**4. Results and discussion**

### **4.1. Synthesis of Na+-titanosilicate and H+-titanosilicate**

The X-ray powder diffraction pattern of air-dried Na+-titanosilicate, as shown in Fig. 1(a), exhibited several 00l reflections corresponding to a basal spacing of 1.08 nm. The peak positions of this synthetic sample agreed closely with previously reported values [3,5]. Slow titration of Na+-titanosilicate with 0.1 N HCl produced H+-titanosilicate by exchanging Na+ for H+ in interlayers. The X-ray powder diffraction pattern of air-dried H+-titanosilicate (Fig. 1(b)), exhibited 00l reflections corresponding to a basal spacing of 0.92 nm. This decrease in basal spacing relative to the Na+ form indicates a loss of interlayer H2O due to H+ for Na+ exchange. Also, the general broadening of diffraction peaks indicated that stacking disorder had occurred during this proton exchange. SEM morphologies of Na+-titanosilicate and H+ titanosilicate are shown in Fig. 2. Na+-titanosilicate particles were composed of plates, and H+-titanosilicate exhibited a similar morphology. The chemical compositions of Na+ titanosilicate and H+-titanosilicate were determined by TGA and EDS analysis. The TGA curve (Fig. 3(a)) indicated that air-dried Na+-titanosilicate lost 8.5 wt% of its total initial weight as water below 200 oC. An additional 1.5 wt% was lost between 200 and 1000 oC, which was assigned to the dehydration loss of surface bound -OH groups. The chemical compositions of Na+-titanosilicate and H+-titanosilicate are shown in Table 1. By combining Na2O, SiO2, TiO2 and weight loss, we obtained an empirical composition for synthetic Na+ titanosilicate of Na4Ti2Si8O22·4H2O, which compares well with those reported previously [3- 6]. H+-titanosilicate, as shown in Fig. 3(b), showed an initial weight loss of 7.5% below 250 oC due to H2O desorption, and a 6 wt% weight loss above 300 oC, which was attributed to the elimination of -OH groups from the structure. Based on water loss and the absence of sodium, we obtained an empirical unit cell composition of H4Ti2Si8O22·4H2O or H+ titanosilicate.

244 Ion Exchange Technologies

examine their thermal resistances.

**2.3. Silylation of H+-titanosilicate** 

OTES–TS, and then dried in the air at 50 oC.

**3. Characterization** 

**4. Results and discussion** 

The SPT derivatives so obtained were also then heated for 5 h at 600 or 700 oC in air to

DDA–OTES mixed solutions were prepared by dissolving OTES and DDA in ethanol (95%). The concentration of OTES in solution was between 0.01 and 0.1 M, and the DDA concentration was held constant at 0.1 M. H+-titanosilicate(DDA–OTES–TS) with intercalated OTES and DDA preparation H+-titanosilicate (0.321 g, 0.5 mmol) was then dispersed in 6 mL (0.01, 0.05, 0.1 M OTES 3 mL + 0.1 M DDA 3 mL) of these solutions (ultrasound, 20 min, at room temperature) and evaporated and dried for 24 h at 50 oC. OTES–TS was recovered by filtering, washed with ethanol until free of DDA using DDA–

