A Covalent Organic Framework–Cadmium Sulfide Hybrid as a Prototype Photocatalyst for Visible‐Light‐Driven Hydrogen Production

CdS nanoparticles were deposited on a highly stable, two‐dimensional (2D) covalent organic framework (COF) matrix and the hybrid was tested for photocatalytic hydrogen production. The efficiency of CdS‐COF hybrid was investigated by varying the COF content. On the introduction of just 1 wt % of COF, a dramatic tenfold increase in the overall photocatalytic activity of the hybrid was observed. Among the various hybrids synthesized, that with 10 wt % COF, named CdS‐COF (90:10), was found to exhibit a steep H₂ production amounting to 3678 μmol h^?1 g^?1, which is significantly higher than that of bulk CdS particles (124 μmol h^?1 g^?1). The presence of a π‐conjugated backbone, high surface area, and occurrence of abundant 2D hetero‐interface highlight the usage of COF as an effective support for stabilizing the generated photoelectrons, thereby resulting in an efficient and high photocatalytic activity.     

Direct On‐Surface Patterning of a Crystalline Laminar Covalent Organic Framework Synthesized at Room Temperature

We report herein an efficient, fast, and simple synthesis of an imine‐based covalent organic framework (COF) at room temperature (hereafter, RT‐COF‐1 ). RT‐COF‐1 shows a layered hexagonal structure exhibiting channels, is robust, and is porous to N₂ and CO₂. The room‐temperature synthesis has enabled us to fabricate and position low‐cost micro‐ and submicropatterns of RT‐COF‐1 on several surfaces, including solid SiO₂ substrates and flexible acetate paper, by using lithographically controlled wetting and conventional ink‐jet printing.     

构建S型异质结COF/CdS以增强太阳光产氢

高效利用太阳能是解决当前能源危机和环境问题的有效途径.光催化制氢技术具有绿色环保、成本低等优势,且氢气可作为能源载体,其燃烧产物仅为水,因此被认为是实现高效利用太阳能的最佳途径之一.为更好地利用太阳能,研究者们致力于开发具有良好可见光活性的光催化剂.CdS因具有良好的电荷转移能力和在可见光区域强吸收的特性,在光催化制氢...     

β-酮烯胺类手性共价有机框架的合成及在毛细管气相色谱中的应用

利用2,4,6-三羟基-1,3,5-苯三甲醛(Tfp)和(S)-2,5-双(2-甲基丁氧基)对苯二甲酸二酰肼(Mth)作为单体, 通过席夫碱反应合成了新型的β-酮烯胺类手性共价有机框架(COF)材料TfpMth COF. 采用粉末X射线衍射、 红外光谱、 热重分析及氮气吸附-脱附等手段对制备的TfpMth COF粉末进行了表征, 结果表明其具有良好的结晶度、 高的孔隙率和优异的热稳定性. 基于此, 以该COF为新型固定相采用原位生长法制备了TfpMth COF键合毛细管柱, 成功分离了一系列直链与支链的烷烃和醇类, 以及苯/环己烷、 乙苯/苯乙烯混合物. 该结果为β-酮烯胺类COF在色谱分离中的应用提供了新思路, 也为研究新型气相色谱固定相提供了参考.     

Molecular screening of metal-organic frameworks for CO2 storage

We report a molecular simulation study for CO2 storage in metal-organic frameworks (MOFs). As compared to the aluminum-free and cation-exchanged ZSM-5 zeolites and carbon nanotube bundle, IRMOF1 exhibits remarkably higher capacity. Incorporation of Na(+) cations into zeolite increases the capacity only at low pressures. By variation of the metal oxide, organic linker, functional group, and framework topology, a series of isoreticular MOFs (IRMOF1, Mg-IRMOF1, Be-IRMOF1, IRMOF1-(NH2)4, IRMOF10, IRMOF13, and IRMOF14) are systematically examined, as well as UMCM-1, a fluorous MOF (F-MOF1), and a covalent-organic framework (COF102). The affinity with CO2 is enhanced by addition of a functional group, and the constricted pore is formed by interpenetration of the framework; both lead to a larger isosteric heat and Henry's constant and subsequently a stronger adsorption at low pressures. The organic linker plays a critical role in tuning the free volume and accessible surface area and largely determines CO2 adsorption at high pressures. As a combination of high capacity and low framework density, IRMOF10, IRMOF14, and UMCM-1 are identified from this study to be the best for CO2 storage, even surpass the experimentally reported highest capacity in MOF-177. COF102 is a promising candidate with high capacity at considerably low pressures. Both gravimetric and volumetric capacities at 30 bar correlate well with the framework density, free volume, porosity, and accessible surface area. These structure-function correlations are useful for a priori prediction of CO2 capacity and for the rational screening of MOFs toward high-efficacy CO2 storage.     

