Effective Iodine Adsorption by Nitrogen-Rich Nanoporous Covalent Organic Frameworks

With the rapid development of the nuclear industry, the effective treatment of radioactive iodine has currently become an urgent but challenging task. Herein, two covalent organic frameworks (COFs), TFBT-1 and TFBT-2, were successfully synthesized for iodine adsorption. Structure analysis revealed that they are both nanoporous materials with one-dimensional channels derived from the packing of the related two-dimensional frameworks. Iodine adsorption experiments demonstrated that both COF materials exhibit effective performance for iodine adsorption, with a maximum amount of upto 3.15 g g–1 for TFBT-1 and 2.60 g g–1 for TFBT-2. The results of experimental analyses of Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy clearly revealed that their high performance is attributed to the strong interactions between the adsorbed iodine and the uniformly located abundant nitrogen adsorption sites in the pores of the two COF materials, which are from both pre-introduced acylamides and in situ-generated Schiff base imine groups. The present work revealed that by introducing the nitrogen-rich sites into the frameworks of the COF materials, effective iodine adsorbents can be achieved

Synergistic Effect of Functionalization and Crystallinity in Nanoporous Organic Frameworks for Effective Removal of Metal Ions from Aqueous Solution

In order to search effective adsorbents for removal of metal ions in water treatments, three nanoporous organic frameworks, TPPA, TPPA-SO3H, and TPBD-SO3H, with or without −SO3H functionalities were selected and synthesized by the Schiff base reactions of 1,3,5-triformylphloroglucinol (TP) and p-phenylenediamine (PA), p-phenylenediaminesulfonic acid (PA-SO3H), and 2,2′-benzidinedisulfonic acid (BD-SO3H), respectively. Characterizations revealed that both TPPA and TPPA-SO3H possess high crystallinity and porosity, while only amorphous powder with irregular pores of TPBD-SO3H was obtained. The Brunauer–Emmett–Teller surface areas of 425.3 and 297.5 m2/g for TPPA and TPPA-SO3H, respectively, were calculated, while only 45.1 m2/g was detected for TPBD-SO3H. Metal ion adsorption experiments revealed that among all three framework materials, TPPA-SO3H shows the best performances in adsorption capacities, removal efficiency, and adsorption rate to all of the tested metal ions, especially Fe3+, Cr3+, and Cd2+ ions. Compared with the absence of −SO3H functionalities in TPPA and the amorphous nature of the extended framework material of TPBD-SO3H, the high performances of TPPA-SO3H should be ascribed to its synergistic effect of functionalization and crystallinity. This study revealed that besides the functional groups, the crystallinity of nanoporous organic frameworks is also a crucial factor in their applications

Gold-Doped Cobalt–Nickel Sulfide Nanosheets for Oxygen Evolution Reaction

The electrolytic water of oxygen evolution reaction is a four-electron transport process, which results in a slow kinetic process coupled with a high oxygen evolution reaction application potential; therefore, the catalysts have become an urgent bottleneck in the research of hydrolysis reactions. Research on the oxygen evolution reaction is booming with various materials such as noble metals and transition metals. Because of their intrinsically excellent charge transport properties and cost-effective features, transition metal sulfides have attracted much investigation. Herein, we combined the synergistic catalysis of transition metals with the modification of trace noble metal atoms to design and synthesize gold-doped cobalt–nickel sulfide nanosheets (Au-CoNiSx NSs) for oxygen evolution reaction. The cobalt–nickel ratio of electrodeposition and the doping of Au on the millimolar scale were studied. The doping of Au atoms promoted the deposition of sulfur elements and led to the formation of more compact nanostructures, thereby improving the OER performance. The optimal electrochemical performance was obtained with Co/Ni = 3:1 and Au addition of 0.5 mmol/L, with an overpotential of 305.9 mV (vs RHE) at a current density of 10 mA/cm2 and a Tafel slope of 60.98 mV/dec. In the chronopotentiometry measurement, there was no significant difference in electrochemical performance within 12 h, indicating that the nanomaterial has good catalytic stability

A Triazole-Containing Metal–Organic Framework as a Highly Effective and Substrate Size-Dependent Catalyst for CO₂ Conversion

A highly porous metal–organic framework (MOF) incorporating both exposed metal sites and nitrogen-rich triazole groups was successfully constructed via solvothermal assembly of a clicked octcarboxylate ligand and Cu­(II) ions, which presents a high affinity toward CO₂ molecules clearly verified by gas adsorption and Raman spectral detection. The constructed MOF featuring CO₂-adsorbing property and exposed Lewis-acid metal sites could serve as an excellent catalyst for CO₂-based chemical fixation. Catalytic activity of the MOF was confirmed by remarkably high efficiency on CO₂ cycloaddition with small epoxides. When extending the substrates to larger ones, its activity showed a sharp decrease. These observations reveal that MOF-catalyzed CO₂ cycloaddition of small substrates was carried out within the framework, while large ones cannot easily enter into the porous framework for catalytic reactions. Thus, the synthesized MOF exhibits high catalytic selectivity to different substrates on account of the confinement of the pore diameter. The high efficiency and size-dependent selectivity toward small epoxides on catalytic CO₂ cycloaddition make this MOF a promising heterogeneous catalyst for carbon fixation

Photoassisted “Gate-Lock” Fluorescence “Turn-on” in a New Schiff Base and Coordination Ability of <i>E–Z</i> Isomers

