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Chemical modification of silica gel with synthesized new Schiff base derivatives and sorption studies of cobalt (II) and nickel (II)
Applied Surface Science 255 (2009) 8798–8803
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Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Chemical modification of silica gel with synthesized new Schiff base derivatives and sorption studies of cobalt (II) and nickel (II) Ahmed Nuri Kursunlu *, Ersin Guler, Hakan Dumrul, Ozcan Kocyigit, Ilkay Hilal Gubbuk Department of Chemistry, Selcuk University, Campus, 42075, Konya, Turkey
A R T I C L E I N F O
A B S T R A C T
Article history: Received 15 April 2009 Received in revised form 3 June 2009 Accepted 11 June 2009 Available online 21 June 2009
In this study, three Schiff base ligands and their complexes were synthesized and characterized by infrared spectroscopy (IR), thermogravimetric analyses (TGA), nuclear magnetic resonance (NMR), elemental analysis and magnetic susceptibility apparatuses. Silica gel was respectively modified with Schiff base derivatives, (E)-2-[(2-chloroethylimino)methyl]phenol, (E)-4-[(2-chloroethylimino)methyl]phenol and N,N0 -[1,4-phenilendi(E)methylidene]bis(2-chloroethanamine), after silanization of silica gel by (3-aminopropyl)trimethoxysilane (APTS) by using a suitable method. Characterization of the surface modification was also performed with IR, TGA and elemental analysis. The immobilized surfaces were used for Co(II) and Ni(II) sorption from aqueous solutions and values of sorption were detected by atomic absorption spectrometer (AAS). ß 2009 Elsevier B.V. All rights reserved.
Keywords: Schiff base Synthesis Sorption isotherm Modification
1. Introduction In recent years, increasing pressure from environmental authorities forced the establishment of discharge limits, which in turn, require an effective use of decontamination and purification methods [1]. Thus, the removal processes of heavy metals from natural waters and solvents contaminated by heavy metal ions are attractive for environment [2]. A series of approaches can be applied to metal ion removal from waters, based on precipitation, exchange resins, membrane filtration and adsorbing methods [3–5]. There are extensive reports on immobilization of modifiers like chelate forming organic reagents, polymers, metal salts, natural compounds and some microorganisms on solid matrices like ion-exchange resins, cellulose, fibers, activated carbon, sand, clay, zeolites, polymers, metal oxides and highly dispersed silica gel [6–8]. These materials have the ability to remove heavy metal ions selectively from aqueous media. Among a series of these important supports, silica gel presents a high thermal, chemical and mechanical stability [9] in metal ion preconcentration [10], ion exchange [11], biotechnology [12], catalysis [13], clean technology and particularly green chemistry for last two decades [14]. The scientific world achieved a new idea by using immobilization technique for nano structures [15,16]. In this technique, synthesized organic molecules containing the desired organic
* Corresponding author. Tel.: +90 332 223 2783. E-mail address: [email protected] (A.N. Kursunlu). 0169-4332/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2009.06.055
functional group are directly attached to the silica gel [17]. A number of previous studies have showed that silica substrates can be modified with ion-chelating organic compounds to remove metal ions from aqueous solutions [18]. Modification of the surface is mostly done by using an appropriate molecule designated as precursor silylating agent. After that, it is possible to immobilize new molecules, to increase the chain of the silylating agent with a variety of other organic functions even more active as chelating agents for many purposes [19]. Immobilization applications of Schiff bases onto silica gel are especially attractive for by lastest studies in scienctific world. Silica gel immobilized with Schiff bases can be used in order to remove some metals ions from aqueous solutions, because of being inexpensive, effective and an alternative sorbent [20]. This study was carried out at two basic steps. On the first step of the study, three Schiff base ligands containing chlorine group were synthesized and nickel (II)–cobalt (II) metal complexes were obtained. These Schiff base ligands were (E)-2-(2-chloropropylidenamino) phenol (I), (E)-4-[(2-chloroethylimino)methyl) phenol (II) and N,N0 -[1,4-phenilendi(E)methylidene]bis(2-chloroethanamine) (III). On the second step of the study, silica gel, which was activated with stock HCI, was modified by (3-aminopropyl)trimethoxysilane. Schiff base ligands which were synthesized on the first step of the study were immobilized chemically to modificated silica structure. Then modificated silica gels were studied for the sorption of nickel (II) and cobalt (II) ions in various concentrations by AAS.
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Fig. 1. Synthesis of I, II and III.
2. Materials and methods 2.1. Experimental Silica gel was provided from Merck (Darmstadt Co.) with particle sizes 0.063–0.200 nm and average pore diameter 6 nm as a sorbent material. Toluene (Merck) was distilled and dried. (3Aminopropyl)trimethoxysilane 98% (APTS, Merck) and cobalt and nickel (II) nitrates were also obtained from Merck. 2-Chloroethylamine hydrochloride salt (Sigma–Aldrich) was reacted with salicylaldehyde, 4-hydroxybenzaldehyde and terephtaldehyde (Fluka) according to method described in Section 2.2 (Fig. 1). 30.0 g raw silica gel in 150 cm3 of stock HCl (37%) was refluxed for 4 h at 100 8C for activation of silica gel particles. The activated silica gel was washed with distilled water and it was dried under vacuum for 24 h [21,22]. Silylant agent, (3-aminopropyl)trimethoxysilane, was used without purification. 2.2. Synthesis of I, II and III A 1:1 equimolar methanolic solution of 2-chloroethylamine hydrochloride (3.32 g, 20 mmol) and salicylaldehyde (20 mmol, 1.7 cm3) were mixed and gently heated for 30 min with constant stirring. Triethylamine (20 mmol, 2.8 cm3) was gradually added to this mixture to remove the hydrochloride salt of 2-chloro ethylamine. The obtained suspension was waited for 1 h in salt– ice bath. During this period, the yellow precipitate was formed. This precipitate washed with ethylacetate and the filtrate was evaporated under reduced pressure and dried in vacuum. The obtained yellowish residue was recrystalized from a mixture of hot ethanol and diethylether (1:2). 4-Hyroxybenzaldehyde was used for the compound II and terephthalaldehyde was used for the compound III according to above described procedure. For I: Yellow; m.p. 78–79 8C, yield: 78.25%, FT-IR(v, cm1): 1638 (C5 5N), 3461 (OH), 2869–2823 (CH2), 826 (Cl). 1H NMR (d, ppm) (DCCI3): 12.9 (s, OH), 7.4–7.1–7.0 (m, 4H, ArH), 8.4, (s, CH) 3.9–3.8 (m, CH2). Anal. calcd. C9H10NOCl: C 58.85, H 5.45, N 7.63; found: C
