J O U R N A L O F C H E M I S T R Y Materials Solvothermal synthesis and characterization of silica-pillared titanium phosphate Xiuling Jiao,a Dairong Chen,bWenqin Pang,a* Ruren Xua and Yong Yuec aDepartment of Chemistry, Jilin University, Changchun 130023, PR China bDepartment of Chemistry, Shandong University, Jinan 250100, PR China cWuhan Institute of Physics, The Chinese Academy of Science, Wuhan 430071, PR China Received 15th April 1998, Accepted 4th August 1998 Silica-pillared titanium phosphate has been synthesized from Ti(OC4H9)4–H3PO4– H2N(CH2)3Si(OC2H5)3–C2H5OH and characterized by XRD, SEM, IR and TGA.The synthesis conditions were investigated and the optimal conditions are reported: crystallization at 180 °C for about 7 days with a batch composition of 1.0 Ti(OC4H9)453.6 H3PO451.0 H2N(CH2)3Si(OC2H5)3533 C2H5OH.XRD analysis gives the lattice parameters of the monoclinic cell as a=1.99952 nm, b=0.41803 nm, c=0.90062 nm, b=97.462°, V= 0.74642 nm3, and Z=2. N2 adsorption–desorption test shows that the pillared compound has a BET surface area of 51 m2 g-1. 2. Characterization Introduction XRD patterns of the products were recorded with a Rigaku Pillaring of layered compounds such as clay minerals, oxides D/MAX-III diVractometer using Cu-Ka radiation (l= and phosphates has been extensively studied for the last 0.15418 nm) at room temperature over the range 3–60°.decade.1–5 Since the first preparative studies by Clearfield Infrared spectra were measured on a Nicolet 5DX FT-IR et al.6 and Alberti et al.7 of a-ZrP, many works have focused instrument using the KBr pellet technique. 13C, 29Si, 31P MAS on the syntheses and characterization of pillared layered NMR spectra were recorded on a Bruker MSL-400 spec- metal(IV) phosphates,8,9 and a review discussed the preptrometer. Inductive coupled plasma analyses (ICP) for the Ti, aration, characterization and properties of pillared layered P, Si contents in the product were obtained from a Leeman metal(IV) phosphates.10 Generally, the pillared compounds are ICP-AES instrument, and elemental analyses for C, H, N prepared by ion exchange of polynuclear species or by the contents were done on a Perkin-Elmer 240C elemental ana- hydrolysis of organometallic precursors, such as lyzer.Thermogravimetric analyses (TGA) were performed on [Al13O4(OH)24(H2O)12]7+, RxSi(OR¾)4-x etc., using the a Perkin-Elmer TGA7 with increasing temperature rate of sol–gel method; several pillared metal phosphates such as 10 °Cmin-1.Water adsorption measurements were carried out silica-pillared a-ZrP,11 silica-pillared a-SnP,12 Al-pillared aon a Cahn 2000 vacuum electron balance at room temperature, ZrP13 etc.14,15 have been obtained.However, intercalation of while N2 adsorption–desorption and BET surface area on the large cations into the interlayer space often results in a low calcined sample (77 K) were measured on an ASAP 2010 yield and low crystallinity of the pillared compounds. For micromeritics apparatus. example, well crystallized silica-pillared titanium phosphate can not be obtained by this method.11,12 Here, we report a new route for the synthesis of well Results and discussion crystallized silica-pillared layered titanium phosphate.The 1. Synthesis pillared compound is hydrothermally synthesized in Ti(OC4H9)4–H3PO4–H2N(CH2)3Si(OC2H5)3–C2H5OH, and The crystalline pillared compound was synthesized from the the product obtained by this method has a high crystallinity.batch composition 1.0 TBOT5(2.0–5.0) H3PO451.0 APTEOS533 EA at 140–240 °C for several days. Hydrolysis may occur in the mixed gel as follows: Experimental H2N(CH2)3Si(OEt)3+nH2O 1. Synthesis �H2N(CH2)3Si(OEt)3-n(OH)n+nEtOH (n3) (1) All the reagents were of analytical grade and were not further The hydrolysized APTEOS then polymerizes continuously. To purified before utilization.adjust the rate of hydrolysis and polymerization, ethanol Tetrabutyltitanate (analytical reagent, TBOT), phosphoric (99.7%) was used as the solvent. The title compound could acid (analytical reagent, 85 wt.