Clay Science 13, 75-80 (2006)

SYNTHESIS AND CHARACTERIZATION OF Zn-SUBSTITUTED (SAUCONITE)

SHINGO YOKOYAMAa,*, KENJI TAMURAa, TAMAO HATTAb, SEIKO NEMOTOb, YUJIRO WATANABEc and HIROHISA YAMADAa,**

aPhotocatalytic Materials Center , National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan bJapan International Research Center for Agricultural Sciences , 1-1, Ohwashi, Tsukuba, Ibaraki 305-8686, Japan College of Environmental Engineering and Architecture, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi,c Ishikawa 921-8510, Japan

(ReceivedNovember 20, 2006. Accepted April 6, 2007)

ABSTRACT

Sauconites were synthesized hydrothermally from a homogeneous gel with stoichiometric chemical composition in a temperature range of 100-200•Ž for up to 14d at autogenous pressure. The synthetic

products were characterized by XRD, SEM, TEM, ICP-AES, FT-IR and XPS. The well-crystallized sauconite without impurities was obtained after 100•Ž treatment. At 150 and 200•Ž, sauconite coexisted with small amount of (Zn4Si2O7(OH)2•EH2O) and willemite (Zn2SiO4). The octahedral coordination of Zn in synthesized sauconite was confirmed by FT-IR and XPS spectra, comparing with those of natural containing Zn in the octahedral layer (hendricksite). The FT-IR spectra of synthetic sauconite showed the characteristic bands at 660cm-1 for Zn-O vibration and 3635cm-1 for 3Zn-OH stretching in the octahedral sheets, which are comparable to those of hendricksite. The Zn (3p)

peak of sauconite in XPS spectrum was observed which corresponded with that of hendricksite. These results indicated that Zn in sauconite was coordinated octahedrally as Zn in hendricksite.

Key words: FT-IR, Hendricksite, Hydrothermal Synthesis, Sauconite, XPS

INTRODUCTION There have been several reports of synthesis of smectite containing Zn in the octahedral sheets (Tiller Smectite has various applications for material sciences and Pickering, 1974;Taylor and Owen, 1984;Luca et al., such as catalysis and new functional nanomaterials due 1992, 1995; Reinholdt et al., 2001; Higashi et al., 2002; to their suitable physicochemical property. Therefore, Nakakuki et al., 2005; Vogels et al., 2005). Recent the hydrothermal synthesis of smectites is a subject of studies (Higashi et al., 2002; Nakakuki et al., 2005; great interest for basic researches in material sciences. Vogels et al., 2005) concluded that Zn-smectite (e.g. Especially, since the synthetic smectite including transi sauconite and Zn-hectorite) are usually synthesized at tion metals has been expected to use in catalytic low-temperature compared with the smectite containing applications (Higashi et al. 2002), several previous other transition metals. Therefore, Zn-smectite would be studies investigated the optimal synthetic condition of expected to be synthesized at low-cost and in large smectites including transition metals (e.g. Ni, Co, and quantities and will contribute to the catalyses in some Cu) (Decarreau, 1980, 1985; Bruce et al., 1986; Torii organic reactions (Luca et al., 1992; Shirai et al., 1999) and Iwasaki, 1988; Urabe et al., 1989; Mosser et al., and also developments of their new application to the 1990;Luca et al., 1991; Yamada et al., 1994;Xiang and field of nanomaterials. Villemure, 1996; Kloprogge et al., 1999; Vogels et al., The characterization of synthesized smectite is impor- 2005). tant for understanding of their physicochemical proper- ties and for developments of their new functions. How- * Present address: Civil Engineering Research Laboratory , Central ever, most studies for the synthesis of smectites lack the Research Institute of Electric Power Industry, 1646 Abiko, Abiko, complete characterization of the products as Kloprogge Chiba 270-1194, Japan. et al. (1999) have previously pointed out. For example, ** Corresponding author: Hirohisa Yamada , Photocatalytic Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, the chemical composition of products and coordination Ibaraki 305-0044, Japan. e-mail:[email protected] of the metals in products have not been noticed in many 76 S. Yokoyama et al.

