On The Surface Properties Of Carbon-silica Adsorbents (carbosils) Modified In The Process
On the Surface Properties of Carbon-Silica Adsorbents (Carbosils) Modified in the Process
of Hydrothermal Treatment with H2O2
R. Leboda1, B. Charmas1, F. Villieras2, J. Skubiszewska-Zięba1, A. Gierak1
1Faculty of Chemistry, Maria Curie - Skłodowska University
20-031 Lublin, Poland
2Laboratoire Environnement et Mineralurgie, UMR 7569,
CNRS-INPL, Ecole Nat. Sup. Geologie,
15 avenue du Charmois, BP40, 54501 Vandoeuvre les Nancy, France
Hydrothermal modification (HTM) is one of the most effective colloid-chemical methods of solids porous structure regulation. On the basis of literature data, different ways of using the hydrothermal method for sorbent and catalysts modification can be distinguished:
– the regulation of porous structure parameters,
– modification of phase composition, including the hydrothermal synthesis of porous substances,
– changing the mechanical properties of granular porous substances,
– changing the surface structure and properties, including chemical modification,
– organothermal processes.
In the case of silica gel hydrothermal modification, the terminal character of the porous structure depends not only on the method of such modification, but also on the primary structure of the silica gel. The investigations carried out showed that:
– During the HTM the skeleton of silica gels becomes more rigid, but does not undergo shrinking,
– High heterogeneity of the porous structure of hydrothermally modified silica gels in comparison with the structure of initial materials is a characteristic feature of these adsorbents,
– Using the method of HTM, wide-pore adsorbents of highly differential structural parameters (pore diameter, globule diameter and specific surface area) can be obtained.
The studies of mechanism of carbon-silica adsorbents hydrothermal modification are interesting from both practical and cognitive points of view. Depending on the preparation conditions such adsorbents can have a mosaic structure of the surface or they can be completely covered with a carbon layer. Application of HTM for modification of such structures makes it possible to obtain materials of greatly changed surface properties. Using the hydrogen peroxide as the modification medium, rather than normal water, makes it possible to obtain greater effects of physical and chemical modification than with the former lower temperatures used in the modification process are generally required.
The aim of this paper is to study the effect of hydrothermal treatment of the carbosil series with hydrogen peroxide under the high pressure conditions on their porous structure and adsorption properties. The modified carbosils were obtained on the basis of mesoporous silica gel (Si-60, SBET=335m2/g) and the products of methylene chloride pyrolysis:
The carbon deposit obtained in this reaction is characterized by very good adhesion to the silica surface and extreme hardness.
Six carbosils containing from 0.7 to 35% w/w carbon were obtained. From the data of low-temperature nitrogen adsorption/desorption there were determined basic parameters of porous structure of non-modified and hydrothermally modified carbosils i.e. the specific surface area SBET, mean radius of pores, volume distribution of pores versus their radii and surface distribution versus pore radii. Moreover, water desorption from the surface of prepared adsorbents was studied using the quasi-isothermal method.
Related articles::