Hydrothermal synthesis of magadiite

Hydrothermal synthesis of magadiite

Applied Clay Science 33 (2006) 73 – 77 www.elsevier.com/locate/clay Technical note Hydrothermal synthesis of magadiite Yuh-Ruey Wang ⁎, Sea-Fue Wang...

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Applied Clay Science 33 (2006) 73 – 77 www.elsevier.com/locate/clay

Technical note

Hydrothermal synthesis of magadiite Yuh-Ruey Wang ⁎, Sea-Fue Wang, Li-Chung Chang Department of Materials and Minerals Resources Engineering, National Taipei University of Technology, Taipei, Taiwan Received 28 December 2004; received in revised form 9 February 2006; accepted 11 February 2006 Available online 24 March 2006

Abstract Intercalation of organic guest species into layered silicates is a way to construct clay mineral–polymer nanocomposites. An example is magadiite Na2Si14O29·9H2O which like smectites intercalates organic species. Using hydrous silica precipitated from water glass with dilute HCl in aqueous dispersions of NaOH and Na2CO3, well-crystallized magadiite as a single phase was synthesized at 150 °C for 24 h or 170 °C for 9 h. © 2006 Elsevier B.V. All rights reserved. Keywords: Hydrothermal synthesis; Magadiite; Crystallization; Layered structure; Kenyaite

1. Introduction Intercalation of organic guest species into inorganic layered silicates is a way to construct clay–polymer nanocomposites. Magadiite with idealized chemical composition Na2Si14O29·9H2O is an example of such silicates which intercalate organic species (Lagaly, 1979; Landis et al., 1991; Schwieger et al., 1991; Dailey and Pinnavaia, 1992). It can be synthesized at low hydrothermal temperature and short reaction time. The hydroxyl groups on the interlayer surface can be reacted with coupling agents to form reactive functional groups that can form covalent bonds with the polymer (Shi et al., 1996). Magadiite was first discovered in the Lake Magadi, Kenya (Eugster, 1967). The structure,

⁎ Corresponding author. Present address: Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, 1, Sec. 3, Chung-Hsiao E. Road, Taipei 106, Taiwan, ROC. Fax: +886 2 27317185. E-mail address: [email protected] (Y.-R. Wang). 0169-1317/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2006.02.001

classification, synthesis and applications of these aluminum-free layered silicate hydrates have been well reviewed by Schwieger and Lagaly (2004). The hydrothermal synthesis of magadiite using water glass solution as starting material and its properties, transformation and related minerals such as kenyaite (Na2 Si22O45·10H2O) and makatite (Na2Si4O9·5H2O) have been investigated by Beneke and Lagaly (1983). In their study, magadiite was precipitated as the first product and then altered to kenyaite at 125 °C during several days to months. Muraishi (1983) studied the crystallization of magadiite in alkali solution of silica gel with molar ratio of SiO2/H2O/Na+/OH− = 1:100:2–4:0.5 at 100 to 180 °C. The effect of anions on the synthesis of magadiite was investigated. The production rate and crystallinity of magadiite could be enhanced by the addition of sodium carbonate (Fletcher and Bibby, 1987). Using the sol–gel technique with the composition of 1SiO 2 /0.28NaOH/0.75PEG200/58H 2 O at 180 °C, 150 °C and 90 °C for 2, 4 and 65 days, the magadiite, kenyaite and octosilicate were synthesized (Feng and Balkus, 2003). Kosuge et al. (1992)

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Table 1 Composition of reactants and conditions of synthesis, (a) amorphous, (m) magadiite, (k) kenyaite, (c) cristobalite Run no.

Temperature (°C)

Time (h)

Molar ratio of starting materials H2SiO3

H2O

NaOH

Na2CO3

1 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

150 150 150 150 150 150 150 150 150 150 150 150 170 170 170 170 170 170 180 180 180 180

18 24 30 36 18 24 30 18 21 24 30 36 18 9 12 15 18 24 12 15 18 24

3.85 3.85 3.85 3.85 5 5 5 7 7 7 7 7 5 7 7 7 7 7 7 7 7 7

100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3 1/3

2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3 2/3

synthesized magadiite from dispersions with a molar ratio of SiO2/NaOH/H2O = 1:0.23:18.5 at 150 °C for 48 h or at 170 °C for 18 h. Kwon et al. (1995) and Kwon and Park (2004) synthesized magadiite from dispersions with molar ratio of SiO2/NaOH/H2O =

