M

Bi

WXa

b

a

ARRA

KBMSE

1

1hpmammpsaspdtwi

mo

ST

0d

Materials Chemistry and Physics 116 (2009) 319–322

Contents lists available at ScienceDirect

Materials Chemistry and Physics

journa l homepage: www.e lsev ier .com/ locate /matchemphys

aterials science communication

iosynthesis and characterization of mesoporous organic–inorganic hybridron phosphate

eijia Zhoua, Wen Hea,b,∗, Xudong Zhanga, Hongshi Zhaoa, Zhengmao Lia, Shunpu Yana,iuying Tiana, Xianan Suna, Xiuxiu Hana

Department of Materials Science and Engineering, Shandong Institute of Light Industry, Jinan 250353, PR ChinaBiomaterials Research Center, South China University of Technology, Guangzhou 510640, PR China

r t i c l e i n f o

rticle history:eceived 26 October 2008eceived in revised form 2 April 2009

a b s t r a c t

Mesoporous organic–inorganic hybrid iron phosphate has been synthesized by a precipitation methodwith yeast cells as biotemplate. The yeast cells are used to regulate the nucleation and growth of ironphosphate. The small-angle X-ray diffraction (SXRD) patterns show a short-range ordered structure in

ccepted 5 April 2009

eywords:iomaterialsicroporous materials

urface properties

the dried and calcined samples. The BJH (Barrett–Joyner–Halenda) models reveal that the average poresizes are at 13.9 nm for dried sample and at 14.8 nm for calcined sample. The sample calcined at 300 ◦Chas the highest specific surface area of 146.2 m2 g−1. Transmission electron microscopy (TEM) analysesreveal a wormhole-like mesoporous structure in the samples. Fourier transform infrared (FT-IR) spectraare used to analyze the chemical bond linkages in hybrid mesoporous FePO4 materials. The FePO4 coated

tivity

lectrical conductivity carbon has higher conduc

. Introduction

Since MCM-41 silica molecular sieves were first reported in992 [1,2], the research in the field of mesoporous materials withigh specific surface area has been a very hot topic. Over theast few decades, mesoporous metal phosphates have attracteduch attention because of their important applications in catalysis,

dsorption and separation [3–6]. Compared with phosphate-basedesoporous materials (Al, Ti, Zr and Ce) [7–10], only a few syntheticethods have been reported for the preparation of mesoporous iron

hosphates [11–13]. In some open-framework iron phosphates, thepaces between particles can be filled with organic molecules, suchs organic–inorganic hybrid mesoporous iron oxophenyl phosphateynthesized using sodium dodecyl sulfate as a template [12]. Ironhosphate has been reported as a good catalyst for selective oxi-ation reactions, e.g. oxidative dehydrogenation of isobutyric acido methacrylic acid [14], and for the selective oxidation of methanehen it was supported by MCM-41 or SBA-15 [15,16]. In particular,

ron phosphate is a useful lithium battery material [17,18].Template is commonly employed for controlling production of

aterials with ordered structure and desired properties. Examplesf the templates varying from copolymers to ordered latex particles

∗ Corresponding author at: Department of Materials Science and Engineering,handong Institute of Light Industry, Jinan 250353, PR China.el.: +86 0531 88522792; fax: +86 0531 88522792.

E-mail address: hewen1960@126.com (W. He).

254-0584/$ – see front matter. Crown Copyright © 2009 Published by Elsevier B.V. All rioi:10.1016/j.matchemphys.2009.04.013

than uncoated one, which has potential use for lithium battery materials.Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.

have been considerably reported, but only a few synthetic methodshave been reported for the preparation of mesoporous materialsusing microbe cells as a template [19]. Here, we have preparedmesoporous organic–inorganic hybrid iron phosphate by a simpleprecipitation method using yeast cells as biotemplate. The meso-porous structure of the synthesized materials is thermally stableup to 300 ◦C. The mesoporous organic–inorganic hybrid iron phos-phate can be used as LiFePO4/C cathode material for Li-ion batteryafter calcination in reducing atmosphere [20].

