Metal organic polymers with dual catalytic sites for oxygen reduction and oxygen evolution reactions

Metal-organic frameworks and covalent organic frameworks have been widely employed in electrochemical catalysis owing to their designable skeletons,controllable porosities,and well-defined catalytic centers.However,the poor chemical stability and low electron conductivity limited their activity,and single-functional sites in these frameworks hindered them to show multifunctional roles in catalytic systems.Herein,we have constructed novel metal organic polymers(Co-HAT-CN and Ni-HAT-CN)with dual catalytic centers(metal-N_(4) and metal-N_(2))to catalyze oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).By using different metal centers,the catalytic activity and selectivity were well-tuned.Among them,Co-HAT-CN catalyzed the ORR in a 4e^(-)pathway,with a half-wave potential of 0.8 V versus RHE,while the Ni-HAT-CN catalyze ORR in a 2e^(-)pathway with H_(2)O_(2) selectivity over 90%.Moreover,the Co-HAT-CN delivered an overpotential of 350 mV at 10 mA cm^(-2) with a corresponding Tafel slope of 24 mV dec^(-1) for OER in a 1.0 M KOH aqueous solution.The experimental results revealed that the activities toward ORR were due to the M-N_(4) sites in the frameworks,and both M-N_(4) and M-N_(2) sites contributed to the OER.This work gives us a new platform to construct bifunctional catalysts.

Recent progress in porous organic polymers and their application for CO_(2) capture

Carbon capture,storage,and utilization(CCSU)is recognized as an effective method to reduce the excessive emission of CO_(2).Absorption by amine aqueous solutions is considered highly efficient for CO_(2) capture from the flue gas because of the large CO_(2) capture capacity and high selectivity.However,it is often limited by the equipment corrosion and the high desorption energy consumption,and adsorption of CO_(2) using solid adsorbents has been receiving more attention in recent years due to its simplicity and high efficiency.More recently,a great number of porous organic polymers(POPs)have been designed and constructed for CO_(2) capture,and they are proven promising solid adsorbents for CO_(2) capture due to their high Brunauer-Emmett-Teller(BET)surface area(SBET),adjustable pore size and easy functionalization.In particular,they usually have rigid skeleton,permanent porosity,and good physiochemical stability.In this review,we have a detailed review for the different POPs developed in recent years,not only the design strategy,but also the special structure for CO_(2) capture.The outlook of the opportunities and challenges of the POPs is also proposed.

Post-synthesis modification of porous organic polymers with amine： a task-specific microenvironment for CO2 capture

A porous organic polymer named FC-POP was facilely synthesized with extraordinary porosity and excellent stability. Further covalent incorporation of various amines including single amine group, multi-amine groups of diethylenediamine （DETA）, and poly-amine groups of polyethylenimine （PEI） to the network gave rise to task-specific modification of the microenvironments to make them more suitable for CO2 capture. As a result, significant boost of CO2 adsorption capacity of 4.5 mmol/g （for FC-POP-CH2DETA, 273 K, 1 bar） and the CO2/N2 selectivity of 736.1 （for FC- POP-CH2PEI） were observed after the post-synthesis amine modifications. Furthermore, these materials can be regener- ated in elevated temperature under vacuum without apparent loss of CO2 adsorption capacity.

Boosting selective C_(2)H_(2)/CH_(4),C_(2)H_(4)/CH_(4) and CO_(2)/CH_(4) adsorption performance via 1,2,3-triazole functionalized triazine-based porous organic polymers