58.52, H 5.30, N 7.46. For II: Yellow-orange; m.p. 110 8C, yield: 71.25%. FT-IR(v, cm1): 1641 (C5 5N), 2963–2907, (CH2), 3453 (OH), 838 (Cl). 1H NMR (d, ppm) (D-CCI3): 9.8 (s, OH), 7.6–6.9 (m, 4H, ArH), 8.2 (s, CH), 3.7–3.8 (m, CH2). Anal. calcd. C9H10NOCl: C 58.85, H 5.45, N 7.63; found: C 58.52, H 5.38, N 7.40. For III; Brooken white; m.p. 138 8C, yield: 65.5%. FT-IR(v, cm1): 1638 (C5 5N), 2863–2840 (CH2), 830 (Cl). 1H NMR (d, ppm) (D-CCI3): 8.3(s, CH), 7.8 (m, 4H, ArH), 8.4 (m, CH), 3.9–3.8 (m, CH2). Anal. calcd. C18H14N2O2Cl2: C 60, H 3.89, N 7.78; found: C 59.70, H 3.78, N 7.65. 2.3. Modification of silica gel by (3-aminopropyl)trimethoxysilane The silica gel phase-bound amino derivative moiety was prepared from reaction with (3-aminopropyl)trimethoxysilane as silylation agent [23–25]. A sample of 10.0 g of activated silica gel was suspended in 50 cm3 of dry toluen and 10.66 mmol APTS was added to this suspension. The mixture was refluxed under dry nitrogen atmosphere for 72 h at 110 8C and the modified silica gel was filtered off, washed twice with toluen, and dried under vacuum at room temperature (Fig. 2). 2.4. Immobilization of (I), (II) and (III) onto silica gel A sample of 5.0 g modified silica gel and 0.8 g of I were added to 60 cm3 of dry toluen. The mixture was reacted under dry nitrogen atmosphere during 72 h [24] in a reflux system at 100 8C. After the solid phase was filtered, it was washed with toluene–ethanol (1:1) and dried under vacuum at 30 8C for 24 h. It was named as I/SiO2 [20]. Other Schiff base ligands, II and III, were immobilized onto modified silica gel according to above procedure and respectively named II/SiO2, III/SiO2 (Fig. 3). 2.5. Characterization Immobilization of Schiff base ligands (I, II and III) onto silica gel followed a sequence of three steps. On the first step Schiff bases were synthesized; as a second step the immobilization of APTS on silica gel was performed and a new surface was obtained (NH2
8800
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Fig. 2. Reaction for modification of silica gel with (3-aminopropyl)trimethoxysilane.
Fig. 3. Immobilization of I, II and III onto modified silica gel.
terminal) and in the final step; I–II–III which were synthesized on the first step of this study were immobilized onto NH2-terminated modificated silica structure. NMR spectra of I, II, III were obtained on a Varian, 400 MHz spectrometer at room temperature. IR spectrums were obtained in the 400–4000 cm1 range by Mattson-1000 FT-IR spectrometer. KBr pellets were used for solid samples. Elemental analysis was performed for silica structures by Truspec CN Elemental Analyzer. Magnetic measures of I were carried out by Sherwood Scientific Magnetic Susceptibility Balance. Amounts of metallic cation remaining in solution were determined by atomic absorption spectrometer, UNICAM Model 930 Flame AAS. TGA measurements were carried out on Setaram Setsys Evolution-1750 Thermogravimetric Analyzer for modified silica gel structures. 2.6. Studies of metal complex formation of Schiff base ligands (I, II and III) 0.367 g (2 mmol) I was solved in 15 cm3 methanol and the temperature of the solution was increased up to 45 8C. Then 2 mmol (0.580 g) nickel (II) nitrate hexahydrate salt was added to this solution. The decreased pH (3.0) of the solution by addition of metal salts was increased to 5.0–5.5 with 0.1 M KOH. The pH of the solution, which is decreased to 3.0 by added metal salts, was increased to 5.0–5.5 with 0.1 M KOH. Cobalt (II) complex was synthesized according to the procedure described above. Walnut green complex for Ni(II) and brown complex for cobalt (II) was obtained and it was entirely washed with ethanol.For Ni(II): Green; m.p. 168 8C, yield: 62.55%, FT-IR(v, cm1): 1615 (C5 5N), 3476 (OH), 2918–2959 (CH2), 780 (Cl). B.M. 2.98. For Co(II): Brown; m.p.172 8C, yield: 61.55%, FT-IR(v, cm1): 1611 (C5 5N), 3377 (OH), 2928–2966 (CH2), 788 (Cl). B.M. 3.85. II and III did not react with Co(II) and Ni(II) due to the nonexistence of suitable functional group. 2.7. Sorption studies of I/SiO2, II/SiO2, III/SiO2 for metal ions The sorption was performed with batch technique in an aqueous solution for divalent nickel and cobalt nitrates at 25 1 8C. 25.0 mg of modified silica structures were suspended in 10.0 cm3 of aqueous solution containing variable amounts of each cation in samples shaker vessel. For these sorption measurements,
different amounts of derived silica samples were suspended 10 cm3 of aqueous solution containing variable amounts of every one of cations, whose concentrations varied over the 10–30 mg/dm3 range in an orbital shaker thermostat for 4 h (optimum condition, at room temperature and pH 6.0) [20,26]. After equilibrium was established, the suspension was filtered and amounts of metallic cations remaining in solution were determined by AAS. The amount of metal ions sorbed by sorbents was calculated as show in below equation: q¼
ðC 0 CÞV W
(1)
where q is the amount of metal ion sorbed onto unit amount of the adsorbent (mmol/g), C0 and C are the concentrations of metal ions in the initial and equilibrium concentrations of the metal ions in aqueous phase (mmol/dm3), V is the volume of the aqueous phase (L), and W is the dry weight of the adsorbent (g). 3. Result and discussion 3.1. Characterization Carbon and nitrogen elemental analyses showed a clear consistency with the increasing amount of slylating agent on surface, as show in Table 1. This values showed that APTS, I, II and III were covalently bonded on activated SiO2. Results of elemental analyses of the raw silica gel, SiNH2, I/SiO2, II/SiO2, and III/SiO2 supported by IR spectrums (Fig. 4). The several peaks were observed in IR spectra such as (i) a band assigned to Si–O–Si stretching frequency for silanol groups at 807 cm1 and (ii) the intense band related to siloxane stretching of these groups at 1100 cm1 (iii) a broad band between 3453 and Table 1 Percentages (%) of carbon (C), and nitrogen (N), for the matrices SiO2, SiNH2 and I/ SiO2, II/SiO2, III/SiO2. Surface
Amount of sample (g)
Carbon (%)
Nitrogen (%)
SiO2 SiNH2 I/SiO2 II/SiO2 III/SiO2
0.1123 0.1019 0.1123 0.1455 0.1254
0 3.70 14.9 11.6 14.0
0 1.15 1.98 2.65 2.52
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Fig. 4. Activated and modified silica gel structures, SiO2, SiNH2, I/SiO2, II/SiO2, III/SiO2.
