G Model
CCLET 5756 No. of Pages 4
X. Chen et al. / Chinese Chemical Letters xxx (2019) xxx–xxx
3
3 4 3 4
Fig. 3. (a) Photographs and (b) UV–vis spectra of β-carotene degradation reactions with Fe O . (c) Photographs and (d) UV–vis spectra of or Se/Fe O .
Fe
Fe
3
O
O
4
, as the characterization peaks agreed well with the standard
(cubic phase) XRD pattern (Fig. 1e, JCPDS No. 89-0688) [42].
simple Fe
for 24 h (Fig. 3a), and the blue-shift in UV–vis spectra was weak
(Fig. 3b). In contrast, using Se/Fe as catalyst, the sample faded
3 4 2
O as catalyst, the sample did not fade after blowing O
3
4
The phenomenon was probably caused by the reduction conditions
of the selenization reaction, in which the selenization agent NaHSe
3 4
O
within 18 h (Fig. 3c), and an obivous blue-shift were observed in
and the excess NaBH
partial Fe to generate the stable Fe species after calcination.
The hypothesis was further confirmed by the X-ray photoelectron
4
were strong reductants and might reduced
UV–vis spectra, reflecting the destruction of C = C conjugation
3
+
3
O
4
system (Fig. 3d). The catalytic activity of Se/Fe
synergic effect of Se with Fe [40], and the Fe
by reducing Fe with NaBH or selenium powder showed poor
3
O
4
attributed to the
3 4
O catalyst prepared
spectroscopy (XPS) analysis, which showed that Se existed as the
2
O
3
4
ꢀ
2ꢁ
2+
low-valent Se and Se species, while Fe was formed by Fe
catalytic activity in β-carotene degradation.
3
+
(
64.7%) and Fe (35.3%) (Figs. S1 and S2 in Supporting informa-
Moreover, the gas chromatography-mass spectrometry
(GC ꢁꢁ MS) analysis demonstrated that in the oxidation reaction
2
ꢁ
ꢀ
tion). Se might exist in iron salt form (FeSe), while Se diffused in
the material. Strong reducibility of the selenization step led to
3 4
catalyzed by Se/Fe O , β-carotene decomposed into a variety of
2
+
much higher Fe ratio of the material (64.7%) than normal Fe
33.33%). The selenized material was marked as Se/Fe in the
following discussions.
3
O
4
fragments, such as the 2,2,6-trimethylcyclohexan-1-one (1), 2,6,6-
trimethylcyclohex-1-ene-1-carbaldehyde (2), (E)-4-(2,6,6-trime-
thylcyclohex-1-en-1-yl)but-3-en-2-one (3), etc. (Scheme 1, for
detailed mass spectra of the products, please see the Supporting
information). Compound 3 was the major product of the reaction
and it could be isolated in 62% yield. β-carotene was observed in
the GC ꢁꢁ MS spectra, showing that the chemical was completely
converted. These results attested that the fade of β-carotene was
caused by the complete C ꢁꢁ C scission leading to small molecules
other than the epoxidation or dihydrogelation reactions, which
might also destroy the conjugation system of color rendering [38].
(
3 4
O
Transmission electron microscope (TEM) image showed that
the material did not contain hollow structures (Fig. 2a), while its
electron diffraction pattern illustrated the existing of crystallines
(
Fig. 2b). High-resolution transmission electron microscope (HR-
TEM) image of the material reflected the primary {311} facet
exposure of Fe and the d(311) spacing was ca. 0.25 nm (Fig. 2c)
43]. Inductively coupled plasma mass spectrometry (ICP-MS)
3 4
O
[
analysis indicated that the weight content of Se in the material was
very low (ca. 0.17%). Elemental mapping analysis was performed to
confirm the constituent of the material and the results were
illustrated in Figs. 2d-g. First, high-angle annular dark field
scanning transmission electron microscope (HAADF-STEM) image
as Z-contrast image is highly sensitive to variations in the atomic
number of atoms in the sample, and the Z contrast intensity is
proportional to the square of the atomic number [44]. Therefore,
the bright area may attribute to the heavy elements in the HAADF-
3 4
The strong catalytic activity of Se/Fe O leading to the oxidative
C ꢁꢁ C scission might attribute to the synergistic effect of Se with Fe,
which has been reported by our group previously [40]. As a
3 4
magnetical mateiral, Se/Fe O was easily recovered and could be
reused for at least five times in β-carotene degradation.
3 4
STEM image of Se/Fe O (Fig. 2d). Elemental mapping images
shows that the material is majorly constituted by Fe and O (Fig. 2e
and f), while the dispersion of Se on the Fe-O frameworks is in
consistent with the bright area of the HAADF-STEM image (Figs. 2g
and d). The Se element was also detected to be dispersed out of the
major Fe-O frameworks for the existing of a few fragments in the
materials (Fig. 2g).
The material was then used as catalyst for polyene contam-
inants degradation and β-carotene was chosen as the model
sample for its bright color easy to judge. In a blank reaction using
Scheme 1. Detecting the β-carotene degradation products by GC–MS.