FULL PAPER

DOI: 10.1002/ejic.200900915

Exfoliated Titanosilicate Material UZAR-S1 Obtained from JDF-L1

César Rubio,[a] Clara Casado,[a] Patricia Gorgojo,[a] Fernando Etayo,[a] Santiago Uriel,[b]

Carlos Téllez,[a] and Joaquín Coronas*[a]

Keywords: Intercalations / Layered compounds / Membranes / Organic–inorganic hybrid composites / Zeolite analogues

A new material, UZAR-S1, has been obtained by exfoliationof the layered precursor microporous titanosilicate JDF-L1.The exfoliation consists of a first stage of proton exchangewith histidine followed by intercalation with nonylamine andfinal extraction in HCl/water/ethanol solution. UZAR-S1 isan exfoliated material composed of sheets of a few nanome-

IntroductionExfoliated materials obtained from layered silicates and

zeolites, due to the fine particles produced (with high aspectratios and with a theoretical thickness as low as that of asingle layer), are useful for catalysis,[1,2] enhancing thepermselectivity of polymer–zeolite nanocomposite mem-branes,[3] the immobilization of enzymes,[4] and producingpolymer-layered silicate nanocomposites with improvedtensile properties.[5]

JDF-L1 refers to a microporous titanosilicate with theempirical formula Na4Ti2Si8O22·4H2O. JDF-L1 containsTiO5 square pyramids in which each oxygen atom at thebase is linked to SiO4 tetrahedra to form continuoussheets.[6] The layers (see Figure S1 in the Supporting Infor-mation) have five-membered rings running parallel to them([100] or [010] equivalent directions) consisting of four SiO4

tetrahedra and one TiO5 pyramid. The layers also contain,running along the [001] direction, six-membered rings com-posed of two square pyramids and two pairs of tetrahedra.One Na atom coordinated with two water molecules isplaced inside such a ring. JDF-L1 possesses the same struc-ture as the AM-1[7] and NTS[8] materials (in fact, all ofthem were prepared on the same Na2O-TiO2-SiO2 basis)and can be considered to be a member of the microporousOPT (octahedral–pentahedral–tetrahedral) family of frame-work silicates.[9]

The exfoliation of this material has not been reportedto date; therefore, we present in this paper the synthesis,

[a] Chemical and Environmental Engineering Department andNanoscience Institute of Aragon, Universidad de Zaragoza,María de Luna 3, 50018 Zaragoza, SpainFax: +34-976-76-1871E-mail: coronas@unizar.es

[b] Organic Chemistry Department, Universidad de Zaragoza,María de Luna 3, 50018 Zaragoza, SpainSupporting information for this article is available on theWWW under http://dx.doi.org/10.1002/ejic.200900915.

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ters of thickness with a high aspect ratio, a BET specific sur-face area of 160 m2/g (JDF-L1 scarcely adsorbs N2), and a Si/Ti atomic ratio below 6. The dispersion of this material incommercial polysulfone results in an improved H2-selectivemixed matrix membrane.

characterization, and mixed-matrix membrane applicationof a new exfoliated titanosilicate obtained from the exfolia-tion of JDF-L1.

Results and Discussion

The lamellar precursor JDF-L1 was synthesized by aseeded secondary growth procedure previously estab-lished.[10] Reaction (a) in Scheme 1 represents the expectedexchange reaction between Na+ cations in JDF-L1 and pro-tonated nonylamine molecules. To favor the intercalationof nonylamine molecules, a proton exchange procedure wasinitiated at pH = 6.0 by using histidine amino acid.

Scheme 1. (a) Ion exchange reaction between the solid JDF-L1 andnonylamine, (b) ion exchange reaction between the solid and histi-dine (i.e. protonation), (c) acid–base equilibrium for nonylamine,and (d) dissociation equilibria for histidine (HA being the zwitter-ion).

After 10 min of reaction with histidine, the pH, initiallyat 6.0, slightly increased to about 6.1, as some protons fromthe solution were exchanged by Na+ cations (reaction b in

