Evolution of Morphology, Fractal Dimensions, and Structure of (Titanium) Aluminosilicate Gel during Synthesis of Zeolites Y and Ti-Y

Abstract

Zeolite Y and Ti-containing zeolite Y (1%, 2% and 5% TiO2) were synthesized by a hydrothermal seed-assisted method. In order to evidence the evolution of morphology, structure, and fractal dimensions during the zeolitization process at certain time intervals, a small volume from the reaction medium was isolated and frozen by lyophilization. The obtained samples were characterized by scanning electron microscopy (SEM), wide-angle X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). The fractal dimension values of the isolated samples, calculated from SAXS data, evidenced a transition from small particles with a smooth surface (2.021) to compact structures represented by zeolite crystallites with rough surfaces (2.498) and specific organization for zeolite Y. The formation of new structures during hydrothermal treatment, the increase in crystallite size and roughness due to the continuous growth were suggested by variation of fractal dimensions values, SEM microscopy images and X-ray diffractograms. The incorporation of titanium in low concentration into the zeolite Y framework led to the obtaining of low fractal dimensions of 2.034–2.275 (smooth surfaces and compact structures). On the other hand, higher titanium concentration (2%) led to an increase in fractal dimensions indicating structures with rougher surfaces and well-defined self-similarity properties. A mechanism for zeolite synthesis was proposed by correlation of the results obtained through morphological, structural, and fractal analysis.

Effects of Aluminosilicate Gel Treatment and TiO2 Loading on Photocatalytic Properties of Au–TiO2/Zeolite Y

“…This mixture was aged for 24 h at room temperature and further, 6 h at 100 °C in a Teflon-lined autoclave. The formation of the aluminosilicate gel and its evolution during the zeolitization process was described in detail in a study recently reported by our group [ 30 ]. In order to obtain the aluminosilicate support with suitable properties for photocatalysis, the treatment of the corresponding gel resulting from mixing sodium silicate with sodium aluminate was completed differently.…”

“…For this purpose, the effects of the experimental conditions during the processing of the synthesis gel on the structural and morphological properties of zeolite Y were evaluated. Previous studies showed the formation of zeolite Y crystalline phase during the sol–gel process [ 30 ]. Compared to the other porous supports used (MCM-48, KIT-6, SBA-15, hierarchical zeolite Y), microporous zeolite Y with the same concentration of TiO 2 (10%) seems to have a lower activity [ 20 ].…”

Fractal Properties of Composite-Modified Carbon Paste Electrodes—A Comparison between SEM and CV Fractal Analysis

“…Since the first studies on fractal objects [6], there have been many reports in the literature showing the fractal nature of surfaces [7]. Moreover, the link between fractal properties and their physical-chemical properties has often been depicted in the last years: the fractal properties of the catalysts [8][9][10][11], zeolites [12], electrodes in electrochemical applications [13][14][15][16][17][18][19], nanoparticles [20,21], dental surfaces [22] have been intensively studied. Understanding the impact of roughness on surface phenomena and, moreover, the fact that most surfaces are self-affine (self-similar and scaling with different amounts in different directions) opened a new chapter in the study of adsorption [10], catalysis [8][9][10][11], and electrochemical processes [14,15,[17][18][19]23,24].…”

Composite Photocatalysts with Fe, Co, and Ni Oxides on Supports with Tetracoordinated Ti Embedded into Aluminosilicate Gel during Zeolite Y Synthesis

“…The first studies regarding the introduction of titanium into the zeolite Y framework by direct synthesis and the effect of Ti concentration on the zeolite structure were carried out by our group [20,21]. Zeolite Y is a faujasite molecular sieve with 7.35 Å diameter pores and a three-dimensional pore structure.…”

“…The preservation of the zeolitic network was obtained for 1 and 2% TiO 2 , and its partial disruption was observed for 5% TiO 2 . The synthesis of Ti-Y and the effect of titanium concentration on the formation of the zeolite Y structure were evaluated by freezing the sol-gel phases at various periods [21].…”