Figure 2. Characterization of the as-prepared
MF@HPB-PPy10-OA. (a) Scanning electron microscope (SEM)
image of MF@HPB-PPy10-OA evaporator at low
magnification. Inset image is high-resolution SEM image of the
cross-section of MF@HPB-PPy10-OA skeleton, showing a
uniform wrapping of the
HPB-PPy10-OA coating
on the MF. (b) High-resolution transmission electron microscope (HR-TEM)
image of HPB-PPy10-OA nanosheets. (c) Energy dispersive
X-ray (EDX) elemental mapping results of
MF@HPB-PPy10-OA. (d-f) Water contact angle behavior of
MF@PPy10-OA, MF@HPB-PPy10-OA and
MF@HPB-PPy10. (g) High-resolution x-ray photoelectron
spectroscopy analysis of Mo-3d on HPB-PPy10-OA. (h)
Cyclic compressive stress-strain curves of
MF@HPB-PPy10-OA (at a set strain of 75 %) and the
digital photographs (inset).
obviously enhanced (Figure S3). Among them, the optimal
MF@HPB-PPy10-OA possesses a
water contact angle of about 106.0 ± 2o (Figure 2e),
corresponding to a HPB loading of about 31.6 wt% (calculated as a
percentage of Mo weight). In such materials, OA has a crucial influence
on the hydrophobic management of their surfaces. The OA-free
MF@HPB-PPy10 displays a strong hydrophilicity with a
contact angle of 78.0 ± 2o (Figure 2f). These results
demonstrate the significant contribution of HPB and OA in balancing and
optimizing the hydrophilic-hydrophobic interfaces of the composite
material. In addition, OA also serves the function of maintaining the
mechanical properties of the material. The compressive stress-strain
measurements (Figure 2g) demonstrate the excellent mechanical properties
of MF@HPB-PPy10-OA. After 50 cycles of compressive
stress-strain measurements (Figure 2g, top, inset), it still maintains
excellent and reversible elastic deformation. Moreover,
MF@HPB-PPy10-OA also exhibits good bendability,
twistability and tailoring properties. In contrast, the elastic
deformation of the OA-free MF@HPB-PPy10 fails to recover
after the compressive stress-strain measurements (Figure 2g, bottom,
inset). During the compressive stress-strain measurements, the
HPB-PPy10 coating on MF@HPB-PPy10 is
prone to peeling. To further confirm the composition of material, its
fourier transform infrared spectra (FTIR), X-ray powder diffraction
(XRD) and XPS are investigated. As shown in the FTIR (Figure S4b), the
characteristic absorption peaks of HPB (including νP-O:
1053.7 cm-1, νMo-O: 954.3
cm-1, νMo-O-Mo: 869.5
cm-1 and 770.8 cm-1) and PPy
(including νC=C: 1533.2 cm-1 and
νC-N: 1147.1 cm-1) and OA
(νC=O: 1703.2 cm-1,
νCH3: 2922.4 cm-1 and
νCH2: 2850.7 cm-1) all are exhibited
on MF@HPB-PPy10-OA, evidencing that the successful
assembly of HPB, PPy and OA on MF. A survey scan of
MF@HPB-PPy10-OA confirms the presence of these elements
(Figure S5), which is consistent with the results of EDX mapping (Figure
2c and Figure S2c). HR-XPS of the corresponding Mo-3d indicates that the
Mo3d3/2 and Mo3d5/2 at 235.3 eV and
232.2 eV are split into two sets of peaks 235.4/232.4 eV and 234.4/231.3
eV, respectively, which are referred to as Mo6+ and
Mo5+.[49,50] This reduced state
of Mo confirms the presence of HPB that is favorable for solar
absorption and photothermal conversion.