Introduction
Objectives
Nanotechnology involves manipulating matter at dimensions of 1 to 100 nanometers, where unique phenomena lead to innovative applications Recent research has focused on the synthesis of nanoscale magnetic materials, which exhibit distinct properties due to their size and shape, positioning them between atomic and bulk solid states The physical and chemical characteristics of these nanomaterials are highly dependent on their dimensions, with each particle acting as a single magnetic domain At the nanoscale, properties such as electrical conductivity, magnetism, and mechanical strength differ significantly from those of bulk materials Consequently, magnetic nanocrystals are increasingly utilized in various fields, including magnetic data storage, ferrofluids, medical imaging, drug targeting, and catalysis As a result, materials scientists are dedicated to developing efficient methods for fabricating nanomaterials with precise size and morphology control.
Zeolites are intricate inorganic polymers formed by a network of SiO4 and AlO4 tetrahedra, valued for their unique microstructure and thermal stability Their applications span across both industrial and academic fields, particularly in the petrochemical industry for separation, adsorption, and catalytic processes Notably, Na-A zeolite serves as an effective molecular sieve and cation exchanger, facilitating heavy metal removal, gas adsorption, and the selective separation of gases and liquids.
Siliceous mudstone and natural zeolite are abundantly distributed all over the world [1.16 - 1.28] It is composed with opal-
CT (SiO2ãnH2O) as the major mineral and small amounts of quartz, smectite and muscovite [1.26 - 1.28] Natural zeolite (mostly composed clinoptilolite phases) contains more than 61 wt % of SiO2,
The presence of 11 wt% Al2O3 and a low cation exchange capacity of 1.24 to 1.25 indicates that these chemically reactive materials are suitable for zeolite synthesis Despite their potential, there is limited research on the synthesis of ZSM-5 zeolite from siliceous mudstone and Na-A zeolite from clinoptilolite.
Water pollution has become a significant environmental issue in industrialized countries, primarily due to wastewater containing high levels of heavy metal ions from factories This contaminated water poses risks to both wildlife and local communities To address this problem, numerous studies have focused on the removal of heavy metal ions, with zeolites being a commonly utilized solution Typically, these studies involve mixing zeolite with a solution rich in heavy metal ions to facilitate ion exchange, followed by a filtration process to separate the zeolite from the solution While this method can achieve high separation rates, it may inadvertently release some adsorbed metal ions due to the pressure involved in filtering Additionally, applying this separation technique in large environmental settings is challenging, as the presence of various materials can complicate the process.
This project explores the detailed synthesis of magnetite nanoparticles and ZSM-5 and Na-A types of zeolite using natural materials Magnetite nanoparticles are synthesized through a co-precipitation method involving ferrous and ferric sulfate along with ammonia solution To achieve a particle size reduction to a few nanometers, the inverse micelle method is utilized Additionally, the study includes the hydrothermal synthesis of ZSM-5 zeolite from siliceous mudstone and the production of Na-A zeolite using natural zeolite.
Recent studies on the synthesis of magnetite nanoparticles and zeolites, specifically ZSM-5 and Na-A, pave the way for the development of a novel composite material that integrates zeolite with magnetite nanoparticles This innovative magnetic product holds significant potential for effectively addressing heavy metal contamination, highlighting its future importance in promoting a green and clean environment.
Thesis layout
This thesis is structured into four chapters, beginning with an overview of the recent synthesis and applications of ferrite nanoparticles and zeolites Chapter 2 focuses on the theoretical review and synthesis methods for magnetite nanoparticles, specifically through co-precipitation and inverse micelle techniques Chapter 3 delves into both theoretical and practical aspects of synthesizing zeolites, particularly ZSM-5 and Na-A types, using a hydrothermal method with natural raw materials Notably, ZSM-5 zeolite is synthesized from siliceous mudstone, while Na-A zeolite is derived from natural zeolite, serving as the primary sources of silica and alumina.
Finally, a concluding part has been explained in chapter 4
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Magnetic materials are categorized based on their reactions to external magnetic fields and the alignment of their magnetic moments The five primary types of magnetism include diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism, and ferrimagnetism.
Diamagnetism is a phenomenon observed in all materials when exposed to an external magnetic field, where atomic current loops generated by the orbital motion of electrons respond by opposing the applied field This weak repulsion occurs in materials with filled electronic subshells, resulting in paired magnetic moments that cancel each other out Diamagnetic materials exhibit negative susceptibility (χ < 0), leading to a slight repulsion from the magnetic field Common examples of diamagnetic materials include quartz (SiO2) and calcite (CaCO3).
Magnetic behavior in materials is largely influenced by unpaired electrons in atomic shells, particularly in the 3d or 4f shells When atomic magnetic moments are uncoupled, the materials exhibit paramagnetism.
Paramagnetic materials moments have small positive magnetic susceptibility (χ≈0) For example, montmorillonite (Na 0.2 Ca 0.1 -
Al 2 Si 4 O 10 (OH) 2 (H 2 O) 10 ) and pyrite (FeS 2 ) are paramagnetic materials
Ferromagnetic materials, such as iron (Fe), nickel (Ni), and cobalt (Co), exhibit aligned atomic magnetic moments of equal strength, enabling direct coupling interactions within their crystalline structure This alignment significantly enhances the flux density of these materials.
