Materials Letters 65 (2011) 244–246

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Materials Letters

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A new synthetic procedure for ordered mesoporous γ-alumina using phthalic acid asan interfacial protector

Fei Huang a, Ying Zheng a,b,⁎, Yihong Xiao b, Yong Zheng b, Guohui Cai b, Kemei Wei b

a College of Chemistry and Materials Science, Fujian Normal University, Fuzhou, Fujian 350007, Chinab National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou, Fujian 350002, China

⁎ Corresponding author. College of Chemistry and MUniversity, Fuzhou, Fujian 350007, China. Fax: +86 591

E-mail address: zhn63200@163.com (Y. Zheng).

0167-577X/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.matlet.2010.10.014

a b s t r a c t

a r t i c l e i n f o

Article history:Received 28 June 2010Accepted 3 October 2010Available online 8 October 2010

Keywords:Sol–gel preparationOrdered alumina2D hexagonal symmetryPhthalic acidNanomaterials

Employing phthalic acid (PA) as an interfacial protector and P123 as a structure-directing agent, orderedmesoporous γ-alumina with 2D hexagonal symmetry was successfully synthesized through the sol–gelmethod. According to the results, the best molar ratio of PA/Al3+ to synthesize the ordered alumina is 0.25 andthe phthalic acid serves as an interfacial protector to protect the aluminum ions at the organic–inorganicinterface from being affected by chloride ions during the whole evaporation process. The resulting aluminapossesses a surface area of 431.98 m2/g and a pore volume of 0.42 cm3/g. After the alumina converted into theγ-alumina phase, the surface area is still 226.37 m2/g and has a pore volume of 0.31 cm3/g.

aterials Science, Fujian Normal83465376.

ll rights reserved.

© 2010 Elsevier B.V. All rights reserved.

1. Introduction

Since the first successful synthesis of thewell-ordered, periodicallyorganized mesoporous silica materials, efforts have been directedtoward extending the group of mesoporous materials to non-silicasystems. Mesoporous alumina, especially, is an interesting materialwith broad applicability as a support for various catalytically activephases [1], such as shape-selective catalysis [2]. Mesoporous aluminasupports with large surface areas, large pore volumes, narrow poresize and suitable surface acidic–basic properties often result infavorable enhancements in catalytic performance [3,4].

Usually, ordered mesoporous aluminas are obtained via a nano-castingmethodwith silica or carbonmaterials as hard templates, suchas SBA-15 [5] and KIT-6 [6]. However, the above synthetic proceduresrequire multiple steps and are time-consuming. Dip-coating proce-dure was also employed byWan et al. to prepare ordered mesoporousalumina with 2D hexagonal mesopores [7]. However, the surface areaof the calcined sample is only 182.4 m2/g. In addition to these, the sol–gel process with surfactants as structure-directing agents (SDAs) isanothermethod to prepare orderedmesoporous alumina. The orderedmesoporous alumina with 2D hexagonal symmetry using P123 asstructure-directing agents (SDAs) was first reported by Niesz et al. [8].However, the synthetic procedure required a strictly controlled agingcondition under N2 flow for several days. Some progress has beenrealized in avoiding the strict control of the aging condition [2,9,10]

and the present study is motivated by the desire to further inves-tigation in the synthesis of ordered mesoporous alumina.

In this paper, we report a new synthetic procedure using phthalicacid as an interfacial protector for the first time to produce orderedmesoporous alumina. Ordered mesoporous alumina with p6mmhexagonal symmetry is successfully obtained when the molar ratioof PA/Al3+ is 0.25, with P123 as the structure-directing agent. Theresulting alumina exhibits a large surface area of 431.68 m2/g and thesurface area still maintains 226.37 m2/g after calcination at 800 °C.

2. Experimental procedure

The chemicals used in this work are all AR grade. Generally, 1 g ofP123 (EO20PO70EO20, EO=ethylene oxide, PO=propylene oxide)was dissolved in 20 ml anhydrous ethanol, then 1.6 ml 35 wt.% HCl,different amounts of phthalic acid and 2.04 g aluminum isopropoxidewere added into the above solution with vigorous stirring. Themixture was covered with PE films and stirred vigorously for 5 h.Solvent evaporation was performed at 60 °C for 48 h in air withoutstirring. The resulting samples were calcined at 400 °C for 4 h witha heating rate of 1 °C min−1 and calcined at 800 °C for 1 h with aheating rate of 10 °C min−1.

Structural analysis of the obtained samples was carried out on aPhillips X'Pert SUPER powder X-ray diffractometer, Cu Ka radiation,k=1.5418 Å). Transmission electron microscopy (TEM) images wereobtained with a Tecnai G2 F20 S-TWIN transmission electron micro-scope at 200 kV. The Barrett–Joyner–Halenda (BJH) pore-size dis-tributions, Brunauer–Emmett–Teller (BET) surface area and total porevolume of the powders were examined via nitrogen adsorption ex-periments. Nitrogen adsorption isotherms of the purified samplewere

Fig. 1. The low-angle XRD patterns of samples [n(phthalic acid)/n(Al3+)]: a=0.05;b=0.15; c=0.25; and d=0.35.

Table 1Surface area (m2/g) of aluminas prepared with different amounts of phthalic acid.

n(phthalic acid)/n(Al3+) 400 °C 800 °C

0 293 1700.05 448 1560.15 459 1780.25 432 2270.35 403 188

Fig. 2. The wide-angle XRD patterns of alumina (PA/Al3+=0.25) calcined at differenttemperatures.