3200 cm1 [24], which is attributed to the presence of the O–H stretching frequency of silanol groups [9], (iv) two peaks between 2946–2923 cm1 assigned to –CH2, (v) the sharp peaks around 1615–1620 cm1, which is attributed to the presence of C5 5N bond of Schiff bases (for I/SiO2, II/SiO2 and III/SiO2). The results of IR spectra showed clearly that APTS, I, II and III were immobilized on silica surface. IR spectrums and elemental analysis results were supported by TGA values for characterizations of I/SiO2, II/SiO2 and III/SiO2. The activated silica gel presents a first mass loss stage of 1.52% from 47 to 107 8C, assigned to physically adsorbed water. A following stage of 2.56% is attributed to condensation of the silanols, to yield siloxane groups, resulting in water loss, from 397 to 807 8C [23]. Namely two distinct mass loss steps occurred in thermogravimetric curve of activated SiO2 [27]. On the contrary, the TGA/DTG spectrum of SiNH2 shows two steps of weight loss, one below 100 8C and the other in region of 340–380 8C [28]. On the other hand, four mass loss steps were observed in TGA curve for I/SiO2, three mass loss steps for II/SiO2 and III/SiO2. The first mass loss of 1.5% from 42 to 110 8C attributes to physically adsorbed water for I/SiO2. The second mass loss of 4.20% at 271 8C and third mass loss of 5.88% at 480 8C was attributed to decomposition of organic groups. As parallel, mass losses of 4.93% and 4.69% in TGA curves of II/SiO2 and III/SiO2 were indicated detaching of organic groups from silica surface. Final steps of decomposition (respectively mass loses of 11.95%, 7% and 7.05%)
Fig. 5. Thermogravimetric curves for I/SiO2, II/SiO2 and III/SiO2 structures.
were attribute to condensation of silanol groups, to yield siloxane groups, coming from water loss, from 590 to 900 8C (Fig. 5 and Fig. 6). 3.2. Sorption studies of modified silica gel structures under determined conditions In the sorption study, the effect of metal ion concentrations of Co(II) and Ni(II) metal ions on the sorption capacities were examined using the batch procedure. 25.0 mg of the sorbent was stirred with 10.0 cm3 of various concentrations of metal ions for 120 min. In order to evaluate the sorption characteristics of metal ions on the I/SiO2, II/SiO2 and III/SiO2, experimental data were fitted to the two well-known sorption isotherm models of Freundlich and Langmuir. The monolayer Langmuir and the empirical Freundlich isotherms are usually represented in the following linearised forms: Langmuir isotherm;
Ce Ce 1 ¼ þ qe qo qo b
Freundlich isotherm; lnqe ¼ lnK F þ
(2) 1 nlnC e
(3)
Where qe is the amount of solute sorbed on the surface of the sorbent (mmol/g), Ce is the equilibrium ion concentration in the solution (mmol/dm3), qo is the maximum surface density at monolayer coverage and b is the Langmuir adsorption constant (L/ mmol), KF is the Freundlich constant (mmol/g) which indicates the
Fig. 6. Derivative thermogravimetry curves for I/SiO2, II/SiO2 and III/SiO2 structures.
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Table 2 Langmuir and Freundlich isotherm parameters (Shaking time 120 min, temperature 25 1 8C, volume 10 cm3, 25.0 mg of I/SiO2, II/SiO2, III/SiO2, metal ion concentration 10 mmol/dm3, pH 6.0). Surface
Metal
Langmuir isotherm qo
b
Freundlich isotherm R2
n
KF
R2
I/SiO2
Co(II) Ni(II)
0.082 0.066
542.00 425.99
0.9819 0.9883
1.50 1.72
1.02 1.11
0.9979 0.9926
II/SiO2
Co(II) Ni(II)
0.095 0.062
343.40 481.42
0.9447 0.9676
1.32 1.80
4.25 0.92
0.9941 0.9901
III/SiO2
Co(II) Ni(II)
0.143 0.073
502.00 1180.9
0.9977 0.9947
1.33 2.33
8.48 0.74
0.9967 0.9936
sorption capacity and represents the strength of the absorptive bond and n is the heterogeneity factor which represents the bond distribution. In the Langmuir isotherm, the plot of Ce/qe versus Ce for the sorption gives a straight line of slope 1/b qo and intercepts 1/ qo. In the Freundlich isotherm, the plot of the ln qe versus ln Ce gives a straight line and KF and n values can be calculated from the intercept and slope of this straight line. The fit of a model to the experimental data are usually evaluated in terms of linear regression analysis where R2 value is used as an indication for the benefit of model fit [29]. On the comparison of the R2 values, we can conclude that in all cases for the sorption of metal ions to the modificated silica gel surfaces Freundlich equation represents a better fit to the experimental data than Langmuir equation for I/ SiO2 and II/SiO2 (Table 2). This result predicts the heterogenty of the sorption sites on these surfaces. But, sorption on III/SiO2 surfaces can be expressed with both Langmuir and Freundlich type sorption isotherms. The Langmuir isotherm is based on the assumption of monolayer adsorption on a homogenous surface. The metal sorption on the modified silica gel surface may occur on both homogeneous surface and heterogeneous surfaces. The results showed that sorption capacity of these metal ions probably differ due to their size, degree of hydration and the value of their binding constant with the sorbent. 4. Conclusion The present investigation was discussed the preparation and use of Schiff base modified silica gel. This study showed that Schiff bases bonded covalently onto silica gel and the new surfaces were acquired. The resulting organic covalently modified silica gel chelating sorbent (I/SiO2, II/SiO2 and III/SiO2) were used for sorption and spectrometric determination of two metals in aqueous solutions. Sorption capacities of obtained silica gel structures were determined generally III/SiO2 > I/SiO2 > II/SiO2. Metal sorption of III/SiO2 was detected more than other modified silica gels due to III bonded covalently from two functional terminals onto silica gel and metal sorption of I/SiO2 was detected more than II/SiO2 due to suitable functional group (OH) for the composition of complexes. The II and III ligands were tested whether or not they are able to adsorb the metals. The complex formation studies (Section 2.6) showed that the II and III compounds did not adsorbed the metals. But after the immobilization, they adsorbed the metals given under Figs. 7–10. These silica structures (I/SiO2, II/SiO2, III/SiO2) can be used in order to remove this metal ions from contaminated or waste water which is an effective and inexpensive material These silica structures (I/SiO2, II/SiO2, III/SiO2) can be used as effective, lower cost material for the removal of this metal ions from contaminated or waste water. In addition to the modified silica gels will study in subsequent applications the possibility of ascendant properties such as
Fig. 7. Langmuir isotherm curves of Co(II) sorption on I/SiO2, II/SiO2 and III/SiO2 surfaces.
Fig. 8. Freundlich isotherm curves of Co(II) sorption on I/SiO2, II/SiO2 and III/SiO2 surfaces.
Fig. 9. Langmuir isotherm curves of Ni(II) sorption on I/SiO2, II/SiO2 and III/SiO2 surfaces.
Fig. 10. Freundlich isotherm curves of Ni(II) sorption on I/SiO2, II/SiO2 and III/SiO2 surfaces.
antimicrobial, antibacterial and antifungal of Schiff bases to be taken into account. Acknowledgments The authors are grateful for the financial support provided by Selcuk University Research Foundation (SUBAP) under projects FBE 2007, 08201031. References [1] A.A. Mozeto, W.F. Jardim, A Qumıca ambiental no Brasil, Quim. Nova. 25 (2002) 7– 11.
