- Email: [email protected]
Pioneer studies on HCl and silylation treatments of chrysotile
Journal of Colloid and Interface Science 289 (2005) 597–599 www.elsevier.com/locate/jcis
Note
Pioneer studies on HCl and silylation treatments of chrysotile Efrain Mendelovici 1 , Ray L. Frost ∗ Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia Received 16 March 2005; accepted 14 May 2005
Abstract In the light of some recent studies on organosilicon derivatives of HCl-leached chrysotile, pioneer works not cited in this area are chronologically and briefly commented on, emphasizing the infrared spectroscopy (FTIR–PAS) characterization of such chrysotile products. The latter have opened a far-reaching potential for the development of, e.g., highly stable hydrophobic or organophilic materials, including fibrous sheet polymers. 2005 Elsevier Inc. All rights reserved. Keywords: Chrysotile; HCl and silylation treatments; FTIR–PAS
Chrysotile asbestos is a fibrous, 1:1-layered magnesium silicate consisting of a sheet of linked silica tetrahedra that is coupled to a brucite-like trioctahedral sheet. The structural misfit between the tetrahedral and octahedral units causes a curvature, which explains the fibrous nature of chrysotile. Acid treatments of chrysotile may give useful information on the activation of this mineral as well as on the mechanism of its interaction with, e.g., organosilicon compounds. The organosilicate products resulting from such interactions may lead to interesting applications, as their surface and reaction properties are determined by the organic components and their mechanical properties by the mineral skeleton (the silicate backbone). The morphological and textural changes resulting from the HCl leaching of chrysotile were reported by Nagy and Bates [1]. Other related works on the solubility and stability of chrysotile products submitted to HCl treatments followed (see, e.g., Mendelovici [2] and references therein). It has been established that the release of magnesium from the octahedral sheet is a diffusion process, depending on the * Corresponding author.
E-mail address: [email protected] (R.L. Frost). 1 Emeritus investigator IVIC, Caracas.
0021-9797/$ – see front matter 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.05.053
concentration of the acid, the pH, the temperature, and the fiber morphology. The synthesis of trimethylsilyl derivatives of silicate minerals ranging from ortho- to tectosilicates by a procedure involving HCl (diluted by isopropanol) and hexamethyldisiloxane as modifying agents (known as the cohydrolysis method) was published by Lentz [3]. Based on this method, treatments of chrysotile by HCl and by HCl plus silylating agents that generate thrimethyl or methylvinyl groups were described in 1967 [4]. As the octahedral magnesium layer was gradually dissolved by HCl, silanol groups were generated. The active silanol groups formed covalent bonds with the organosilyl groups by a protonation and condensation mechanism. The grafting of thrimethylsilyl groups on chrysotile by the cohydrolysis method resulted in stable hydrophobic products of high surface area [4,5]. These products were characterized by surface and chemical analysis methods, as well as by diffraction and electron microscopy, differential thermal analysis, and infrared spectroscopy. The functionality and nature of the coupling agents (organosilyl groups), as well as the structure of the mineral silicate, will determine the characteristics of the resulting products. The grafting of methylsilyl groups on chrysotile and apophyllite by the cohydrolysis method was published in
598
E. Mendelovici, R.L. Frost / Journal of Colloid and Interface Science 289 (2005) 597–599
Table 1 Former studies on the HCl and silylation treatments of chrysotile employing IR spectroscopy Silylating agents
Grafted organosilyl groups
Reference
Hexamethyldisiloxane Methylvinyldichlorosilane
Trimethyl Methylvinyl
[4]
Hexamethyldisiloxane
Trimethyl
[5]
Trimethylchlorosilane
Trimethyl
[6]
Dimethylallylchlorosilane
Trimethylallyl
[8]
Gamma-methacryloxypropyltrimethoxysilane
Methacryl
[10]
Dimethylphenyldichlorosilane Dimethyldichlorosilane
Dimethylphenyl Dimethyl
[13]