J. Coronas et al.FULL PAPERScheme 1). The necessary amount of nonylamine was thenadded to the solution. When the reaction with histidinecontinued for about 30 min, steady state was quicklyreached for the proton exchange reaction in terms of pH(6.15–6.20). This situation led to proton-exchanged JDF-L1 (H-JDF-L1). The H-JDF-L1 whose XRD pattern isshown in Figure 1 was obtained after 120 min of proton-ation with histidine. All the XRD reflections in the startingmaterial are present in H-JDF-L1 even though smallchanges in the baseline are evident. This is the reason whysurfactant molecules for swelling were added at a pH rela-tively far from the final value. In agreement with the ideathat the proton exchange process itself may produce struc-tural changes, it has been reported that layered silicateAMH-3 became XRD-amorphous upon proton exchangewith histidine,[11] whereas the crystallinity of JDF-L1 wasseriously affected in 0.1 HCl.[12] The layered characteris-tics of swollen JDF-L1 are revealed in Figure 1 by a seriesof new peaks at 2θ = 2.94°, 5.91°, and 8.89° with index-ations of (001), (002), and (003), respectively. Figure S2 alsoshows the first two reflections as revealed by low-angleXRD analysis. The separation between the layers of swollenJDF-L1 was estimated for 6 samples in 29.6�1.4 Å.

Figure 1. XRD patterns of JDF-L1 and its derivatives. The simu-lated pattern was obtained by using data from Roberts et al.[6].

After adding the amine to the solution with the aminoacid and the JDF-L1, the pH suddenly increased to 8.9 andthen to only 9.0 after 12 h of swelling reaction. At pH =9.0, [BH+]/[B] equals 44 (equation c in Scheme 1), and non-ylamine is present in the swelling solution basically in itsprotonated form, favoring the exchange process. In anyevent, the intercalation of neutral nonylamine moleculesshould not be disregarded. The working pH is close to thepKa3 of the amino acid (9.2), which might be attributed toits buffering action (see reactions d in Scheme 1). It is worthmentioning that, by keeping the same amine concentration,swelling was produced without protonation to a lesser ex-tent in terms of decreasing intensities coming from JDF-L1(see Figure S3). In addition, the amino acid was not ad-sorbed on the layered material. The XRD pattern, in whichno peaks could be found at low angles, and the TGA analy-

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sis, from which only dehydration effects could be inferred(9.2 wt.-% of weight loss at 900 °C) are in agreement withthis conclusion.

The amount of amine can be calculated by TGA (Fig-ure 2) as approximately 28 wt.-%. This is comparable to theamount of dodecylamine intercalated in layered silicateAMH-3 with higher basal spacing (41 Å), consistent witha bilayer surfactant configuration.[11] This total amount ofamine can be divided into two parts: that coming from pro-tonated amine (removed at about 150–275 °C) and thatfrom nonprotonated amine (removed at temperatureshigher than approximately 275 °C), similar to the distinc-tion made in lamellar zeolite MCM-22P.[13] UZAR-S1 wasobtained by extracting the amine with an HCl/H2O/ethanol(5:17:870, molar ratio) solution (Figure 2). Protonatedamine molecules were only removed from the interlayerspace by ion exchange, whereas the repeated washing (10washings and ultrasound curve in Figure 2) would only beeffective for part of the nonprotonated amine. UZAR-S1,similar to other delaminated porous materials,[2,14,15] is es-sentially XRD-amorphous or exhibits broad reflections(Figure 1).

Figure 2. Weight losses as obtained by TGA of (from bottom totop): swollen JDF-L1, ultrasound-treated swollen JDF-L1, UZAR-S1 obtained from swollen JDF-L1 upon HCl treatment, as-madeJDF-L1, NH4-UZAR-S1 obtained from swollen JDF-L1 uponNH4Cl treatment.

The amount of ammonium in NH4-UZAR-S1, upontreatment with NH4Cl/H2O/ethanol (5:17:870, molar ratio)solution, calculated as approximately 8.8 wt.-% (Figure 2),gave rise to an ammonium/nonylamine molar ratio of 2.7,indicating that the swelling of the material was producedwithout exhausting its ion exchange capacity. This is inagreement with the Na values in the EDX analyses inTable 1, which show important remains of Na after swellingand low Na contents after HCl extraction. UZAR-S1 main-tains a high Si/Ti ratio lower than 6, while delaminated tit-anosilicate Del-Ti-MWW had a Si/Ti atomic ratio in therange 35–46,[2] and TiITQ-6 a Ti content of 1.0 wt.-%.[14]

Exfoliated Titanosilicate Material UZAR-S1 Obtained from JDF-L1

Table 1. Atomic coefficients as obtained by EDX analysis in morethan 20 different particles for each sample.[a]

Sample Na Ti Si

Theoretical (Na4Ti2Si8O22) 4 2 8As-made 2.0 (�1.0) 2 5.6 (�1.8)Swollen JDF-L1 1.3 (�0.3) 2 6.4 (�1.8)UZAR-S1 (II)[b] 0.2 (�0.0) 2 11.3 (�3.4)

[a] The ICP analysis carried out for swollen JDF-L1 gave Na andTi atomic coefficients of 1.8 and 2. [b] Obtained after two stagesof swelling/extraction with HCl.

