The bonding properties of the as-prepared samples were verified by Fourier transform infrared (FTIR). Fig. S5 (Supporting information) shows the FTIR spectra of H
3BTC and the as-obtained materials. Similar spectra were observed for M1, M2, M3 and M4, demonstrating that they have the same bonding properties. Compared to H
3BTC, the disappearance of the C—OH absorption at 1278 cm
-1 for Co-doped MIL-96 indicates that the H
3BTC ligand is deprotonated and coordinates to the metal center. The structural characterization was further confirmed by powder X-ray diffraction (PXRD). The PXRD patterns of M1, M2, M3 and M4 are shown in
Fig. 1a. It can be seen that M1, M2, M3 and M4 show similar patterns to simulated MIL-96 [
34], indicating that the Co doping does not cause framework changes of MIL-96.
Fig. 1b shows the crystal structure of MIL-96. The effects of the four different cosolvents as modulators on the morphology and size of the materials were monitored by scanning electron microscopy (SEM). The SEM image shows that M1, obtained with TMAH as a cosolvent, has a hexagonal prism shape and an average diameter of about 4 μm (
Fig. 1c). M2, synthesized using DMA as a cosolvent, displays an icosahedron morphology with an average diameter of about 5 mm. However, some octadecahedron particles with an average size of about 3 μm were also observed under these conditions (
Fig. 1d). M3, obtained using DMF as a cosolvent, has a hexagonal spindle shape with a diameter of about 3 μm (
Fig. 1e). When TEA was used as a cosolvent, an elliposoid shape was obtained for M4 and its edges became smooth. In addition, its average diameter decreased to 300-400 nm (
Fig. 1f). Consequently, it can be seen that the alkaline reagent influence significant the morphology and size of the materials. As a cosolvent for dissolving H
3BTC, alkaline reagent can accelerate the deprotonation process of H
3BTC [
35] thus promoting the formation of MOFs; the different influence of the alkaline reagent on the deprotonation process of H
3BTC lead to different nucleation rates and crystal plane growth.