Synthesis of Nanosize MCM-48 with High Thermal Stability

Synthesis of Nanosize MCM-48 with High Thermal Stabilit

Hydrothermal Transformation and Characterization of Porous Silica Templated by Surfactants

The effect of hydrothermal conditions on the interactions between surfactant molecules and silicate species plays a key role in the structural transformations of silica precursors. In this work the structures of different siliceous products obtained at various synthesis temperatures have been characterized by powder X-ray diffraction (XRD), FT-IR spectroscopy, 27Al and 29Si magic angle spinning (MAS) NMR, N2 adsorption/desorption measurements, and thermogravimetric analysis. The XRD results show that the removal of other soluble ions from synthesis mixture is a primary step for preparation of the mesostructure in the CTAB−silicate−water synthesis system. Increasing the hydrothermal temperature may lead to the various structures of porous silica and change the behaviors of surfactants in the synthesis mixture. With the increase of hydrothermal temperature from 100 °C to above 165 °C or the prolonging of reaction time at a fixed temperature of 170 °C, the transformation sequence of the following structural phases is identified by XRD:  hexagonal MCM-41 → lamellar M41S → ZSM-5. Comparison with the results from XRD, pore structure measurement, FT-IR, and NMR demonstrates that the intermediate product from the hexagonal mesostructure to microporous crystallite is the lamellar phase rather than the ill-defined hexagonal structure. DTG results indicate that the formation of different structures could result from the different surfactant templating molecules. The main contribution of this work lies in attempts to provide an effective route for controlling conditions of the formation of different mesoporous phases and to understand the cooperation of surfactant molecules and inorganic species

Synthesis of Zeolite EMT with Aid of Sodium Phosphate

Synthesis of Zeolite EMT with Aid of Sodium Phosphat

Investigation of Synthesizing MCM-41/ZSM-5 Composites

MCM-41/ZSM-5 composites were prepared using a dual templating method through a process of two-step crystallization. Mesoporous MCM-41 was first synthesized using the self-assembling of surfactant cetyltrimethylammonium bromide and subsequently the amorphous wall of MCM-41 was recrystallized with a structure-directing agent tetrapropylammonium bromide, which was introduced into the MCM-41 wall through a pretreatment process. A solid to solid-phase transformation mechanism was presented for the recrystallization of MCM-41 framework. Two kinds of stable MCM-41/ZSM-5 composites can be synthesized during the course of recrystallization. Crystallized mesoporous MCM-41 containing only short-range ordered ZSM-5 structure was first synthesized in the early stage of the recrystallization. With the increase of recrystallization time, some discrete micron-sized ZSM-5 crystals were produced and firmly attached to the loose aggregates of crystallized MCM-41, and another kind of MCM-41/ZSM-5 composite containing interconnected mesopore and micropore was therefore obtained. Because of improved acidity and a 2-fold pore system, both MCM-41/ZSM-5 composites are more advantageous than amorphous MCM-41 and a mechanical mixture of MCM-41 and ZSM-5 in acid catalysis

Efficient reference-less transmission matrix retrieval for a multimode fiber using fast Fourier transform

Transmission matrix (TM) linearly maps the incident and transmitted complex fields, and has been used widely due to its ability to characterize scattering media. It is computationally demanding to reconstruct the TM from intensity images measured by a reference-less experimental setup. Removing reference beam for interference gains the advantage of simple experimental setup. However, the long computational time still limits its practical application. We propose an efficient reference-less TM retrieval method for multimode fiber (MMF). Our method adopts a data acquisition scheme which employs Fourier transform matrix in the design of the incident fields. We develop a nonlinear optimization algorithm to solve the TM retrieval problem in a parallel manner. The data acquisition scheme allows the algorithm to be implemented with fast Fourier transform (FFT), and hence achieves great efficiency improvement. Further, our method acquires intensity images at a defocus plane and correct the error of relative phase offset of TM recovered from the intensity images measured at one fixed plane. We validate the proposed TM retrieval method with both simulations and experiments. By using FFT, our TM retrieval algorithm achieves 1200x speed-up in computational time, and recovers $2286 \times 8192$ TM of a 0.22 NA and $50 \ \mu m$ diameter MMF with 124.9 seconds by a computer of 32 CPU cores. With the advantages of efficiency and the correction of phase offset, our method paves the way for the application of reference-less TM retrieval in real practice

Preparation of Zeolite ANA Crystal from Zeolite Y by in Situ Solid Phase Iso-Structure Transformation

A new method has been explored to synthesize zeolite ANA crystals with regular icositetrahedron in aqueous media via transformation of zeolite Y under the conditions of low temperature, short reaction time, and without organic template. The products are perfect, almost 100% crystals. The samples prepared at different crystallization stages are measured by XRD, TEM, and SEM to investigate the transformation mechanism from zeolite Y to zeolite ANA. It has been demonstrated for the first time that the mechanism of forming a zeolite ANA polycrystal with sphere or shell morphologies is the in situ solid phase iso-structure transformation (Is-SPIST) of zeolite Y. The Is-SPIST mechanism is also supported by the results of steam-induced crystallization experiments and other assistant means, including the same Si/Al ratio, the same weight, the same particle size, and the same morphology before and after transformation of zeolite Y to zeolite ANA. It is also observed that a spherical or shell ANA polycrystal is constructed via the reconstruction from its exterior to interior, to form an ANA single crystal with a solid or hollow icositetrahedron. The main driving force of the reconstruction is considered to be the grain boundary energy existing between polycrystalline grains. This process also obeys the mechanism of in situ solid phase reconstruction (Is-SPR). Furthermore, the size and morphology of the zeolite ANA single crystal can be modified by surfactants

Fabrication of Ordered Porous Structures by Self-Assembly of Zeolite Nanocrystals

Fabrication of Ordered Porous Structures by Self-Assembly of Zeolite Nanocrystal