Method for preparing nano polyporous material with large specific surface area by vacuum freeze-drying process

Abstract

The invention provides a method for preparing nano porous materials with a large specific surface area by a vacuum freeze drying method with short period, simple process and non environmental pollution, which comprises the following steps: (1) taking an organosilane presursor or metal alkoxide as a raw material to synthesize wet gel; (2) allowing the wet gel to stand for 1 to 7 days, and performing aging on the wet gel; (3) using ethanol to clean the wet gel for 1 to 2 days; (4) adding a modifier into the wet gel for soakage for 1 to 2 days, performing solvent displacement, and modifying a three-dimensional network structure of the wet gel; and (5) placing the obtained product into a freeze drying box for prefreezing and vacuum drying. The method is to adopt a novel drying method, namely the vacuum freeze drying method, to dry the wet gel on the premise of maintaining the structure of the wet gel. The drying method has short period and simple process, avoids environmental pollution, cannot damage the network structure of the gel, reduces the production cost, and accelerates the large-scale commercialized application process of nano porous super heat-insulating materials, catalystsand catalyst carrier materials.

Description

Technical field [0001] The invention relates to the technical field of chemistry and chemical engineering, in particular to a method for preparing a nanoporous material with a large specific surface area. technical background [0002] Compared with bulk materials and general nanomaterials, nanoporous materials have a large specific surface area, high porosity, low density, high permeability, assemblability, high adsorption and many other properties, making them useful in thermal insulation, catalytic materials and separation Science and other fields show new performance and potential application value. [0003] Metal oxide nanomaterials are different from bulk materials and individual atoms. Its special structure level enables it to have surface effect, volume effect, quantum size effect, etc., which can not only maintain the superior physical and chemical properties of nanoparticles, but also have the large specific surface, high gas permeability, and assemblability of porous mat...

AI Technical Summary

Problems solved by technology

However, during the preparation and application of metal oxide nanoparticles, there are the following problems: 1. Agglomeration is easy to occur; 2. It is easy to grow up during use and gradually lose the characteristics of nanoparticles

[0006] Silica airgel has been successfully prepared by supercritical drying since the 1930s. Supercritical drying technology can ensure that the structure of silica airgel is not damaged during the drying process, but the supercritical drying process requires high-pressure equipment and control. The conditions are relatively harsh, the whole drying process takes a long time, and the preparation efficiency is low, so the preparation cost of airgel is expensive, and the mechanical properties of the obtained airgel are poor, which limits the large-scale application of block airgel, so normal pressure And non-critical condition drying has attracted extensive attention

Through the two-step hydrolysis and polycondensation of TEOS, combined with ethanol solvent replacement and TEOS ethanol solution soaking and aging, the non-supercritical drying of block airgel was realized under the graded drying of ethanol whose surface tension is much smaller than water. The resulting SiO 2 Xerogel has a certain strength and good shape, and its microstructure, particle size and pore distribution are also completely consistent, but the mechanical properties are poor, and a complete block of xerogel cannot be obtained.

[0007] In summary, although these preparation methods can achieve atmospheric drying to a certain extent and reduce production costs, they also bring a series of problems, such as the tedious solvent exchange process of atmospheric drying, which requires a large amount of organic solvent replacement and takes a long time. , pollute the environment; thermal conductivity increases, mechanical properties are poor, and dry gels with intact structures cannot be obtained, etc.