ABSTRACT
The vinylene-linked covalent organic frameworks (viCOFs) have been generally synthesized in the presence of homogeneous catalysts such as KOH or trifluoroacetic acid. However, highly ordered viCOFs cannot always be obtained due to the uncommitted growth of viCOF layers in the homogeneous system with ubiquitous catalysts. Here, we propose a scalable protocol to restrict the growth of viCOFs along the two-dimensional (2D) plane by introducing a heterogeneous catalyst, polyoxometalates (POMs). With the unique Brønsted alkalinity and catalytic surface, POMs induce the growth of 2D viCOF layers along the surface of the catalytic substrate and restrain the generation of out-of-plane branches. Based on this protocol, six typical 2D viCOFs with high crystallinity and porosity were synthesized within a shorter reaction time as compared with the reported works using the common homogeneous catalysts for viCOF synthesis. On the basis of the density functional theory calculations and experimental results, a bottom intercalation growth pattern of viCOFs was revealed during the heterogeneous reaction. The unique growth pattern greatly promotes the orderly assembly of monomers, thus shortening the reaction time and improving the crystallinity of viCOFs. Furthermore, this heterogeneous catalysis strategy is suitable for the gram-scale preparation of 2D viCOFs. These results provide a novel avenue for the synthesis of high-quality viCOFs and may bring new insights into the synthetic methodology of COFs.
ABSTRACT
Porous organic polymers (POPs) with inherent porosity, tunable pore environment, and semiconductive property are ideally suitable for application in various advanced semiconductor-related devices. However, owing to the lack of processability, POPs are usually prepared in powder forms, which limits their application in advanced devices. Herein, we demonstrate an example of information storage application of POPs with film form prepared by an electrochemical method. The growth process of the electropolymerized films in accordance with the Volmer-Weber model was proposed by observation of atomic force microscopy. Given the mechanism of the electron transfer system, we verified and mainly emphasized the importance of porosity and interfacial properties of porous polymer films for memristor. As expected, the as-fabricated memristors exhibit good performance on low turn-on voltage (0.65 ± 0.10 V), reliable data storage, and high on/off current ratio (104). This work offers inspiration for applying POPs in the form of electropolymerized films in various advanced semiconductor-related devices.
ABSTRACT
The tunable pore walls and skeletons render covalent organic frameworks (COFs) as promising absorbents for gold (Au) ion. However, most of these COFs suffered from low surface areas hindering binding sites exposed and weak binding interaction resulting in sluggish kinetic performance. In this study, COFs have been constructed with synergistic linker and linkage for high-efficiency Au capture. The designed COFs (PYTA-PZDH-COF and PYTA-BPDH-COF) with pyrazine or bipyridine as linkers showed high surface areas of 1692 and 2076 m2 gâ1, providing high exposed surface areas for Au capture. In addition, the Lewis basic nitrogen atoms from the linkers and linkages are easily hydronium, which enabled to fast trap Au via coulomb force. The PYTA-PZDH-COF and PYTA-BPDH-COF showed maximum Au capture capacities of 2314 and 1810 mg g-1, higher than other reported COFs. More importantly, PYTA-PZDH-COF are capable of rapid adsorption kinetics with achieving 95% of maximum binding capacity in 10 min. The theoretical calculation revealed that the nitrogen atoms in linkers and linkages from both COFs are simultaneously hydronium, and then the protonated PYTA-PZDH-COF are more easily binding the AuCl4 â, further accelerating the binding process. This study gives the a new insight to design COFs for ion capture.
ABSTRACT
Covalent organic frameworks (COFs) have attracted considerable attention as adsorbents for capturing and separating gold from electronic wastes. To enhance the binding capture efficiency, constructing hydrogen-bond nanotraps along the pore walls was one of the most widely adopted approaches. However, the development of absorbing skeletons was ignored due to the weak binding ability of the gold salts (Au). Herein, we demonstrated skeleton engineering to construct highly efficiently absorbs for Au capture. The strong electronic donating feature of diarylamine units enhanced the electronic density of binding sites (imine-linkage) and thus resulted in high capacities over 1750â mg g-1 for all three COFs. Moreover, the absorbing performance was further improved via the ionization of diarylamine units. The ionic COF achieved 90 % of the maximal adsorption capacity, 1.63â times of that from the charge-neutral COF within ten minutes, and showed remarkable uptakes of 1834â mg g-1 , exceptional selectivity (97.45 %) and cycling stability. The theoretical calculation revealed the binding sites altering from imine bonds to ionic amine sites after ionization of the frameworks, which enabled to bind the AuCl4 - via coulomb force and contributed to enhanced absorbing kinetics. This work inspires us to design molecular/ionic capture based on COFs.
