Search

Tetrazole-functionalized covalent organic frameworks via successive cycloaddition can be applied to efficient electrocatalytic H2O2 production and Li–S batteries.

The development of functional covalent organic frameworks (COFs) with specific properties is an emerging research field. In the current work, COF-SQ-Ph was synthesized through the aza-Diels-Alder reaction between phenylacetylene and the matrix COF-SQ (triazine-based COF) generated from the organic monomers 2, 4, 6-tris(4-aminophenyl)-1, 3, 5-triazine and 2, 5-dimethoxyterephthalaldehyde in flask. The functionalized COF-SQ-Ph with an extended π-conjugated structure and enhanced structural stability was used as the sulfur loading recipient to prepare sulfur cathodes for lithium-sulfur batteries. Sulfur-impregnated COF-SQ-Ph marked as COF-SQ-Ph-S displayed better cycling stability with a specific capacity of 618 mA h g−1 after 150 cycles due to the lithiophilic interaction between lithium polysulfides and nitrogen atoms from quinoline and triazine moieties in COF-SQ-Ph-S. The functionalization of triazine-based COFs through a cycloaddition reaction in flask could promote the large-scale preparation of tailored COFs and the post-synthesis modification of COF-SQ.

In order to reduce the negative impact of the extra carbon coating on the electrochemical properties of the commonly sandwiched carbon nanotubes@tin dioxide@carbon (CNT@SnO2@C) composites, the external C coating has been designed as a porous carbon in this work. The well-designed porous carbon coating offers an attractive advantage compared to the common carbon coatings, namely, it can not only better mitigate the volumetric variation of SnO2 by means of its spongy structure with better flexibility and rich free space, but also accelerate the lithium-ions diffusion by virtue of its open tunnel-like architecture. For this reason, this composite prepared here shows outstanding electrochemical performance stemming from the cooperative effect of inner CNT supporting and externally porous carbon coating, displaying 819.3 and 576.0 mAh g−1 at 200 and even 1000 mA g−1 after even 500 cycles, respectively. This surface engineering strategy may be valuable for enhancing the cyclical durability of other metal oxides with higher theoretical specific capacities.

A pyrimidine-modified covalent organic framework (COF-Pyr) was designed to be synthesized via the Povarov reaction. The nitrogen atom on the pyrimidine showed excellent coordination ability to metal ions. Their stable metal composite material (Co@COF-Pyr) exhibited remarkable performance for electrocatalytic oxygen evolution reaction (OER) in 1.0 m KOH aqueous solution. The overpotential was 450 mV at 10 mA cm-2 . The Co@COF-Pyr with large specific surface area (392 m2 g-1 ) and regular crystal structure provided free passage for H2 O to move and make them fully contact with the uniformly dispersed cobalt ions on the surface. Thus, the turnover frequency of Co@COF-Pyr was 0.1 s-1 at the overpotential of 370 mV, which was higher than most reported OER catalysts. This work provided a new way to design and prepare nitrogen-containing heterocyclic functionalized COFs. They can be combined with metal ions to expand the application of COFs in the field of electrocatalysis.

Open metal site (OMS) seated in a luminescent lanthanide (Ln) metal center offers an opportunity for rationally tuning the spectroscopic behavior of lanthanide-organic frameworks aiming for a wide range of sensing applications. However, given the spherical nature of common coordination geometries of trivalent lanthanides and the generally strong Ln-O bonds, the lanthanide based OMS is rarely reported and difficult to be functionalized. We report here a unique europium-organic framework containing abundant quasi-OMS that is protected by an abnormal weak Eu-O bond. These quasi-OMSs offer reversible direct binding sites for water molecules probed by X-ray crystallography, leading to sensitive, visible, and ratiometric luminescent sensing toward humidity and water content in organic solvents. The specific recognition of water based on quasi-luminescent-OMSs gives rise to a superior water detection limit down to 0.0003% v/v, which is one order of magnitude lower than that of Karl Fischer method.

Metal nanoparticles (MNPs)/metal–organic frameworks (MOFs) composites have become a research hotspot because the cooperation between MNPs and MOF can effectively improve the catalytic performance. However, development of a simple method to disperse the tiny MNPs on MOF is still a great challenge. In this work, a AuPdPt/Cu-MOF composite was prepared successfully by a one-step reduction process. First, Cu-MOF with one-dimensional nanorod structure was prepared by using surfactant PVP to control morphological growth. Second, the AuPdPt/Cu-MOF composite was synthesized by reducing the metal precursor to AuPdPt nanoparticles (NPs) supported on the surface of Cu-MOF. Encouragingly, synergistic effect between Au, Pd, and Pt, along with high dispersion of AuPdPt NPs on Cu-MOF nanorods, leading to excellent catalytic activities toward the benzyl alcohol with a conversion rate of 66%. Thus, this simple strategy to design promising MNPs/MOF composite can provide various opportunities in the field of catalysis.

