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Microporous and Mesoporous Materials 84 (2005) 297–301

Controlled delamination and intercalation of layered microporousaluminophosphate by a novel two-step method

Chen Wang, Weiming Hua, Yinghong Yue *, Zi Gao *

Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials,

Fudan University, Shanghai 200433, PR China

Received 28 April 2005; received in revised form 4 May 2005; accepted 5 May 2005Available online 12 July 2005

Abstract

Pure phase benzylamine and aniline intercalates of layered microporous aluminophosphate [Al3P4O16][CH3(CH2)3NH3]3 wereobtained for the first time by a novel two-step method, including a delamination step in alkaline medium and an intercalation stepin acidic medium. The pH value and the dielectric constant of the solution used in these two steps were decisive for the success ofpreparation of the new intercalates. XRD and various other techniques were employed for the characterization of the intercalateproducts and the elucidation of the working principle of the novel method.� 2005 Elsevier Inc. All rights reserved.

Keywords: Layered microporous aluminophosphate; Two-step method; Delamination; Aromatic amine intercalation

1. Introduction

Numerous microporous aluminophosphates withnon-unity Al/P ratios have been synthesized using solvo-thermal method [1,2]. The structures of these materialsare diversified, including 1-D chain, 2-D layer and 3-Dopen framework structures. Their frameworks are nega-tively charged, and the charges are compensated by pro-tonated organic ammonium cations located between thechains and sheets or in the channels. The stoichiometriesof the framework anions are of AlP2O

3�8 , Al2P3O

3�12 ,

Al3P4O3�16 , Al3P5O

6�20 , Al4P5O

3�20 , Al5P6O

3�24 and etc.

Among them 2-D layered aluminophosphates are ofparticular interest because of their potential applicationin separation, catalysis or as functional materials [3].

1387-1811/$ - see front matter � 2005 Elsevier Inc. All rights reserved.doi:10.1016/j.micromeso.2005.05.008

* Corresponding authors. Tel.: +86 21 65642409; fax: +86 2165641740.

E-mail addresses: yhyue@fudan.edu.cn (Y. Yue), zigao@fudan.edu.cn (Z. Gao).

Delamination and intercalation of these layered com-pounds are critical for the preparation of high surfacearea catalysts, thermally stable pillared materials andself-consistent films [3]. However, they are more difficultto bring about than those of ordinary layered metalphosphates due to the instability of the microporoussheets and their strong interaction with the protonatedorganic ammonium cations. Delamination and interca-lation of layered aluminophosphates with [Al3P4O16]

3�

and [Al2P3O12]3� stoichiometries by C2–C12 alkyl

amines by a one-pot method were reported in our previ-ous works [4–6]. Controlling the dielectric constant ofthe solution and the concentration of the alkylaminein the medium is decisive for gaining success. SaturatedC2–C8 alkylamine intercalates of these aluminophos-phates are obtained in solutions with dielectric constantof 50–70 and an amine concentration of 10 mmol/g.

Aromatic intercalates are more easily to be function-alized, e.g., various functional groups, such as sulfonicand nitro-group, can be readily substituted on thebenzene ring. To extend the application of microporous

298 C. Wang et al. / Microporous and Mesoporous Materials 84 (2005) 297–301

aluminophosphates, the intercalation of the layeredstructures with aromatic amines has been attempted[7]. A saturated benzylamine (pKa of 9.34) intercalateof aluminophosphate with [Al3P4O16]

3� stoichiometryhas been obtained using the one-pot method underappropriate conditions. However, for aniline with lowerbasicity (pKa of 4.60) the intercalation is unsuccessfulunder similar conditions, indicating that the basicity ofamine may affect the delamination and intercalationprocesses besides the dielectric constant of the solutionand the concentration of the amine.