Product

a a, m m m a, m m m a a, m m m m m m m m m m m m m, k, c m, k, c

1:0.23:18.5 and NaOH/Na2CO3 = 1:2 at 150 °C for 24 h. They also used sodium silicate solution, neutralized with acids such as HCl, H2SiF6, H2SO4, CH3COOH, as silicate source to obtain magadiite and kenyaite at 150 °C for 48–96 h. To lower the

Fig. 1. XRD patterns of samples with molar ratio of SiO2/(NaOH + Na2CO3) = 3.85, synthesized at 150 °C for 18, 24, 30 and 36 h (sample nos. 1–4).

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temperature and reaction time of crystallization, we used SiO2·xH2O precipitated from water glass solution with dilute HCl. 2. Experimental procedure Raw materials were water glass (42°Be′, 29% SiO2, 18.2% Na2O, molar ratio of SiO2/Na2O = 3.2), HCl (96%, SHOWA), Na2CO3 (99%, SHOWA) and NaOH (96%, SHOWA). Hydrous silica was precipitated from water glass solution with dilute HCl (the volume ratio of HCl/H2O = 1:4), washed with deionized water and air-dried at 80 °C. The particle size of hydrous silica was analyzed by the dynamic light scattering particle size analyzer (Horiba LB-500). Hydrothermal experiments were carried out in a steel autoclave with Teflon lining under autogenous pressure at 150 to 180 °C (Table 1). We used the ratios NaOH/ Na2CO3 = 1/2 and H2O/(NaOH + Na2CO3) = 100 as reported by Fletcher and Bibby (1987). Magadiite formed readily in the presence of CO2− 3 (Fletcher and Bibby, 1987; Kwon et al., 1995; Feng and Balkus, 2003). The reaction products were filtered, washed with deionized water and dried at 80 °C. The samples were characterized by X-ray diffraction (Rigaku D/ MAX-B) and SEM (HITACHI S4700).

3. Results and discussion Magadiite content and crystallinity of samples synthesized from the dispersions with the molar ratio

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of SiO2/(NaOH + Na2CO3) = 3.85 to 7 increased with the reaction time (Fig. 1). The typical reflections of magadiite were obtained at 150 °C after 24 h. The intensity of the reflections increased with the reaction time. Fig. 2 shows XRD patterns of samples synthesized at 150 °C for 24 h at different SiO2/ (NaOH + Na2CO3) ratios. The crystallinity increases with this ratio. Well-crystallized magadiite as a single phase was obtained for the composition SiO2/(NaOH + Na2CO3) = 5 and 7, and H2O/(NaOH + Na2CO3) = 100 at 150 °C for 24 h. These samples showed a higher crystallinity than the samples prepared at 150 °C and 48 h (Kosuge et al., 1992). This advantage may be attributed to the small particle size of hydrous silica with 0.1–0.9 μm (d50 = 0.35 μm), and its high solubility and rapid dissolution at hydrothermal condition. Fig. 3 shows the X-ray diffraction patterns of magadiite synthesized at 170 °C for 9, 12, 15, 18 and 24 h and the composition of SiO2/(NaOH + Na2CO3) = 7 and H2O/(NaOH + Na2CO3) = 100. Magadiite was obtained after 9 h. Magadiite content increased with reaction time up to 15 h, but decreased after 15 h due to the conversion of magadiite to kenyaite and cristobalite. This result is similar to those reported in the previous papers (Fletcher and Bibby, 1987; Kwon et al., 1995; Feng and Balkus, 2003). It is noteworthy that cristobalite was formed and quartz in the previous reports.

Fig. 2. XRD patterns of samples synthesized at 150 °C for 24 h and molar ratios H2O/(NaOH + Na2CO3) = 100, (a) SiO2/(NaOH + Na2CO3) = 3.85 (No. 2), (b) SiO2/(NaOH + Na2CO3) = 5 (No. 7), (c) SiO2/(NaOH + Na2CO3) = 7 (No. 11).

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Fig. 3. X-ray diffraction pattern of samples obtained from dispersions SiO2/(NaOH + Na2CO3) = 7 and H2O/(NaOH + Na2CO3) = 100 at 170 °C for 9, 12, 15, 18, and 24 h.

