Journal of Colloid and Interface Science 240, 533–538 (2001) doi:10.1006/jcis.2001.7663, available online at http://www.idealibrary.com on Silylating Agents Grafted onto Silica Derived from Leached Chrysotile Maria G. Fonseca, ∗ Andrea S. Oliveira,† and Claudio Airoldi† ,1 ∗ Faculdade de Ciˆ encias e Tecnologia, Universidade Estadual da Para´ ıba, Campina Grande, Para´ ıba, Brazil; and †Instituto de Qu´ ımica, Universidade Estadual de Campinas, Caixa Postal 6154, 13083-970 Campinas, S˜ ao Paulo, Brazil Received October 5, 2000; accepted April 30, 2001; published online July 12, 2001 Silica from leached chrysotile fibers (SILO) was silanized with trialkoxyaminosilanes to yield inorganic–organic hybrids desig- nated SILx (x = 1–3). The greatest amounts of the immobi- lized agents were quantified as 2.14, 1.90, and 2.18 mmol g −1 on SIL1, SIL2, and SIL3 for–(CH 2 ) 3 NH 2 , –(CH 2 ) 3 NH(CH 2 ) 2 NH 2 , and –(CH 2 ) 3 NH(CH 2 ) 2 NH(CH 2 ) 2 NH 2 groups attached to the inorganic support. The infrared spectra forall modified silicas showed the ab- sence of the Si–OH deformation mode, originally found at 950 cm −1 , and the appearance of asymmetric and symmetric C–H stretching bands at 2950 and 2840 cm −1 . Other important bands associated with the organic moieties were assigned to ν as (NH) at 3478 and ν sym (NH) at 3418 cm −1 . The NMR spectrum of the solid precursor material suggested two different kinds of silicon atoms: silanol and siloxane groups, between −90 and 110 ppm; however, additional species of silicon that contain the organic moieties bonded to silicon at −58 and −66 ppm appeared after chemical modification. These modified silicas showed a high adsorption capacity for cobalt and copper cations in aqueous solution, in contrast to the original SILO matrix, confirming the unequivocal anchoring of silylating agents on the silica surface. C  2001 Academic Press Key Words: silanization; chrysotile; silica; adsorption. 1. INTRODUCTION Silylation is characterized by the displacement of active hy- drogen atoms usually attached to silanol groups by organosi- lyl derivatives of silane coupling agents of the general formula (R ′ O) 3 SiR (1, 2). This organic molecule contains the moiety R in which functional centers are attached and the alkoxy R ′ O groups that are normally formed by short chains. These latter groups are easily hydrolyzed when dispersed in solvent water or simply by the water of hydration on the surface of the substrate used in the chemical process. The selection of a desirable functional group on the R moiety during the immobilization depends upon the subject of each application (3). Thus, properties such as wetta- bility, corrosion, resistance, interfacial electrical resistance, and adhesive function for biocompounds or cation adsorption are derived to explore the desired R groups (3). 1 To whom correspondence should be addressed. E-mail: airoldi@iqm. unicamp.br. The application of such methods of immobilization can yield grafting surfaces where defined coupling agents are covalently bonded onto inorganic supports. The final products of the an- chored surfaces have great utility in many areas such as chemi- cally bonded phases in chromatography (4, 5), preconcentration and extraction of cations from solutions (6–8), catalytic pro- cesses (9, 10), and biomaterial immobilization (11, 12). Among a variety of matrices, such as oxides, glasses, and clay minerals, which contain available OH-end groups bonded on a surface, silica gel has been extensively modified with a great variety of alkoxysilane agents with different functionali- ties, for example, amino (13), mercaptan (14), epoxy (15), and methacrylate (16). Today, increasing interest in inorganic materials has been focused not only on those obtained from natural sources but also on properties associated with the surface reactivity. One of these matrices is natural chrysotile that presents predominantly a serpentine fibrous form, represented by the general formula Mg 3 Si 2 O 5 (OH) 4 . This constitution consists of repetition of the two main parts, representing the basic Mg(OH) 2 and the acidic SiO 2 units. In such an arrangement the octahedral magnesium atom has a shared oxygen with the tetrahedral silicon atoms in a sandwiched form (17, 18). Despite this well-organized in- organic structure, even this kind of compound is affected by chemicals. Thus, drastic leaching of concentrated mineral acids on chrysotile fibers can transform this natural polymer by remov- ing the magnesium component, resulting in an excellent source of silica. The leached asbestos product exhibits changes in tex- tural properties, such as surface area, microporosity, and bulk density, that can show improvement on properties in comparison to the synthetic chromatographic silica gel (19). Taking into account the existence of the large number of silanol groups on a leached chrysotile product, this investiga- tion focused on immobilization of amino organofunctional tri- alkoxysilanes by exploring the action of three distinct amino alkoxysilane agents on a leached chrysotile precursor. 2. EXPERIMENTAL Chemicals Chrysotile samples, 7 ML, with fiber length less than 2.0 mm were supplied by the SAMA mine, Urua¸ cu, Goi´ as, Brazil. The 533 0021-9797/01 $35.00 Copyright C  2001 by Academic Press All rights of reproduction in any form reserved.