Synthesis of silica particles with lamellar and wormhole-like bi-modal mesopores using anionic surfactant as the template

Silica particles with lamellar and wormhole-like bi-modal mesopores have been synthesized using anionic surfactant (N-lauroylsarcosine sodium) as the template. The particles with diameters of 300―500 nm possess bi-modal mesopores with pore sizes of 3 nm and 12 nm, which were ascribed to the disordered wormhole-like mesophase and lamellar mesophase, respectively. The BET surface area of the particles was 536 m2/g and the pore volume was 0.83 cm3/g. The lamellar mesophase and cylindrical mesophase were formed...     

High-temperature synthesis of stable ordered mesoporous silica materials by using fluorocarbon-hydrocarbon surfactant mixtures

Highly ordered hexagonal mesoporous silica materials (JLU-20) with uniform pore sizes have been successfully synthesized at high temperature (150-220 degrees C) by using fluorocarbon-hydrocarbon surfactant mixtures. The fluorocarbon-hydrocarbon surfactant mixtures combine the advantages of both stable fluorocarbon surfactants and ordered hydrocarbon surfactants, giving ordered and stable mixed micelles at high temperature (150-220 degrees C). Mesoporous JLU-20 shows extraordinary stability towards hydrothermal treatment (100 % steam at 800 degrees C for 2 h or boiling water for 80 h), thermal treatment (calcination at 1000 degrees C for 4 h), and toward mechanical treatment (compressed at 740 MPa). Transmission electron microscopy images of JLU-20 show well-ordered hexagonal arrays of mesopores with one-dimensional (1D) channels and further confirm that JLU-20 has a two-dimensional (2D) hexagonal (P6 mm) mesostructure. 29Si HR MAS NMR spectra of as-synthesized JLU-20 shows that JLU-20 is primarily made up of fully condensed Q4 silica units (delta=-112 ppm) with a small contribution from incompletely cross-linked Q3 (delta=-102 ppm) as deduced from the very high Q4/Q3 ratio of 6.5, indicating that the mesoporous walls of JLU-20 are fully condensed. Such unique structural features should be directly attributed to the high-temperature synthesis, which is responsible for the observed high thermal, hydrothermal, and mechanical stability of the mesoporous silica materials with well-ordered hexagonal symmetry. Furthermore, the concept of "high-temperature synthesis" is successfully extended to the preparation of three-dimensional (3D) cubic mesoporous silica materials by the assistance of a fluorocarbon surfactant as a co-template. The obtained material, designated JLU-21, has a well-ordered cubic Im3m mesostructure with fully condensed pore walls and shows unusually high hydrothermal stability, as compared with conventional cubic mesoporous silica materials such as SBA-16.     

Mixed surfactants-directed the mesoporous silica materials with various morphologies and structures

A new mixed surfactants system using alkyl carboxylic acids and quaternized poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl] urea] (PEPU) as the co-template was used to synthesize mesoporous silica materials with various morphologies and structures, including flakes, regular spheres, nanoparticles, and tube-spheres. The cationic polymer connected the anionic surfactant micelle to the anionic polysilicate species to induce the synthesis of the mesoporous silica materials. The structure and property of the surfactant and the cationic polymer determined the formation of mesoporous silica, and also had a signification influence on the morphology and structure of the final materials. To further explore the possible formation mechanism of these mesoporous materials, zeta potential was utilized to evaluate the interaction between the anionic surfactant and the cationic co-template. In addition, the structure, morphology, and porosity of these materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption-desorption measurements.     

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.     

