Robust High-performance Bifunctional Porous Cobalt MOF-Based Catalysts for Overall Water Splitting.

MOF-based materials, as bifunctional catalysts for electrocatalytic water splitting, play an important role in the application and development of clean fuel hydrogen energy. This study presents a series of novel 3D Co-based MOFs with layered networks, including [Co(4,4'-bipy)0.5(aip)(CH3OH)·H2O]n (Co-MOF 1), [Co2(1,3'-bit)(aip)2(CH3OH)·H2O]n (Co-MOF 2), [Co(4,4'-bipb)(aip)]n (Co-MOF 3), and [Co2(4,4'-bipe)(aip)2·1.5H2O]n (Co-MOF 4). Their single-crystal structures of Co-MOFs 1-4 are characterized and analyzed before being applied in alkaline solutions for water decomposition (OER and HER). The electrocatalytic tests indicate that Co-MOFs 1-4 exhibit a good performance. Notably, Co-MOF 4 exhibits great behavior which has low overpotentials of 94 and 188 mV (OER) as well as 185 and 352 mV (HER) at the currents of 10 and 100 mA cm-2, respectively. In comparison with Co-MOFs 1-3, Co-MOF 4 has the lowest Tafel slopes, highest ECSA, and smallest resistance. The immanent qualities, such as distinct interwoven long chain layered structure, unsaturated coordination modes, and synergistic catalytic qualities among Co ions, contribute to explaining the results. The fundamentals provide valuable information for the investigation of innovative MOF-based bifunctional electrocatalysts for overall water splitting.

Pillar-Layered Porous Metal-Organic Frameworks with Co2N2O8 Clusters and Tetragonal Ligands for CO2 Conversion.

Converting CO2 to valuable chemicals and fuels is a viable method to establish a carbon-neutral energy cycle in the environment. Metal-organic frameworks (MOFs), characterized by dispersed active sites, high porosity, etc., have displayed a great application prospect in the electrochemical/chemical CO2 reduction reaction (CO2RR) process. Herein, we proposed a one-step production to establish a series of pillar-layered porous MOFs, [Co2(L)(bimb)]n (MOF 1) and [Co4(L)2(bidpe)2]n (MOF 2) [H4L = 5'-(4-carboxyphenyl)-(1,1':2',1″-terphenyl)-4,4',4″-tricarboxylic, bimb = 1,4-bis(imidazol-1-yl)-butane, bidpe = 4'-bis(imidazolyl) diphenyl ether], for preferential conversion of CO2 via ligand adjustment and increase of active sites' density. According to single-crystal X-ray diffraction studies, [Co2(L)(bimb)]n exhibits pillar-layered binuclear 3D frameworks with a 2,4,6-linked 3-nodes new topology structure, while [Co4(L)2(bidpe)2]n displays pillar-layered tetranuclear interspersed networks with a 4,6-linked 2-nodes fsc topology structure through a ligand adjustment strategy. Meanwhile, the pillar-layered structure of the MOFs with abundant active sites is conducive to mass diffusion and benefits the conversion of CO2. MOFs 1-2 exhibit good electrocatalytic activity for CO2RR in 0.5 M KHCO3 solution. Especially, the current density of MOF 2 generated at -0.90 V (vs. RHE) reaches -81.6 mA·cm-2, which is 3.1 times higher than that under an Ar atmosphere. In addition, MOFs 1-2 can be used as a heterogeneous catalyst for chemical conversion of CO2. The results are expected to provide inspiration for rational design to develop stable and high-efficiency MOF-based electrocatalysts for CO2RR.

Integrating porphyrin-based nanoporous organic polymers with electrochemical aptasensors for ultratrace detection of kanamycin.

The synthesis and characterization of two new porphyrin-based porous organic polymers (POPs) via Sonogashira cross-coupling reaction and leverage the two obtained POPs is reported for the fabrication of electrochemical aptasensors to detect kanamycin at an ultratrace level. The resultant electrochemical aptasensor demonstrates a high linear relationship with the logarithmic value of kanamycin concentration in the range 5 × 10-5-5 µg/L with the limit of detection of 17.6 pg/L or 36.3 fM. During the analysis of real samples from milk and river, a relative standard deviation of less than 4.39%, and good recovery values in the range 97.0-105% were obtained.

