FIGURE 6 XRD patterns of the tubular MXene/SS membranes with different
electrophoresis time.
In this work, the MXene/SS2.5 membrane was chosen for
EDS characterization in order to confirm the element distribution. The
SEM image of a cross-section of the MXene/SS2.5 membrane
was shown in Figure 7A. Figure 7B-E represented the EDS images of C, Ti,
O, and F, respectively, indicating the uniform distribution of each
element. There was no obvious cross-sectional distribution in Figure 7B
because the electric conductive adhesive sticking to the MXene membrane
also contained C element. Subsequently, XPS and FTIR analysis of the
tubular MXene/SS membranes were performed to investigate the chemical
bonds in the membranes. As shown in Figure 8A, the MXene membrane was
primarily consisted of four elements (C, Ti, O, and F), while there were
no peaks belonging to Al element, indicating that it had been etched off
thoroughly in the MXene membrane, which was also consistent with the XRD
characterization results. A more detailed high-resolution XPS spectra
analysis of the four elements is shown in Figure 8B-E. Five different
chemical groups appeared in the spectrum of Ti element, namely Ti-C
(454.8 eV), Ti2+ (455.7 eV), Ti3+(456.5 eV), Ti-O (458.1 eV), and Ti-F (459.6 eV). It should be noted
that the chemical bond of Ti-O accounted for about 5.5% of the total Ti
element. That’s because the MXene nanosheets were prepared by chemical
etching, it was inevitable that a small amount of Ti atoms would be
oxidized.61,62 The high-resolution XPS spectra of O1s
could be resolved into four components as 529.4, 530.0, 531.3, and 532.5
eV, and their corresponding chemical bonds were O-Ti, O-Ti/OH, O-C/OH,
H2Oad, respectively. The C1s spectrum also consisted of
four sub-peaks, representing chemical bonds of C-Ti (281.7 eV), C-C
(284.7 eV), C-O(285.8 eV), and C-O=C/C-F (288.5 eV), which were
consistent with the literatures.63-65 The fitted
curves in the F1s spectrum correspond to two chemical bonds of F-Ti
(684.7 eV) and F-C (686.4 eV), respectively. In this work, the
functional groups that combined with oxygen on the surface of the
prepared membranes were further characterized to use FTIR. As shown in
Figure 8F, there were two stretching vibration peaks in the FTIR spectra
of the tubular MXene/SS membrane, which belonged to -OH at 3457
cm-1 and C=O at 1641 cm-1. -OH
denoted the -OH functional group on the membrane surface or the adsorbed
water between the interlayers, while C=O represented the terminal
functional groups at the edge of the MXene
nanosheets.49