In this paper, a novel two-step method for delamina-tion and intercalation of layered aluminophosphate[Al3P4O16][CH3(CH2)3NH3]3 (abbreviated as AlP) isreported. In this method the delamination and intercala-tion processes proceed separately and sequentially underdifferent controlled conditions, so that the dielectric con-stant and the pH value of the medium in these two stepscan be varied to suit a wider variety of intercalatingagents and to guarantee the success of exfoliation andreassembly of the aluminophosphate in the experiment.

2 4 6 8 10 12 14 16 18

e

d

c

b

a

Inte

nsity

/a.u

.

2θ/degree

Fig. 1. XRD patterns of (a) original AlP and AlP delaminated insolutions with ethanol/water ratio of (b) 3:1; (c) 1:1; (d) 1:3; (e) 0 afteran hour.

2. Experimental

2.1. Sample preparation

AlP was prepared according to the procedures in theliterature [8]. Al(iPrO3)3 (1.0 g) and phosphoric acid(0.63 ml) were added to butyl alcohol (7.86 ml). Themixture was stirred until homogeneous, and then butyl-amine (2.47 ml) was added under stirring. The gel wastransferred to an autoclave and heated at 180 �C underautogenerous pressure for 10 d. The product was fil-tered, washed and dried in air.

For delamination, 200 mg of AlP and 20 ml of thebuffer solution were placed in a closed bottle, stirredcontinuously for about 8 h, centrifuged and then driedin air. The delaminated aluminophosphate (�200 mg)and a calculated amount of benzylamine or aniline wereadded into 20 ml of ethanol/water mixture. Phosphoricacid or sulfuric acid was then added to adjust the pHvalue of the solution. The mixture was stirred for 1 d,and the final product was obtained by centrifugation.

2.2. Characterization

X-ray powder diffraction (XRD) patterns of the sam-ples were recorded on a Rigaku D/MAX-IIA diffrac-

Table 1Time for complete delamination of AlP in the different solutions

Ethanol/water ratio 3:1 1:1Dielectric constant [9] 39.40 54.75pH value 10 10Time for complete delamination (h) – 6

tometer with CuKa radiation at 30 kV and 20 mA anda Ni filter. Scanning electron microscopic (SEM)images were obtained on a Philips XL-30 scanningelectron microscope. UV–vis spectra of the sampleswere recorded on a Shimadzu UV-2450 UV–visiblespectrometer equipped with an integrating sphereattachment.

3. Results

3.1. Delamination of AlP

The XRD pattern of the as-synthesized AlP is shownin Fig. 1a. The (001) peak at 9.20� corresponds to aninterlayer spacing of 0.96 nm, which is consistent withthe single-crystal X-ray diffraction data in the literature[8]. The delamination of AlP was carried out in solutionswith different ethanol/water ratios at pH of 10, and theobservations of the systems by XRD were summarizedin Fig. 1 and Table 1. AlP delaminates completely inpure water within 1 h, forming a clear colloidal solution.As the ethanol/water ratio is increased, the exfoliationof AlP becomes more difficult and the colloidizationprocess is retarded. In the solution with ethanol/waterratio of 3:1, the layered structure of AlP remains intactafter 10 h. This result is consistent with our previous

1:3 0 0 0 068.35 80.37 80.37 80.37 80.3710 10 9 8 73 1 2 6 –

2 4 6 8 10 12 14 16 18

e

d

c

b

a

Inte

nsity

/a.u

.

2θ/degree

Fig. 2. XRD patterns of (a) original AlP and AlP delaminated insolutions with (b) pH = 7; (c) pH = 8; (d) pH = 9; (e) pH = 10 after anhour.

2 4 6 8 10 12 14 16 18

d

c

b

a

Inte

nsity

/a.u

.

2θ/degree

Fig. 3. XRD patterns of AlP intercalated by benzylamine in solutionswith ethanol/water ratios of (a) 1:3; (b) 1:1; (c) 3:1; (d) pure ethanol atpH = 4.

2 10 12 14 16 18

a

b

c

d

Inte

nsity

/a.u

.