Bicontinuous cubic mesoporous materials with biphasic structures

The replication of amphiphilic systems within an inorganic silica matrix allows the study of the fundamental properties of mesostructural changes, that is, kinetic and structural parameters. Herein we report a detailed study of the transition between cubic bicontinuous mesostructure with space groups Ia$\bar 3The replication of amphiphilic systems within an inorganic silica matrix allows the study of the fundamental properties of mesostructural changes, that is, kinetic and structural parameters. Herein we report a detailed study of the transition between cubic bicontinuous mesostructure with space groups Ia ?3d and Pn ?3m symmetry, which are associated with the minimal G and D surfaces, respectively. The transition may be induced through micellar swelling of the anionic amphiphilic surfactant N-lauroyl alanine by trimethylbenzene. Rich kinetic behaviour is observed and has been exploited to prepare particles with biphasic structures. Transmission electron microscopy evidence indicates that there is epitaxial growth from one mesostructure to the other involving the [111] and [110] orientations of the Ia ?3d and Pn ?3m symmetry structures, respectively. From kinetic studies, we show that the formation of the Ia ?3d mesophase is preceded by a hexagonal phase (plane group p6mm) and an epitaxial relationship has been observed involving the sixfold or ?3 axis orientations of both structures. Our data suggests that the Pn ?3m mesostructure is kinetically stable at low temperatures whereas the Ia ?3d mesostructure is the more stable structure after prolonged periods of hydrothermal treatment. We present evidence from transmission electron microscopy and small-angle X-ray diffractograms and also electron crystallography modelling of the unit cells at particular points in the structural change.     

Study of the Pm3n space group of cubic mesoporous silica.

By using a Gemini surfactant, [C14H25N+(CH3)2-(CH2)2-N+(CH3)2C14H25]2 Br-(C(14-2-14)), with a short spacer group (s = 2) as structure-directing agent and sodium silicate as precursor, high-quality, ordered cubic mesoporous silica with space group Pm3n was prepared by the S+I-route (S = surfactants, I = precursor). The samples were characterized by small-angle X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption. The results showed that the pore structure of the resulting mesoporous silica belonged to the cubic system (space group Pm3n). The unit-cell parameter of the cubic system was in the range of 8.81-9.14 nm. The high-quality cubic mesoporous structure was formed at molar ratios of C(14-2-14) to sodium silicate of 0.33:1 to 0.16:1 and a molar ratio of ethyl acetate to sodium silicate of 2:1. N2 adsorption-desorption curves revealed type IV isotherms and H1 hysteresis loops. The primary pore volume, and the most probable pore size according to the Barrett-Joyner-Halenda (BJH) model, increased with increasing molar ratio of C(14-2-14) to sodium silicate.     

Polymeric surfactants based on oleic acid. II. Copolymerization of sodium acrylamidostearate and 10-undecen-1-ol in a lamellar liquid crystal

Copolymerization of sodium acrylamidostearate (NaAAS) and 10-undecen-1-ol (UdOH) was performed in the lamellar liquid crystal (LLC) formed by NaAAS, UdOH, and water. After the polymerization the lamellar structure remained, and the disorder of the lamellar liquid crystal was, to some extent, reduced. Surface tension, small-angle X-ray diffraction, dynamic light scattering, viscosity, and fluorescence methods were used to study the properties of the copolymer. The polymeric surfactant behaves like polyelectrolyte and is more surface active than its precursor, i.e., NaAAS. The polymeric surfactant is capable of forming uni-molecular micelles through coiling of its hydrophobic chains. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2863–2872, 1999     

Synthesis and characterization of organic-inorganic hybrid mesoporous silica materials with new templates

1-Hexadecane-3-methylimidazolium bromide and 1-hexadecane-2,3-dimethylimidazolium bromide were used as new templates for the syntheses of periodic mesoporous organosilica (PMO) materials; using these new templates, ethane-bridged PMO materials were successfully synthesized and characterized under basic conditions.     

Synthesis of highly-ordered mesoporous silica particles using mixed cationic and anionic surfactants as templates

We applied a molecular assembly formed in an aqueous surfactant mixture of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium octylsulfate (SOS) as templates of mesoporous silica materials. The hexagonal pore size can be controlled between 3.22 and 3.66 nm with the mixed surfactant system. In addition, we could observe the lamellar structure of the mixed surfactants with precursor molecules, which strongly shows the possibility of precise control of both the pore size and the structure of pores by changing the mixing ratio of surfactants. Moreover, use of the cationic surfactant having longer hydrophobic chain like stearyltrimethylammonium bromide (STAB) caused the increase in d(100) space and shifted the point of phase transition from hexagonal phase to lamellar phase to lower concentration of SOS.     