Uranium, which was abundant in the ocean but existed in the form of uranyl tricarbonate ([UO2(CO3)3]4−) with an extremely low concentration of 3.3 ppb, was a significant element of nuclear energy. It is of immediate significance to the research into uranium extraction by the exploration of adsorbents for environment and resource sustainability. Herein, the new ionic covalent organic frameworks (iCOFs) named COF-DG containing the guanidine groups was designed and synthesized via Schiff base reaction between diaminoguanidine hydrochloride and 1,3,5-triformylphloroglucinol. The adsorption performance indicated that the COF-DG possessed an uptake capacity of 65.6 mg g−1 toward the [UO2(CO3)3]4−, attributed to the chemical interaction and anion exchange between [UO2(CO3)3]4− and the cationic COF-DG with Cl−, as well as the electrostatic attraction. Besides, the COF-DG exhibited a higher affinity and selectivity toward [UO2(CO3)3]4− in the presence of the competing anions. Furthermore, the COF-DG displayed an antibacterial rate of 82% against Gram-negative bacteria Escherichia coli owing to the guanidine groups. This work contributes new insights into the further development of iCOFs, for applying as a potential candidate in uranium extraction from seawater in practical engineering. The new ionic covalent organic frameworks named COF-DG was designed and exploited via Schiff base reaction, which exhibited a higher affinity and selectivity toward the [UO2(CO3)3]4−.

Covalent organic frameworks (COFs) with pre-designed structure and customized properties have been employed as sulfur storage materials for lithium-sulfur (Li-S) batteries. In this work, a cationic mesoporous COF (COF-NI) was synthesized by grafting a quaternary ammonium salt group onto the pore channel of COFs via a one-pot three components tandem reaction strategy. The post-functionalized COFs were utilized as the matrix framework to successfully construct the Li-S battery with high-speed capacity and long-term stability. The experimental results showed that, after loading active material sulfur, cationic COF-NI effectively suppressed the shuttle effect of the intermediate lithium polysulfide species in Li-S batteries, and exhibited better cycle stability than the as-obtained neutral COF (COF-Bu). For example, compared with COF-Bu based sulfur cathode (521 mA h g−1), the cationic COF-NI based sulfur cathode maintained a discharge capacity of 758 mA h g−1 after 100 cycles. These results clearly showed that appropriate pore environment of COFs can be prepared by rational design, which can reduce the shuttle effect of lithium polysulfide species and improve the performance of Li-S battery.

Designing efficient and stable non-precious metal HER (hydrogen evolution reaction) electrocatalysts with high large current density adaptability is significant for industrial application of hydrogen production by water electrolysis. Herein, a facile strategy was developed to construct a multi-phase Ni3P-Co2P-(Ni-Co) film with self-supporting hierarchically micro/nano-porous structure by using bubble template method electrodeposition of self-supporting micro-porous NiCoP film, oxygen-free annealing for phase separation producing Ni3P-Ni-Co2P-Co structure, and acid etching for constructing surface nano-porous structure. The effective active sites for HER was significantly increased due to the hierarchically micro/nano-porous structure, which not only enlarged the surface roughness, but enhanced the bubble detachment by improving the hydrophilicity. Meanwhile, the HER electrolysis durability was improved benefiting from the Ni3P-Co2P phases with high corrosion resistance (especially in acid solution) and the self-supporting film structure without binder. Consequently, the NiCoP-OA-AE film exhibited high HER catalytic performance, which delivered a current density of 10 mA cm−2 at a low overpotential of 42.9 and 39.7 mV in 1 M KOH and 0.5 M H2SO4, respectively. It also possessed high long-term electrolysis durability, and the cell voltage of water electrolysis using self-supporting porous NiCoP-OA-AE||IrO2-Ta2O5 electrolyzer at 500 mA cm−2 for 250 h in 0.5 M H2SO4 is only 2.9 V.