X-ray diffraction data were recorded using a Bruker diffractometer using Cu K*a* radiation. The chemical compositions of Na+-titanosilicate and H+-titanosilicate were analyzed by energy dispersive spectroscopy (EDS; Link system AS1000-85S) and by thermo-gravimetric analysis (TGA; Dupont 9900 thermoanalyser, 10 oC/min to 900 oC, 100 ml/min N2 purge). Scanning electron micrograph (SEM) measurements were carried out using a JEOL JSM-840A SEM. Samples, were stuck onto adhesive tape, sputter coated with gold and morphological variations were examined. Transmission electron micrographs (TEM) were obtained with a JEOL JEM-200 CX transmission electron microscope operating at 200 kV, using a thin-section technique. Powdered samples were embedded in Epoxy resin and then sectioned with a diamond knife. Microtome sectioned samples were examined. Solid-state 29Si MAS NMR experiments were performed on a Bruker DSX-400 spectrometer (KBSI Daegu center, Korea) operating at 79.5 MHz. 29Si MAS NMR spectra were obtained using 30- 40o pulse width at a spinning rate of 6 kHz. Cross-polarization experiments were carried out with delay times of 3 s, 90o pulse of 5 s, and contact times of 2000 μs. The chemical compositions of Na+-titanosilicate and H+-titanosilicate were analyzed by energy-dispersive X-ray spectrometer (EDS, Link system AS1000–85S) and thermogravimetric analysis (TGA, 10 oC/min to 900 oC, 100 cm3/min N2 purge). The composition of the product was determined by CHN analysis (CHNS-932 (Leco)). The FT-IR spectrum was recorded on a Digilab FTS-40 FT-IR unit using the KBr disk method. Raman spectra were obtained using a Jobin Yvon/Horiba LabRAM spectrometer equipped with an integral microscope (Olympus BX

41). The 632.8 nm line of an air-cooled He/Ne laser was used as an excitation source.

The X-ray powder diffraction pattern of air-dried Na+-titanosilicate, as shown in Fig. 1(a), exhibited several 00l reflections corresponding to a basal spacing of 1.08 nm. The peak

**4.1. Synthesis of Na+-titanosilicate and H+-titanosilicate** 

**Figure 1.** X-ray diffraction patterns of (a) Na+-titanosilicate and (b) H+-titanosilicate.

**Figure 2.** SEM micrographs of (a) Na+-titanosilicate and (b) H+-titanosilicate.

**Figure 3.** TGA curves of (a) Na+- titanosilicate and (b) H+-titanosilicate.


a EDS data. HT = H+ -titanosilicate.

**Table 1.** Composition of Synthetic Na+-titanosilicate and H+-titanosilicate

#### **4.2. Silica-pillaring**

246 Ion Exchange Technologies

**Figure 2.** SEM micrographs of (a) Na+-titanosilicate and (b) H+-titanosilicate.

**Figure 3.** TGA curves of (a) Na+- titanosilicate and (b) H+-titanosilicate.

Mixtures of H+-titanosilicate, DDA and TEOS produced intercalation compounds in which DDA and TEOS were simultaneously intercalated into the interlayer regions. Intercalation compounds of the gel type were recovered by vacuum filtration, which allowed unreacted DDA and TEOS to be removed. The recovered gels were DDA/TEOS co-intercalated H+ titanosilicates. In these compounds, DDA molecules between layers are solvated by TEOS molecules, which results in an additional interlayer expansion. Addition of water to the gels caused the rapid hydrolysis of TEOS in interlayer spaces. This hydrolysis occurred rapidly (within 5 min) in pure water because of the catalytic effect of DDA, and resulted in the formation of siloxane-pillared H+-titanosilicates. The calcination of siloxane-pillared H+-titanosilicate derivatives for 5 h at 500 oC resulted in the formation of silica-pillared H+-titanosilicate (SPT) derivatives. Fig. 4 shows X-ray diffraction patterns of SPT derivatives prepared at H+-titanosilicate:DDA:TEOS reaction stoichiometries of 1:10:14 (SPT-1), 1:10:16 (SPT-2), 1:10:18 (SPT-3) and 1:10:20 (SPT-4). SPT derivatives exhibited refractions corresponding to a basal spacing of 4.16–4.32 nm, which depended on the molar ratio of DDA to TEOS (with the exception of SPT-1). These results indicate that the molar ratio of DDA to TEOS is an important factor for successful pillaring. If the DDA/TEOS ratio is too high, the interlayer space is maintained by template DDA, and gallery TEOS cannot form a pillar firm enough between layers. Accordingly, in this situation the removal of DDA by calcination can cause the disordered collapse of interlayer spaces, which results in severe peak broadening or peak disappearance, as observed in SPT-1. Since the H+-titanosilicate layer sheet thickness is 0.92 nm, the corresponding gallery heights are 3.24–3.40 nm, which are nearly double the chain length of DDA (1.65 nm). This implies that DDA molecules in the gallery are arranged as molecular assemblies as lamellar bilayers and that TEOS produce firm enough silicapillars to prop the expanded gallery after the removal of DDA. Moreover, gallery height was found to increase slightly as the molar ratio of TEOS was increased. This implies that pillar size and strength depends on the quantity of gallery TEOS. The basal spacings and gallery heights of SPT derivatives are summarized in Table 2.