Figure 2.1 Spins arrangements of (a) ferromagnetism, (b) antiferromagnetism and (c) ferrimagnetism
(a) Moments of individual atoms aligned
(b) Moments of alternating atom to atom
Above the Neel temperature (T N), thermal energy causes atoms with equal and opposite alignment to randomly fluctuate, resulting in a loss of long-range order and leading the material to exhibit paramagnetic behavior This phenomenon occurs as unequal alternated moments align antiparallel, resulting in zero net magnetization.
Ferrimagnetism is a property exhibited whose atoms or ions tend to assume an ordered arrangement in zero applied field below a certain temperature known as the Neel temperature (e.g., Fe3O4 and
In a magnetic domain, significant net magnetization arises from the antiparallel alignment of neighboring non-equivalent sublattices, resembling ferromagnetism However, once the temperature exceeds the Neel temperature, the material transitions to a paramagnetic state.
2.1.2 Crystal structure of spinel ferrite
The spinel ferrite structure, represented as MFe2O4, features a cubic close-packed arrangement of oxygen atoms, with bivalent metal ions (M²⁺) and ferric ions (Fe³⁺) occupying distinct crystallographic sites These sites, known as A and B-sites, exhibit tetrahedral and octahedral oxygen coordination, respectively, leading to differing local symmetries.
The spinel structure features two cation sites for metal cation occupancy, comprising 8 A-sites with tetrahedral coordination and 16 B-sites with octahedral coordination A normal spinel occurs when A-sites are occupied by Me 2+ cations and B-sites by Fe 3+ cations, while an inverse spinel has A-sites fully occupied by Fe 3+ cations and B-sites randomly filled with Me 2+ and Fe 3+ cations Most spinel structures exhibit an intermediate degree of inversion, with both cation types present in varying proportions Magnetically, spinel ferrites are characterized by ferrimagnetic behavior, as the magnetic moments of cations in the A and B-sites align anti-parallel, resulting in a net moment of spins due to the greater number of B-sites compared to A-sites.
The selection of divalent metal cations and their distribution between A-sites and B-sites create a customizable magnetic system Based on this cation distribution, various types of ferrospinels can be identified.
(1) Normal spinel structure, where all Me 2+ ions occupy A-sites; structural formula of such ferrites isMe 2 + [Fe 2 3 + ]O 4 2 − This type of distribution takes place in zinc ferrites Zn 2 + [Fe 2 3 + ]O 4 2 −
The inverse spinel structure is characterized by the arrangement of Me 2+ ions in B-sites and the equal distribution of Fe 3+ ions between A and B-sites, represented by the structural formula Fe 3 + [Me 2 + Fe 3 2 + ]O 2 4 − Notable examples of ferrites with this structure include Fe3O4, NiFe2O4, and CoFe2O4.
(3) Mixed spinel structure, when cations Me 2+ and Fe 3+ occupy both
A and B-sites; structural formula of this ferrite is
Me , where δ is the degree of inversion
MnFe2O4 represent this type of structure and has an inversion degree of δ = 0.2 and its structural formula, therefore, is
The magnetic properties of ferrites arise from the combined magnetic moments of their individual sublattices The exchange interactions among the electrons of ions within these sublattices vary in strength, with the interaction between magnetic ions of sublattices A and B (A-B interaction) being the most significant In contrast, the A-A interaction is approximately ten times weaker, while the B-B interaction is the least intense This predominant A-B interaction is responsible for the occurrence of complete or partial antiferromagnetism in ferrites.
Figure 2.3 Magnetic structure of Fe3O4 magnetite
In case of Fe3O4 inverse spinel ferrite (Figure 2.3), the two
Fe3O4 exhibits ferrimagnetism due to the antiferromagnetic coupling of Fe3+ ions in tetrahedral and octahedral sites through A-B interaction exchange, resulting in canceled moments of ±5μB The unpaired moment from the octahedral Fe2+ ions, attributed to four uncompensated parallel spins, contributes a value of 4μB.
Domain is a group of spins all pointing in the same direction The domains are separated by domain walls, which have a
The evolution of coercivity (H C) in octahedral particles as a function of diameter (D) is depicted in Figure 2.4 When the particle size exceeds a critical threshold (D c), specific to each material, the transition from multi-domain to mono-domain or single-domain occurs In a demagnetized state, the magnetic domains are oriented randomly, resulting in complete cancellation of magnetization and an overall magnetization of zero.
"non-magnetic" material can be transformed into a strongly magnetic body easily due to the orientation of the domains or magnetization of the material when a magnetic field is applied [2.1, 2.2, 2.8]
Figure 2.4 Coercivity as a function of the particle diameter (D) of a magnetic particle
As the diameter D decreases to values below the critical diameter Dc, the coercivity Hc becomes inversely proportional to D, resulting in a significant increase in coercivity due to the unfavorable formation of domain walls In this regime, changes in magnetization cannot occur solely by shifting domain walls, which typically requires only a weak magnetic field Once the particle size falls below Dc, they enter the single-domain state If the particle size continues to decrease beyond the single-domain threshold, thermal fluctuations begin to influence the magnetic moments, causing the particles to exhibit superparamagnetic behavior with large moments This superparamagnetism is characterized by zero coercivity and becomes prominent above the blocking temperature, where thermal energy allows the magnetic moment to relax during measurement.
Figure 2.5 Hysteresis loop of a multi-domain magnetic material, where H is the magnetic applied field amplitude and M is the magnetization