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.