Nitrogen-Rich Covalent Organic Frameworks Composited High-Temperature Proton Exchange Membranes with Ultralow Volume Expansion and Reduced Phosphoric Acid Leakage.

Phosphoric acid (PA) leakage and volume expansion are critical factors limiting long-term stable operation of PA-doped polybenzimidazole (PBI) for high-temperature proton exchange membrane fuel cells. Enhancing the interaction between the polymer matrix and PA provides an effective way to minimize PA loss and inhibit excessive membrane swelling. The covalent organic frameworks (COFs) are helpful in improving the performance of PA-PBI membranes due to the robust frameworks, adjustable structures, and good compatibility with polymers. Here, in this work, we synthesized porous COFs named TTA-DFP containing triazine rings and pyridine groups at room temperature for as short as 2 h without oxygen isolation. TTA-DFP was then blended with commercial poly[2,2'-(p-oxidiphenylene)-5,5'-benzimidazole] (OPBI) to prepare composite membranes. The abundant alkaline N sites in TTA-DFP exhibit strong interactions with PA and OPBI, which not only provide more proton transport pathways to promote proton conduction but also immobilize PA in acidophilic micropores to reduce PA leakage. The composite membranes exhibit a much lower volume swelling ratio than that of the OPBI membrane. The PA retention of the composite membrane after 120 h of treatment at 80 °C and 40% relative humidity can reach as high as 84.6%. Particularly, the proton conductivity of the composite membrane doped with 15 wt% TTA-DFP achieves 0.112 S cm-1 at 180 °C without humidification with a swelling ratio of 24.1%. In addition, it has an optimal peak power density of 824.4 mW cm-2 at 180 °C, which is 1.7 times that of the OPBI membrane. The stability of the composite membrane is much better than that of OPBI at a current density of 0.3 A cm-2 at 140 °C for 120 h.

Preparation of N-Halamine Gelatin Sponge and Its Application in the Treatment of Skin Infection.

Nowadays, there has been an increasing research interest into N-halamine compounds due to their wide antimicrobial properties and no drug resistance. Most of the research mainly focuses on small molecular N-halamines, while few studies are on macromolecule N-halamines. In this work, antibacterial N-halamine polymer materials based on proteins (GS-Cl) were synthesized with an antibacterial component of oxidative chlorine, a support component of a gelatin sponge. After carrying out systematic characterization, the GS-Cls exhibited well-defined porous morphology and had a high efficiency in the killing of Gram-positive bacteria (E. coli) and Gram-negative bacteria (S. aureus). The loading of oxidative chlorine (Cl+%) could be controlled by changing the NaClO concentrations and chlorination times. The biocompatibility was confirmed as well. In vivo experiments suggested that the GS-Cl sample could effectively promote the healing of skin wounds in mice E. coli and S. aureus infection models. These studies show that proteins can be chlorinated and endowed with antimicrobial properties, which has great application potential in the treatment of bacteria-infected wounds.

Replacing CC Unit with B←N Unit in Isoelectronic Conjugated Polymers for Enhanced Photocatalytic Hydrogen Evolution.

Three linear isoelectronic conjugated polymers PCC, PBC, and PBN are synthesized by Suzuki-Miyaura polycondensation for photocatalytic hydrogen (H2 ) production from water. PBN presented an excellent photocatalytic hydrogen evolution rate (HER) of 223.5 µmol h-1 (AQY420  = 23.3%) under visible light irradiation, which is 7 times that of PBC and 31 times that of PCC. The enhanced photocatalytic activity of PBN is due to the improved charge separation and transport of photo-induced electrons/holes originating from the lower exciton binding energy (Eb ), longer fluorescence lifetime, and stronger built-in electric field, caused by the introduction of the polar B←N unit into the polymer backbone. Moreover, the extension of the visible light absorption region and the enhancement of surface catalytic ability further increase the activity of PBN. This work reveals the potential of B←N fused structures as building blocks as well as proposes a rational design strategy for achieving high photocatalytic performance.