Electrochemical Interfacial Polymerization toward Ultrathin COF Membranes for Brine Desalination

Ultrathin covalent organic framework (COF) membranes are urgently demanded in molecular/ionic separations. Herein, we reported an electrochemical interfacial polymerization strategy to fabricate ultrathin COF membranes with thickness of 85 nm, by actively manipulate self-healing effect and self-inhibiting effect. The resulting COF membrane exhibited superior performance in brine desalination with the permeation flux of 92 kg m⁻² h⁻¹ and the rejection of 99.96 %. Our electrochemical interfacial polymerization strategy enriches the fabrication approach of COF membranes and facilitates the rational design of ultrathin membranes.     

An Azine‐Linked Covalent Organic Framework: Synthesis,Characterization and Efficient Gas Storage

A azine‐linked covalent organic framework, COF‐JLU2, was designed and synthesized by condensation of hydrazine hydrate and 1,3,5‐triformylphloroglucinol under solvothermal conditions for the first time. The new covalent organic framework material combines permanent micropores, high crystallinity, good thermal and chemical stability, and abundant heteroatom activated sites in the skeleton. COF‐JLU2 possesses a moderate BET surface area of over 410 m² g^?1 with a pore volume of 0.56 cm³ g^?1. Specifically, COF‐JLU2 displays remarkable carbon dioxide uptake (up to 217 mg g^?1) and methane uptake (38 mg g^?1) at 273 K and 1 bar, as well as high CO₂/N₂ (77) selectivity. Furthermore, we further highlight that it exhibits a higher hydrogen storage capacity (16 mg g^?1) than those of reported COFs at 77 K and 1 bar.     

Mixed matrix membrane comprising polyimide with crystalline porous imide‐linked covalent organic framework for N2/O2 separation

An imide‐linked covalent organic framework (COF) was successfully synthesized by directly heating a mixture of melamine and biphenyltetracarboxylic dianhydride (BPDA) in a tubular oven at 335°C. The crystalline and nanostructure of this COF was characterized by X‐ray diffraction (XRD) and Brunauer‐Emmett‐Teller (BET). A mixed matrix membrane (MMM) was prepared by blending the COF into the commercial P84 polyimide in solution. It is found that the COF particles not only act as gas channels for N₂ and O₂ permeation but also provided an inverse permselective property with higher permeability of N₂. The effect of COF nanostructure and its loading amount on N₂ and O₂ permeability and selectivity has been investigated.     

Covalent Organic Framework (COF‐1) under High Pressure

COF‐1 has a structure with rigid 2D layers composed of benzene and B₃O₃ rings and weak van der Waals bonding between the layers. The as‐synthesized COF‐1 structure contains pores occupied by solvent molecules. A high surface area empty‐pore structure is obtained after vacuum annealing. High‐pressure XRD and Raman experiments with mesitylene‐filled (COF‐1‐M) and empty‐pore COF‐1 demonstrate partial amorphization and collapse of the framework structure above 12–15 GPa. The ambient pressure structure of COF‐1‐M can be reversibly recovered after compression up to 10–15 GPa. Remarkable stability of highly porous COF‐1 structure at pressures at least up to 10 GPa is found even for the empty‐pore structure. The bulk modulus of the COF‐1 structure (11.2(5) GPa) and linear incompressibilities (k_[100]=111(5) GPa, k_[001]=15.0(5) GPa) were evaluated from the analysis of XRD data and cross‐checked against first‐principles calculations.     