2. Experimental

2.1. Materials and methods

The starting materials used in this study included ferric chloride (FeCl3·6H2O,99.0%, Sinopharm Chemical Reagent Co., Ltd), disodium hydrogen phosphate(Na2HPO4·12H2O, 99.0%, Tianjin Bodi Chemical Co., Ltd), sodium acetate(CH3COONa·3H2O, 99.0%, Tianjin Bodi Chemical Co., Ltd) and baker’s yeast cells(instant dry yeast, Angel Yeast Co., Ltd). All chemical reagents were in analyticalgrade.

Quantitative yeast cells were cultivated in 30 ml glucose aqueous solution for30 min at 36 ◦C. 0.01 mol FeCl3·6H2O was dissolved in 20 ml distilled water, and0.01 mol Na2HPO4·12H2O was dissolved in 50 ml distilled water. The FeCl3 solutionwas dropped into the yeast cells solution with vigorous stirring. The FeCl3/yeastsolution was continuously stirred at room temperature for 2 h to obtain a Fe-cellssuspension. The Na2HPO4 solution was added to the Fe-cells suspension under a

constant stirring condition, and superfluous sodium acetate aqueous solution wasused to adjust pH value to 5.5 (the best activity of yeast cells), then the mixture washomogenized for 2 h and aged for 48 h. The reaction can be descripted as follows(Eq. (1)):

FeCl3 + Na2HPO4 + NaAC → FePO4 + 3NaCl + HAC (1)

ghts reserved.

320 W. Zhou et al. / Materials Chemistry and Physics 116 (2009) 319–322

Table 1The BET specific surface area of hybrid iron phosphate with varied yeast cellsamounts.

Yeast cells weight (g)

B

llpa

2

drsm7AfmposwtI

3

swr0

ttpmmitccmdcbpa

iiFror

Fig. 1. Small-angle XRD patterns of mesoporous iron phosphate: (a) the freeze dry-ing sample; (b) the sample heated at 300 ◦C for 2 h.

TT

BE

0 0.4 0.8 1.2 1.6 2.0 3.0

ET (m2 g−1) 90.3 103.2 120.2 106.3 82.9 52.5 36.7

The resultant materials were washed with distilled water and ethanol, and col-ected using centrifugation method. The wet sample was then freeze-dried andapping finish. The resultant hybrid FePO4 samples were heated at different tem-eratures 80, 300, 400, 500, 600 and 700 ◦C for 2 h, and the BET specific surface areand conductivities of the products were determined.

.2. Characterizations

The small-angle X-ray diffraction (SXRD) technique was performed on an X-rayiffractometer with Cu K� (� = 0.15418 nm) irradiation (X’Pert PRO, PANalytical X-ay Company, Holland). The data were collected in the range between 1.1◦ and 10◦ inteps of 0.03◦ and the integration time of 17 s per step. BJH (Barrett–Joyner–Halenda)odels and the N2 adsorption–desorption isotherms (NADI) were carried out at

7 K using a computer controlled sorption analyzer (Micromeritics, Gemini V2.0,merica) operating in the continuous mode. The microstructural and morphological

eatures of iron phosphate powders were investigated with a transmission electronicroscope (JEM-100X, JEOL, Japan), using an accelerating voltage of 100 kV. Sam-

les for TEM were prepared by air-drying a drop of a sonicated ethanol suspensionf particles onto a gelatin-coated copper mesh. The chemical bond linkages of theamples were studied by FT-IR spectroscopy (NEXUS 470, Nicolet, USA) by a KBrafer technique. The conductivities of iron phosphate samples calcined at different

emperatures were determined using a LCR measuring instrument (ZL-10, Shanghainstrument Research Institute, China).

. Results and discussion

To investigate the effect of yeast amount on the BET specificurface area of hybrid iron phosphate samples, a series of samplesith different amounts of yeasts was prepared. According to BET

esults (Table 1), the optimum amount of instant dry yeast should be.8 g in order that the good mesoporous structure can be obtained.