The as-made JDF-L1 sample shows micrometric crystalswith a sheet growth habit (Figure 3a). The TEM image inFigure 3b corresponds to swollen JDF-L1, where an ap-proximate atomic spacing of 3 nm is observed. Similar toother exfoliated porous materials, UZAR-S1 consists ofsheets of JDF-L1 only a few nanometers thick (images3c,d). In the higher magnification Figure 3d, each approxi-mately 5 nm thick sheet of UZAR-S1 is composed of onlythree to five layers. As in the situation described forMCM22-P,[16] each layer appears as two dark bands sepa-rated by a bright band that corresponds to the galleryspace. The two orthogonal five-membered channels of JDF-L1 may constitute the dark bands. Note that after the HClextraction treatment (Figure 3d) the fine particles tend tobe more aggregated and their edges are less sharp than be-fore.

Figure 3. SEM or TEM images of: as-made JDF-L1, the inset cor-responding to a single particle (a), swollen JDF-L1 (b), exfoliatedJDF-L1 before acid extraction (c), exfoliated and extracted JDF-L1 (UZAR-S1) (d).

JDF-L1 scarcely adsorbs N2, and this is reflected by aBET specific surface area of 29.6 m2/g (29.8 m2/g for theprotonated sample). The protonated form of JDF-L1 pro-duced in the presence of HCl has a BET specific surfacearea of only 5.0 m2/g.[12] Activation of UZAR-S1 was car-

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ried out either by calcination at 200–650 °C or by HCl ex-traction. With calcination, an optimum BET specific sur-face area of 59.1 m2/g was found at 400 °C, whereas thechemical extraction of UZAR-S1 produced a surface areaof 116 m2/g. This means a BET specific surface area fourtimes higher for UZAR-S1 than for JDF-L1. Furthermore,two and three sequential cycles of swelling and extractiongave rise to a BET specific surface area of 160 and 204 m2/g, respectively. However, there are structural differences be-tween these samples, as will be discussed next. In any event,this was mainly external surface area, as the t-plot analysisdemonstrated. This suggests that the five- and six-mem-bered rings of JDF-L1 and UZAR-S1, supposing that thelayer porosity is preserved upon delamination, are not ac-cessible to N2. On the other hand, even though the level ofdelamination in terms of surface area is not as high as inother exfoliation examples,[1] the avoidance of agglomera-tion by calcination can be important when the homogen-eous dispersion of the exfoliated material in the polymermatrix is pursued, as will be shown later.

From the point of view of solid-state 29Si NMR spectro-scopic analysis, unlike titanosilicate ETS-10, which displaysfour lines associated with three different Si(3Si, 1Ti) sitesand one Si(4Si, 0Ti) site,[17] JDF-L1 displays a single peakat –109.1 ppm related to a single Si(3Si, 1Ti) site,[7,8] asshown in Figure 4. The swollen JDF-L1 also has a singleresonance at the same chemical shift, which indicates thatthe layered Si and Ti coordination was maintained. Afterdelamination two new lines appeared for sample UZAR-S1at about –102.9 and –111.9 ppm, the first attributed toSi(3Si, 0Ti) and Si(2Si, 1Ti) sites and the second to Si(4Si,0Ti) sites. The Si(2Si, 1Ti) sites would have been generatedfrom the breaking of Si–O–Si bonds, consistent with thefine, high length/width ratio particles observed by TEM.The Si(3Si, 0Ti) and Si(4Si, 0Ti) sites would be the resultof the leaching of Ti (see Table 1) during the amine extrac-tion in HCl/H2O/ethanol. A second swelling and subse-quent acid extraction treatment [UZAR-S1(II)] led to ahigh Si(4Si, 0Ti) contribution, associated to the condensa-tion of silica tetrahedra.[11] Note the resonances at –108.3and –106.7 ppm for samples UZAR-S1(I) and UZAR-S1(II) related to unconverted JDF-L1.

The performance of UZAR-S1 was tested as a mixed-matrix membrane filler. The same nanometer-like particlesproduced upon the exfoliation of JDF-L1 observed beforeare shown in Figure 5a,b. The aggregate in Figure 5a indi-cates that, even though the swelling and exfoliation affectmost of the precursor material (as inferref from XRD andNMR), some particles with relatively large sizes would beretained. A sheet surrounded by nanometer-like particleswas characterized by tilting to confirm their high aspectratio nature (Figure 5c). The dark-contrast areas changedas the tilting angle evolved from 0° to 20°, thus indicatingthe presence of sheet-like particles.

