Materials Chemistry and Physics 70 (2001) 25–37 Properties of thin polyethylene glycol layers on the surface of silica gel and pyrocarbon/silica gel Effect of topography and morphology of carbon deposit Roman Leboda a,∗ , Vladimir M. Gun’ko b , Jadwiga Skubiszewska-Zi¸ eba a , Andrzej Gierak a , Patryk Oleszczuk a a Department of Chemical Physics, Faculty of Chemistry, Maria Curie-Sklodowska University, M.C. Sklodowska Sq. 3, 20-031 Lublin, Poland b Institute of Surface Chemistry, 31 Prospect Nauki, 03680 Kiev, Ukraine Received 25 January 2000; received in revised form 8 April 2000; accepted 30 June 2000 Abstract The structural and energetic heterogeneity of silica gel and pyrocarbon/silica gel adsorbents was studied by means of the adsorption methods. The properties of polyethylene glycols (PEG 4000, PEG 1500) in a mixture with the solid adsorbents have been investigated using different probe molecules for gas chromatography. The carbosils investigated possessed a mosaic structure due to carbon deposit distribution features. The mechanism of formation of polyethylene glycol layers on the carbosils surface depends on the chemical structure and amount of pyrocarbon. Chemical and structural heterogeneity of the adsorbent surface is of great importance in this case. From the practical point of view, it was interesting to study the effect of such heterogeneity on the selectivity of the chromatographic columns in relation to the model mixtures. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Carbon–silica adsorbents; Polyethylene glycol; Gas chromatography; Selectivity; Heterogeneity 1. Introduction Hybrid carbon–silica adsorbents (carbosils, CS) have probably the most unique surface properties of all the known sorbents [1–11]. The adsorbents comply with the patchy model of adsorption site topography introduced into adsorption theory for heterogeneous solid surfaces [12,13]. It is possible to control both the amount and quality of carbon deposit on the silica surface [1–6,9–11]. That is why, carbosils create new means of a theoretical study of stationary liquid phase properties according to the structure of adsorbent surface sites. As for the data presented here, the fundamental investigations by Di Corcia and Liberti [14,15] on the mechanism and possibilities of so-called gas–liquid–solid chromatography (GLSC) are of significant importance. This technique has been discussed in detail elsewhere [16–18]. The latter publication quotes a lot of data about usefulness of application of combination of var- ious carbon sorbents or combination of carbon sorbents with non-carbonaceous materials for preconcentration of organic pollutants in the environmental samples. It seems ∗ Corresponding author. Tel.: +48-81-537-5716; fax: +48-81-533-3348. E-mail address: leboda@hermes.umcs.lublin.pl (R. Leboda). quite probable that carbon–mineral adsorbents can replace multi-bed sorbents in the columns for isolation and pre- concentration of the trace amounts of substances from different media. It should be stressed that recently there have been published many interesting suggestions about preparation of carbon–mineral adsorbents whose possible application have not been fully recognized [19–22]. Appli- cability of carbon–silica adsorbents (including those with graphitized carbon deposit [23]) in the trace analysis has already been partially proved [24]. The studies of adsorp- tion, chromatographic and thermodynamic properties of carbosil/polyethylene glycol (PEG) deposited in various amounts on the mosaic CS surfaces can be useful to eluci- date the effect of morphology of these adsorbents on their adsorptive characteristics in a mixture with PEG. 2. Experimental 2.1. Materials Silica gel (POCh, Gliwice, Poland) (purified with 3N HCl solution) was utilized to prepare carbon–mineral adsorbent. Carbosil was synthesized using pyrolysis of n-octanol (1 ml 0254-0584/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0254-0584(00)00474-0