The effect of surface functionalization of mesoporous silicas with propylimidazol on porosity, pore connectivity and tortuosity (Journal article)

Armatas, G. S./ Salmas, C. E./ Androutsopoulos, G. P./ Pomonis, P. J.

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.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
Keywords: nitrogen sorption measurements,porous solids,catalytic activity,size distribution,hysteresis,model,prediction,particles,clays
ISSN: 0167-2991
Link: <Go to ISI>://000180452700039
Publisher: Elsevier
Appears in Collections:Άρθρα σε επιστημονικά περιοδικά ( Ανοικτά)

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