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Synthesis and characterization of copper(II)-phenanthroline complex grafted organic groups modified MCM-41
Materials Chemistry and Physics 71 (2001) 174–178
Synthesis and characterization of copper(II)-phenanthroline complex grafted organic groups modified MCM-41 Shan Zheng, Lian Gao∗ , Jingkun Guo State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Ding-Xi Road, Shanghai 200050, PR China Received 10 July 2000; received in revised form 6 December 2000; accepted 18 December 2000
Abstract The preparation of copper(II)-phenanthroline complex functionalized MCM-41 has been described. The modification of the internal pore surface of mesoporous MCM-41 with 3-aminopropyl or 3-methacryloyloxypropyl yielded two different functional groups by using 3-aminopropyltriethoxysilane and (3-methacryloyloxypropyl)trimethoxysilane as the precursors. Copper(II)-phenanthroline complex was grafted onto the functional MCM-41, via the coordination of the metal ion with the functional groups. The metal ion complex functionalized mesoporous materials were characterized by powder X-ray diffraction, fourier transform infrared and nitrogen adsorption/desorption at 77 K, as well as electron spin resonance at 293 K. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Mesoporous MCM-41; 3-Aminopropyl functional MCM-41; 3-Methacryloyloxypropyl functional MCM-41; Copper(II) complex functionalized MCM-41
1. Introduction The development of mesoporous silicates such as MCM-41 has generated interests due to the potential applications of mesoporous materials such as catalyst, catalyst support, separation medium and host material for inclusion compounds [1,2]. The high specific surface areas, narrow pore size distribution and tailorable pore size ranging from 1.5 to10.0 nm with varying synthetic conditions have added a new dimension to intrapore chemistry that had previously focused on zeolites as hosts [3]. In mesoporous MCM-41, an estimated 8–27% of silicon atoms are linked with reactive hydroxyl groups, which has been utilized to covalently anchor functional groups or metal oxide onto the inner surface walls [4,5]. Functional groups 3-chloropropyl– [6], 3-aminopropyl– [7], chlorotriphenyl– [8] and so on could be grafted onto the internal walls of MCM-41 via Si–O–Si bonds. Jacobs and co-workers [9] reported that sulfonic acid functionalized mesoporous silicates performed well in typical strong acid catalyzed reactions. Also, metal oxides such as TiO2 [10], Fe2 O3 [11] and MnO2 [12] are anchored ∗ Corresponding author. Tel.: +86-216-251-2990, ext: 6321; fax: +86-216-251-3903. E-mail address: [email protected] (L. Gao).
and modified the mesopores through the co-condensation between metal oxide and ≡Si–OH in MCM-41. Transition metal ions grafted into zeolites were conventionally used as heterogeneous catalysts for the transformation of small organic molecules [13,14]. Moreover, the one-dimensional mesoporous channels in MCM-41 were ready to immobilize large organometallic complexes. Manganese(II)-2,2’-bipyridine complex incorporated into MCM-41 by an impregnation method exhibited higher catalytic activity for the oxidation of styrene than the corresponding homogeneous catalyst [15]. Iron(II)-8-quinolinol were supported in the mesoporous host and were found to be active with hydroxylation of phenol using H2 O2 [16]. But, it is not satisfied to utilize these metal complexes incorporated mesoporous materials circularly because of the incompact hydrogen bonds between complex and mesoporous materials. In this paper, mesoporous MCM-41 was modified with functional groups 3-aminopropyl or 3-methacryloyloxypropyl. Therefore, the mesopores of the compounds were tailored by the organic functional groups. And then copper(II)-phenanthroline complex was grafted compactly onto the functional MCM-41 via the coordination bonds, and attached to stationary phase. The as-synthesized copper(II) complex functionalized MCM-41 were characterized by X-ray diffraction
0254-0584/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 4 - 0 5 8 4 ( 0 1 ) 0 0 2 7 6 - 0
S. Zheng et al. / Materials Chemistry and Physics 71 (2001) 174–178
