Synthesis and characterization of silica sphere-packing mesoporous materials. Silica mesoporous materials were synthesised using a methodolgogy based in the modification of the Stobe–Fink–Bohn (SFB) method, to get porous materials with a develped mesoporosity (original) (raw)
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A study on the structural properties of mesoporous silica spheres
Materials Letters, 2007
The mesoporous silica spheres were prepared by using sodium silicate as silica precursor, and low concentration of CTAB and propanol as templating agents. The resulting spherical particles were characterised by low angle PXRD, N 2 adsorption-desorption studies, pore size distribution, BET-surface area, surface morphology analysis and FTIR. From PXRD data and electron probe microanalysis, it was observed that the propanol:CTAB molar ratio 8.5:1 is the optimum for preparing the mesoporous silica spheres. With excess of propanol the orderliness of mesoporous silica has been disturbed forming agglomerate particulates. Again the BJH pore diameter and cell parameter (a) go on decreasing with the increase in the propanol:CTAB molar ratio.
Preparation of Spherical Hexagonal Mesoporous Silica
Journal of Porous Materials, 2005
A series of hexagonal mesoporous silica (HMS) have been synthesized by the neutral assemble pathway in water-alcohol cosolvent systems, using dodecylamine (DDA) and tetraethyl orthosilicate (TEOS) as the starting materials. These materials were characterized with powder X-ray diffraction, nitrogen sorption measurement, differential thermal analysis, and transmission electron microscopy. The XRD patterns of these samples exhibited a strong intense reflection at low angle, suggesting the excellent mesostructures of the samples. The particle size of HMS decreased and the morphology of HMS exhibited high textural porosity as the HMS was prepared with high addition rate of TEOS. The particle size of HMS prepared without aging was smaller than that aged for 18 h, due to the reaction time of TEOS was not enough to form complete particles. Addition of NaCl and HCl hindered the formation of HMS mesoporous structure. In contrast, addition of 1-butanol did not affect the formation of HMS mesoporous structure. The sphereical HMS silica with uniform size has been synthesized by adjusting DDA and TEOS concentrations. The shape of HMS became larger and more spherical as the concentrate on of DDA decreased. The stirring rate of the reaction mixture had no effect on either the shape or the size of the spheroid HMS silicas. However, the particles started to crack at higher stirring rates.
2020
In this paper, a facile method for preparing sub-micron spherical mesoporous silica by the sol-gel process and cationic surfactant cetyltrimethylammonium bromide (CTAB) as a soft template was reported. Moreover, the effect of surfactant concentration on the specific surface area and the total pore volume was investigated. The specific surface area, pore characteristic, morphology, chemical composition, and structure of mesoporous silica were studied using various methods. The N2 adsorption test showed that increasing the CTAB concentration from 4.6 mM to 7.2 mM increases the specific surface area from 416.48 to 564.07 m2g-1. However, the maximum pore volume was obtained at 5.9 mM CTAB. The spherical shape of the powders was confirmed by field emission scanning electron microscopy. Besides, X-ray diffraction, fourier transform infrared spectra, and energy dispersive spectrometry analysis indicated that the synthesized samples are SiO2, with an amorphous structure. Based on the struct...
Incorporation of chemical functionalities in the framework of mesoporous silica
Chem. Commun …, 2011
Mesoporous silica, which shows well-defined pore systems, tunable pore diameters (2-30 nm), narrow pore size distributions and high surface areas (4600 m 2 g À1 ), is frequently modified using different methodologies (including in situ and post-synthetic strategies) to introduce various chemical functionalities useful in applications like catalysis, separation, drug delivery, and sensing. This contribution aims to provide a critical overview of the various strategies to incorporate chemical functionalities in mesoporous silica highlighting the advantages of the in situ methods based on the bottom-up construction of mesoporous silica containing various chemical functionalities in its structure.
Detailed investigation on properties of novel commercial mesoporous silica materials
Microporous and Mesoporous Materials, 2019
A detailed investigation on the main characteristics was conducted on a novel and unique group of industrially produced mesoporous silica material. Six materials from a TMPS group were selected in the respect to their pore size ranging from 1.8 nm up to 4.2 nm. Four of the selected samples were also made with silica doping making them potentially attractive for water adsorption applications with the advantage of the pore-tuning possibilities for specific use. The surface area, pore volume and pore size distribution of these materials were established by standard nitrogen adsorption at T = 77.4 K showing typical values of mesoporous silica materials such as high surface area in the range from 600 to 750 m 2 g −1 and pore volumes reaching 0.38 cm 3 g −1 in the case of the smallest TMPS-1.5A and 0.98 cm 3 g −1 in the case of the largest TMPS-4R. The wall thickness was found out regular around 1.5~2 nm with lower values attributed to bigger pore sized samples promising good structural integrity. Specific heat showed regular values through all the samples at~0.85 J g −1 K −1. Additional information on the structural characteristics and the effect on the amount of silanol group presence and the difference on regular and aluminium-doped samples were studied by means of 29 Si DD/MAS NMR. Additionally, elemental analysis by EDS was conducted as well. All the characteristics of the TMPS materials were compared to the standard mesoporous silica materials SBA-15 and MCM-41.
