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dc.contributor.advisor Kim, Cheol Gi - Mohamed Abbas Ali Ahmed - 2016-12-06T06:25:55Z - 2016-02-12T06:25:55Z - 2015 -
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dc.description.abstract Functional magnetic nanoparticles have great importance in various fields of applications, including nanoscience, nanotechnology, environmental chemistry and biomedical applications. Although many groups have successfully described the synthesis of functional magnetic materials using various approaches and technologies, a facile, rapid, eco-friendly and economically feasible synthesis procedure that combines all the materials into a single system has remained elusive.
The shape of the synthesized nanoparticles is also an important consideration when evaluating potential practical applications. Especially for biomedical applications, the nanocube surface with specified crystal plane is expected to enhance the ability to immobilize biofunctional groups because the surface to whole volume (S/V) ratio is higher than for other shapes (e.g., octahedron, dodecahedron, icosahedron and sphere shape). Therefore, integration of cube-shaped magnetic nanoparticles (MNPs) in the form of iron oxide (Fe3O4) and, thereafter, functionalization of the surface with application-specific materials would likely enhance its performance and thus becomes a promising material for various applications.
Here I have developed, a novel one-pot sonochemical approach for the synthesis of size controlled high magnetization iron oxide nanocubes as a core in aqueous medium, without the use of surfactant. The surface of Fe3O4 nanocubes were subsequently functionalized with various inorganic materials, including silica (SiO2), titania (TiO2), carbon (C), silver (Ag) and gold (Au) and applied in several applications (including catalytic and bio-sensing applications).
Recently, two approaches (the Stober and microemulsion methods) have emerged as the major routes for the functionalization of MNP surfaces for synthesizing of core/shell nanostructures. These methods are advantageous because they produce a uniform shell with controlled thickness, however, they require complicated environmental procedures, large amounts of surfactant and long synthesis times (in the range of 6-48 h). Here I have succeeded in developing a facile, eco-friendly and time-reducing sonochemical approach for functionalization of MNPs surfaces based on the exceptional reaction conditions generated from ultrasound of high temperatures (5000 K) and pressures (~20 MPa) with high cooling rates (~1010 K/S), thus allowing the formation of many unique materials composites. Furthermore, I have also developed a modified sol-gel method for the coating of particle surfaces using only polyvinylpyrolidone (PVP) as an amphiphilic polymer. Notably, the total reaction time for the synthesis of the core/shell nanostructures was found to be shorter than the previously reported methods.
MNPs are frequently functionalized or coated with SiO2 to improve their stability, biocompatibility and functionality, giving them promise for many bio-medical applications, such as magnetic resonance imaging (MRI) contrast agents, magnetically-targeted drug delivery vehicles and agents for hyperthermia. Here I have developed a sonochemical technique as well as a modified sol-gel approach for obtaining uniform Fe3O4/SiO2 core/shell nanocubes. Furthermore, the thickness of the silica shell is easily controlled in the range of 4-18 nm by adjusting the reaction parameters. The core/shell nanocubes samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). The as-prepared Fe3O4/SiO2 core/shell nanocubes showed good stability in air for at least 4 month as well as against annealing condition of up to 300 °C in presence of hydrogen gas as a strong reducing agent. Furthermore, high magnetization value of 50.7 emu/g was obtained for the sample with thin silica thickness (4 nm) as a consequence of shell thickness controlled. Moreover, the biocompatibility of the core/shell nanocube was enhanced in comparison to that of pristine Fe3O4 nanocubes. In addition, the Fe3O4/SiO2 nanocubes were functionalized by Aminopropyltriethoxysilane, and then conjugated with streptavidin-Cy3 successfully as indicated by optical fluorescence microscopy.
On the other hand, I used the developed sonochemical techniques for the functionalization of Fe3O4 nanocubes by TiO2 as well as Carbon. At first, Fe3O4/TiO2 nanocubes were successfully synthesized through hydrolysis and condensation of iron (II) sulfate heptahydrate and titanium isopropoxide (as precursors of Fe3O4 and TiO2, respectively) using single reaction sonochemical process. XRD, TEM, EDS and FTIR were used to characterize the crystal structure, size and morphology, elemental composition, metal-metal and metal-oxygen bonds of the core/shell nanocubes, respectively. The magnetic properties of the samples were measured by VSM at room temperature. Catalytic measurements on the samples showed an excellent efficiency for the degradation of methylene blue, and this efficiency was further promoted remarkably by addition of hydrogen peroxide (H2O2) within only 5 minutes of reaction time in the absence of ultraviolet irradiation. Even after recycling the sample for six times, the introduced catalyst was found to retain as much as 90% of initial efficiency. A possible reaction mechanism for the sonochemical deposition of TiO2 on the surface of Fe3O4 nanocubes and also for the degradation process of methylene blue by the introduced catalyst will be discussed in this thesis. However, PVP as an amphiphilic polymer was used as a surface linker in case of synthesizing the Fe3O4/C core/shell nanocubes.