Direct Solar‐to‐Electrochemical Energy Storage in a Functionalized Covalent Organic Framework

A covalent organic framework integrating naphthalenediimide and triphenylamine units (NT‐COF) is presented. Two‐dimensional porous nanosheets are packed with a high specific surface area of 1276 m² g^?1. Photo/electrochemical measurements reveal the ultrahigh efficient intramolecular charge transfer from the TPA to the NDI and the highly reversible electrochemical reaction in NT‐COF. There is a synergetic effect in NT‐COF between the reversible electrochemical reaction and intramolecular charge transfer with enhanced solar energy efficiency and an accelerated electrochemical reaction. This synergetic mechanism provides the key basis for direct solar‐to‐electrochemical energy conversion/storage. With the NT‐COF as the cathode materials, a solar Li‐ion battery is realized with decreased charge voltage (by 0.5 V), increased discharge voltage (by 0.5 V), and extra 38.7 % battery efficiency.     

A novel amidoxime-functionalized covalent organic framework for removal of U(VI) from uranium-containing wastewater with appreciable efficiency and selectivity

Journal of Radioanalytical and Nuclear Chemistry - This work fabricated a novel two-dimensional (2D) amidoxime-functionalized covalent organic framework (COF) (named HDU-102-AO) for U(VI)...     

A MOF@COF Composite with Enhanced Uptake through Interfacial Pore Generation

Herein, we describe a new class of porous composites comprising metal–organic framework (MOF) crystals confined in single spherical matrices made of packed covalent‐organic framework (COF) nanocrystals. These MOF@COF composites are synthesized through a two‐step method of spray‐drying and subsequent amorphous (imine‐based polymer)‐to‐crystalline (imine‐based COF) transformation. This transformation around the MOF crystals generates micro‐ and mesopores at the MOF/COF interface that provide far superior porosity compared to that of the constituent MOF and COF components added together. We report that water sorption in these new pores occurs within the same pressure window as in the COF pores. Our new MOF@COF composites, with their additional pores at the MOF/COF interface, should have implications for the development of new composites.     

A Two-dimensional Dual-pore Covalent Organic Framework for Efficient Iodine Capture

Effectively capturing volatile radioiodine generated during the nuclear fission process is considered to be a safe way to the utilization of nuclear power. Here we report a new two-dimensional covalent organic framework(2D COF), ETTA-PyTTA-COF, as a highly efficient iodine adsorbent, which is constructed through the condensation reaction between 4,4’,4’’,4’’’-(ethene-1,1,2,2-tetrayl)-tetrabenzaldehyde(ETTA) and 1,3,6,8-tetrakis(4-aminophenyl)pyrene(PyTTA). The ETTA-PyTTA-COF possesses a permanent 1D channel porous structure with a high Brunauer-Emmet-Teller(BET) surface area of 1519 m²/g and excellent chemical and thermal stability. It shows ultrahigh iodine adsorption capability, which can reach up to 4.6 g/g in vapor owing to its high BET surface area, large π-conjugated structure and plenty of imine groups in the skeleton of the COF as effective iodine sorption sites.     

Electronic Structure of a Semiconducting Imine‐Covalent Organic Framework

Imine COF (covalent organic framework) based on the Schiff base reaction between p‐phenylenediamine (PDA) and benzene‐1,3,5‐tricarboxaldehyde (TCA) was prepared on the HOPG‐air (air=humid N₂) interface and characterized using different probe microscopies. The role of the molar ratio of TCA and PDA has been explored, and smooth domains of imine COF up to a few μm are formed for a high TCA ratio (>2) compared to PDA. It is also observed that the microscopic roughness of imine COF is strongly influenced by the presence of water (in the reaction chamber) during the Schiff base reaction. The electronic property of imine COF obtained by tunneling spectroscopy and dispersion corrected density functional theory (DFT) calculation are comparable and show semiconducting nature with a band gap of ≈1.8 eV. Further, we show that the frontier orbitals are delocalized entirely over the framework of imine COF. The calculated cohesive energy shows that the stability of imine COF is comparable to that of graphene.     