(XRD), fourier transform infrared (FTIR), nitrogen sorption at 77 K and electron spin resonance (ESR) spectra at 293 K. 2. Experimental 2.1. Synthesis of mesoporous MCM-41 MCM-41(Si/Al = 35) was synthesized by mixing cetyltrimethylammonium bromide (CTAB), NaOH, NaAlO2 , fumed SiO2 (99%) and distilled water under the autogenous hydrothermal conditions according to procedure [17]. The as-synthesized MCM-41 was calcined in air at 873 K for 6 h to remove the surfactant CTAB. 2.2. Modification of MCM-41 with 3-aminopropyl or 3-methacryloyloxypropyl One gram of calcined MCM-41 was placed in a 100 ml round bottom flask with 50 ml dry hexane and 5.0 ml 3-aminopropyltriethoxysilane or (3-methacryloyloxypropyl) trimethoxysilane. The mixture was stirred and refluxed at 343 K for 12 h under the protection of nitrogen flow. The white solid was washed repeatedly with ethanol and then dried at 353 K for 12 h. 3-Aminopropyl functional MCM-41 was named MCM-ap and 3-methacryloyloxypropyl functional was named MCM-mp. 2.3. Complexes grafted onto functional MCM-ap or MCM-mp Copper ion complex: [Cu(phen)2 Cl]OH·3H2 O was previously synthesized according to the published procedure [18]. 0.02 M solution of copper(II)-phenanthroline complex was prepared by dissolving the appropriate amount of the complex into 50 ml distilled water. 1.0 g MCM-ap or MCM-mp was added and the mixture was then stirred for 12 h at room temperature. The solid products were washed with distilled water and ethanol by filtration. At last, the solids were dried in a vacuum oven at 353 K overnight. The copper(II) functionalized MCM-41, MCM-ap-Cu(phen)2 appeared blue, while MCM-mp-Cu(phen)2 appeared pale blue. 2.4. Characteristic technique C, N, H organic elemental analysis were conducted on elementar varioel (Table 1). The Cu2+ content in complex
175
compound was determined by AA 6401 atomic absorption spectrometer. XRD pattern were collected on Rigaku D/max rb diffractometer, using Cu K␣ (λ = 1.5418 Å) radiation at 40 kV and 60 mA over the scan range 1.8–10◦ . FTIR spectra were recorded from KBr pellets (1 wt.% sample and 99% KBr) using Nicolet 7900 spectrophotometer. N2 adsorption–desorption isotherms at 77 K were conducted on micromeritics ASAP 2010 micropore analysis system. The samples were outgassed at 473 K for 4 h. Cu(II) ESR spectra were recorded on Bruker ER-200D ESR spectrometer.
3. Results and discussion The schematic diagram in Fig. 1 summarizes the reactions between template-free MCM-41 and copper(II)-phenanthroline complex. Firstly, organic groups 3-aminopropyl or 3-methacryloyloxypropyl, modified the inner inorganic walls of MCM-41 and yielded functional ligands by using (EtO)3 Si(CH2 )3 NH2 and (MeO)3 Si(CH2 )3 OCOC(CH3 )= CH2 as the precursors. No water is involved in the synthesis system to prevent precursors hydrolyzing and influencing on the co-condensation. Then, in the second step, [Cu(phen)2 Cl]+ complex goes into the pores of organic ligands functional MCM-41 and Cu(II) is coordinated by amine or vinyl ligands. So, metal ion complex and MCM-41 are linked with organic functional groups, and modified the inner pore walls of mesoporous materials. But, the degrees of the amine and vinyl ligands to copper center are different, amine ligands has strong coordinative ability as compared to vinyl. The elemental analysis results of the as-synthesized copper(II) complex functionalized MCM-41 are listed in Table 1. XRD patterns of the functionalized MCM-41 are shown in Fig. 2 (Table 2). The patterns show Bragg peaks at low reflection angles, which are typical of mesoporous MCM-41 [19]. The sharper intensity of (1 0 0) reflection is decreased with the addition of functional ligands and metal ion complex. Other Bragg peaks became weak and diffuse, implying poor crystallinity, which could be due to contrast matching between the silica walls and the content of the channels after functionalization. Fig. 3 shows the IR spectra between 3200 and 400 cm−1 of the organic functional group MCM-41 and copper(II) complex functionalized MCM-41. Spectrum (Fig. 3(a)) from template-free MCM-41 shows bands at 1080, 796 and 445 cm−1 . Bands at similar wavenumbers in the spectra
Table 1 Elemental analysis results Samples
C (%)
N (%)
H (%)
MCM-ap MCM-mp MCM-ap-Cu(phen)2 MCM-mp-Cu(phen)2
6.99 16.67
2.44 –
1.81 2.71
Cu2+ (wt.%)
Cu2+ /Si molar ratio
Cu2+ /NH2 or Cu2+ /C=CH2 molar ratio
2.15 0.46
0.027 0.003
0.200 0.037
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S. Zheng et al. / Materials Chemistry and Physics 71 (2001) 174–178
Fig. 1. The schematic reactions between calcined MCM-41 and copper complex [Cu(phen)2 Cl]+ . (1) 3-Aminopropyltriethoxysilane, (2) (3-methacryloyloxypropyl)trimethoxysilane, (3) copper(II)-phenanthroline complex.