2θ/degree4 6 8

Fig. 4. XRD patterns of benzylamine intercalates in pure ethanolsolution at (a) pH = 7; (b) pH = 6; (c) pH = 5; (d) pH = 4.

C. Wang et al. / Microporous and Mesoporous Materials 84 (2005) 297–301 299

observations showing that delamination of the alumino-phosphate sheets is favored when the dielectric constantof the solution is increased [4].

The effect of pH on the delamination of AlP wasstudied as well, and the results were given in Fig. 2and Table 1. As the pH of the solution decreases from10 to 7, the colloidization of AlP is retarded. In the solu-tion with pH of 7, the exfoliation of AlP is incompleteafter a long period of time. From these observations itcan be concluded that the delamination process is facil-itated in basic solutions.

3.2. Intercalation of benzylamine

The intercalation of the delaminated AlP with benzyl-amine was carried out in solutions with different etha-nol/water ratios at pH of 4, and the results wereillustrated in Fig. 3. The intercalation does not takeplace in pure water solution and the solution with anethanol/water ratio of 1:3, namely in solution with highdielectric constants. As the ethanol/water ratio of thesolution is increased to 1:1, a pure phase of benzylamineintercalate with an interlayer spacing of 1.44 nm isformed. The peak intensity of the benzylamine interca-late is maximized in pure ethanol solution.

The intercalation of benzylamine was conducted atdifferent pH in pure ethanol solution, and the resultswere shown in Fig. 4. A new intercalate with a d-spacingof 1.51 nm appears at pH of 5. The amount of this newphase increases with a further increase of pH while thatof the other phase with a d-spacing of 1.44 nm decreases.At pH of 7, the intercalate with the d-spacing of 1.44 nmdisappears and a pure phase with the d-spacing of1.51 nm is obtained. The phase transition associatedwith the pH of the solution is probably caused by a dif-

ferent arrangement of benzylamine molecules in theinterlayer region. At lower pH (below 7), the strongerinteraction between the protonized amine and the oxy-gen atom of the layer forces the amine to tilt a smallerangle with respect to the layer plane and reduces theinterlayer distance. In one-pot method, two intercalateswith d-spacing of 1.51 and 1.74 nm were obtained in-stead of one pure phase [7]; the latter is probably anintercalate packed with a bilayer of butylamine in theinterlayer region, since butylamine is present in the sys-tem during intercalation.

The SEM images of the original AlP and the benzyl-amine intercalate are shown in Fig. 5a and b. The ori-ginal AlP is composed of large regular thin plate-like

2 4 6 8 10 12 14 16 18

Inte

nsity

/a.u

.

2θ/degree

Fig. 6. XRD pattern of the aniline intercalate.

200 250 300 350 400 450 5000.0

0.1

0.2

0.3

0.4

0.5

0.6

Benzylamineintercalate

Aniline intercalate

Original AlP

Ref

lect

ance

cha

nge

Wavelength (nm)

Fig. 7. Diffuse reflectance spectra of AlP and the intercalates.

Fig. 5. SEM images of (a) AlP; (b) benzylamine intercalate; (c) anilineintercalate.

300 C. Wang et al. / Microporous and Mesoporous Materials 84 (2005) 297–301

crystals with the size about 6 · 15 · 0.1 lm. The crys-tals of the benzylamine intercalate are more irregular,and they take the form of thin flakes with non-uniformsize.

3.3. Intercalation of aniline

The intercalation of aniline, a base weaker than ben-zylamine, was successful using this two-step methodonly when pure ethanol was employed as the solventand 98% sulfuric acid was added to adjust the pH ofthe solution to 4 instead of 85% phosphoric acid to min-

imize the amount of water in the system. This shows thatmedium with low dielectric constant is necessary for thereassembly of aniline intercalate, and gives the reasonfor the failed tests using one-pot method. The XRD pat-tern of the aniline intercalate with a d-spacing of1.42 nm is illustrated in Fig. 6, and the SEM imagebenzylamine intercalate.