A.N. Kursunlu et al. / Applied Surface Science 255 (2009) 8798–8803 [2] A.G.S. Prado, J.A.A. Sales, R.M. Carvalho, J.C. Rubim, C. Airoldi, Immobilization of 5amino-1,3,4-thiadiazole-thiol onto silica gel surface by heterogeneous and homogeneous routes, J. Non-Cryst. Solids 323 (2004) 61–67. [3] B. Lee, Y. Kim, H. Lee, J. Yi, Synthesis of functionalized porous silicas via templating method as heavy metal ion adsorbent; the introduction of surface hydrophlicity onto the surface of adsorbents, Microporous Mesoporous Mater. 50 (2001) 77–90. [4] J.S. Kim, J. Yi, Selective removal of copper ions from aqueous solutions using modified silica beads impregnated with LIX 84, J. Chem. Technol. Biotechnol. 74 (1999) 544–550. [5] J.S. Kim, J. Yi, The removal of copper ions from aqueous solutions using silica supports immobilized with 2-hydroxy-5-nonylacetophenoneoxime, Sep. Sci. Technol. 34 (1999) 2957–2971. [6] L.N.H. Arakaki, C. Airoldi, Ethylenimine in the synthetic routes of a new silylating agent: chelating ability of nitrogen and sulfur donor atoms after anchoring onto the surface of silica gel, 19 Polyhedron (2000) 367–373. [7] M. Salavati-Niasari, M. Bazarganipour, Covalent functionalization of multi-wall carbon nanotubes (MWNTs) by nickel(II) Schiff-base complex: synthesis, characterization and liquid phase oxidation of phenol with hydrogen peroxide, Appl. Surf. Sci. 255 (2008) 2963–2970. [8] L.N.H. Arakaki, C. Airoldi, O relevante papel do agente sililante na modificac¸ao de superficies de polimeros, Quim. Nova. 22 (1999) 246–253. [9] A. Goswami, A.K. Singh, Silica gel functionalized with resacetophenone: synthesis of a new chelating matrix and its application as metal ion collector for their flame atomic absorption spectrometric determination, Anal. Chim. Acta 454 (2002) 229–240. [10] P.M. Padilha, L.A.de.M. Gomes, C.C.F. Padilha, J.C. Moreira, N.L. Dias Filho, Determination of metal ions in natural waters by flame-AAS after preconcentration on 5amino-1,3,4-thiadiazole-2-thiol modified silica gel, Anal. Lett. 32 (1999) 1807–1820. [11] J.G.P. Espinola, S.F. Oliveira, W.E.S. Lemus, A.G. Souza, C. Airoldi, J.C.A. Moreira, Chemisorption of Cu-II and Co-II chlorides and beta-diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane, Colloids Surf. A 166 (1–3) (2000) 45–50. [12] K.M.R. Kallury, W.E. Lee, M. Thompson, Enhanced stability of urease immobilized onto phospholipid covalently bound to silica, tungsten, and fluoropolymer surfaces, Anal. Chem. 65 (1993) 2459–2467. [13] G. Ozyilmaz, The effect of spacer arm on hydrolytic and synthetic activity of Candida rugosa lipase immobilized on silica gel, J. Mol. Catal. B-Enzym. 56 (2009) 231–236. [14] J.H. Clark, D.J. Macquiarrie, Catalysis of liquid phase organic reactions using chemically modified mesoporous inorganic solids, Chem. Commun. 8 (1998) 853–860. [15] P.K. Jal, S. Patel, B.K. Mishra, Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions, Talanta 62 (2004) 1005–1028.
8803
[16] X. Chang, Z. Li, Y. Cui, X. Zhu, Z. Zang, Silica gel-immobilized-vanillin derivatives as selective solid-phase extractants for determination of chromium (III) in environmental samples by ICP-OES, Microchem. J. 90 (2008) 71–76. [17] R. Qu, M. Wang, C. Sun, Y. Zhang, C. Ji, H. Chen, Y. Meng, P. Yin, Chemical modification of silica-gel with hydroxyl- or amino-terminated polyamine for adsorption of Au(III), Appl. Surf. Sci. 255 (2008) 3361–3370. [18] I. Hatay, R. Gup, M. Erso¨z, Silica gel functionalized with 4-phenylacetophynone 4aminobenzoylhydrazone: synthesis of a new chelating matrix and its application as metal ion collector, J. Hazard. Mater. 150 (2008) 546–553. [19] V.L.S.A. Filha, A.F. Wanderley, de Sousa S K.S., J.G.P. Espinola, M.G. da Fonseca, T. Arakaki, L.N.H. Arakaki, Thermodynamic properties of divalent cations complexed by ethylenesulfide immobilized on silica gel, Colloids Surf. A 279 (2006) 64–68. [20] I.H. Gu¨bbu¨k, R. Gu¨p, M. Erso¨z, Synthesis, characterization, and sorption properties of silica gel-immobilized Schiff base derivative, J. Colloid Interface Sci. 320 (2008) 376–382. [21] B. Gao, S. He, J. Guo, R. Wang, Immobilization of antioxidant on nanosilica and the antioxidative behavior in low density polyethylene, Mater. Lett. 61 (2007) 877– 883. [22] L.N.H. Arakaki, J.G.P. Espinola, S.F. Oliveira, J.M.P. Freitas, A.G. Gouveia, C. Airoldi, Chemisorption of Cu(II) chloride and nitrate in aqueous and non-aqueous solutions on matrix containing ethylenimine anchored on thiol modified silica gel surface, Colloid Surf. A 203 (2002) 129–136. [23] A.G.S. Prado, J.A.A. Sales, C. Airoldi, The increased termal stability associated with humic acid anchored onto silica gel, J. Therm. Anal. Calorim. 70 (2002) 191–197. [24] A.G.S. Prado, C. Airoldi, The pesticide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (Diuron) immobilized on silica gel surface, J. Colloid Interface Sci. 236 (2001) 161– 165. [25] C. Airoldi, L.N.H. Arakaki, Immobilization of ethylenesulfide on silica surface through sol–gel process and some thermodynamic data of divalent cation interactions, Polyhedron 20 (2001) 929–936. [26] E. Bascetin, H. Haznedarog˘lu, A.Y. Erkol, The adsorption behavior of cesium on silica gel, Appl. Radiat. Isot. 59 (2003) 5–9. [27] J.A.A. Sales, F.P. Faria, A.G.S. Prado, C. Airoldi, Attachment of 2-aminomethylpyridine molecule onto grafted silica gel surface and its ability in chelating cations, Polyhedron 23 (2004) 719–725. [28] V.D. Chaube, S. Shylesh, A.P. Singh, Synthesis, characterization and catalytic activity of Mn(III)- and Co(II)-salen complexes immobilized mesoporous alumina, J. Mol. Catal. A: Chem. 241 (2005) 79–87. [29] A. Ayar, O. Gezici, M. Kucukosmanoglu, Adsorptive removal of methylene blue and methyl orange from aqueous media by carboxylated diaminoethane sporopollenin: on the usability of an aminocarboxilic acid functionality-bearing solidstationary phase in column techniques, J. Hazard. Mater. 146 (2007) 186–193.