of crystalline and amorphous SiO2 have been assigned to characteristic vibrations of Si–O–Si bridges crosslinking the silicate network [20,21]. The modification of –(CH2 )3 NH2 and –(CH2 )3 OCOC(CH3 )=CH2 , are evident from the high wavenumber part of the spectra, where the transmission bands at 2925 and 2852 cm−1 form the asymmetric and symmetric vibrations of CH2 units (Fig. 3(b) and (d)). In MCM-mp (Fig. 3(d)), the sharp peak appeared at 1630 cm−1 , characteristic of the vibration of vinyl in 3-methacryloyloxypropyl. As the concentration of copper(II)-phenanthroline increases (Fig. 3(c)), the significant peak at about 1520 cm−1 is due to the vibration of C=C in ligands phenanthroline. While in Fig. 3(e), it could not be observed due to the little quantity of [Cu(phen)2 Cl]+ grafted onto MCM-mp. N2 sorption isotherm is an efficient way for providing information about the pore system of mesoporous materials. All the samples give similar adsorption/desorption isotherms of N2 (shown in Fig. 4). The absence of hystersis indicates a reversible type IV isotherm [22]. The BET surface areas
Table 2 The data of d1 0 0 and a from XRD
Fig. 2. XRD of samples (a: calcined MCM-41, b: MCM-ap, c: MCM-mp, d: MCM-ap-Cu(phen)2 and e: MCM-mp-Cu(phen)2 ).
Fig. 3. FTIR of samples (a: calcined MCM-41, b: MCM-ap, c: MCM-ap-Cu(phen)2 , d: MCM-mp and e: MCM-mp-Cu(phen)2 ).
Samples
d1 0 0 (nm)
aa (nm)
MCM-41 MCM-ap MCM-ap-Cu(phen)2 MCM-mp MCM-mp-Cu(phen)2
4.04 4.11 4.08 3.94 4.01
4.69 4.75 4.71 4.55 4.63
a
a = 2d1 0 0 × 3−1/2 .
and specific pore volume of copper ion complex functionalized MCM-41 reduces remarkably compared to calcined MCM-41 (illustrated in Table 3). Therefore, the surface areas and pore volume could be tailored by the grafted functional groups. The BJH pore size distribution is based on the Kelvin equation and has been widely used in mesoporous materials. We are principally interested in changes in the pore size distributions because of the modification
S. Zheng et al. / Materials Chemistry and Physics 71 (2001) 174–178
177
Fig. 5. The ESR spectra of (a) MCM-ap-Cu(phen)2 and (b) MCM-mpCu(phen)2 .
–NH2 , –C=CH2 and –Cl to metal ion are relatively weak in comparison to –phen. Thus, the coordination state of Cu(II) is unaffected by the process of grafting.