Table 2 shows the BET specific surface area and conductivi-ies of the hybrid iron phosphate samples calcined at differentemperatures 80, 300, 400, 500, 600 and 700 ◦C. When the sam-les were calcined at 300 ◦C, the specific surface area reached aaximum of 146.2 m2 g−1. It can be explained that the organicatters wrapped by iron phosphate nanoparticles can transform

nto porous carbon after heat processing. The electrical conduc-ivities of hybrid iron phosphate samples have a similar trend inhanges with the BET results. After calcinated at 300 ◦C, obtainedarbon can improve the conductivities of samples with a maxi-um value of 6.7 × 10−4 S cm−1. The conductivities of the products

ecrease with the increasing temperatures, because that electricarbon was removed and iron phosphate particles would growigger and bigger gradually. Therefore, 300 ◦C should be the idealrocessing temperature due to the highest BET specific surface areand conductivity value.

The SXRD patterns of the dried and calcined samples are shownn Fig. 1. The low-angle peak at 1.4◦ for d100 plane correspond-

ng to d-spacing of 6.1 nm in the dried sample can be seen inig. 1a. The diffraction peak is weak and broad due to a short-ange ordered structure, which is obtained by the accumulation ofrganic–inorganic hybrid iron phosphate nanoparticles. The mate-ial calcined at 300 ◦C for 2 h can be without loss of the low-angle

Fig. 2. N2 adsorption–desorption isotherms of mesoporous organic–inorganichybrid iron phosphate samples (a, freeze drying; b, heated at 300 ◦C) are measuredat 77 K, the corresponding pore size distribution (BJH) are shown in the inset.

able 2he relationship between BET specific surface area, electrical conductivity and treatment temperature.

Heat treatment temperature (◦C)

80 300 400 500 600 700

ET (m2 g−1) 120.2 146.2 98.8 62.3 26.7 9.7lectrical conductivity (S cm−1) 1.1 × 10−9 6.7 × 10−4 4.6 × 10−5 1.6 × 10−8 6.1 × 10−10 1.6 × 10−10

istry and Physics 116 (2009) 319–322 321

pIt

sntpa1tfdooastao

spitvphwbont

sttbiactw(IaaaFrwc

Fig. 3. TEM images of mesoporous organic–inorganic hybrid iron phosphate: (a)freeze drying and (b) heated at 300 ◦C for 2 h.

W. Zhou et al. / Materials Chem

eak at 1.3◦ (Fig. 1b), and the d-spacing is slightly shifted to 6.9 nm.t can be inferred that the resultant hybrid iron phosphate has ahermally stable mesostructure up to 300 ◦C.

The nitrogen adsorption–desorption isotherms and the corre-ponding pore size distribution curves are shown in Fig. 2. Theitrogen adsorption–desorption isotherms should be classified asype IV (H2), which is typical for mesoporous systems. The meso-orous organic–inorganic hybrid iron phosphate (Fig. 2a) possessesspecific surface area of 120.2 m2 g−1 with an average pore size of3.9 nm (inset of Fig. 2a), as determined by adsorption branch ofhe BJH. After heat treatment at 300 ◦C (Fig. 2b), the specific sur-ace area increases to 146.2 m2 g−1. The pore size distribution curveisplays a single shape with a maximum value of 14.8 nm (insetf Fig. 2b), which shifts to higher value due to the combustion ofrganic matters. The H2 loops at relative pressure P/P0 of 0.9 (Fig. 2and b) represent the ink-bottle-shaped or cage type pores. The poreizes calculated by the SXRD disagree with the result of BJH due tohe different measurement mechanisms. The best ordered pores atbout 6 nm were obtained by SXRD and the strongest distributionsf pore volume at about 14 nm were obtained by BJH models.

TEM images of the dried and calcined hybrid iron phosphateamples are shown in Fig. 3a and b. A disordered wormhole-likeorous structure can be observed obviously, and the mesoporos-

ty is not ordered. Fig. 3a shows the presence of some isolatediny particles sized at 10 nm, which form soft aggregation witharied shapes. During freeze drying process, the well-dispersivearticles accumulate together to form porous aggregates. Aftereat treatment at 300 ◦C, large agglomerates with a disorderedormhole-like porous structure are observed in Fig. 3b. The accessi-le pores are connected at random, lacking discernible long-rangerder in the pore arrangement among the small iron phosphateanoparticles. It is indicative that the mesoporosity is mainly dueo interparticle porosity rather than intraparticle porosity.

