Spatial Regulation of Acceptor Units in Olefin-Linked COFs toward Highly Efficient Photocatalytic H2 Evolution.

Covalent organic frameworks (COFs)-based photocatalysts have received growing attention for photocatalytic hydrogen (H2 ) production. One of the big challenges in the field is to find ways to promote energy/electron transfer and exciton dissociation. Addressing this challenge, herein, a series of olefin-linked 2D COFs is fabricated with high crystallinity, porosity, and robustness using a melt polymerization method without adding volatile organic solvents. It is found that regulation of the spatial distances between the acceptor units (triazine and 2, 2'-bipyridine) of COFs to match the charge carrier diffusion length can dramatically promote the exciton dissociation, hence leading to outstanding photocatalytic H2 evolution performance. The COF with the appropriate acceptor distance achieves exceptional photocatalytic H2 evolution with an apparent quantum yield of 56.2% at 475 nm, the second highest value among all COF photocatalysts and 70 times higher than the well-studied polymer carbon nitride. Various experimental and computation studies are then conducted to in-depth unveil the mechanism behind the enhanced performance. This study will provide important guidance for the design of highly efficient organic semiconductor photocatalysts.

Engineering Olefin-Linked Covalent Organic Frameworks for Photoenzymatic Reduction of CO2.

It is of profound significance concerning the global energy and environmental crisis to develop new techniques that can reduce and convert CO2 . To address this challenge, we built a new type of artificial photoenzymatic system for CO2 reduction, using a rationally designed mesoporous olefin-linked covalent organic framework (COF) as the porous solid carrier for co-immobilizing formate dehydrogenase (FDH) and Rh-based electron mediator. By adjusting the incorporating content of the Rh electronic mediator, which facilitates the regeneration of nicotinamide cofactor (NADH) from NAD+ , the apparent quantum yield can reach as high as 9.17±0.44 %, surpassing all reported NADH-regenerated photocatalysts constructed by crystalline framework materials. Finally, the assembled photocatalyst-enzyme coupled system can selectively convert CO2 to formic acid with high efficiency and good reusability. This work demonstrates the first example using COFs to immobilize enzymes for artificial photosynthesis systems that utilize solar energy to produce value-added chemicals.

Green synthesis of olefin-linked covalent organic frameworks for hydrogen fuel cell applications.

Green synthesis of crystalline porous materials for energy-related applications is of great significance but very challenging. Here, we create a green strategy to fabricate a highly crystalline olefin-linked pyrazine-based covalent organic framework (COF) with high robustness and porosity under solvent-free conditions. The abundant nitrogen sites, high hydrophilicity, and well-defined one-dimensional nanochannels make the resulting COF an ideal platform to confine and stabilize the H3PO4 network in the pores through hydrogen-bonding interactions. The resulting material exhibits low activation energy (Ea) of 0.06 eV, and ultrahigh proton conductivity across a wide relative humidity (10-90 %) and temperature range (25-80 °C). A realistic proton exchange membrane fuel cell using the olefin-linked COF as the solid electrolyte achieve a maximum power of 135 mW cm-2 and a current density of 676 mA cm-2, which exceeds all reported COF materials.

COF-inspired fabrication of two-dimensional polyoxometalate based open frameworks for biomimetic catalysis.

The development of highly efficient and robust biomimetic catalysts is an essential and feasible strategy to overcome the intrinsic drawbacks of natural enzymes. Inspired by the synthetic strategy of covalent organic frameworks, we adopted a covalent-bond-driven strategy to prepare polyoxometalate (POM) based open frameworks (NKPOM-OFs = Nankai University POM-OFs) with abundant Mo[double bond, length as m-dash]O groups that can mimic the active center of sulfite oxidase. Four 2-dimensional (2D) NKPOM-OFs were designed and synthesized via the condensation reaction of linear amino-containing POMs with planar tetra-aldehyde monomers. Benefitting from the high crystallinity, the structures of 2D POM-OFs can be successfully determined from structural simulations. The results unveiled that NKPOM-OFs possessed 2D staggered stacking layered structures with the sql topology. All these NKPOM-OFs exhibited high crystallinity and stability and demonstrated outstanding performance to serve as biomimetic catalysts of sulfite oxidase with good recyclability. Notably, exfoliation of NKPOM-OFs under ultrasonic treatment can significantly boost the catalytic activity with almost two times faster reaction rates. This study not only enriches the facile and versatile synthesis strategy for POM-OFs but also provides new biomimetic platforms for biocatalysis.

State-of-the-Art and Prospects of Biomolecules: Incorporation in Functional Metal-Organic Frameworks.

Given the unique properties of metal-organic frameworks (MOFs) including adjustable porosity, high surface area, and easy modification, they have attracted great attention as excellent solid supports for the incorporation of biomolecules. The formed biomolecules-MOFs composites show promising prospects in various fields such as biocatalysis, drug delivery, and biosensing. This review focuses on the state-of-the-art of biomolecules-incorporation using MOFs. Moreover, the relationship between properties of MOFs and biomolecules-incorporation is also discussed and highlighted. We hope this work will inspire the innovation in this emerging field for highly efficient synthesis of biomolecules-MOFs composites with various properties and advanced applications.

Separation and determination of ephedrine and pseudoephedrine by combination of flow injection with capillary electrophoresis.

A simple, rapid, and accurate method for the separation and determination of ephedrine and pseudoephedrine using direct UV absorbance detection has been developed by the combination of flow injection with capillary electrophoresis for the first time. The buffer solution used is a 40 mM borate solution with the pH adjusted to 9.5 using a 2 M NaOH solution. The linear calibration range is 50 to 1000 microg/mL (r = 0.9996) for both analytes, and the recoveries are 91.2-108.2% for ephedrine and 92.6-107.3% for pseudoephedrine, respectively. The relative standard deviation of the peak area is 1.6% for ephedrine and 1.3% for pseudoephedrine (n = 6) at a concentration of 500 microg/mL, respectively. A series of samples is injected repeatedly without current interruption and subsequent rinsing, and the contents of these two alkaloids in three marketed drugs and the medical plant, Ephedra sinica, are determined with satisfactory results by this method.