4. Conclusions
Fig. 4. (a) Adsorption/desorption isotherms of nitrogen at 77K of functionalized MCM-41 (a: calcined MCM-41, b: MCM-ap, c: MCM-mp, d: MCM-ap-Cu(phen)2 and e: MCM-mp-Cu(phen)2 ); (b) pore size distribution by BJH method.
with the organic groups or metal ion complexes. The average pore diameter is shifted from 2.76 nm (MCM-41) to 2.09 nm (MCM-mp-Cu(phen)2 ). The average pore diameter decreased significantly corresponding to the various groups grafted. Copper ion is highly sensitive to ESR spectroscopy at room temperature [23,24]. Fig. 5 shows the ESR spectra of MCM-ap-Cu(phen)2 and MCM-mp-Cu(phen)2 . There is no signal difference between the metal ion complex precursors and metal ion complex functionalized MCM-41. The three small peaks with g// = 2.290 and the sharp singlet with g⊥ = 2.065 are attributed to copper ion. The set of parameters is similar to that observed for the complex [Cu(phen)2 Cl]OH, suggesting similar environments for Cu(II) in both samples. Because the coordinative ability of Table 3 The BET surface area, pore volume and most probable diameter of samples Samples
ABET (m2 g−1 )
VBJH (cm3 g−1 )
DBJH (nm)
MCM-41 MCM-ap MCM-ap-Cu(phen)2 MCM-mp MCM-mp-Cu(phen)2
1128 734 636 859 856
1.45 0.97 0.87 0.99 0.96
2.76 2.21 2.19 2.13 2.09
The organosilane modified surface of MCM-41 can readily bind metal ion complex such as [Cu(phen)2 Cl]+ . Copper(II) complex functionalized MCM-41 were synthesized via the coordination of organosilane to Cu(II). The introduced groups were observed clearly in IR spectra. The BET surface areas, specific pore volume and average pore diameters of MCM-ap-Cu(phen)2 , MCM-mp-Cu(phen)2 decreases remarkably as compared to the pristine MCM-41, and the mesopore was tailored by the grafted functional groups and complex. Copper(II) ESR spectra exhibits the coordination state of Cu(II) is unaffected by the process of grafting. References [1] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.-W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J. Am. Chem. Soc. 114 (1992) 10834. [2] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Wartuli, J.S. Beck, Nature 359 (1992) 710. [3] K. Moller, T. Bein, Chem. Mater. 10 (1998) 2950. [4] S. O’Brien, J.M. Keates, S. Barlow, M.J. Drewitt, B.R. Payne, D. O’Hare, Chem. Mater. 10 (1998) 4088. [5] T. Ishikawa, M. Matsuda, A. Yasukawa, K. Kandori, S. Inagaki, T. Fukushima, S. Kondo, J. Chem. Soc. Faraday Trans. 92 (1996) 1985. [6] P. Sutra, D. Brunel, Chem. Commun. (1996) 2485. [7] C.J. Liu, S.G. Li, W.Q. Pang, C.M. Che, Chem. Commun. (1997) 65. [8] J. Chen, Q. Li, R. Xu, F. Xiao, Angrew. Chem. Int. Ed. Engl. 34 (1995) 2694. [9] M. Wan Rhijn, D.W. De Vos, B.F. Sels, W.D. Bossaert, P.A. Jacobs, Chem. Commun. (1998) 317. [10] Z. Luan, E.M. Maes, P.A.W. Van der Heide, D. Zhao, R.S. Czernuszewicz, L. Kevan, Chem. Mater. 11 (1999) 3680. [11] T. Abe, Y. Tachibana, T. Uematsu, M. Iwamoto, Chem. Commun. (1995) 1617. [12] R. Burch, N. Cruise, D. Gleeson, S.C. Tsang, Chem. Commun. (1996) 951.
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[13] A. Corma, A. Martinez, V. Martinez-Soria, J.B. Monton, J. Catal. 153 (1995) 25. [14] G.A. Ozin, S. Ozkar, Chem. Mater. 4 (1992) 511. [15] Z. Luan, J. Xu, L. Kevan, Chem. Mater. 10 (1998) 3699. [16] C. Liu, Y. Shan, X. Yang, X. Ye, Y. Wu, J. Catal. 168 (1997) 35. [17] S. Zheng, L. Gao, J. Guo, J. Inorg. Mater. 15 (2000) 844. [18] H.Y. Shen, D.Z. Liao, X.H. Jiang, S.P. Yan, G.L. Wang, X.K. Yao, H.G. Wang, Acta Chim. Sinica 57 (1999) 316. [19] M. Grün, I. Lauer, K.K. Unger, Adv. Mater. 9 (1997) 254.
