A Composite Fe–V/g-C N for Liquid-Phase Selective Oxidation of Methanol with O Oxidant
3
4
2
were depicted in Fig. 1. The strong peaks at 2θ = 27.5
and 13.1° indexed to (002) and (100) diꢂraction planes
oꢀ the graphite-like carbon nitride (g-C N ) [16] were
calcined temperature. It was clearly that the composites
Fe–V/g-C N -550 and Fe–V/g-C N -600 were composed
3
4
3
4
oꢀ three crystallizes, FeVO , V O and g-C N with the
3
4
4
2
5
3
4
observed (Fig. 1a). The peak at 2θ = 13.1° could be
ascribed to an in-plane structure motiꢀ, such as the hole
to hole distance oꢀ tri-s-triazine units, while the peak
at 2θ = 27.5° was derived ꢀrom the stacked interlayers
oꢀ g-C N [17]. When Fe and V elements were incor-
molar ratio oꢀ FeVO :V O :g-C N estimated to be ≈
4 2 5 3 4
1.6:1:1 (5.73:3.46:3.57 mmol) ꢀor the Fe–V/g-C N -550
3
4
sample by the contents oꢀ Fe: 19.8% and V: 24.3% in the
composite. The determined contents oꢀ Fe and V elements
by ICP-MS indicated that the amount oꢀ the precursor
g-C N was obviously reduced ꢀrom 2.0 to 0.33 g dur-
3
4
porated, the diꢂraction peaks at the (002) plane were
3
4
sharply decreased and shiꢀted ꢀor Fe–V/g-C N -400 and
ing the preparation oꢀ Fe–V/g-C N -550. This reduction
3
4
3
4
Fe–V/g-C N -450 (Fig. 1b, c), and almost disappeared
oꢀ g-C N amount was mainly attributed to the action oꢀ
3
4
3 4
ꢀ
or Fe–V/g-C N -500 (Fig. 1d). While, the diꢂraction
Fe species since this reduction was not ꢀound during the
preparation oꢀ VO /g-C N [14]. Usually, Fe(III) or Fe(II)
3
4
peaks at 13.1° related to the (100) plane were obviously
x
3
4
changed to be weaker and wider ꢀor Fe–V/g-C N -400,
was prone to coordinating to NH groups to ꢀorm Fe–NH
3
4
2
2
Fe–V/g-C N -450 and Fe–V/g-C N -500, implying that
complexes [18]. This interaction between Fe species and
3
4
3
4
the Fe and V species could reduce the crystalline degree
–NH in g-C N molecules greatly aꢂected crystallization
2
3
4
and shiꢀt diꢂraction peak oꢀ the g-C N via interacting
oꢀ g-C N , even caused its decomposition at high calcined
3
4
3
4
with its surꢀace ꢀunctional groups on in-plane structure
temperature. The ꢀormation progress oꢀ V O and FeVO
2 5 4
motiꢀ and the stacked interlayers oꢀ g-C N . Interestingly,
crystallizes ꢀor Fe–V/g-C N -550 and Fe–V/g-C N -600,
3
4
3
4
3
4
the sharp diꢂraction peaks at 2θ = 15.6°, 20.5°, 26.4°,
as well as the decrease in crystalline degree oꢀ Fe–V/g-
3
1.3°, 34.6° assigned to V O and at 16.9°, 25.3°, 27.8°
C N -400, Fe–V/g-C N -450 and Fe–V/g-C N -500 could
2 5
3
4
3
4
3
4
to FeVO crystallizes arose as the calcined temperature
be also observed in SEM images oꢀ these samples. As
4
elevated up to 550 and 600 °C (Fig. 1e, ꢀ) although the
shown in Fig. 2, g-C N presented laminated crystallizes
3
4
crystalline degree oꢀ Fe–V/g-C N -550 was higher than
(Fig. 2a) and a part oꢀ the laminated crystalline was broken
into some pieces when the Fe and V compounds intro-
duced. Moreover, these pieces grew in quantity as the cal-
cined temperature raised ꢀrom 400 to 500 °C (Fig. 2b–d).
Subsequently, the crystalline degree oꢀ the composite
materials Fe–V/g-C N -550 and Fe–V/g-C N -600 was
3
4
that oꢀ Fe–V/g-C N -600 (Fig. SI1). Meanwhile, the (002)
3
4
plane diꢂraction oꢀ g-C N again appeared at 2θ = 27.5°
3
4
ꢀ
or Fe–V/g-C N -550 and Fe–V/g-C N -600, accompa-
3 4 3 4
nied by stronger and wider peaks observed at 13.1° as
well. The stronger and wider peaks ꢀor the (100) plane
was also due to the strong interaction between Fe or V spe-
cies and the in-plane structure motiꢀ oꢀ g-C N at higher
3
4
3
4
heightened although the sheet-like crystalline remark-
ably aggregated, which was in agreement with the results
obtained by XRD patterns as shown in Fig. 1d, e.
3
4
For ꢀurther determining the surꢀace composition and
structure oꢀ the sample Fe–V/g-C N , the SEM–EDX was
3
4
used to detect the element composition by scanning six diꢀ-
ꢀ
erent areas, including large sheets and small ꢃakes or pieces
as shown in Fig. SI2. The presence oꢀ C, N, O, Fe and V
lines was conꢁrmed on all these areas, which suggested that
V O , FeVO and g-C N crystalline would be uniꢀormly
2
5
4
3
4
distributed on the Fe–V/g-C N -550 surꢀace, whether on the
3
4
small ꢃakes or big sheets even though they were too tiny
crystals to be observed by SEM. Also, the EDX elemental
mapping was applied to elucidate the scattering degree oꢀ
C, N, O, Fe and V elements on Fe–V/g-C N -550 surꢀace.
3
4
The mapping results as shown in Fig. 3 presented that the
distribution oꢀ C, N, O, Fe and V elements was very uniꢀorm
by highly-dispersed dots. Besides, TEM image oꢀ Fe–V/g-
C N -550 indicated that the composite material was com-
3
4
posed oꢀ aggregated globular particles with about 30–50 nm
and abundant pores on the surꢀace were clearly observed as
white dots (Fig. 4a). Further, a high-resolution TEM image
Fig. 1 XRD patterns oꢀ g-C N and Fe–V/g-C N -t at various cal-
3
3
4
4
3
3
4
4
cined temperatures. (a) g-C N , (b) Fe–V/g-C N -400, (c) Fe–V/g-
suggested that three lattice ꢀringes ꢀor V O , FeVO and
C N -450, (d) Fe–V/g-C N -500, (e) Fe–V/g-C N -550, and (ꢀ) Fe–
2
5
4
3
4
3
4
3
4
V/g-C N -600
g-C N crystalline particles were ꢀound with interplanar
3
4
3 4
1
3