pH-Responsive Flexible Copper Electrode with Switchable Wettability for Electrocatalytic Hydrogen/Oxygen Evolution Reactions and Urea Oxidation Reaction.

The development of a pH-responsive electrode with switchable wettability is of great importance in water electrolysis. Here, we designed a pH-responsive copper mesh/copolymer electrode to eliminate the adhesion of hydrogen/oxygen bubbles under high-speed water electrolysis by adjusting the wettability of the electrode surface. Furthermore, the kinetics of water oxidation and urea oxidation reactions on the as-prepared copper mesh/copolymer electrode were explored. Most noteworthy, the flexible water electrolysis performance of the as-prepared pH-responsive electrode was investigated for the first time. The results indicate that the copper mesh/copolymer electrode accelerates the hydrogen evolution reaction, oxygen evolution reaction, and urea oxidation reaction under better surface wettability, while it inhibits these reactions under poor surface wettability. The results provide insight into the development of unusual water electrolyzers with different pH electrolytes and the design of water electrolysis electrodes.

Preparation and characterization of functionalized chitosan/polyvinyl alcohol composite films incorporated with cinnamon essential oil as an active packaging material.

In this study, amphiphilic chitosan (NPCS-CA) was synthesized by grafting quaternary phosphonium salt and cholic acid onto the chain of chitosan, aiming to develop an active edible film based on NPCS-CA and polyvinyl alcohol (PVA) incorporated with cinnamon essential oil (CEO) by the casting method. The chemical structure of the chitosan derivative was characterized by FT-IR, 1H NMR and XRD. Through the characterization of FT-IR, TGA, mechanical and barrier properties of the composite films, the optimal proportion of NPCS-CA/PVA was determined as 5/5. And, the tensile strength and elongation at break of the NPCS-CA/PVA (5/5) film with 0.4 % CEO were 20.32 MPa and 65.73 %, respectively. The results revealed that the NPCS-CA/PVA-CEO composite films exhibited an excellent ultraviolet barrier property at 200-300 nm and significantly reduced oxygen permeability, carbon dioxide permeability and water vapor permeability. Furthermore, the antibacterial property of film-forming solutions against E. coli, S. aureus, and C. lagenarium was distinctly improved with the increase of NPCS-CA/PVA proportion. And, the multifunctional films effectively extended the shelf-life of mangoes at 25 °C based on the characterization of surface changes and quality indexes. The NPCS-CA/PVA-CEO films could be developed as biocomposite food packaging material.

Interfacial Synthesis of an Ultrathin Two-Dimensional Polymer Film via [2 + 2] Photocycloaddition.

A carbon-carbon-linked, ultrathin, two-dimensional (2D) polymer film was prepared at the air/water interface through photochemically triggered [2 + 2] cycloaddition. The preorganization of the monomers on the water surface and the subsequent photo-polymerization led to the successful preparation of the ultrathin 2D polymer film. The obtained film is continuous, free standing, and has a large area (over 50 µm2). Transmission electron microscopy (TEM) and atomic force microscopy (AFM) give clear evidence of the ultrathin film morphology. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) indicate successful photo-induced [2 + 2] polymerization.

Amphiphilic chitosan/carboxymethyl gellan gum composite films enriched with mustard essential oil for mango preservation.

In this paper, amphiphilic chitosan and carboxymethyl modified gellan gum were synthesized to develop an active edible fresh-keeping material. The optimal weight ratio of CMCS-g-CA/CMGG was determined as 5:2 through the characterization of Fourier transform infrared (FT-IR), Thermogravimetric analysis (TGA), mechanical and barrier properties of the composite films. In addition, the water vapor permeability and oxygen permeability of CMCS-g-CA/CMGG composite films incorporated with mustard essential oil were all declined, and the antibacterial property of the composite film solutions against E. coli, S. aureus and Bacillus anthracis was distinctly improved with the increase of mustard essential oil (MEO) dosage. Furthermore, the CMCS-g-CA/CMGG + 2.0 µL/mL MEO composite film exhibited an effective preservation on mango fruits during 20 days of storage based on the characterization of surface appearance and quality indexes of fruits. Hence, the multifunctional CMCA-g-CA/CMGG/MEO composite films can be served as a prospective eco-friendly packaging material for fruit preservation.