following works [6,7]. According to the latter works, fibrous, sheet polymers may be derived from chrysotile by an extraction–grafting process. The modification of chrysotile by methylallylsilanes and by octamethylcyclotetrasiloxane in acid medium was also reported [8,9]. On the other hand, chrysotile was treated by some alkoxysilanes such as gamma-methacryloxypropyltrimethoxysilane and delta-aminobutylmethyldiethoxysilane in the presence and absence of HCl [10]. Based on information from these works another fibrous silicate, palygorskite (attapulgite), was successfully reacted with HCl [11] and with some alkoxysilanes [12]. With palygorskite, as well, the grafting of the organic moieties took place via HCl-induced silanol groups. The preparation of methyl and phenylsilyl derivatives of chrysotile in the presence or absence of HCl was recently described [13]. Careful and detailed band assignments were achieved employing Fourier-transformed IR photoacoustic spectroscopy (FTIR–PAS) and band component analysis [13]. The appearance of an absorption band at about 960 cm−1 , which we assigned to silanol groups, was ubiquitous in HCl-treated products, whereas when the reaction was carried out in the absence of HCl no such band was detected. Band assignments were also based on references reported from former studies of neat chrysotile by IR absorption spectroscopy using dispersive spectrometers [14]. Referring to the appearance of the 960-cm−1 band attributed to silanol groups in HCl-modified chrysotile products [13], Wypych et al. confirmed and reported the same band in HClleached chrysotile, which they called disordered silica [15]. In addition to the silanol band, the IR spectrum of disordered silica exhibited frequencies similar to those of the original silica-like sheet structure of chrysotile. Beside the effect of the HCl attack on the structure of chrysotile, the presence and absence of the 960-cm−1 band are related to the degree of coupling of the silanol groups with the organic moieties in the silylated products, where steric hindrance also played a role. In a recent work Fonseca et al. [16] grafted some alkoxysilanes such as 3-aminopropylthrimethoxysilane on HCl-leached chrysotile. In the discussion of the IR spec-
troscopy results of their modified chrysotile products, they assigned the IR frequencies on the basis of previous studies on silica gel treatments. However, they did not refer to the earlier mentioned studies on the products resulting from treatment of chrysotile by HCl and silylating agents. Most of these studies—which are listed here in Table 1—include IR spectroscopy, especially the one published in this journal employing FTIR–PAS and band analysis [13]. The IR spectra of such silylated derivatives display and identify (beside the specific frequencies due to grafted, heterogeneous organic moieties) structural bands similar to those reported later by Fonseca et al. [16], highlighting the ubiquitous 960 cm−1 frequency attributed to HCl-induced silanol groups. Such groups are the main bridge in the grafting mechanism of organosilyl compounds on chrysotile (and other silicates) by covalent bonding, which led the way to the preparation of a wide range of interesting new stable products. Although the list displayed in Table 1 is not exhaustive, we suggest that it should be cited in future works related to the modification of HCl-leached chrysotile by silylating agents.
References [1] B. Nagy, T.F. Bates, Am. Mineral. 37 (1952) 1055. [2] E. Mendelovici, in: I.Th. Rosenquist (Ed.), Proceedings of the Third European Clay Conference, Oslo, 1977, p. 118. [3] C.W. Lentz, Inorg. Chem. 3 (1964) 574. [4] E. Mendelovici, Les derives methyles et vinyliques des asbestos— chrysotile, Th. Doct. Sc. Agr., Louvain, Belgium, 1967. [5] J.J. Fripiat, E. Mendelovici, Bull. Soc. Chim. 2 (1968) 483. [6] S.E. Frazier, J.A. Bedford, J. Hower, M.E. Kenney, Inorg. Chem. 6 (1967) 1693. [7] J.P. Linsky, T.R. Paul, M.E. Kenney, J. Polym. Sci. A-2 9 (1971) 143. [8] L. Zapata, J. Castelein, J.P. Mercier, J.J. Fripiat, Bull. Soc. Chim. 1 (1972) 54. [9] E. Ruiz-Hitzky, A. Van Meerbeek, Colloid Polym. Sci. 256 (1978) 135. [10] E. Mendelovici, Acta Cient. Venez. Suppl. 1 (1970) 81. [11] E. Mendelovici, Clays Clay Miner. 21 (1973) 115. [12] E. Mendelovici, D. Carroz Portillo, Clays Clay Miner. 24 (1976) 177.
E. Mendelovici, R.L. Frost / Journal of Colloid and Interface Science 289 (2005) 597–599
[13] E. Mendelovici, R.L. Frost, J.T. Kloprogge, J. Colloid Interface Sci. 238 (2001) 273. [14] J.T. Kloprogge, R.L. Frost, L. Rintoul, Phys. Chem. Chem. Phys. 1 (1999) 2559.
599
[15] F. Wypych, W.H. Schreiner, E. Richard Jr., J. Colloid Interface Sci. 276 (2004) 167. [16] M.G. Fonseca, A.S. Oliveira, C. Airoldi, J. Colloid Interface Sci. 240 (2001) 533.
