The effect of surface functionalization of mesoporous silicas with propylimidazol on porosity, pore connectivity and tortuosity
(EN)
Armatas, G. S.
(EN)
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
(EL)
Armatas, G. S.
(EN)
Mesoporous silica was gradually functionalized with silano-(trimethoxy)-propylimidazole (STPI) groups. The degree of surface functionalization n=0, 0.23, 0.30, 0.40, 0.52, 0.60 and 0.85 was controlled by previous knowledge of surface acidity, determined by TPD/NH3. From N-2 adsorption/desorption measurements the specific surface area S-p (m(2) g(-1)), the specific pore volume V-p (cm(3) g(-1)) and the corresponding pore size distributions PSD were determined while the connectivity c of the solids was calculated according to the method of Seaton. The increase of functionalization resulted in a linear drop of S-p and V-p while the maximum D-max of the PSD and the Full Width at Half Maximum, FWHMsimilar to2sigma of distribution drop in a regular way whereas the ratio (D-max/2sigma) remains practically constant. The connectivity c also decreases from c=12.5 at n=0 to c=3 at n=0.60-0.85 presumably because of blocking of channels connecting various pores. Next, the co-called Corrugated Pore Structure Model, CPSW, was employed for the estimation of tortuosity tau of the porous solids and the simulation of the experimental adsorption/desorption isotherms. From those CPSM simulations the corresponding specific surface areas S-cpsm (m(2)g(-1)), specific pore volume V-cpsm (cm(3) g(-1)) and the corresponding pore size distribution PSDcpsm were estimated. The tortuosity tau of the system drops with the degree of functionalization from tau=4.22 at n=0 to tau=3.37 at functionalization n=0.23 while subsequently remains practically constant at about tau=3.40+/-0.10, for the same reasons which affect the connectivity i.e. blocking of various pore channels. The comparison between the parameters V-p on one hand and V-cpsm, is quite satisfactory while the S-cpsm values appear systematically higher by almost 8-23% compared to the S-p ones. Similarities and discrepancies between the results obtained by the two methods are discussed.
(EN)
