Adsorption (2013) 19:331–338
DOI 10.1007/s10450-012-9455-6
In situ SAXS investigation of dibromomethane adsorption
in ordered mesoporous silica
Evangelos P. Favvas · Konstantinos L. Stefanopoulos ·
Achilles Vairis · John W. Nolan · Karsten D. Joensen ·
Athanasios C. Mitropoulos
Received: 22 October 2012 / Accepted: 7 December 2012 / Published online: 3 January 2013
© Springer Science+Business Media New York 2012
Abstract A SAXS/WAXS apparatus with the aid of a spe-
cially designed sample cell capable for performing both
SAXS and WAXS experiments was used for adsorption
studies in nanoporous materials. The applicability of the in-
strument for structural investigations and its ability for ad-
sorption experiments because of the advanced sample envi-
ronment were demonstrated by carrying out in situ SAXS
measurements during gas physisorption. SAXS profiles of
ordered mesoporous silica were measured at selected equi-
librium points alongside a dibromomethane (CH
2
Br
2
) ad-
sorption isotherm at 293 K. SBA-15 was the adsorbent of
choice because it consists of a regular 2D hexagonal ar-
ray of cylindrical mesopores that gives rise to Bragg re-
flections in the small-angle regime. CH
2
Br
2
was selected
as a contrast-matching fluid because it has almost the same
electron density as silica. We obtained high-quality data
comparable to those resulting from experiments performed
in synchrotron light sources which produce intense beams
E.P. Favvas ( ) · K.L. Stefanopoulos
Institute of Physical Chemistry, NCSR Demokritos, Ag. Paraskevi
Attikis, 153 40, Athens, Greece
e-mail: favvas@chem.demokritos.gr
K.L. Stefanopoulos ( )
e-mail: stefan@chem.demokritos.gr
A. Vairis
Department of Mechanical Engineering, Crete Institute of
Technology, Estavromenos, Heraklion, 710 04, Greece
E.P. Favvas · J.W. Nolan · A.C. Mitropoulos
Department of Petroleum & Natural Gas Technology, Cavala
Institute of Technology, Ag. Loukas, 654 04, Cavala, Greece
K.D. Joensen
SAXSLAB ApS., Gl. Skovlundevej 54, 2740, Skovlunde,
Denmark
of x-rays and support advanced instrumentation for high-
resolution diffraction and SAXS studies. The Bragg peaks
of the pore lattice are clearly visible for the evacuated sam-
ple and at the early stages of the adsorption process. The in-
tensity decrease and the elimination of the Bragg peaks for
the saturated sample suggest that an almost perfect contrast
matching was achieved. A model has been used for monitor-
ing the fluid condensation and evaporation regime in SBA-
15 by taking into account both the Bragg scattering and the
diffuse scattering for spatially random pore filling. The re-
sults show the absence of spatial correlations between filled
pores suggesting random pore filling.
Keywords SAXS/WAXS · Adsorption cell · In situ ·
SBA-15 · Hysteresis loop · Condensation/evaporation
1 Introduction
Membranes, powders, catalysts and surfactants are some
materials with various applications in the chemical and
petrochemical industries. A common property of these ma-
terials is their porous structure, which is commonly pro-
duced by compaction, desiccation, aggregation, chemical
decomposition, etc. Adsorption measurements (Gregg and
Sing 1982), are abundantly used for the characterization
of porous solids by providing information on their struc-
tural properties such as surface area, pore volume, pore size
distribution, etc. Porous materials with ordered pore struc-
ture have received increasing interest because of their po-
tential application in the fields of electronics, photonics and
life sciences (Hoa et al. 2006). Further, characterization of
those materials resulted in a better understanding of the
adsorption mechanism because of their simple geometries
and their well-defined pore sizes (Thommes et al. 2006;