Porous Organic Polymers for Selective Palladium Recovery and Heterogeneous Catalysis.

Palladium (Pd) recycling from waste materials is an important approach in order to meet the growing demand for Pd originating from its broad range of applications including automotive industry, electronics and catalysis. In this article, we discuss the design principles of solid-sorbents for efficient recovery of Pd from waste sources with a particular emphasis on porous organic polymers (POPs), which emerged as promising porous materials for Pd recovery due to their tunable chemical functionality, stability and porosity. We discuss the critical role of binding sites and porosity in the Pd uptake capacity, adsorption kinetics and selectivity. We also highlight the use of captured Pd within the polymer networks as heterogeneous catalysts for cross-coupling reactions.

Magnetically Guided Synthesis of Anisotropic Porous Carbons toward Efficient CO2 Capture and Magnetic Separation of Oil.

Conventional synthetic strategies do not allow one to impart structural anisotropy into porous carbons, thus leading to limited control over their textural properties. While structural anisotropy alters the mechanical properties of materials, it also introduces an additional degree of directionality to increase the pore connectivity and thus the flux in the designed direction. Accordingly, in this work the structure of porous carbons prepared from resorcinol-formaldehyde gels has been rendered anisotropic by integrating superparamagnetic colloids to the sol-gel precursor solution and by applying a uniform magnetic field during the sol-gel transition, which enables the self-assembly of magnetic colloids into chainlike structures to template the growth of the gel phase. Notably, the anisotropic pore structure is maintained upon pyrolysis of the gel, leading to hierarchically porous carbon monoliths with tunable structure and porosities. With an advantage granted to anisotropic materials, these porous carbons showed higher porosity, a higher CO2 uptake capacity of 3.45 mmol g-1 at 273 K at 1.1 bar, and faster adsorption kinetics compared to the ones synthesized in the absence of magnetic field. Moreover, these materials were also used as magnetic sorbents with fast adsorption kinetics for efficient oil-spill cleanup and retrieved easily by using an external magnetic field.

Porous organic polymers for CO2 capture, separation and conversion.

Porous organic polymers (POPs) have long been considered as prime candidates for carbon dioxide (CO2) capture, separation, and conversion. Especially their permanent porosity, structural tunability, stability and relatively low cost are key factors in such considerations. Whereas heteratom-rich microporous networks as well as their amine impregnation/functionalization have been actively exploited to boost the CO2 affinity of POPs, recently, the focus has shifted to engineering the pore environment, resulting in a new generation of highly microporous POPs rich in heteroatoms and featuring abundant catalytic sites for the capture and conversion of CO2 into value-added products. In this review, we aim to provide key insights into structure-property relationships governing the separation, capture and conversion of CO2 using POPs and highlight recent advances in the field.

Porous shape-persistent rylene imine cages with tunable optoelectronic properties and delayed fluorescence.

A simultaneous combination of porosity and tunable optoelectronic properties, common in covalent organic frameworks, is rare in shape-persistent organic cages. Yet, organic cages offer important molecular advantages such as solubility and modularity. Herein, we report the synthesis of a series of chiral imine organic cages with three built-in rylene units by means of dynamic imine chemistry and we investigate their textural and optoelectronic properties. Thereby we demonstrate that the synthesized rylene cages can be reversibly reduced at accessible potentials, absorb from UV up to green light, are porous, and preferentially adsorb CO2 over N2 and CH4 with a good selectivity. In addition, we discovered that the cage incorporating three perylene-3,4:9,10-bis(dicarboximide) units displays an efficient delayed fluorescence. Time-correlated single photon counting and transient absorption spectroscopy measurements suggest that the delayed fluorescence is likely a consequence of a reversible intracage charge-separation event. Rylene cages thus offer a promising platform that allows combining the porosity of processable materials and photochemical phenomena useful in diverse applications such as photocatalysis or energy storage.

Molten Salt Templated Synthesis of Covalent Isocyanurate Frameworks with Tunable Morphology and High CO2 Uptake Capacity.