**Figure 4.** X-ray diffraction patterns for calcined silica-pillared H+-titanosilicate prepared at H+ titanosilicate:DDA:TEOS reaction stoichiometries of: (a) 1:10:14 (SPT-1), (b) 1:10:16 (SPT-2), (c) 1:10:18 (SPT-3) and (d) 1:10:20 (SPT-4).


SPT = silica-pillared H+-titanosilicate; ( ) = gallery height; gallery height = basal spacing – 0.92 nm (thickness of H+ titanosilicate); HT = H+-titanosilicate.

**Table 2.** Basal spacing, gallery heights and surface area analyses (m2/g) for SPT products.

Fig. 5 also exhibits XRD peaks for SPT derivatives heated for 5 h at 600 or 700 °C in air. XRD peaks of SPT samples were well preserved after heat treating to 700 oC. Basal spacings and gallery heights are shown in Table 3. Basal spacing was also not altered by exposure to high temperatures. This indicates that control of DDA/TEOS ratio and the rapid hydrolysis of TEOS in water contribute to the formation of firm silica-pillars. Here, TEOS is not lost from interlayer spaces during hydrolysis, because of its waterinsolubility and rapid hydrolysis.

(SPT-3) and (d) 1:10:20 (SPT-4).

SPT-2 4.16

SPT-3 4.25

SPT-4 4.32

titanosilicate); HT = H+-titanosilicate.

and rapid hydrolysis.

**Figure 4.** X-ray diffraction patterns for calcined silica-pillared H+-titanosilicate prepared at H+ titanosilicate:DDA:TEOS reaction stoichiometries of: (a) 1:10:14 (SPT-1), (b) 1:10:16 (SPT-2), (c) 1:10:18

SPT-1 - 618 511 106 1.4

HT 0.92 5 - -

**Samples d-spacing(nm)** *S***BET** *S***mic** *S* **H-K pore size (nm)** 

SPT = silica-pillared H+-titanosilicate; ( ) = gallery height; gallery height = basal spacing – 0.92 nm (thickness of H+-

Fig. 5 also exhibits XRD peaks for SPT derivatives heated for 5 h at 600 or 700 °C in air. XRD peaks of SPT samples were well preserved after heat treating to 700 oC. Basal spacings and gallery heights are shown in Table 3. Basal spacing was also not altered by exposure to high temperatures. This indicates that control of DDA/TEOS ratio and the rapid hydrolysis of TEOS in water contribute to the formation of firm silica-pillars. Here, TEOS is not lost from interlayer spaces during hydrolysis, because of its waterinsolubility

**Table 2.** Basal spacing, gallery heights and surface area analyses (m2/g) for SPT products.

(3.24) 535 406 129 2.8

(3.33) 538 415 123 3.0

(3.40) 570 420 150 3.4

**Figure 5.** X-ray diffraction patterns of SPT derivatives heated for 5 h at 600 or 700 oC in air.

Typical SEM images of SPT are exhibited in Fig. 6. Most of the platelets in samples were unaffected by hydrolysis, though they swelled slightly more than H+-titanosilicate. The small particles observed around platelets were probably broken platelets and amorphous SiO2 caused by the hydrolysis of surface TEOS. The amount of platelet destruction was found to be related to the hydrolysis conditions used, e.g., reaction time pH of solution, and polarity of the solvent. However, this platelet destruction did not reflect SPT gallery structure destruction, probably because the gallery structure within broken platelet particles is preserved.

