EFFECT OF COMPLEXING AGENTS ON nife NANOMATERIAL BY ELECTROCHEMICAL METHOD

For centuries, science has explored and continually redefined the frontiers of our knowledge. For a recently, we knew the concept of ever smaller scalenanoscale one billionth of a meter. Nanoparticles are particles with size measured in nanometers. According to International Organization for Standardization (ISO) Technical Specification 80004, a nanoparticle is defined as a nanoobject with all three external dimensions in the nanoscale, whose longest and shortest axes do not differ significantly, with a significant difference typically being a factor of at least 3. They have greater surface area per weight than larger particles, which causes them to be more reactive to some other molecules. Nanoparticles are used and being evaluated for use, in many fields as medicine, manufacturing, materials, environment, energy and electronics. In particular, magnetic nanoparticles are useful for a wide range of applications from data storage to medicines. If subjected to a magnetic field, the nanoparticles show a high magnetization that is very uniform throughout the material. The fact thatsoft magnetic nanoparticles can quickly switch magnetization direction once the external magnetic field is reversed makes them ideal for use in highfrequency electric circuits used, for example, in mobile phones. In particular, magnetic oxide nanomaterials, including iron oxide ( Fe3O4 and γFe2O3), spinel ferrites (MFe2O4 ; M = Mn, Zn, Cr, Ni, or Co) and hexagonal ferrite ( MFe12O19, M=Ba and Sr) are attracting much attention due to their wide application potentials in advanced magnets, electronic devices, information storage, magnetic resonance imaging (MRI), and drugdelivery technology. Thus, the synthesis and applications of nano structured magnetic ferrite has become a particularly important research field.20 Two approaches often represent manufacture of nanomaterials are “topdown” and “bottom–up”. “Topdown” refers to making nanoscale structures by machining, template and lithographic techniques, whereas “bottomup”, or molecular nanotechnology, applies to building organic and inorganic materials into defined structures, atombyatom or moleculebymolecule, often by selfassembly or self organization. In particularly, in the second approach, the nanoparticles are grown using electrodeposition from liquid solution or chemical vapor deposition (CVD). The synthesis from solution is more advantageous because it can produce large quantities of nanoparticles with relatively cost low and inexpensive infrastructure. While vapor growth is used mainly for semiconducting materials, the deposition from solution is employed for both metallic and semiconducting structures.7 The advanced physical properties of composite coatings quickly became clear and during the 1990s, new areas such as electrocatalysts and photoelectrocatalysts were considered. With the emergence of nanostructured materials over the last decade, electrodeposition techniques have provided a route to a variety of new nanomaterials. These include nano crystalline deposits, nanowires, nanotubes, nanomultilayers and nanocomposites. Strengthened composite coatings, enhanced electrical resistance in printed circuit boards, improved giant magnetoresistance in memory storage systems and increased microhardness for microdevices in microelectromechanical systems have been the focus of numerous studies 7. In this thesis, the work focused on effect of complexing agents on NiFe nanomaterial by Electrochemical method.

Ghh VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF PHYSICS NGUYEN KHANH CHI EFFECT OF COMPLEXING AGENTS ON NiFe NANOMATERIAL BY ELECTROCHEMICAL METHOD Submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Physics (International Standard Program) HaNoi - 2019 VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF PHYSICS NGUYEN KHANH CHI EFFECT OF COMPLEXING AGENTS ON NiFe NANOMATERIAL BY ELECTROCHEMICAL METHOD Submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Physics (International Standard Program) Supervisor: Assoc Prof Dr Le Tuan Tu HaNoi - 2019 ACKNOWLEDGEMENTS Firstly, I would like to express my sincere gratitude to Assoc Prof Dr Le Tuan Tu for his valuable guides and advice I am profoundly grateful to teachers at Department of Cryogenics, Faculty of Physics, VNU University of Science for their enthusiastic teaching during those four years I would also like to thank my friends for their advices, sharing, help and friendship not only in my study but also in my life I would like to express my profound and heartfelt thanks to my family I am where I am today because of having family’s support in the past time Finally, I would like to thank my family for unwavering support and encouraging me to keep up at work Nguyễn Khánh Chi LIST OF NOTATIONS ABBREVIATIONS Abbreviation Explanation Hc Coercivity Ms Saturation