Patent Application
20050244322
The present invention relates to a silica-based mesoporous material and a preparation process therefore. Specifically, the present invention relates to a hollow-structured mesoporous silica material and a preparation process therefore. More specifically, the present invention relates to a hollow-structured mesoporous silica material having specific channel arrays and a preparation process therefore.
Silica, as an inorganic porous material, is widely used in the fields of rubber, pesticide, medicine, paper making, plastic processing, paint, insulation, thermal insulation and catalysis, due to its particular properties, such as high purity, low density, large specific surface area, and hydrogen bonds with varying strength formed between surface silanol groups and active silane bonds.
According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), molecular sieves with pore diameters of less than about 2.0 nm are defined as microporous molecular sieves, and molecular sieves with pore diameters ranging from 2.0 to 50 nm are defined as mesoporous molecular sieves. The scientists at Mobil Corporation in 1992 discovered the M41S family (MCM-41, MCM-48, MCM-50) of silica-based mesoporous molecular sieves, which started a new epoch in the molecular sieve area (See, Beck J. S., Vartuli J. C., Roth W. J., A new family of mesoporous molecular sieves prepared with liquid template, J. Am. Chem. Soc., 1992, 114:10834-10843). Compared with conventional microporous molecular sieves, mesoporous molecular sieves have both larger pore sizes and specific surface areas (1000 m2/g) and shell thickness, and hence have higher chemical and thermal stabilities. Therefore, the discovery of the material gives rise to a lot of attention from researchers in many fields of heterogeneous catalysis, adsorption and advanced inorganic materials.
Increasing innovations of synthesis techniques in the recent two years have generated silica-based molecular sieve series such as HMS, MSU and SBA. Subsequently, the occurrence of many non-silica based mesoporous materials such as Al2O3, Fe2O3, WO3, V2O5, TiO2 and ZrO2, partial metallic sulfides, phosphate molecular sieves, and the above-mentioned silica-based mesoporous molecular sieve derivatives with metal heteroatoms results in an increasing development of the research on mesoporous molecular sieves and an extension of regular pore diameters of molecular sieves from micropore to mesopore. See, for example, Yang P., Zhao D., Margolese D. I., Generalized synthesis of large pore mesoporous metal oxides with semicrystalline frameworks, Nature, 1998, 396:152-155; and Holland B. T., Blanford C. F., Stein A., Synthesis of macroporous materials with highly ordered three-dimensional arrays of spheroidal voids, Science, 1998, 281:538-540. In the field of heterogeneous catalysis, mesoporous molecular sieves as catalysts or catalyst supports not only exhibit great potential applications in the catalysis of heavy residual oil and barrel bottom oil in crude oil processing, but also provide a more economical and less-polluting technique pathway for macromolecule catalysis, adsorption and separation, which are difficult to realize for zeolite molecular sieves. See, for example, Beck J. S., Socha R. S., Shihaabi D. S., U.S. Pat. No. 5,143,707 (1993); and Feng X., Fryxell G. C., Wang L. Q., Science, 1997, 276: 923-926, both which are incorporated herein by reference.
In addition, mesoporous materials with controllable and regular nano-sized pores can be used as a micro-reactor for nanoparticles, which provides an important material foundation for the investigation on many special performances of nanomaterials, such as small-scale effects, surface effects and quantum effects. For example, the loading and synthesis of semiconductors such as CdS and GaAs in mesoporous materials will have an important role in many aspects of optical communication, information storage and data processing. The assembly of nanoparticles with mesoporous materials not only manifests many inherent characteristics of nanoparticles, but also generates some new particular properties such as mesoporous fluorescence enhanced effects, optical nonlinear enhanced effects and abnormal magnetism, which are not possessed by nanoparticles and mesoporous materials. Furthermore, some performances can be controlled by design according to our own wish. For example, the location of optical absorption rims and absorption bands can be adjusted greatly by controlling the dimension of nanoparticles, surface state and pore diameters and porosity of mesoporous materials, thereby forming composite mesoporous materials and generating novel functional materials. Such mesoporous materials loading electron-transmitted filaments or molecule leads, such as regularly arrayed carbon filaments loaded in MCM-41, will build a foundation for the research and development of future microelectron and photoelectric devices. The research on mesoporous materials thus has become interesting in the world and generated a new aspect for multidiscipline in recent years.