Designed Construction of 2D Honeycomb Cationic MOF Materials for Selective Removal of Sulfonic Anionic Dyes.

Various carcinogenic dyes in water bodies are difficult to degrade due to their stability to light and oxidants, causing extended pollution. In this study, MOF 1 ({[Co(tib)2]·(H2O)2·SO4}n) and MOF 2 ({[Cu(tib)2]·(H2O)2·SO4}n) (tib = 1,3,5-tirs(1-imidazolyl)benzene) were synthesized by the solvothermal method. MOFs 1 and 2 were successfully characterized by single-crystal X-ray diffraction (XRD) and powder X-ray diffraction (PXRD). Based on the structural characteristics of MOFs 1 and 2, we designed two cationic MOF material skeletons, namely, MOFs I and II ([Co(tib)22+]n and [Cu(tib)22+]n), which were obtained by calcination in combination with the thermogravimetric curve to remove the free components in the lattice. As expected, MOFs I and II showed an excellent adsorption effect on sulfonic anionic dyes. Notably, the adsorption capacity of MOF I can reach 2922.8 mg g-1 for Congo Red (CR) at room temperature (RT). The adsorption process fits the pseudo-second-order kinetic model and Freundlich isotherm model. Moreover, zeta potential tests and quantum chemical calculations indicate that electrostatic interactions and hydrogen bond between the hydroxyl group on the sulfonic acid group and the N atom on the imidazole ring mainly promote the adsorption of CR dyes on MOF I. MOFs I and II are revealed as a promising novel adsorption material to remove hazardous organic aromatic pollutants with high efficiency in future endeavors.

A Significant Fluorescence Turn-On Probe for the Recognition of Al3+ and Its Application.

An easy prepared probe, BHMMP, was designed and synthesized, which displayed a significant fluorescence enhancement (over 38-fold) and obvious color change in the recognition of Al3+. The binding ratio of probe BHMMP to Al3+ was determined as 1:1, according to Job plot. The binding mechanism was fully clarified by the experiments, such as FT-IR spectrum, ESI-MS analysis, and 1H NMR titration. A DFT study further confirmed the binding mode of BHMMP to Al3+. The limit of detection (LOD) for Al3+ was determined as low as 0.70 µM, based on the fluorescence titration of BHMMP. Moreover, the results from real sample experiments, including real water samples, test papers, and cell images, well-demonstrated that BHMMP was capable of sensing Al3+ in environmental and biological systems.

Highly Stable Acid-Induced Emission-Enhancing Cd-MOFs: Synthesis, Characterization, and Detection of Glutamic Acid in Water and Fe Ions in Acid.

Two novel 3D fluorescent metal-organic frameworks (MOFs), [Cd(L)(bbibp)]n (1) and [Cd(L)(bbibp)0.5]n (2), where H2L = 4,4'-(4,4'-bipyridine-2,6-diyl)dibenzoic acid and bbibp = 4,4'-bis(benzoimidaz-1-yl)biphenyl, were acquired through a conventional method and characterized via IR spectra, single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, powder X-ray diffraction (PXRD), scanning electron microscopy, N2 adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The crystal framework of Cd-MOF 1 remained stable in the range of pH = 1.0-12.0. Interestingly, the emission peak of 1 showed a red shift and exhibited a fluorescence turn-on effect in an acidic environment. X-ray diffraction measurement revealed that the crystal structure of 1 remained unchanged after immersion in a pH = 1.0 solution. In addition, Cd-MOFs 1 and 2 displayed fluorescent quenching to l-glutamic acid with high sensitivity and selectivity. Meanwhile, 1 showed high selectivity in recognizing Fe3+ under acidic conditions, which made 1 capable of detecting Fe3+ in acidic industrial wastewater. Finally, the fluorescent sensing mechanism was carefully studied by PXRD, transient fluorescence lifetime, XPS, and UV spectroscopy.

Recent Advances in Metal-Organic-Framework-Based Nanocarriers for Controllable Drug Delivery and Release.

Metal-organic frameworks (MOFs) have a good designability, a well-defined pore, stimulus responsiveness, a high surface area, and a controllable morphology. Up to now, various MOFs have been widely used as nanocarriers and have attracted lots of attention in the field of drug delivery and release because of their good biocompatibility and high-drug-loading capacity. Herein, we provide a comprehensive summary of MOF-based nanocarriers for drug delivery and release over the last five years. Meanwhile, some representative examples are highlighted in detail according to four categories, including the University of Oslo MOFs, Fe-MOFs, cyclodextrin MOFs, and other MOFs. Moreover, the opportunities and challenges of MOF-based smart delivery vehicles are discussed. We hope that this review will be helpful for researchers to understand the recent developments and challenges of MOF-based drug-delivery systems.

