Study On The Applications Of Multifunctional Nagnetic Iron Oxide Nanoparticles

Multifunctional magnetic iron oxide nanoparticles have received great attention in the science of nano techno logy due to their important properties. Multifunctional magnetic iron oxide nanoparticles combine different functionalities and components, each with its unique characteristics into a single nanocomposite. These nanocomposites are high functional materials and can be used for different potential applications. Different techniques have been reported to synthesize multifunctional nanocomposites for various applications. But most of the reported techniques use toxic or expensive chemicals and involve complex procedures. It is therefore important to prepare the multifunctional nanocomposites through simple methods. Considering the magnetic properties of iron oxide nanoparticles we have designed multifunctional nanocomposites of iron oxide nanoparticles for different applications of protein and drug adsorption and desorption, and also catalysis. This thesis consists of three projects.1. Magnetic iron oxide nanoparticles were prepared by a facile co-precipitation method and then functionalized with citrate simply by heating the aqueous solution of sodium citrate with iron oxide nanoparticles. The effect of concentration of sodium citrate on the stability of nanoparticles was studied. These prepared nanoparticles were very small in size and well stable which is due to electrostatic force of repulsion caused by carboxyl groups after functionalization with citrate. The adsorption and desorption of protein (BSA) on these citrate modified magnetic iron oxide nanoparticles were studied using different buffers at different pH. The protein adsorption is maximum (83mg/g) at its electrostatic point and the mechanism of adsorption is considered to be mostly electrostatic. The desorption of protein from nanoparticles was carried out using an alkaline solution of high pH which was confirmed by SDS-PAGE, Ultraviolet-visible (UV-Vis), fluorescence spectroscopy and SDS-PAGE, which indicated that the protein molecules did not undergo any changes in its structure. 2. The effect of gold nanoseeds with different sizes on the gold shell was investigated. Gold nanoparticles of two different sizes (～3nm and～15nm) were prepared and attached to the surface of amine functionalized silica coated iron oxide nanoparticles. The gold nanoparticles assembled on the surface were used as seeds for further gold shell formation. The results of Energy-dispersive X-ray spectroscopy (EDX) indicated that the amount of Au attached to iron oxide nanoparticles is higher for bigger gold nanoparticles as compared to smaller gold nanoparticles. Similarly, after the formation of gold shell higher amount of Au was found for larger gold nanoparticles. However, both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results show that a complete, uniform, and compact gold shell was formed in case of using small gold nanoseeds, but for larger gold nanoseeds the shell formed was discontinuous and was not compact, while most of gold nanoparticles were found to be aggregated on the surface. All the nanocomposites have high magnetization values. The nanocomposites showed high efficiency in catalysis, among which Nanocomp-2, with a thin gold shell showed excellent catalytic activity and reusability.3. Multifunctional nanocomposites were prepared by simple steps. First iron oxide nanoparticles were prepared through hydrothermal method, and then coated with small silica layer using sol-gel technique. The resulting nanoparticles were amine functionalized by the reaction of APTES. Then gold nanoparticles were attached on the surface of amine functionalized nanoparticles which were used as nanoseeds for further gold shell formation. At last an outer mesoporous silica shell was formed using Tetraethyl orthosilicate (TEOS) as the silica precursor and Cetyltrimethylammonium bromide (CTAB) as the tempelating agent. The multifunctional nanocomposites with mesoporous silica having magnetization, near-infrared (NIR) plasmon resonance, and catalytic behavior. These nanocomposites, with an inner magnetite core, an outer mesoporous silica shell, and a gold shell sandwiched between a thin silica layer and a thick outer silica shell, were characterized using different techniques, such as TEM, X-ray diffraction (XRD), FTIR, vibrating sample magnetometer (VSM), UV-Vis spectroscopy, X-ray photoelectron spectrometry (XPS), dynamic light scattering (DLS), zeta potential, N2adsorption/desorption, and thermal gravimetric analysis (TGA). The results indicated that the nanocomposites have high magnetization (21.4emu/g) due to the inner magnetite core, significant absorbance in the NIR region due to the gold shell, large surface area (315m//g), and mesopores (2.1nm) in the outer silica shell. The outer mesoporous silica shell was investigated for adsorption and release behavior of drug molecular as well as for attaching of dye molecules, while the gold shell was investigated for its catalytic behavior. The prepared multifunctional magnetic nanocomposites show adsorption and sustained release of Ibuprofen. Catalytic behavior of nanocomposites was investigated using the reduction of4-nitrophenol into4-aminophenol as model reaction, while the catalyst can be easily separated from reaction medium by an external magnet due to the magnetic property and can be reused.