The mesoporous materials are synthesized through the self-assembly process in the world, which can be classified into two stages: (1) growth of the precursor of organic/inorganic liquid crystal phases, in which organic/inorganic liquid crystal textural phases with nano-sized lattice constants are formed by self-assembling of surfactants having amphiphilic groups, i.e., having both hydrophilic and hydrophobic groups with polymerizable inorganic monomer molecules or oligomer thereof (inorganic source) under certain circumstance; and (2) formation of mesoporous pores (mesopores), in which the mesoporous channels are formed by the remained space which is obtained by removing surfactants through high temperature or chemical methods.
At present, many applications of mesoporous materials need preparation of film shape. Recently, mesoporous materials with specific morphologies are reported in the published literatures. For example, Yang et al. prepared oriented film of mesoporous silica having channels parallel to mica surface by adopting mica as support. (Yang H, Kuperman A, Coombs N., Suzan Mamlche-Afara & Geoffrey A. Ozin, Synthesis of oriented film of mesoporous silica on mica, Nature, 1996, 379: 703-705.) Other mesoporous materials with various states, such as mesoporous silica fibers, mesoporous silica spheres with diameters of several millimeters and non-oriented mesoporous films with a thickness of 75 nm formed on the surface of nonporous silica spheres with a diameter of 420 nm have been described. (Whittingham M S, Current Opinion in Solid State & Mater. Sci., 1996, 1, 227.) Owing to their channels parallel to the surfaces of the support, the internal diffusion resistance of the mesoporous material will be increased greatly.
The main problem in the research on mesoporous materials is that much attention is mainly paid to MCM-41 and less research on other mesoporous materials. The previous investigation indicated that there is a larger internal diffusion resistance in its one-dimension channels, which is confirmed by estimating the Knudsen diffusion coefficient DK=7.3×10−2 cm2/s (in terms of methane). Since the internal diffusion resistance increases, mass transfer becomes difficult. It is very necessary to develop new synthetic systems and routes for preparing silica-based mesoporous materials with various morphologies including films, fibers and microspheres.
Accordingly, one aspect of the present invention is to provide a mesoporous silica material having specific channel arrays. A further aspect of the present invention is to provide a preparation process for the above-mentioned mesoporous silica material.
The present invention relates to a hollow-structured mesoporous silica material comprising a hollow silica particle that has a shell having a plurality of channels oriented substantially perpendicular to the inner surface of the shell.
The present invention further relates to a process for preparation of hollow-structured mesoporous silica material, in which thin-shell type of mesoporous materials with different morphologies are prepared by growing and synthesizing mesoporous silica on the surface of calcium carbonate nanoparticles with different shapes as inorganic templates, and then removing the inorganic templates to prepare mesoporous materials with different hollow shapes.
Specifically, the present invention relates to a process for preparation of the hollow-structured mesoporous silica material, comprising the steps of:
More specifically, the invention relates to a process for preparation of the above-mentioned hollow-structured mesoporous silica material, comprising the steps of:
The present invention further relates to the use of the hollow-structured mesoporous silica material in many fields such as preparation of catalyst, pesticide and optical fiber.
The present invention provides a hollow-structured mesoporous silica material comprising a hollow silica particle that has a shell having a plurality of channels oriented substantially perpendicular to the inner surface of the shell.
The hollow-structured mesoporous silica material can have different shapes such as spherical, needle-like and cubic shape, depending on the shapes of the inorganic templates used for preparing the mesoporous silica material.
The mesoporous silica material can have a wide range of particle diameters of, for example, from 10 to about 500 nm, preferably from 40 to about 150 nm and more preferably from 50 to about 120 nm, which depends on the diameters of inorganic template particles for preparing the mesoporous material.
The mesoporous silica material can have a shell with a substantially uniform thickness of from 5 to about 500 nm, preferably from 8 to about 20 nm and more preferably from 10 to about 15 nm.