At 180 °C and 18 h, the reflections of magadiite, kenyaite and cristobalite (Fig. 4) were observed, and the content of kenyaite and cristobalite increased with increasing reaction time. Kwon et al. (1995) used amorphous SiO2 as a starting material and obtained similar results. Fig. 4 also shows that the effect of

temperature on the production of magadiite is more important than the reaction time and concentration. In order to obtain magadiite as a single phase, the reaction temperature must be below 170 °C as reported by Beneke and Lagaly (1983). Fig. 5 shows the SEM photos of magadiite with a rosettes-

Fig. 4. X-ray diffraction pattern of samples obtained from dispersions SiO2/(NaOH + Na2CO3) = 7 and H2O/(NaOH + Na2CO3) = 100, (a) at 150 °C for 18 h (No. 9), (b) at 170 °C for 18 h (No. 18), (c) at 180 °C for 18 h (No. 22), (d) at 180 °C for 24 h (No. 23).

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dispersions of hydrous silica (precipitated from water glass solutions with dilute HCl) in NaOH + Na2CO3 solutions. References

Fig. 5. SEM photos of magadiite with a rosettes-like shape synthesized at (a) 150 °C for 24 h (No. 11) and (b) 170 °C for 9 h (No. 15).

like shape, synthesized at the 150 °C for 24 h and 170 °C for 9 h, respectively. The diameter of a “flower” and a “pedal” are about 5–7 μm and 2– 3 μm, respectively. 4. Conclusions The well-crystallized magadiite as a single phase was synthesized at 150 °C for 24 h or at 170 °C for 9 h from

Beneke, K., Lagaly, G., 1983. Kenyaite—synthesis and properties. Am. Mineral. 68, 818–826. Dailey, J.S., Pinnavaia, T.J., 1992. Silica pillared derivatives of Hqmagadiite, a crystalline hydrated silica. Chem. Mater. 4, 855–863. Eugster, H.P., 1967. Hydrous sodium silicates from Lake Magadii, Kenya: precursors of bedded chert. Science 157, 1177–1181. Feng, F., Balkus Jr., K.J., 2003. Synthesis of kenyaite, magadiite and octosilicate using poly(ethylene glycol) as a template. J. Porous Mater. 10, 5. Fletcher, R.A., Bibby, D.M., 1987. Synthesis of kenyaite and magadiite in the presence of various anions. Clays Clay Miner. 35 (4), 318–320. Kwon, O.-Y., Park, K.-W., 2004. Synthesis of layered silicates from sodium silicates solution. Bull. Korean Chem. Soc. 25 (1), 25. Kosuge, K., Yamazaki, A., Tsunashima, A., Otsuka, R., 1992. Hydrothermal synthesis of magadiite and kenyaite. J. Ceram. Soc. Jpn. 100, 326–331 (in Japanese, with English Abstr.). Kwon, O.-Y., Jeong, S.-Y., Suh, J.-K., Lee, J.-M., 1995. Hydrothermal syntheses of Na-magadiite and Na-kenyaite in the presence of carbonate. Bull. Korean Chem. Soc. 16 (No. 8), 737–741. Lagaly, G., 1979. Crystalline silicic acids and their interface reactions. Adv. Colloid Interface Sci. 11, 105–148. Landis, M.E., Aufdembrink, B.A., Chu, P., Johnson, I.D., Kirker, G. W., Rubin, M.K., 1991. Preparation of molecular sieves from dense, layered metal oxides. J. Am. Chem. Soc. 113, 3189–3190. Muraishi, H., 1983. Crystallization of silica gel in alkaline solutions at 100 to 180 °C: characterization of SiO2-Y by comparison with magadiite. Am. Mineral. 74, 1147. Schwieger, S., Lagaly, G., 2004. Alkali silicates and crystalline silicic acids. In: Auerbach, S.M., Carrado, K.E., Dutta, P.K. (Eds.), Handbook of Layered Materials. Marcel Dekker. Inc., New York, pp. 541–629. Schwieger, S., Werner, P., Bergk, K.-H., 1991. A new synthetic layered silicate of type metal silicate. Colloid Polym. Sci. 269, 1071–1073. Shi, H., Lan, T., Pinnavaia, T.J., 1996. Hybrid organic–inorganic nanocomposites formed from an epoxy polymer and a layered silicic acid (magadiite). Chem. Mater. 8, 1584–1587.