Some questions on the mechanism of changing of silica sorbents structural characteristics under hydrothermal treatment

Changes in the pore character of silicas caused by surface bonding and polymer coating

“…It is assumed that during the HT the globular structure of the MSG changes to a cylindrical pore structure [4], the pores of which are more accessible to the derivatization agents because the number of sections with a negative surface curvature is insignificant in this case; these samples possess a lower specific surface area and thus smaller quantities of the modifier are necessary for their derivatization (6% mass in case of the Si-300 ODS sample).…”

“…The modification of the physical nature of the material such as through hydrothermal treatment (HT) [1][2][3] leads to a more fundamental change of the pore-size distribution than a chemical modification. It is assumed that wide-pore silica gels prepared by means of hydrothermal treatment of mesoporous silica gels have pores of a more cylindrical shape compared to silica gels with a globular structure prepared from sols [4].…”

A detailed discussion of the influence of the amount of deposited polymer on the retention properties of polymer‐coated silicas

“…We used a silica gel with 40-nm average pore diameter obtained using hydrothermal treatment (see Section 2). In this case, problems concerned with the accessibility of the surface by the modifier are solved firstly using a silica with a larger pore size and secondly due to the conversion of the silica skeleton from a globular to the cylindrical structure as a result of the hydrothermal treatment [5]. On the other hand, if inaccessible parts exist in the system, then the coating with the polymer completely "ignores" them, i. e., the polymer either fills such pores or isolates them through a durable polymer film.…”

“…An important tool for this is provided particularly by hydrothermal treatment in an autoclave. We assume [5] that, during the hydrothermal treatment, the globular structure of the parent silica is converted to a cylindrical structure due to the dissolution of the silica and re-precipitation on the parts with the most negative surface curvature, i. e., in the places of contact of the initial structure-forming particles. This phenomenon can also be observed when analyzing scanning electron micrographs of silica particles prepared by different techniques, including hydrothermal treatment [6].…”