magnetit nanopartiküllerin yüzey modifikasyonu ve manyetit nanopartiküllerin organik maddelerle veya polimerlerle kaplanması halen daha araştırıcılar tarafından ilgi duyulan ve gelişmeye açık yöntemlerdir. Literatürde bu yöntemlerle iligili oldukça fazla reçete yer almaktadır. Bu çalışmada ATRP yöntemiyle sentezlenen P(GMA)?nın , PS-b-P(GMA)?nın asit ile hidroliz edilmesi incelenmiş ve elde edilen hidroliz ürünleri ile manyetit nanopartikül sentezi yapılmıştır. Ayrıca PVA ticari polimeri ile de manyetit nanopartikül sentezi yapılmıştır. P(GMA)?nın hidroliz ürünü PDHPM kaplı manyetit nanopartikül sentezi organik çözücüde gerçekleştirilmiş ve oluşan manyetit nanopartikülün suda redispers olduğu görülmüştür. PS-b-P(GMA)?nın hidroliz ürünü PS-b-PDHPM ile tanecik-kabuk tipinde manyetit nanopartikül sentezi invers emülsiyon ortamında (Toluen/Su) gerçekleştirilmiş ve oluşan manyetit nanopartikülün DMF çözüsünde dispers olabildiği görülmüştür. Son olarak PVA kaplı manyetit nanopartikül sentezi ise sürfaktan varlığında suda gerçekleştirilmiş ve oluşan manyetit nanopartikülün suda redispers olduğu görülmüştür. FT-IR spektrumları elde edilen manyetit nanopartiküllerin yapısında manyetit bulunduğunu göstermiştir. Yapılan ESEM analizi sonucunda manyetit nanopartiküllerin küresel yapıda olduğu görülmüş ve DLS analizi ile taneciklerin ortalama çapları, polidispersiteleri belirlenmiştir. Buna gore PDHPM kaplı manyetit nanopartiküllerin ortalama tanecik çapları 167 nm, polidispersiteleri 0.164, PS- PDHPM içeren tanecik-kabuk tipindeki manyetit nanopartiküllerin ortalama tanecik çapları polidispersiteleri belirlenmiştir. Buna gore PDHPM kaplı manyetit nanopartiküllerin ortalama tanecik çapları 167 nm, polidispersiteleri 0.164, PS-PDHPM içeren tanecik-kabuk tipindeki manyetit nanopartiküllerin ortalama tanecik çapları 260,3 nm, polidispersiteleri 0.236, PVA kaplı manyetit nanopartiküllerin ortalama tanecik çapı 70,8 nm, polidispersiteleri 0.271 bulunmuştur. Elde edilen manyetit nanopartiküllerin titreşimli örnek manyetometre analizleri yapılmış ve buradan doyum manyetizasyonları, koersiviteleri ve ağırlıkça Fe3O4 yüzdeleri hesaplanmıştır. PDHPM kaplı manyetit nanopartiküllerin doyum manyetizasyonu 44.5 emu/g, ağırlıkça Fe3O4 yüzdesi %49.4, PS-PDHPM içeren tanecik-kabuk tipindeki manyetit nanopartiküllerin doyum manyetizassyonu 3.1 emu/g, ağırlıkça Fe3O4 yüzdesi %3.4 ve PVA kaplı manyetit nanopartiküllerin 12.7 emu/g, ağırlıkça Fe3O4 yüzdesi %14.1 bulunmuştur. PDHPM kaplı manyetit nanopartikülün koersivitesi 50 Oe bulunmuş, diğer iki manyetit nanopartikülün koersivitesi ise sıfır (0)?a yakın bulunmuştur.
Özet (Çeviri)
Magnetite is a naturally occuring mineral having formula, Fe3O4. It shows strong magnetization abilities comparable with those of superparamagnetic metal alloys such as ?-Fe2O3 and ?-Fe2O3. Not being oxidable, magnetite is superior to the other magnetic materials. Since it?s laboratory synthesis from Fe(II) /Fe(III) mixtures by coprecipitation of their hydroxides, the synthetic magnetite has found great interest due to it?s widespread application in various fields. From application point of view, the magnetite powder in nanosize has broader use in magnetic data memory devices, in loudspeakers, laser printing, magnetic resonance imaging (MRI), hyperthermia theraphy, targeted drug delivery, bioseparation and electromagnetic shielding coatings etc. Preparation of magnetite nanoparticles (MNPs) however, needs special attention while preparing by wet chemical methods, due to high coalesence tendency of the preformed nanoparticles. Neverthless, recent developments in the area have shown that MNPs even with 10-20 nanometers of sizes can readily be attained. Among those dropwise addition of the solution of Fe(III) /Fe(II) mixtures and reaction of Fe(III) salt with high boiling alcohols worth to mention. Apparently the first approach depends on unbalanced stochiometry of hydroxil ion and iron oxides. In the second approach magnetite formation takes place by partial reduction of Fe(III) to Fe(II) at the temperatures around 200oC. Although the mechanism has not been clearly disclosed yet, most probably Fe(II) formation occurs by oxidation of OH group of the alcohol. However, why the precipitation of the oxides takes place in a such combination is not well understood yet. There appears a number of new procedures in the literature for fabrication of MNPs and their stable in oil and water dispersions. For instance, excellent and stable dispersions of oleic acid stabilized oil dispersions have been commercialized in small scales. Despite those significant developments in nano size magnetite synthesis, covalent modification of the partical surfaces is still a challenging that needs further development. Coating of magnetite nanoparticles with organics especially essential for medical applications. This is due to biological incompatibility of naked MNPs. In this respect there are few successfull methods of coating of magnetic nanoparticles. Zhang group reported coating of MNPs via atom transfer radical polymerization (ATRP) method using surface bond chloropropionic acid as initiator. Although, a thick polystyrene layer is formed at the end of this process the resulting nanoparticles are not well redispersible and suffers from further oxidation of the magnetic core. In another successfull coating process described by Chu group, MNPs have been prepared in an inverse micro emulsion system consisting of methacrylic acid /N,N methylene bis acrylamide and bis (2-ethyl hexyl sulfosuccinate) as emulsifier. Polymerization of the