Since kinetic diameters of H2 and CH4 are 0.289 and0.38 nm, respectively, the bare polysulfone and the UZAR-S1–polysulfone composite membranes were tested for theH2/CH4 separation (Table 2). While the H2 permeability

J. Coronas et al.FULL PAPER

Figure 4. 29Si MAS NMR spectra of JDF-L1 and derived materi-als.

Figure 5. TEM images of a 4 wt.-% UZAR-S1–polysulfone nano-composite membrane: large aggregate (a), nanometer-like particles(b), and observations with tilting (from 0° to 20°) (c).

showed a small decrease from 11.8 to 11.5 Barrer, the H2/CH4 selectivity increased from 58.9 for pure polysulfone to69.2 for 4 wt.-% UZAR-S1–polysulfone membrane. The im-provement in the membrane separation ability resides in thesix-membered rings that UZAR-S1 has along the [001] di-rection, supposing that this new material keeps the layerporosity of JDF-L1. In consequence, the molecular sievingability of the sheets of UZAR-S1 is transferred to the com-posite membrane, favoring the transport of the smallestmolecule (H2). Other polymers to fabricate the mixed ma-trix membranes and other gas mixtures to be separated areunder investigation using UZAR-S1. Finally, the fact thatJDF-L1, after treatment with a mixture of dilute acid andhydrogen peroxide, could selectively oxidize phenol to qui-none[6] suggests that delaminated titanosilicate UZAR-1with a larger specific surface area than JDF-L1 may be use-

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ful in analogous situations. Besides, the material could betested in the acylation processes where ETS-10-based cata-lysts similar in chemical composition have successfully beenapplied.[19] In this case, a good performance of UZAR-S1may be expected due to an easier access to the protons thanin other catalysts with larger particle size or smaller aspectratio than UZAR-S1.

Table 2. H2/CH4 separation performance at 35 °C for pure polysul-fone Udel® and 4 wt.-% UZAR-S1–Udel® membranes. Averagevalues correspond to 3 (pure Udel®[18]) and 4 (mixed matrix) dif-ferent membranes.

Sample Permeability [Barrer] H2/CH4

Membrane H2 CH4 Selectivity

Pure Udel® 11.8 (�0.2) 0.2 (�0.01) 58.9 (�0.1)4 wt.-% UZAR-S1–Udel® 11.5 (�0.5) 0.17 (�0.01) 69.2 (�3.7)

Conclusions

UZAR-S1, a new delaminated material, has been pro-duced by the exfoliation of layered microporous titanosilic-ate JDF-L1. The delamination process used here comprisesfour stages: protonation with amino acid histidine, swellingwith nonylamine, the delamination itself, and activation.UZAR-S1, after being activated by chemical extractionwith an ethanol solution of HCl, which minimizes the lossof texture as compared with calcination, has an externalspecific surface area of 160 m2/g, more than five timesgreater than that of the JDF-L1 precursor. The extractionwith an ethanol solution of NH4Cl indicates that the swell-ing of JDF-L1 was achieved without exhausting the ion ex-change capacity of the latter. In agreement with this, theEDX analysis shows a significant amount of sodium afterswelling. One important feature of UZAR-S1, also revealedby EDX, is that the extracted material, in spite of under-going some Ti leaching, maintained a Si/Ti atomic ratiolower than 6. This reinforces the titanosilicate nature ofUZAR-S1.

29Si NMR spectroscopy and especially TEM analysis,which provides evidence for the existence of nanometer-like,high aspect ratio particles, confirm that UZAR-S1 is a de-laminated material. As a first attempt to exploit UZAR-S1,4 wt.-% UZAR-S1–polysulfone mixed matrix membraneshave been shown to achieve a better performance in theseparation of a H2/CH4 mixture than the pure polymer.

Experimental SectionThe lamellar precursor JDF-L1 was synthesized at 230 °C for 24 hby a seeded secondary growth procedure using the following molarcomposition: SiO2/TiO2/Na2O/H2O 4.2:1:2.9:101.[10] The swollenJDF-L1 was prepared by intercalation of nonylamine (97 wt.-%,Fluka) molecules after proton exchange in the presence of anamino acid. In a typical procedure, -histidine (0.2 , 99% min.,Sigma–Aldrich) was prepared by dissolving the amino acid(2.561 g) in deionized water (82.5 g) at 60 °C whilst stirring until atransparent solution was achieved and a pH of 7.5 was measured.

