Molecular sieve manufacturer explains molecular sieve characterization analysis method - gas adsorption

Among the numerous existing methods for characterization and analysis of molecular sieves, gas adsorption is still the standard method and the most widely used technology. This is because the theory of gas adsorption is mature, and this method also has the advantages of easy access to experimental instruments and strong operability. At a certain temperature and pressure, gas adsorption can accurately determine the amount of gas adsorbed by solid materials, thereby fitting important parameters related to pore structure such as pore volume, specific surface area, pore size distribution, and pore surface properties.
Nitrogen and argon are the most reused adsorbents. Generally, the adsorption isotherm is measured under the following conditions: at liquid nitrogen temperature, the pressure increases from vacuum to standard atmospheric pressure. According to the type of adsorption isotherm, the pore structure with different pore diameters can be accurately distinguished. For microporous materials such as molecular sieves, argon is superior to nitrogen because the fourth moment present in nitrogen molecules enhances their interaction with the non-uniform surface in the molecular sieve framework structure, thereby increasing the difficulty of evaluating pore size and morphology. Due to the fact that the analysis of gas adsorption results is based on simplified models, the validity of various assumptions in the adsorption model determines the accuracy of the analysis results.
For example, BET specific surface area is usually given in analysis reports related to molecular sieves. However, since the basis of BET fitting is multi-layer adsorption, the actual situation of microporous filling does not fully meet the conditions of multi-layer adsorption, so the BET data provided in the report cannot represent the true physical surface area. Especially for materials with multi-level pore structures, the influence of mesoporous structures on multi-layer adsorption makes data analysis more complex. However, for regular studies, the BET specific surface area can also be used as a data proportional to the adsorption capacity.
For NaY, it has a typical type I nitrogen adsorption desorption isotherm, which is usually the manifestation of chemical adsorption of non porous materials or physical adsorption of materials with microporous structure. After post modification, the sample has type IV nitrogen adsorption desorption isotherm, which indicates that mesoporous structure is formed in the molecular sieve. In addition, samples prepared by different modification methods have hysteresis loops with different shapes. The hysteresis loop in the multi-layer physical adsorption isotherm region is usually related to the capillary condensation in the mesoporous structure. Although the various factors that affect the adsorption hysteresis loop are still not very clear, the shape of the hysteresis loop is usually determined to be related to the special pore configuration. Hunan Providence New Materials Co., Ltd is a professional molecular sieve manufacturer which can provide USY zeolite, NaY zeolite, REY zeolite, ZSM-5 zeolite, welcome to consult.