[20] M.R. Almeida, C.G. Partano, J. Appl. Phys. 68 (1990) 4225. [21] E.I. Kamitsos, A.P. Patsis, G. Kordas, Phys. Rev. B 48 (1993) 12499. [22] P.L. Llewelln, Y. Grillet, F. Schuth, H. Reicher, L.K. Unger, Microporous Mater. 3 (1994) 345. [23] Y.V. Subba Rao, D.E. De Vos, T. Bein, P.A. Jacobs, Chem. Commun. 1997, 355. [24] J. Xu, Z. Luan, T. Wasowicz, L. Kevan, Microporous Mesoporous Mater. 22 (1998) 179.
Synthesis and characterization of copper(II)-phenanthroline complex grafted organic groups modified MCM-41 Shan Zheng, Lian Gao∗ , Jingkun Guo State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Ding-Xi Road, Shanghai 200050, PR China Received 10 July 2000; received in revised form 6 December 2000; accepted 18 December 2000
Abstract The preparation of copper(II)-phenanthroline complex functionalized MCM-41 has been described. The modification of the internal pore surface of mesoporous MCM-41 with 3-aminopropyl or 3-methacryloyloxypropyl yielded two different functional groups by using 3-aminopropyltriethoxysilane and (3-methacryloyloxypropyl)trimethoxysilane as the precursors. Copper(II)-phenanthroline complex was grafted onto the functional MCM-41, via the coordination of the metal ion with the functional groups. The metal ion complex functionalized mesoporous materials were characterized by powder X-ray diffraction, fourier transform infrared and nitrogen adsorption/desorption at 77 K, as well as electron spin resonance at 293 K. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Mesoporous MCM-41; 3-Aminopropyl functional MCM-41; 3-Methacryloyloxypropyl functional MCM-41; Copper(II) complex functionalized MCM-41
1. Introduction The development of mesoporous silicates such as MCM-41 has generated interests due to the potential applications of mesoporous materials such as catalyst, catalyst support, separation medium and host material for inclusion compounds [1,2]. The high specific surface areas, narrow pore size distribution and tailorable pore size ranging from 1.5 to10.0 nm with varying synthetic conditions have added a new dimension to intrapore chemistry that had previously focused on zeolites as hosts [3]. In mesoporous MCM-41, an estimated 8–27% of silicon atoms are linked with reactive hydroxyl groups, which has been utilized to covalently anchor functional groups or metal oxide onto the inner surface walls [4,5]. Functional groups 3-chloropropyl– [6], 3-aminopropyl– [7], chlorotriphenyl– [8] and so on could be grafted onto the internal walls of MCM-41 via Si–O–Si bonds. Jacobs and co-workers [9] reported that sulfonic acid functionalized mesoporous silicates performed well in typical strong acid catalyzed reactions. Also, metal oxides such as TiO2 [10], Fe2 O3 [11] and MnO2 [12] are anchored ∗ Corresponding author. Tel.: +86-216-251-2990, ext: 6321; fax: +86-216-251-3903. E-mail address: [email protected] (L. Gao).
