Photon Factory Activity Report 2005 #23 Part B (2006)
Chemistry

10B, 12C/2004G278

Characterization of micro and mesoporous Fe(III) materials utilizing organic
template followed by carboxylates exchange
1Yasuo Izumi,1,* Dilshad Masih,1 Ken-ichi Aika,1 and Yoshimi Seida2
Tokyo Institute of Technology, Nagatsuta 4259-G1-16, Midori-ku, Yokohama 226-8502
2
Institute of Research and Innovation, 1201 Takada, Kashiwa 277-0861

Introduction
Arsenic contamination in drinking water is serious
worldwide environmental problem and recent regulationof the concentration is 10 ppb. Sorption method is mosteconomic way to remove arsenic [1]. In this work, micro
IIIand mesoporous Fe materials were prepared utilizingorganic template followed by smaller carboxylates(formate, acetate, and propionate) exchange. The
transformation in the synthesis was characterized using
Fe K-edge synchrotron XAFS.
Experimental section
50 ml of FeIICl2 was mixed with 10 ml of Na
dodecylsulfate (0.07 M) followed by the addition of 10 mlof H2O2 (0.25 M). The solution was stirred for 1h andfiltered. Obtained FeOx(OH)y composite was mixed withNa formate, acetate, or propionate (0.05 M for each) inethanol. Obtained anion-exchanged FeOx(OH)y andethanol-washed FeOx(OH)y in the absence of carbocylate
was heated in N2 gas flow [1]. Fe K-edge XAFS spectra
were measured at beamline 12C and 10B in transmission
mode at 20 – 290 K for FeOx(OH)y samples evacuated at
290 K and filled in a cell equipped with Kapton windows.
Results and discussion
The EXAFS spectra were measured for FeOx(OH)ycomposite, acetate-exchanged FeOx(OH)y, the one heatedat 423 K, ethanol-washed FeOx(OH)y, and the one heatedat 473 K. In all the Fourier-transform spectra [1], strong
peak appeared at 1.5 – 1.6Å (phase shift uncorrected) due
to the Fe-O bond. A medium peak at 2.7 – 2.8Å (phaseshift uncorrected) was clearly observed due the Fe•••Feinteraction.
For crystallines α-Fe2O3, α-FeO(OH), and γ-FeO(OH),the Fe-O bond distance was between 2.0305 – 2.034Å
and the coordination number NFe-O was 6 for theoctahedral [FeO6] coordination (Table 1). Obtained Fe-Obond distance FeOx(OH)y composite and the derivativeIIImicroporous Fe materials were between 2.043 – 2.088Å,slightly relaxed from those for standard compounds(Table 1). Associated NFe-O values fell within 4.6 – 6.0.
Relatively smaller value (4.6) given for acetateexchanged FeOx(OH)y may be because of less complete
array of [FeO6] units due to highly dispersed microporous
nature and/or surface reduction by acetate or ethanol. TheRFe•••Fe values also elongated (3.213 – 3.245Å) compared to
the value for γ-FeO(OH) (3.066Å). These values werewithin the range of Fe•••Fe distance for edge-shared[FeO6] units (2.97 – 3.28Å) [2]. Obtained NFe•••Fe values(1.8 – 3.1), suggesting highly dispersed, unsaturated
IIInature of microporous Fe materials.
IIIIn summary, Fe K-edge analyses demonstrated that Fematerials studied consisted of edge-shared [FeO6]
octahedral units and the unsaturated nature.
References[1] Y. Izumi, D. Masih, K. Aika, Y. Seida, Micropor.
Mesopor.Mater. 2006, in press.
[2] Y. Izumi, D. Masih, K. Aika, Y. Seida, J. Phys. Chem.
B. 2005, 109(8), 3227 – 3232.
* yizumi@chemenv.titech.ac.jp
aTable 1: Best Fit Results of Fe K-edge EXAFS for FeOx(OH)y Composite and the Derivative Porous Materials
Fe-OSample
FeOx(OH)y composite
Acetate-exchanged FeOx(OH)yAcetate-exchanged FeOx(OH)yheated at 423 K
Ethanol-washed FeOx(OH)yα-Fe2O3bα-FeO(OH)bγ-FeO(OH)a20k-range R-range N–1for fit (Å ) for fit (Å)
3.7 – 12.0 1.11 – 3.13 6.0(±0.8)
3.7 – 12.0 1.14 – 3.08 4.6(±0.6)
3.7 – 11.6 1.09 – 3.15 5.6(±0.5)
3.7 – 11.9 1.11 – 3.10 5.1(±1.6)
66b

Values in parenthesis are estimated fit errors.

Users' Report

6bR
(Å)
2.070
(±0.013)2.065(±0.005)
2.043(±0.005)
2.088(±0.027)2.03052.021
2.034

Fe•••Fe∆E0(eV)–1.0(±1.0)
0.0(±1.1)
1.9(±0.9)–7.0(±3.5)∆σN2(Å )–0.0002 1.8(±0.0007) (±0.2)–0.0009 2.5(±0.0004) (±0.4)0.00103.1(±0.0002) (±0.2)–0.0027 2.6(±0.0031) (±0.1)
72662

See the references 17 and 18 of ref. 1.

R(Å)
3.245
(±0.003)
3.213(±0.020)3.241(±0.013)3.233(±0.011)3.12933.015,
3.390
3.066∆E0(eV)–1.0(±0.5)
0.4(±3.4)–2.1(±2.0)–0.3(±1.4)∆σ
Goodness2(Å )of Fit0.0009198(±0.0003)
0.0022141(±0.0007)
0.0049264(±0.0003)
0.0047136(±0.0005)
2