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Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Chemical modification of silica gel with synthesized new Schiff base derivatives and sorption studies of cobalt (II) and nickel (II) Ahmed Nuri Kursunlu *, Ersin Guler, Hakan Dumrul, Ozcan Kocyigit, Ilkay Hilal Gubbuk Department of Chemistry, Selcuk University, Campus, 42075, Konya, Turkey
A R T I C L E I N F O
A B S T R A C T
Article history: Received 15 April 2009 Received in revised form 3 June 2009 Accepted 11 June 2009 Available online 21 June 2009
In this study, three Schiff base ligands and their complexes were synthesized and characterized by infrared spectroscopy (IR), thermogravimetric analyses (TGA), nuclear magnetic resonance (NMR), elemental analysis and magnetic susceptibility apparatuses. Silica gel was respectively modified with Schiff base derivatives, (E)-2-[(2-chloroethylimino)methyl]phenol, (E)-4-[(2-chloroethylimino)methyl]phenol and N,N0 -[1,4-phenilendi(E)methylidene]bis(2-chloroethanamine), after silanization of silica gel by (3-aminopropyl)trimethoxysilane (APTS) by using a suitable method. Characterization of the surface modification was also performed with IR, TGA and elemental analysis. The immobilized surfaces were used for Co(II) and Ni(II) sorption from aqueous solutions and values of sorption were detected by atomic absorption spectrometer (AAS). ß 2009 Elsevier B.V. All rights reserved.
Keywords: Schiff base Synthesis Sorption isotherm Modification
1. Introduction In recent years, increasing pressure from environmental authorities forced the establishment of discharge limits, which in turn, require an effective use of decontamination and purification methods [1]. Thus, the removal processes of heavy metals from natural waters and solvents contaminated by heavy metal ions are attractive for environment [2]. A series of approaches can be applied to metal ion removal from waters, based on precipitation, exchange resins, membrane filtration and adsorbing methods [3–5]. There are extensive reports on immobilization of modifiers like chelate forming organic reagents, polymers, metal salts, natural compounds and some microorganisms on solid matrices like ion-exchange resins, cellulose, fibers, activated carbon, sand, clay, zeolites, polymers, metal oxides and highly dispersed silica gel [6–8]. These materials have the ability to remove heavy metal ions selectively from aqueous media. Among a series of these important supports, silica gel presents a high thermal, chemical and mechanical stability [9] in metal ion preconcentration [10], ion exchange [11], biotechnology [12], catalysis [13], clean technology and particularly green chemistry for last two decades [14]. The scientific world achieved a new idea by using immobilization technique for nano structures [15,16]. In this technique, synthesized organic molecules containing the desired organic
* Corresponding author. Tel.: +90 332 223 2783. E-mail address: [email protected] (A.N. Kursunlu). 0169-4332/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2009.06.055
functional group are directly attached to the silica gel [17]. A number of previous studies have showed that silica substrates can be modified with ion-chelating organic compounds to remove metal ions from aqueous solutions [18]. Modification of the surface is mostly done by using an appropriate molecule designated as precursor silylating agent. After that, it is possible to immobilize new molecules, to increase the chain of the silylating agent with a variety of other organic functions even more active as chelating agents for many purposes [19]. Immobilization applications of Schiff bases onto silica gel are especially attractive for by lastest studies in scienctific world. Silica gel immobilized with Schiff bases can be used in order to remove some metals ions from aqueous solutions, because of being inexpensive, effective and an alternative sorbent [20]. This study was carried out at two basic steps. On the first step of the study, three Schiff base ligands containing chlorine group were synthesized and nickel (II)–cobalt (II) metal complexes were obtained. These Schiff base ligands were (E)-2-(2-chloropropylidenamino) phenol (I), (E)-4-[(2-chloroethylimino)methyl) phenol (II) and N,N0 -[1,4-phenilendi(E)methylidene]bis(2-chloroethanamine) (III). On the second step of the study, silica gel, which was activated with stock HCI, was modified by (3-aminopropyl)trimethoxysilane. Schiff base ligands which were synthesized on the first step of the study were immobilized chemically to modificated silica structure. Then modificated silica gels were studied for the sorption of nickel (II) and cobalt (II) ions in various concentrations by AAS.
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Fig. 1. Synthesis of I, II and III.
2. Materials and methods 2.1. Experimental Silica gel was provided from Merck (Darmstadt Co.) with particle sizes 0.063–0.200 nm and average pore diameter 6 nm as a sorbent material. Toluene (Merck) was distilled and dried. (3Aminopropyl)trimethoxysilane 98% (APTS, Merck) and cobalt and nickel (II) nitrates were also obtained from Merck. 2-Chloroethylamine hydrochloride salt (Sigma–Aldrich) was reacted with salicylaldehyde, 4-hydroxybenzaldehyde and terephtaldehyde (Fluka) according to method described in Section 2.2 (Fig. 1). 30.0 g raw silica gel in 150 cm3 of stock HCl (37%) was refluxed for 4 h at 100 8C for activation of silica gel particles. The activated silica gel was washed with distilled water and it was dried under vacuum for 24 h [21,22]. Silylant agent, (3-aminopropyl)trimethoxysilane, was used without purification. 2.2. Synthesis of I, II and III A 1:1 equimolar methanolic solution of 2-chloroethylamine hydrochloride (3.32 g, 20 mmol) and salicylaldehyde (20 mmol, 1.7 cm3) were mixed and gently heated for 30 min with constant stirring. Triethylamine (20 mmol, 2.8 cm3) was gradually added to this mixture to remove the hydrochloride salt of 2-chloro ethylamine. The obtained suspension was waited for 1 h in salt– ice bath. During this period, the yellow precipitate was formed. This precipitate washed with ethylacetate and the filtrate was evaporated under reduced pressure and dried in vacuum. The obtained yellowish residue was recrystalized from a mixture of hot ethanol and diethylether (1:2). 4-Hyroxybenzaldehyde was used for the compound II and terephthalaldehyde was used for the compound III according to above described procedure. For I: Yellow; m.p. 78–79 8C, yield: 78.25%, FT-IR(v, cm1): 1638 (C5 5N), 3461 (OH), 2869–2823 (CH2), 826 (Cl). 1H NMR (d, ppm) (DCCI3): 12.9 (s, OH), 7.4–7.1–7.0 (m, 4H, ArH), 8.4, (s, CH) 3.9–3.8 (m, CH2). Anal. calcd. C9H10NOCl: C 58.85, H 5.45, N 7.63; found: C
58.52, H 5.30, N 7.46. For II: Yellow-orange; m.p. 110 8C, yield: 71.25%. FT-IR(v, cm1): 1641 (C5 5N), 2963–2907, (CH2), 3453 (OH), 838 (Cl). 1H NMR (d, ppm) (D-CCI3): 9.8 (s, OH), 7.6–6.9 (m, 4H, ArH), 8.2 (s, CH), 3.7–3.8 (m, CH2). Anal. calcd. C9H10NOCl: C 58.85, H 5.45, N 7.63; found: C 58.52, H 5.38, N 7.40. For III; Brooken white; m.p. 138 8C, yield: 65.5%. FT-IR(v, cm1): 1638 (C5 5N), 2863–2840 (CH2), 830 (Cl). 1H NMR (d, ppm) (D-CCI3): 8.3(s, CH), 7.8 (m, 4H, ArH), 8.4 (m, CH), 3.9–3.8 (m, CH2). Anal. calcd. C18H14N2O2Cl2: C 60, H 3.89, N 7.78; found: C 59.70, H 3.78, N 7.65. 2.3. Modification of silica gel by (3-aminopropyl)trimethoxysilane The silica gel phase-bound amino derivative moiety was prepared from reaction with (3-aminopropyl)trimethoxysilane as silylation agent [23–25]. A sample of 10.0 g of activated silica gel was suspended in 50 cm3 of dry toluen and 10.66 mmol APTS was added to this suspension. The mixture was refluxed under dry nitrogen atmosphere for 72 h at 110 8C and the modified silica gel was filtered off, washed twice with toluen, and dried under vacuum at room temperature (Fig. 2). 2.4. Immobilization of (I), (II) and (III) onto silica gel A sample of 5.0 g modified silica gel and 0.8 g of I were added to 60 cm3 of dry toluen. The mixture was reacted under dry nitrogen atmosphere during 72 h [24] in a reflux system at 100 8C. After the solid phase was filtered, it was washed with toluene–ethanol (1:1) and dried under vacuum at 30 8C for 24 h. It was named as I/SiO2 [20]. Other Schiff base ligands, II and III, were immobilized onto modified silica gel according to above procedure and respectively named II/SiO2, III/SiO2 (Fig. 3). 2.5. Characterization Immobilization of Schiff base ligands (I, II and III) onto silica gel followed a sequence of three steps. On the first step Schiff bases were synthesized; as a second step the immobilization of APTS on silica gel was performed and a new surface was obtained (NH2
8800
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Fig. 2. Reaction for modification of silica gel with (3-aminopropyl)trimethoxysilane.
