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Publication Title | Synthesis of Modified Mesoporous Materials and Comparative Studies of Removal of Heavy Metal from Aqueous Solutions

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302 Ge P., et al.

(c) using bisilylating organic precursors that lead to meso- porous organo silicas.

The three methods have different advantages and disad-

vantages. Post-synthesis has the advantage of easily leading to the morphology destruction and the disadvantage of a low ratio of modified functional groups. Meanwhile, co- condensation, as we know, has a uniform distribution of functional groups inside the mesopore channels with a shortage of smaller pore size [33-34]. Using bisilylating organic precursors is rarely reported.

The mesoporous materials bearing such groups as thiol [35-37] and amino [38-40] often have been reported. However, reports about ureido-modified mesoporous mate- rials are scarce. Moreover, few reports have compared the ability of different templates the synthesize mesoporous binding ureido as adsorbents.

In this paper, rarely used A-1160 ((C2H5O)3SiC3H6NHCONH2, Mav=222.4, bearing ureido) as a binding group modified by mesoporous adsorbents were fabricated and the adsorp- tion character of different adsorbents binding ureido using various structure-directing agents (P123 and CTAB) were compared [41].

Experimental Procedures

Synthesis of Adsorbent A

The synthesis of adsorbent A was carried out according to [34] using cetyltrimethylammonium (CTAB) and tetram- ethylammonium hydroxide (TMAOH) as hybrid surfactant templates, and tetraethyl orthosilicate (TEOS, 98%, MAV=208.33) as the silica source. The typical synthesis process is as follows: 2.19 g CTAB was dissolved in 40 g dry ethanol at room temperature and stirred for 2 h. In the meantime, 2.22 g A-1160, 3.6 g TMAOH and 20 g dry ethanol were mixed and also stirred for 2 h. Then 6.6 g TEOS was slowly added into the mixed solution of the above two to obtain a gel (the molar composition of the mixture was 0.25 A-1160: 1TEOS: 0.188 CTAB: 0.309 TMAOH: 40.76 ethanol). After 1 h stirring, the result was transferred into a Petri dish for solvent evaporation. The product slurry was transferred inside a polypropylene bot- tle at 90oC for 3 d under static conditions. After filtration, it was then submitted to a continuous reflux run overnight in ethanol/HCl at 70oC to extract the surfactant templates. Then it was filtered, stirred with 1 mol/L NaHCO3 solution for 24h and washed with deionized water for neutralization. Finally, it was dried under vacuum.

Preparation of Adsorbent B

Preparation of adsorbent using a triblock copolymer

(Pluronic P123, EO20PO70EO20,Mav = 5800) was sim- ilar to that used in synthesis of adsorbent A with CTAB, except that 4 g P123 replaced 2.19 g CTAB, 0.4 g HCl and 3.6 g H2O replaced 3.6 g TMAOH.

Metal Ion Adsorption on the Functionalized Mesoporous Silica

Metal nitrates (analytical grade) were dissolved in deionized water in order to prepare the initial metal ion solution with different concentrations (1, 2, 10 mmol/l, respectively). In a typical run, approximately 50 mg of each mesoporous silica A, B, and 10 ml metal ion solution were placed in stoppered vials and subject to ultrasound for 25 min. at room temperature.

Effect of the pH

Metal nitrates (analytical grade) were dissolved in deionized water with a concentration of 1 mmol/l. The solu- tion was adjusted to desired pH levels ranging from 2 to 7. 10 ml of above solutions and approximately 50 mg adsor- bent B were placed in stoppered vials and subject to ultra- sound for 25 min. at room temperature. The resulting solu- tion was separated by a 0.45 μm Uniflo filter and the filtrate was analyzed using ICP/OES spectroscopy.

Metal Ion Competitive Adsorption

Ion competitive adsorption studies were performed by treating 10 mL of a mixed metal solution containing equimolar amounts (1 mmol/ L of Cu2+ + Co2+, Cu2+ +Ni2+ and Cu2+ + Zn2+ ions) with 50 mg of adsorbent B for 25 min. sonicating, at room temperature. The resulting solution was separated by a 0.45 μm Uniflo filter and the filtrate was ana- lyzed using ICP/OES spectroscopy.

Results and Discussion

Solid-State NMR Spectra

The successful grafting of the functional groups on mesoporous MCM-41 can be proven by the solid-state NMR spectra.

Fig. 1 depicts the 13C CP-MAS NMR spectra of MCM- 41 with ureido using CTAB and P123 as directing agent, respectively ((a) and (b)). The 13C CP-MAS NMR spectrum of ureido-grafted MCM-41 using CTAB as agent shows 7 peaks at chemical shifts at 9 ppm, 15 ppm, 23 ppm, 33 ppm, 43 ppm, 57 ppm, and 161 ppm. The three carbon atoms related to the ligand ring, numbered 3, 4, and 5, give signals at 9 ppm, 15 ppm, and 33 ppm, respectively. The signal due to methylene 2 of the ethoxy group appears at 57 ppm and the signal of the methyl group at 23 ppm. The aro- matic carbon labeled 6 is assigned to the signal at 161 ppm. Finally, the signal due to the methyl in the heterocycle num- bered 7 appears at 43 ppm. These results provide evidence that the preparation of the new material was successful.

The solid-state 29Si MAS-NMR spectra for both ((a) and (b)) confirm the covalent bond formed between the silylating and the silanol groups dispersed on the MCM-41 surface (Fig. 2). Unmodified groups show two main peaks

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