Rational Design of MOF/COF Hybrid Materials for Photocatalytic H2 Evolution in the Presence of Sacrificial Electron Donors

Crystalline and porous covalent organic frameworks (COFs) and metal‐organic frameworks (MOFs) materials have attracted enormous attention in the field of photocatalytic H₂ evolution due to their long‐range order structures, large surface areas, outstanding visible light absorbance, and tunable band gaps. In this work, we successfully integrated two‐dimensional (2D) COF with stable MOF. By covalently anchoring NH₂‐UiO‐66 onto the surface of TpPa‐1‐COF, a new type of MOF/COF hybrid materials with high surface area, porous framework, and high crystallinity was synthesized. The resulting hierarchical porous hybrid materials show efficient photocatalytic H₂ evolution under visible light irradiation. Especially, NH₂‐UiO‐66/TpPa‐1‐COF (4:6) exhibits the maximum photocatalytic H₂ evolution rate of 23.41 mmol g^?1 h^?1 (with the TOF of 402.36 h^?1), which is approximately 20 times higher than that of the parent TpPa‐1‐COF and the best performance photocatalyst for H₂ evolution among various MOF‐ and COF‐based photocatalysts.     

Hot π‐Electron Tunneling of Metal–Insulator–COF Nanostructures for Efficient Hydrogen Production

A metal–insulator–semiconductor (MIS) photosystem based on covalent organic framework (COF) semiconductors was designed for robust and efficient hydrogen evolution under visible‐light irradiation. A maximal H₂ evolution rate of 8.42 mmol h^?1 g^?1 and a turnover frequency of 789.5 h^?1 were achieved by using a MIS photosystem prepared by electrostatic self‐assembly of polyvinylpyrrolidone (PVP) insulator‐capped Pt nanoparticles (NPs) with the hydrophilic imine‐linked TP‐COFs having =C=O?H?N= hydrogen‐bonding groups. The hot π‐electrons in the photoexcited n‐type TP‐COF semiconductors can be efficiently extracted and tunneled to Pt NPs across an ultrathin PVP insulating layer to reduce protons to H₂. Compared to the Schottky‐type counterparts, the COF‐based MIS photosystems give a 32‐fold‐enhanced carrier efficiency, attributed to the combined enhancement of photoexcitation rate, charge separation, and oxidation rate of holes accumulated in the valence band of the TP‐COF semiconductor.     

Heterogenization of Salen Metal Molecular Catalysts in Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution

Integrating a molecular catalyst with a light harvester into a photocatalyst is an effective strategy for solar light conversion. However, it is challenging to establish a crystallized framework with well-organized connections that favour charge separation and transfer. Herein, we report the heterogenization of a Salen metal complex molecular catalyst into a rigid covalent organic framework (COF) through covalent linkage with the light-harvesting unit of pyrene for photocatalytic hydrogen evolution. The chemically conjugated bonds between the two units contribute to fast photogenerated electron transfer and thereby promote the proton reduction reaction. The Salen cobalt-based COF showed the best hydrogen evolution activity (1378 μmol g⁻¹ h⁻¹), which is superior to the previously reported nonnoble metal based COF photocatalysts. This work provides a strategy to construct atom-efficient photocatalysts by the heterogenization of molecular catalysts into covalent organic frameworks.     

Application of GO/COF as a novel,efficient and recoverable catalyst in the Knoevenagel reaction

Hybrid composite based on graphene oxide (GO) and covalent organic framework (COF) [GO/COF] was developed via a simple solvothermal method, at which GO was applied as a platform to load COF based on melamine and terephthaldehyde. The synthesized hybrid nanocomposite was characterized by FT-IR, XRD, EDX and SEM techniques. Morphological analyses carried out by SEM confirm the successful growth of COF over GO. Then, the resultant composite was employed as an amazing and cost-effective catalyst in the condensation of several aldehydes with malononitrile and produced the corresponding coupling products in high yields (up to 84%) at room temperature under solvent-free conditions with an amount of catalyst, 15 mg in a very short reaction time of 10 min. The catalyst could be reused without a noteworthy drop in catalytic activity at least eight times. The use of GO/COF catalyst outcomes under mild reaction conditions in very short reaction time, exceptional catalytic activity, high recyclability and an easy work-up process for the Knoevenagel condensation.     

