Figure 4 . (a) XRD patterns of MnS/24PCNFs and (Zn,
Mn)S/24PCNFs. (b) Fitted XPS spectra S 2p in (Zn, Mn)S/24PCNFs. (c)
N2 adsorption-desorption curves and structural
parameters, TEM graphs of (d ,e) MnS/24PCNFs and (f, g) (Zn,
Mn)S/24PCNFs. (h) high revolution TEM graphs and lattice fringe
analyses, (i) elemental mapping graphs of elements Zn, Mn and S of (Zn,
Mn)S/24PCNFs.
Chemical compositions and states of elements in the desulfurized
sorbents MnS/24PCNFs and (Zn,
Mn)S/24PCNFs were characterized using XPS technology. As shown in
Figure. S17a, the desulfurization process introduced element S into
sorbents MnOx /24PCNFs and
Zn@MnOx /24PCNFs. High-resolution XPS spectra of
the S 2p in MnS/24PCNFs showed characteristic peaks at 161.90 and 163.11
eV, which could be derived from the bond of S-Mn-S, while the peaks at
163.73 and 164.91 eV were attributed to the bond Mn-S, implying that the
main sulfide products were manganese sulfides (Figure.
S18b).49-51 While for the XPS spectra of S 2p in
sorbent (Zn, Mn)S/24PCNFs, the peaks at 161.25, 162.44 eV and 163.70,
164.85 eV should be attributed to the bonds of Zn-S and Mn-S,
respectively.52 Besides, the proportion of bond Zn-S
was much higher than that belonged to MnS when referring to the
multiples fitting of the S 2p peaks (Figure. 4b). In addition, the
characteristic peaks belonged to SO42-may be the result of the adsorption of water by SO2generated from the oxidation of H2S.53Moreover, by comparing the O 1s spectra of
MnOx /24PCNFs and
Zn@MnOx /24PCNFs before and after desulfurization,
it was found that the relative content of Mn-O decreased, and the
fitting peak of Zn-O disappeared in the O 1s spectra of (Zn,
Mn)S/24PCNFs. These also indicate that desulfurization reaction is a
replacement process between O2- and
S2- (Figure. S17c-d).
Structural performance of desulfurized MnS/24PCNFs and (Zn, Mn)S/24PCNFs
has been investigated and represented in Figure. 4c and Table S2. The
pore volume and pore size increased from 0.140 cm3g-1, 7.957 nm of MnOx /24PCNFs
to 0.164 cm3 g-1, 12.621 nm of
MnS/24PCNFs, respectively, while the specific surface area decreased
from 70.280 m2 g-1 of
MnOx /24PCNFs to 52.119
m2g-1 of MnS/24PCNFs. By combining the TEM graphs of
sorbent MnOx /24PCNFs displayed in Figure. 4d and
e, it could be seen that the nanosized particles
MnOx transferred into MnS particles with diameter
about 8-12 nm, meaning that the pore structure of
MnOx /24PCNFs before and after desulfurization
changed obviously. The larger particle volume of the desulfurized
products generated new structures with larger pore size and reduced the
proportion of micro-pores that contributed a lot to the specific surface
area. In the contrast, opposite
trend in structural parameters of sorbents
Zn@MnOx /24PCNFs and (Zn, Mn)S/24PCNFs has been
observed. Specifically, the specific surface area and pore volume
increased of from 113.854 m2 g-1,
0.180 cm3 g-1 of
Zn@MnOx /24PCNFs to 198.300 m2g-1, 0.196 cm3 g-1of (Zn, Mn)S/24PCNFs, respectively (Table S2). The N2adsorption-desorption isotherm type (IV) and hysteresis ring type (H4)
of sorbent (Zn, Mn)S/24PCNFs were similar to that of
Zn@MnOx /24PCNFs, except for the sharp increasing
in the region 0 <P P0-1< 0.1, representing the existence of massive micro-pores
instead of macro- or meso-pores (Figure. 4c). The structural variations
between sorbents before and after desulfurization were mainly attributed
to the fact that O2- in manganese oxide was replaced
by S2- in H2S during desulfurization,
which increased the size of active components and thus blocked
meso-pores into micro-pores, and this is why the specific surface area
increased and pore size decreased from 6.336 to 3.949 nm in the
meantime.54 TEM analysis was also performed to observe
the morphology changes of (Zn, Mn)S/24PCNFs. The particle size of
desulfurization products was found to be in range of 9.1-23.0 nm, which
was increased as compared to that of fresh sorbent due to the fact that
the MnS and ZnS are much larger than MnOx and ZnO
in molecular size (Figure. 4f and g). High-resolution TEM images of (Zn,
Mn)S/24PCNFs in Figure. 4h implied the presence of zinc sulfide and
manganese sulfide according to the lattice fringes with spacing
distances of 0.3345 and 0.2964 nm, respectively. In addition, elemental
mapping graphs in Figure. 4i indicated the even distribution of the
elements Zn and Mn after desulfurization, meaning the high stability of
the as-prepared sorbent.
Furthermore, deconvoluted peaks of Mn 2p3/2 spectrum of
MnS/24PCNFs were resolved into three parts, namely 640.73 and 642.03 eV,
attributing to Mn2+ of MnS and MnO, respectively,
while the peak located at 645.32 eV could be attributed to
Mn4+ (Figure. S17e). However, the Mn
2p3/2 peak of used (Zn, Mn)S/24PCNFs was consisted of
four separated peaks (Figure. S17f), the difference from MnS/24PCNFs was
that the peak represented Mn4+ at 641.10 eV and the
peak located at binding energies of 644.87 corresponded to the shake-up
satellite. Moreover, as shown in Figure. S18g, the two peaks at binding
energies of 1021.51 and 1044.56 eV were consistent with
Zn2p3/2 and Zn2p1/2, respectively,
indicating the oxidation state of Zn was
Zn2+.55