Design of five two-dimensional Co-metal-organic frameworks for oxygen evolution reaction and dye degradation properties.

Two-dimensional (2D) metal-organic frameworks (MOFs) have been extensively investigated as oxygen evolution reaction (OER) materials because of their numerous advantages such as large specific surface areas, ultrathin thicknesses, well-defined active metal centers, and adjustable pore structures. Five Co-metal-organic frameworks, namely, [Co(L) (4.4'-bbidpe)H2O]n [YMUN 1 (YMUN for Youjiang Medical University for Nationalities)], {[Co2(L)2 (4.4'-bbibp)2]·[Co3(L) (4.4'-bbibp)]·DMAC}n (YMUN 2), [Co(L) (3,5-bip)]n (YMUN 3), [Co(L) (1,4-bimb)]n (YMUN 4), and [Co(L) (4.4'-bidpe)H2O]n (YMUN 5), were designed and fabricated from flexible dicarboxylic acid 1,3-bis(4'-carboxylphenoxy)benzene (H2L) and rigid/flexible imidazole ligands. Their frameworks consist of two-dimensional lamellar networks with a number of differences in their details. Their frameworks are discussed and compared, and their oxygen evolution reaction electrochemical activities and photocatalysis dye degradation properties are investigated.

Zn-MOFs based luminescent sensors for selective and highly sensitive detection of Fe3+ and tetracycline antibiotic.

Either reduced or excessive metal ions level in biological systems might induce serious metabolic diseases, and the abuse of antibiotics has seriously affected the environment. Despite the significant progress in the development of fluorescence probes over the past decade, the ability to sensitively and selectively detect these metal ions and antibiotics remains a pressing problem. Herein, we demonstrated some effective fluorescence probes for sensing metal ions and antibiotics, six novel and stable Zn(II) metal-organic frameworks (Zn-MOFs), namely [Zn3(L)2(1,4-bimb)3]n (1), [Zn3(L)2(4,4'-bbibp)2(H2O)2]n·2(CH3CN) (2), [Zn(HL)(4,4'-bidpe)]n (3), [Zn(HL)(4,4'-bibp)]n (4), [Zn(HL)(3,5'-bip)]n (5) and [Zn(HL)(1,3'-bit)]n (6) (flexible H3L = 5-(2-carboxylphenoxy)isophthalic acid, semi-flexible 1,4-bimb = 1,4-bis(imidazol-l-ylmethyl) benzene, rigid 4,4'-bbibp = 4,4'-bis(benzoimidazo-1-ly)biphenyl, semi-flexible 4,4'-bidpe = 4,4'-bis(imidazolyl)diphenyl ether, rigid 4,4'-bibp = 4,4'-bis(imidazolyl)biphenyl, rigid 3,5'-bip = bis(1-imidazoly)pyridine and rigid 1,3-bit = 1,3-bis(l-imidazoly)toluene) have been successfully synthesized via solvothermal conditions and further characterized by IR spectra, elemental analysis, powder X-ray diffraction (PXRD), single-crystal X-ray diffraction, and thermogravimetric (TG) analysis. These Zn MOFs have exhibited diversely architectural frameworks via the assistant N-donor ligands: 1, 2, 5 and 6 show unprecedented topological networks, 1 affords a 3-nodal (3, 4, 4)-connect 2-fold interpenetrating topology structure with the Point Schläfli symbol of (5·6·7·92·10)2(5·6·7)2(5·73·82), 2 shows a 3-nodal (3, 4, 6)-c topology with (4·82)2(42·811·10·12)(86), 5 and 6 display 3-nodal (2, 2, 4)-c topology with (2·44·6)(2)(4). 3 and 4 show 4-connected sql topology with (44·62). As expected, Zn MOFs 1-6 not only revealed a highly sensitive and selective fluorescence quenching effect on Fe3+ ions in aqueous solution, but also toughed the interference of a myriad of other metal ions. It is noteworthy that they could also be used as luminescent sensors for detection of tetracycline antibiotic.