Nitrogen-rich porous organic polymers have shown great potentials in gas adsorption/separation,photocatalysis,electrochemistry,sensing and so on.Herein,1,2,3-triazole functionalized triazine-based porous organic polymers(TT-POPs)have been synthesized by the copper-catalyzed azide-alkyne cycloaddition(Cu-AAC)polymerization reactions of 1,3,5-tris(4-azidophenyl)-triazine with 1,4-diacetylene benzene and 1,3,5-triacetylenebenzene,respectively.The characterizations of N2 adsorption at 77 K show TTPOPs possess permanent porosity with BET surface areas of 666 m^(2)·g^(-1)(TT-POP-1)and 406 m^(2)·g^(-1)(TT-POP-2).The adsorption capacities of TT-POPs for CO_(2),CH4,C2H2 and C2H4,as well as the selective separation abilities of CO_(2)/N2,CO_(2)/CH_(4),C_(2)H_(2)/CH_(4) and C_(2)H_(4)/CH_(4) were evaluated.The gas selective separation ratio of TT-POPs was calculated by the ideal adsorbed solution theory(IAST)method,wherein the selective separation ratios of C_(2)H_(2)/CH_(4) and C_(2)H_(4)/CH_(4) of TT-POP-2 was 48.4 and 13.6(298 K,0.1 MPa),which is comparable to other adsorbents(5.6–120.6 for C_(2)H_(2)/CH_(4),10–26 for C_(2)H_(4)/CH_(4)).This work shows that the 1,2,3-triazole functionalized triazine-based porous organic polymer has a good application prospect in natural gas purification.

Polarization engineering in porous organic polymers for charge separation efficiency and its applications in photocatalytic aerobic oxidations

Photocatalytic aerobic oxidation reactions are largely governed by the efficiency of charge separation and subsequent reactive oxygen species(ROS) generation. Herein, we report a polarization engineering strategy to promote the charge separation and ROS generation efficiency by substituting the benzene unit with furan/thiophene in porous organic polymers(POPs). Benefiting from the extent of local polarization, the thiophene-containing POP(JNU-218) exhibits the best photocatalytic performance in aerobic oxidation reactions, with a yield much higher than those for the furan-containing POP(JNU-217) and the benzenecontaining POP(JNU-216). Experimental studies and theoretical calculations reveal that the increase of local polarization can indeed reduce the exciton binding energy, and therefore facilitate the separation of electron-hole pairs. This work demonstrates a viable strategy to tune charge separation and ROS generation efficiency by modulating the dipole moments of the building blocks in porous polymeric organic semiconductors.

Electron donor–acceptor (D-A) tuning to achieve soluble covalent organic polymers for optoelectronic devices

Covalent organic polymers(COPs)have emerged as a unique class of luminescent polymers with pre-designed quasi-ordered architectures.However,their layered stacks and limited solubility preclude further processing for large-scale applications in devices,especially optoelectronic equipment.Herein,a universal strategy to adjust the electron donor–acceptor(D-A)moieties of the building blocks in COPs is proposed,achieved by in situ charge exfoliation of COP blocks into few-layer true solutions in(Lewis)acid and base media.The electron D-A moieties of the building blocks endow the COPs with the ability to accept or donate electrons,by altering the electron cloud distribution as well as the relative energy levels of the frontier molecular orbitals.The resultant soluble COPs can easily be processed into a uniform film by solution processing via the spin-coat method.The obtained COP-N achieves efficient and stable perovskite electroluminescence as a novel hole injection material on indium tin oxide,and the operating lifetime for a perovskite quantum dot light-emitting diodes device exceeds that of a poly(ethylene dioxythiophene):polystyrene sulphonate counterpart.This straightforward electronic regulation strategy provides a new avenue for the rational synthesis of processable reticular molecular polymers for practical electronic devices.

(Catecholate)Cu^(I)_(2)-Displayed Porous Organic Polymers as Efficient Heterogeneous Catalysts for the Mild and Selective Aerobic Oxidation of Alcohols

Porous organic polymers(POPs)containing catalytically active sites are of paramount importance for heterogeneous catalysis.However,the catalytically active sites of reported POPs are mostly limited to mononuclear metal species.Herein,we report the reaction between catechol-containing POPs(Cat-POPs)and[CuIMes]n to afford the corresponding Cu^(I)_(2)-CatPOPs with a putative vicinal binuclear(catecholate)Cu^(I)_(2)moiety.The resulting Cu^(I)_(2)-CatPOPs exhibit high Brunauer–Emmett–Teller surface areas,good stability,and excellent catalytic activity toward the aerobic oxidation of a broad range of primary and secondary alcohols under mild conditions,with either 2,2,6,6-tetramethylpiperidinyl-N-oxyl or 9-azabicyclo[3.3.0]nonane-N-oxyl as the cocatalyst.As green aerobic oxidation catalysts,the Cu^(I)_(2)-CatPOPs are much more active than the correspondingmononuclear CuIICatPOPs,where each catecholate moiety only supports one CuII center;CuI-ConPOPs,where the binding sites for CuI is a nonvicinal 1,4-dihydroxybenzene moiety;and the homogeneous analogue(3,6-di-tert-butyl catecholate)Cu^(I)_(2).These results are consistent with a proposed vicinal binuclear Cu^(I)_(2)structure that can efficiently activate molecular oxygen for the aerobic oxidation of alcohols,mechanistically similar to that observed in dicopper-containing oxygenases.Our results demonstrate the facile preparation of POPs with binuclear catalytically active sites that function as green heterogeneous catalysts for efficient oxidation of alcohols.

