Preparation and Characterization of Montmorillonites Pillared by Cationic Silicon Species

Abstract

Abstract--The hydrolysis of 2-(2-trichlorosilylethyl)pyridine (TCSEP) or 3-aminopropyltrimethoxysilane (APTMS) yields a complex mixture of oligomers, the composition of which is a function of time. zgSi NMR measurements show that the same oligosilsesquioxanes can be obtained from both compounds after prolonged hydrolysis. Ion exchange by monlmorillonite with the pillaring solution obtained from TCSEP results in partial intercalation, with a noticeable fraction of the clay exchange sites occupied by protons not by the Si cationic species. Calcination of this pillared clay results in a mixture of phases showing 1.86 or 1.56 nm basal spacings. Pillaring of the same montmorillonite by the solution obtained by partial hydrolysis of APTMS results in a homogeneous solid with a basal spacing of 2 nm, which reduces to 1.65 nm upon calcination above 773 K. The microporous volume (pores < 1 nm) of these Siclays, determined after calcination at 773 K, 0.15 ml/g for the PILC obtained from TCSEP, and 0.186 ml/g for the PILC obtained from APTMS is comparable to that measured for AI or Zr pillared clays. A better thermal stability is observed for the clay pillared by APTMS, which retains a large microporosity (0.167 ml/g) up to 973 K in air. These Si-pillared clays show a small number of weakly acidic sites and some strongly acidic sites retaining ammonia up to 723 K, which are most likely localized on the clay layers.

Characterization of the Solids Obtained by Pillaring of Griffithite (High Iron Content Saponite) with Al-Oligomers

“…After dialysis, the basal spacings remain constant in griffithite (18.71, 19.07 and 18.91 ,~), while in Yunclillos saponite, the spacing increases until 18.33 A. The peaks are now narrower and more symmetric than before dialysis, indicating that the washing of the samples completes the intercalation process, as has been observed by other authors (Lahav et al 1978;Figueras et al 1990;Fetter et al 1994).…”

“…Although montmorillonite is the preferred clay mineral used in pillaring studies (Lahav et al 1978;Figueras et al 1990;Fetter et al 1994;Ge et al 1994;Kloprogge et al 1994;Lahodny-Sarc and Khalaf 1994;Mokaya and Jones 1994;Storaro et al 1995), saponite has also been intensely studied in the recent years. Both natural saponites (Usami et al 1992;Chevalier et al 1992;Schoondheydt et al 1992Schoondheydt et al , 1993Schoondheydt et al , 1994Li et al 1993;Malla and Komarneni 1993;Lambert et al 1994;Bergaoui, Lambert, Suquet and Che 1995) and synthetic saponites (Bergaoui, Lambert, Franck et al 1995;Bergaoui, Lambert, Vicente-Rodrfguez et al 1995) have been used in these studies, and new data about the mechanism of pillaring process have been obtained.…”

Physicochemical study of amino-functionalized organosilicon cubes intercalated in montmorillonite clay: H-binding and metal uptake

“…In this context, cubic siloxanes of the type X 8 Si 8 O 12 , where X-(CH 3 ) 3 NH 2 , -(CH 3 ) 3 NR 2 and -(CH 3 ) 3 NH(CH 2 ) 2 NH 2 , have been successfully employed as precursor reagents for pillaring inorganic layered solids such as clay [19][20][21][22][23] {metal (IV) -H-phosphates} [24] or photonic titanoniobates [25]. Protonation of the amino groups generates oligomeric cationic species with bulky organic groups that can be easily inserted into the lamellar zone of a phyllomorphous clay, in amounts exceeding the cation-exchange capacity of the mineral, and then can be removed by thermal treatment leaving behind silica pillared structures [19,21]. On the other hand, the various mono-or bifunctional aminosilanes possess the ability to bind heavy metal ions, M n+ (e.g., Cu 2+ , Pb 2+ , Hg 2+ , Cd 2+ , Zn 2+ ), yielding metal complexes, M n+ x [X 8 Si 8 O 12 ] y , and this important property makes them efficient adsorbent materials in which the metal center can be coordinated to the functionalized group of the siloxane octamer.…”

Iron-substituted cubic silsesquioxane pillared clays: Synthesis, characterization and acid catalytic activity

“…Silsesquioxanes possess a pronounced aptitude to form three dimensional cage-like highly symmetric frameworks known as polyhedral oligosilsesquioxanes (POSS) with cubic, hexagonal, octagonal, decagonal, dodecagonal or even open cage-like morphology [3][4][5]. Cubic silsesquioxanes (cubes), synthesized from the hydrolytic condensation of the corresponding trifunctional organo-silicon monomers, is the most common polyhedral structure and provide the opportunity to design and ''construct" materials with extremely well-defined dimensions and behaviour [3][4][5][6][7][8][9][10][11][12][13] In this context, cubic silsesquioxanes of the type X 8 Si 8 O 12 where X is A(CH 3 ) 3 NH 2 , A(CH 3 ) 3 NR 2 and A(CH 3 ) 3 NH(CH 2 ) 2 NH 2 have been successfully employed as precursor reagents for pillaring inorganic layered solids such as clays [14][15][16][17][18][19], metal (IV) hydrogen phosphates [20][21][22], photonic titanoniobates [23], graphenes and graphene oxide [3,[24][25][26], graphene oxide nanoribbons [27], halloysite nanotubes [28] and perovskites [29]. Protonation of the amino groups generates oligomeric cationic species with expendable and bulky organic groups that can easily be inserted into the interlayer space of a phyllomorphous clay in amounts exceeding the cation exchange capacity of the mineral and can successively be removed by thermal treatment, resulting in silica pillared structures [15,14].…”