ABSTRACT
Covalent organic frameworks (COFs) are a type of crystalline porous polymers that possess ordered structures and eternal pores. Because of their unique structural characteristics and diverse functional groups, COFs have been used in various application fields, such as adsorption, catalysis, separation, ion conduction, and energy storage. Among COFs, the fluorine-containing COFs (fCOFs) have been developed for special applications by virtue of special physical and chemical properties resulting from fluorine element, which is a nonmetallic halogen element and possesses strong electronegativity. In the organic chemistry field, introducing fluorine into chemicals enables those chemicals to exhibit many interesting properties, and fluorine chemistry increasingly plays an important role in the history of chemical development. The introduction of fluorine in COFs can enhance the crystallinity, porosity, and stability of COFs, making COFs having superior performances and some new applications. In this review, the synthesis and application of fCOFs are systematically summarized. The application involves photocatalytic production of hydrogen peroxide, photocatalytic water splitting, electrocatalytic CO2 reduction, adsorption for different substances (H2 , pesticides, per-/polyfluoroalkyl substances, polybrominated diphenyl ethers, bisphenols, and positively charged organic dye molecules), oil-water separation, energy storage (e.g., zinc-ion batteries, lithium-sulfur batteries), and proton conduction. Perspectives of remaining challenges and possible directions for fCOFs are also discussed.
Subject(s)
Fluorine , Metal-Organic Frameworks , Halogens , PolymersABSTRACT
Porous organic polymers (POPs) composed of organic building units linked via covalent bonds are a class of lightweight porous network materials with high surface areas, tuneable pores, and designable components and structures. Owing to their well-preserved characteristics in terms of structure and composition, POPs applied as electrocatalysts have shown promising activity and achieved considerable advances in numerous electrocatalytic reactions, including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, CO2 reduction reaction, N2 reduction reaction, nitrate/nitrite reduction reaction, nitrobenzene reduction reaction, hydrogen oxidation reaction, and benzyl alcohol oxidation reaction. Herein, we present a systematic overview of recent advances in the applications of POPs in these electrocatalytic reactions. The synthesis strategies, specific active sites, and catalytic mechanisms of POPs are summarized in this review. The fundamental principles of some electrocatalytic reactions are also concluded. We further discuss the current challenges of and perspectives on POPs for electrocatalytic applications. Meanwhile, the possible future directions are highlighted to afford guidelines for the development of efficient POP electrocatalysts.
ABSTRACT
Covalent organic frameworks (COFs) with structural designability and tunability of photophysical properties enable them to be a promising class of organic luminescent materials by incorporating well-designed fluorescent units directly into the periodic skeletons. The photophysical properties of COFs are mainly affected by the structural features, which determine the conjugation degree, charge delocalization ability, and exciton dynamics of COFs. To understand the relationship between COF structures and their photophysical properties, two COFs with the same pyrene chromophore units but different linkages (imine or vinylene) were designed and synthesized. Interestingly, different linkages endow COFs with huge differences in solid-state photoluminescence quantum yield (PLQY) for imine- and vinylene-linked pyrene-based COFs, which possess PLQY values of 0.34 % and 15.43 %, respectively. The femtosecond-transient absorption spectra and time-dependent density functional theory reveal the different charge-transfer pathways in imine- and vinylene-linked COFs, which influence the exciton relaxation way and fluorescence intensity. In addition, an effective white-light device was obtained by coating the vinylene-linked COF on a light-emitting diode strip.
ABSTRACT
Constructing a powerful photocatalytic system that can achieve the carbon dioxide (CO2 ) reduction half-reaction and the water (H2 O) oxidation half-reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with a crystalline topological network, named viCOF-bpy-Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust -C=C- bond linkages. The charge-separation ability of viCOF-bpy-Re is promoted by low polarized π-bridges between rhenium complexes and triazine ring units, and the efficient charge-separation enables the photogenerated electron-hole pairs, followed by an intramolecular charge-transfer process, to form photogenerated electrons involved in CO2 reduction and photogenerated holes that participate in H2 O oxidation simultaneously. The viCOF-bpy-Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate (190.6â µmol g-1 h-1 with about 100 % selectivity) and oxygen (O2 ) evolution (90.2â µmol g-1 h-1 ) among all the porous catalysts in CO2 reduction with H2 O as sacrificial agents. Therefore, a powerful photocatalytic system was successfully achieved, and this catalytic system exhibited excellent stability in the catalysis process for 50â hours. The structure-function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.
