Mesoporous Vinylene-Linked Covalent Organic Frameworks with Heteroatom-Tuned Crystallinity and Photocatalytic Behaviors.

Owing to its prominent π-delocalization and stability, vinylene linkage holds great merits in the construction of covalent organic frameworks (COFs) with promising semiconducting properties. However, carbon-carbon double bond formation reaction always exhibits relatively low reversibility, unfavorable for the formation of high crystalline frameworks through self-error correction and assembling processes. In this work, we report a heteroatom-tuned strategy to build up a series of two-dimensional (2D) vinylene-linked COFs by Knoevenagel condensation of an electron-deficient methylthiazolyl-based monomer with different triformyl substituted (hetero-)aromatic derivatives. The resulting COFs show high-quality periodic mesoporous structures with high surface areas. Embedding heteroatoms into the backbones enables significantly improving their crystallinity, and finely tailoring their semiconducting structures. Upon visible light stimulation, one of the as-prepared COFs with donor-π-acceptor structure could deliver a nearly seven-fold increase in the catalytic activity of hydrogen generation as compared with the other two. Meanwhile, in combination with high crystallinity and the matched conduction band energy level, such kind of COFs can be able to selectively generate singlet oxygen and superoxide radicals in a high ratio of up to 30:1, allowing for catalyzing aerobic thioanisole oxidation in distinctly tunable activities through the substituent electronic effect of the substrates.

Pyridazine-Promoted Construction of Vinylene-Linked Covalent Organic Frameworks with Exceptional Capability of Stepwise Water Harvesting.

In this study, we successfully developed two novel vinylene-linked covalent organic frameworks (COFs) using 2-connected 3,6-dimethylpyridazine through Knoevenagel condensation. These COFs featured finely tailored micro-/nano-scale pore sizes, high surface areas and stable non-polar vinylene linkages. Finely resolved powder X-ray diffraction patterns demonstrated highly crystalline structures with a hexagonal lattice in the AA layer stacking. The resulting one-dimensional channels possess strong hydrogen-bond accepting sites arising from the decorated cis-azo/azine units with two pairs of fully exposed lone pair electrons, endowing the as-prepared COFs with exceptional water absorption properties. The g-DZPH-COF exhibited successive steep water uptake steps starting from low relative pressures (P/PSTA = 0.1), with the remarkable water uptake capacity of 0.26 g/g at P/PSTA = 0.2 (25°C), which is the optimal value recorded among the reported COFs. Dynamic vapour sorption measurements revealed the fast kinetics of these COFs, even in the cluster formation process. Water uptake and release cycling tests demonstrated their outstanding hydrolytic stability, durability, and adsorption-desorption retention ability.

Hexatopic Vertex-Directed Approach to Vinylene-Linked Covalent Organic Frameworks with Heteroporous Topologies.

A D3h-symmetric hexatopic monomer was first prepared by attaching the three-fold ditopic moiety 2,6-dimethylpyridine to the meta-positions of a phenyl ring. It was further condensed at its six pyridylmethyl carbons with linear ditopic aromatic dialdehydes, resulting in two vinylene-linked COFs with heteroporous topologies, as revealed by powder X-ray diffraction (PXRD), nitrogen sorption, and pore-size distribution analyses, as well as transmission electron microscopy (TEM) image. The linear- and cross-conjugations, respectively, arising from the 2,6-linked pyridines and meta-linked phenylenes in the hexatopic nodes rendered the resultant COFs with well-patterned π-delocalization, allowing for efficiently catalyzing the bromination of aromatic derivatives with the pore-size-dependent conversion yields and regioselectivity under the irradiation of green light.

Covalent Organic Framework (COF) Derived Ni-N-C Catalysts for Electrochemical CO2 Reduction: Unraveling Fundamental Kinetic and Structural Parameters of the Active Sites.