To confirm the substitution of aromatic amines intothe intercalates, the latter were characterized by meansof diffuse reflectance spectroscopy (DRS). The DRSspectra of the original AlP and the intercalates are illus-trated in Fig. 7. The two sharp peaks at �220 and�260 nm on the spectra of the benzylamine and anilineintercalates can be attributed to the E and B adsorptionbands of phenyl ring respectively, whereas in the spec-trum of AlP only a broad peak is observed.

C. Wang et al. / Microporous and Mesoporous Materials 84 (2005) 297–301 301

4. Discussion

In one-pot method, the delamination and intercala-tion of AlP proceed simultaneously in the same medium,and they can be regarded as a metathetical reaction asshown below [7]:

B�jþHA1A1HþjB� þ 2A2

$ B�jþHA2A2HþjB� þ 2A1 ð1Þ

where B� is the aluminophosphate sheet; A1 is butyl-amine; A2 is aromatic amine and H+ is proton. Thechemical driving force for the substitution of A2 forA1 is the difference in their basicity. The larger the differ-ence is, the readier the substitution reaction proceeds. Inthe meantime, the dielectric constant of the medium isalso decisive for the reaction, since the reaction takesplace in an ionic solution and the Coulombic interac-tions between the ions depend directly on the dielectricconstant of the solvent. If the Coulombic interactionsare so strongly reduced by the solvent that the ions inter-act only weakly, it would be impossible for them to con-glomerate or assemble into crystals. This explains thedifferent behavior of various amines in one-pot method.

The situations are quite different in the two-stepmethod suggested in this work. Here, the delaminationand intercalation processes are separated, and they pro-ceed in different mediums. The delamination step pro-ceeds in an alkaline solution, whereas the intercalationstep proceeds in an acidic solution. In the delaminationstep,

B�jþHA1A1HþjB� þ 2OH� $ 2B� þ 2A1 þ 2H2O

ð2Þthe basic OH� anions in the solution facilitate thedeprotonation of the butylamine template and conse-quently the exfoliation of the layered AlP. The exfoli-ated sheets of AlP are structurally stable not only incolloidal state but also after centrifuging and drying inair, so they can be separated from the original aminetemplate. In the intercalation step,

2B� þ 2A2 þ 2Hþ $ B�jþHA2A2HþjB� ð3Þ

the new intercalate is crystallized out from the acidicsolution due to the protonation of the aromatic amine.Besides the basicity and acidity, the dielectric constantof the medium for each step in the two-step methodcan also be adjusted individually, so that a higher dielec-tric constant could be selected for better delaminationand a suitable lower dielectric constant for the intercala-tion of amines with different basicity.

5. Conclusion

The intercalation of [Al3P4O16][CH3(CH2)3NH3]3 byaromatic amines with either high or low basicity suchas benzylamine (pKa = 9.34) and aniline (pKa = 4.60)can be achieved using a novel two-step method, includ-ing a delamination step in alkaline medium and an inter-calation step in acidic medium. The pH value and thedielectric constant of the solution used in these two stepswere decisive for the success of preparation of the newintercalates. The advantages or contributions of thenew two-step method can be summarized into the fol-lowing: (1) the delamination and intercalation of layeredmicroporous aluminophosphate can be controlled con-veniently through adjusting the pH and the dielectricconstant of the solution used for the two steps; (2) ascompared with the one-pot method, more new interca-lates of layered microporous aluminophosphates couldbe obtained; (3) pure phase intercalate is formed in thesystem instead of mixed crystals; (4) the concept devel-oped in the present work could be applied to the prepa-ration of other new layered or intercalated materials. Insummary, this novel two-step method paves the way tofurther applications for the layered microporousmaterials.

Acknowledgements

This work was supported by the Chinese Major StateBasic Research Development Program (Grant No.2000077507) and the Shanghai Major Basic ResearchProgram (Grant No. 03DJ14004).

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