The first convergent total synthesis for the proposed structures of microcyclamides MZ602 (1) and MZ568 (2) has been accomplished in 11 linear steps with 12.5 and 16.8% overall yield, respectively. Key features of the syntheses include a one-pot cascade reaction to construct core Boc-l-Ile-Thz-OAllyl fragment 5, and a removable pseudoproline (ΨMe,Me pro) inducer assisted cyclization of thiazole-containing all-l linear peptides. The spectral data (1H NMR, 13C NMR, and HRMS) of synthetic MZ602 (1) were quite similar to those of the proposed natural microcyclamide MZ602, except to an opposite sign of the optical rotation value. Surprisingly, the synthetic MZ568 (2) presented large discrepancies in characteristic spectral data from those of the reported natural product, although the absolute configuration of key intermediate 36 was unambiguously determined by single-crystal X-ray analysis in our work. These findings revealed that the proposed structures of natural microcyclamides MZ602 and MZ568 required revision.

FeTi catalysts prepared by a CTAB-assisted process exhibited good resistance to H2O and SO2 when tested in the selective catalytic reduction (SCR) at low temperatures. The physicochemical properties of the catalysts and the NO reaction behaviour under the influence of H2O and SO2 were extensively characterized using BET, TEM, TPD-MASS, TPSR and in-situ DRIFTS. It was found that catalyst deactivation in the early stage of H2O and SO2 introduction was mainly caused by pore plugging, resulting from the ammonium-sulfate salts deposition, while the active phase sulfation and competitive adsorption became the dominant catalyst-inhibiting factors in the later stage. SO2 not only greatly inhibited NO adsorption on the catalyst surface, hindering the reaction through the Langmuir–Hinshelwood path, but also inhibited the reaction between adsorbed NH3 and NO (Eley–Rideal path). Moreover, H2O promoted the transformation of NH4HSO4 to (NH4)2SO4, suggesting the “combined inhibition” of SO2 and H2O, which was also reflected by in-situ DRIFTS that a clear increase of NH3 adsorbed sites and sulfate species could be detected, thus resulting in more serious deactivation.

Slow lithium storage reaction kinetics and huge volume changes are the main limiting factors for the large-scale application of transition metal oxide anode materials for lithium ion batteries. Developing multi-structure and carbon coating films is a promising solution. Herein, a facile strategy for synthesizing novel binder-free 3D porous Fe3O4–Fe2P–Fe@C films is proposed based on the electrodeposition of self-supporting porous FeOOH–FeP–Fe films, glucose coating to form FeOOH–FeP–Fe@Glucose films, and oxygen-free annealing treatment for the decomposition of FeOOH into Fe3O4, phase separation of FeP into Fe2P–Fe3P and pyrolysis of glucose into C. The binder-free Fe3O4–Fe2P–Fe@C film anode exhibits high reversible capacity (914 mA h g−1 after 200 cycles at 0.1 A g−1), superior rate capability (518 mA h g−1 at 5 A g−1), and stable long cycling performance (723 mA h g−1 after 500 cycles at 2 A g−1). The excellent lithium storage performance of the Fe3O4–Fe2P–Fe@C anode is attributed to the synergistic effects of the self-supporting 3D porous film structure, multi-phase structure, and carbon coating, which not only enhances the Li+ and electron transport to accelerate the reaction kinetics, but also buffers the volume changes to improve the structure stability during reversible charge-discharge process.

Cycloaddition reaction using CO2 as a starting material to form a cyclic carbonate has been applied to chemical fixation of CO2. In order to further increase the reaction efficiency, herein, a bifunctional catalyst (CPBrs) containing metalloporphyrin and quaternary phosphonium salt groups was prepared, and the related catalytic performance for CO2 conversion was also studied. The catalytic system possesses multiple active sites of zinc porphyrin (Lewis acids) and quaternary phosphonium bromide salts (nucleophilic reagents), which can cooperatively work together to enhance the efficiency of cycloaddition reaction. At the same time, CPBrs (CPBr-1 and CPBr-2) are microporous polymers with permanent microporous pore structure and high specific surface areas (342–370 m2 g−1). Their moderate capacities (5.76 and 8.81% at 1 bar/273 K) to capture carbon dioxide were also beneficial for CO2 conversion. The activity of the bifunctional catalyst is higher than that of the catalyst with a single component. The corresponding highest yield to catalyze cycloaddition reaction between methyl substituented propylene oxide and CO2 is up to 95% (2.5 MPa, 90 °C). What is more, the porous nature of catalysts provides the recoverability of the catalyst, and the efficiency of the catalyst CPBr-2 remains high (above 90% yield) after five catalytic recycle.