Electrochemical CO2 reduction is a potential approach to convert CO2 into valuable chemicals using electricity as feedstock. Abundant and affordable catalyst materials are needed to upscale this process in a sustainable manner. Nickel-nitrogen-doped carbon (Ni-N-C) is an efficient catalyst for CO2 reduction to CO, and the single-site Ni-Nx motif is believed to be the active site. However, critical metrics for its catalytic activity, such as active site density and intrinsic turnover frequency, so far lack systematic discussion. In this work, we prepared a set of covalent organic framework (COF)-derived Ni-N-C catalysts, for which the Ni-Nx content could be adjusted by the pyrolysis temperature. The combination of high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure evidenced the presence of Ni single-sites, and quantitative X-ray photoemission addressed the relation between active site density and turnover frequency.

Highly Efficient Electroreduction of CO2 on Nickel Single-Atom Catalysts: Atom Trapping and Nitrogen Anchoring.

Construction of single atom catalysts (SACs) with high activity toward electroreduction of CO2 still remains a great challenge. A very simple and truly cost-effective synthetic strategy is proposed to prepare SACs via a impregnation-pyrolysis method, through one-step pyrolysis of graphene oxide aerogel. Compared with other traditional methods, this process is fast and free of repeated acid etching, and thus it has great potential for facile operation and large-scale manufacturing. Both X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy images confirm the presence of isolated nickel atoms, with a high Ni loading of ≈2.6 wt%. The obtained 3D porous Ni- and N-codoped graphene aerogel exhibits excellent activity toward electroreduction of CO2 to CO, in particular exhibiting a remarkable CO Faradaic efficiency of 90.2%. Density functional theory calculations reveal that free energies for the formation of intermediate *COOH on coordinatively unsaturated NiN sites are significantly lower than that on NiN4 site, suggesting the outstanding activities of CO2 electroreduction originate from coordinatively unsaturated NiN sites in catalysts.

Intentional construction of high-performance SnO2 catalysts with a 3D porous structure for electrochemical reduction of CO2.

Herein, SnO2-NC (SnO2-nanocube) and SnO2-NF (SnO2-nanoflake) electro-catalysts featuring a large specific surface area and 3D porous structure were successfully constructed via acid etching and sulfurization-desulphurization methods, respectively. As catalysts for the electrochemical reduction of CO2, the faradaic efficiency (FHCOO-+CO = 82.4%, 91.5%, respectively) and partial current density (jHCOO-+CO = 10.7 and 11.5 mA cm-2, respectively) of SnO2-NCs and SnO2-NFs were enhanced in comparison with SnO2-NPs (SnO2-nanoparticles, FHCOO-+CO = 63.4%, jHCOO-+CO = 5.7 mA cm-2) at -1.0 V vs. RHE. The enhanced catalytic activity is attributed to their uniform 3D porous structure, high specific surface area and excellent wettability. Additionally, the morphology of SnO2-NCs and SnO2-NFs was largely preserved after electrolyzing for 12 h (after 12 h of electrolysis), indicating the effective buffering effect of the 3D structure in electrolysis. Naturally, the current density and faradaic efficiency of the SnO2-NC and SnO2-NF catalysts remained nearly unchanged after long-term stability measurements, revealing great stability.

Nitrogen-Doped Graphene Quantum Dots Enhance the Activity of Bi2 O3 Nanosheets for Electrochemical Reduction of CO2 in a Wide Negative Potential Region.

Large numbers of catalysts have been developed for the electrochemical reduction of CO2 to value-added liquid fuels. However, it remains a challenge to maintain a high current efficiency in a wide negative potential range for achieving a high production rate of the target products. Herein, we report a 2D/0D composite catalyst composed of bismuth oxide nanosheets and nitrogen-doped graphene quantum dots (Bi2 O3 -NGQDs) for highly efficient electrochemical reduction of CO2 to formate. Bi2 O3 -NGQDs demonstrates a nearly 100 % formate Faraday efficiency (FE) at a moderate overpotential of 0.7 V with a good stability. Strikingly, Bi2 O3 -NGQDs exhibit a high activity (average formate FE of 95.6 %) from -0.9 V to -1.2 V vs. RHE. Additionally, DFT calculations reveal that the origin of enhanced activity in this wide negative potential range can be attributed to the increased adsorption energy of CO2 (ads) and OCHO* intermediate after combination with NGQDs.