ABSTRACT
Porous organic polymer films (PFs) with intrinsical porosity and tuneable pore environment are ideally suited for application in electronic devices. However, the huge challenges still exist for construction of electronic devices based on PFs owing to lack of robustness, processability, and controllable preparation. Herein, we report the electrochemical preparation of carbazole-based porous organic polymer films (eCPFs) as switchable materials for the memristors. These eCPFs possess the characteristics of controllable thickness/size, high stability, and excellent porosity. Carbazole and cyano groups are introduced into the eCPFs to constructing electron transfer systems. Thus, the memristors constructed based on these eCPFs exhibit excellent switching performance, reliability, and reproducibility. The electrochemically controllable preparation method of porous organic polymer membranes proposed in this paper provides a feasible idea for the developments of electronic devices.
ABSTRACT
The cycloaddition of carbon dioxide (CO2) with epoxides to yield highly value-added cyclic carbonates is an effective way to chemically utilize and convert CO2. Here, a heterogeneous catalyst of imidazole ionic liquid-decorated covalent organic framework with polyoxometalates (POM@ImTD-COF) was constructed by the covalent modification of ionic liquids to COFs and the electrostatic interaction between POMs and ionic liquids. The obtained POM@ImTD-COF shows high catalytic activity for CO2 cycloaddition reaction under mild conditions (1 atm and 80 °C) in the presence of a co-catalyst, and the catalytic activity of POM@ImTD-COF has no obvious decrease during reusing five times. The excellent catalytic performance is mainly attributed to the synergistic effect of ionic liquids, POMs, and COFs. In the cycloaddition process, ionic liquids and the co-catalyst weaken the C-O bond of epoxides and promote the ring opening of epoxides. POMs as the Lewis acids facilitate the insertion of CO2 to form reaction intermediates. The multiple activation effect of ionic liquids and POMs together with the CO2 adsorption effect and well-dispersed active sites in COFs contribute to the remarkable catalytic performance.
ABSTRACT
Polyaniline, as a kind of conductive polymer with commercial application prospects, is still under researches in its synthesis and applications. In this work, polyaniline was fabricated on flexible substrates including carbon cloths and polyethylene naphthalate byin situelectropolymerization method. The synthesized flexible electrodes were characterized by scanning electron microscopy, High resolution transmission electron microscope, atomic force microscope, Fourier transform infrared, x-ray diffraction, and x-ray photoelectron spectroscopy. Owing to the conductivity and the reversible redox property, the polyaniline/carbon cloth electrodes show excellent properties such as decent supercapacitor performance and good detection capability toward ascorbic acid. As supercapacitors, the electrodes exhibit a specific capacitance as high as 776 F g-1at a current density of 1 A g-1and a long cycle life of 20 000 times in the three-electrode system. As ascorbic acid sensors, the flexible electrodes demonstrate stable response to ascorbic acid in the range of 1-3000µM with an outstanding sensitivity (4228µA mM-1cm-2), low detection limit (1µM), and a fast response time. This work holds promise for high-performance and low-cost flexible electrodes for both supercapacitors and non-enzymatic ascorbic acid sensors, and may inspire inventions of self-powered electrochemical sensor.
ABSTRACT
Lithium-sulfur batteries are considered as the next generation of energy storage systems because of their high theoretical specific capacity and energy density. Unfortunately, the sluggish reaction kinetics, weak adsorption toward to lithium polysulfides, and slow lithium ion diffusion impede the smooth electrochemical process, resulting in the lithium-sulfur batteries with the unsatisfactory cycling stability and rate performance. Since it is recognized that polar metal oxides and doped nitrogen in carbon materials have chemical interaction with lithium polysulfides, a nanostructured nitrogen-doped porous carbon/MoO2 composite is synthesized through a simple hydrothermal method by using graphene oxide nanoribbon and phosphomolybdic acid hydrate as precursors. The porous nanostructure promotes the charge and mass transport, while MoO2 nanoparticles immobilize lithium polysulfides via strong chemisorption and enhance the redox kinetics of polysulfides owing to the efficient catalytic activity in liquid-solid boundary. Consequently, the as-obtained nanostructured porous carbon/MoO2-based sulfur cathode exhibits low polarization, high initial discharge capacity (1403 mAh g-1 at 0.1 C), good rate capabilities (584 mAh g-1 at 4 C), and impressive cycling performance at 1 C (503 mAh g-1 after 500 cycles with capacity fade rate of 0.07% per cycle).