studies. In the present paper, we investigated the low and Zn, 20mg of sample was mixed with Na2CO3 and temperature synthesis of saponite containing Zn in the H3BO3 powder. After melting the mixture by heating, octahedral sheets (sauconite) with ideal compositions of the mixture was dissolved by a HCl solution, and finally Na0 .66Zn6(S17.34Al0.66)O20(OH)2. The obtained products pure water was added to the solution to make 100mL of were characterized by the powder X-ray diffraction a final solution. For Na, 10mg of sample was dissolved (XRD) method for randomly oriented samples and in 1mL HF and 1mL of H2SO4 solutions. After the samples treated with ethylene glycol, scanning electron solution was evaporated, the dried residue was dissolved microscope (SEM), transmission electron microscope in 1mL of HCl solution with heating, pure water was

(TEM), and inductively coupled plasma atomic emis- added to the solution to make 100mL of a final solution. sion spectrometry (ICP-AES). Furthermore, the coordi- IR transmission spectra were recorded on a FT-IR nation of Zn in synthesized sauconite was confirmed by spectrometer (PERKIN ELMER Spectrum 2000) using fourier transform infrared spectrometer (FT-IR) and X- the standard KBr pressed disk method. The IR spectra ray photoelectron spectrometer (XPS). were collected at 100times scans and were recorded between 4000-400cm-1. EXPERIMENTAL METHODS XPS (GAMMADATA-SCIENTA ESCA-300) with a monochromatized AlKƒ¿ X-ray source (1kW) was ap- Hydrothermal Synthesis plied to confirmation of Zn coordination in sauconite. The starting gel with stoichiometric hydrated compo- The base pressure of the analytical chamber was 10-7 sition of sauconite (Na0 .66Zn6(Si7.34Al0.66)O20(OH)2) was Pa. Wide spectra were obtained using analyzer pass prepared by the following technique. Tetraethyl ortho- energy of 300eV. Narrow spectra of the O (1s), Zn (2p), silicate (31.10g, Kanto Chemicals) was added to 200 and Si (2s) were collected to obtain chemical state in- mL ethanol at about 60•Ž for 3h. To this solution formation, using analyzer pass energy of 150eV. The was added ZnCl2 (16.63g, Kanto Chemicals) and C (1s) peak near 285.0eV was used for the compensation AlCl3•E6H2O (3.24g, Wako Chemicals) dissolved to of peak drift. In this study, the binding energy scales 250 mL deionized water. This ethanol/water solution were adjusted to the highest C (1s) peak position equal to was stirred magnetically with a Teflon-coated stirring 285.0eV. bar for 2h to obtain homogeneous solution, and then 3 To confirm the coordination of Zn in products, M NaOH solution was added dropwise at a constant natural hendricksite from Sterling Hill, representing the rate about 1.6mL/min until a final pH of 10 was Zn member of the trioctahedral mica group (Frondel obtained. After the solution was stirred for 1day, the and Ito, 1966; Frondel and Einaudi, 1968) is used as a precipitate was filtered several times with deionized reference. The of hendricksite was de- water. The solid were redispersed in 250mL deionized termined by Robert and Gasperin (1985). They found water, and 0.58g of NaOH was added. The suspension Zn to be exclusively in octahedral coordination and was aged with stirring at room temperature overnight to randomly distributed; there is no evidence of ordering of form a uniform gel. Zn. The obtained gel was placed in a Teflon cup fitted

into a stainless steel pressure vessel and treated hydro- RESULTS AND DISCUSSION thermally in a temperature range of 100-200•Ž for up to 14d under autogenous pressure. After the hydro- X-ray diffraction analyses thermal treatments, the solid and solution were sepa- The results of hydrothermal synthesis of Zn-saponite, rated by centrifugation at 15,000rpm for 15 minutes sauconite, at different temperatures and durations are and the solids were washed using deionized water. Then summarized in Table 1. Figure 1 shows the XRD it was freeze-dried for over 2d.