FT-IR spectra of yeast cells, the dried and calcined hybrid FePO4amples are shown in Fig. 4. Band assignments (Fig. 4a) are referredo the literatures [21,22]. The broad band at 3358 cm−1 is ascribedo the O–H stretching vibration. The band around 2927 cm−1 cane ascribed to CH2 asymmetric stretching vibration. The dom-

nant bands near 1651 and 1541 cm−1 are assigned to amide Ind amide II, the characteristic IR absorption of protein in yeastells. The band at 1045 cm−1 is ascribed to C–O stretching vibra-ion of carbohydrates found in the RNA, the DNA and the cellall of yeast cells [23]. In Fig. 4b, the characteristic peaks of O–H

3408 cm−1), CH2 (2925 cm−1) and the protein (1635 cm−1, amideand 1538 cm−1, amide II) in dried hybrid FePO4 samples all shiftt different degrees. The FT-IR spectrum of trigonal FePO4 exhibitsbroad maximum between 900 and 1200 cm−1 which can be

ssigned to the P–O vibration of PO43−. In the case of amorphous

ePO4, the bondings among all kinds of atoms are only partiallyeserved because of poor symmetric structure. Comparing Fig. 4aith b, the chemical interactions between yeast cells and FePO4 are

omplicated, which include O–H, amino group and possible elec-

Fig. 4. FT-IR spectra of yeast cells and mesoporous organic–inorganic hybrid ironphosphates treated by different processes: (a) pure yeast cells, (b) freeze drying, (c)450 ◦C and (d) 650 ◦C.

Fig. 5. A schematic view for the formation of mesoporous organic–inorganic hybrid iron phosphate with yeast cells as a biotemplate.

3 istry a

tcia[

mFpoyb[ayowpna

4

haitttutoomsv

[

[[[[[[[

[[[[[

22 W. Zhou et al. / Materials Chem

rostatic interaction [24,25]. After calcined at 450 and 650 ◦C, theharacteristic peaks of yeast cells gradually disappear as shownn Fig. 4c and d. These bands (Fig. 4d) at 647 cm−1 (Fe–O–Fe)nd 1045 cm−1 (Fe–O–P) serve as an identity of crystalline FePO412].

On the basis of above results, a possible synthesis mechanism ofesoporous organic–inorganic hybrid iron phosphate is shown in

ig. 5. The yeast cells as a template provide nucleation sites for ironhosphate. A schematic presentation of iron phosphate formationn/in yeast cells: (a) The increased local concentration of Fe3+ on/ineast cells was caused by electrostatic and chemical interactionsetween Fe3+ and hydroxyl or amino groups of biomacromolecules25,26]. (b) After the addition of phosphate and sodium acetatequeous solution, iron phosphate crystal nucleus formed on/ineast cells. The continuing condensation leaded to the formationf iron phosphate nanoparticles [27]. (c) The biomacromoleculesere encapsulated by iron phosphate nanoparticles and the inter-article pores were formed by the agglomeration of iron phosphateanoparticles and organic matters, which were confirmed by SXRDnd BJH models.

. Conclusions

Using yeast cells as biotemplate, mesoporous organic–inorganicybrid iron phosphate was synthesized with a precipitation methodt room temperature. Yeast cells provide nucleation sites andnduce growth of iron phosphate nanoparticles, and organic mat-ers of yeast cells are encapsulated by iron phosphate nanoparticleso form sponged aggregates with mesostructure. After calcina-ion, the carbon obtained by carbonization of organic matters issed as a functional material, which increases the conductivities ofhe samples with a maximum value of 6.7 × 10−4 S cm−1. FePO4/C

btained by calcination at 300 ◦C has a high specific surface areaf 146.2 m2 g−1. We can develop an application of FePO4/C cathodeaterials for lithium-ion batteries. The universal technique pre-

ented here is an economical and simple way for the preparation ofarious hybrid materials with mesoporous structure.

