One-pot Construction of Metal Nanoparticles Loaded COF Catalysts for Aqueous Hydrogenation Reactions.

The catalysis performance of metal nanoparticles (NPs) will be significantly deteriorated because of their spontaneous agglomeration during practical applications. Covalent-organic frameworks (COFs) materials with functional groups and well-defined channels benefit for the dispersion and anchor of metal ions and the confined growth of metal NPs, working as an ideal platform to compose catalytic systems. In this article, we report a one-pot strategy for the preparation of metal NPs loaded COFs without the need of post-modification. During the polymerization process, the pre-added metal ions were stabilized by the rapidly formed COF oligomers and hardly disturb the construction of COFs. After reduction, metal NPs are uniformly anchored on the COF matrix. Eventually, a wide spectrum of metal NPs, including Au, Pd, Pt, AuPd, CuPd, CuPt and CuPdPt, loaded COFs are successfully prepared. The versatility and metal ions anchoring mechanism are verified with four different COF matrixes. Taking AuPd NPs as example, the resultant AuPd NPs loaded COF materials can selectively decompose ammonium formate and produce hydrogen in-situ, exhibiting over 99 % conversion of hydrodechlorination for chlorobenzenes and nitro-reduction reaction for nitroaromatic compounds under ambient temperature in aqueous solution.

A Thermally Promoted Homogenous-Floating-Concentrating Strategy Synthesizing Highly Crystalline Triazine/hydroxyl-Rich COFs for 4-Nitrophenol Adsorption.

In this work, a "thermally promoted homogenous-floating-concentrating" strategy is reported for the rapid synthesis of highly crystalline triazine/hydroxyl-rich COFs under mild conditions, using for the effectively adsorbing 4-nitrophenol (4-NP) in aqueous solutions. This strategy originates from an optimized "homogenous-floating-concentrating" method as reported in the previous work. Both gradually improving concentration and heat treatment promote the condensation reaction between amino and aldehyde groups, resulting in high crystallinity and shorter reaction time. The obtained COFs demonstrate better crystallinity and higher surface area in comparison with the counterparts prepared by solvothermal strategy. A maximum surface area of 2391 m2 g-1 is achieved. The COFs exhibit excellent 4-NP adsorption capacity (Qmax = 1402.0 mg g-1 ), which is attributed to abundant triazine/hydroxyl-groups on the COF skeleton and their strong H-bonding interaction with 4-NP.

A selective sensing platform for the simultaneous detection of ascorbic acid, dopamine, and uric acid based on AuNPs/carboxylated COFs/Poly(fuchsin basic) film.

In this study, an electrochemical sensing strategy was developed based on the synergies of gold nanoparticles (AuNPs) doped carboxylated covalent organic frameworks (ACOFs) and poly(fuchsin basic) film for the simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). This strategy not only took advantage of the adopted materials but also made use of the H-bonding and electrostatic interaction between the three compounds and materials. For this sensing, a poly-BFu film was formed on the surface of bare glass carbon electrode (GCE) under a constant potential. AuNPs was highly dispersed and immobilized on the constructed ACOF-TaTp to obtain AuNPs@ACOF. The constructed sensor AuNPs@ACOF/p-BFu/GCE combined the merits of high surface area, hydrophilicity, conductivity, and selective affinity, consequently exhibiting high sensitivity and selectivity toward the simultaneous detection of AA, DA, and UA with wide linear response ranges of 25-1500 µM, 0.75-40 µM, and 1-200 µM, respectively. The corresponding detection limits were 12.0 µM, 0.15 µM, and 0.22 µM. The simultaneous determination of UA in real human urine sample further confirmed the practicability of the designed electrode.

Hydrophobic Two-Dimensional MoS2 Nanosheets Embedded in a Polyether Copolymer Block Amide (PEBA) Membrane for Recovering Pyridine from a Dilute Solution.