Synthesis of carbon tubes with mesoporous wall structure using designed silica tubes as templates

Hollow silica tubes with mesoporous wall structure were synthesized through the sol-gel reactions of tetraethoxysilane and n-octadecyltrimethoxysilane (TEOS/C18-TMS) on the surface of ammonium dl-tartrate crystals. Novel hollow carbon tubes with mesoporous walls and rectangular-shaped channels were fabricated using the silica tubes as templates.     

Synthesis of thermally stable mesoporous cerium oxide with nanocrystalline frameworks using mesoporous silica templates

Highly ordered mesoporous cerium oxides, composed of nanocrystalline pore walls and exhibiting high thermal stability even at 973 K, were synthesized using mesoporous silica templates with hexagonal p6mm and cubic Ia3d symmetries.     

Synthesis of mesoporous silica for adsorption of chlordiazepoxide and its determination by HPLC: Experimental design

In this work, mesoporous silica (SBA‐15‐NH₂) was used as an efficient adsorbent for extraction of chlordiazepoxide from different samples based on dispersive nanomaterial‐ultrasound assisted microextraction followed by high‐performance liquid chromatography. The prepared sorbent was characterized by fourier transform infrared spectroscopy, scanning electron microscopy, low‐angle X‐ray diffraction, thermal analysis, and N₂ adsorption‐desorption surface area measurement. Several variables affecting the extraction efficiency of the chlordiazepoxide, including the amounts of adsorbent, time of adsorption, pH and volume of desorption solvent were optimized by central composite design combined with desirability function. The values of variables were set as 10 mg of SBA‐15‐NH₂, 15 min adsorption time, pH = 7.3 and 1 mL methanol. The linear response (0.998) was obtained in the range of 0.006–10 µgmL^?1 with detection limit 0.0014 µg/mL and extraction recovery was in the range of 91–96% with relative standard deviation < 6%.     

Extraction of cationic surfactant templates from mesoporous materials by CH(3)OH-modified CO(2) supercritical fluid

Extraction of cationic surfactant templates from MCM-41, MCM-48, SBA-1 and SBA-3 has been conducted using CH₃OH-modified CO₂ supercritical fluid. The supercritical fluid extraction (SFE) has been integrated with thermogravimetry (TG), X-ray diffraction (XRD) and N₂ adsorption-desorption to evaluate extraction efficiency and structural stability of mesoporous materials. Experiments of optimization indicate that the conditions of 90 bar, 85 °C, CH₃OH/CO₂ = 0.1/1.0 ml/min and 3 h are most suitable for the SFE of cationic templates. 76-95% of the cationic templates can be extracted from the mesoporous materials. XRD and N₂ adsorption-desorption studies illustrate that SFE possesses some advantages over calcination in maintaining mesoporous uniformity and structural stability when used to remove templates. The impact of curing on mesoporous structure is also dealt with.     

Study of adsorption properties of synthesized mesoporous silica doped with dysprosium and modified with nickel

Mesoporous silica (MPS) modified with nickel and MPS doped with dysprosium and modified with nickel have been synthesized by the template method. The adsorbents are characterized by various techniques such as transmission electron microscopy, scanning electron microscopy, X-ray diffraction, inductively coupled plasma spectroscopy, and X-ray fluorescence analyses. The adsorption properties of the synthesized samples have been investigated by inverse gas chromatography. Furthermore, thermodynamic characteristics of the adsorption of test compound belonging to different classes of organic compounds were obtained. In addition, the contributions of the energy of specific interactions to the total adsorption energy were calculated. It is also shown that entropy plays the determining role in the adsorption of test compounds on synthesized mesoporous materials.