To functionalize Fe3O4 nanocubes with noble metals such as Ag and Au nanodots, I used the sonochemical technique and the seed mediated growth method, respectively, to obtain two different structures of Fe3O4/SiO2/Ag and Fe3O4/Au nanocubes. XRD, EDS, TEM, and FTIR analyses revealed that the Fe3O4 nanocubes were successfully functionalized using these two facile methods. The resulting Fe3O4/SiO2/Ag nanocubes showed excellent catalytic efficiency toward the reduction of p-nitraoaniline to p-phenylenediamine within very short times and a recycling efficiency of 88 % for up to 15 cycles.
In addition, based on this developed sonochemical approach, I have succeeded in synthesizing different types of ferrite nanoparticles including Co-Fe2O4, NiZn-Fe2O4, and MnZn-Fe2O4. TEM results showed that different morphologies structures of spherical, cubic and mixed shapes with different particle sizes were obtained in the range of 20 to 110 nm by changing the synthesis solvent medium and compositions. I obtained high saturation magnetization value with superparamagnetic properties for the synthesized ferrite NPs samples. The obtained ferrite nanoparticles with high crystallinity, high magnetic moment, and desirable superparamagnetic properties are expected to be promising materials for various biomedical applications; and the facile aqueous approach of the sonochemical method is expected to be a promising route for the synthesis of different ferrite materials.
ⓒ 2015 DGIST
dc.description.tableofcontents 1.Introduction 1--
1.1 Iron oxide (Fe3O4) nanoparticles 2--
1.2 Motivation 4--
1.3 objective and thesis outline 8--
References 10--
2.Sonochemical method, experiments and characterizations techniques 13--
2.1 Synthesis methods of MNPs 13--
2.1.1 Sonochemistry 13--
2.1.2 Sonochemical mechanism for synthesis of Fe3O4 NPs 18--
2.1.3 Functionalization with different inorganic group 19--
2.2 Characterization of materials 19--
2.2.1 Phase determination and crystallite size measurement 19--
2.2.2 Microscopy studies (shape and size studies) 20--
2.2.3 Magnetic measurement 21--
2.2.4 Catalytic activity test 22--
2.2.5 Spectroscopic studies 23--
2.2.6 X-ray photoelectron spectroscopic studies 24--
References 24--
3.Facile sonochemical synthesis of high moment iron oxide (Fe3O4) nanocubes 26--
3.1 Introduction 26--
3.2 Experimental 29--
3.2.1 Materials 29--
3.2.2 Synthesis of iron oxide nanocubes 29--
3.2.3 Characterization 30--
3.3 Results and discussion 31--
3.3.1 Structure Characterization 31--
3.3.2 Morphology characterization 33--
3.3.3 Magnetic Properties 37--
3.4 Conclusion 42--
Refrences 43--
4.Functionalization of iron oxide (Fe3O4) nanocubes with silica (SiO2), titania (TiO2), and carbon (C) 46--
4.1 Fe3O4/SiO2 core/shell nanocubes: Novel coating approach with tunable silica thickness and enhancement in stability and biocompatibility 46--
4.1.1 Introduction 46--
4.1.2 Experimental section 49-- Materials 49-- Synthesis of hydrophilic iron oxide (Fe3O4) nanocubes 49-- Synthesis of core/shell Fe3O4/SiO2 nanocubes 49-- Streptavidin-Cy3 loading on APTES modified Fe3O4/SiO 2 Nanocube 50-- Characterization 51-- Cell viability test 52--
4.1.3 Results and discussion 52--
4.1.4 Conclusion 63--
4.2 A novel one-pot approach for synthesis of iron oxide/silica and iron oxide/carbon core/shell nanocubes 64--
4.2.1 Introductio 64--
4.2.2 Experimental 66-- Materials 66-- Synthesis of Fe3O4/SiO2 core/shell nanocubes using a sonochemicalmethod 66-- Synthesis of Fe3O4/C core/shell nanocubes using a sonochemical method 67-- Synthesis of Fe3O4/SiO2 nanocomposites without ultrasound 67-- Synthesis of Fe3O4/C nanocomposites without ultrasound 68-- Characterization 68--
4.2.3 Results and discussion 69--
4.2.4 Conclusion 79--