Pyrylium-based porous organic polymers via Knoevenagel condensation for efficient visible-light-driven heterogeneous photodegradation

Pyrylium salts are a type of representative and convincing example of versatility and variety not only as a nodal point in organic transformations but also as an attractive building block in functional organic materials. Herein, we report an effective synthetic protocol to fabricate a new pyrylium-containing porous organic polymers(POPs), named TMP-P, via Knoevenagel condensation with 2,4,6-trimethylpyrylium salt(TMP) as the key building block and 1,4-phthalaldehyde as the linker. The resulting ionic polymer TMPP exhibited efficient visible-light-driven heterogeneous photodegradation of Rhodamine B, owing to the presence of wide visible light absorption and a narrow optical band gap triggered pyrylium core in the framework.

A novel metal-free porous covalent organic polymer for efficient room-temperature photocatalytic CO_(2) reduction via dry-reforming of methane

At room temperature,the conversion of greenhouse gases into valuable chemicals using metal-free catalysts for dry reforming of methane(DRM) is quite promising and challenging.Herein,we developed a novel covalent organic porous polymer (TPE-COP) with rapid charge separation of the electron–hole pairs for DRM driven by visible light at room temperature,which can efficiently generate syngas (CO and H_(2)).Both electron donor (tris(4-aminophenyl)amine,TAPA) and acceptor (4,4',4'',4'''-((1 E,1'E,1''E,1'''E)-(ethene-1,1,2,2-tetrayltetrakis (benzene-4,1-diyl))tetrakis (ethene-2,1-diyl))tetrakis (1-(4-formylbenzyl)quinolin-1-ium),TPE-CHO) were existed in TPE-COP,in which the push–pull effect between them promoted the separation of photogenerated electron–hole,thus greatly improving the photocatalytic activity.Density functional theory (DFT) simulation results show that TPE-COP can form charge-separating species under light irradiation,leading to electrons accumulation in TPE-CHO unit and holes in TAPA,and thus efficiently initiating DRM.After 20 h illumination,the photocatalytic results show that the yields reach 1123.6 and 30.8μmol g^(-1)for CO and H_(2),respectively,which are significantly higher than those of TPE-CHO small molecules.This excellent result is mainly due to the increase of specific surface area,the enhancement of light absorption capacity,and the improvement of photoelectron-generating efficiency after the formation of COP.Overall,this work contributes to understanding the advantages of COP materials for photocatalysis and fundamentally pushes metal-free catalysts into the door of DRM field.

Engineering porous organic polymers for carbon dioxide capture

As atmospheric CO_2 levels rise, the development of physical or chemical adsorbents for CO_2 capture and separation is of great importance on the way towards a sustainable low-carbon future. Porous organic polymers are promising candidates for CO_2 capture materials owing to their structural flexibility, high surface area, and high stability. In this review, we highlight high-performance porous organic polymers for CO_2 capture and summarize the strategies to enhance CO_2 uptake and selectivity, such as increasing surface area, increasing interaction between porous organic polymers and CO_2, and pore surface functionalization.