Zinc-Coordinated Nitrogen-Codoped Graphene as an Efficient Catalyst for Selective Electrochemical Reduction of CO2 to CO.

Electrochemical reduction of CO2 to value-added chemicals by using renewable electricity offers a promising strategy to deal with rising CO2 emission and the energy crisis. Single-site zinc-coordinated nitrogen-codoped graphene (Zn-N-G) catalyzes the electrochemical reduction of CO2 to CO. The Zn-N-G catalyst exhibits excellent intrinsic activity toward CO2 reduction, reaching a faradaic efficiency of 91 % for CO production at a low overpotential of 0.39 V. X-ray absorption fine structure and X-ray photoelectron spectroscopy both confirm the presence of isolated Zn-Nx moieties, which act as the key active sites for CO formation. DFT calculations reveal the origin of enhanced activity for CO2 reduction on Zn-N-G catalysts. This work provide further understanding of the active centers on transition metal-nitrogen-carbon (M-N-C) catalysts for electrochemical reduction of CO2 to CO.

Nanocellulose-Based Antibacterial Materials.

In recent years, nanocellulose-based antimicrobial materials have attracted a great deal of attention due to their unique and potentially useful features. In this review, several representative types of nanocellulose and modification methods for antimicrobial applications are mainly focused on. Recent literature related with the preparation and applications of nanocellulose-based antimicrobial materials is reviewed. The fabrication of nanocellulose-based antimicrobial materials for wound dressings, drug carriers, and packaging materials is the focus of the research. The most important additives employed in the preparation of nanocellulose-based antimicrobial materials are presented, such as antibiotics, metal, and metal oxide nanoparticles, as well as chitosan. These nanocellulose-based antimicrobial materials can benefit many applications including wound dressings, drug carriers, and packaging materials. Finally, the challenges of industrial production and potentials for development of nanocellulose-based antimicrobial materials are discussed.

Fabrication of cellulose/graphene paper as a stable-cycling anode materials without collector.

Flexible and foldable devices attract substantial attention in low-cost electronics. Among the flexible substrate materials, paper has several attractive advantages. In our study, we fabricate cellulose/graphene paper by wet end formation (papermaking). The cationic polyacrylamide remarkably improve the retention ratio of graphene of cellulose/graphene slurry. Besides, cellulose/graphene paper exhibits well mechanical properties such as its flexibility and folding endurance. And we replace copper foil collector with cellulose/graphene paper in lithium-ion batteries without collector, and investigate its electrochemical properties. The obtained results show that cellulose/graphene paper presents excellent charge-discharge stability after 1600th cycles as the anode of lithium-ion batteries. These advantages highlight the potential applications of cellulose/graphene paper as anode materials for lithium-ion batteries.

2,3-Dialdehyde nanofibrillated cellulose as a potential material for the treatment of MRSA infection.

Nanocellulose materials have undergone rapid development in recent years as promising biomedical materials due to their excellent physical and biological properties, in particular their biocompatibility, biodegradability, and low cytotoxicity. In this study, we prepared 2,3-dialdehyde nanofibrillated cellulose (DANFC) by sodium periodate oxidation, which is a mild oxidation process. With increasing oxidation time, the antimicrobial activity of DANFC against both Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA) improved. DANFC also displays good biocompatibility with mammalian cells, and shows good blood compatibility. In addition, animal studies and histology results reveal that DANFC can accelerate wound healing and enhance the formation of blood vessels and epithelium.