and modified the mesopores through the co-condensation between metal oxide and ≡Si–OH in MCM-41. Transition metal ions grafted into zeolites were conventionally used as heterogeneous catalysts for the transformation of small organic molecules [13,14]. Moreover, the one-dimensional mesoporous channels in MCM-41 were ready to immobilize large organometallic complexes. Manganese(II)-2,2’-bipyridine complex incorporated into MCM-41 by an impregnation method exhibited higher catalytic activity for the oxidation of styrene than the corresponding homogeneous catalyst [15]. Iron(II)-8-quinolinol were supported in the mesoporous host and were found to be active with hydroxylation of phenol using H2 O2 [16]. But, it is not satisfied to utilize these metal complexes incorporated mesoporous materials circularly because of the incompact hydrogen bonds between complex and mesoporous materials. In this paper, mesoporous MCM-41 was modified with functional groups 3-aminopropyl or 3-methacryloyloxypropyl. Therefore, the mesopores of the compounds were tailored by the organic functional groups. And then copper(II)-phenanthroline complex was grafted compactly onto the functional MCM-41 via the coordination bonds, and attached to stationary phase. The as-synthesized copper(II) complex functionalized MCM-41 were characterized by X-ray diffraction
0254-0584/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 4 - 0 5 8 4 ( 0 1 ) 0 0 2 7 6 - 0
S. Zheng et al. / Materials Chemistry and Physics 71 (2001) 174–178
(XRD), fourier transform infrared (FTIR), nitrogen sorption at 77 K and electron spin resonance (ESR) spectra at 293 K. 2. Experimental 2.1. Synthesis of mesoporous MCM-41 MCM-41(Si/Al = 35) was synthesized by mixing cetyltrimethylammonium bromide (CTAB), NaOH, NaAlO2 , fumed SiO2 (99%) and distilled water under the autogenous hydrothermal conditions according to procedure [17]. The as-synthesized MCM-41 was calcined in air at 873 K for 6 h to remove the surfactant CTAB. 2.2. Modification of MCM-41 with 3-aminopropyl or 3-methacryloyloxypropyl One gram of calcined MCM-41 was placed in a 100 ml round bottom flask with 50 ml dry hexane and 5.0 ml 3-aminopropyltriethoxysilane or (3-methacryloyloxypropyl) trimethoxysilane. The mixture was stirred and refluxed at 343 K for 12 h under the protection of nitrogen flow. The white solid was washed repeatedly with ethanol and then dried at 353 K for 12 h. 3-Aminopropyl functional MCM-41 was named MCM-ap and 3-methacryloyloxypropyl functional was named MCM-mp. 2.3. Complexes grafted onto functional MCM-ap or MCM-mp Copper ion complex: [Cu(phen)2 Cl]OH·3H2 O was previously synthesized according to the published procedure [18]. 0.02 M solution of copper(II)-phenanthroline complex was prepared by dissolving the appropriate amount of the complex into 50 ml distilled water. 1.0 g MCM-ap or MCM-mp was added and the mixture was then stirred for 12 h at room temperature. The solid products were washed with distilled water and ethanol by filtration. At last, the solids were dried in a vacuum oven at 353 K overnight. The copper(II) functionalized MCM-41, MCM-ap-Cu(phen)2 appeared blue, while MCM-mp-Cu(phen)2 appeared pale blue. 2.4. Characteristic technique C, N, H organic elemental analysis were conducted on elementar varioel (Table 1). The Cu2+ content in complex
175
compound was determined by AA 6401 atomic absorption spectrometer. XRD pattern were collected on Rigaku D/max rb diffractometer, using Cu K␣ (λ = 1.5418 Å) radiation at 40 kV and 60 mA over the scan range 1.8–10◦ . FTIR spectra were recorded from KBr pellets (1 wt.% sample and 99% KBr) using Nicolet 7900 spectrophotometer. N2 adsorption–desorption isotherms at 77 K were conducted on micromeritics ASAP 2010 micropore analysis system. The samples were outgassed at 473 K for 4 h. Cu(II) ESR spectra were recorded on Bruker ER-200D ESR spectrometer.
