C16H33N Research Articles

X-ray structural modeling of silicate mesoporous mesophase material

Rietveld’s technique in combination with a continuous electron density representation was applied to structural modeling of highly ordered pure siliceous mesoporous mesophase material C16-SiO2-MMM of the MCM-41 type prepared by hydrothermal synthesis in the presence of C16H33N(CH3)3Br. Several important characteristics of the material in both as-synthesized and calcined forms were revealed. In particular, it was found that mesopores in the materials are of true hexagonal shape, and the wall electron density seems to be not continuous.

Characterization of Ordered Mesoporous Gallium MCM-41 Synthesized at Room Temperature

A series of highly ordered mesoporous gallium-containing MCM-41 molecular sieves with variable Si/Ga (100−10) ratios have been synthesized at room temperature. The synthesized Ga−MCM-41 was investigated by powder X-ray diffraction, transmission electron microscopy, thermal analysis, N2 adsorption measurement, and 29Si and 71Ga nuclear magnetic resonance (NMR); optimal synthesis conditions have thus been established. We were successful in synthesizing highly ordered material at room temperature using gallium nitrate as the source of gallium, and the surfactant was the cetyltrimethylammonium cation [(C16H33N(CH3)3]+. 71Ga NMR of calcined and uncalcined Ga−MCM-41 demonstrated that gallium was substituted for Si with tetrahedral coordination in the Ga−MCM-41 structure. N2 adsorption measurements indicate that high mesoporosity exists over the entire range of Ga−MCM-41 with an average pore diameter of 38.3 Å.

Formation Process of MCM-41 Precursor and Porous Texture of MCM-41

The formation process of the MCM-41 precursors (silicate/surfactant complex) was investigated on the basis of the pH titration curves of Na4SiO4 in the presence of [C16H33N(CH3)3]Cl. Measurements of the pH titration curves were carried out using the computer-controlled gravimetric titrator constructed in our laboratory. The white precipitate (MCM-41 precursor) was abruptly formed at pH 11.1 (298 K) and at pH 9.9 (343 K). Formation of the MCM-41 precursor can be explained by coagulation of the rod-like micelle colloids whose surface is covered by the condensed silicate anions of (HSiO3)nn−. The porous texture of the MCM-41 samples whose precursors were synthesized under different conditions was analyzed on the basis of the adsorption isotherms of nitrogen at 77 K. It has been shown that the MCM-41 sample whose precursor was prepared at pH 9.9 and 343 K shows one sharp peak (rp = 1.65 nm) in the pore size distribution curve, but the MCM-41 samples whose precursors were prepared at pH 6.5–5.0 and 343 K give two peaks (rp = 1.66 nm and rp = 2.12–2.36 nm). The appearance of the second peak (rp = 2.12–2.36 nm) has been considered to be in connection with the destruction of the MCM-41 precursor into small fragments in acidic medium.

Analysis of Nitrogen Adsorption Isotherms for a Series of Porous Silicas with Uniform and Cylindrical Pores: A New Method of Calculating Pore Size Distribution of Pore Radius 1–2 nm

Two kinds of the porous silicas with uniform and cylindrical pores were prepared from calcined Na4SiO4and cationic surfactants ([C16H33N(CH3)3]Cl and [C18H37N(CH3)3]Br). In this paper, we call these porous silicas PS-C16 and PS-C18. PS-C16 was calcinedin vacuoat 873–1273 K in order to prepare a series of porous silicas having different pore sizes. All nitrogen adsorption isotherms for a series of the porous silicas show no hysteresis in the adsorption and desorption branches. The nitrogen adsorption isotherms were analyzed by thetmethod, and the pore surface area (Sp), the pore volume (Vp), and the core volume (Vc) were determined. The pore radius (rp), the core radius (rc), and the adsorbed thickness on the pore wall (tpore) were computed from the measured values ofSp,Vp, andVc. We can determine the relationship between the Polanyi adsorption potential and the core radius in the range ofrc= 0.6–1.2 nm. On the basis of the present data, we propose a new method of calculating the pore size distribution in the range ofrp= 1–2 nm.

The Synthesis and Characterisation of Ordered Mesoporous Materials Incorporating Organo-Siloxanes

AbstractOrganically-functionalized mesoporous silicas have been prepared at room temperature, in a base-catalysed reaction, by the co-condensation of tetraethoxysilane and organosiloxanes ((C2H5O)3Si-R; R = C6H5 or n-C8H17) in the presence of surfactant (C16H33N(CH3)3Br) templates. The resulting materials are covalently linked, hexagonally ordered, hybrid inorganicorganic networks.

Functional micellar catalysis. Part 4. Catalysis of activated ester hydrolysis by surfactant systems as chymotrypsin models

Micelles made up of each of five surfactants of general structure C16H33N(CH3)2(CH2)nFH [(I), n= 2, FH = OH; (II), n= 1, FH = C(Ph)NOH; (III), n= 1, FH = CO·C(Ph)NOH;(IV), n= 1, FH = imidazol-4-yl (lm); (V), n= 2, FH = NH·CO·lm], of the bifunctional surfactant C16H33N(CH3)(CH2lm)(CH2CH2OH)(VI), of Nα-myristoylhistidine (VII), and of N-methylmyristohydroxamic acid (VIII) have been investigated as catalysts of p-nitrophenyl acetate (PNPA) and hexanoate (PNPH) hydrolysis in the pH range 7–8. The activity of α-chymotrypsine toward PNPA at pH 7.95 has also been measured. The kinetic analysis was carried out under the same conditions in each instance and rate data are directly compared. A nucleophilic mode of action is indicated for each type of micelle and differences in the rate of acylation and turnover are discussed with reference to related micellar systems and to the enzyme α-chymotrypsin.