TABLE 1. The components in products and d (060) values of sauconite. Characterization of products The products were characterized using XRD, SEM, TEM, FT-IR and XPS. For identification, the XRD patterns of products were obtained using random

oriented and the ethylene-glycolated samples by XRD

with FeKƒ¿ radiation (RIGAKU RINT 2200) . Each sample was scanned at 40kV, 30mA, 0.01•‹2ƒÆ steps and a scan range of 2-85•‹2ƒÆ. Morphology of products were observed by SEM

(JEOL JSM-5600LV) and was also examined by TEM t 100kV (JEOL JEM 1010). a The chemical compositions were obtained from chem- ical analyses determined by ICP-AES (Nippon Jarrell- Ash IRIS AP). A solution for ICP-AES measurement was prepared by the following procedure: for Si, Al *Mineral identification was carried out based on XRD analyses . Synthesis and Characterization of Sauconite 77

consistent with that of typical smectite (Brindley, 1984). The d (060) refractions of 1.53-1.54•ð observed in all

products confirmed its identification as a trioctahedral Zn-smectite, sauconite. The full width at half maximum of the d (001) reflection of sauconite was decreased with the temperature (i.e. 4.07 to 3.11 degree), but was not decreased with the durations. This result implied that the crystallinity of sauconite increased with the temper- ature. The intensity of hemimorphite in XRD patterns

increased with the temperature and the treatment time . The above results show that sauconite are formed

preferentially at lower temperature, and hemimorphite occurred as a high-temperature phase of sauconite . Willemite, however, appears to be more stable than

sauconite and hemimorphite at higher temperatures . These results may evaluate the natural occurrence con- dition of sauconite, hemimorphite and willemite. In the previous study (Higashi et al., 2002), there is little or no crystallization of sauconite at 100•Ž. They concluded that sauconite with no detectable impurities were obtained in the temperature range 125-200•Ž with some Zn-deficient compositions. In this study, sauconite has been crystallized at lower temperature compared to Higashi et al. (2002) by using the homogeneous precip- itates with higher reactivity. This difference of the op- timal synthetic condition for sauconite would be resulted the difference of Zn/Si ratio of starting gel since other experimental approach is almost same. The present reactivity is compared with that of the new synthesis

procedure under non-hydrothermal condition at 90•Ž using a stoichiometric mixture containing Si/Al gel , Zn- nitrate, urea and water (Vogels et al., 2005). The present results provides sufficiently the optimal synthetic con- dition for sauconite with high-crystallinity and large

quantities. Furthermore, these is a possibility that sau- conite would be able to synthesis at more short time when treat using present starting materials because sau- conite was synthesized at 100•Ž within 1 day.

Morphology and chemical compositions of synthesized

products The SEM-images of the product at 100•Ž for 14d

(S10) and 150•Ž for 14d (S15) were shown in Fig. 2. S10 included the agglomerate with rough surface and the

FIG. 1. XRD patterns of synthetic products treated at different aggregate of small particle that would be formed at experimental conditions. •œ: hemimorphite (ideal formula; the sample preparation (e.g. wash, drying and crush) Zn4Si2 O7 (OH)2•EH2O); •£: willemite (i.e: ideal formula; Zn2SiO4). (Fig. 2a). In S15, the aggregate of small particles were observed with hemimorphite of several ten im in length patterns of the products recorded after increasing tem- (Fig. 2b). perature and durations. At 100•Ž, sauconite with no The TEM image of the synthesized sauconite in S10 detectable impurities was obtained for up to 14d . was shown in Fig. 3. The morphology of the synthe- Sauconite formed at 150•Ž for 1-14d and at 200•Ž sized sauconite shows typically the two-dimensional for 1-3d are coexisted with hemimorphite (ideal for- flake of a few gm in length because of the sample mula; Zn4Si2O7(OH)2•1H2O) as a impurities. After the preparation, in which the product was dispersed by treatment at 200•Ž for 7d, sauconite formed with both water solution on a microgrid. Some synthesized sau- hemimorphite and willemite (ideal formula; Zn2SiO4) as conite particle fanned from thicker particle (Fig. 3). The impurity. SAED pattern shows diffuse rings of spots consistent The basal spacing of synthetic products expanded to with turbostratic stacking of layers related by random 17•ð on treatment with ethylene glycol. The behavior is rotation about the c*. However, it is also an accom- 78 S. Yokovama et al.

