CONTROLLED SYNTHESIS AND SURFACE MODIFICATION OF
Materials Science and Engineering, Master Thesis, 2012
Prof. Dr. Yusuf Z. Menceloğlu (Thesis Supervisor),
Asst. Prof. Mehmet Yıldız, Asst. Prof. Fevzi Çakmak Cebeci, Asst. Prof. Gözde İnce, Prof. Dr. Ersin Serhatlı (Istanbul Technical University)
Date &Time: February 3rd, 2012 - 10:00
Place: FENS G032
Keywords: Titanium dioxide, Anatase, Sol-gel method, Synthesis conditions, Surface modification, Silane coupling agents
TiO2 nanoparticles were synthesized with simplified sol-gel method using water as solvent and Titanium tetraisopropoxide as precursor. The synthesized materials were characterized by DLS, STA, XRD and C13 NMR. These characterization methods provide valuable information to understand crystal type and size of nanoparticles, effect of synthesis parameters, change in particle size of TiO2 sols, thermal behavior and pH dependence of particles.
The effects of synthesis conditions such as water: precursor molar ratio, amount of acid catalyst, amount of chelating agent, reaction temperature and time on properties of TiO2 particles were investigated. High water: precursor molar ratio ensures small particle size and stable particles in aqueous suspension of TiO2. Additionally, increasing acid amount results in smaller particle size and stable particles with higher surface potential. Results clearly shows that acid catalyst has crucial effect on particle synthesis and it is not possible obtain particles without acid catalyst. In this work acetic acid was used as chelating agent and similar to other parameters effects fine particles can be obtained with higher acetic acid. Reaction temperature and time also serve for smaller size and stable particle. However, effects of these parameters are not significant compared to other parameters.
Isoelectric point of TiO2 sols was measured between pH 5 and 6. Lower and higher pH values results in stable sols which is needed for smooth applications. Additionally, it was observed that significant change in particle size occurs after synthesis reaction during rest of TiO2 sol samples. This changed was associated to uncompleted reactions of precursor and C13 NMR was used to understand this behavior. XRD patterns of samples showed that anatase crystal particles were obtained without calcinations process only with drying at 800C oven. Furthermore, it is determined with XRD measurements that water: precursor molar ratio does not have effect on crystal structure of the particles. Phase transition from anatase to rutile crystal phase was determined between 500 and 6000C. Simultaneous thermal analysis of TiO2 samples was support this phase transition temperature.
Surface modification of TiO2 nanoparticles was done with aminopropyl triethoxysilane and modified particles were characterized by FTIR, STA and Elemental Analysis. Effects of modification conditions such as modifier concentration, TiO2 concentration and reaction time were investigated. Increasing concentration of modifier has significant effect on amount of surface modification. On the other hand, after certain concentration amount of grafted amino silane is not affected. These results were verified with STA and Elemental Analysis. When TiO2 concentration increases, reaction between surface OH group and alkoxy group of modifier increases and higher mass loss is observed in thermal analysis due to degradation of grafted organic materials. Moreover, longer reaction time results in higher coverage of modifier on the surface of the particle.