Heterogeneous metal–organic framework composites are widely used to catalyze the synthesis reaction of organic materials. Here, we report the use of a heterogeneous catalyst to catalyze the reaction of alcohols and amines to synthesize imines directly using a one-pot method. A low-dimensional Cu-MOF prepared by a simple surfactant-assisted method shows the morphology of nanorods. Cu-MOF nanorods provide an ideal support for preparing supported metal nanocatalysts. A reduction method was applied to immobilize the ultrafine noble metal Au and Pd nanoparticles on the surface of Cu-MOF nanorods to form a Cu-MOF/Au–Pd composite catalyst. Cu-MOF/Au–Pd catalyst is used to catalyze the reaction between alcohols and amines to form imines. Due to the synergy between different metal nanoparticles, it can effectively catalyze the reaction to form imines. In addition, Cu2+ in Cu-MOF/Au–Pd catalyst facilitates the adsorption of substances by excess electrons and promotes product formation. After 12 h of catalytic reaction, the yield of imine is as high as 95%.

Photocatalytic reactions are promising strategies for converting solar energy into chemical energy. In this work, a MOF-based composite UiO-67-IrF with Ir complex and an electron-withdrawing group (trifluoromethyl group) is prepared and used as a photocatalyst for cross-dehydrogenation coupling reactions. For comparison, UiO-67-Ir without trifluoromethyl group and their pristine MOF UiO-67-bpy were also obtained. Both Ir-bearing composites (UiO-67-IrF and UiO-67-Ir) have crystalline and porous structure and high specific surface area (> 762 m2 g−1) and can effectively utilize visible light for cross-dehydrogenative coupling reactions. Notably, UiO-67-IrF with trifluoromethyl group has a lower specific surface area, but owns higher photocatalytic performance (yields about 82–89%) than its counterpart UiO-67-Ir, due to its better light absorption and charge separation under visible-light exposure.

Owing to specific formation of five-membered or six-membered cyclic esters between boric acid groups and cis-diol molecules, boric acid bearing fluorescent materials can not only selectively capture but also specifically identify cis-diol substances. In this work, a novel covalent organic framework containing boric acid groups (COF-BA) was prepared through post-modification via the aza-Diels-Alder cycloaddition reaction. COF-BA with good stability, a permanent pore structure, a high specific surface area (606 m2 g-1) and a uniform pore size (2.59 nm) exhibited unique selectivity toward the cis-diol guest molecule 1,2-dihydroxyanthracene-9,10-dione (1,2-Doa) with a high adsorption capacity of 177.95 mg g-1. However, as for the isomers of 1,2-Doa (1,4-dihydroxyanthracene-9,10-dione and 2,6-dihydroxyanthracene-9,10-dione), the corresponding uptake capacities are distinctively decreased to 40.86 mg g-1 and 3.05 mg g-1, respectively. It is worth noting that the COF-BA can be recovered and recycled. Moreover, because the formation of the quinoline enhanced the conjugation effect of the COF skeleton, it was unexpectedly found that COF-BA possessed an intrinsic fluorescence property and could be used as an optical sensor for 1,2-Doa.

A fluorine-rich covalent organic framework, COF-(CF3)2, was designed and prepared by post-functionalization via the Povarov reaction in a flask in order to take up fluorinated pesticides. Compared with those obtained by a synthetic method performed in a Pyrex tube, the as-prepared COFs in our process not only possess higher specific surface areas, but also can be obtained on a large scale. It's worth noting that COF-(CF3)2 exhibits strong chemical stability even in KMnO4 or NaBH4 solutions, which is highly beneficial for its practical applications. Considering the strong and selective fluorine–fluorine interactions, COF-(CF3)2 was used for the uptake of fluorinated pesticides and showed higher adsorption capacities for trifluralin (151 mg g−1) and fipronil (171 mg g−1). We also found unexpectedly that COF-(CF3)2 possesses strong fluorescence due to the enhanced conjugated system via cycloaddition functionalization. This unique property can be applied in detecting trifluralin through fluorescence quenching induced by their interaction.