Nitrogen Dense Distributions of Imidazole Grafted Dipyridyl Polybenzimidazole for a High Temperature Proton Exchange Membrane.

The introduction of basic groups in the polybenzimidazole (PBI) main chain or side chain with low phosphoric acid doping is an effective way to avoid the trade-off between proton conductivity and mechanical strength for high temperature proton exchange membrane (HT-PEM). In this study, the ethyl imidazole is grafted on the side chain of the PBI containing bipyridine in the main chain and blended with poly(2,2'-[p-oxydiphenylene]-5,5'-benzimidazole) (OPBI) to obtain a series of PBI composite membranes for HT-PEMs. The effects of the introduction of bipyridine in the main chain and the ethyl imidazole in the side chain on proton transport are investigated. The result suggests that the introduction of the imidazole and bipyridine group can effectively improve the comprehensive properties as HT-PEM. The highest of proton conductivity of the obtained membranes under saturated phosphoric acid (PA) doping can be up to 0.105 S cm-1 at 160 °C and the maximum output power density is 836 mW cm-2 at 160 °C, which is 2.3 times that of the OPBI membrane. Importantly, even at low acid doping content (~178%), the tensile strength of the membrane is 22.2 MPa, which is nearly 2 times that of the OPBI membrane, the proton conductivity of the membrane achieves 0.054 S cm-1 at 160 °C, which is 2.3 times that of the OPBI membrane, and the maximum output power density of a single cell is 540 mW cm-2 at 160 °C, which is 1.5 times that of the OPBI membrane. The results suggest that the introduction of a large number of nitrogen-containing sites in the main chain and side chain is an efficient way to improve the proton conductivity, even at a low PA doping level.

Direct Ink Writing of Phenylethynyl End-Capped Oligoimide/SiO2 to Additively Manufacture High-Performance Thermosetting Polyimide Composites.

The three-dimensional (3D) printing of a SiO2-filled thermosetting polyimide (SiO2@TSPI) composite with outstanding performance is realized via the direct ink writing (DIW) of polyamide acid (PAA) composite ink and thermal treatment conducted thereafter. The composite ink consists of phenylethynyl-terminated PAA and silica nanoparticles, where the SiO2 nanoparticles serve as the rheology modifier that is necessary for the DIW technique to obtain self-supporting feedstock during 3D printing and the reinforcement filler that is used to enhance the performance of the final composite. As a result, printed parts with complex geometry and robust thermal stability are obtained. Due to the extrusion-based DIW technique, the printed structures exhibit anisotropic mechanical strength that highly depends on printing roads. This simple and convenient means of realizing 3D structures of thermosetting polyimides is a promising strategy in aerospace and other fields.

Preparation and application of quick hemostatic gauze based on biomimetic mineralized thrombin.

Thrombin is a serine protease known as activated coagulation factor II and is primarily applied as an effective local hemostatic agent. However, its clinical application is hindered by drawbacks, such as high sensitivity to the surrounding environment, instability and poor storage stability, easy inactivation, and low bioavailability. The biological functions of biomacromolecules in harsh environments can be preserved through biomineralization. Despite the success of biomimetic mineralization, limited consideration has been given to the mineral-based methods and the effect of various metal ions on enzyme activity. To explore an efficient technique for biomimetic mineralized thrombin, six kinds of ion/thrombin hybrid microflowers and two kinds of thrombin/MOF were synthesized in this work. The results showed that Zn-HNFs-G exhibits good hemostatic effect and maintains high enzymatic activity when exposed to high-temperature conditions. Meanwhile, Fe-HNFs-G, Thrombin@ZIF-8-G and Thrombin@MAF-7-G possess negligible enzyme protection.

Copper Peroxide-Loaded Gelatin Sponges for Wound Dressings with Antimicrobial and Accelerating Healing Properties.