**Figure 6.** SEM micrographs of SPT derivatives: (a) SPT-1, (b) SPT-2, (c) SPT-3, and (d) SPT-4.

**Figure 7.** Nitrogen adsorption isotherms of SPT derivatives.

Fig. 7 illustrates typical N2 adsorption/desorption isotherms for SPT. All isotherms, except for SPT-1, showed a well-defined step indicative of framework-confined mesoporosity similar to MCM-41 related materials [39]. The nearly linear portions of the adsorption curves in the partial pressure region 0.03–0.35 are also indicative of small mesopores (~0.2–3.0 nm diameter) [40]. BET surface areas and microporous and non-microporous surface areas for SPT products are summarized in Table 3. Surface areas were obtained by fitting adsorption data below P/P0 = 0.1 to the BET equation [40]. H+-titanosilicate had a total surface area of 5.0 m2/g due to adsorption at non-porous external surfaces, but SPT products had dramatically larger total surface areas of between 535 and 618 m2/g, which depended on the DDA/TEOS molar ratio used. Furthermore, most this surface area was attributable to the presence of micropores of <2 nm in diameter.


*S*BET is the N2 BET surface area; *S*mic and *S* are the microporous and nonmicroporous surface areas, respectively, obtained from *t*-plots of the nitrogen adsorption data. H-K pore size = Horvath and Kawazoe pore size (obtained from nitrogen adsorption data). a,bdata heated at 600 oC and 700 oC, respectively.

**Table 3.** Basal spacing, gallery height and surface area analyses (m2/g) for SPT derivatives heated for 5 h at 600 oC and 700 oC.

**Figure 8.** Pore size distributions of SPT derivatives.

**Figure 7.** Nitrogen adsorption isotherms of SPT derivatives.

**Basal spacing (nm)**

4.07 (3.15)

4.14 (3.22)

4.22 (3.30)

*S*BET is the N2 BET surface area; *S*mic and *S* are the microporous and nonmicroporous surface areas, respectively, obtained from *t*-plots of the nitrogen adsorption data. H-K pore size = Horvath and Kawazoe pore size (obtained from

**Table 3.** Basal spacing, gallery height and surface area analyses (m2/g) for SPT derivatives heated for 5

micropores of <2 nm in diameter.

SPT-2 4.14

SPT-3 4.23

SPT-4 4.28

h at 600 oC and 700 oC.

SPT-1 - -

(3.22)

(3.31)

(3.36)

nitrogen adsorption data). a,bdata heated at 600 oC and 700 oC, respectively.

**Samples** 

Fig. 7 illustrates typical N2 adsorption/desorption isotherms for SPT. All isotherms, except for SPT-1, showed a well-defined step indicative of framework-confined mesoporosity similar to MCM-41 related materials [39]. The nearly linear portions of the adsorption curves in the partial pressure region 0.03–0.35 are also indicative of small mesopores (~0.2–3.0 nm diameter) [40]. BET surface areas and microporous and non-microporous surface areas for SPT products are summarized in Table 3. Surface areas were obtained by fitting adsorption data below P/P0 = 0.1 to the BET equation [40]. H+-titanosilicate had a total surface area of 5.0 m2/g due to adsorption at non-porous external surfaces, but SPT products had dramatically larger total surface areas of between 535 and 618 m2/g, which depended on the DDA/TEOS molar ratio used. Furthermore, most this surface area was attributable to the presence of

*S***BET** *S***mic** *S*

429a 394b 122a 111b

**(nm) 600 oC 700 oC** 

551a 505b

**H-K pore size** 

> 3.2a 3.0b

Horvath and Kawazoe analysis [41] of the N2 adsorption data (Fig. 8), yielded pore sizes of 2.8– 3.4 nm, which is similar to the gallery height (3.24–3.40 nm). This indicates that DDA plays an important structure-directing role during silica-pillaring. Furthermore, pore size distributions depended to some extent on DDA/TEOS molar ratio, which reflects differences in DDA molecular assemblies in the interlayer space caused by changing DDA/TEOS molar ratios.