A two-dimensional molybdenum disulfide (MoS2) nanosheet, as a new type of inorganic material with high hydrophobicity and excellent physicochemical stability, holds great application potential in the preparation of a high separation performance organic-inorganic hybrid membrane. In this work, high hydrophobic MoS2 was embedded in hydrophobic polyether copolymer block amide (PEBA) to prepare PEBA/MoS2 organic-inorganic hybrid membranes. The structure, morphology, and hydrophobicity of the hybrid membrane were characterized by scanning electron microscopy, thermogravimetric analysis, contact angle goniometry, X-ray diffraction, infrared spectroscopy analysis, and atomic force microscopy. The effect of embedding of MoS2 on the swelling degree and pervaporation separation performance of the PEBA/MoS2 hybrid membrane was studied with a 1.0 wt % pyridine dilute solution. The results indicated that with increasing the MoS2 content, the separation factor of PEBA/MoS2 increased first and then decreased, while it showed a downward trend in the permeation flux. When the MoS2 content in the PEBA/MoS2 hybrid membrane was 10.0 wt %, the permeation flux was 83.4 g m-2 h-1 (decreased by 21.5% compared with the pure PEBA membrane), and the separation factor reached a maximum value of 11.11 (increased by 37.6% compared with the pure PEBA membrane). Meanwhile, the effects of feed temperature on the pervaporation separation performance of PEBA/MoS2 hybrid membranes were also studied. In addition, as the PEBA/MoS2 hybrid membrane has excellent thermal stability, it is expected to be a promising material for recovering pyridine from wastewater.

Homogeneous Polymerization of Self-standing Covalent Organic Framework Films with High Performance in Molecular Separation.

Covalent organic frameworks (COFs) are typically isolated as microcrystalline powders. It remains fundamentally challenging to fabricate COFs into high-quality self-standing films to take full advantage of their ordered pore channels for molecular separation. Here, we report a new strategy for fabricating self-standing imine-linked COF films via homogeneous polymerization where films emerge from clear solutions without forming amorphous precipitates. The abundant basic nitrogen atoms of the monomers acted as a reaction controller to realize the homogeneous polymerization and also promoted the tight self-aggregation of COF crystallites to form compact films via H-bonding. The chemically supported self-standing COF films on nylon membranes were also developed via an in situ growth method. The resulting films showed an unprecedentedly ultrafast permeance of 2822 L m-2 h-1 MPa-1 with a high rejection rate (99.8%) in the filtration of a congo red (CR) solution, demonstrating the advantage of this new strategy in fabricating high-quality self-standing COF films.

A sensitive and reliable dopamine biosensor was developed based on the Au@carbon dots-chitosan composite film.

A novel composite film of Au@carbon dots (Au@CDs)-chitosan (CS) modified glassy carbon electrode (Au@CDs-CS/GCE) was prepared in a simple manner and applied in the sensitive and reliable determination of dopamine (DA). The CDs had carboxyl groups with negative charge, which not only gave it have good stability but also enabled interaction with amine functional groups in DA through electrostatic interaction to multiply recognize DA with high specificity, and the Au nanoparticle could make the surface of the electrode more conductive. Compared with the bare GCE, CS/GCE, and CDs-CS/GCE electrodes, the Au@CDs-CS/GCE had higher catalytic activity toward the oxidation of DA. Furthermore, Au@CDs-CS/GCE exhibited good ability to suppress the background current from large excess ascorbic acid (AA) and uric acid (UA). Under the optimal conditions, selective detection of DA in a linear concentration range of 0.01-100.0 µM was obtained with the limit of 0.001 µM (3S/N). At the same time, the Au@CDs-CS/GCE was also applied to the detection of DA content in DA's injection with satisfactory results, and the biosensor could keep its activity for at least 2 weeks.

Carbon dots and chitosan composite film based biosensor for the sensitive and selective determination of dopamine.

A simple, sensitive and reliable dopamine (DA) biosensor was developed based on a carbon dots (CDs) and chitosan (CS) composite film modified glassy carbon electrode (CDs-CS/GCE). Under optimal conditions, the CDs-CS/GCE showed a better electrochemical response for the detection of DA than that of the glassy carbon electrode (GCE). The oxidation peak current (Ipa) of DA was linear with the concentration of DA in the range from 0.1 µM to 30.0 µM with the limit of detection as 11.2 nM (3S/N). The CDs-CS/GCE was applied to the detection of DA content in an injection solution of DA with satisfactory results.