magnetization Mr Remanent magnetization B Magnetic field flux density H Magnetic field intensity NPs Nanoparticles VSM A vibrating sample magnetometer/magnetometry CV Cyclic Voltammetry XRD X-Ray diffraction EDS Energy Dispersive X-ray Spectroscopy SEM Scanning Electron Microscopy CMS Center of Material Science VNU Vietnam National University LIST OF FIGURES CONTENTS INTRODUCTION For centuries, science has explored and continually redefined the frontiers of our knowledge For a recently, we knew the concept of ever smaller scalenanoscaleone billionth of a meter Nanoparticles are particles with size measured in nanometers According to International Organization for Standardization (ISO) Technical Specification 80004, a nanoparticle is defined as a nano-object with all three external dimensions in the nanoscale, whose longest and shortest axes not differ significantly, with a significant difference typically being a factor of at least They have greater surface area per weight than larger particles, which causes them to be more reactive to some other molecules Nanoparticles are used and being evaluated for use, in many fields as medicine, manufacturing, materials, environment, energy and electronics In particular, magnetic nanoparticles are useful for a wide range of applications from data storage to medicines If subjected to a magnetic field, the nanoparticles show a high magnetization that is very uniform throughout the material The fact thatsoft magnetic nanoparticles can quickly switch magnetization direction once the external magnetic field is reversed makes them ideal for use in high-frequency electric circuits used, for example, in mobile phones In particular, magnetic oxide nanomaterials, including iron oxide ( Fe 3O4 and γ-Fe2O3), spinel ferrites (MFe2O4 ; M = Mn, Zn, Cr, Ni, or Co) and hexagonal ferrite ( MFe 12O19, M=Ba and Sr) are attracting much attention due to their wide application potentials in advanced magnets, electronic devices, information storage, magnetic resonance imaging (MRI), and drug-delivery technology Thus, the synthesis and applications of nano structured magnetic ferrite has become a particularly important research field.[20] Two approaches often represent manufacture of nanomaterials are “topdown” and “bottom–up” “Top-down” refers to making nanoscale structures by machining, template and lithographic techniques, whereas “bottom-up”, or molecular nanotechnology, applies to building organic and inorganic materials into defined structures, atom-by-atom or molecule-by-molecule, often by self-assembly or self- organization In particularly, in the second approach, the nanoparticles are grown using electrodeposition from liquid solution or chemical vapor deposition (CVD) The synthesis from solution is more advantageous because it can produce large quantities of nanoparticles with relatively cost low and inexpensive infrastructure While vapor growth is used mainly for semiconducting materials, the deposition from solution is employed for both metallic and semiconducting structures.[7] The advanced physical properties of composite coatings quickly became clear and during the 1990s, new areas such as electrocatalysts and photoelectrocatalysts were considered With the emergence of nanostructured materials over the last decade, electrodeposition techniques have provided a route to a variety of new nanomaterials These include nano crystalline deposits, nanowires, nanotubes, nanomultilayers and nanocomposites Strengthened composite coatings, enhanced electrical resistance in printed circuit boards, improved giant magnetoresistance in memory storage systems and increased microhardness for microdevices in micro-electro-mechanical systems have been the focus of numerous studies [7] In this thesis, the work focused on effect of complexing agents on NiFe nanomaterial by Electrochemical method CHAPTER 1: MAGNETIC NANOPARTICLES In this chapter, the basics of nanomagnetics will first be presented followed by a review on the synthesis and functionalization of magnetic nanoparticles 1.1 Classification of Magnetic Nanoparticles A classification of nanostructured magnetic morphologies was desirable because of the correlation between nanostructure and magnetic properties Among many schemes proposed by various researchers, we have chosen here the following classification, which was designed to emphasize the magnetic behavior-related physical mechanisms Figure 1.1 Schematic presentation of different types of magnetic nanostructured materials ( Leslie-Pelecky and Rieke 1996 ) The classification is illustrated in Figure 1.1 [18] Type A is denoted for systems consisting isolated particles with nanoscale diameters Since the interparticle interactions can be ignored for these systems, their unique magnetic properties are completely attributable to the isolated components with their reduced sizes Another type, type D, is assigned to bulk