FIG. 3. TEM photograph and SAED pattern of synthesized sauconite treated at 100•Ž for 14d.

TABLE 2. Chemical compositions of the product treated at 100•Ž for 14d (S10). FIG. 2. SEM photographs of (a) the product treated at 100•Ž for 14d (S10) and (b) the product treated 150•Ž for 14d (S15). modation of separate reflection spots with symmetrical hexagonal net imbedded within the diffuse rings. The chemical compositions of S10, which has no impurity, were summarized in Table 2. The atomic ratios were determined for Si (7.18), Al (0.64), Zn (6.20) and Na (0.96). Zn and Na compositions were slightly higher than those of the ideal formula for sauconite probably due to the adsorption of Zn and Na in interlayer spaces and surface of sauconite.

Confirmation of Zn coordination in synthesized sauconite The octahedral coordination of Zn in synthesized sauconite was confirmed by FT-IR and XPS spectra, comparing with those of natural mica containing Zn in the octahedral layer (hendricksite). The FT-IR spectra of sauconite (S10) were almost comparable those of natural hendricksite (Fig. 4). But the small difference (e.g. the band around 620cm-1) originated from the difference of chemical compositions between the obtained sauconite and hendricksite because FIG. 4. IR spectra (range 4000-400cm-1) of (a) starting gel, (b) the natural hendricksite included Mg, Fe and Mn as major product treated at 100•Ž for 14d (S10) and (c) hendricksite (Zn- elements (Frondel and Einaudi, 1968). The broad and mica). Synthesis and Characterization of Sauconite 79

Zn-O vibration (Higashi et al., 2002; Nakakuki et al., 2005). The band around 450cm-1 is consistent with the assignment to Si-O bending vibration as suggested by the synthetic series (Wilkins and Ito, 1967). These FT-IR results showed that Zn in sauconite would be coordinated octahedrally. There are a few researches on XPS analysis for clay (e.g. Ebina et al., 1999; Wittberg and Wang, 1999;Gier and Johns, 2000; Nakakuki et al., 2005). The XPS spectra of sauconite (S10) and hendricksite was shown in Figs. 5 and 6. The spectra assigned to Zn2p1/2, Zn2p3/2, Nals, Ols, Si2s, Zn3s, Al2s, Si2p, Zn3p and Al2p are observed in wide spectra (Fig. 5). In addition, the peaks related Mn (Mn2p3), Mg (Mg a) and K (K2s and K2p) were observed in wide spectrum of hendrick- site (Fig. 5). The binding energy of Zn3p peaks for sauconite (S10) and hendricksite are nearly the same (Fig. 6 and Table 3), and are comparable to those of the Binding Energy [eV] previous study for Zn-hectorite (Nakakuki et al., 2005). The binding energy of Zn2p peaks is corresponding to FIG. 5. XPS spectra (wide scan) of (a) starting gel, (b) the product that of Zn3(OH)6 octahedral sheet. These results showed treated at 100•Ž for 14d (S10) and (c) hendricksite (Zn-mica). that Zn in sauconite was coordinated octahedrally. The O(1s) peak of sauconite (S10) (531.60eV) showed higher binding energy compared to hendricksite (528.89 eV) (Fig. 6 and Table 3). O (1s) banding energy of sharp bands in the range of 3600-3200cm-1 and around sauconite was corresponding with previously reported 1600cm-1, respectivelyare assigned to interlayer water. banding energy of other smectite (i.e. 531.4-532.1eV) The distinct band at 3635cm-1 is comparable to that of by Ebina et al. (1999). It is well known what O (1s) 3Zn-OH stretching vibration (3635cm-1) for synthetic binding energy of a lattice (O2-), a structural MgZn-talc (Wilkins and Ito, 1967) In the lattice vibra- hydroxide (OH-) and adsorbed oxygen species (e.g. tion region 1200-400cm-1 the distinctive bands around H2O) is different in same XPS studies about oxygen 1000, 660 and 450cm-1 were observed, and the band species on minerals (McIntyre and Zetaruk, 1977; Har- frequencies are nearly the same for sauconite, hendrick- vey and Linton, 1981; Nesbitt and Muir, 1994). Since site and synthetic Zn-smectites in the previous studies sauconite has a great deal of adsorbed water (e.g. (Higashi et al., 2002; Nakakuki et al., 2005). The broad interlayer water) compared with hendricksite, the differ- bands around 1000cm-1 were assigned to Si-O stretch- ence of O (1s) binding energy between sauconite and ing vibration in the tetrahedral sheets. The character- hendricksite would be due to effect of adsorbed water of istic bands in the 660cm-1 region has been assigned to sauconite.

