4TH International Congress on Technology - Engineering & SCIENCE - Kuala Lumpur - Malaysia (2017-08-05)

Porous Clay Heterostructures: Synthesis, Metal Incorporation And Characterization

Porous clay heterostructures (PCHs) based on cationic layered clays are interesting materials because of their large surface areas and unique combined micro- and mesoporosity. They are synthesized by separating the clay layers by silica pillars. First, the clay layers are intercalated by the hexagonal organic cation. The in-situ silica pillars synthesis by the hydrolysis of silica source around the organic micelle under ammonia catalysis. The template removal either by calcination or extraction creates a new type of pillared clays with intragalleries between the silica pillars in mesopore dimensions while the silica wall provides the microporosity [1,2]. The possibility of design of the surface properties of PCHs by metal doping is another advantage in terms of the diversity of application areas. The catalytic properties can be tuned by one pot or post modifications with species interacting with the silanols of surface. Pure titanium only possesses Lewis acidity while Bronsted acidity is gained by the silica and the ones which are created form Ti-O-Si chemical bonds that is why titania-silica materials have been extensively used as photo catalysts, acid catalysts and oxidation catalysts [3]. PCHs structures have been synthesized by doing modifications on the recipe of Guo and Zhang [4] with improvements using SWy-2 (Wyoming Na-Montmorillonite) standard clay mineral and bentonite from Middle Anatolia as the hosts via in-situ micelle formation with subsequent silica condensation using with different clay/Si ratios. Intercalating was achieved by use of cetyl trimethyl ammonium bromide (CTAB) as surfactant by a molar ratio of clay/CTAB as 2.0. Tetraethyl ortho silicate (TEOS) and titanium (IV) isopropoxide (TIP) were used as the silica and titania sources, respectively. To assist template shaping and accelerating silica condensation under ammonia-catalyzed conditions, the co-surfactant octylamine (OA) was used. Titanium was incorporated to the silica matrix in one-pot synthesis taking the Metal/Si ratio as the parameter. The combined results from all several characterization techniques strongly suggest that novel PHCs and Ti/PHCs were synthesized successfully. PHCs with superior properties obtained in the literature have been obtained. All samples resembled Type II isotherms with uniform and similar sized mesopores with surface area values over 1000 m2/g. The pillared structure was confirmed by X-ray diffraction (XRD) by the observed increase in basal spacing value up to 4.3 nm and titanium incorporation caused a little increase in the channel spacing by not causing noticeable textural properties. The formation of silica pillars within the clay bundles were observed in TEM images. The sharp increase in FTIR intensity of Si-O-Si and silica amount both in ICP and XPS results confirmed the formation of SPC. Carbon analysis and TGA results showed the success of template removal. The titanium incorporation caused a little increase in the channel spacing by not causing noticeable textural properties. The loading success was confirmed by the chemical analysis and it resulted increases in quantity of acid centers.
Keywords: heteroclay, in-situ, hydrothermal synthesis, characterization
Burcu Yeter, Suna Balcı, Fatma Tomul