Comparison of the adsorption properties of dysprosium-doped mesoporous silicas, modified with copper and silver, by inverse gas chromatography
Abstract
Template synthesis is a promising method for the preparation of mesoporous silica, allowing con-trolling the pore diameter and surface area of MSM due to its large surface area (700-1500 m2/g). It is possi-ble to vary the selectivity of absorption of substances due to the rigid structure of the inorganic matrix, the availability of pores for the penetration of bulk molecules of organic substances, as well as the possibility of modifying materials. The studies performed during recent years were devoted to the production of new mes-oporous materials doped with rare earth elements, materials with special, poorly studied properties. Previous-ly, the authors of the study investigated the adsorption properties of mesoporous silica gel doped with dys-prosium and modified with nickel and established that the incorporation of dysprosium into the structure of the material changes the adsorption properties of silica.
The aim of this study was the comparison of the adsorption properties of synthesised mesoporous silica gels doped with dysprosium and modified with copper and silver.
Two samples of mesoporous silica were synthesised by the template method: mesoporous silica doped with dysprosium and modified with copper (Dy-Cu/MS) and mesoporous silica doped with dysprosi-um and modified with silver (Dy-Ag/MS).
The textural and morphological properties of the samples were investigated by low-temperature ni-trogen adsorption-desorption, scanning electron microscopy, X-ray phase analysis, inductively coupled plas-ma mass spectrometry, and X-ray fluorescence analysis. It was found that the introduction of dysprosium into the structure of a silica mesoporous material leads to a decrease in its surface area from 600 m2/g up to 514 2/g. The synthesised samples were characterised by an average pore diameter of 3.4-7.2 nm. The synthesised Dy-Ag/MS sample is characterised by the highest specific pore volume of 2.3 cm3/ g.
The thermodynamic characteristics of adsorption (differential heat of adsorption and change in standard differential molar entropy during adsorption) for tested organic compounds were obtained by the method of inverse gas chromatography. It was found that doping and the subsequent modification lead to changes in the heats of adsorption for compounds prone to different types of specific interactions. Thus, based on the comparison of the adsorption properties of the synthesised samples, it can be concluded that Dy-Cu/MS exhibits the most expressed adsorption properties in relation to the studied polar test compounds. On the Dy-Cu/MS sample, methanol was adsorbed with a higher heat than ethanol, which was probably due to the low pore volume of the sample.
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