The mesoporous silica material can have an average pore diameter of from 2 to about 50 nm, preferably from 2 to about 10 nm and more preferably from 2 to about 5 nm.
The present invention further provides a process for preparation of the above-mentioned mesoporous silica material, in which thin-shell type of mesoporous materials with different morphologies are prepared by growing and synthesizing mesoporous silica on the surface of calcium carbonate nanoparticles with different shapes as inorganic templates, and then removing the inorganic templates.
Specifically, the present invention provides a process for preparation hollow-structured mesoporous silica material, comprising the steps of:
The organic solvent is typically ethanol or methanol, or the like.
The inorganic templates used in the present invention are selected from the group consisting of calcium carbonate, magnesium carbonate and barium carbonate, which can have various shapes, such as cubic, spindle, petal-like, needle-like, laminar, spherical and fibroid shapes.
A spindle-shaped calcium carbonate is described in Japanese published patent applications 5-238730, 59-26927, 1-301510 and 2-243513, in which calcium carbonate with desired shapes can be prepared by adding an agent for controlling crystal form to the conventional stirring vessel or bubbling tower.
A needle-like calcium carbonate is described in U.S. Pat. No. 5,164,172, and can be obtained from calcium hydroxide suspension in the presence of crystal seeds of needle-like calcium carbonate and phosphoric acid by carbonization process. Furthermore, there have been a large number of patent documents that describe the preparation of various calcium carbonates, which is thinner, more controllable and has more complete shapes, such as Japanese published patent applications 59-223225 and 62-278123.
A process for preparing superfine calcium carbonate in high-gravity environment generated by a rotating packed bed (RPB) reactor has been developed by Beijing University of Chemical Technology, for example, those described in Chinese patent ZL95105343.4, and Chinese patent applications 00100355.0 and 00129696.5, which are incorporated herein by reference.
The synthetic procedure for calcium carbonate of different shapes used herein can be found in Chinese patent applications 01145312.5 and 02105389.9. Calcium carbonate with a narrow size distribution and different shapes can be synthesized by adjusting the speed of RPB and other process conditions, such as the concentrations of initial reactants, temperature, pH values and the selection of the agent for controlling crystal formation, to control nucleation and growth of calcium carbonate, and hence finely controlling the mixing characteristics of carbonation reaction.
In Chinese patent application 01145312.5, calcium carbonate of different shapes, such as spindle, petal-like, fibroid, laminar, needle-like and spherical shapes, were synthesized by carbonizing calcium hydroxide and carbon dioxide under a high gravity environment, for example in a RPB reactor. A superfine whisker-like calcium carbonate was provided in Chinese patent application 02105389.9. The above-mentioned patent documents are incorporated herein by reference.
According to the process in the present invention, the inorganic template suspension used has a concentration of from 1.5 to about 25% by weight and preferably from 5 to about 10% by weight of the inorganic template.
The surfactant used, as an organic template, can have a concentration of from 1.5 to about 20%, relative to the weight of the mixture.
According to the process in the present invention, the surfactant can be any surfactant suitable for preparing mesoporous materials in the art, for example those described in J. Inorg. Mater. 1999, 14(3): 333-342, including but not limited to, the surfactants having amphiphilic groups, preferably quaternary ammonium surfactant, preferably cetyltrimethylammonium halide and more preferably cetyltrimethylammonium bromide (CTMAB). A typical surfactant can be selected from the group consisting of a cationic surfactant of long-chain alkyl quaternary ammonium salts with low molecular weight CnH2n+1NMe3X, wherein n=10 to about 22, X=Br—, Cl— or OH—; a surfactant with multi-functional groups NH2(CH2)nNH2, wherein n=10 to about 22; and a surfactant with high molecular weight selected from PEO-PPO-PEO, and a nonionic Gemini surfactant.
According to the process in the present invention, the surfactant used herein can have a wide range of concentration, including the concentration for forming spherical or rod-shaped micelles, such as from 1.5 to about 20%, preferably from 1.8 to about 10% and more preferably from 2.0 to about 5%, relative to the weight of the suspension.