Note
Pioneer studies on HCl and silylation treatments of chrysotile Efrain Mendelovici 1 , Ray L. Frost ∗ Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia Received 16 March 2005; accepted 14 May 2005
Abstract In the light of some recent studies on organosilicon derivatives of HCl-leached chrysotile, pioneer works not cited in this area are chronologically and briefly commented on, emphasizing the infrared spectroscopy (FTIR–PAS) characterization of such chrysotile products. The latter have opened a far-reaching potential for the development of, e.g., highly stable hydrophobic or organophilic materials, including fibrous sheet polymers. 2005 Elsevier Inc. All rights reserved. Keywords: Chrysotile; HCl and silylation treatments; FTIR–PAS
Chrysotile asbestos is a fibrous, 1:1-layered magnesium silicate consisting of a sheet of linked silica tetrahedra that is coupled to a brucite-like trioctahedral sheet. The structural misfit between the tetrahedral and octahedral units causes a curvature, which explains the fibrous nature of chrysotile. Acid treatments of chrysotile may give useful information on the activation of this mineral as well as on the mechanism of its interaction with, e.g., organosilicon compounds. The organosilicate products resulting from such interactions may lead to interesting applications, as their surface and reaction properties are determined by the organic components and their mechanical properties by the mineral skeleton (the silicate backbone). The morphological and textural changes resulting from the HCl leaching of chrysotile were reported by Nagy and Bates [1]. Other related works on the solubility and stability of chrysotile products submitted to HCl treatments followed (see, e.g., Mendelovici [2] and references therein). It has been established that the release of magnesium from the octahedral sheet is a diffusion process, depending on the * Corresponding author.
E-mail address: [email protected] (R.L. Frost). 1 Emeritus investigator IVIC, Caracas.
0021-9797/$ – see front matter 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.05.053
concentration of the acid, the pH, the temperature, and the fiber morphology. The synthesis of trimethylsilyl derivatives of silicate minerals ranging from ortho- to tectosilicates by a procedure involving HCl (diluted by isopropanol) and hexamethyldisiloxane as modifying agents (known as the cohydrolysis method) was published by Lentz [3]. Based on this method, treatments of chrysotile by HCl and by HCl plus silylating agents that generate thrimethyl or methylvinyl groups were described in 1967 [4]. As the octahedral magnesium layer was gradually dissolved by HCl, silanol groups were generated. The active silanol groups formed covalent bonds with the organosilyl groups by a protonation and condensation mechanism. The grafting of thrimethylsilyl groups on chrysotile by the cohydrolysis method resulted in stable hydrophobic products of high surface area [4,5]. These products were characterized by surface and chemical analysis methods, as well as by diffraction and electron microscopy, differential thermal analysis, and infrared spectroscopy. The functionality and nature of the coupling agents (organosilyl groups), as well as the structure of the mineral silicate, will determine the characteristics of the resulting products. The grafting of methylsilyl groups on chrysotile and apophyllite by the cohydrolysis method was published in
598
E. Mendelovici, R.L. Frost / Journal of Colloid and Interface Science 289 (2005) 597–599
Table 1 Former studies on the HCl and silylation treatments of chrysotile employing IR spectroscopy Silylating agents
Grafted organosilyl groups
Reference
Hexamethyldisiloxane Methylvinyldichlorosilane
Trimethyl Methylvinyl
[4]
Hexamethyldisiloxane
Trimethyl
[5]
Trimethylchlorosilane
Trimethyl
[6]
Dimethylallylchlorosilane
Trimethylallyl
[8]
Gamma-methacryloxypropyltrimethoxysilane
Methacryl
[10]
Dimethylphenyldichlorosilane Dimethyldichlorosilane
Dimethylphenyl Dimethyl
[13]