monomers in this emulsion directly give polymer coated magnetite nanoparticles. Emulsion polymerization of styrene in the presence of ironoxide nanoparticles has been demonstrated by Asher group to give polystyrene nanospheres with magnetic particles inside. Moreover, precious metal coating has been considered much more useful and bio-compatible in medical applications. O?Connor and co outhers, published a method for preparing gold coated magnetic nanoparticles in one step. In their process FeCl3 solution in N-methyl pyrrolidinone is editted to sodium naftaline solution at room temperature. Thereafter benzyl pyridine capping agent is edit at elevated temperature. Gold coating is then created by addition of 4-chloro auric acid in N-methyl pyrrolidinone. Gold coating of MNPs is of special interest due to easy reaction of the gold layer with thiol end functional molecules or macromolecules. İnverse micro emulsion method reported is based on the reduction of FeSO4 by NaBH4 in oil in water system using cetyltrimethyl ammonium bromide (CTAB) as surfactant and butanol as co-surfactant. In the presence of octane as continuous phase addition of tetra-chloro auric acid has been demonstrated to give gold coated iron nanoparticles. Coating of magnetic with a silica shell has been studied by few groups. One common approach for the silica coating is formation of silica nanoparticles by Stöbers sol-gel process in the presence of MNPs using TEOS (Tetraethoxysilane) and water. Hydrophilic surfaces of resulting particles allows further modification. As mentioned above, despite those significant developments coating of magnetic nanoparticles is still in it?s infancy and needs further investigations. In this work, we have studied preparing of polymer coated MNPs in one pot. The method investigated is aimed at concommittant formation and coating of MNPs. Our new methodology is simply based on instanteneous crosslinking of polyvinyl alcohol (PVA) with Fenton reagent in aqueous solution at room temperature. In this reaction Fe(II) is oxidized to Fe(III) while an OH radical is forming from hydrogen peroxide. Proton abstraction of the OH radical from PVA backbone yields macroradicals combination of which results in instanteneous crosslinking, so that Fe(III) salt formed remaines entrapped within the crosslinked polymer matrix. It was shown that a proper choice of Fe(II) / H2O2 molar ratio gives PVA coated iron salt mixture in 2 / 1 Fe(III) / Fe(II) molar ratio. Final treatment of this heteregenous mixture with ammonia gives PVA coated magnetite particles in submicron sizes, mostly being in 300-550 nm size. In our ongoing works this chemistry was exploited for preparing nanosizes magnetite nanoparticles tightly coated with PVA glycidol functional acrylic polymer. For preparing polymer coated MNPs, in this work commercial PVA, poly(2,3-di hydroxy propyl methacrylate) P(DHPM) and polystyrene-b-P(DHPM) were used. PHPM and the block copolymers were prepared in well defined structures using ATRP technique. Magnetite formation was carried out in homogeneous solution for the case with PDHPM, whereas mini-emulsion system was used for the case with PVA. We have obtained stable solution/dispersions in each case. To isolate MNPs from the mixtures, we have used thermal aging or magnetic separation techniques. Inverse emulsion system (water in oil) was employed for the case of the block copolymers using Span 80 as emulsifying agent. This process yielded core-shell MNPs containing 3,1 percent of magnetite. Among those the material obtained using PVA coating material has shown to be only partially hydrophilic, but not redispersible in any organic solvent or their mixtures. ESEM pictures shows that the particle sizes are in 17-19 nm size range. It?s magnetization behavior examined by VSM (Vibration Sample Magnetometer) technique revealed that, the sample containing 14.1 % magnetite shows no detectible coercivity, which is agreement with their sizes. The magnetite material prepared in the presence of PDHPM has a partical size range of 19-29 nm as inferred from ESEM pictures. This material was found to be easily redispersible in water although it has the highest magnetite content (49.1%). Although it has showed a reversible magnetization curve it represented a slight coercivity around 50 Oe. The material obtained from the block copolymer (PS-b-PDHPM) showed a low but reversible saturation magnetization around 3,4 emu/g, but no detectable coercivity. This result is in agreement with their sizes inferred from ESEM pictures (24-38 nm). As a result Fenton reaction can be applicable in preparing both hydrophilic and hdrophobic magnetite nanoparticles entrapped within polymer matrixes in one reaction flask which has not been reported so far. The simple strategy presented in this work can easily be employed for preparing polymer compatible or bio-compatible magnetite nanoparticles. Although magnetite nanoparticles derived from PVA is not easily redispersible, its further surface modification with suitable monomers or low moleculer weight organics may be used to impart redispersibility and bio-compatibility. The resulting material might be used in medicine for hyperthermia theraphy or so on. As a result Fenton reagent is a vesatile tool for preparing magnetite nanoparticles entrapped in suitable polymers or block copolymers having hyroxil side groups. The procedure is attractive due to its starting from commercially available or readily attainable polymer materials and its simplicity of process.
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