3. Results and discussion The schematic diagram in Fig. 1 summarizes the reactions between template-free MCM-41 and copper(II)-phenanthroline complex. Firstly, organic groups 3-aminopropyl or 3-methacryloyloxypropyl, modified the inner inorganic walls of MCM-41 and yielded functional ligands by using (EtO)3 Si(CH2 )3 NH2 and (MeO)3 Si(CH2 )3 OCOC(CH3 )= CH2 as the precursors. No water is involved in the synthesis system to prevent precursors hydrolyzing and influencing on the co-condensation. Then, in the second step, [Cu(phen)2 Cl]+ complex goes into the pores of organic ligands functional MCM-41 and Cu(II) is coordinated by amine or vinyl ligands. So, metal ion complex and MCM-41 are linked with organic functional groups, and modified the inner pore walls of mesoporous materials. But, the degrees of the amine and vinyl ligands to copper center are different, amine ligands has strong coordinative ability as compared to vinyl. The elemental analysis results of the as-synthesized copper(II) complex functionalized MCM-41 are listed in Table 1. XRD patterns of the functionalized MCM-41 are shown in Fig. 2 (Table 2). The patterns show Bragg peaks at low reflection angles, which are typical of mesoporous MCM-41 [19]. The sharper intensity of (1 0 0) reflection is decreased with the addition of functional ligands and metal ion complex. Other Bragg peaks became weak and diffuse, implying poor crystallinity, which could be due to contrast matching between the silica walls and the content of the channels after functionalization. Fig. 3 shows the IR spectra between 3200 and 400 cm−1 of the organic functional group MCM-41 and copper(II) complex functionalized MCM-41. Spectrum (Fig. 3(a)) from template-free MCM-41 shows bands at 1080, 796 and 445 cm−1 . Bands at similar wavenumbers in the spectra
Table 1 Elemental analysis results Samples
C (%)
N (%)
H (%)
MCM-ap MCM-mp MCM-ap-Cu(phen)2 MCM-mp-Cu(phen)2
6.99 16.67
2.44 –
1.81 2.71
Cu2+ (wt.%)
Cu2+ /Si molar ratio
Cu2+ /NH2 or Cu2+ /C=CH2 molar ratio
2.15 0.46
0.027 0.003
0.200 0.037
176
S. Zheng et al. / Materials Chemistry and Physics 71 (2001) 174–178
Fig. 1. The schematic reactions between calcined MCM-41 and copper complex [Cu(phen)2 Cl]+ . (1) 3-Aminopropyltriethoxysilane, (2) (3-methacryloyloxypropyl)trimethoxysilane, (3) copper(II)-phenanthroline complex.
of crystalline and amorphous SiO2 have been assigned to characteristic vibrations of Si–O–Si bridges crosslinking the silicate network [20,21]. The modification of –(CH2 )3 NH2 and –(CH2 )3 OCOC(CH3 )=CH2 , are evident from the high wavenumber part of the spectra, where the transmission bands at 2925 and 2852 cm−1 form the asymmetric and symmetric vibrations of CH2 units (Fig. 3(b) and (d)). In MCM-mp (Fig. 3(d)), the sharp peak appeared at 1630 cm−1 , characteristic of the vibration of vinyl in 3-methacryloyloxypropyl. As the concentration of copper(II)-phenanthroline increases (Fig. 3(c)), the significant peak at about 1520 cm−1 is due to the vibration of C=C in ligands phenanthroline. While in Fig. 3(e), it could not be observed due to the little quantity of [Cu(phen)2 Cl]+ grafted onto MCM-mp. N2 sorption isotherm is an efficient way for providing information about the pore system of mesoporous materials. All the samples give similar adsorption/desorption isotherms of N2 (shown in Fig. 4). The absence of hystersis indicates a reversible type IV isotherm [22]. The BET surface areas
Table 2 The data of d1 0 0 and a from XRD
Fig. 2. XRD of samples (a: calcined MCM-41, b: MCM-ap, c: MCM-mp, d: MCM-ap-Cu(phen)2 and e: MCM-mp-Cu(phen)2 ).
Fig. 3. FTIR of samples (a: calcined MCM-41, b: MCM-ap, c: MCM-ap-Cu(phen)2 , d: MCM-mp and e: MCM-mp-Cu(phen)2 ).
Samples
d1 0 0 (nm)
aa (nm)
MCM-41 MCM-ap MCM-ap-Cu(phen)2 MCM-mp MCM-mp-Cu(phen)2
4.04 4.11 4.08 3.94 4.01
4.69 4.75 4.71 4.55 4.63
a
a = 2d1 0 0 × 3−1/2 .
and specific pore volume of copper ion complex functionalized MCM-41 reduces remarkably compared to calcined MCM-41 (illustrated in Table 3). Therefore, the surface areas and pore volume could be tailored by the grafted functional groups. The BJH pore size distribution is based on the Kelvin equation and has been widely used in mesoporous materials. We are principally interested in changes in the pore size distributions because of the modification
S. Zheng et al. / Materials Chemistry and Physics 71 (2001) 174–178
177
Fig. 5. The ESR spectra of (a) MCM-ap-Cu(phen)2 and (b) MCM-mpCu(phen)2 .