Fig. 3. Immobilization of I, II and III onto modified silica gel.
terminal) and in the final step; I–II–III which were synthesized on the first step of this study were immobilized onto NH2-terminated modificated silica structure. NMR spectra of I, II, III were obtained on a Varian, 400 MHz spectrometer at room temperature. IR spectrums were obtained in the 400–4000 cm1 range by Mattson-1000 FT-IR spectrometer. KBr pellets were used for solid samples. Elemental analysis was performed for silica structures by Truspec CN Elemental Analyzer. Magnetic measures of I were carried out by Sherwood Scientific Magnetic Susceptibility Balance. Amounts of metallic cation remaining in solution were determined by atomic absorption spectrometer, UNICAM Model 930 Flame AAS. TGA measurements were carried out on Setaram Setsys Evolution-1750 Thermogravimetric Analyzer for modified silica gel structures. 2.6. Studies of metal complex formation of Schiff base ligands (I, II and III) 0.367 g (2 mmol) I was solved in 15 cm3 methanol and the temperature of the solution was increased up to 45 8C. Then 2 mmol (0.580 g) nickel (II) nitrate hexahydrate salt was added to this solution. The decreased pH (3.0) of the solution by addition of metal salts was increased to 5.0–5.5 with 0.1 M KOH. The pH of the solution, which is decreased to 3.0 by added metal salts, was increased to 5.0–5.5 with 0.1 M KOH. Cobalt (II) complex was synthesized according to the procedure described above. Walnut green complex for Ni(II) and brown complex for cobalt (II) was obtained and it was entirely washed with ethanol.For Ni(II): Green; m.p. 168 8C, yield: 62.55%, FT-IR(v, cm1): 1615 (C5 5N), 3476 (OH), 2918–2959 (CH2), 780 (Cl). B.M. 2.98. For Co(II): Brown; m.p.172 8C, yield: 61.55%, FT-IR(v, cm1): 1611 (C5 5N), 3377 (OH), 2928–2966 (CH2), 788 (Cl). B.M. 3.85. II and III did not react with Co(II) and Ni(II) due to the nonexistence of suitable functional group. 2.7. Sorption studies of I/SiO2, II/SiO2, III/SiO2 for metal ions The sorption was performed with batch technique in an aqueous solution for divalent nickel and cobalt nitrates at 25 1 8C. 25.0 mg of modified silica structures were suspended in 10.0 cm3 of aqueous solution containing variable amounts of each cation in samples shaker vessel. For these sorption measurements,
different amounts of derived silica samples were suspended 10 cm3 of aqueous solution containing variable amounts of every one of cations, whose concentrations varied over the 10–30 mg/dm3 range in an orbital shaker thermostat for 4 h (optimum condition, at room temperature and pH 6.0) [20,26]. After equilibrium was established, the suspension was filtered and amounts of metallic cations remaining in solution were determined by AAS. The amount of metal ions sorbed by sorbents was calculated as show in below equation: q¼
ðC 0 CÞV W
(1)
where q is the amount of metal ion sorbed onto unit amount of the adsorbent (mmol/g), C0 and C are the concentrations of metal ions in the initial and equilibrium concentrations of the metal ions in aqueous phase (mmol/dm3), V is the volume of the aqueous phase (L), and W is the dry weight of the adsorbent (g). 3. Result and discussion 3.1. Characterization Carbon and nitrogen elemental analyses showed a clear consistency with the increasing amount of slylating agent on surface, as show in Table 1. This values showed that APTS, I, II and III were covalently bonded on activated SiO2. Results of elemental analyses of the raw silica gel, SiNH2, I/SiO2, II/SiO2, and III/SiO2 supported by IR spectrums (Fig. 4). The several peaks were observed in IR spectra such as (i) a band assigned to Si–O–Si stretching frequency for silanol groups at 807 cm1 and (ii) the intense band related to siloxane stretching of these groups at 1100 cm1 (iii) a broad band between 3453 and Table 1 Percentages (%) of carbon (C), and nitrogen (N), for the matrices SiO2, SiNH2 and I/ SiO2, II/SiO2, III/SiO2. Surface
Amount of sample (g)
Carbon (%)
Nitrogen (%)
SiO2 SiNH2 I/SiO2 II/SiO2 III/SiO2
0.1123 0.1019 0.1123 0.1455 0.1254
0 3.70 14.9 11.6 14.0
0 1.15 1.98 2.65 2.52
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Fig. 4. Activated and modified silica gel structures, SiO2, SiNH2, I/SiO2, II/SiO2, III/SiO2.
