Synthesis of mesoporous MCM-48 using fumed silica and mixed surfactants

Currently, opening up the possibility of low-cost mineral for preparing ordered mesoporous materials is of significant importance. In the present work, hexagonally ordered mesoporous aluminosilicate molecular sieve was hydrothermally synthesized from natural halloysite without addition of silica or aluminum reagents. The mesoporous structure of the synthesized materials was confirmed by small angle X-ray diffraction and nitrogen sorption analysis. Scanning electron microscope and transmission electron microscope observations indicated that highly ordered two-dimensional hexagonal mesoporous structure was obtained. Wide angle X-ray diffraction and Fourier transform infrared spectroscopy were also used to examine the variations of chemical structures. The surface area of the prepared material after being calcined at 550 °C was 524.6 m2/g and the pore volume was 0.87 cm3/g. 27Al solid state magic angle spinning nuclear magnetic resonance spectrum showed that all of aluminum species were tetrahedrally coordinated into the framework of the mesoporous material. A possible mechanism for the formation of aluminosilicate molecular sieves from natural halloysite was also discussed accordingly.

Synthesis and characterization of ordered mesoporous aluminosilicate molecular sieve from natural halloysite

Synthesis of nanosize MCM-41 loaded with TiO2 and study of its photocatalytic activity

High-quality cubic MCM-48 is successfully synthesized using a new silica source known as silatrane and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent via sol–gel process. The effects of synthesis parameters, viz. crystallization temperature, crystallization time, surfactant concentration, quantity of NaOH, and silica source, on the product structure are investigated. The synthesized samples are characterized using X-ray diffractometer (XRD), N2 adsorption–desorption isotherms, and electron microscopy. Optimally, this product is synthesized from samples crystallized at 140°C for 16 h with a CTAB/SiO2 ratio of 0.3 and NaOH/SiO2 ratio of 0.5. The XRD result exhibits a well-resolved pattern, corresponding to the Ia3d space group of MCM-48. The BET surface area of this product is as high as 1,300 m2/g with a narrow pore-size distribution of 2.86 nm. The scanning electron microscopic (SEM) images also show the truncated octahedral shape and well-ordered pore system of MCM-48 particles.

Synthesis of MCM-48 from silatrane via sol–gel process

Characterization of CoMCM-41 mesoporous molecular sieves obtained by the microwave irradiation method

The hydrothermal synthesis of Si-MCM-48 mesoporous molecular sieves was carried out using a ternary SiO 2 :CTAOH:H 2 O system wherein differently manufactured amorphous silica powders such as fumed silica (FMDS), spray dried precipitated silica (SDPS) and flash dried precipitated silica (FDPS) were used as silica source materials. The changes in structural/textural properties were evaluated using powder XRD, N 2 adsorption–desorption and scanning electron microscopy techniques. Studies on the progressive development of MCM-48 mesophases revealed that, the reactivity of the silica source follow the trend: FMDS > SDPS > FDPS. MCM-48 synthesized using low cost FDPS has exhibited thicker pore walls but poorer orderness, while MCM-48 prepared from relatively expensive FMDS has thinner pore walls and more ordered structure. Moreover, the extent of contraction caused by calcinations, agglomerate size and structural stability were found to depend on the reactivity of the silica source used.

U.S. Taralkar

Papers

Structural evolutions of hydrothermally prepared mesostructured MCM-48 silica using differently manufactured amorphous silica powders