–NH2 , –C=CH2 and –Cl to metal ion are relatively weak in comparison to –phen. Thus, the coordination state of Cu(II) is unaffected by the process of grafting.
4. Conclusions
Fig. 4. (a) Adsorption/desorption isotherms of nitrogen at 77K of functionalized MCM-41 (a: calcined MCM-41, b: MCM-ap, c: MCM-mp, d: MCM-ap-Cu(phen)2 and e: MCM-mp-Cu(phen)2 ); (b) pore size distribution by BJH method.
with the organic groups or metal ion complexes. The average pore diameter is shifted from 2.76 nm (MCM-41) to 2.09 nm (MCM-mp-Cu(phen)2 ). The average pore diameter decreased significantly corresponding to the various groups grafted. Copper ion is highly sensitive to ESR spectroscopy at room temperature [23,24]. Fig. 5 shows the ESR spectra of MCM-ap-Cu(phen)2 and MCM-mp-Cu(phen)2 . There is no signal difference between the metal ion complex precursors and metal ion complex functionalized MCM-41. The three small peaks with g// = 2.290 and the sharp singlet with g⊥ = 2.065 are attributed to copper ion. The set of parameters is similar to that observed for the complex [Cu(phen)2 Cl]OH, suggesting similar environments for Cu(II) in both samples. Because the coordinative ability of Table 3 The BET surface area, pore volume and most probable diameter of samples Samples
ABET (m2 g−1 )
VBJH (cm3 g−1 )
DBJH (nm)
MCM-41 MCM-ap MCM-ap-Cu(phen)2 MCM-mp MCM-mp-Cu(phen)2
1128 734 636 859 856
1.45 0.97 0.87 0.99 0.96
2.76 2.21 2.19 2.13 2.09
The organosilane modified surface of MCM-41 can readily bind metal ion complex such as [Cu(phen)2 Cl]+ . Copper(II) complex functionalized MCM-41 were synthesized via the coordination of organosilane to Cu(II). The introduced groups were observed clearly in IR spectra. The BET surface areas, specific pore volume and average pore diameters of MCM-ap-Cu(phen)2 , MCM-mp-Cu(phen)2 decreases remarkably as compared to the pristine MCM-41, and the mesopore was tailored by the grafted functional groups and complex. Copper(II) ESR spectra exhibits the coordination state of Cu(II) is unaffected by the process of grafting. References [1] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.-W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J. Am. Chem. Soc. 114 (1992) 10834. [2] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Wartuli, J.S. Beck, Nature 359 (1992) 710. [3] K. Moller, T. Bein, Chem. Mater. 10 (1998) 2950. [4] S. O’Brien, J.M. Keates, S. Barlow, M.J. Drewitt, B.R. Payne, D. O’Hare, Chem. Mater. 10 (1998) 4088. [5] T. Ishikawa, M. Matsuda, A. Yasukawa, K. Kandori, S. Inagaki, T. Fukushima, S. Kondo, J. Chem. Soc. Faraday Trans. 92 (1996) 1985. [6] P. Sutra, D. Brunel, Chem. Commun. (1996) 2485. [7] C.J. Liu, S.G. Li, W.Q. Pang, C.M. Che, Chem. Commun. (1997) 65. [8] J. Chen, Q. Li, R. Xu, F. Xiao, Angrew. Chem. Int. Ed. Engl. 34 (1995) 2694. [9] M. Wan Rhijn, D.W. De Vos, B.F. Sels, W.D. Bossaert, P.A. Jacobs, Chem. Commun. (1998) 317. [10] Z. Luan, E.M. Maes, P.A.W. Van der Heide, D. Zhao, R.S. Czernuszewicz, L. Kevan, Chem. Mater. 11 (1999) 3680. [11] T. Abe, Y. Tachibana, T. Uematsu, M. Iwamoto, Chem. Commun. (1995) 1617. [12] R. Burch, N. Cruise, D. Gleeson, S.C. Tsang, Chem. Commun. (1996) 951.
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