Synthesis and characterization of carboxymethyl chitosan/epoxidized soybean oil based conjugate catalyed by UV light, and its application as drug carrier for fusarium wilt.

In this paper, a cationic photoinitiator (TAS) was used as a catalyst for the ring opening reaction of carboxymethyl chitosan (CMCS) and epoxidized soybean oil (ESO) under UV light to prepare CMCS-g-ESO conjugate, and the structure of the product was characterized by FT-IR, 1H NMR and GPC. Then, the spinosad-loaded microcapsules (SSD@CMCS-g-ESO) were prepared by ultrasonic self-assembly method. The results showed that TAS could catalyze the ring opening reaction of CMCS and ESO under UV-irradiation and the optimum reaction time was 1 h, with the molecular weight of 15,745. The average particle size of SSD@CMCS-g-ESO was about 2.16 µm, and the encapsulation efficiency (EE) and drug loading content (LC) of SSD@CMCS-g-ESO were 85.39 ± 2.05% and 20.17 ± 1.84%, respectively. In vitro release revealed that SSD@CMCS-g-ESO exhibited sustained-release and pH-responsive property, and the accumulative release in the buffer solution of pH = 6.5 and 7.4 was higher than in pH = 9.0. Furthermore, SSD@CMCS-g-ESO had a good antifungal properties against Fusarium oxysporum f. sp. cubense (Foc) compared with the unencapsulated SSD at the same drug dose. This work indicated that photo-chemical reactions could be used to prepare bio-based carrier materials to construct drugs delivery system for targeted treatment of fusarium wilt.

Preparation of a Large Amount of Ultrathin Graphdiyne.

We report a facile strategy to prepare a large amount of ultrathin graphdiyne (GDY) with good crystallinity in the mixture of oil-water systems. By simply mixing the solution of GDY monomer in CHCl3 and the copper acetate solution as a catalyst in water and stirring at room temperature, ultrathin GDY films with a thickness of ∼4 nm were obtained in a yield of 95 %. This work provides a feasible path for the substantial preparation of GDY films and may pave the way to the development of substantial preparation of the GDY materials.

Preparation and characterization of chitosan derivatives modified with quaternary ammonium salt and quaternary phosphate salt and its effect on tropical fruit preservation.

In this paper, HACC modified with (5-Carboxypentyl) (triphenyl) phosphonium bromide (HA-CS-NP) was synthesized. Then, a multifunctional food packaging composite film with good thermal stability and antibacterial functions was fabricated by HA-CS-NP and poly (vinyl alcohol) (PVA). The tensile strength and elongation at break of HA-CS-NP/PVA composite film at the weight ratio of 3/7 were 20.32 ± 1.02 MPa and 65.73 ± 3.29%, respectively. And, the inhibition rates of HA-CS-NP (0.5%) on Mango C. lagenarium and Papaya C. gloeosporioides on day 6 were up to 80.92 ± 4.12%. Compared with CK group, the weight loss of experimental groups were 23.96 ± 2.46 g/206 ± 7.25 g (mangoes) and 59.45 ± 3.06 g/496 ± 6.37 g (papaya), reduced by 35.76 ± 1.15%. Moreover, the final hardness value of the fruits coated with composite films was 4.94 ± 0.23 kg/cm3 and increased by 20.79 ± 1.04%, and the rot index was reduced by 71.43 ± 3.24%. The multifunctional HA-CS-NP/PVA coating has broad prospects in the application of food packaging.

Facile construction of fully sp2-carbon conjugated two-dimensional covalent organic frameworks containing benzobisthiazole units.