ABSTRACT
99TcO4- is highly radioactive and hazardous to both the environment and public health, meanwhile, it is quite challenging to have it efficiently removed. Herein an imidazolium-based cationic porous polymer (ImPOP-1) is evaluated for removal of TcO4-, with nonradioactive ReO4- as the surrogate for experimental operation. It is demonstrated that ImPOP-1 is a rare example that can integrate high adsorption capacity (610 mg g-1), fast kinetics (93.3% in 30 s), and high selectivity (72.9% in 1000 times excess of SO42- ions) in one material. The distribution coefficient Kd is among the top up to 3.2 × 105 mL g-1. ImPOP-1 also displays high adsorption performance over a wide range of pH values, and removal efficiency up to 64.3% in a highly alkaline solution (3 M NaOH). Recyclability experiments demonstrate that ImPOP-1 can be reused at least four times. The ImPOP-1 also retains a consistent adsorption capacity up to 609 ± 6.1 mg g-1 between three different batches of samples. In addition, a real-scenario experiment shows that ImPOP-1 can remove 97.4% of ReO4- in a simulated Hanford LAW stream.
Subject(s)
Radioactive Waste , Adsorption , Cations , Polymers , PorosityABSTRACT
In this study, we have prepared novel pyrrole-formaldehyde polymers through polymerizing pyrrole and formaldehyde in the mixture solvent of water and ethanol by using hydrochloric acid as a catalyst. The as-synthesized polymers possess a nitrogen content of 6.7 atom % and are composed of spherical particles with the diameter of approximately 1-3 µm. A series of nitrogen-doped porous carbons with high specific surface areas (680-2340 m2 g-1) were successfully obtained through the activation treatment of the polymer spheres. The porous properties and surface chemistry of the as-prepared porous carbons are tuned by choosing different activating agents and changing the activation temperature. The morphology, porous properties, and chemical composition of the obtained nitrogen-doped porous carbons are revealed by various characterization methods, such as scanning electron microscopy, nitrogen sorption measurement, and X-ray photoelectron spectroscopy. The as-prepared nitrogen-doped porous carbons as gas adsorbents display high carbon dioxide uptake capacities of 3.80-5.81 mmol g-1 at 273 K and 1.0 bar. They also show excellent carbon dioxide adsorption capacities (2.40-3.37 mmol g-1 at 1.0 bar) and good gas selectivities (CO2/N2 selectivities of 16.9-70.2) at 298 K.
ABSTRACT
Proton-exchange membrane fuel cells, emerging as green and sustainable energy sources, have attracted extensive attention in recent decades. Porous organic polymers, which feature in high surface area values, tunable pore sizes, excellent thermal and chemical stabilities, and the flexibility to incorporate specific functional groups, have recently displayed their striking images as potential electrolytes for fuel cells. In this work, BO-CMP-1 and BO-CMP-2 that possess rich π-structure and permanent porosity and have high thermal and chemical stability were synthesized through Suzuki-Miyaura coupling reaction. Owing to their rigid structures and abundant electrophilic substitution positions, these two novel porous polymers were covalently decorated with dense sulfonic acid groups by postsulfonation, as denoted by SBO-CMP-1 and SBO-CMP-2. The proton conductivity of SBO-CMPs is systematically studied to evaluate their performance as proton-conductive materials. It was found that their performance is highly humidity- and temperature-dependent and they show relatively high proton conductivity. For SBO-CMP-1 and SBO-CMP-2, their proton conductivities are 1.29 × 10-2 and 5.21 × 10-3 S cm-1, respectively, at 70 °C and 100% relative humidity. Low activation energy values of 0.32 eV for SBO-CMP-1 and 0.40 eV for SBO-CMP-2 suggest the Grotthuss mechanism for proton conduction.
ABSTRACT
In this work, a series of highly porous sulfur-doped carbons are prepared through physical activation methods by using polythiophene as a precursor. The morphology, structure, and physicochemical properties are revealed by a variety of characterization methods, such as scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and nitrogen sorption measurement. Their porosity parameters and chemical compositions can be well-tuned by changing the activating agents (steam and carbon dioxide) and reaction temperature. These sulfur-doped porous carbons possess specific surface area of 670-2210 m2 g-1, total pore volume of 0.31-1.26 cm3 g-1, and sulfur content of 0.6-4.9 atom %. The effect of porosity parameters and surface chemistry on carbon dioxide adsorption in sulfur-doped porous carbons is studied in detail. After a careful analysis of carbon dioxide uptake at different temperatures (273 and 293 K), pore volumes from small pore size (less than 1 nm) play an important role in carbon dioxide adsorption at 273 K, whereas surface chemistry is the key factor at a higher adsorption temperature or lower relative pressure. Furthermore, sulfur-doped porous carbons also possess good gas adsorption selectivity and excellent recyclability for regeneration.