3200 cm1 [24], which is attributed to the presence of the O–H stretching frequency of silanol groups [9], (iv) two peaks between 2946–2923 cm1 assigned to –CH2, (v) the sharp peaks around 1615–1620 cm1, which is attributed to the presence of C5 5N bond of Schiff bases (for I/SiO2, II/SiO2 and III/SiO2). The results of IR spectra showed clearly that APTS, I, II and III were immobilized on silica surface. IR spectrums and elemental analysis results were supported by TGA values for characterizations of I/SiO2, II/SiO2 and III/SiO2. The activated silica gel presents a first mass loss stage of 1.52% from 47 to 107 8C, assigned to physically adsorbed water. A following stage of 2.56% is attributed to condensation of the silanols, to yield siloxane groups, resulting in water loss, from 397 to 807 8C [23]. Namely two distinct mass loss steps occurred in thermogravimetric curve of activated SiO2 [27]. On the contrary, the TGA/DTG spectrum of SiNH2 shows two steps of weight loss, one below 100 8C and the other in region of 340–380 8C [28]. On the other hand, four mass loss steps were observed in TGA curve for I/SiO2, three mass loss steps for II/SiO2 and III/SiO2. The first mass loss of 1.5% from 42 to 110 8C attributes to physically adsorbed water for I/SiO2. The second mass loss of 4.20% at 271 8C and third mass loss of 5.88% at 480 8C was attributed to decomposition of organic groups. As parallel, mass losses of 4.93% and 4.69% in TGA curves of II/SiO2 and III/SiO2 were indicated detaching of organic groups from silica surface. Final steps of decomposition (respectively mass loses of 11.95%, 7% and 7.05%)
Fig. 5. Thermogravimetric curves for I/SiO2, II/SiO2 and III/SiO2 structures.
were attribute to condensation of silanol groups, to yield siloxane groups, coming from water loss, from 590 to 900 8C (Fig. 5 and Fig. 6). 3.2. Sorption studies of modified silica gel structures under determined conditions In the sorption study, the effect of metal ion concentrations of Co(II) and Ni(II) metal ions on the sorption capacities were examined using the batch procedure. 25.0 mg of the sorbent was stirred with 10.0 cm3 of various concentrations of metal ions for 120 min. In order to evaluate the sorption characteristics of metal ions on the I/SiO2, II/SiO2 and III/SiO2, experimental data were fitted to the two well-known sorption isotherm models of Freundlich and Langmuir. The monolayer Langmuir and the empirical Freundlich isotherms are usually represented in the following linearised forms: Langmuir isotherm;
Ce Ce 1 ¼ þ qe qo qo b
Freundlich isotherm; lnqe ¼ lnK F þ
(2) 1 nlnC e
(3)
Where qe is the amount of solute sorbed on the surface of the sorbent (mmol/g), Ce is the equilibrium ion concentration in the solution (mmol/dm3), qo is the maximum surface density at monolayer coverage and b is the Langmuir adsorption constant (L/ mmol), KF is the Freundlich constant (mmol/g) which indicates the
Fig. 6. Derivative thermogravimetry curves for I/SiO2, II/SiO2 and III/SiO2 structures.
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Table 2 Langmuir and Freundlich isotherm parameters (Shaking time 120 min, temperature 25 1 8C, volume 10 cm3, 25.0 mg of I/SiO2, II/SiO2, III/SiO2, metal ion concentration 10 mmol/dm3, pH 6.0). Surface
Metal
Langmuir isotherm qo
b
Freundlich isotherm R2
n
KF
R2
I/SiO2
Co(II) Ni(II)
0.082 0.066
542.00 425.99
0.9819 0.9883
1.50 1.72
1.02 1.11
0.9979 0.9926
II/SiO2
Co(II) Ni(II)
0.095 0.062
343.40 481.42
0.9447 0.9676
1.32 1.80
4.25 0.92
0.9941 0.9901
III/SiO2
Co(II) Ni(II)
0.143 0.073
502.00 1180.9
0.9977 0.9947
1.33 2.33
8.48 0.74
0.9967 0.9936
sorption capacity and represents the strength of the absorptive bond and n is the heterogeneity factor which represents the bond distribution. In the Langmuir isotherm, the plot of Ce/qe versus Ce for the sorption gives a straight line of slope 1/b qo and intercepts 1/ qo. In the Freundlich isotherm, the plot of the ln qe versus ln Ce gives a straight line and KF and n values can be calculated from the intercept and slope of this straight line. The fit of a model to the experimental data are usually evaluated in terms of linear regression analysis where R2 value is used as an indication for the benefit of model fit [29]. On the comparison of the R2 values, we can conclude that in all cases for the sorption of metal ions to the modificated silica gel surfaces Freundlich equation represents a better fit to the experimental data than Langmuir equation for I/ SiO2 and II/SiO2 (Table 2). This result predicts the heterogenty of the sorption sites on these surfaces. But, sorption on III/SiO2 surfaces can be expressed with both Langmuir and Freundlich type sorption isotherms. The Langmuir isotherm is based on the assumption of monolayer adsorption on a homogenous surface. The metal sorption on the modified silica gel surface may occur on both homogeneous surface and heterogeneous surfaces. The results showed that sorption capacity of these metal ions probably differ due to their size, degree of hydration and the value of their binding constant with the sorbent. 4. Conclusion The present investigation was discussed the preparation and use of Schiff base modified silica gel. This study showed that Schiff bases bonded covalently onto silica gel and the new surfaces were acquired. The resulting organic covalently modified silica gel chelating sorbent (I/SiO2, II/SiO2 and III/SiO2) were used for sorption and spectrometric determination of two metals in aqueous solutions. Sorption capacities of obtained silica gel structures were determined generally III/SiO2 > I/SiO2 > II/SiO2. Metal sorption of III/SiO2 was detected more than other modified silica gels due to III bonded covalently from two functional terminals onto silica gel and metal sorption of I/SiO2 was detected more than II/SiO2 due to suitable functional group (OH) for the composition of complexes. The II and III ligands were tested whether or not they are able to adsorb the metals. The complex formation studies (Section 2.6) showed that the II and III compounds did not adsorbed the metals. But after the immobilization, they adsorbed the metals given under Figs. 7–10. These silica structures (I/SiO2, II/SiO2, III/SiO2) can be used in order to remove this metal ions from contaminated or waste water which is an effective and inexpensive material These silica structures (I/SiO2, II/SiO2, III/SiO2) can be used as effective, lower cost material for the removal of this metal ions from contaminated or waste water. In addition to the modified silica gels will study in subsequent applications the possibility of ascendant properties such as
Fig. 7. Langmuir isotherm curves of Co(II) sorption on I/SiO2, II/SiO2 and III/SiO2 surfaces.
Fig. 8. Freundlich isotherm curves of Co(II) sorption on I/SiO2, II/SiO2 and III/SiO2 surfaces.
Fig. 9. Langmuir isotherm curves of Ni(II) sorption on I/SiO2, II/SiO2 and III/SiO2 surfaces.
Fig. 10. Freundlich isotherm curves of Ni(II) sorption on I/SiO2, II/SiO2 and III/SiO2 surfaces.
antimicrobial, antibacterial and antifungal of Schiff bases to be taken into account. Acknowledgments The authors are grateful for the financial support provided by Selcuk University Research Foundation (SUBAP) under projects FBE 2007, 08201031. References [1] A.A. Mozeto, W.F. Jardim, A Qumıca ambiental no Brasil, Quim. Nova. 25 (2002) 7– 11.