The use of reactive molten salts, i.e., ZnCl2, as a soft template and a catalyst has been actively investigated in the preparation of covalent triazine frameworks (CTFs). Although the soft templating effect of the salt melt is more prominent at low temperatures, close to the melting point of ZnCl2, leading to the formation of abundant micropores, a significant mesopore formation is observed that is due to the partial carbonization and other side reactions at higher temperatures (>400 °C). Evidently, high-temperature synthesis of CTFs in various eutectic salt mixtures of ZnCl2 with alkali metal chloride salts also leads to mesopore formation. We reasoned that using the isocyanate moieties instead of cyano groups in the monomer, 1,4-phenylene isocyanate, could enable efficient interactions between carbonyl moieties and alkali metal ions to realize efficient salt templating to form covalent isocyanurate frameworks (CICFs). In this direction, the trimerization of 1,4-phenylene diisocyanate was carried out under ionothermal conditions at different reaction temperatures using ZnCl2 (CICF) and the eutectic salt mixture of KCl/NaCl/ZnCl2 (CICF-KCl/NaCl) as the reactive solvents. We observed notable differences in the morphologies of the two polymers, whereas CICF showed irregular-shaped micrometer-sized particles, the CICF-KCl/NaCl exhibited a filmlike morphology. Moreover, favorable ion-dipole interactions between alkali metal cations and oxygen atoms of the monomer facilitated two-dimensional growth and the formation of a purely microporous framework in the case of CICF-KCl/NaCl along with a near theoretical retention of the nitrogen content at 500 °C. The CICF-KCl/NaCl showed a BET surface area of 590 m2 g-1 along with a CO2 uptake capacity of 5.9 mmol g-1 at 273 K and 1.1 bar because of its high microporosity and nitrogen content. On the contrary, in the absence of alkali metal ions, CICF showed high mesopore content and a moderate CO2 uptake capacity. This study underscores the importance of the strength of the interactions between the salts and the monomer in the ionothermal synthesis to control the morphology, porosity, and gas uptake properties of the porous organic polymers.

Bimetallic metal organic frameworks with precisely positioned metal centers for efficient H2 storage.

We demonstrated that the ratio and position of two different metal ions, Pd and Cu, can be precisely controlled within MOFs through predesigned metal clusters. These MOF structures incorporating Pd-Cu paddle wheel units were synthesised simply by reacting Pd-Cu acetate metal clusters and tritopic organic linkers at room temperature. Pd-Cu open metal sites were found to be uniformly distributed throughout the MOFs with a ca. 1 : 1 ratio. The incorporation of Pd into the MOF structure also led to enhanced affinity towards H2 with Qst values up to 8.9 kJ mol-1.

Synthesis of Highly Porous Coordination Polymers with Open Metal Sites for Enhanced Gas Uptake and Separation.

Metal-containing amorphous microporous polymers are an emerging class of functional porous materials in which the surface properties and functions of polymers are dictated by the nature of the metal ions incorporated into the framework. In an effort to introduce coordinatively unsaturated metal sites into the porous polymers, we demonstrate herein an aqueous-phase synthesis of porous coordination polymers (PCPs) incorporating bis(o-diiminobenzosemiquinonato)-Cu(II) or -Ni(II) bridges by simply reacting hexaminotriptycene with CuSO4·5H2O [Cu(II)-PCP] or NiCl2·6H2O [Ni(II)-PCP] in H2O. The resulting polymers showed surface areas of up to 489 m2 g-1 along with a narrow pore size distribution. The presence of open metal sites significantly improved the gas affinity of these frameworks, leading to an exceptional isosteric heat of adsorption of 10.3 kJ·mol-1 for H2 at zero coverage. The high affinities of Cu(II)- and Ni(II)-PCPs toward CO2 prompted us to investigate the removal of CO2 from natural and landfill gas conditions. We found that the higher affinity of Cu(II)-PCP compared to that of Ni(II)-PCP not only allowed for the tuning of the affinity of CO2 molecules toward the sorbent, but also led to an exceptional CO2/CH4 selectivity of 35.1 for landfill gas and 20.7 for natural gas at 298 K. These high selectivities were further verified by breakthrough measurements under the simulated natural and landfill gas conditions, in which both Cu(II)- and Ni(II)-PCPs showed complete removal of CO2. These results clearly demonstrate the promising attributes of metal-containing porous polymers for gas storage and separation applications.

Catalyst-Free Synthesis of Porous Graphene Networks as Efficient Sorbents for CO2 and H2.

Reported is a catalyst-free synthetic route for the preparation of porous graphene networks (PGNs) incorporating benzimidazole linkages through the condensation reaction between ester-functionalized graphene sheets and organic aromatic amine linkers. PGNs showed remarkable thermal stability at temperatures of up to 350 °C in air. This emphasizes the importance of the formation of robust CC bonds by means of the Johnson-Claisen rearrangement for the covalent functionalization of graphene layers. PGNs exhibited high surface areas up to 732 m2 g-1 and showed the highest CO2 uptake capacity (3.75 mmol g-1 at 273 K, 1 bar) along with a remarkable CO2 /N2 selectivity (130 at 273 K, 1 bar) of all the GO and graphene frameworks reported to date. PGNs as low-cost, efficient solid sorbents also exhibited high affinity towards H2 (1.2 wt % at 77 K, 1 bar).

Heavy Hymenolepis nana infection possibly through organic foods: report of a case.

We encountered a patient with heavy Hymenolepis nana infection. The patient was a 44-year-old Korean man who had suffered from chronic hepatitis (type B) for 15 years. A large number of H. nana adult worms were found during colonoscopy that was performed as a part of routine health screening. The parasites were scattered throughout the colon, as well as in the terminal ileum, although the patient was immunocompetent. Based on this study, colonoscopy may be helpful for diagnosis of asymptomatic H. nana infections.