FIG. 6. XPS spectra (narrow scan) of (a) starting gel, (b) the product treated at 100•Ž for 14d (S10) and (c) hendricksite (Zn-mica) . 80 S. Yokoyama et al.

TABLE3. Binding energy (eV)* of Si2p, Zn3p, Al2p and O1s in of smectite clay minerals: A critical review. Clays and Clay starting gel, S10 and hendricksite. Minerals, 47, 529-554. LUCA,V., CHEN,X. and KEVAN,L. (1991) Characterization of Cu(II)- substituted fluorohectoriteclay and interaction with adsorbates by electron spin resonance, electron spin echo modulation, and infra- red spectroscopies. Chemistryof Materials, 3, 1073-1081. LUCA,V., KEVAN,L., RHODES,C.N. and BROWN,D.R. (1992) A synthetic Zn-substituted smectite clay alkylation catalyst. Clay

*Binding energy is recorded using each highest peak positions Minerals, 27, 515-519. . LUCA,V., MACLACHAN,D.J., HOWE,R.F. and BRAMLEY,R. (1995) Synthesis and characterization of (Zn, Ti)-substituted layered sili- cate. Journal of Materials Chemistry,5, 557-564. MCINTYRE,N.S. and ZETARUK,D.G. (1977) X-ray photoelectron CONCLUSIONS spectroscopic studies of iron oxides. Analytical Chemistry, 49, 1521-1529. The saponite containing Zn in the octahedral sheet, MOSSER,C., MESTDAGH,M., DECARREAU,A. and HERBILLON,A.J. sauconite, was synthesized hydrothermally at distinctly (1990) Spectroscopic (ESR, EXAFS) evidence of Cu for (Al-Mg) lower temperature, that is at 100•Ž, from homogeneous substitution in octahedral sheets of silicates. Clay Minerals, 25, 271-282. gel with stoichiometric hydrated composition. XRD, NAKANUIU,T., FUJIMURA,K., AISAWA,S., HIRAHARA,H. and NARITA, SEM and TEM analyses revealed that the products E. (2005) Synthesisand physicochemicalproperties of Zn-hectorite. were the well-crystallized smectites. FT-IR and XPS Clay Science, 12, 285-291. analyses confirmed that Zn in synthetic sauconite was NESBITT,H.W. and Mum, I.J. (1994) X-ray photoelectron spectro- coordinated octahedrally. scopic study of a pristine pyrite surface reacted with water vapour and air. Geochimicaet CosmochimicaActa, 58, 4667-4679. REINHOLDT,M., MIEHE-BRENDLE,J., DELMOTTE, L., TUILIER,M.-H., ACKNOWLEDGMENTS DRED,R., CORTES,R. and FLANK,A.-M. (2001) Fluorine route synthesis of containing Mg or Zn and charac- We are grateful to Mr. H. Uno (Hosei University) for the exper- terization by XRD, thermal analysis, MAS NMR, and EXAFS imental supports. The authors express their utmost gratitude to Mr. K. spectroscopy.European. Journal of InorganicChemistry, 2831-2841. Kurashima (National Institute for Materials Science) for help with ROBERT,J.