Metal-Directed Assembly of Five 4-Connected MOFs: One-Pot Syntheses of MOF-Derived MxSy@C Composites for Photocatalytic Degradation and Supercapacitors

In this work, a series of divalent metal ions (M = CoII, ZnII, CdII, NiII, and CuII) have been used to react with phthalic acid (H2pa) and 1,4-bis(imidazol-1-yl)benzene (bib) under proper solvethermal conditions, which afforded five metal–organic frameworks (MOFs) with the identical formula [M(pa)(bib)]∞, named Co-, Zn-, Cd-, Ni-, and Cu-MOF, respectively. Co-MOF and Zn-MOF are isoporphous, and present a diamondoid framework. Cd-MOF shows a distorted 2D (4,4) layer just like the herringbone. Ni-MOF and Cu-MOF are also isostructural, and illustrate a 3D CdSO4 net. These topologies are all based on the 4-connected node linked by the ligands pa2- and bib. It is the character of the metal ion that causes the structural diversity, which indicates that the metal ion plays an essential role in the self-assembly of MOFs. Furthermore, five well-dispersed MxSy@C composites have been successfully synthesized through the one-pot sulfurization of MOF precursors, which prevents the sintered phenomenon in the stepwise carbonization–sulfurization process. Interestingly, the metal species originating from the MOF precursor exerts a crucial effect on the preparation of MOF-derived material, such as the pore-effect of Zn and Cd vapor, and catalytic graphitization of Ni species. Significantly, the pure ZnS and CdS samples, obtained by getting rid of carbon from corresponding composites, show moderate photocatalytic activities for degradation of MB dye under the visible light irradiation. Meanwhile, the other three MxSy@C composites have been intensively investigated on the supercapacitive properties. Especially, the NiS2@C electrode exhibits outstanding specific capacitances (806 F g–1 at 5 mV s–1 and 833 F g–1 at 0.5 A g–1) in 2 M KOH aqueous solution. Moreover, the NiS2@C composite displays excellent long-term cycle, and can be applied as an electrode material in the supercapacitor.