Density Functional Study of Electrocatalytic Carbon Dioxide Reduction in Fourth-Period Transition Metal-Tetrahydroxyquinone Organic Framework

This study investigates the utilisation of organometallic network frameworks composed of fourth-period transition metals and tetrahydroxyquinone (THQ) in electrocatalytic CO2 reduction. Density functional theory (DFT) calculations were employed in analysing binding energies, as well as the stabilities of metal atoms within the THQ frameworks, for transition metal TM-THQs ranging from Y to Cd. The findings demonstrate how metal atoms could be effectively dispersed and held within the THQ frameworks due to sufficiently high binding energies. Most TM-THQ frameworks exhibited favourable selectivity towards CO2 reduction, except for Tc and Ru, which experienced competition from hydrogen evolution reaction (HER) and required solution environments with pH values greater than 5.716 and 8.819, respectively, to exhibit CO2RR selectivity. Notably, the primary product of Y, Ag, and Cd was HCOOH; Mo produced HCHO; Pd yielded CO; and Zr, Nb, Tc, Ru, and Rh predominantly generated CH4. Among the studied frameworks, Zr-THQ displayed values of 1.212 V and 1.043 V, corresponding to the highest limiting potential and overpotential, respectively, while other metal-organic frameworks displayed relatively low ranges of overpotentials from 0.179 V to 0.949 V. Consequently, it is predicted that the TM-THQ framework constructed using a fourth-period transition metal and tetrahydroxyquinone exhibits robust electrocatalytic reduction of CO2 catalytic activity.

Saddle-Shaped Building Blocks: A New Concept for Designing Fully Conjugated 3D Organic Semiconducting Materials

Currently, most organic semiconducting materials (OSMs) are π-conjugated structures in one or two dimension (2D), where the lack of layer-layer π-conjugation connection greatly blocks their electron delocalization and transport. The 3D fully conjugated materials could solve this issue because they can provide efficient charge-transport pathways throughout the whole 3D skeleton, in which the suitable 3D building block is the key to the development of fully conjugated 3D OSMs. Cyclooctatetraene (COT) and its derivatives are good candidates due to their π-conjugation with 3D saddle-shaped architecture. In this Concept, we discuss the key features of saddle-shaped COT-based derivatives and their synthetic strategy, then we present the current development of using the COT derivatives as building blocks to construct the 3D fully conjugated organic small compound- and polymer-based OSMs. The properties and perspectives of these OSMs in photovoltaics, electro-catalysis and electrical conductivities are also discussed. These recent advances in the developing 3D fully conjugated materials could potentially open up a new frontier in the design of OSMs.

Biomimetic Design of Hollow Flower-Like g-C3N4@PDA Organic Framework Nanospheres for Realizing an Efficient Photoreactivity

Organic framework polymers have attracted much interest due to the enormous potential design space offered by the atomically precise spatial assembly of organic molecular building blocks. The morphology control of organic frameworks is a complex issue that hinders the development of organic frameworks for practical applications. Biomimetic self-assembly is a promising approach for designing and fabricating multiple-functional nanoarchitectures. A bioinspired hollow flower-like organic framework nanosphere heterostructure comprised of carbon nitride and polydopamine (g-C3N4@PDA) is successfully synthesized via a mild and green method. This heterostructure can effectively avoid the agglomeration of nanosheets to better access the hollow nanospheres with high open-up specific surface area. The electron delocalization of g-C3N4 and PDA under visible light can largely promote photoelectron transfer and enhance the photocatalytic activity of the g-C3N4@PDA. Furthermore, the g-C3N4@PDA can effectively enhance the generation of reactive oxygen species under irradiation, which can lead to cell apoptosis and enhance the performance for cancer therapy. Therefore, the as-prepared g-C3N4@PDA provides a paradigm of highly efficient photocatalyst that can be used as nanomedicine toward cancer therapy. This study could open up a new avenue for exploiting more other potential hollow nanosphere organic frameworks.

