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A. Molinari et al. / Catalysis Today 161 (2011) 64–69
Table 1
BET specific surface areas and porosity details of pure and modified supports.
2
3
Samples
BET specific surface area (m /g)
BJH total porosity (cm /g)
BJH pore size (determined on maximum) (Å)
MCM-41
FeIIIP/MCM-41
SiO2
960
826
97
0.73
0.71
0.44
0.41
25
23
∼100
FeIIIP/SiO2
93
∼100
ted spectra were obtained by the Kubelka–Munk transformation
the support corresponds to ∼1% (w/w). The diffuse reflectance
2
III
III
(
F(R) = 1 − R /2R) versus the wavelength. N adsorption/desorption
UV–vis spectra of Fe P/MCM-41 and of Fe P/SiO indicate that the
2
2
experiments were carried out at 77 K by means of ASAP2020 instru-
ment (Micromeritics).
structure of the porphyrin remains unchanged during the immobi-
lization procedure (see Supplementary Data).
Adsorption experiments of the mono-alcohols (1-pentanol
The effect of porphyrin addition on specific surface area and
III
III
III
and 2-pentanol) were carried out suspending Fe P/MCM-41 or
porosity of Fe P/MCM-41 and of Fe P/SiO has been evalu-
2
III
Fe P/SiO (33 g/l) in 300 L of CH CN solutions containing increas-
ated by means of BET [21] and BJH [22] model applied to N2
adsorption/desorption isotherms carried out at 77 K. The results
summarized in Table 1 show that the specific surface area decreases
for both samples in the presence of the iron porphyrin, but
the change is much more relevant in the MCM-41 case. At the
same time, for both supports, the presence of the iron porphyrin
decreases the total porosity in a very limited extent.
2
3
ing concentrations of both alcohols and keeping in the dark for
0 min under magnetic stirring. The amounts of adsorbed alco-
2
hols were obtained by GC analysis evaluating their concentration
decrease in the solution. For sensitivity reason, we carried out these
experiments reducing the volume of alcoholic solution and increas-
ing the amount of solid sample in respect to the photocatalytic
experiments.
In order to evaluate better the modification of the samples
III
induced by the Fe -porphyrin presence, it is useful to examine
2
.3. Photocatalytic experiments
Figs. 1 and 2, which report the shape of the isotherms and the
curves relative to pore size distribution respectively. It appears
clearly that the MCM-41 sample presents a significant modification
due to the presence of porphyrin. More specifically, the isotherm
shape typical of a MCM-41 material (Fig. 1, solid-line curve) results
modified (Fig. 1, circle-symbol curve): the first capillary conden-
Photocatalytic experiments were carried out inside a closed
Pyrex tube of 15 ml capacity at 298 ± 1 K joined through an inlet
III
III
tube to a balloon filled with O . Fe P/MCM-41 or Fe P/SiO
2
2
(
4.5 g/l) was dispersed in 3 ml of a CH CN solution containing 1,4-
3
pentanediol (3% as volume percentage v/v) and stirred (120 min)
to reach equilibrium conditions before irradiation. Photochemical
excitation was performed irradiating the sample in the pyrex tube
with an external Helios Q400 Italquartz medium-pressure Hg lamp,
selecting wavelengths higher than 350 nm with a cut-off filter. The
photon flux, measured with a MACAM UV203X ultraviolet radiome-
ter, was 15 mW/cm . At the end of the photocatalytic experiment,
the sample was centrifuged, the products that remained adsorbed
on the irradiated powders were extracted with CH Cl2 (2 times
0
sation, typically narrow and present at p/p = 0.35 for unmodified
MCM sample, moves downwards and it is accompanied by another
not so evident capillary condensation (indicated in the figure by
0
an arrow) which covers up to p/p = 0.65, indicating a modification
in the very regular mesoporous structure of MCM sample. More-
over, the porphyrin-containing material shows a small hysteresis
loop associated to this capillary condensation (the hysteresis loop
2
0
is evidenced in the figure by an arrow and closes at p/p = 0.42, in
2
agreement with what expected for the tensile strength of N used as
2
with aliquots of 3 ml each), and the organic phases were analyzed
by GC. Products analyses were carried out by using a HP 6890 gas
chromatograph, equipped with a flame ionisation detector and a
DB-WAX capillary column. Quantitative analyses were performed
with calibration curves obtained with standard samples. Each
experiment was repeated three times in order to evaluate the error,
which remained in the ± 5% interval around mean values. Homo-
geneous reactions were carried out dissolving the iron porphyrin
adsorptive gas). This indicates a modification in the pore shape with
respect to what observed for unmodified MCM-41. In fact, the pres-
ence of a hysteresis loop is compatible with ink-bottle-like pores;
i.e., pores characterized by cavities with a small access. A last cap-
illary condensation (and corresponding hysteresis loop) is present
0
at very high values of relative pressure (p/p > 0.90), indicating the
possible presence of large mesoporosity, probably induced by inter-
particle spaces due to particle aggregation, but this feature seems
to be not affected by the presence of the porphyrin, so it will be not
considered anymore.
III
−5
(
Fe (1), 2 × 10 M) obtained through metallation of compound
(
1) of Scheme 1A in mixtures of CH CN and 1,4-pentanediol (3%,
3
v/v). Unfortunately, photocatalytic experiments were impossible
to carry out because of the formation of a precipitate involving the
iron porphyrin complex.
No analogous modification is evidenced by isotherms relative to
SiO samples with or without porphyrin (see Supplementary Data).
2
The curves are those typical of an almost not porous system (an
hysteresis loop is visible in the range of relative pressure 0.75–1 but
it is probably caused by particle aggregation, as mentioned above
for MCM samples) and no visible changes are induced by porphyrin
presence.
No oxidation products were obtained when blank experiments
were run in the dark or irradiating in the absence of photocatalyst.
Other experiments were carried out in order to test the stability
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of Fe P/MCM-41 system: after the first run the photocatalyst was
◦
recovered, washed with CH Cl2 and CH CN, dried at 80 C for 1 h
2
3
In order to confirm the consideration made above, the BJH
model has been applied to adsorption branch and the following
can be attained (compare Table 1 and Fig. 2). Total mesoporos-
and then reused in a new experiment. This procedure has been
repeated up to five cycles.
III
ity decreases slightly in the case of Fe P/MCM-41 compared to
3
. Results and discussion
unmodified MCM material, but the pore size changes in average
value and distribution, the pores formed in the presence of por-
phyrin being smaller and presenting a larger distribution. Again, no
3.1. Textural characterization
analogous modifications were evidenced in the case of SiO systems
(see Supplementary Data).
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III
In the Fe P/MCM-41 and Fe P/SiO prepared materials, the
2
iron porphyrin complex is covalently linked on the surface of the
support, as schematized in Scheme 1B. The loading of Fe P on
In conclusion, the morphological features of MCM-41 have
been clearly changed by porphyrin presence. The modification of
III