Silikalit-1 sentez karışımlarında başlangıçta oluşan nanotaneciklerin çekirdeklenme ve kristal büyümesi süreçlerindeki rolleri bilinmemektedir. Bu çalışmada, sentez sırasında meydana gelen olayların ayrıntılı olarak izlenmesi yoluyla çekirdeklenme ve tanecik büyümesi süreçlerinin aydınlatılması için 9TPAOH-480H2O-25SiO2 bileşimi ile hazırlanan sentez çözeltisi kullanılarak, 100°C’de deneyler yapılmıştır. Ortalama tanecik boyutlarının zamanla değişimlerinin izlenmesi için dinamik ışık saçılımı (DLS) yönteminden, faz analizleri için x-ışını kırınımından (XRD), fonksiyonel grupların belirlenmesi için de Fourier Transform Infrared spektroskopisinden (FTIR) yararlanılmıştır. TPA+ katyonunun örneklerin yapılarındaki yerinin belirlenmesi için termal gravimetrik analiz (TGA) uygulanmıştır. Azot adsorpsiyonu ile örneklerin mikrogözenek hacimleri ve gözenek boyutu dağılımları belirlenmiş, atomik kuvvet mikroskobu (AFM) ile son ürünün boyutu ve morfolojisi görüntülenmiştir. Sentezin başında çözeltide bulunduğu belirlenen, ortalama boyutları 2 nm olan taneciklerin, sıcaklığın artırılmasıyla kısa bir süre içinde, yerlerini ortalama boyu 20 nm olan taneciklerden oluşan ikinci bir popülasyona bıraktığı görülmüştür. Bu popülasyonun ortalama tane boyutunun belirli bir süre boyunca sabit kaldığı, ancak bu süre içinde tanelerin bileşimleri ve yapılarının değiştiği belirlenmiştir. Daha sonra ortalama boyutlar gerçekleşen aglomerasyon sonucunda aniden artmış ve ortaya lineer olarak büyümeye başlayan üçüncü bir tane popülasyonu çıkmıştır. XRD ve TGA sonuçları kristalinitenin ilk belirtilerinin bu noktada oluştuğunu göstermiştir. Büyüme mekanizması olarak tanecik eklenmesinin geçerli olduğu görülmüş, tüm analizler bu sonucu doğrulamıştır.

Zeolites are crystalline microporous aluminosilicates. They have gained importance in catalysis, adsorption and ion-exchange applications due to their pores and channels of molecular dimensions. The achievement of the synthesis of colloidal zeolites with increased external surface areas and shortened diffusion paths, made the use of these materials in new emerging fields such as microelectronics, biochemistry and membrane separations possible and attractive. The possibilities of synthesizing zeolites from clear solutions instead of heterogeneous mixtures containing gel phases, and the applicability of light scattering techniques to these solutions have allowed the monitoring of nucleation and particle growth during synthesis, which has been an impetus for the studies in this field. Silicalite-1 has been the first zeolite synthesized with colloidal dimensions from clear solutions. The roles of nanoparticles, formed at the very beginning in silicalite-1 synthesis mixtures, in nucleation and crystal growth processes are not well-known. The purpose of this study was to investigate the nucleation and crystal growth mechanisms of silicalite-1 and to shed light on the roles of the nanoparticles during crystallization. Experiments were performed at 100 °C using a reaction mixture with the composition of 9TPAOH-480H2O-25SiO2. Dynamic light scattering technique (DLS) was used to observe the variation of average particle size with time, X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) were used for phase identification. Thermal gravimetric (TG) analyses were performed to determine the position of the TPA+ cation in the structures of the samples. The micropore volume and the pore size distribution of the samples were determined by nitrogen adsorption while the size and morphology of the final product were imaged by atomic force microscopy (AFM). Additionally, the alkalinity of the solution and the surface charges of the particles, which may be helpful in explaining the mechanism, were monitored by pH and zeta potential measurements. It was observed that the particles present in the solution at the beginning of the synthesis, having an average size of 2 nm, were replaced by a second population consisting of particles with an average size of 20 nm, shortly after the temperature was increased. The average particle size of this population remained constant for some period, while the compositions and structures of the particles were observed to change according to the TG analyses. Afterwards, a sudden increase was observed in the particle size, due to agglomeration, giving rise to a third population growing at a constant rate. XRD, FTIR and TG analyses showed that the first indications of crystallinity appeared at this point. This results indicate that the evolution of crystallinity started right at the point of sudden increase in particle size. Before the sudden increase in particle size, the samples were basically mesoporous in nature but also contained micropores to some extent, according to the nitrogen adsorption isotherms. In parallel to the crystallinity increase, starting with the growth of the particles, the zeolitic micropore volume increased while the mesopores decreased. The variations in pH and zeta potential values were very informative about the course of crystallization. pH values increased parallel to the increase in the crystallinity of the growing particles (third population) and then remained constant. Two sudden drops were observed in the zeta potential of the particles. The first one occurred when particle size increased suddenly and the second one took place when the particle growth stopped. The first sudden decrease in zeta potential when the particle size exhibited a sudden increase was the indication of the increase in negative surface charge, due to loss in surface area as a result of the sudden agglomeration that took place at that stage in the course of crystallization. AFM analyses applied to the final product indicated that the growth process took place mainly by particle addition to the growing crystals. Size growth stopped when the solution was depleted of the growth units, probably as a result of the decrease in silica concentration and increase in the pH of the solution. The continuing increase in the crystallinity of the particles after size growth stopped implied that monomer addition from solution also took place.