Controllable Syntheses of MOF-Derived Materials.

Metal-organic frameworks (MOFs), as an important kind of porous inorganic-organic hybrid materials with inherent outstanding physicochemistry characteristics, can be widely applied as versatile precursors for the facile preparation of functional MOF-derived materials. However, there are plenty of sophisticated factors during the synthetic process, which is far from reaching the goal of effectively controlling the nature of MOF-derived materials (such as the composition, morphology and surface area). Therefore, it is urgently necessary to develop regular protocols and concepts for controllable syntheses of MOF-derived materials. In this minireview, we mainly summarize and analyze complicated factors in the fabrication of MOF-derived materials according to recently reported literatures, and this provides a new insight into the rational design and syntheses of MOF-derived materials.

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.

In this work, five new cadmium metal-organic frameworks (Cd-MOFs 1-5) have been synthesized from solvothermal reactions of Cd(NO3 )2 ⋅4 H2 O with isophthalic acid and 1,4-bis(imidazol-1-yl)-benzene under different solvent systems of CH3 OH, C2 H5 OH, (CH3 )2 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 [424 ⋅64 ] based on the Cd6 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 m2 g-1 , 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-1 at 5 mV s-1 and 156 F g-1 at 0.5 Ag-1 ). Meanwhile, the APC-dmf electrode shows excellent cycling stability (ca. 84.2 % after 5000 cycles at 1 Ag-1 ), which can be applied as a suitable electrode material for supercapacitors.

Benzoate Acid-Dependent Lattice Dimension of Co-MOFs and MOF-Derived CoS2@CNTs with Tunable Pore Diameters for Supercapacitors.

Herein three novel cobalt metal-organic frameworks (Co-MOFs) with similar ingredients, [Co(bib)(o-bdc)]∞ (1), [Co2(bib)2(m-bdc)2]∞ (2), and {[Co(bib)(p-bdc)(H2O)](H2O)0.5}∞ (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 CoS2@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 CoS2@CNTs) have been well characterized. Topology and Brunauer-Emmett-Teller analyses elucidate that the bdc2- 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)-CoS2@CNT possesses hierarchical morphology, moderate specific surface area, proper pore diameter distribution, and high graphitization, which lead to remarkable specific capacitances (839 F g-1 at 5 mV s-1 and 825 F g-1 at 0.5 A g-1) in 2 M potassium hydroxide solution. In addition, the (p)-CoS2@CNT electrode exhibits good electrochemical stability and still retains 82.9% of initial specific capacitance at the current density of 1 A g-1 after 5000 cycles.

Controlling the BET Surface Area of Porous Carbon by Using the Cd/C Ratio of a Cd-MOF Precursor and Enhancing the Capacitance by Activation with KOH.

Herein, four new cadmium metal-organic frameworks (Cd-MOFs), [Cd(bib)(bdc)]∞ (1), [Cd(bbib)(bdc)(H2 O)]∞ (2), [Cd(bibp)(bdc)]∞ (3), and [Cd2 (bbibp)2 (bdc)2 (H2 O)]∞ (4), have been constructed from the reaction of Cd(NO3 )2 ⋅4 H2 O with 1,4-benzenedicarboxylate (H2 bdc) and structure-related bis(imidazole) ligands (1,4-bis(imidazol-1-yl)benzene (bib), 1,4-bis(benzoimidazol-1-yl)benzene (bbib), 4,4'-bis(imidazol-1-yl)biphenyl (bibp), and 4,4'-bis(benzoimidazol-1-yl)biphenyl (bbibp)) under solvothermal conditions. Cd-MOF 1 shows a 2D (4,4) lattice with parallel interpenetration, whereas 2 displays an interesting 3D interpenetrating dia network, 3 exhibits an unusual 3D interpenetrating dmp network, and 4 presents a 3D self-catenated pillar-layered framework with a Schäfli symbol of [43 ⋅63 ]2 ⋅[46 ⋅616 ⋅86 ]. The structural diversity indicates that the backbone of the bis(imidazole) ligand (including the terminal group and spacer) plays a crucial role in the assembly of mixed-ligand frameworks. By using the pore-forming effect of cadmium vapor, for the first time we have utilized these Cd-MOFs as precursors to further prepare porous carbon materials (PCs) in a calcination-thermolysis procedure. These PCs show different porous features that correspond to the topological structures of Cd-MOFs. Significantly, it was found that the specific surface area and capacitance of PCs are tuned by the Cd/C ratio of the MOF. Furthermore, the as-synthesized PCs were processed with KOH to obtain activated porous carbon materials (APCs) with higher specific surface area and porosity, which greatly promoted the energy-storage capacity. After full characterization, we found that APC-bib displays the largest specific surface area (1290 m2 g-1 ) and total pore volume (1.37 cm3 g-1 ) of this series of carbon materials. Consequently, APC-bib demonstrates the highest specific capacitance of 164 F g-1 at a current density of 0.5 A g-1 , and also excellent retention of capacitance (≈89.4 % after 5000 cycles at 1 A g-1 ). Therefore, APC-bib has great potential as the electrode material in a supercapacitor.