following works [6,7]. According to the latter works, fibrous, sheet polymers may be derived from chrysotile by an extraction–grafting process. The modification of chrysotile by methylallylsilanes and by octamethylcyclotetrasiloxane in acid medium was also reported [8,9]. On the other hand, chrysotile was treated by some alkoxysilanes such as gamma-methacryloxypropyltrimethoxysilane and delta-aminobutylmethyldiethoxysilane in the presence and absence of HCl [10]. Based on information from these works another fibrous silicate, palygorskite (attapulgite), was successfully reacted with HCl [11] and with some alkoxysilanes [12]. With palygorskite, as well, the grafting of the organic moieties took place via HCl-induced silanol groups. The preparation of methyl and phenylsilyl derivatives of chrysotile in the presence or absence of HCl was recently described [13]. Careful and detailed band assignments were achieved employing Fourier-transformed IR photoacoustic spectroscopy (FTIR–PAS) and band component analysis [13]. The appearance of an absorption band at about 960 cm−1 , which we assigned to silanol groups, was ubiquitous in HCl-treated products, whereas when the reaction was carried out in the absence of HCl no such band was detected. Band assignments were also based on references reported from former studies of neat chrysotile by IR absorption spectroscopy using dispersive spectrometers [14]. Referring to the appearance of the 960-cm−1 band attributed to silanol groups in HCl-modified chrysotile products [13], Wypych et al. confirmed and reported the same band in HClleached chrysotile, which they called disordered silica [15]. In addition to the silanol band, the IR spectrum of disordered silica exhibited frequencies similar to those of the original silica-like sheet structure of chrysotile. Beside the effect of the HCl attack on the structure of chrysotile, the presence and absence of the 960-cm−1 band are related to the degree of coupling of the silanol groups with the organic moieties in the silylated products, where steric hindrance also played a role. In a recent work Fonseca et al. [16] grafted some alkoxysilanes such as 3-aminopropylthrimethoxysilane on HCl-leached chrysotile. In the discussion of the IR spec-
troscopy results of their modified chrysotile products, they assigned the IR frequencies on the basis of previous studies on silica gel treatments. However, they did not refer to the earlier mentioned studies on the products resulting from treatment of chrysotile by HCl and silylating agents. Most of these studies—which are listed here in Table 1—include IR spectroscopy, especially the one published in this journal employing FTIR–PAS and band analysis [13]. The IR spectra of such silylated derivatives display and identify (beside the specific frequencies due to grafted, heterogeneous organic moieties) structural bands similar to those reported later by Fonseca et al. [16], highlighting the ubiquitous 960 cm−1 frequency attributed to HCl-induced silanol groups. Such groups are the main bridge in the grafting mechanism of organosilyl compounds on chrysotile (and other silicates) by covalent bonding, which led the way to the preparation of a wide range of interesting new stable products. Although the list displayed in Table 1 is not exhaustive, we suggest that it should be cited in future works related to the modification of HCl-leached chrysotile by silylating agents.
References [1] B. Nagy, T.F. Bates, Am. Mineral. 37 (1952) 1055. [2] E. Mendelovici, in: I.Th. Rosenquist (Ed.), Proceedings of the Third European Clay Conference, Oslo, 1977, p. 118. [3] C.W. Lentz, Inorg. Chem. 3 (1964) 574. [4] E. Mendelovici, Les derives methyles et vinyliques des asbestos— chrysotile, Th. Doct. Sc. Agr., Louvain, Belgium, 1967. [5] J.J. Fripiat, E. Mendelovici, Bull. Soc. Chim. 2 (1968) 483. [6] S.E. Frazier, J.A. Bedford, J. Hower, M.E. Kenney, Inorg. Chem. 6 (1967) 1693. [7] J.P. Linsky, T.R. Paul, M.E. Kenney, J. Polym. Sci. A-2 9 (1971) 143. [8] L. Zapata, J. Castelein, J.P. Mercier, J.J. Fripiat, Bull. Soc. Chim. 1 (1972) 54. [9] E. Ruiz-Hitzky, A. Van Meerbeek, Colloid Polym. Sci. 256 (1978) 135. [10] E. Mendelovici, Acta Cient. Venez. Suppl. 1 (1970) 81. [11] E. Mendelovici, Clays Clay Miner. 21 (1973) 115. [12] E. Mendelovici, D. Carroz Portillo, Clays Clay Miner. 24 (1976) 177.
E. Mendelovici, R.L. Frost / Journal of Colloid and Interface Science 289 (2005) 597–599
[13] E. Mendelovici, R.L. Frost, J.T. Kloprogge, J. Colloid Interface Sci. 238 (2001) 273. [14] J.T. Kloprogge, R.L. Frost, L. Rintoul, Phys. Chem. Chem. Phys. 1 (1999) 2559.
599
[15] F. Wypych, W.H. Schreiner, E. Richard Jr., J. Colloid Interface Sci. 276 (2004) 167. [16] M.G. Fonseca, A.S. Oliveira, C. Airoldi, J. Colloid Interface Sci. 240 (2001) 533.