Relationships among pore size, connectivity, dimensionality of capillary condensation, and pore structure tortuosity of functionalized mesoporous silica (Journal article)

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

Seven mesoporous forms of silica were prepared by controlled and gradual functionalization of the original SiO2 surface with silano-(trimethoxy)-propyl-imidazole groups. The degree of surface functionalization was n = 0.00, 0.23, 0.30, 0.40, 0.52, 0.60, and 0.85 and was controlled by previous knowledge of surface acidity, determined by temperature-programmed desorption of NH3. From N-2 adsorption/desorption measurements, the specific surface area S-p (m(2) g(-1)), the specific pore volume VP (cm(3) g(-1)), and the corresponding pore size distributions (PSDs) were determined. The connectivity c of the solids was also calculated according to the method of Seaton, and the dimensionality of capillary condensation D-cc was found using the thermodynamic method of Neimark. The increase of functionalization. resulted in a linear drop of S-p and V-p, and the maximum D-max of the PSD and the full width at half-maximum, fwhm similar to2sigma, of the 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. The D-cc values decrease with increasing n values. Next, the co-called corrugated pore structure model, CPSM, 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 area S-CPSM (m(2) g(-1)), the 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 the initial functionalization (n = 0.23) and subsequently remains practically constant at about tau = 3.40 +/- 0.10, for the same reasons which affect the connectivity, that is, blocking ofvarious pore channels. The comparison between the parameters V-p and V-CPSM is quite satisfactory. The S-CPSM values appear systematically higher by 8-23% compared to the S-p ones. The dimensionality of capillary condensation D-cc is related to the variance 2sigma of the PSD. The reasons and the limits of this relationship are discussed.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
Keywords: nitrogen sorption measurements,porous solids,catalytic activity,fractal dimension,hysteresis,model,aluminophosphates,prediction,particles,supports
ISSN: 0743-7463
Link: <Go to ISI>://000182389100009
Publisher: American Chemical Society
Appears in Collections:Άρθρα σε επιστημονικά περιοδικά ( Ανοικτά)

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