Construction of Porous Aromatic Frameworks with Exceptional Porosity via Building Unit Engineering

The construction of excellent porous organic frameworks (POFs) with high surface areas and stability is always a tremendous challenge in synthetic chemistry. The geometric configuration and reactive group of building unit are crucial factors to influence the structure and porosity of the resulting product. Herein, the design, synthesis, and characterization of two porous aromatic framework (PAF) materials, named PAF-100 and PAF-101, are reported via a strategy of building unit engineering. PAF-100 and PAF-101 present high Brunauer-Emmett-Teller surface areas exceeding 5000 m² g^-1 and uniform pore size distributions. Furthermore, PAF-100 and PAF-101 show high methane uptake with value of 742 and 622 cm³ g^-1 , respectively, at 298 K and 70 bar. The successful synthesis of PAFs with exceptional porosity from engineered building unit is powerful for constructing highly porous POFs.

Mesoporous Polymer Frameworks from End-Reactive Bottlebrush Copolymers

Reticulated nanoporous materials generated by versatile molecular framework approaches are limited to pore dimensions on the scale of the utilized rigid molecular building blocks (<5 nm). The inherent flexibility of linear polymers precludes their utilization as long framework connectors for the extension of this strategy to larger length scales. We report a method for the fabrication of mesoporous frameworks by using bottlebrush copolymers with reactive end blocks serving as rigid macromolecular interconnectors with directional reactivity. End-reactive bottlebrush copolymers with pendant alkene functionalities were synthesized by a combination of controlled radical polymerization and polymer modification protocols. Ru-catalyzed cross-metathesis cross-linking of bottlebrush copolymers with two reactive end blocks resulted in the formation of polymer frameworks where isolated cross-linked domains were interconnected with bottlebrush copolymer bridges. The resulting materials were characterized by a continuous network pore structure with average pore sizes of 9-50 nm, conveniently tunable by the length of the utilized bottlebrush copolymer building blocks. The materials fabrication strategy described in this work expands the length scale of molecular framework materials and provides access to mesoporous polymers with a molecularly tunable reticulated pore structure without the need for templating, sacrificial component etching, or supercritical fluid drying.

Twisted Aromatic Frameworks: Readily Exfoliable and Solution-Processable Two-Dimensional Conjugated Microporous Polymers

Twisted two-dimensional aromatic frameworks have been prepared by overcrowding the nodes with bulky and rigid substituents. The highly distorted aromatic framework with alternating out-of-plane substituents results in diminished interlayer interactions that favor the exfoliation and dispersion of individual layers in organic media.

Three-Dimensional Arylene Diimide Frameworks for Highly Stable Lithium Ion Batteries

Lithium ion batteries are the best commercial technology to satisfy the energy storage needs of current and emerging applications. However, the use of transition-metal-based cathodes precludes them from being low-cost, sustainable, and environmentally benign, even with recycling programs in place. In this study, we report a highly stable organic material that can be used in place of the transition-metal cathodes. By creating a three-dimensional framework based on triptycene and perylene diimide (PDI), a cathode can be constructed that mitigates stability issues that organic electrodes typically suffer from. When a lithium ion battery is assembled using the PDI-triptycene framework (PDI-Tc) cathode, a capacity of 75.9 mAh g^-1 (78.7% of the theoretical value) is obtained. Importantly, the battery retains a near perfect Coulombic efficiency and >80% of its capacity after cycling 500 times, which is the best value reported to date for PDI-based materials.

An Ultrastable and Easily Regenerated Hydrogen-Bonded Organic Molecular Framework with Permanent Porosity

A robust hydrogen-bonded organic framework HOF-TCBP (H₄ TCBP=3,3',5,5'-tetrakis-(4-carboxyphenyl)-1,1'-biphenyl) has been successfully constructed and structurally characterized. It possesses a permanent 3D porous structure with a 5-fold interpenetrated dia topological network. This activated HOF-TCBP has a high BET surface area of 2066 m²  g^-1 and is capable of highly selective adsorption and separation of light hydrocarbons under ambient conditions. It shows excellent thermal stability, as demonstrated by PXRD experiments and N₂ adsorption tests. Practical use of HOF-TCBP is facilitated by the ease of its preparation and renewal through rotary evaporation.