Catalytic conversion of hydrogen peroxide (H2O2) to more toxic hydroxyl radicals (•OH) is a good choice for sterilization and anti-infection, but endogenous H2O2 is insufficient to achieve satisfactory sterilization efficacy. Despite great efforts, designing and developing antimicrobial materials that specifically and effectively self-supply H2O2 at the wound site remain as tremendous challenges. Here, we report a pH-responsive copper peroxide-loaded wound dressing made from copper hydroxide and gelatin sponge and then reacted with H2O2. In vitro experiments show that the prepared wound dressing has good bactericidal properties against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Pseudomonas aeruginosa (P. aeruginosa). Moreover, the as-prepared wound dressing can release •OH specifically in the bacterial-infected skin wound, rather than in normal tissues, and in vivo skin wound-healing experiments proved that the synthesized copper peroxide-loaded gelatin sponge could combat E. coli effectively; in addition, Cu2+ released from the gelatin sponge could stimulate angiogenesis and collagen deposition simultaneously. The study provides a strategy to improve antibacterial efficacy and reduce the toxic side effects through the release of •OH by bacterial self-activation.

Hydrogel sunscreen based on yeast /gelatin demonstrates excellent UV-shielding and skin protection performance.

Traditional organic and inorganic sunscreens suffer from the disadvantages of low stability and poor biocompatibility. In the study, we developed a novel hydrogel sunscreen based on the yeast and gelatin, which demonstrated excellent UV protection property and broad absorption of UV across UVA and UVB region. Yeast was used as effective component and gelatin as matrix to fabricate the hydrogel, which is high hydrated and reasonable to simulate natural living tissue. As a common probiotic, yeast shows safety and satisfactory UV protection capability. Furthermore, the hydrogel sunscreen shows excellent biocompatibility and UV protection performance both in vitro and in vivo. Moreover, they can be prepared conveniently and provide an eco-friendly strategy, which provides experience and inspiration of probiotics in the cosmetics application.

Secondary dialkylammonium salt/crown ether [2]pseudorotaxanes as nanostructured platforms for proton transport.

Multivalent secondary dialkylammonium salt/crown ether [2]pseudorotaxane, supramolecular polymer networks have been obtained by mixing surfactant-encapsulated clusters with dibenzo[24]crown-8 groups and star polymers end functionalized with dibenzylammonium ions. This induces remarkable enhancements and rational control of proton conductivity of the supramolecular networks.

A novel off-on fluorescent chemosensor for Al3+ derived from a 4,5-diazafluorene Schiff base derivative.

The performance of a chemosensor is closely related to its structure. A new Schiff bass (DFSB) based on 4,5-diazafluorene units has been synthesized in this work. The interaction of DFSB with different metal ions has been studied using UV-vis absorption spectra and fluorescent spectra. The results show that DFSB is a highly selective and sensitive probe for Al3+ ions over other commonly coexisting metal ions in ethanol. A very obvious fluorescence enhancement effect was observed, and a turn-on ratio over 1312-fold was triggered with the addition of 10 equiv. of Al3+ ions. What is more, such fluorescent responses could be detected by the naked eye under a UV-lamp. The lowest detection limit for Al3+ was determined as 3.7 × 10-8 M. The complex solution (DFSB-Al3+) exhibited reversibility with EDTA. These results may be caused by the unique molecular structure.

A Turn-on and Reversible Fluorescence Sensor for Zinc Ion Based on 4,5-Diazafluorene Schiff Base.

A new 4,5-diazafluorene-based fluorescent chemosensor has been synthesized by Schiff base condensation of 9,9-bis(3,5-dimethyl-4-aminophenyl)-4,5-diazafluorene with salicylaldehyde. The interaction of Schiff base with different metal ions has been studied over photofluorescent spectra. The results showed that Schiff base exhibited 194-fold enhancements in fluorescence at 465 nm after Zn(2+) ions. Such fluorescent responses could be detected by naked eye under UV-lamp. The complex solution (L-Zn(2+)) exhibited reversibility with EDTA.