4.3 Fe3O4/TiO2 core/shell nanocubes: Single-batch surfactantless synthesis characterization and efficient catalysts for methylene blue degradation 80--
4.3.1 Introduction 80--
4.3.2 Experimental 82-- Materials 82-- Synthesis of Fe3O4/TiO2 core/shell nanocube 83-- Catalytic activity test 83-- Characterization 84--
4.3.3 Results and discussion 84-- Formation mechanism and morphology 84-- Structure characterization 87-- Magnetic properties 90-- Catalytic activity of the Fe3O4/TiO2 nanocubes 91-- Mechanism proposed for catalytic activity 94-- Reusability properties 95--
4.3.4 Conclusion 96--
References 97--
5.Functionalization of iron oxide (Fe3O4) nanocubes with noble metals (Ag and Au) 103--
5.1 A novel approach for the synthesis of ultrathin silica-coated iron oxide nanocubes decorated with silver nanodots (Fe3O4/SiO2/Ag) and their superior catalytic reduction of 4-nitroaniline 103--
5.1.1 Introduction 103--
5.1.2 Experimental section 106-- Materials 106-- Synthesis of iron oxide (Fe3O4) nanocubes using the sonochemical method 106-- Synthesis of the Fe3O4/SiO2 nanocubes using an ultrasonic assisted sol-gel method 107-- Synthesis of Fe3O4/SiO2/Ag nanocubes using sonochemical method 107-- Synthesis of silica (SiO2) nanoparticles using Sonochemical method 108-- Synthesis of silver decorated silica (SiO2/Ag) nanoparticles using sonochemical method 108-- Synthesis of silver (Ag) nanoparticles using sonochemical method 108-- Catalytic test 109-- Analysis methods 109--
5.1.3 Results and discussion 110--
5.1.4 Catalytic efficiency 118--
5.1.5. Conclusion 121--
5.2 A novel approach for facile synthesis of iron oxide-gold core-satellite nanocubes 122--
5.2.1 Introduction 122--
5.2.2 Experimental section 124-- Materials 124-- Synthesis of hydrophilic iron oxide (Fe3O4) nanocubes 124-- Synthesis of Fe3O4/Au core/satellite nanocubes 124-- Characterization 125--
5.2.3 Results and discussion 125--
5.2.4 Conclusion 130--
References 131--
6.Shape and size controlled synthesis of different magnetic oxide nanoparticles 136--
6.1 Introduction 136--
6. 2 Experimental section 138--
6.2.1 Materials 138--
6.2.2 Synthesis of CoFe2O4 nanoparticles 138--
6.2.3 Synthesis of NiZn-Fe2O4 nanoparticles 139--
6.2.4 Synthesis of MnZn-Fe2O4 nanoparticles 139--
6.2.5 Characterization 140--
6.3 Results and discussion. 140--
6.3.1 Shape and size controlled synthesis and characterization of CoFe2O4 NPs 140-- Structure characterization of CoFe2O4 nanoparticles 140-- Morphology characterization of CoFe2O4 nanoparticles 141-- Magnetic Properties of CoFe2O4 nanoparticles 145--
6.3.2. Synthesis and characterization of Ni Zn-Fe2O4 nanoparticles 149-- Structural characterization 149-- Morphology characterization of NiZn-Fe2O4 NPs 151-- FT-IR studies of NiZn-Fe2O4 NPs 153-- Magnetic properties of NiZn-Fe2O4 NPs 153--
6.3.3. Synthesis and characterization of MnZn-Fe2O4 nanoparticles 155-- Structure characterization of MnZn-Fe2O4 NPs 155-- Morphology characterizations of MnZn-Fe2O4 NPs 156-- Magnetic properties of Mn-Zn ferrite NPs 157--
6.4 Conclusions 159--
References 159--
Summary 163--
List of publication 168--
Acknowledgement 171--
Curriculum Vitae 172
dc.format.extent 172 -
dc.language.iso en en_US
dc.publisher DGIST en_US
dc.subject Sonochemical en_US
dc.subject Iron oxide (Fe3O4) en_US
dc.subject Core/Shell en_US
dc.subject Catalyst en_US
dc.subject Bio-sensing Applications en_US
dc.title Sonochemical synthesis of functionalized core/shell iron oxide nanocubes for catalytic and bio-applications en_US
dc.title.alternative 기능화의 초음파 화학 합성코어 / 쉘 산화철 나노 큐브촉매에 대한바이오 응용 -
dc.type Thesis en_US
dc.identifier.doi 10.22677/thesis.2067927 -
dc.description.alternativeAbstract 기능성 자성 나노 입자는 나노 과학, 나노 기술, 환경 화학, 바이오-메디컬 등 여러 분야에서 주목하고 있다. 이미 많은 연구실에서 기능성 물질의 여러 가지 합성 방법과 기술에 대해 다루었지만 여전히 쉽고 빠르며 경제적으로 실현 가능한 합성 방법에 대해 활발한 연구가 진행되고 있다.
