Modulating Benzothiadiazole-Based Covalent Organic Frameworks via Halogenation for Enhanced Photocatalytic Water Splitting

Two-dimensional covalent organic frameworks (2D COFs), an emerging class of crystalline porous polymers, have been recognized as a new platform for efficient solar-to-hydrogen energy conversion owing to their pre-designable structures and tailor-made functions. Herein, we demonstrate that slight modulation of the chemical structure of a typical photoactive 2D COF (Py-HTP-BT-COF) via chlorination (Py-ClTP-BT-COF) and fluorination (Py-FTP-BT-COF) can lead to dramatically enhanced photocatalytic H₂ evolution rates (HER=177.50 μmol h⁻¹ with a high apparent quantum efficiency (AQE) of 8.45 % for Py-ClTP-BT-COF). Halogen modulation at the photoactive benzothiadiazole moiety can efficiently suppress charge recombination and significantly reduce the energy barrier associated with the formation of H intermediate species (H*) on polymer surface. Our findings provide new prospects toward design and synthesis of highly active organic photocatalysts toward solar-to-chemical energy conversion.     

Biomimetic double network hydrogels: Combining dynamic and static crosslinks to enable biofabrication and control cell-matrix interactions

Hydrogels are promising candidates for recapitulation of the native extracellular matrix (ECM), yet recreating molecular and spatiotemporal complexity within a single network remains a challenge. Double network (DN) hydrogels are a promising step towards recapitulating the multicomponent ECM and have enhanced mechanical properties. Here, we investigate DNs based on dynamic covalent and covalent bonds to mimic the dynamicity of the ECM and enable biofabrication. We also investigate the spatiotemporal molecular attachment of a bioactive adhesive peptide within the networks. Using oxidized alginate (dynamic network, Schiff base) and polyethylene glycol diacrylate (static network, acrylate polymerization) we find an optimized procedure, where the dynamic network is formed first, followed by the static network. This initial dynamically cross-linked hydrogel imparts self-healing, injectability, and 3D printability, while the subsequent DN hydrogel improves the stability of the 3D gels and imparts toughness. Rheology and compression testing show that the toughening is due to the combination of energy dissipation (dynamic network) and elasticity (static network). Furthermore, where we place adhesive sites in the network matters; we find distinct differences when an adhesive peptide, Arg-Gly-Asp (RGD), is attached to the different networks. This DN strategy bring us closer to understanding and recreating the complex multicomponent ECM—pushing us past a materials view of cell adhesion—while enabling injectabiltiy and printing of tough hydrogels.     

Functional Liquid Crystal Elastomers Based on Dynamic Covalent Chemistry

The marriage of liquid crystal elastomers with dynamic covalent chemistry can be a new paradigm for the development of dynamic and intelligent polymers with versatile functionalities, which is of paramount significance for many emerging applications such as adaptive optics, soft robotics, bioinspired camouflage, 3D/4D printing technology and beyond. Read more in the Review by Wang, Feng et al. ( 10.1002/chem.202201957 )     

凸显“本质联系证据推理”的离子键与共价键教学

针对离子键与共价键在教学中存在本质分离、联系割裂和忽视“证据推理”素养发展目标的问题,依据元素周期律中金属性和非金属性的递变规律进行推理,并寻找证据进行证实或证伪,以认清离子键与共价键的静电作用的成键本质和辩证统一的关系,发展学生证据推理的核心素养,提高学生的逻辑思维能力。     

Glass transition broadening via nanofiller-contiguous polymer network in aromatic thermosetting copolyester nanocomposites

The glass transition is a genuine imprint of temperature-dependent structural relaxation dynamics of backbone chains in amorphous polymers, which can also reflect features of chemical transformations induced in macromolecular architectures. Optimization of thermophysical properties of polymer nanocomposites beyond the state of the art is contingent on strong interfacial bonding between nanofiller particles and host polymer matrix chains that accordingly modifies glass transition characteristics. Contemporary polymer nanocomposite configurations have demonstrated only marginal glass transition temperature shifts utilizing conventional polymer matrix and functionalized nanofiller combinations. We present nanofiller-contiguous polymer network with aromatic thermosetting copolyester nanocomposites in which carbon nanofillers covalently conjugate with cure advancing crosslinked backbone chains through functional end-groups of constituent precursor oligomers upon an in situ polymerization reaction. Via thoroughly transformed backbone chain configuration, the polymer nanocomposites demonstrate unprecedented glass transition peak broadening by about 100 °C along with significant temperature upshift of around 80 °C. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1595–1603     

Metal–Covalent Organic Frameworks (MCOFs): A Bridge Between Metal–Organic Frameworks and Covalent Organic Frameworks

Many sophisticated chemical and physical properties of porous materials strongly rely on the presence of the metal ions within the structures. Whereas homogeneous distribution of metals is conveniently realized in metal–organic frameworks (MOFs), the limited stability potentially restricts their practical implementation. From that perspective, the development of metal–covalent organic frameworks (MCOFs) may address these shortcomings by incorporating active metal species atop highly stable COF backbones. This Minireview highlights examples of MCOFs that tackle important issues from their design, synthesis, characterization to cutting-edge applications.     

Design,Synthesis and Characterization of Nickel-Functionalized Covalent Organic Framework NiCl@RIO-12 for Heterogeneous Suzuki–Miyaura Catalysis

A series of nickel-decorated covalent organic frameworks, NiCl@RIO-12, were prepared using the post-synthetic modification strategy, that is, by reacting NiCl₂ with pristine RIO-12 under alkaline conditions. Interestingly, they retained their crystallinity and the amount of nickel incorporated could be tuned from 3.6 to 25 wt % according to the reaction conditions. The incorporation of a higher amount of nickel in NiCl@RIO-12 consistently led to a lower Brunauer–Emmett–Teller surface area. Additionally, no agglomeration of nickel particles was found and a relatively homogeneous dispersion of nickel could be ascertained by SEM and TEM-EDS. The paramagnetic material exhibited promising catalytic activity in Suzuki–Miyaura cross-coupling under microwave heating. Thus, NiCl@RIO-12 notably demonstrated good thermal stability and its recyclability showed no substantial loss of activity after 3 cycles.     

Sulfonated 2D Covalent Organic Frameworks for Efficient Proton Conduction

Open 1D channels found in covalent organic frameworks are unique and promising to serve as pathways for proton conduction; how to develop high-rate yet stable transporting systems remains a substantial challenge. Herein, this work reports a strategy for exploring proton-conducting frameworks by engineering pore walls and installing proton-containing polymers into the pores. Amide-linked and sulfonated frameworks were synthesized from imine-linked precursors via sequentially engineering to oxidize into amide linkages and to further anchor sulfonic acid groups onto the pore walls, enabling the creation of sulfonated frameworks with high crystallinity and channel ordering. Integrating sulfonated polyether ether ketone chains into the open channels enables proton hopping to across the channels, greatly increases proton conductivity and enables a stable continuous run. These results suggest a way to explore proton-conducting COFs via systematic engineering of the wall and space of the open nanochannels.