Papers by Keyword: Mesoporous Molecular Sieve

Abstract: At present, most of molecular sieves (MCM-48) are prepared by using dual template agents. In this paper, the effect of different template agents on the synthesis of MCM-48 under the same conditions is studied. MCM-48 was synthesized by different combinations of templates (CTAB + TEAOH, CTAB + TBAB, CTAB + P123). The specific surface areas of them were compared under different crystallization temperature and different crystallization time. The results show that the specific surface area of MCM-48 prepared by CTAB + TEAOH is higher than that of other dual template agnets at the same crystallization time and temperature when the molar ratio of CTAB to another template is 9.

Abstract: The hydrothermal synthesis of MCM-48 molecular sieves with CTAB and TEAOH as dual template agents and alkaline silica sol as silicon source has been systematically studied. The samples prepared at different crystallization temperature and time were analyzed by XRD, IR, nitrogen adsorption and desorption. The result shows that the best crystallization temperature and time are 100°C and 48h, respectively. According to BJH algorithm, the specific surface area of the sample is 1088 ~ 1669 m²/g, the pore size is 2.48 ~ 2.54 nm, and the pore volume is 1.2064 ~ 1.263 0cm³/g. Because it has high specific surface area, it can be widely used in catalytic adsorption, environmental engineering, biomedicine and other fields. Keywords: MCM-48; mesoporous molecular sieve; high specific surface area; dual template agents; alkaline silica sol

Abstract: In the past decade, molecular sieves are applied to the flame retardant research areas. This article introduces the types and functional features of molecular sieve, especially the properties of mesoporous molecular sieve, the function of porous channel system, the method of controlling the aperture and the way of functional modification. On the basis of induction and analysis of molecular sieve in fire-retardant research, I have made three points: (1) Molecular is a good kind of fire-retardant synergist; (2) A little molecular added is enable to improve the ability of fire-retardant materials; (3)Bringing the molecular sieve into woody material is in the trend of smog-retardant, low-poisonous, environment-friendly.

Abstract: In this study, MCM-41 was synthesized by hydrothermal method, using non-toxic sodium metasilicate nonahydrate as the silicon source, cetyl trimethyl ammonium bromide (CTAB) as template, and sulfuric acid as the pH value adjustment agent. The effects of ratio of template agent to silicon source, pH value, crystallization temperature and crystallization time on the yield and crystallization of MCM-41 were investigated. MCM-41 was then characterized by XRD, FTIR, SEM, TEM and N₂ adsorption-desorption testing techniques. Rhodamine B adsorption studies were carried out to study the effects of pH value and reaction time on the adsorption properties of MCM-41. The resulting MCM-41 had smooth surface with a pore size of 3-4nm and an average diameter particle of about 5μm. It had high specific surface area up to 784m²/g, thus adsorption rate of MCM-41 for rhodamine B obtained 93% when pH=3, t=15min. The reaction fitting curve of the Lagergren first order reaction model was lg (q_e-q_t) =-0.00586-0.803t, R² = 0.97582.

Abstract: The mesoporous materials with pore size expansion were synthesized by hydrothermal method with cetyltrimethylammonium bromide (CATB) as template. The N, N-dimethyl formamide (DMFA) amine was selected to expand the pore size of these materials. The samples were characterized by XRD, N₂ adsorption and SEM. The pore size could be changed with post treatment temperature. The range of pore size was 3.94 - 5.83 nm. The pore size didn't increase with the increasing of post treatment temperature. The SEM pictures of materials with pore expansion by post-hydrothermal treatment clearly revealed that the resulting particles were almost perfectly spherical in shape. The XRD analysis showed the typical Bragg reflections of the hexagonal V-MCM-41 material by DMFA at 130 °C for 48 h in the post hydrothermal synthesis.

Abstract: Ordered hexagonally mesoporous molecular sieve Al-MCM-41 with Si/Al (atom) ratio=9 was prepared by hydrothermal synthesis using raw kaolin. X-ray diffraction (XRD), Nitrogen adsorption desorption, Transmission Electron Microscope (TEM) and Energy Dispersive X-ray Detector (EDX) were employed to characterise raw kaolin, calcined kaolin, as-synthesized and calcined Al-MCM-41. The results indicated that characteristic reflections of raw kaolin disappeared after calcination, both of as-synthesized and calcined Al-MCM-41 exhibited well ordered hexagonally mesoporous molecular sieve structure.

Abstract: Mesoporous MCM-41 molecular sieve was synthesized hydrothermally and selected tetraethoxysilane as silica source. Solid superacid SO₄^2- / SnO₂ was supported on MCM-41 by dipping and roasting. The samples were characterized by XRD, TEM, and FT-IR. Solid superacid evenly dispersed on MCM-41 with a good pore structure. Their catalytic activities were evaluated in the isomerization of α-pinene. The results show that samples had a good conversion rate and selectivity.

Abstract: Pure silica mesoporous molecular sieve (MMS) solid has been synthesized at 100°C by hydrothermal process. The effect of synthesis duration from 2 to 10 days has been investigated on the physicochemical properties of mesoporous molecular sieve. Samples were characterized by low angle XRD, N₂ adsorption-desorption and HRTEM analysis. XRD patterns of the as-synthesized samples showed four well-defined diffraction peaks corresponding to 100, 110, 200 and 210 planes. These peaks are the fingerprint characteristics of MCM-41 mesoporous material. The high intensity diffraction peaks were observed in 8-days sample that define the high ordering of the pores and long range order. N₂ adsorption-desorption results showed that all samples possessed a type IV isotherm having hysteresis loop of type H1 which is an identification of mesoporous material. Calcined samples exhibited high surface area i.e., 984-1036 m² g^-1, pore volume i.e., 1.00-1.13 cm³ g^-1 and average pore diameter i.e., 3.04-3.30 nm. A hexagonal pore structure was found in the synthesized materials by HRTEM analysis, which confirms that the synthesized materials are MCM-41. HRTEM analysis showed the effect of synthesis duration on the materials and found that 8-days sample exhibited highly ordered hexagonal pore structure like honeycomb structure. All the samples were calcined at 550°C to remove the template and to study the changes in the mesoporous framework. The results showed that the mesoporous structure remained intact after calcination at 550°C, indicating that the mesoporous materials exhibit high thermal stability.

Abstract: Al-containing mesoporous molecular sieves(Al-MCM-41) were synthesized at ambient temperature. The structures of samples were characterized by XRD, N₂-adsorption/desorption isotherms and FT-IR, etc. The evaluation results showed that Al-MCM-41 had higher catalytic activity for isomerization conversion of endo-tetrahydrodicyclo-pentadiene (endo-TCD) into exo-tetrahydrodicyclo-pentadiene (exo-TCD) and adamantane (AdH). Loading inorganic acid on the surface of Al-MCM-41 led increase of its catalytic activity and the yield of adamantane.

Abstract: Mesoporous V-MCM-41 materials with good hydrothermal stability had been synthesized by microwave-assisted hydrothermal method. The samples by microwave-assisted hydrothermal synthesis and conventional heating remain the same mesoporous structure by XRD and N₂ adsorption analysis. The V-MCM-41 materials by microwave-assisted hydrothermal synthesis show the good hydrothermal stability, close to that of the materials by conventional heating. The high surface area of the sample by 720 W microwave treatment for 8 min was the same as that of the sample by conventional heating (110 °C for 12 h).