Solvent‐Induced Cadmium(II) Metal‐Organic Frameworks with Adjustable Guest‐Evacuated Porosity: Application in the Controllable Assembly of MOF‐Derived Porous Carbon Materials for Supercapacitors

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.

Porous Carbon-Based Supercapacitors Directly Derived from Metal–Organic Frameworks

“…They also investigated the role of different solvents for Cd-MOF carbon precursors in the preparation of MOF-derived PCs [74]. Five different solvents (methanol, ethanol, isopropanol, DMF, NMP = N-methyl-2-pyrrolidone) were used to synthesize a series of new Cd-MOFs under the same mixed ligand system (bib and H 2 ipa = isophthalic acid).…”

Six Isomorphous Window‐Beam MOFs: Explore the Effects of Metal Ions on MOF‐Derived Carbon for Supercapacitors

“…We previously found that the capacitance of MOF-derived carbon is closely related to many factors from the MOF precursors,s uch as the organic ligand, solvent, and topological structure. [22][23][24] As the central node of the MOFs, the metal ion undoubtedly plays an important role in the capacitance of MOF-derived carbon, and deservesb es ystematically researched.…”

“…The series of isomorphous MOFs have been previously reported and synthesized by solvothermal reactions. [23,24] According to these reported methods, plenty of impurities will appear in the Teflonlined autoclave. In this work, we planned to use the series of MOFs as precursors to prepare MOF-derived carbon, so it is very important to collect al arge amount of pure MOF raw materials.…”

Frontispiece: Controllable Syntheses of MOF‐Derived Materials

“…To investigate this aspect, in our recent research, five new Cd-MOFsw ere prepared by solvothermalr eactions of Cd II ion with isophthalic acid and bib ligand under different solvent systemso fC H 3 OH, C 2 H 5 OH, (CH 3 ) 2 CHOH,D MF and N-methyl-2pyrrolidone( NMP), respectively ( Figure 6). [40] The solventn ot only behaves as the structure-directing agent for the self-assembly of Cd-MOFs, but also induces the different guest-evacuated porosity of MOFs,w hich was facilitated to perform as ystematical study on the effect of solvent. The porosity of MOFs could be employed as the template to produce the pore of carbon materials.T he resultss how that the specific surface area of MOF-derived carboni sc onsistent with the porosity of Cd-MOFs, and the latter is adjusted by the solvent.…”

“…The effect of solvent on the porosity of Cd-MOFs and specifics urface area of correspondingMOF-derived carbon. Reproducedw ith permission from reference [40]. Copyright 2017,Wiley-VCH. respectively.M oreover,t he addition of CTAB together with tris(hydroxymethyl)aminomethane( TRIS) brings about ac ooperative effect, which modulates the final morphology of ZIF-8 from cubic to octahedral, hexapods, burr puzzles and flowerlike shapes as the amount of TRIS increases.…”