Potential applications of porous organic polymers as adsorbent for the adsorption of volatile organic compounds

Volatile organic compounds(VOCs)with high toxicity and carcinogenicity are emitted from kinds of industries,which endanger human health and the environment.Adsorption is a promising method for the treatment of VOCs due to its low cost and high efficiency.In recent years,activated carbons,zeolites,and mesoporous materials are widely used to remove VOCs because of their high specific surface area and abundant porosity.However,the hydrophilic nature and low desorption rate of those materials limit their commercial application.Furthermore,the adsorption capacities of VOCs still need to be improved.Porous organic polymers(POPs)with extremely high porosity,structural diversity,and hydrophobic have been considered as one of the most promising candidates for VOCs adsorption.This review generalized the superiority of POPs for VOCs adsorption compared to other porous materials and summarized the studies of VOCs adsorption on different types of POPs.Moreover,the mechanism of competitive adsorption between water and VOCs on the POPs was discussed.Finally,a concise outlook for utilizing POPs for VOCs adsorption was discussed,noting areas in which further work is needed to develop the next-generation POPs for practical applications.

Spatial control of palladium nanoparticles in flexible click-based porous organic polymers for hydrogenation of olefins and nitrobenzene

Two flexible click-based porous organic polymers （CPP-F1 and CPP-F2） have been readily synthesized. SEM images show CPP-F1 is a 3D network, while CPP-F2 exhibits a granular morphology. Pd（OAc）2 can be easily incorporated into CPP-F1 and CPP-F2 to form Pd@CPP-F1 and Pd@CPP-F2, respectively. The interactions between the polymers and palladium are confirmed by solid-state 13C NMR, IR and XPS. Palladium nanoparticles （NPs） are formed after hydrogenation of olefins and nitrobenzene. Palladium NPs in CPP-F1 are well dispersed on the external surface of the polymer, while palladium NPs in CPP-F2 are located in the interior pores and on the external surface. In comparison with NPs in CPP-F1, the dual distribution of palladium NPs in CPP-F2 results in higher selectivity in the hydrogenation of 1,3-cyclohexadiene to cyclohexane. The catalytic systems can be recycled several times without obvious loss of catalytic activity or agglomeration of palladium NPs. Hot filtration, mercury drop tests and ICP analyses suggest that the catalytic systems proceed via a heterogeneous pathway.

Recent development of efficient electrocatalysts derived from porous organic polymers for oxygen reduction reaction

Porous organic polymers(POPs) have recently emerged as promising candidates for catalyzing oxygen reduction reaction(ORR).Compared to conventional Pt-based ORR catalysts, these newly developed porous materials, including both non-precious metal based catalysts and metal-free catalysts, are more sustainable and cost-effective. Their porous structures and large surface areas facilitate mass and electron transport and boost the ORR kinetics. This mini-review will give a brief summary of recent development of POPs as electrocatalysts for the ORR. Some design principles, different POP structures, key factors for their ORR catalytic performance, and outlook of POP materials will be discussed.

Hollow click-based porous organic polymers for heterogenization of [Ru（bpy）3]2＋ through electrostatic interactions

A facile approach for the heterogenization of transition metal catalysts using non-covalent interactions in hollow click-based porous organic polymers （H-CPPs） is presented. A catalytically active cationic species, [Ru（bpy）3]〉 （bpy = 2,2＇-bipyridyl）, was immobilized in H-CPPs via electrostatic interactions. The intrinsic properties of [Ru（bpy）3]〉 were well retained. The resulting Ru- containing hollow polymers exhibited excellent catalytic activity, enhanced stability, and good recyclability when used for the oxidative hydroxylation of 4-methoxyphenylboronic acid to 4-methoxyphenol under visible-light irradiation. The attractive catalytic performance mainly resulted from efficient mass transfer and the maintenance of the chemical properties of the cationic Ru complex in the H-CPPs.

Morphology design of microporous organic polymers and their potential applications:an overview

Microporous organic polymers(MOPs) have attracted considerable research interest because of their well-defined porosity,high surface area, lightweight nature, and tunable surface chemistry. The morphology of MOPs are demonstrated to play a significant role in various applications although limited examples manifesting the importance of the MOP morphology in numerous applications have been reported. This review summarizes the recent progress in the design of MOPs using different techniques, including hard and soft template and direct synthesis methods. In addition, their applications, which possibly attribute to their shape, are discussed. Furthermore, the advantages and disadvantages of different methods are discussed, as well as their development and future challenges.