Developing a facile strategy for the construction of vinylene-linked fully π-conjugated covalent organic frameworks (COFs) remains a huge challenge. Here, a versatile condition of Knoevenagel polycondensation for constructing vinylene-linked 2D COFs was explored. Three new examples of vinylene-linked 2D COFs (BTH-1, 2, 3) containing benzobisthiazoles units as functional groups were successfully prepared under this versatile and mild condition. The electron-deficient benzobisthiazole units and cyano-vinylene linkages were both integrated into the π conjugated COFs skeleton and acted as acceptor moieties. Interestingly, we found the construction of a highly ordered and conjugated D-A system is favorable for photocatalytic activity. BTH-3 with benzotrithiophene as the donor with a strong D-A effect exhibited an attractive photocatalytic HER of 15.1 mmol h-1g-1 under visible light irradiation.

Control of the Surface Disorder by Ion-Exchange to Achieve High Open-Circuit Voltage in HC(NH2 )2 PbI3 Perovskite Solar Cell.

The ionic nature of organic trihalide perovskite leads to structural irregularity and energy disorder at the perovskite surface, which seriously affects the photovoltaic performance of perovskite solar cells. Here, the origin of the perovskite surface disorder is analyzed, and a facial ion-exchange strategy is designed to regulate the surface chemical environment. By the reconstruction of terminal irregular Pb-I bonds and random cations, the repaired surface is characteristic of the reduced band tail states, consequent to the suppression of the uplift of quasi-Fermi level splitting and photocarrier scattering. The optimized device gets a high open-circuit voltage and operational stability. These findings fully elaborate the underlying mechanism concerning perovskite surface problem, giving guidance on tailoring the energy disorder.

Highly Efficient Preparation of Single-Layer Two-Dimensional Polymer Obtained from Single-Crystal to Single-Crystal Synthesis.

A two-dimensional polymer (2DP) single crystal (T-2DP) with submillimeter size was synthesized by single-crystal to single-crystal transformation based on photochemical [2 + 2]-cycloaddition. A successful conversion from monomer to polymer was achieved in the single-crystal state. The structure information with an atomic resolution of both the monomer and 2DP was given through single-crystal X-ray diffraction. By simply treated with trifluoroacetic acid (TFA) under mild conditions, an unprecedented efficiency of exfoliation was achieved. The triazine core in T-2DP could be protonated by TFA, which resulted in a solution-like sample with >60% of monolayers. The size of the exfoliated monolayer reaches to several hundreds of µm2. This is another precious example of 2DP single crystal with nearly perfect structure and large enough size. The successful preparation of the highly desirable 2DP "solution" for a long time containing large sized and large amount of 2DP monolayers may open up new prospects for the basic properties study and the applications of 2DPs.

Donor-Acceptor Interactions Induced Interfacial Synthesis of an Ultrathin Fluoric 2D Polymer by Photochemical [2+2] Cycloaddition.

Invited for the cover of this issue is the group of Prof. Dr. Yingjie Zhao at Qingdao University of Science and Technology. The image depicts the ultrathin two-dimensional polymer reported in this work. Read the full text of the article at 10.1002/chem.202004797.

Donor-Acceptor Interactions Induced Interfacial Synthesis of an Ultrathin Fluoric 2D Polymer by Photochemical [2+2] Cycloaddition.

Two-dimensional polymers (2DPs) have attracted much interest due to their unique 2D atomic-thick covalent network with periodically linked monomers. The preparation of mono- or few-layered 2DPs with highly ordered structures is still a big challenge. Herein, we report a preparation of ultrathin 2DP film based on photo-triggered [2+2] cycloaddition at the air/water interface. The pre-assembly process induced by the D-A interactions before the polymerization plays a key role in constructing the highly ordered structure. The precise structure and chemical compositions of the continuous 2DP films were proved by selected area electron diffraction (SAED), Tip-Enhanced Raman Spectroscopy (TERS) and molecular-mechanics-based structural simulation.

Construction of Thiazolo[5,4-d]thiazole-based Two-Dimensional Network for Efficient Photocatalytic CO2 Reduction.