Atmospheric chemistry of CH3CHF2 (HFC-152a): kinetics, mechanisms, and products of Cl atom- and OH radical-initiated oxidation in the presence and absence of NO(x)

Smog chamber/Fourier transform infrared (FTIR) and laser-induced fluorescence (LIF) spectroscopic techniques were used to study the atmospheric degradation of CH3CHF2. The kinetics and products of the Cl(2P(3/2)) (denoted Cl) atom- and the OH radical-initiated oxidation of CH3CHF2 in 700 Torr of air or N2; diluents at 295 +/- 2 K were studied using smog chamber/FTIR techniques. Relative rate methods were used to measure k(Cl + CH3CHF2) = (2.37 +/- 0.31) x 10(-13) and k(OH + CH3CHF2) = (3.08 +/- 0.62) x 10(-14) cm3 molecule(-1) s(-1). Reaction with Cl atoms gives CH3CF2 radicals in a yield of 99.2 +/- 0.1% and CH2CHF2 radicals in a yield of 0.8 +/- 0.1%. Reaction with OH radicals gives CH3CF2 radicals in a yield >75% and CH2CHF2 radicals in a yield <25%. Absolute rate data for the Cl reaction were measured using quantum-state selective LIF detection of Cl(2P(j)) atoms under pseudo-first-order conditions. The rate constant k(Cl + CH3CHF2) was determined to be (2.54 +/- 0.25) x 10(-13) cm3 molecule(-1) s(-1) by the LIF technique, in good agreement with the relative rate results. The removal rate of spin-orbit excited-state Cl(2P(1/2)) (denoted Cl) in collisions with CH3CHF2 was determined to be k(Cl + CH3CHF2) = (2.21 +/- 0.22) x 10(-10) cm3 molecule(-1) s(-1). The atmospheric photooxidation products were examined in the presence and absence of NO(x). In the absence of NO(x)(), the Cl atom-initiated oxidation of CH3CHF2 in air leads to formation of COF2 in a molar yield of 97 +/- 5%. In the presence of NO(x), the observed oxidation products include COF2 and CH3COF. As [NO] increases, the yield of COF2 decreases while the yield of CH3COF increases, reflecting a competition for CH3CF2O radicals. The simplest explanation for the observed dependence of the CH3COF yield on [NO(x)] is that the atmospheric degradation of CH3CF2H proceeds via OH radical attack to give CH3CF2 radicals which add O2 to give CH3CF2O2 radicals. Reaction of CH3CF2O2 radicals with NO gives a substantial fraction of chemically activated alkoxy radicals, [CH3CF2O]. In 1 atm of air, approximately 30% of the alkoxy radicals produced in the CH3CF2O2 + NO reaction possess sufficient internal excitation to undergo "prompt" (rate >10(10) s(-1)) decomposition to give CH3 radicals and COF2. The remaining approximately 70% become thermalized, CH3CF2O, and undergo decomposition more slowly at a rate of approximately 2 x 10(3) s(-1). At high concentrations (>50 mTorr), NO(x) is an efficient scavenger for CH3CF2O radicals leading to the formation of CH3COF and FNO.     

A Hollow Microtubular Triazine‐ and Benzobisoxazole‐Based Covalent Organic Framework Presenting Sponge‐Like Shells That Functions as a High‐Performance Supercapacitor

In this paper we report the construction of a hollow microtubular triazine‐ and benzobisoxazole‐based covalent organic framework (COF) presenting a sponge‐like shell through a template‐free [3+2] condensation of the planar molecules 2,4,6‐tris(4‐formylphenyl)triazine (TPT‐3CHO) and 2,5‐diaminohydroquinone dihydrochloride (DAHQ‐2HCl). The synthesized COF exhibited extremely high crystallinity, a high surface area (ca. 1855 m² g^?1), and ultrahigh thermal stability. Interestingly, a time‐dependent study of the formation of the hollow microtubular COF having a sponge‐like shell revealed a transformation from initial ribbon‐like crystallites into a hollow tubular structure, and confirmed that the hollow nature of the synthesized COF was controlled by inside‐out Ostwald ripening, while the non‐interaction of the crystallites on the outer surface was responsible for the sponge‐like surface of the tubules. This COF exhibited significant supercapacitor performance: a high specific capacitance of 256 F g^?1 at a current density of 0.5 A g^?1, excellent cycling stability (98.8 % capacitance retention over 1850 cycles), and a high energy density of 43 Wh kg^?1. Such hollow structural COFs with sponge‐like shells appear to have great potential for use as high‐performance supercapacitors in energy storage applications.