Effect of synthesis time and treatment on porosity of mesoporous silica materials
Adsorption-journal of The International Adsorption Society, 2009
Nitrogen adsorption at 77 K on mesoporous silica materials (MPS) with varying synthesis time and treatment conditions was investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were also used to characterize the mesoporous materials. This study was performed at 6, 24 and 72-h synthesis times. It is shown that 6-h is not enough for complete formation of the MPS material and at least 24-h is necessary. The pore structure starts decaying for the 72-h synthesis time. The three-after-synthesis treatment conditions used were 1) washed, 2) washed and calcined and 3) directly calcined after synthesis. Ethanol/HCl mixtures were used for washing and calcinations were performed at 550°C. Among these samples, directly washed sample yields the lowest adsorption capacity while washed and calcined sample yields the highest adsorption capacity. Hence, it is concluded that washing stabilizes the structure before high temperature treatment.
Textural and Structural Properties of Mesoporous Silica Synthesized Under Refluxing Conditions
Journal of Porous Materials, 2005
Mesoporous silica with pore sizes of 3-6 nm has been synthesized under refluxing and autogenous pressure conditions of hydrothermal synthesis from precursor gels having different alkaline pH. The mesoporous silica prepared is characterized by powder X-ray diffraction, nitrogen adsorption-desorption measurement and scanning electron microscopy. Thermal stability has been tested by XRD analysis of mesoporous silica after thermal treatment at 823 K, 6 h; 1023 K, 1 h and 1223 K, 1 h. The results indicate that the mesoporous silica prepared under refluxing condition from precursor gel of pH 11 has large surface area (ca.1103 m 2 g −1 ) and pore volume (ca. 0.868 cm 3 g −1 ) and is thermally stable at 1223 K. The surface area, pore volumes and pore wall thickness increase as the pH of the precursor gel is increased for refluxing condition of synthesis. The comparison of textural properties revealed that the refluxing condition is advantageous over autogenous pressure condition for obtaining mesoporous silica with higher surface area (852 m 2 g −1 ), pore volume (0.894 cm 3 g −1 ) and pore diameter >4 nm with wall thickness of 1.59 nm, when synthesized from precursor gel of pH 9.2. The 29 Si NMR spectra showed that a great part of the Si atoms exists as silanol groups. The mesoporous silica made at the lower pH (9.2) under refluxing conditions have more condensed framework. In calcined mesoporous silica, the proportion of partly condensed silica (Q 3 ) is higher than fully condensed silica (Q 4 ).
Synthesis and swelling of large pore diameter mesoporous silica spheres
Journal of Materials Chemistry, 2007
A synthetic protocol has been developed for the production of spherical SBA-15 type mesoporous silica particles with macroscopic particle diameters between 1 and 5 mm and mesopore diameters between 6 and 11 nm. Controlled expansion of the mesopores within silica spheres was achieved using supercritical carbon dioxide (sc-CO 2 ). Our method uses the tunable density of sc-CO 2 to induce the controlled swelling of the triblock copolymer surfactant templating mixtures of P123 (PEO 20 PPO 69 PEO 20 ) and cetyltrimethylammonium bromide (CTAB). At pressures of approximately 482 bar, pore diameters of up to 109 Å can be achieved in the P123-CTAB mixtures whilst pore ordering is still retained. This represents a pore expansion of approximately 28%, similar to that previously reported by us using a similar swelling technique (Hanrahan et al., Chem. Mater., 2004, 16, 424; Langmuir, 2005, 21, 4163). It is suspected that the spheres are formed via an emulsion templating technique with the CTAB controlling the emulsion droplet size and the P123 acting as the structure directing agent. Scanning electron microscopy (SEM) and multi angle laser light scattering (MALLS) confirmed the presence of spherical particles and particle size respectively. Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) and nitrogen absorption techniques confirmed that the sc-CO 2 treatment did not effect the hexagonal ordering of the silica. Turbidity measurements were utilized to study the growth of the spheres during the silica condensation reaction.