자성 나노 입자의 형태는 여러 분야의 어플리케이션에 있어 자성 나노 입자의 특성 평가에 대한 중요한 지표로 사용된다. 특히, 앞서 말했던 바이오-메디컬 어플리케이션에서는 6면체 형태의 나노 입자가 바이오기능성 물질의 결합에 대한 면적 효율을 높이기 위한 가장 적합한 구조이다. 6면체 나노 입자가 8면체, 12면체, 20면체 또는 구 형태의 나노 입자에서보다 전체 부피에 대한 표면적 비가 높기 때문이다. 그래서 자성 나노 입자의 6면체 제작과 표면 기능화는 나노 입자의 성능 향상과 앞으로의 응용에 있어 매우 중요한 기술이 될 것이다.
우선, 유일하게 수성 용매에서 합성할 수 있고, 사이즈를 조절이 가능한 Sonochemical 합성 방법으로 높은 자화 특성을 갖는 6면체의 Fe₃O₄를 합성하였다. 그리고 바이오 센싱, 촉매 등 앞으로의 응용단계를 위해 Silica (SiO₂), Titania (TiO₂), 탄소 (C), 은 (Ag), 금 (Au) 등의 다양한 재료들로 6면체의 Fe₃O₄ 자성 나노 입자를 표면 처리하였다.
최근, 자성 나노 입자의 표면 처리는 일반적으로 Stober 방법과 Microemulsion 방법이 주로 사용되고 있다. 이러한 방법들은 core/shell 구조의 합성이 가능하고 Shell의 두께 조절을 균일하게 합성할 수 있다는 이점이 있지만, 많은 양의 계면활성제 사용, 6 ~ 48 시간의 긴 반응 시간 등의 문제점을 가지고있다. 이 실험에서는 Sonochemical 합성 방법으로 높은 온도 (5000 K), 압력 (~20 MPa), 빠른 냉각 속도 (~10¹⁰ K/S) 등의 반응 조건을 조절하여 이러한 문제점을 개선하였고, 그로 인해 전체 합성 및 코팅 공정 시간이 기존 반응 시간에 비해 매우 단축되었다. 또한, 양쪽 친매성 고분자인 PVP (polyvinylpyrrolidone)를 코팅하기 위한 Sol-gel 방법도 연구하였다.
Silica (SiO₂) 코팅된 자성 나노 입자는 MRI 조영제, Drug delivery, Hyperthermia 등의 바이오 메디컬 어플리케이션에 있어 안전성, 생체 적합성, 기능성이 우수하다. 앞으로의 이러한 응용을 위해서 Sonochemical 합성 방법과 Sol-gel 코팅 방법으로 Fe₃O₄/SiO₂ core/shell의 자성 나노 입자 만드는 방법을 연구하였다. 반응 조건을 달리함으로써 Silica shell의 두께를 4–18 nm의 범위 내에서 조절이 가능하다. (XRD), (TEM), (EDS), (FT-IR), (VSM) 장비로 Fe₃O₄/SiO₂ core/shell 형태의 6면체 자성 나노 입자의 특성을 분석하였다. Fe₃O₄/SiO₂ core/shell의 자성 나노 입자는 공기 중 노출에도 최소 4 개월 동안 안정성을 유지하였고, 강한 환원제인 H₂ 기체가 존재하는 300 ℃ 가열 조건에서도 안정성을 유지하였다. 또한, 4nm의 두께로 silica 코팅된 자성 나노 입자는 50.7 emu/g 정도의 높은 자화값을 가졌다. 생체 적합성도 Fe₃O₄ 나노 입자에 비해core/shell silica 코팅된 자성 나노 입자가 훨씬 우수하였다. 또한 Aminopropyltriethoxysilane으로 코팅된 Fe₃O₄/SiO₂ 자성 나노 입자와 streptavidin-Cy3가 결합되어 있는 것을 Optical fluorescence microscopy로 확인하였다.