**Figure 9.** Pore size distributions and nitrogen adsorption isotherms of SPT-4 heated at (a) 600 oC or (b) 700 oC.

Fig. 9 shows typical isotherm and pore size distributions for SPT-4 heat treated at 600 or 700 oC. Surface areas and pore sizes are also shown in Table 3. Heat treatment hardly affected the pore size distribution and surface area of SPT-4, demonstrating the thermally stability of SPT derivatives.

**Figure 10.** Schematic for the preparation of mesoporous silica-pillared H+-titanosilicate.

Fig. 10 presents a schematic representation of mesoporous silica-pillared layered titanosilicate.

The XRD patterns of DDA–OTES–TS treated with 0.01, 0.05, 0.1 M OTES-0.1 M DDA-ethanol solution are shown in Fig. 11. Treatment of H+-titanosilicate with the OTES–DDA mixed solution ensured successful silylation by OTES. Dried OTES–DDA–TS powder consists of H+-titanosilicate with intercalated OTES and DDA. In the gallery, DDA changes into dodecylammonium cations [CH3(CH2)11NH3+] as a result of the interaction with acidic silanol groups. Here, condensation between adjacent layers can not occur because of the large expansion of the interlayer space, with basal spacing between ~3.87 nm (Fig. 11(b-d)) by DDA. However, increasing concentrations of OTES broaden the reflections and decrease the basal spacing because of the high degree of grafting that reduces the amount of intercalated DDA. The XRD patterns of DDA–OTES–TS after washing with ethanol to remove the DDA showed that an increasing concentration of OTES broadened the reflections and decreased the basal spacing, because a high degree of grafting reduces the amount of intercalated OTES (Fig. 11(e-g)). The interlayer space had a basal spacing of ~2.95 nm (Fig. 11(e-g)). This small increase in basal spacing indicates that OTES molecules arrange with paraffin-type in the gallery.

titanosilicate.

with paraffin-type in the gallery.

**Figure 10.** Schematic for the preparation of mesoporous silica-pillared H+-titanosilicate.

Fig. 10 presents a schematic representation of mesoporous silica-pillared layered

The XRD patterns of DDA–OTES–TS treated with 0.01, 0.05, 0.1 M OTES-0.1 M DDA-ethanol solution are shown in Fig. 11. Treatment of H+-titanosilicate with the OTES–DDA mixed solution ensured successful silylation by OTES. Dried OTES–DDA–TS powder consists of H+-titanosilicate with intercalated OTES and DDA. In the gallery, DDA changes into dodecylammonium cations [CH3(CH2)11NH3+] as a result of the interaction with acidic silanol groups. Here, condensation between adjacent layers can not occur because of the large expansion of the interlayer space, with basal spacing between ~3.87 nm (Fig. 11(b-d)) by DDA. However, increasing concentrations of OTES broaden the reflections and decrease the basal spacing because of the high degree of grafting that reduces the amount of intercalated DDA. The XRD patterns of DDA–OTES–TS after washing with ethanol to remove the DDA showed that an increasing concentration of OTES broadened the reflections and decreased the basal spacing, because a high degree of grafting reduces the amount of intercalated OTES (Fig. 11(e-g)). The interlayer space had a basal spacing of ~2.95 nm (Fig. 11(e-g)). This small increase in basal spacing indicates that OTES molecules arrange

OTES–TS, (c) 0.1 M DDA-0.05 M OTES–TS, (d) 0.1 M DDA-0.1 M OTES–TS, (e) 0.01 M OTES–TS, (f) 0.05 M OTES–TS and (g) 0.1 M OTES–TS.