Water-dispersible and soluble porous organic polymers for biomedical applications

Porous organic polymers(POPs)have become an emerging class of advanced porous organic materials owing to their structural diversity and tailored functions in solid state and organic media.Creating water-soluble and related water-dispersible POPs is still very challenging in the research area of porous organic materials.Their porosity-based functions with diverse topological architectures in aqueous media offer promising platforms in bio-related fields.This review highlights recent progress on water soluble or dispersible POPs for biomedical applications including bioimaging and biosensing,nanocarriers for drug delivery and tumor targeting,phototherapeutics,protein and gene delivery,biomacromolecule encapsulation and discrimination,and anti-microbial activity.

Metallocorrole-based porous organic polymers as a heterogeneous catalytic nanoplatform for efficient carbon dioxide conversion

Metallocorrole macrocycles that represent a burgeoning class of attractive metal-complexes from the porphyrinoid family,have attracted great interest in recent years owing to their unique structure and excellent performance revealed in many fields,yet further functionalization through incorporating these motifs into porous nanomaterials employing the bottom-up approach is still scarce and remains synthetically challenging.Here,we report the targeted synthesis of porous organic polymers(POPs)constructed from custom-designed Mn and Fe-corrole complex building units,respectively denoted as CorPOP-1(Mn)and CorPOP-1(FeCl).Specifically,the robust CorPOP-1(Mn)bearing Mn-corrole active centers displays superior heterogeneous catalytic activity toward solvent-free cycloaddition of carbon dioxide(CO_(2))with epoxides to form cyclic carbonates under mild reaction conditions as compared with the homogeneous counterpart.CorPOP-1(Mn)can be easily recycled and does not show significant loss of reactivity after seven successive cycles.This work highlights the potential of metallocorrole-based porous solid catalysts for targeting CO_(2) transformations,and would provide a guide for the task-specific development of more corrole-based multifunctional materials for extended applications.

Construction of Ionic Porous Organic Polymers(iPOPs)via Pyrylium Mediated Transformation

Two new ionic porous organic polymers(iPOPs)with different counter anions were successfully fabricated via well-known pyrylium mediated transformation into pyridinium.13C solid-state NMR,XPS,and FTIR were analyzed and confirmed the formation of pyridinium in the network.Containing charged and aromatic networks,both iPOPs exhibit a high affinity towards toxic hexavalent chromium Cr(Ⅵ)ions.What is more,it has been demonstrated that both CO2 adsorption and Cr(Ⅵ)removal properties can be tuned by simply varying counter anions.

Selective Carbon Dioxide Capture in Antifouling Indole-based Microporous Organic Polymers

Intermolecular synergistic adsorption of indole and carbonyl groups induced by intermolecular hydrogen bonding makes microporous organic polymer(PTICBL)exhibit high CO2 uptake capacity(5.3 mmol·g^-1at 273 K)and selectivities(CO2/CH4=53,CO2/N2=107 at 273 K).In addition,we find that indole units in the PTICBL networks inhibit the attachment of bacteria(E.coil and S.aureus)on the surface of PTICBL and extend its service life in CO2 capture.

In-situ self-templating synthesis of 3D hierarchical porous carbonsfrom oxygen-bridged porous organic polymers for highperformance supercapacitors

It is a big challenge to well control the porous structure of carbon materials for supercapacitor application.Herein,a simple in-situ self-templating strategy is developed to prepare three-dimensional(3D)hierarchical porous carbons with good combination of micro and meso-porous architecture derived from a new oxygen-bridged porous organic polymer(OPOP).The OPOP is produced by the condensation polymerization of cyanuric chloride and hydroquinone in NaOH ethanol solution and NaCl is in-situ formed as by-product that will serve as template to construct an interconnected 3D hierarchical porous architecture upon carbonization.The large interface pore architecture,and rich doping of N and O heteroatoms effectively promote the electrolyte accessibility and electronic conductivity,and provide abundant active sites for energy storage.Consequently,the supercapacitors based on the optimized OPOP-800 sample display an energy density of 8.44 and 27.28 Wh·kg^(−1)in 6.0 M KOH and 1.0 M Na2SO4 electrolytes,respectively.The capacitance retention is more than 94%after 10,000 cycles.Furthermore,density functional theory(DFT)calculations have been employed to unveil the charge storage mechanism in the OPOP-800.The results presented in this job are inspiring in finely tuning the porous structure to optimize the supercapacitive performance of carbon materials.