Sonochemical 합성 방법으로 탄소 (C)와 Titania (TiO₂)를 사용하여 자성 나노 입자의 표면처리를 해보았다. Titanium isopropoxide와 iron(Ⅱ) sulfate heptahydrate가 가수분해와 응축 현상을 거치며 무정형 Titania로 코팅된 Fe₃O₄ 자성 나노 입자가 합성되었다. (XRD), (TEM), (EDS), (FT-IR)를 사용하여 Fe₃O₄/TiO₂ core/shell 자성 나노 입자의 결정 구조, 크기, 형태, 성분 분석, 금속-금속 결합, 금속-산소 결합을 확인하였고, (VSM)으로 상온에서의 자성 나노 입자의 자기적 특성을 측정하였다. 또한, Fe₃O₄/TiO₂를 촉매로 사용한 methlyene blue 분해 반응에서 좋은 효율을 보였으며 hydrogen peroxide (H2O2) 조건에서는 자외선 조사 없이도 5분 이내에 반응을 하여 더 높은 효율성을 보여주었다. 6번의 재사용 후에도 초기 효율의 90% 가량의 효율을 유지하였다. Titania의 Sonochemical deposition에 대한 반응 메커니즘과 Methylene blue에서의 분해 촉매 반응 메커니즘은 뒤에서 논의할 예정이다. 양쪽 친매성 고분자인 PVP (polyvinylpyrrolidone)는 Fe3O4/C core/shell 자성 나노 입자 합성에서 두 물질을 연결해주는 역할을 해주었다. Au 또는 Ag nanodot으로 코팅된 Fe3O4/SiO2/Ag and Fe3O4/Au 구조의 nanocube를 합성하기 위해 Sonochemical method와 Seed mediated growth method를 사용하였다. XRD, EDS, TEM, FT-IR 분석 장비를 통해 두 method로 nano-dot 코팅된 Fe3O4의 특성을 확인하였다. Fe3O4/SiO2/Ag 자성 나노 입자는 p-Nitraoaniline을 p-Phenylenediamine로 환원시키는 반응에서 15 회 사용에서도 88%의 효율을 보이는 우수한 촉매로서의 역할을 하였다.
Sonochemical 합성 방법을 기반으로 Co-Fe2O4, NiZn-Fe2O4, MnZn-Fe2O4 와 같은 여러 종류의 산화철 나노 입자를 합성해보았다. 합성 용매에 따라 6면체, 구 형태 등 다양한 나노 입자의 형태와 20~110 nm 범위 내에서 사이즈 조절이 가능함을 TEM을 통해 관측할 수 있었다. 또한 이렇게 합성된 나노 입자는 높은 자화값을 가지고 초상자성 특성을 갖는다. Sonochemical 합성 방법은 다양한 산화철 나노 입자 합성에 있어 수성 용매로 하는 매우 용이한 합성법이라 할 수 있고, 고결정성, 초상자성, 고자화율 특성을 갖는 산화철 나노 입자는 앞으로의 폭넓은 바이오 응용에 있어 전도 유망한 물질이라고 할 수 있다.
ⓒ 2015 DGIST
- Ph. D. -
dc.contributor.department Emerging materials Science -
dc.contributor.coadvisor Lee, Chang Soo - 2015. 8 -
dc.publisher.location Daegu -
dc.description.database dCollection -
dc.contributor.alternativeDepartment 대학원 신물질과학전공 -
dc.contributor.affiliatedAuthor Mohamed Abbas Ali Ahmed -
dc.contributor.affiliatedAuthor Kim, Cheol Gi -
dc.contributor.alternativeName 아흐메드 모하메드 -
dc.contributor.alternativeName 김철기 -
dc.contributor.alternativeName 이창수 -
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