%) and 3-aminopropyltriethoxy- not be obtained with ethanol (95%) or water as solvent. silane (APTEOS, Aldrich) were used as titanium, phosphorus Further experiments indicated that the crystallization reaction and silica sources.To adjust the hydrolysis and polymerization accelerated upon increasing the H3PO4 content in gel mixture, rate of APTEOS in the hydrothermal process, ethanol (EA, and an unknown phase formed when the reaction time was analytical reagent, 99.7%) was selected as the solvent. In a prolonged to 15 days. Crystallization at 180 °C for about 7 typical synthesis, phosphoric acid was added to a homo- days with the batch composition of 1.0TBOT53.6 H3PO451.0 geneously mixed solution of TBOT and EA under stirring.APTEOS533 EA was optimal. APTEOS was added dropwise to this mixture and a white gel formed. The gel was placed into a Teflon-lined stainless steel 2. Characterization autoclave and heated to 140–240 °C for about 7 days.It was then cooled to room temperature and the product was reco- Fig. 1 shows the SEM of the as-prepared crystals. The crystals are homogeneous with sheet-like morphology indicating that vered by filtration, thoroughly washed with deionized water, and dried at room temperature. the solid is phase pure. The average particle size is about 2 mm. J. Mater. Chem., 1998, 8, 2831–2834 2831Table 1 X-Ray powder diVraction data and indexing results of silicapillared layered titanium phosphate h k l dobs/A° dcal/A° 2hobs/ ° 2hcalc/ ° 1 0 0 19.87 19.83 4.443 4.453 2 0 0 9.94 9.91 8.889 8.913 3 0 0 6.60 6.61 13.405 13.387 2 0 1 6.25 6.24 14.159 14.173 3 0 1 5.71 5.67 15.506 15.599 4 0 0 4.95 4.96 17.905 17.881 1 0 2 4.50 4.48 19.713 19.791 0 1 0 4.20 4.18 21.136 21.237 1 1 0 4.07 4.09 21.820 21.709 5 0 0 3.97 3.97 22.376 22.404 0 1 1 3.79 3.79 23.454 23.479 3 1 0 3.53 3.53 25.208 25.188 5 0 2 3.17 3.18 28.127 28.066 4 0 2 3.12 3.12 28.587 28.569 2 0 3 2.96 2.96 30.168 30.182 2 1 2 2.85 2.85 31.362 31.403 3 1 2 2.68 2.68 33.408 33.390 5 1 2 2.53 2.53 35.352 35.463 Fig. 1 Scanning electron micrograph of as-synthesized powder. 8 0 1 2.47 2.47 36.343 36.310 Fig. 2 gives the XRD pattern of the title compound. The product recovered is of high crystallinity. It can be seen from V=0.74642 nm3. From the unit cell parameters and the PMO Fig. 2 that the XRD pattern of the as-prepared product is and TiMO bond lengths and the structure of layered titanium similar to that of the c-phase structure,14,16 although the peak phosphate, the result of Z=2 can be obtained.positions and intensities are diVerent. Because of the replace- Further experiments shows that no significant change of the ment of H3O+ in the interlayer space of c-TiP by interlayer spacing is observed when the calcination temperature NH3+(CH2)3(O)SiOSi(O)(CH2)3NH3+ in the title compound, is lower than 300 °C, and the significant change of the basal the basal spacing of the as-prepared product is much larger spacing takes place between 300 and 500 °C, decreasing from than that of c-TiP.This replacement further leads to a change 1.93 nm to 1.42 nm. Upon increasing the calcination temperaof b value and an increase of the unit cell volume. The ture, the basal spacing decreases to 1.40 nm. The pillared similarity of the layer structures of c-TiP and the title com- compound is stable up to 700 °C (Fig. 3). pound can also be seen from the XRD patterns, although the The 13C MAS NMR spectrum (Fig. 4) exhibits three peaks basal space reflections are diVerent. We therefore assume that at 42.96, 20.99, and 10.21 ppm, which are attributed to Ca, Cb the layer structure of the as-synthesized product is similar to and Cc in H3N+CaH2CbH2CcH2Si, respectively,17 which indithat of c-TiP.The diVerence between the XRD patterns can cates that EA and other organic materials do not exist in the be attributed to the influence of the silica pillar to the product. The disappearance of these resonances after calciphosphate layer, and even to the lattice structure of the cryst. nation at 600 °C reveals that the organic material is lost The X-ray powder diVraction data were indexed with the at 600 °C.TREOR program (Table 1). The cell is monoclinic with a= 1.99952 nm, b=0.41803 nm, c=0.90062 nm, b=97.462° and Fig. 3 XRD patterns of as-prepared samples (a), and of samples Fig. 2 XRD pattern of the title compound. calcined at 200 (b), 300 (c), 400 (d), 500 (e), 600 (f ), 700 °C (g). 