Morphology, structure and compositions analysis
The XRD patterns of the synthesized Cu-MOFs and ZIF-9(Co) are shown in
Figure S1(a, b), which are consistent with the results reported in the
literature [27, 28, 29]. After Cu-MOF and Co-MOFs are respectively
phosphated, Cu-P and Co-P samples can be obtained. After fully
phosphating ZIF-9,there exist typical diffraction peaks in 2θ = 31.60º,
35.18º, 36.34º, 46.19º, 48.18º, and 56.27º, as shown in Figure 2(a). The
analysis can be indexed to the JCPDS#65-1474 standard card of CoP. The
corresponding crystal planes are (011), (200), (111), (112), (211), and
(202). The weakening of the intensity of all the peaks of CoP indicates
relatively low degree of crystallization [30]. In the XRD pattern of
Cu-P (Figure 2(b)), the corresponding characteristic peaks of
Cu3P (JCPDS#74-1067) and Cu element (JCPDS#70-3038)
can be corresponded.
The
characteristic peaks of Cu3P appear at 28.43º, 35.86º,
38.90º, 41.38º, 44.91º, 46.02º, 47.08º, 53.30º, 56.74º, 58.14º, 66.34º
and 73.01°, corresponding to (111), (112), (022), (211), (300), (113),
(122), (104), (311), (222), (223), and (322) crystal planes. The obvious
diffraction peaks of (111) and (200) plane diffraction of elemental Cu
are located at 43.17° and 50.29°. Figure 2(c) shows the results of
Cu-Co-xP-2 (x = 1, 2, 3, 4.) composite catalysts obtained by phosphating
at different degrees. The outer layer of ZIF-9 was gradually
phosphorylated to produce diffraction peaks related to CoP. With the
increasing of phosphating degree in the composite samples, the content
of phosphide (Cu3P, CoP) gradually increases, and the
intensity of the related diffraction peaks gradually increases. Because
the crystallinity of the outer phosphide is relatively low, the related
diffraction peaks of the internal unphosphorized Cu-MOFs is enhanced.
The spectrums of Cu-Co-x (x = 1, 2, 3, 4) obtained by adjusting the mass
of nucleated Cu-MOFs and maintaining the quality of the outer layer
ZIF-9 are shown in Figure S1(c). There are both Cu-MOFs and ZIF-9 peaks,
and the diffraction peaks related to Cu-MOFs increase as the mass of
Cu-MOFs increases. Cu-Co-x (x = 1, 2, 3, 4) was phosphorylated to obtain
Cu-Co-2P-x (x = 1, 2, 3, 4.) composite catalyst (Figure 2(d)). With the
increasing of the mass of Cu-MOFs under the same phosphatization degree,
the diffraction peaks related to Cu-MOFs gradually decrease. Therefore,
the Cu-Co-2P-4 sample only contains the diffraction peaks of
Cu3P, Cu and CoP, and there are no peaks of MOFs.