**Figure 11.** XRD patterns of (a) as-prepared H+-titanosilicate, (b) 0.1 M DDA-0.01 M

The FT-IR spectrum of H+-titanosilicate and OTES–TS is shown in Fig. 12. The band at 1469 cm-1 has been assigned to the asymmetric –CH3 deformation of –Si–CH3 [42,43], while the 2852, 2922 and 2960 cm-1 bands corresponded to –CH2CH3. The –OH stretching band is seen at 3208 cm-1 in –OH form and the H2O bending vibration is seen at 1619 and 1645 cm cm-1. In the OTES–TS spectrum, the absorption band from the Si–O–Si type of motion overlaps with strong Si–O–Ti absorption bands at 586 and 866 cm-1. However, additional bands were observed at 631, 699, 776, 909, 1054, 1149 cm-1 in the OTES–TS spectra. These bands were also observed in the spectrum of titanosilicate [44–47] and probably arose from Ti–O–Si linkages formed by silylation. The bonding of the alkylsilyl groups with the silicate layers was revealed by the Raman spectra (Fig. 13). Titanosilicate is composed of –(Si–O)4–Ti–O– units with their Si-O-Si environments observed at around 600 cm-1, Ti–O–Si: 960 cm-1 and – OH: 970, 1100, 3600 cm-1 [48–51]. The reaction products exhibit Raman bands at 223, 328, 385, 429, 477, 600, 920, 1029, 1078 and 1301 cm-1, respectively. The spectra also showed a substantial increase in the relative intensity of Ti–O–Si signals due to the increase in formed Ti–O–Si units by the silylation of interlayer Ti–OH groups.

**Figure 12.** FT-IR spectra of (a) as-prepared H+-titanosilicate, (b) 0.01 M OTES–TS, (c) 0.05 M OTES–TS and (d) 0.1 M OTES–TS.

TGA data from DDA–OTES–TS and insert of OTES–TS treated in N2 at a heating rate of 10 oC/min are shown in Fig. 14. The weight loss of DDA–OTES–TS in the temperature range from 100 to 250 oC was ~23.0 wt.% and was probably caused by water and DDA contained between the interlayers. A weight loss of ~25 wt.% was recorded between 250 and 650 oC, because the TS surface organic chains group was thermally cracked in this temperature range (Fig. 14). These values represent the loadings of organic functions on OTES–TS and are in agreement with the C, H, N contents of 9.4–20.6 wt.% obtained by chemical analysis. The composition of the products determined by the C, H, N analysis is summarized in Table 1. The C, H, N content in OTES–TS increased with increasing OTES concentration. The C content in DDA–OTES–TS decreased with increasing OTES concentration because DDA adsorption decreases at higher OTES content. The almost constant N content indicates that the sum of OTES and DDA remain nearly independent from the degree of silylation.

and (d) 0.1 M OTES–TS.

from the degree of silylation.

**Figure 12.** FT-IR spectra of (a) as-prepared H+-titanosilicate, (b) 0.01 M OTES–TS, (c) 0.05 M OTES–TS

TGA data from DDA–OTES–TS and insert of OTES–TS treated in N2 at a heating rate of 10 oC/min are shown in Fig. 14. The weight loss of DDA–OTES–TS in the temperature range from 100 to 250 oC was ~23.0 wt.% and was probably caused by water and DDA contained between the interlayers. A weight loss of ~25 wt.% was recorded between 250 and 650 oC, because the TS surface organic chains group was thermally cracked in this temperature range (Fig. 14). These values represent the loadings of organic functions on OTES–TS and are in agreement with the C, H, N contents of 9.4–20.6 wt.% obtained by chemical analysis. The composition of the products determined by the C, H, N analysis is summarized in Table 1. The C, H, N content in OTES–TS increased with increasing OTES concentration. The C content in DDA–OTES–TS decreased with increasing OTES concentration because DDA adsorption decreases at higher OTES content. The almost constant N content indicates that the sum of OTES and DDA remain nearly independent

**Figure 13.** Raman spectra of (a) as-prepared H+-titanosilicate, (b) OTES, (c) 0.01 M OTES–TS, (d) 0.05 M OTES–TS and (e) 0.1 M OTES–TS.