A.N. Kursunlu et al. / Applied Surface Science 255 (2009) 8798–8803 [2] A.G.S. Prado, J.A.A. Sales, R.M. Carvalho, J.C. Rubim, C. Airoldi, Immobilization of 5amino-1,3,4-thiadiazole-thiol onto silica gel surface by heterogeneous and homogeneous routes, J. Non-Cryst. Solids 323 (2004) 61–67. [3] B. Lee, Y. Kim, H. Lee, J. Yi, Synthesis of functionalized porous silicas via templating method as heavy metal ion adsorbent; the introduction of surface hydrophlicity onto the surface of adsorbents, Microporous Mesoporous Mater. 50 (2001) 77–90. [4] J.S. Kim, J. Yi, Selective removal of copper ions from aqueous solutions using modified silica beads impregnated with LIX 84, J. Chem. Technol. Biotechnol. 74 (1999) 544–550. [5] J.S. Kim, J. Yi, The removal of copper ions from aqueous solutions using silica supports immobilized with 2-hydroxy-5-nonylacetophenoneoxime, Sep. Sci. Technol. 34 (1999) 2957–2971. [6] L.N.H. Arakaki, C. Airoldi, Ethylenimine in the synthetic routes of a new silylating agent: chelating ability of nitrogen and sulfur donor atoms after anchoring onto the surface of silica gel, 19 Polyhedron (2000) 367–373. [7] M. Salavati-Niasari, M. Bazarganipour, Covalent functionalization of multi-wall carbon nanotubes (MWNTs) by nickel(II) Schiff-base complex: synthesis, characterization and liquid phase oxidation of phenol with hydrogen peroxide, Appl. Surf. Sci. 255 (2008) 2963–2970. [8] L.N.H. Arakaki, C. Airoldi, O relevante papel do agente sililante na modificac¸ao de superficies de polimeros, Quim. Nova. 22 (1999) 246–253. [9] A. Goswami, A.K. Singh, Silica gel functionalized with resacetophenone: synthesis of a new chelating matrix and its application as metal ion collector for their flame atomic absorption spectrometric determination, Anal. Chim. Acta 454 (2002) 229–240. [10] P.M. Padilha, L.A.de.M. Gomes, C.C.F. Padilha, J.C. Moreira, N.L. Dias Filho, Determination of metal ions in natural waters by flame-AAS after preconcentration on 5amino-1,3,4-thiadiazole-2-thiol modified silica gel, Anal. Lett. 32 (1999) 1807–1820. [11] J.G.P. Espinola, S.F. Oliveira, W.E.S. Lemus, A.G. Souza, C. Airoldi, J.C.A. Moreira, Chemisorption of Cu-II and Co-II chlorides and beta-diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane, Colloids Surf. A 166 (1–3) (2000) 45–50. [12] K.M.R. Kallury, W.E. Lee, M. Thompson, Enhanced stability of urease immobilized onto phospholipid covalently bound to silica, tungsten, and fluoropolymer surfaces, Anal. Chem. 65 (1993) 2459–2467. [13] G. Ozyilmaz, The effect of spacer arm on hydrolytic and synthetic activity of Candida rugosa lipase immobilized on silica gel, J. Mol. Catal. B-Enzym. 56 (2009) 231–236. [14] J.H. Clark, D.J. Macquiarrie, Catalysis of liquid phase organic reactions using chemically modified mesoporous inorganic solids, Chem. Commun. 8 (1998) 853–860. [15] P.K. Jal, S. Patel, B.K. Mishra, Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions, Talanta 62 (2004) 1005–1028.
8803
[16] X. Chang, Z. Li, Y. Cui, X. Zhu, Z. Zang, Silica gel-immobilized-vanillin derivatives as selective solid-phase extractants for determination of chromium (III) in environmental samples by ICP-OES, Microchem. J. 90 (2008) 71–76. [17] R. Qu, M. Wang, C. Sun, Y. Zhang, C. Ji, H. Chen, Y. Meng, P. Yin, Chemical modification of silica-gel with hydroxyl- or amino-terminated polyamine for adsorption of Au(III), Appl. Surf. Sci. 255 (2008) 3361–3370. [18] I. Hatay, R. Gup, M. Erso¨z, Silica gel functionalized with 4-phenylacetophynone 4aminobenzoylhydrazone: synthesis of a new chelating matrix and its application as metal ion collector, J. Hazard. Mater. 150 (2008) 546–553. [19] V.L.S.A. Filha, A.F. Wanderley, de Sousa S K.S., J.G.P. Espinola, M.G. da Fonseca, T. Arakaki, L.N.H. Arakaki, Thermodynamic properties of divalent cations complexed by ethylenesulfide immobilized on silica gel, Colloids Surf. A 279 (2006) 64–68. [20] I.H. Gu¨bbu¨k, R. Gu¨p, M. Erso¨z, Synthesis, characterization, and sorption properties of silica gel-immobilized Schiff base derivative, J. Colloid Interface Sci. 320 (2008) 376–382. [21] B. Gao, S. He, J. Guo, R. Wang, Immobilization of antioxidant on nanosilica and the antioxidative behavior in low density polyethylene, Mater. Lett. 61 (2007) 877– 883. [22] L.N.H. Arakaki, J.G.P. Espinola, S.F. Oliveira, J.M.P. Freitas, A.G. Gouveia, C. Airoldi, Chemisorption of Cu(II) chloride and nitrate in aqueous and non-aqueous solutions on matrix containing ethylenimine anchored on thiol modified silica gel surface, Colloid Surf. A 203 (2002) 129–136. [23] A.G.S. Prado, J.A.A. Sales, C. Airoldi, The increased termal stability associated with humic acid anchored onto silica gel, J. Therm. Anal. Calorim. 70 (2002) 191–197. [24] A.G.S. Prado, C. Airoldi, The pesticide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (Diuron) immobilized on silica gel surface, J. Colloid Interface Sci. 236 (2001) 161– 165. [25] C. Airoldi, L.N.H. Arakaki, Immobilization of ethylenesulfide on silica surface through sol–gel process and some thermodynamic data of divalent cation interactions, Polyhedron 20 (2001) 929–936. [26] E. Bascetin, H. Haznedarog˘lu, A.Y. Erkol, The adsorption behavior of cesium on silica gel, Appl. Radiat. Isot. 59 (2003) 5–9. [27] J.A.A. Sales, F.P. Faria, A.G.S. Prado, C. Airoldi, Attachment of 2-aminomethylpyridine molecule onto grafted silica gel surface and its ability in chelating cations, Polyhedron 23 (2004) 719–725. [28] V.D. Chaube, S. Shylesh, A.P. Singh, Synthesis, characterization and catalytic activity of Mn(III)- and Co(II)-salen complexes immobilized mesoporous alumina, J. Mol. Catal. A: Chem. 241 (2005) 79–87. [29] A. Ayar, O. Gezici, M. Kucukosmanoglu, Adsorptive removal of methylene blue and methyl orange from aqueous media by carboxylated diaminoethane sporopollenin: on the usability of an aminocarboxilic acid functionality-bearing solidstationary phase in column techniques, J. Hazard. Mater. 146 (2007) 186–193.