Ramis Mustafa Öksüzoğlu

Synthesis, characterization and catalytic behavior of functionalized mesoporous SBA-15 with various organo-silanes

Mesoporous silica SBA-15 has been synthesized and functionalized by one-step synthesis method to widen their various application possibilities. In this study, phenyltrimethoxysilane (PTMS), 3-mercaptopropyltrimethoxysilane (MPTMS) and trimethoxypropylsilane (TMPS) were used as silane precursors for the functionalization, and after treated with HCl solution, their catalytic activities were evaluated in the lactic acid-methanol esterification. The presence of anchoring of functional groups on SBA-15 was proved by XRD, FT-IR, BET surface area and pore size distributions. Good catalytic activity was observed especially for SBA-15-SO(3)H-MPTMS, and the catalytic activity order was determined as follows: SBA-15-SO(3)H-MPTMS>SBA-15-TMPS>SBA-15-PTMS, which is directly associated with the surface area, pore size and pore volume. As compared with homogeneous catalyst, SBA-15-SO(3)H-MPTMS heterogeneous catalyst shows remarkable performance, such as separation, recovery and reusability.

High-surface-area SBA-15–SO3H with enhanced catalytic activity by the addition of poly(ethylene glycol)

The influence of poly(ethylene glycol) (PEG) and synthesis temperature in the synthesis of SBA-15–SO3H was investigated to evaluate the catalytic activity in the esterification of propionic acid with methanol. The catalysts were characterized by means of surface and structure analyses; X-ray diffraction, FT-IR, scanning electron microscopy, Thermo-gravimetric and N2 adsorption/desorption techniques. It was found that, by the addition of PEG, the surface area and porosity of SBA-15–SO3H increased, while the structure and size of mesopores remained unchanged. Nitrogen sorption measurements indicate that PEG introduces additional pores into the pore walls of SBA-15–SO3H. Thus, a simple way of improving the porosity of mesoporous SBA-15–SO3H was presented that could enhance transport of substrates through the porous system and allow the generation of stable mesoporous replicas, important for catalytic applications and also beneficial for replication and nanocasting purposes.

Effect of calcination temperature on the structural and magnetic properties of Ni/SBA-15 nanocomposite

The effect of calcination temperature on the structural and magnetic properties of Ni/SBA-15 nanocomposite prepared by reductant-impregnation method was studied using SBA-15 mesoporous silica as support. The structure, morphology and magnetic properties of the samples were characterized using X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectrometry, N2 adsorption/desorption (BET and BJH), vibrating sample magnetometer, and FT-IR. Characterization results showed the presence of crystalline phases characteristics of the Ni and/or NiO, and that the structural characteristics of the support were maintained after the impregnation of nickel ions followed by calcinations. Calcination process helps in crystallization and formation of the desired phase such as well crystalline NiO and Ni nano-particles. Moreover, this heat resulted in significant effects on different properties of the products such as the crystallite size, homogeneity, particle distribution, porosity, surface area and the sintering process. Magnetic measurements suggested that the magnetic properties in nanocomposites is probably the sum of two contributions: superparamagnetic and ferromagnetic one depending on the calcination temperature. Calcination at high temperatures affects both of the structural and magnetic properties of Ni/SBA-15. Because the location of the Ni particles depends on the pore size of the support, the uniformity of particle size was related to the interaction between the Ni particles and support.

Ferromagnetic Resonance and X-Ray Reflectivity Studies of Pulsed DC Magnetron Sputtered NiFe/IrMn/CoFe Exchange Bias

Ferromagnetic resonance and X-ray specular reflectivity measurements were performed on Ni 81 Fe 19 /Ir 20 Mn 80 / Co 90 Fe 10 exchange bias trilayers, which were grown using the pulsed-DC magnetron sputtering technique on Si(100)/SiO 2 (1000 nm) substrates, to investigate the evolution of the interface roughness and exchange bias and their dependence on the NiFe layer thickness. The interface roughness values of the samples decrease with increasing NiFe thickness. The in-plane ferromagnetic resonance measurements indicate that the exchange bias field and the peak-to-peak line widths of the resonance curves are inversely proportional to the NiFe thickness. Furthermore, both the exchange bias field and the interface roughness show almost the same dependence on the NiFe layer thickness. The out-of plane angular dependent measurements indicate that the exchange bias arises predominantly from a variation of exchange anisotropy due to changes in interfacial structure. The correlation between the exchange bias and the interface roughness is discussed.

MAGNETIC MESOPOROUS SILICA NANOCOMPOSITES PREPARED WITH DIFFERENT SIZED Fe3O4: STRUCTURAL AND MAGNETIC PROPERTIES, CATALYTIC EFFECTS

The magnetically separable mesoporous silica nanocomposites were successfully prepared through a one-pot method including the co-condensation of tetraethoxysilane (TEOS) as silica precursor and 3-mercaptopropyl trimethoxysilane (MPTMS) as functionalizing agent accompanied with hydrogen peroxide for oxidation of mercapto groups and triblock copolymers as structure directing agent in the presence of ferromagnetic and superparamagnetic Fe 3 O 4 nanoparticles. By incorporating the superparamagnetic (near zero coercivity) Fe 3 O 4 nanoparticles to the mesoporous silica (SBA-15) and functionalizing with sulfonic acid groups instead of ferromagnetic Fe 3 O 4 nanoparticles, we developed versatile nanocomposite having superior properties with respect to magnetism, catalysis and porosity. Reducing the particle size of Fe 3 O 4 from the ferromagnetic regime to the superparamagnetic regime, the pore closure could be eliminated because of the more open pore as well as saving magnetic properties.