Ratio In Synthesis Gel Research Articles

A study on the synthesis of [Fe,B]-MFI zeolites using hydrothermal method and investigation of their properties

Synthesis of MFI-type zeolites with boron and iron in their framework using conventional hydrothermal method was investigated. The effect of several parameters including gel composition and pH on the crystallization of zeolites was systematically studied. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 physical adsorption analysis. The XRD patterns showed that the crystallization of boroferrisilicate zeolite takes place at pH values higher than 9 with molar ratio of Si/(Fe+B)≥8.3. The crystallinity and BET surface area of zeolites was decreased by increasing the amount of Fe3+ ions in the synthesis gel. The SEM images revealed that Fe/B ratio of synthesis gel could also influence the morphology of zeolite particles. The drug loading capacity of boroferrisilicates with different Fe/B ratios was evaluated by loading of doxorubicin (DOX) as a model drug. Among zeolites with Fe/B ratios of 0.5, 1 and 2, higher loading efficiency was achieved for sample with lower iron content. However, for sample with Fe/B=∞ which the formation of iron oxide particles on the external surface of sample was confirmed by XRD and SEM analysis, the DOX loading efficiency was remarkably high. Since the desorption of DOX molecules from zeolites surface was prevented by the strong interaction between drug molecules and the surface of heteroatom-substituted zeolites, the release efficiency for all boroferrisilicate zeolites was low.

Synthesis of NaX zeolite: Influence of crystallization time, temperature and batch molar ratio SiO2/Al2O3 on the particulate properties of zeolite crystals

Abstract In this study, the effects of crystallization time, temperature and SiO 2 /Al 2 O 3 molar ratio in the synthesis gel on the end products (NaX zeolite) were investigated. The results revealed that crystallization time and temperature determined whether or not NaX zeolite was formed. Furthermore, SiO 2 /Al 2 O 3 molar ratio was found to play a significant role in the particulate properties of the crystalline end products. A single phase NaX zeolite was obtained only with the SiO 2 /Al 2 O 3 molar ratio of 1.5–4.0; the NaA zeolite was developed at SiO 2 /Al 2 O 3 = 1.0 in addition to the NaX zeolite. However, at SiO 2 /Al 2 O 3 = 0.5, a single phase NaA zeolite was generated. The Si/Al molar ratios of NaX zeolites were tested to be 1.38, 1.33, 1.29, 1.24 and 1.18 for the SiO 2 /Al 2 O 3 molar ratios of 4.0, 3.5, 2.9, 2.0 and 1.5. The corresponding samples had the mean particle sizes of 464, 548, 689, 836 and 980 nm, with the particle size distribution ranges of 120–810, 202–815, 445–975, 605–1096 and 770–1218 nm, respectively. N 2 adsorption–desorption results showed that the BET surface areas and micropore volume of the end product increased with the decrease of SiO 2 /Al 2 O 3 molar ratio in synthesis gel, but all the NaX zeolite particles have relatively high total pore volumes. In addition, the effect of molar ratio of SiO 2 /Al 2 O 3 on the amount of NaX zeolite formed in the products was also considered.

Preparation of MCM-41 with high thermal stability and complementary textural porosity

Preparation of mesoporous molecular sieve MCM-41 with complementary textural porosity and high thermal stability that results from thicker wall has been achieved by decreasing surfactant/silicon ratio of synthesis gel. MCM-41 material obtained by using the surfactant/silicon molar ratio of 0.10 consists of large and well-defined spherical particles. A further decrease in the ratio results in the formation of MCM-41 silica with the bimodal framework meopores and complementary textural porosity. The textural porosity results from the loose aggregate structure. The resultant materials retain ordered channels and large BET surface area even after thermal treatment at 1273 K for 1 h in air. The complementary textural porosity decreases the length of the one-dimensional mesopores and provides the facilitating framework access for the diffusion of mass.

Preparation of high thermal stability MCM-41 in the low surfactant/silicon molar ratio synthesis systems

The preparation of a mesoporous molecular sieve MCM-41 both with bimodal framework and textural mesopores and with high thermal stability that results from a thicker wall has been achieved by decreasing surfactant/silicon ratio of synthesis gel. The resultant material retains porosity and large BET surface area even after thermal treatment at 1273 K for 1 h in air.