**Figure 14.** TGA of (a) 0.1 M DDA-0.01 M OTES–TS, (b) 0.1 M DDA-0.05 M OTES–TS, (c) 0.1 M DDA-0.1 M OTES–TS, (d) 0.01 M OTES–TS, (e) 0.05 M OTES–TS, (f) 0.1 M OTES–TS.


1) Evaluated by CHN analysis

2) Evaluated by CHN calculation (Contains CHN of 0.1M DDA, 0.01, 0.05, 0,1M-OTES)

3) Washed with EtOH

**Table 4.** Chemical composition of silylated titanosilicate.

The solid-state 29Si MAS NMR spectra for silylated H+-titanosilicate show Q3 (-105.7 ppm), Q4 (-110 to -112 ppm), and T2 (-50 to -60 ppm) signals with diverse environments of silicon (Fig. 15). The increase of the Q3/Q4 ratio compared with H+-titanosilicate clearly indicates the grafting of OTES molecules to the surface silanol groups. The new peaks (T2) near -59.5 ppm, in 0.1 M OTES–TS were attributed to the Si atoms of the grafted OTES molecules. In general, Si atoms of the silicate network exhibited signals (Q3 and Q4) in the range of -102 and -112 ppm, whereas Si atoms in the silylating agent grafted to the surface showed signals (T2) at -50 to -60 ppm. Caravajal et al. [52], Impens et al. [53], Lin et al. [43] and D'Amore and Schwarz [54] all reported the mechanism and solid NMR data for the silylation of amorphous silica, alumina and Ti-MCM-41 with alcoxysilane. The Si signals for OTES silylated on silica was in the range of -49 to -68 ppm, depending upon the bonding type. Caravajal et al. [55] and Shimojima et al.[30] also showed that Si signals for alkyltrichlorosilane grafted on kanemite appeared between -56 and -65 ppm. The signals from 0.5 M DDA-0.1 M OTES–TS were similar to signals of kanemite silylated by alkyltrichlorosilane. The TEM image (Fig. 16) explains the reason why OTES–TS samples, in spite of partial destruction of platelets in the outer appearance in the SEM, exhibit uniform distance distributions and ordered basal spacing. The crosssection of an OTES–TS platelet shows several silicate sheets with uniform spacing of ~2.95 nm. A hypothetical diagram for the silylation by OTES and the intercalation of DDA during the evaporation of the solvent is shown in Fig. 17. The evaporation of ethanol starts at the outside of the particles, resulting in a higher concentration of DDA and OTES on the external surface and subsequently promoting the intercalation of OTES and DDA (Fig. 17(b and c)). The evaporation of residual ethanol in the gallery results in the silylation of OTES (Fig. 17d). The water molecules contained in ethanol catalyze the interlayer surface silylation of OTES during the evaporation of ethanol. The condensation of alkoxysilane is known to be catalyzed by bases. DDA as a gallery expander can also play a role as catalyst for the grafting of OTES into the surface silanol groups.

**Figure 15.** 29Si MAS NMR spectra of (a) as-prepared H+-titanosilicate, (b) 0.01 M OTES– TS, (c) 0.05 M OTES–TS and (d) 0.1 M OTES–TS.

**Figure 16.** Transmission electron micrographs for OTES–TS.

**Composition Weight Percent** 

**C 1) H 1) N 1) CHN 2) SiO2, TiO2 (%)** 

20.1 25.2 29.0 1.4 7.1 14.2

77.9 71.73 70.48 87.16 81.03 74.32

**Silylated-TS** 

0.01 M OTES 3) 0.05 M OTES 3) 0.10 M OTES 3)

3) Washed with EtOH

1) Evaluated by CHN analysis

surface silanol groups.