Rapid photoresponse (1.0–8.0 min) through fluorescence “turn-on” signaling displayed by a novel Schiff base (L) creating “gate lock” via intramolecular C–H···N interaction in photoisomerized product (L′) has been described. Coordination chemistry of pre- and postirradiated species demonstrated a drastic change in the reactivity which has been supported by NMR, HRMS, UV–vis, emission, electrochemical, and complexation studies

Red-Light-Based Effective Photocatalysis of a Photosensitive Covalent Organic Framework Triggered Singlet Oxygen

The direct application of low-energy red light for photochemical transformations is synthetically appealing but practically challenging. Covalent organic frameworks (COFs) exhibit significant potential within this domain, owing to their broad spectrum of absorption and their prevalence in photochemical reactions, despite the fact that these photocatalysts are now mainly focused on using ultraviolet (UV) and blue light. In this study, an imidazole-linked porphyrin-based COF, PyPor-COF, which exhibits a wide absorption band ranging from 200 to 700 nm, especially strong red light absorption from 630 to 700 nm, is expected to be applied in red light photocatalytic reactions. PyPor-COF possesses the capacity to selectively generate singlet oxygen (1O2) with a high efficiency, which renders it an efficient photosensitizer for photocatalytic reactions of olefin cleavages and thioanisole photooxidation under red light. The present study demonstrates the intriguing prospect of photoactive COFs with red light absorption as a type II photosensitizer with high potential for utilization in red light photocatalyses

Photoassisted “Gate-Lock” Fluorescence “Turn-on” in a New Schiff Base and Coordination Ability of <i>E–Z</i> Isomers

Rapid photoresponse (1.0–8.0 min) through fluorescence “turn-on” signaling displayed by a novel Schiff base (<b>L</b>) creating “gate lock” via intramolecular C–H···N interaction in photoisomerized product (<b>L</b>′) has been described. Coordination chemistry of pre- and postirradiated species demonstrated a drastic change in the reactivity which has been supported by NMR, HRMS, UV–vis, emission, electrochemical, and complexation studies

A Robust Aluminum Metal-Organic Framework with Temperature-Induced Breathing Effect

A robust, yet flexible, Al-based metal-organic framework (MOF), Al2(OH)2(bpydc)·0.5H2O (1np), is synthesized via a hydrothermal strategy utilizing 2,2′-bipyridine-5,5′-dicarboxylate (bpydc2–) as the organic ligand. The structure of 1np is built from infinite trans chains of corner-sharing AlO4(OH)2 octahedra interconnected by bpydc2– ligands, forming a three-dimensional framework. 1np is robust, because of its superior thermal, hydrothermal, and chemical stability. The flexibility of 1np is reflected in the activation by the removal of unreacted H2bpydc molecules and/or occluded solvent molecules, followed by degassing at 250 °C, leading to the large pore form (1lp) of the title compound. A reversible structural change from 1lp to 1np is achieved via the hydration in water at 200 °C. The unusual combination of rigidity and flexibility enables precise control and fixation of the swelling magnitude in this MOF material

Effective Photocatalytic Initiation of Reactive Oxygen Species by a Photoactive Covalent Organic Framework for Oxidation Reactions

Reactive oxygen species (ROS) play a vital role in both chemistry and physiology. Developing effective photocatalysts becomes a feasible approach to trigger the generation of ROS. Herein, a photosensitive covalent organic framework (COF) was rationally designed and constructed by incorporating the photoactive triphenylamine moieties into its skeleton, characterizations of which not only showed the success formation of the highly crystalline and stable framework, but also revealed the photoactive property derived from triphenylamine-based building block. Electron paramagnetic resonance measurements displayed that the COF was an effective photocatalyst for generating ROS with one unpaired electron, that is, superoxide radical anion (O2• –). Subsequently, its high efficiency, selectivity, and reusability in photocatalytic aerobic oxidation of sulfides confirmed that the COF is a promising photocatalyst in the applications of ROS-involved reactions, demonstrating that precisely embedding organic photochromic groups into COFs could be a powerful strategy to fabricate metal-free heterogeneous photocatalysts for targeted reactions

A Triazole-Containing Metal–Organic Framework as a Highly Effective and Substrate Size-Dependent Catalyst for CO₂ Conversion

A highly porous metal–organic framework (MOF) incorporating both exposed metal sites and nitrogen-rich triazole groups was successfully constructed via solvothermal assembly of a clicked octcarboxylate ligand and Cu­(II) ions, which presents a high affinity toward CO₂ molecules clearly verified by gas adsorption and Raman spectral detection. The constructed MOF featuring CO₂-adsorbing property and exposed Lewis-acid metal sites could serve as an excellent catalyst for CO₂-based chemical fixation. Catalytic activity of the MOF was confirmed by remarkably high efficiency on CO₂ cycloaddition with small epoxides. When extending the substrates to larger ones, its activity showed a sharp decrease. These observations reveal that MOF-catalyzed CO₂ cycloaddition of small substrates was carried out within the framework, while large ones cannot easily enter into the porous framework for catalytic reactions. Thus, the synthesized MOF exhibits high catalytic selectivity to different substrates on account of the confinement of the pore diameter. The high efficiency and size-dependent selectivity toward small epoxides on catalytic CO₂ cycloaddition make this MOF a promising heterogeneous catalyst for carbon fixation