The ratio of the inorganic template and the surfactant is from 1 to about 20, preferably from 2 to about 10 and more preferably from 3 to about 5.
The ratio of silicon source (in terms of the weight of silica) and the inorganic template is from 0.05 to about 300, preferably from 0.1 to about 10 and more preferably from 0.15 to about 5.
In the process of the invention, the pH value can be controlled in a range of from 8 to about 14, preferably from 10 to about 14 and more preferably from 12 to about 14 by adding an alkali substance including sodium hydroxide, potassium hydroxide, lithium hydroxide, urea, ammonium bicarbonate, aqueous ammonia, ammonium chloride, and the like. The reaction temperature is typically from 10 to about 200° C. and preferably from 25 to about 150° C. The reaction time is typically from 10 minutes to 36 hours and the calcination time is typically from 0.2 hours to 100 hours. According to an embodiment of the invention, thin-shell type of mesoporous nanospheres, which are synthesized by adopting calcium carbonate with a diameter of about from 40 to about 50 nm as the inorganic template, has a diameter of about 60 nm, a specific surface area αBET of 1016.72 m2/g, an average pore size of 3.94 nm and a pore volume of 1.002 cm3/g.
According to another embodiment of the invention, mesoporous hollow tubes, which are synthesized by adopting needle-like calcium carbonate with a diameter of 200-300 nm and an aspect ratio of about 5 as inorganic templates, and CTAB with a concentration of 2%, have a shell with thickness of about 40 nm, specific surface area aBET of 565.9 m2/g, a pore volume of 0.6218 cm3/g and an average pore size of 4.39 nm.
The thin-shell type of mesoporous nanospheres according to the invention was characterized by transmission electron microscopy (FE-TEM, JEOL JEM-2010F, Acceleration: 200 KV) and scanning electron microscopy (FEG-SEM, Resolution: 1.5 nm), as shown in
It can be seen from
The pore diameter, D, of the mesopores at 2θ=2.4° on crystal plane (100) is 3.58 nm, which is obtained by measuring the Small-angle X-ray diffraction (XRD) pattern of hollow silica nanospheres with a diffraction meter (SIEMENS D5005D) with CuKα radiation of 0.15406 nm in wavelength at 40 kV, 100 mA at an interval of 0.02°.
The pore size distribution of the mesoporous hollow spheres was measured with ASAP 2010 Surface Area Analyzer (Micromeritics Instrument Corporation, USA), as shown in
The mesoporous nanospheres have a narrow pore size distribution, as shown in
The mesoporous hollow tube according to the invention was characterized by transmission electron microscopy (FE-TEM, JEOL JEM-2010F, Acceleration: 200 KV) and scanning electron microscopy (PEG-SEM, Resolution: 1.5 nm), as shown in
As shown in
The N2 adsorption and desorption isotherms of mesoporous hollow tube in the invention were measured on an ASAP 2010 Surface Area Analyzer (Micromeritics Instrument Corporation, USA), as shown in
As shown in
There are three kinds of modes for growing mesoporous films on matrix as follows:
In view of the lowest energy principle, it is easy to carry out the two growing modes shown in
Mesoporous films reported in the literatures so-far can be grown mainly according to mode b and c, in which TEOS and acidic solution of cetyltrimethyl-ammonium chloride were mixed, and then nucleated on the surface of fresh dissociated mica at a temperature of 80° C. to obtain oriented-grown and continuous mesoporous silica film with oriented channels parallel to the mica surface. (Yang P., Zhao D., Margolese D. I., Generalized synthesis of large pore mesoporous metal oxides with semicrystalline frameworks, Nature, 1998, 396: 152-155.)
As the channel shapes of the obtained tubular mesoporous materials, the mesoporous channels obtained herein are perpendicular to the surface of calcium carbonate used as inorganic templates, as shown in
The following mechanism can have a reasonable explanation for the experimental phenomena. The synthesis route of hollow mesoporous material is shown in
(1) Calcium carbonate as the inorganic template 10 in the suspension has a small size and a high surface energy, thereby adsorbing the surfactant CTMAB. When CTMAB is enriched on the surface of calcium carbonate, the concentration of CTMAB on the surface of calcium carbonate is higher than that in bulk liquid phase, reaching the second critical micelle concentration (cmc2).