ABSTRACT
Polycarbazoles with rigid skeletons and electron-rich conjugated systems are beneficial to form permanent porous materials with intrinsic photoelectric properties. In recent years, the research related to porous polycarbazoles becomes a hot topic in the field of porous organic polymers. The preparation methods for porous polycarbazoles are diverse, commonly represented by the oxidation coupling reaction and the Friedel-Crafts reaction. Other methods such as nitrile-based trimerization, electrochemical polymerization, and classic C-C coupling reactions are also reported. Porous polycarbazoles generally possess large specific surface area, permanent pore structure, and high thermal and chemical stability, which show potential applications in gas storage and separation, catalysis, sensors, and electronics. In this review, the recent research progress on the synthetic methods, functions, and applications of porous polycarbazoles is summarized.
Subject(s)
Carbazoles/chemistry , Polymerization , Polymers/chemistry , Adsorption , Carbazoles/chemical synthesis , Catalysis , Oxidation-Reduction , Polymers/chemical synthesis , PorosityABSTRACT
By considering the high reactivity of fluorinated iron-porphyrin and good stability of porphyrin-based porous polymers, fluorinated iron-porphyrin conjugated porous polymers (FPOP-3-6) were synthesized through direct C-H arylation polymerization. The obtained materials are chemically and thermally stable, of which FPOP-3 exhibits the highest Brunauer-Emmett-Teller specific surface area (about 840â m2 g-1 ). For functional studies of the obtained polymers as heterogeneous catalysts, catalytic transformation of cycloketones into lactones by oxygen through Baeyer-Villiger oxidation was used as a model reaction. Fluorinated phenyl substituents of the iron-porphyrin not only are beneficial to the conversion, but also can stabilize the porphyrin to resist catalyst breakdown. The polymer FPOP-3, with high porosity, exhibits the best catalytic efficiency and recycling effect. The recovered catalyst also shows good catalytic activities after recycling three times with a small loss in yield.
ABSTRACT
Core-shell structured nitrogen-doped porous carbon@silica material with uniform structure and morphology was synthesized via a sol-gel method. During this process, a commercial triblock copolymer and the in situ formed pyrrole-formaldehyde polymer acted as cotemplates, while tetraethyl orthosilicate acted as silica precursor. The synergetic effect of the triblock copolymer and the pyrrole-formaldehyde polymer enables the formation of the core-shell structure. Herein, the pyrrole-formaldehyde polymer acted as not only the template, but also the nitrogen-doped carbon precursor of the core. The obtained core-shell structured porous material possesses moderate Brunauer-Emmett-Teller specific surface area (410 m2 g-1) and pore volume (0.53 cm3 g-1). Moreover, corresponding hollow silica spheres or nitrogen-doped porous carbon spheres can be synthesized by calcining the core-shell structured material in air or etching it with HF. The X-ray photoelectron spectroscopy results reveal that the nitrogen states of the obtained material are mainly pyridinic-N and pyridonic-N/pyrrolic-N, which are beneficial for carbon dioxide adsorption. The carbon dioxide uptake capacity of the nitrogen-doped carbon spheres can reach 12.3 wt % at 273 K and 1.0 bar, meanwhile, the material shows good gas adsorption selectivities for CO2/CH4 and CO2/N2.
ABSTRACT
Lithium-sulfur batteries have attracted great concern because of the high theoretical capacity of sulfur (1675 mA h g-1). However, the poor electrical conductivity and volumetric expansion of sulfur along with the dissolution of lithium polysulfides largely limit their practical application. In this study, nitrogen-doped graphene aerogel (NGA) with high nitrogen content and porosity is used as a host for the impregnation of sulfur. The effects of sulfur impregnation on the specific surface area, pore volume, and microstructure of NGA supported sulfur composite (S@NGA) are well investigated. Furthermore, NGA is also processed into a NGA film, which is sandwiched between a separator and S@NGA cathode. The lithium-sulfur battery with such a configuration delivers a high reversible capacity of 1514 mA h g-1 at 0.1 C, excellent rate performance (822 mA h g-1 at 2.0 C), and good cycling stability (946 mA h g-1 at 0.5 C even after 100 cycles). The enhanced electrochemical performance can be ascribed to the introduction of the NGA interlayer, the unique interconnected porous structure, and strong interaction between the three-dimensional nitrogen-doped graphene network and the homogeneously dispersed sulfur and/or lithium polysulfides.