Fractal analysis of bentonite modified with heteropoly acid using nitrogen sorption and mercury intrusion porosimetry

Abstract

Experimental adsorption isotherms were used to evaluate the specific surface area and the surface fractal dimensions of acid-activated bentonite samples modified with a heteropoly acid (HPW). The aim of the investigations was to search for correlations between the specific surface area and the geometric heterogeneity, as characterized by the surface fractal dimension and the content of added acid. In addition, mercury intrusion was employed to evaluate the porous microstructures of these materials. The results from the Frankel-Halsey-Hill method showed that, in the p/p0 region from 0.75 to 0.96, surface fractal dimension increased with increasing content of heteropoly acid. The results from mercury intrusion porosimetry (MIP) data showed the generation of mesoporous structures with important topographical modifications, indicating an increase in the roughness (fractal geometry) of the surface of the solids as a consequence of the modification with the heteropoly acid. By comparison, MIP is preferable for the characterization because of its wide effective probing range.

Specifična površina i fraktalna dimenzija površine uzaraka kiselinski aktiviranog bentonita modifikovanog heteropoli kiselinom (HPW) izračunate su na osnovu podataka iz adsorpcionih izotermi azota. Cilj ovog istraživanja bio je da se nađe korelacija između specifične površine i geometrijske heterogenosti, kao i zavisnost fraktalne dimenzije površine od sadržaja dodate heteropoli kiseline. Takođe, metoda živine porozimetrije je korišćena za ispitivanje porozne mikrostrukture sintetisanih uzoraka. Rezultati Frankel-Halsey-Hill metode, primenjene u oblasti relativnog pritiska od 0,75 do 0,96, pokazuju da fraktalna dimenzija površine raste sa porastom sadržaja heteropoli kiseline. Rezultati živine porozimetrije su pokazali da je došlo do značajnih topografskih promena (porast hrapavosti) i razvoja mezoporozne strukture uzoraka, kao posledica modifikacije heteropoli kiselinom. Poređenje je pokazalo da je metoda živine porozimetrije primenljiva u širem opsegu prečnika pora.