materials with nanoscale structure This type is featured by a significant fraction ( up to 50 % ) of the sample volume composed of grain bound-aries and interfaces Compared with type A systems, the interparticle interactions cannot be ignored and the bulk magnetic properties for type D are indeed dominated by the interactions It is believed that the length scale of the interactions can span up to many grains and is critically related to the interphase characteristics Because of the existence of the interactions and grain boundaries, the magnetic behaviors of type D nanostructures cannot be predicted theoretically simply by considering only the polycrystalline materials with reduced length scales Other than type A and type D, intermediate forms such as core– shell nanoparticles (type B) and nanoparticle-based nanocomposites (type C) are classified, as shown in Figure 1.1 In type B, the shells on magnetic nanoparticles, which may not be magnetic themselves, are usually used to reduce interparticle interactions For type C systems, the magnetic properties of nano composites are determined by the faction of magnetic nanoparticles as well as the characteristics of the matrix material [18] 1.2 Single-domain particles Single-domainand multidomain are important for ultrafine magnetic particles Domain walls have a characteristic width and energy associated with their formation and existence They separate domains – groups of spins all pointing in the same direction and acting cooperatively Reversing magnetization is primarily achieved by the motion of domain walls Figure 1.2 illustrates the dependence of coercivity on particle size by an experimental investigation Multidomain is the case for large particles in which domain walls form energyfavorably As the particle size decreases below a critical diameter D c, single-domain particles form where the formation of domain walls becomes energetically unfavorable Thus, magnetization reversal cannot be obtained readily leading to larger coercivities because of the lack of nucleation and motion of the domain walls If the particle size continues to decrease, the spins are increasingly influenced by thermal fluctuations and this phenomenon is called superparamagnetism The estimated single-domain diameter for some materials in the shape of spherical particles is listed [7] 10 Figure 2.10 Schematic diagram of VSM The vibrating sample magnetometer (VSM) generates hysteresis curves based on the principles of magnetic induction In a VSM, a sample is attached to a vibrating rod and allowed to vibrate in a magnetic field produced by electromagnets As the magnetization of the samples increases due to the increasing magnitude of the field, the change in flux induces a resulting in a voltage signal measured by induction coils located near the samples The signal is usually small, and is measured by a lock-in amplifier at a frequency specified by the signal from the sample vibrator The signal measured by the induction coils is directly proportional to the magnetization of the sample, and independent of the external field intensity Plotting the induction vs magnetic field intensity (H) results in a hysteresis curve representative of the stabilize magnetic moment although it can lack adequate sensitivity on ultra thin films or samples with only small amounts of the magnetic moment [18] 30 Figure 2.3 VSM system VSM measurement was conducted at VNU University of Technology CHAPTER 3: RESULTS AND DISCUSSION 3.1 Cyclic voltammetry result of NiFe The cyclic voltammetry were recorded at scan potential limits between -1.5 V and V Figure 3.1 shows CV characteristic curve of 0.01 M NiCl2.6H2O solution 31 Figure 3.4 Cyclic voltammetry of 0.01 M NiCl2.6H2O solution Figure 3.1 demonstrates the cyclic voltammetry of Ni in the solution containing 0.01 M NiCl2.6H2O The graph indicates that Ni 2+ ions reduced in the range between -1.0 V and -0.5 V The reduction peak of these ions was observed at -1.0 V The chemical equation representing the reduction of Ni: Ni2+ +2e-→Ni0 (3.1) By conducting cyclic voltammetry measurement for 0.01 M FeCl2 4H2O solution, a CV diagram was obtained as provided in Figure 3.2 As can be seen, the cyclic voltammetry of Fe in the solution was conducted with scanning potential region from -1.5 V to V Within that range, the reduction of Fe 2+ ions started at -0.6 V and expanded to -1.25 V The reduction peak was obviously seen at -0.8 V The representing equation for this process is : Fe2+ + 2e-→Fe0 32 (3.2) Figure Cyclic voltammetry of 0.01 M FeCl2.4H2O solution Figure 3.6 CV characteristic curve of electrolyse solution containing FeCl2 and NiCl2 The cyclic voltammetries were recorded at scan potential limits between -1.5 V and V Figure 3.3 gives data on the cyclic voltammetry of NiFe solution The voltammetry of FeCl2 and NiCl2 solution express that reduction peak varied from -0.8 V to -1 V with current density around 