-L. and GASPERIN,M. (1985) Crystal structure refinement TEM observation, Mr. Y. Yajima (National Institute for Materials of hendricksite, a Zn- and Mn-rich trioctahedral potassium mica: Science) for help with ICP-AES analysis. a contribution to the crystal chemistry of -bearing minerals. Tschermaks Mineralogischeand Petrographische Mitteilungen, 34, REFERENCES 1-14. SHIRAI,M., AOKI,K., TORII,K. and ARAI,M. (1999) Acidity and 1- BRINDLEY, G.W. (1984) Order-disorder in clay mineral structures. Pp. butene isomerization of synthesizedsmectite-type catalysts contain- 125-195 in: Crystal Structures of Clay Minerals and their X-ray ing different divalent cations. Applied Catalysis A-General, 187, Identification (G.W. Brindley and G. Brown, editors). Mineralog- 141-146. ical Society, London. TAYLOR,P. and OWEN,D.G. (1986) Hydrothermal synthesis of zinc BRUCE, L.A., SANDERS, J.V. and TURNEY, T.W. (1986) Hydrothermal silicates from borosilicate glasses and from mixtures of zinc oxide synthesis of cobalt clays. Clays and Clay Minerals, 34, 25-36. and silica. Polyhedron, 3, 151-155. DECARREAU, A. (1980) Cristallogenese experimentale des smectites TILLER,K.G. and PICKERING,J.G. (1974)The synthesisof zinc silicates magnesiennes: Hectorite, stevensite. Bulletin de Mineralogie, 103, at 20 C and atmospheric pressure. Clays and Clay Minerals, 22, 579-590. 409-416. DECARREAU, A. (1985) Partitioning of divalent elements between TORII,K. and IWASAKI,T. (1988) Synthesis of novel Ni-hectorite octahedral sheets of trioctahedral; smectites and water. Geochimica inorganic complexes. Chemistry Letters, 2045-2048. et Cosmochimica Acta, 49, 1537-1544. URABE,K., KOGA,M. and IZUMI,Y. (1989) Synthetic Ni-substituted EBINA, T., IWASAKI, T., ONODERA, Y. and CHATTERJEE, A. (1999) A saponite as a catalyst for selectivedimerization of ethane. Journal comparative study of DFT and XPS with reference to the adsorp- of the Chemical Society, Chemical Communications,807-808. tion of caesium ions in smectites. Computational Materials Science, VOGELS,R.J.M.J., KLOPROGGE,J.T. and GEUS,J.W. (2005) Synthesis 14, 254-260. and characterization of saponite clays. American Mineralogist,90, FRONDEL, C. and ITO, J. (1966) Hendricksite, a new species of mica. 931-944. American Mineralogist, 51, 1107-1123. XIANG,Y. and VILLEMURE,G. (1996) Electrodes modified with syn- FRONDEL, C. and EINAUD, M. (1968) Zinc-rich from Sterling thetic clay minerals: Electrochemistryof cobalt smectites. Clays and Hill, New Jersey. American Mineralogist, 53, 1752-1754. Clay Minerals, 44, 515-521. GIER, S. and JOHNS, W.D. (2000) Heavy metal-adsorption on micas YAMADA,H., AZUMA,N. and KEVAN,L. (1994) Electron spin reso- and clay minerals studied by X-ray photoelectron spectroscopy. nance study of Ni (I) stabilized in nickel-substitutedand nickel ion- Applied Clay Science, 16, 289-299. exchanged synthetic hydroxyhectorites.Journal of Physical Chem- HARVEY, D.T. and LINTON, R.W. (1981) Chemical characterization of istry, 98, 13017-13021. hydrous ferric oxides by X-ray photoelectron spectroscopy. Ana- WILKINS,R.W.T. and ITO,J. (1967) Infrared spectra of some synthetic

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