A. Tarlani et al. / Journal of Solid State Chemistry 203 (2013) 255–259
257
2.6. Styrene oxide ring opening
In a typical reaction, SBA-15-NH
2
-TACTO2-Cr (0.005 g) was
added to the solution of styrene oxide (0.124 g, 1 mmol) in
methanol (5 mL). The mixture was stirred till full conversion. After
filtration through a short pad of alumina and evaporation, chro-
matography on silica eluted with petroleum ether/ethyl acetate
(
85:15) of the residue led to the product which was identified from
1
comparison of HNMR data with those of literature [22,23].
3
. Results and discussion
3.1. Catalyst characterization
Preparation of the catalyst is depicted in Scheme 1.
The FT-IR spectra of the samples in the range of 500–4000 cm
−
1
are depicted in Fig. 1. The main features of the SBA-15 spectra
include a large broad band between 3200 and 3600 cm− which is
attributed to O–H stretching νs,(OH) of the surface silanol group and
the remaining physically adsorbed water molecules. The strong
bands at about 1090 and 806 cm− correspond to the νas,(Si–O–Si)
and νs,(Si–O) respectively. Silanol groups of SBA-15 give the char-
1
1
−
1
acteristic band at 960 cm . This peak declines by the reaction of
silanol group with the ethoxy group of APTMS [24]. In the FT-IR
−
1
2
spectra of SBA-15-NH , the bands at 3298 and 2939 cm are
related to NH and CH stretchings respectively [25]. FT-IR spectra of
the immobilized ligand on the surface obtained after soxhelating
for 8 h. The only way of the grafting is the condensation between
amino group of SBA-15-NH
2
and the C¼O group of the ligand. Two
−1
ν
(C¼O) groups of the pure ligand appear at 1649 cm . By anchor-
ing the ligand, this bond shifts a little to lower frequency. It could
be concluded that one of the C¼O groups is replaced by the new
bond. In the last step, Cr (III) inserts into the N4 cycle because the
−
1
new band of Cr–N emerges at 424 cm . Besides, the bending band
of NH is shifted from 1581 to 1548 cm− which is in accordance
with the literature [26]. Such an effect should be observed for the
stretching of 3277 cm− , which is not clear because of the presence
of the wide band of the adsorbed water in that region. These
points indicate the coordination through N4 macrocycle.
1
1
Thermogravimetric analysis (TGA) of the samples showed the
lowest weight loss for bare SBA-15 with the approximate amount
of 5% which is mainly attributed to the loss of adsorbed water
(Fig. 2.). The TGA spectrum of functionalized SBA-15 and grafted
ligand showed 10% and 30% weight loss above 350 1C that is
attributed mainly to the decomposition of organic groups and
emphasizes the successful accomplishment of the process and
high loading of the ligand (about 37%) [27]. According to TG
analysis, nearly 1.45 and 0.93 mmol of amine groups and the
ligand is grafted on the surface respectively. It can be concluded
that 64% of the amine groups reacted with the macrocyclic ligand.
Fig. 3 represents low angle XRD patterns of SBA-15 and its
modified samples. SBA-15 shows intense diffraction peak of (100)
at 2θ¼0.991 and two secondary patterns corresponding to (110)
and (200) reflections about 2θ¼21 which are indicative of the
hexagonal symmetry and textural uniformity of the mesopore. The
Fig. 1. FT-IR spectra of the parent SBA-15, grafted amine into the pores(SBA-15-
NH
surface (SBA-15-NH
5-NH -TACTO -Cr).
2
), pure macrocyclic ligand before grafting (TACTO
2
), grafted ligand on the
2
-TACTO ) and chromium ion coordinated into the ligand (SBA-
2
1
2
2
with characteristic behavior of the mesoporous materials as
defined by IUPAC [28]. The sharp increase in the adsorption step
low-angle XRD patterns of SBA-15-NH
2
, SBA-15-NH
2
-TACTO2 and
between relative pressures (P/P
textural properties of SBA-15 is kept over grafting by macrocyclic
ligand with no significant change in N sorption isotherm [20]. The
relative pressure (P/P ) of the modified samples is shifted to a
lower value in comparison to the parent materials, indicating
decrease in specific surface area. BJH method showed narrow pore
diameter distributions which is in agreement with good quality of
SBA-15 [29].
0
) of 0.4–1 indicated that the
SBA-15-NH -TACTO2-Cr are similar to that of the parent SBA-15
2
with a reduction in the intensity indicating modifications inside
the mesopore (Scheme 1). By modification of the pores, intensity
of the peaks decreases and the sharp peak is shifted to higher
angles which indicates the decrease of the surface area [17].
Therefore, SBA-15 structure remained intact under the conditions
used for grafting.
2
0
The porosity of samples (BJH and BET) was measured by N
adsorption–desorption (Figs. 4 and 5). These isotherms are type IV
2
Table 1 provides characteristic parameters SBET and pore
diameter of the species. The SBA-15 has the maximum surface