(2) The surfactant CTMAB micelles 20 will be perpendicular in axial direction to the surface 12 of calcium carbonate by means of complicated synergistic effects such as weak non-covalent bond of smaller directionality, such as coulomb's force, hydrogen bond, steric hindrance, van der waals force and weak ionic bond or ionic strength, and forms hexagonal arrays through self-assembly according to the lowest energy principle.
(3) Under the alkaline condition, a silicon source such as TEOS is hydrolyzed to generate silicic acid oligomer having multiple coordination sites, which fills, agglomerates and deposits around the hexagonal array micelles to generate the shell 30 as the framework thickness of MCM-41.
(4) A calcination treatment at 550° C. decomposes the micelles 20 of the surfactant such as CTMAB, which is used as an organic template, into gases, thereby leaving mesoporous channels 40 in the shell 30. After inorganic template 10 of calcium carbonate is dissolved in HCl solution, the reaction products of CaCl2 and CO2 diffuse out of mesoporous channels, and thereby forming mesoporous materials 50 with hollow structure.
The thin-shell type of mesoporous material in the present invention has short mesoporous channels with a small diffusion resistance, which helps to transfer the reactive substance. In particular, it is very suitable for preparing egg-albumen type catalyst loaded with noble metal.
The present invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
8.7 g of cubic CaCO3 powders with a particle diameter of 40 nm were added to 50 g of de-ionized water. 2.5 g of CTMAB, 13.2 g (about 15 ml) of analytical pure aqueous ammonia (25 wt %) and 60 g of ethanol were then added in sequence. After stirring the mixture at a speed of 300 rpm for 15 minutes, tetraethylorthosilicate (TEOS) was added with the ratio of SiO2/CaCO3=0.15 (by weight) and the suspension was stirred for another 2 hours. The mixture was then filtered, and the filter cake was rinsed with ethanol, dried at 90° C. in muffle furnace, and calcinated at 550° C. for 5 hours. The templates were dissolved with a dilute hydrochloric acid, and pH is maintained below 1, and finally dried to obtain the product.
8.7 g of needle-like CaCO3 powders with a diameter of 200-300 nm and an aspect ratio of 5 were added into 50 g of de-ionized water. 2.5 g of CTMAB, 13.2 g (about 15 ml) of analytical pure aqueous ammonia (25 wt %) and 60 g of ethanol were then added in sequence. After stirring the mixture at a speed of 300 rpm for 15 minutes, tetraethylorthosilicate (TEOS) was added with the ratio of SiO2/CaCO3=0.2 (by weight) and the suspension was stirred for another 2 hours at a room temperature. The mixture was then filtered, and the filter cake was rinsed with ethanol, dried at 90° C. in a muffle furnace, and calcinated at 550° C. for 5 hours. The templates were dissolved with a dilute hydrochloric acid, and pH is maintained below 1, and finally dried to obtain the product.
10 g of spherical BaCO3 powders with a diameter of 100 nm were added to 50 g of de-ionized water. 3 g of CTMAB, 13.2 g (about 15 ml) of aqueous ammonia (25 wt %) and 60 g of ethanol were then added into the suspension in sequence. After stirring the mixture at a speed of 300 rpm for 15 minutes, tetraethylorthosilicate (TEOS) was added with the ratio of SiO2/CaCO3=0.2 (by weight) and the suspension was stirred for another 2 hours at a room temperature. The mixture was then filtered, and the filter cake was rinsed with ethanol, dried at 90° C., and calcinated at 550° C. in a muffle furnace for 5 hours. The templates were dissolved with a dilute hydrochloric acid, and pH is maintained below 1, and finally dried to obtain the product.
Although the present invention has been described with reference to specific examples, the skilled person in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 02160383.9 | Dec 2002 | CN | national |