0.10 M DDA-0.01 M OTES 0.10 M DDA-0.05 M OTES 0.10 M DDA-0.10 M OTES 16.80 22.08 23.05 9.38 14.53 20.60

2) Evaluated by CHN calculation (Contains CHN of 0.1M DDA, 0.01, 0.05, 0,1M-OTES)

**Table 4.** Chemical composition of silylated titanosilicate.

3.55 4.27 4.80 2.65 3.45 4.00

The solid-state 29Si MAS NMR spectra for silylated H+-titanosilicate show Q3 (-105.7 ppm), Q4 (-110 to -112 ppm), and T2 (-50 to -60 ppm) signals with diverse environments of silicon (Fig. 15). The increase of the Q3/Q4 ratio compared with H+-titanosilicate clearly indicates the grafting of OTES molecules to the surface silanol groups. The new peaks (T2) near -59.5 ppm, in 0.1 M OTES–TS were attributed to the Si atoms of the grafted OTES molecules. In general, Si atoms of the silicate network exhibited signals (Q3 and Q4) in the range of -102 and -112 ppm, whereas Si atoms in the silylating agent grafted to the surface showed signals (T2) at -50 to -60 ppm. Caravajal et al. [52], Impens et al. [53], Lin et al. [43] and D'Amore and Schwarz [54] all reported the mechanism and solid NMR data for the silylation of amorphous silica, alumina and Ti-MCM-41 with alcoxysilane. The Si signals for OTES silylated on silica was in the range of -49 to -68 ppm, depending upon the bonding type. Caravajal et al. [55] and Shimojima et al.[30] also showed that Si signals for alkyltrichlorosilane grafted on kanemite appeared between -56 and -65 ppm. The signals from 0.5 M DDA-0.1 M OTES–TS were similar to signals of kanemite silylated by alkyltrichlorosilane. The TEM image (Fig. 16) explains the reason why OTES–TS samples, in spite of partial destruction of platelets in the outer appearance in the SEM, exhibit uniform distance distributions and ordered basal spacing. The crosssection of an OTES–TS platelet shows several silicate sheets with uniform spacing of ~2.95 nm. A hypothetical diagram for the silylation by OTES and the intercalation of DDA during the evaporation of the solvent is shown in Fig. 17. The evaporation of ethanol starts at the outside of the particles, resulting in a higher concentration of DDA and OTES on the external surface and subsequently promoting the intercalation of OTES and DDA (Fig. 17(b and c)). The evaporation of residual ethanol in the gallery results in the silylation of OTES (Fig. 17d). The water molecules contained in ethanol catalyze the interlayer surface silylation of OTES during the evaporation of ethanol. The condensation of alkoxysilane is known to be catalyzed by bases. DDA as a gallery expander can also play a role as catalyst for the grafting of OTES into the

1.75 1.92 1.67 0.81 0.99 1.08

> The narrow pore size distributions (~0.7 nm peak width at half peak maximum) of SPT derivatives are similar to those of the related MCM-41 (~0.5 nm peak width), which is produced using a surfactant template [39]. This indicates that DDA molecules play a decisive role in pore formation in SPT derivatives, and that they form molecular assemblies similar to those formed by surfactant micelles. An optimal DDA/TEOS molar ratio in interlayer regions could afford near ideal conditions for the formation of micellar neutral amine assemblies, and such conditions favor the DDA-templated hydrolysis of TEOS. Tanev and Pinnavaia [56]

demonstrated that the assembly of hexagonal mesoporous metal oxides can also be achieved by hydrogen bonding between neutral amine and TEOS. In porous materials formed by this gallery-templated reaction, specific surface areas are composed of the surfaces of micropores, where pore walls act as pillars and mesopores. Therefore, the lateral spacing between pillars in conventional pillared layered materials is not the sole contributor to increased microporosity.

**Figure 17.** Schematic representation of the intercalation and silylation of DDA and OTES for H+ titanosilicate.

SPT derivatives exhibit a broad pore size distribution as compared with MCM-41. Furthermore, they offer new opportunities for the rational design of heterogeneous catalyst systems because of their complementary chemical functionality, thermal stability, and stable pore size distribution to the small mesopore range (1.0–2.0 nm). In addition, the existence of five-coordinated titanium(V) in the interlayer surfaces of SPT derivatives makes then promising potential oxidation catalysts.