Hierarchically Flower-like N-Doped Porous Carbon Materials Derived from an Explosive 3-Fold Interpenetrating Diamondoid Copper Metal-Organic Framework for a Supercapacitor.

A peculiar copper metal-organic framework (Cu-MOF) was synthesized by a self-assembly method, which presents a 3-fold interpenetrating diamondoid net based on the square-planar Cu(II) node. Although it exhibits a high degree of interpenetration, the Cu-MOF still exhibits a one-dimensional channel, which provides a template for constructing porous materials through the "precursor" strategy. Furthermore, the explosive ClO4(-) ion, which resided in the channel, could induce the quick decomposition of organic ingredients and release a huge amount of gas, which is beneficial for the porosity of postsynthetic materials. Significantly, we first utilize this explosive MOF to prepare a series of Cu@C composites through the calcination-thermolysis method at different temperatures, which contain copper particles exhibiting various shapes and combinations with the carbon substrate. Considering the hole-forming effect of copper particles, Cu@C composites were etched by HCl to afford a sequence of hierarchically flower-like N-doped porous carbon materials (NPCs), which retain the original morphology of the Cu-MOF. Interestingly, NPC-900, originating from the calcination of the Cu-MOF at 900 °C, exhibits a more regular flower-like morphology, the largest specific surface area, abundant porosities, and multiple nitrogen functionalities. The remarkable specific capacitances are 138 F g(-1) at 5 mV s(-1) and 149 F g(-1) at 0.5 A g(-1) for the NPC-900 electrode in a 6 M potassium hydroxide aqueous solution. Moreover, the retention of capacitance remains 86.8% (125 F g(-1)) at 1 A g(-1) over 2000 cycles, which displays good chemical stability. These findings suggest that NPC-900 can be applied as a suitable electrode for a supercapacitor.

1D-3D mixed-ligand frameworks with an unusual dmp topology tuned by intersection angles of isomeric benzenedicarboxylates: magnetic properties, gas-dependent calcination-thermolysis and energy storage performances.

In this work, three isomeric benzenedicarboxylates, 1,2-benzenedicarboxylic acid (o-H2bdc), 1,3-benzenedicarboxylic acid (m-H2bdc), and 1,4-benzenedicarboxylic acid (p-H2bdc) have been utilized as the ancillary ligands to perform a systematic study on the structural diversity of mixed-ligand frameworks. The solvothermal reactions of Co(NO3)2 with these aromatic acids and the primary ligand 4,4'-bis(imidazolyl)biphenyl (bibp) afford three novel coordination polymers, {[Co6(bibp)3(o-bdc)6(H2O)](CH3CN)1.5}∞ (1), [Co(bibp)(m-bdc)]∞ (2), and [Co(bibp)(p-bdc)]∞ (3). Owing to the different orientations of the carboxylate groups, the benzenedicarboxylates adopt various bridging modes to connect the Co(II) ions into a series of 1D carboxylate∩cobalt architectures based on the 1D chain, binuclear and single-ion magnetic units, respectively. These 1D architectures are further decorated by the bibp ligand to afford a 1D belt for , 2D double-bridging (4,4) sheet for 2, and an unusual 3D dmp framework for 3. Significantly in 3, three equivalent frameworks are interlocked with each other to represent an unprecedented three-fold interpenetrating dmp network. The structural diversity indicates that the benzenedicarboxylate plays an essential role in the assembly of mixed-ligand frameworks, and the orientation of the carboxylate group exerts an important influence on the nucleation, dimensionality and also interpenetration. Furthermore, the magnetic properties of 1 and 2 have been studied by fitting the experimental data as possible, and the magneto-structural correlation of 2 has also been well discussed. Importantly, CoO and Co3O4 were obtained from the controllable thermolysis of crystals of 1 via simple calcination treatment under different gas environments. The as-synthesized cobalt oxides display good crystallinity and appear as micro- or nanoparticles, which can be applied as supercapacitor electrodes as demonstrated by their energy storage performance in 2 M KOH electrolyte.