Ordered Mesoporous Silica Materials Of Mcm-41 Type
ORDERED MESOPOROUS SILICA MATERIALS OF mcm-41 TYPE
A. Deryło-Marczewska, J. Goworek, R. Kusak
Faculty of Chemistry, Maria Curie-Sklodowska University,
Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland
e-mail:annad@hermes.umcs.lublin.pl
The synthesis of a new class of silicate materials of M41S type with uniform pores and large internal surface has stimulated considerable interest in their structure formation, mechanism and possible applications [1,2]. These materials were prepared using surfactant molecules as templates.
The most popular member of this class of materials is MCM-41 with long, hollow channels arranged in a hexagonal structure. Ordered mesoporous MCM-41 adsorbents are characterised by high specific surface area of up to 1500 m2/g and specific pore volume of 1.5 cm3/g. The use of quaternary ammonium surfactants as an organic template with various number of carbon atoms provide to obtain MCM-41 silicas of unform pores from 2 nm to about 15 nm.
In the present work two basic types of MCM-41 silicas were prepared at various conditions of synthesis using n-octadecyltrimethylammonium bromide (MCM-41(18)) and cetyl pyridinium chloride (MCM-41(16)) as templating surfactants [3]. The specific surface areas (SBET) and the total pore volumes (Vt) of investigated silicas were obtained from nitrogen isotherms at 77 K (Fig.1, Tab. 1). The values of parameters characterising mesoporous structure of synthesised materials (the primary mesopore volume, Vp, and the external surface area, Sex) were estimated by applying the αs-method (Fig. 1, Tab. 1) [4]. The calculations of pore dimensions (D) (Table 1) and pore size distributions PSD follow the Barret, Joyner and Halenda (BJH) procedure.
Table1. Structural parameters of investigated MCM-41
Sample
SBET, m2/g
Sex, m2/g
Vt, cm3/g
Vp, cm3/g
D, nm
MCM-41(16)
1130
90
0.89
0.73
3.2
MCM-41(18)
1200
215
1.35
0.87
4.5
Figure1. The nitrogen adsorption/desorption isotherms (a=f(p/po)) and αs plots (a=f(αs)) on MCM-41(16) and MCM-41(18).
The main disadvantage of MCM-41 is that this silica is composed of loose microcrystalites and can be hardly applied as column packings for chromatographic separations. Thus, the attempts were undertaken to prepare combined silica compounds of small MCM-41(18) agglomerates deposited on silica gel particles (0.2 – 0.5 mm) for column chromatography. The adsorption properties of synthesised new silica sorbent were investigated using gas chromatography and compared with commercial mesoporous silica gel Si100. As the testing mixed samples the liquid mixtures of aliphatic and aromatic hydrocarbons were used. The results of chromatographic analysis on Si100/MCM-41 silica were compared with those on commercial silica gel Si-100.
References
1. C.T.Kresge, M.E.Leonowicz, W.J.Roth, J.C.Vartuli, J.S.Beck, Nature (1992)359.
2. J.S.Beck, J.C.Vartuli, W.J.Roth, M.Leonowicz, C.T.Kresge, K.D.Schmitt, C.T.W.Chu, D.H.Olson, E.E.Sheppard, S.B.McCullen, J.B.Higgins, J.L.Schlenker, Am. Chem.Soc. 114(1992)10834.
3. G.Grün, K.K.Unger, A.Matsumoto, K.Tsatsumi, in: B.McEnaney, (Ed), Adsorption and its application in environmental protection, Elsevier: Amsterdam, 1999, vol.2, p.659.
4. A.Sayari, P.Liu, M. Kruk, M.Jaroniec, Chem. Mater. 9(1997)2499.
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