Herein three novel cobalt metal-organic frameworks (Co-MOFs) with similar ingredients, [Co(bib)(o-bdc)] (1), [Co(bib)(m-bdc)] (2), and {[Co(bib)(p-bdc)(HO)](HO)} (3), have been synthesized from the reaction of cobalt nitrate with 1,4-bis(imidazol-1-yl)benzene (bib) and structure-related aromatic acids (1,2-benzenedicarboxylic acid = o-bdc, 1,3-benzenedicarboxylic acid = m-bdc, and 1,4-benzenedicarboxylic acid = p-bdc) by the solvothermal method. It is aimed to perform systematic research on the relationship among the conformation of benzoate acid, lattice dimension of Co-MOF, and pore diameter of MOF-derived carbon composite. Through the precursor strategy, Co-MOFs 1-3 have been utilized to synthesize porous cobalt@carbon nanotube composites (Co@CNTs). After the in situ gas-sulfurization, secondary composites CoS@CNTs were successfully obtained, which kept similar morphologies of corresponding Co@CNTs without destroying previous highly dispersed structures. Co-MOFs and two series of composites (Co@CNTs and CoS@CNTs) have been well characterized. Topology and Brunauer-Emmett-Teller analyses elucidate that the bdc ion could control the pore diameters of MOF-derived carbon composites by adjusting the lattice dimension of Co-MOFs. The systematic studies on electrochemical properties demonstrate that (p)-CoS@CNT possesses hierarchical morphology, moderate specific surface area, proper pore diameter distribution, and high graphitization, which lead to remarkable specific capacitances (839 F g at 5 mV s and 825 F g at 0.5 A g) in 2 M potassium hydroxide solution. In addition, the (p)-CoS@CNT electrode exhibits good electrochemical stability and still retains 82.9% of initial specific capacitance at the current density of 1 A g after 5000 cycles.

No abstract

In this work, five new cadmium metal-organic frameworks (Cd-MOFs 1-5) have been synthesized from solvothermal reactions of Cd(NO ) ⋅4 H O with isophthalic acid and 1,4-bis(imidazol-1-yl)-benzene under different solvent systems of CH OH, C H OH, (CH ) CHOH, DMF, and N-methyl-2-pyrrolidone (NMP), respectively. Cd-MOF 1 shows a 3D diamondoid framework with 1D rhombic and hexagonal channels, and the porosity is 12.9 %. Cd-MOF 2 exhibits a 2D (4,4) layer with a 1D parallelogram channel and porosity of 23.6 %. Cd-MOF 3 has an 8-connected dense network with the Schäfli symbol of [4 ⋅6 ] based on the Cd cluster. Cd-MOFs 4-5 are isomorphous, and display an absolutely double-bridging 2D (4,4) layer with 1D tetragonal channels and porosities of 29.2 and 28.2 %, which are occupied by DMF and NMP molecules, respectively. Followed by the calcination-thermolysis procedure, Cd-MOFs 1-5 are employed as precursors to prepare MOF-derived porous carbon materials (labeled as PC-me, PC-eth, PC-ipr, PC-dmf and PC-nmp), which have the BET specific surface area of 23, 51, 10, 122, and 96 m g , respectively. The results demonstrate that the specific surface area of PCs is tuned by the porosity of Cd-MOFs, where the later is highly dependent on the solvent. Thereby, the specific surface area of PCs could be adjusted by the solvent used in the synthese of MOF precusors. Significantly, PCs have been further activated by KOH to obtain activated carbon materials (APCs), which possess even higher specific surface area and larger porosity. After a series of characterization and electrochemical investigations, the APC-dmf electrode exhibits the best porous properties and largest specific capacitances (153 F g at 5 mV s and 156 F g at 0.5 Ag ). Meanwhile, the APC-dmf electrode shows excellent cycling stability (ca. 84.2 % after 5000 cycles at 1 Ag ), which can be applied as a suitable electrode material for supercapacitors.