[[[

[

nd Physics 116 (2009) 319–322

Acknowledgements

This work was financially supported by the National Natural Sci-ence Foundation of China (Grant Nos. 50572029 and 50732003),Natural Science Foundation Cooperative Project Grant of Guang-dong (Grant No. 04205786) and the Natural Science Foundation ofShandong, China (Grant No. Y2008F39). Authors also thank JingyunMa and the Analytical Center of Shandong Institute of Light Industryfor the technological support.

References

[1] J.S. Beck, J.C. Vartuli, W.J. Roth, J. Am. Chem. Soc. l14 (1992) 10834.[2] C.T. Kresge, M.E. Leonowiez, W.J. Roth, Nature 359 (1992) 710.[3] C. Serre, A. Auroux, A. Gervasini, Angew. Chem. Int. Ed. 41 (2002) 1594.[4] C.N.R. Rao, S. Natarajan, A. Choudhury, Acc. Chem. Res. 34 (2001) 80.[5] J. Yu, R. Xu, Acc. Chem. Res. 36 (2003) 481.[6] A. Corma, Chem. Rev. 97 (1997) 2373.[7] B.T. Holland, P.K. Isbester, C.F. Blanford, J. Am. Chem. Soc. 119 (1997) 6796.[8] Z.L. Yin, Y. Sakamoto, J.H. Yu, S.X. Sun, O. Terasaki, R.R. Xu, J. Am. Chem. Soc. 126

(2004) 8882.[9] J. Jimenez-Jimenez, P. Maireles-Torres, P. Olivera-Pastor, Adv. Mater. 10 (1998)

812.10] C.C. Tang, Y. Bando, D. Golberg, R.M. Cerium, Angew. Chem. Int. Ed. 44 (2005)

576.[11] X.F. Guo, W.P. Ding, X.G. Wang, Chem. Commun. (2001) 709.12] N.K. Mal, A. Bhaumik, M. Matsukata, Ind. Eng. Chem. Res. 45 (2006) 7748.13] D.H. Yu, J.H. Qian, N.H. Xue, Langmuir 23 (2007) 382.14] M. Ai, K. Ohdan, Appl. Catal. A: General 150 (1997) 13.15] X.X. Wang, Y. Wang, Q.H. Tang, J. Catal. 217 (2003) 457.16] Y. Wang, X.X. Wang, Z. Su, Catal. Today 155 (2004) 93.17] P.P. Prosini, M. Lisi, S. Scaccia, J. Electrochem. Soc. 149 (2002) 297.18] J. Santos-Pena, P. Soudan, C.O. Areán, G.T. Palomino, S. Franger, J. Solid State

Electrochem. 10 (2006) 1.19] S.A. Davis, S.L. Burkett, N.H. Mendelson, Nature 385 (1997) 420.20] B.Q. Zhu, Xi, H. Li, Z.X. Wang, H.J. Guo, Mater. Chem. Phys. 98 (2006) 373.21] J. Schmitt, H.C. Flemming, Int. Biodeterior. Biodegrad. 41 (1998) 1.22] S. Lin, G.D. Rayson, Environ. Sci. Technol. 32 (1998) 1488.23] D.E. Nivens, J. Schmitt, J. Sniateckl, Appl. Spectrosc. 47 (1993) 668.

24] S. Mandal, S. Phadtare, M. Sastry, Curr. Appl. Phys. 5 (2005) 118.25] M. Sastry, Pure Appl. Chem. 74 (2002) 1621.26] A. Gole, C. Dash, V. Ramachandran, S.R. Sainkar, A.B. Mandale, M. Rao, M. Sastry,

Langmuir 17 (2001) 1674.27] B. Wang, P. Liu, W.G. Jiang, H.H. Pan, X.R. Xu, R.K. Tang, Angew. Chem. Int. Ed. 47

(2008) 3560.