Fig. 3. TEM images (a): [110] orientation and (b): [001] orie

245F. Huang et al. / Materials Letters 65 (2011) 244–246

determined at −196 °C using nitrogen in a conventional volumetrictechnique by Quantachrome Nova 4200.

3. Results and discussion

Fig. 1 shows the low-angle X-ray diffraction (XRD) patterns ofcalcined sampleswith the addition of differentmolar ratios of PA/Al3+.For molar ratio of PA/Al3+ is 0.05, no diffraction reflection peak isobserved, which indicates that the obtained alumina is amorphous.When the molar ratio of PA/Al3+ is 0.15, a weak diffraction reflectionpeak appears around 1°, which is weaker than the sample whenthe molar ratio of PA/Al3+ is 0.25. According to the TEM observation,the above peak can be attributed to p6mm hexagonal symmetry[2,5,6,8,10]. However, no diffraction reflection can be observed whenthe molar ratio of PA/Al3+ is 0.35.

The BET surface areas of the calcined samples with the addition ofdifferentmolar ratios of PA/Al3+ are shown in Table 1. Comparedwiththe sample prepared without the addition of PA, the samples showhigher surface areas when the molar ratio of PA/Al3+ is in the rangeof 0.05–0.35. After being calcined at 800 °C, the surface area of thesample first increases when the molar ratio of PA/Al3+ increases from0.05 to 0.25, then decreases with further increasing the molar ratio ofPA/Al3+ to 0.35. Combined with the low-angle XRD dates (Fig. 1), it istherefore concluded that the best molar ratio of PA/Al3+ to synthesizeordered alumina is 0.25.

The wide-angle XRD patterns of calcined aluminas (PA/Al3+=0.25) are shown in Fig. 2. Calcination at 400 °C gives rise to themesostructure with an amorphous wall, and then the amorphouswall is converted to the γ-alumina phase [2,5,6,10–18] after furthertreatment at a temperature of 800 °C.

Fig. 3 presents the TEM micrographs of the sample (PA/Al3+=0.25) calcined at 400 °C. The alignment of cylindrical pores along the[110] direction and the highly ordered hexagonal arrangement ofpores along the [001] direction are observed, which indicates that themesostructure is p6mm hexagonal symmetry.

Fig. 4 shows the nitrogen adsorption–desorption isotherms andpore-size distribution curves for calcined aluminas. All samplesexhibit the typical type IV curves with H1-shaped hysteresis loops,suggesting their uniform mesopores. The surface area of the sampledecreases obviously from 431.98 m2/g to 303.86 m2/g with increasingthe calcined temperature from 400 °C to 600 °C. However, the porevolume is 0.42 cm3/g and 0.44 cm3/g after being calcined at 400 °Cand 600 °C. Combined with the nitrogen adsorption–desorption iso-therms (Fig. 4a), a plausible explanation is that the ordering degree ofthe mesostructure increases when the calcined temperature increasesfrom 400 °C to 600 °C.When the alumina transformed into γ-alumina,it still exhibits a surface area of 226.37 m2/g and a pore volume of

ntation of alumina (PA/Al3+=0.25) calcined at 400 °C.

Fig. 4. (a) Nitrogen isotherms and (b) pore-size distribution curves of alumina (PA/Al3+=0.25) calcined at different temperatures.

246 F. Huang et al. / Materials Letters 65 (2011) 244–246

0.31 cm3/g. The ordering degree of the mesostructure begins todecrease at this calcined temperature. There is a narrow pore-sizedistribution centered at 4.2 nm for all calcined aluminas.

Based on the above results, it can be seen that the phthalic acidplays an important role in the formation of the ordered mesostruc-ture. In our experiments, chloride ion can strongly coordinate withaluminum ions, and it might destroy the balance of the organic–inorganic interface and disturb the assembly process, leading to long-range disordered mesostructures [2,10]. We propose that the effect ofphthalic acid on the formation of the ordered mesostructure is thesame as citric acid [2] and salicylic acid [10]. Because of the existenceof o-carboxyl, the phthalic acid acts as a competitor against chlorideion, and can coordinate with aluminum ions. Meanwhile, phthalicacid can also interact with the block copolymers through hydrogenbonding and the van der Waals force. Through all these interactions,phthalic acid can protect the aluminum ions at the organic–inorganicinterface from being affected by chloride ions, which coordinate withaluminum ions through the whole evaporation process. According tothe low-angle XRD dates in Fig. 1, the ordered mesostructure can beobtained when the molar ratio of PA/Al3+ is in the range of 0.15–0.25,demonstrating that only appropriate chelation between PA and Al3+

can lead to an ordered assembly, which is similar to citric acid [2].

4. Conclusion

In summary, employing phthalic acid (PA) as the interfacial protectorand P123 as the structure-directing agent, a new synthetic procedurehas been developed to obtain ordered mesoporous γ-alumina. Theresulting alumina has a surface area of 431.98 m2/g and a pore volumeof 0.42 cm3/g. After calcination at 800 °C, the alumina transformed intoγ-alumina and the surface area and pore volume are still 226.37 m2/gand 0.31 cm3/g respectively. These aluminas with highly ordered

mesostructure andnarrowpore-size distribution are promising potentialmaterials in shape-selective catalysis.

Acknowledgements

The work was supported by the National Key Technology R&D Pro-gram (2007BEA08B01), the Joint Research Program of Fuzhou University(No: DH-548), and the Science Foundation of Fujian Education Depart-ment of China (No: JA10073).

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