10-3 (A.dm-2) The reduction process increasingly occurred at -1.0 V 33 3.2 SEM images of samples Figure 0.7 Micrographs of nanoparticles We have activator: • H3BO3 0.7 M for nano particle • SDS 10 ml, PVP ml, TSC ml • Deposition time: 1800 s • Current: I = 10 A TSC and PVP is molding agent and surfactant, if we increase TSC the shape of particle increase in one direction When we have activated, the shape of the particle has changed into a nanorods 34 Figure 0.5 Micrographs of nanorods 35 After sample was fabricated by the electrodeposition method withpulse, NiFe nanoparticles were collected.The results obtained from the SEM image show small crystals with size of crystal particles about 60 nm NiFerods were collected, the results obtained from the SEM image show small crystals with size of NiFe nanorods about 40 x 400 nm It can be seen that diameter of particles was smallest at 3V and largest at 8V as the larger potential is applied, the faster metal ions deposit on anode, which leads to agglomeration and large size of particle.This proves the effect of cathodic overpotetialon the particle size Thus, when increasing the voltage, the size of particles became larger 3.3 EDS result Figure 3.6 EDS spectrum of sample with 320 nm-diameter particles Figure 3.6 denotes that NiFe sample consisted of Ni and Fe, the appearance of Ni and Fe peak were evident Ni with ratio of Fe percentage is much less than Ni, with Ni 69 % and Fe 31 % Besides, it canbe seen that EDS spectrum of other element is oxygen This might result from oxides of the substrate However, the quantity of O was relatively modest compared with Fe and Ni Hence, one can conclude that Fe, Ni elements caused the magnetic properties of NiFe hyteresis curve 36 From EDS result, we guest NiFe rods has anisotropy Table Percentage of Ni, Fe in NiFe particles and NiFe rods Percentage NiFe particles 69 % Ni 31 % Fe NiFe rods 74,5 % Ni 35,5 % Fe Specifically, nanoparticles with ratio 69 % Ni and 31 % Fe representing the most soft magnetic properties by conducting EDS Nanorods with ratio 74,5 % Ni and 35,5 % Fe and in diameter representing the most soft magnetic properties When we have activated, the shape of the particle has changed into a nano rods Percentage of Ni increase and percentage of Fe decrease Agents complexing include SDS, PVP, TSC effect of shape on NiFe particles Addition, agents complexing to change the percentage of Ni, Fe in NiFe particles and NiFe rods 3.4 Magnetic properties Magnetic moment (emu) 0.06 0.03 0.00 -0.03 -0.06 -8000 -4000 4000 Magnetic field H (Oe) Figure 3.7 Hysterisis of Nanoparticles 37 8000 Magnetic moment (emu) 0.009 0.006 0.003 0.000 -0.003 -0.006 -0.009 -1000 -500 500 1000 Magnetic field H (Oe) Figure 3.8 Hysterisis of Nanorods It is clear that the curves have small values of coercivity (from 25.13 to 50 Oe) Their low coercivity also proves that NiFe nanoparticles are soft magnetic materials Table Coercivity of Nanoparticles and Nanorods Nanoparticles Hc 35 Nanorods 32 From the table, we can see that Coercivity of Nanorods smaller than Nanoparticles Although agent complexings affected shape and percentage of NiFe particles also NiFe rods, the coercivity of nanorods change very small than NiFe nanoparticles Thence, we can use agents complexing to change shape and percentage of NiFe particles and NiFe rods 38 CONCLUSION In summary, in this thesis work, a number of results were obtained Firstly, NiFe magnetic nanoparticles were fabricated with particles size about 60 nm to 120 nm with V to V cathodic overpotential, clarifed that the size of particle increase with the cathode voltage Overall, particles were observable and apparently uniform From the Cyclic voltammetry results, the reduction of NiFe solution was founded to peak at -1.0 V By VSM measurement, the maximum Hc values were approximate 25.1 to 50.5 Oe when diameter decreased from 120 to 60 nm Specifically, nanoparticles with ratio 69.% Ni and 31.% Fe and 120 nm in diameter representing the most soft magnetic properties by conducting EDS Dependence of their magnetic properties on the particle size has been clarified A suitable Ni–Fe particle size, atomic percentage and solvent should be responsible for the improvement of the initial magnetic softness These results apparently agree well with theoretical overview and preceding research of soft magnetic NiFe materials.When we have activated, the shape of the particle has changed into a nano rods Percentage of Ni increase and percentage of Fe decrease The coercivity of nanorods smaller than nano particles Although agent complexings affected shape and percentage of NiFe particles 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CHAPTER 1: MAGNETIC NANOPARTICLES... be synthesized by a number of physical or chemical methods, one of them is electrodeposition method that is low-cost and effective There are several types of electrodeposition method as shown