Exfoliated Titanosilicate Material UZAR-S1 Obtained from JDF-L1

Then, once at room temperature, HCl (6 , Scharlau) was addeddropwise to adjust the pH to 6. Proton exchange occurred uponaddition of JDF-L1 (660 mg) over 10 min before adding an aque-ous nonylamine solution (0.23 , 5.419 g of the amine in 165 g ofdeionized water). The pH then increased abruptly to a value ofabout 9, maintained during the reaction, which was carried outwith stirring at 60 °C for 12 h. Once the reaction was completed,the white, viscous and homogeneous dispersion was destabilized inan ultrasound bath for 15 min with the same amount in volume ofacetone. The resulting product was centrifuged at 10000 rpm for15 min, the solid (about 500 mg) being recovered in acetone anddried at 70 °C for 3 h. To remove the amine and then produce whatis referred to as UZAR-S1 in this paper, the latter solid (200 mg)was mixed with a solution (50 mL) with molar composition HCl/H2O/ethanol 5:17:870. This solution was prepared by using HCl(37%, Scharlau) and ethanol (min. 99.8%, Scharlau), and the reac-tion proceeded under reflux at 55 °C for 8 h. The dispersion ob-tained was washed five times with deionized water and centrifuged.The solid recovered was dried at 100 °C for 20 h.

The materials were characterized by X-ray diffraction using a D-Max Rigaku X-ray diffractometer (Cu-Kα radiation, λ = 1.5418 Å).Certain samples were calcined under vacuum at 200–650 °C for10 h. After degassing at 200 °C for 10 h, a Micromeritics Tristar3000 instrument was used to analyze the BET specific surface area.SEM (JEOL 6400) images were obtained on Au-coated specimensoperating at 20 kV. This equipment allowed EDX analysis of C-coated samples. TEM (JEOL-2000 FXII) observations at 200 kVwere carried out on samples (powders and sliced sections of com-posite membranes) prepared by repeated dispersion in deionizedwater before being poured onto the carbon grid. Solid-state MAS29Si NMR spectra were recorded with a Bruker AV400 WB spec-trometer operating at a resonance frequency of 79.49 MHz andwith a 4 mm probe. The measurements were carried out with acontact time of 3.5 ms, a pulse width of 4 µs, a recycle delay of5 s, and a spinning rate of 10 kHz. Chemical shifts referred to 3-(trimethylsilyl)-1-propanesulfonic acid. For the membrane prepara-tion, polysulfone Udel® P-3500 (kindly supplied by Solvay Ad-vanced Polymers) was degassed at 120 °C for 4 h under vacuum toremove adsorbed water.

For the pure membrane, polysulfone (0.4 g) was dissolved in dichlo-romethane (3.6 mL) and stirred for 1 d, leading to a viscous solu-tion. The fabrication procedure for the mixed matrix membranewith UZAR-S1 (obtained after one stage of swelling/extraction)involved a previous dispersion stage of the filler in the solvent (ina proportion of 90/10 wt.-% solvent/UZAR-S1–polymer mixture)for 15 min in an ultrasound bath. Polysulfone was then added, andthe whole mixture was magnetically stirred for 1 d. Subsequently,the membranes were cast on flat glass plates and then left overnightpartially closed to slow down the natural evaporation of solventunder ambient conditions. The solutions were dried for 1 d at roomtemperature. Once dried, the films were placed for the same periodunder 10 mbar pressure at 120 °C to remove the remaining solvent.Membranes around 100 µm in thickness with 4 wt.-% of inorganiccharge were prepared. The permeation characterization of themembranes at 35 °C was performed in a previously describedsetup.[18]

Supporting Information (see footnote on the first page of this arti-cle): Views of the JDF-L1 structure (Figure S1); low-angle X-ray

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diffraction pattern of swollen JDF-L1 (Figure S2); X-ray diffrac-tion pattern of swollen JDF-L1 without previous protonation (Fig-ure S3); SEM images of swollen JDF-L1 and UZAR-S1 (Fig-ure S4).

Acknowledgments

Financial support from the Spanish Science and Innovation Minis-try (MAT2007-61028) and the Aragon Government (PI035/09) isgratefully acknowledged. C. C. and P. G. also acknowledge theirrespective grants from the Spanish Juan de la Cierva and FPUprograms.

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Received: September 15, 2009Published Online: November 20, 2009