Exploring cost-effective electrochemical catalysts instead of traditional precious metals for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with outstanding performance plays a vital role in the development of renewable resources. Herein, heterometallic anchored nitrogen-doped carbon materials are fabricated derived from metallophthalocyanine based conjugated microporous polymers (CMPs) consisting of a varying coordinated environment, which hold great promise as competing electrochemical catalyst alternatives due to their intrinsic hierarchical porosity and highly homogenous distribution of catalytic sites. The synergic heterometallic arrangement within the nitrogen-doped carbon framework leads to enhanced catalytic performances in both ORR and OER processes compared with its monometallic counterparts. Benefiting from the engineering strategy and unique structure, the as-prepared heterometallic catalyst presents remarkable ORR/OER bifunctional activity along with desirable long-time durability. The strategy proposed here highlights the potential of heterometallic phthalocyanine as a building block precursor in the rational design of high-efficiency carbon-based ORR/OER bifunctional catalysts.

The postsynthetic modification provided effective approaches for the functionalization of imine covalent organic frameworks (COFs). To address the rapid decline of sulfur cathodes caused by the shuttle effect of soluble lithium polysulfide, cationic COFs (COF-PA-AI) used as sulfur-loaded matrix materials for lithium-sulfur (Li-S) batteries was designed and prepared by cycloaddition. Benefiting from the ordered channels and the strong interaction between quaternary ammonium cations and polysulfide anions, COF-PA-AI/S displayed faster electrochemical kinetics, greater tolerance to high current shocks, and better rate performance as the cathode. Besides, the discharge capacity of COF-PA-AI/S also remained at 665.3 mA h/g after 200 cycles at 0.5 °C, which was higher than that of COF-Ph/S. This work not only demonstrated the possibility of a postfunctionalization method based on the intermediate COF-PA but also expanded the scope of application of the COFs and provided a new idea for the application of COF materials to the cathodes of Li-S batteries.

Owing to specific formation of five-membered or six-membered cyclic esters between boric acid groups and cis-diol molecules, boric acid bearing fluorescent materials can not only selectively capture but also specifically identify cis-diol substances. In this work, a novel covalent organic framework containing boric acid groups (COF-BA) was prepared through post-modification via the aza-Diels-Alder cycloaddition reaction. COF-BA with good stability, a permanent pore structure, a high specific surface area (606 m2 g-1) and a uniform pore size (2.59 nm) exhibited unique selectivity toward the cis-diol guest molecule 1,2-dihydroxyanthracene-9,10-dione (1,2-Doa) with a high adsorption capacity of 177.95 mg g-1. However, as for the isomers of 1,2-Doa (1,4-dihydroxyanthracene-9,10-dione and 2,6-dihydroxyanthracene-9,10-dione), the corresponding uptake capacities are distinctively decreased to 40.86 mg g-1 and 3.05 mg g-1, respectively. It is worth noting that the COF-BA can be recovered and recycled. Moreover, because the formation of the quinoline enhanced the conjugation effect of the COF skeleton, it was unexpectedly found that COF-BA possessed an intrinsic fluorescence property and could be used as an optical sensor for 1,2-Doa.

In this work, a novel heterogeneous compfosite catalyst was synthesized via the immobilization of platinum and polyoxometalate into MOFs containing bipyridine groups. The resulting UiO-67-Pt-Z has a high specific surface area (446 m2 g−1), which is beneficial to adsorb more methane molecules in the methane catalysed transformation, and the homogeneous distribution of Pt and POM can improve the catalytic efficiency of the catalyst. Under mild reaction conditions, methanol, ethanol, and acetic acid can be obtained in 2 h. Our work provides a new catalyst for the rapid catalytic oxidation of methane to high value-added oxygenates and broadens new ideas for exploring effective methane direct conversion in future work.

Lithium‑sulfur batteries have been considered as a promising chemical power source owing to the low costs, high energy densities, and nontoxicity. However, sulfur-based cathodes have several shortcomings, including poor electrochemical activity and fast capacity attenuation. In this work, manganese dioxide (MnO2) and nitrogen-doped porous graphene (pNGA) were introduced to the sulfur cathode to improve its electrochemical activity and prevent the rapid decay of capacity. The pNGA/MnO2 composite with a three-dimensional architecture was fabricated by steam etching of nitrogen-doped graphene aerogel and chemical deposition of MnO2 nanoparticles. In this structure, the nitrogen-doped porous graphene acts as a skeleton to form a conductive network. The MnO2 particles anchored on graphene sheets have a good interaction with polysulfides. The as-prepared pNGA/MnO2@S cathode shows an excellent comprehensive electrochemical performance. The calculated specific capacities are 1144, 1007, 920, 852, and 762 mA h g−1 at 0.1C, 0.2C, 0.5C, 1C, and 2C respectively. In addition, the pNGA/MnO2@S cathode displays a good cycling performance: the specific capacity maintains at 887 mA h g−1 at 0.5C over 100 cycles.