2832 J. Mater. Chem., 1998, 8, 2831–2834Fig. 4 13C MAS NMR spectrum of as-prepared product (from TMS). 29Si CP MAS NMR spectra (Fig. 5) for as-synthesized and calcined products have two resonances at -66.80 and -103.85 ppm, which are assigned to the silicon atoms as shown in Fig. 6.18 This result confirms that APTEOS is thoroughly hydrolyzed and polymerized. 31P MAS NMR spectra (Fig. 7) of the powder give two Fig. 7 31P MAS NMR spectra of as-prepared (a) and calcined (b) resonances at -12.95, -25.22 ppm with an intensity ratio of samples (from H3PO4). about 152, which shift to -14.14 and -29.45 ppm after calcination at 500 °C for 3 h with a peak area ratio of 151. The 31P MAS NMR spectrum of intercalated a-phase structure metal(IV) phosphates either have a single resonance or have several similar shifts,1,10,12,13,19 although there are two crystallographically inequivalent P sites in the structure, and only after thermal treatment are two 31P shifts obtained.1 Thus from the two 31P resonances of the as-prepared compound and the shape of the shifts, these peaks should be assigned to two diVerent phosphorus atoms—P(OTi)2(OH)2 and P(OTi)4.20 This indicates that the structure of the phosphate layer is similar to that of c-TiP, which also has these two diVerent phosphorus atoms.After calcination, the two resonances shift to -14.14 and -29.45 ppm and the area ratio changes to about 151, these resonances can be attributed to P(OTi)2(OH) (OSi) and P(OTi)4. The replacement of OH with OSi causes the resonances to shift from -12.95 and -25.22 ppm to -14.14 and -29.45 ppm, and the area ratio of these resonances for the calcined sample is consistent with the P/Si ratio in the product, i.e.only half of the P are linked Fig. 5 29Si CP MAS NMR spectra for as-prepared (a) and calcined to OSi—the molar ratio of P(OTi)2(OH)(OSi) to P(OTi)4 (b) product (from TMS). is 151. Fig. 8 shows the IR spectra of as-synthesized samples and those heated to 200, 300, 400, 500, 600, 700 °C, respectively.The bands for the as-synthesized sample are assigned as follows: 3479, hydrogen bound OH; 3261, NH3+ stretching; 2917, CH2 stretching; 1623, NH3+ asymmetric deformation H2O bending; 1525, NH3+; 1475, CH2 bending; 1398, PMO, 1215, CMCMCMN; 1152, PMO; 1004, PMO; 962, SiMOMSi; 798, NH3+ in-plane rocking; 701, NH3+ out-of-plane deformation; 646, TiMO, 549, 512, 470, TiMO.No significant changes of the spectra were observed below 300 °C except for the shift of the bands around 1000–900 cm-1, indicating the distortion of the structure. Significant changes of the spectra above 300 °C result from the decomposition and loss of organic materials. The weight loss from room temperature to 300 °C (about 3%, Fig. 9) is assigned to the loss of water in the interlayer space, while that from 300–600 °C (about 19%) is attributed Fig. 6 Schematic representation of the product. to the loss of the organic material. The weight loss between J. Mater. Chem., 1998, 8, 2831–2834 2833644 and 732 °C is attributed to the loss of water from the silanol groups. N2 adsorption–desorption tests indicate a BET surface area of ca.51 m2 g-1 and the amount of N2 adsorption is small.From the basal spacing of the calcined sample, the interlayer space is about 7 A° , which is large enough to adsorb the N2 molecules. The interlayer region is occupied by the silica pillar for each P(OTi)2(OH)2 is connected to one silica pillar, which prevents the N2 molecules from entering.The results further indicate that there are no mesopores in the calcined product, as there is little hysteresis on the N2 adsorption–desorption curve when P/P0 is higher than 0.5, which shows that the pillared phosphate is a cross-linked compound rather than a porous one. However, adsorption of water shows that the pillared compound (600 °C, 0.5 h) has the capacity to adsorb small polar molecules.The uptake of water at P/P0=0.3 is as high as about 10% by weight. Fig. 10 shows the water adsorption isotherm of the sample. We thank the National Natural Scientific Foundation and the Key Laboratory of Synthesis and Preparative Chemistry, Jilin University for financial support. References 1 L. Li, X. Liu, Y. Ge, L. Li and J. Klinowski, J. Phys. 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