The efficient conversion of CO2 to chemical fuels driven by solar energy is still a challenging research area in photosynthesis, in which the conversion efficiency greatly relies on photocatalytic coenzyme NADH regeneration. Herein, a photocatalyst/biocatalyst synergetic system based on a conjugated microporous polymer (CMP) was prepared for sustainable and highly selective photocatalytic reduction of CO2 to methanol. Two thiazolo[5,4-d]thiazole-linked CMPs (TZTZ-TA and TZTZ-TP) were designed and synthesized as photocatalysts. Slight skeleton modification led to a great difference in their photocatalytic performance. Triazine-based TZTZ-TA exhibited an unprecedentedly high NADH regeneration efficiency of 82.0% yield within 5 min. Furthermore, the in situ photocatalytic NADH regeneration system could integrate with three consecutive enzymes for efficient conversion of CO2 into methanol. This CMP-enzyme hybrid system provides a new avenue for accomplishing the liquid sunshine from CO2.

A highly selective and active metal-free catalyst for ammonia production.

We report a facile surface-induced method for the in situ growth of single-/few-layered crystalline fluorographdiyne film on the surface of carbon fibers (cFGDY). The crystallized structure of cFGDY was directly confirmed by the scanning/transmission electron microscopy (SEM/TEM), high-resolution TEM (HRTEM) and computer simulation, selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. cFGDY showed a 9-fold stacking mode. Our results show that cFGDY is a metal-free electrocatalyst with unique structure and excellent performance for ammonia production from nitrogen and water efficiently at room temperature and ambient pressure, achieving a high NH3 production rate and Faraday efficiency in neutral conditions. This work provides an efficient catalyst system with determined chemical and electronic structures for highly selective and active nitrogen reduction, serving as a promising platform towards the development of novel metal-free catalysts.

Confined Interfacial Synthesis of Highly Crystalline and Ultrathin Graphdiyne Films and Their Applications for N2 Fixation.

Graphdiyne (GDY), as a new carbon allotrope, possessing both sp- and sp2 -hybridized carbon atoms, has attracted extensive attention due to great application potentials in various fields. To realize a fundamental understanding of the intrinsic properties of GDY, the controllable synthesis of ultrathin and highly crystalline GDY is necessary and challenging. Herein, a confined interfacial synthetic strategy towards highly crystalline ultrathin GDY at the water/oil/organogel interface, with greatly improved control over GDY structures, is reported. The morphology and chemical composition of GDY was characterized accordingly. After loading with gold, the as-prepared hydrophobic Au/GDY system showed excellent performance in the nitrogen reduction reaction, reaching the highest yield of 4.15 µg cm-2 h-1 with a Faraday efficiency of 1.95 %.

Construction of Fully Conjugated Covalent Organic Frameworks via Facile Linkage Conversion for Efficient Photoenzymatic Catalysis.

Covalent organic frameworks (COFs) with improved stability and extended π-conjugation structure are highly desirable. Here, two imine-linked COFs were converted into ultrastable and π-conjugated fused-aromatic thieno[3,2-c]pyridine-linked COFs (B-COF-2 and T-COF-2). The successful conversion was confirmed by infrared and solid-state 13C NMR spectroscopies. Furthermore, the structures of thieno[3,2-c]pyridine-linked COFs were evaluated by TEM and PXRD. It is noted that a slight difference in the structure leads to totally different photoactivity. The fully π-conjugated T-COF-2 containing triazine as the core exhibited an excellent photocatalytic NADH regeneration yield of 74% in 10 min.

Interfacial Synthesis of a Monolayered Fluorescent Two-Dimensional Polymer through Dynamic Imine Chemistry.

A fluorescent monolayered two-dimensional polymer (2DP) containing both tetraphenylethylene (TPE) and imine linkages is synthesized at air-water interface using the Langmuir-Blodgett method. We designed TPE-based monomers with long distances between the TPE and the imine linkages to avoid the charge transfer and therefore keep the fluorescence. A monolayered 2DP provided with more than 104 µm2 in domain size and around 0.8 nm thickness was obtained through a successive Schiff base reaction at air-water interface. The nanostructures and fluorescent property of 2DP films were characterized by optical microscopy, SEM, TEM, AFM and fluorescence spectrum. Most importantly, the tip-enhanced Raman spectroscopy (TERS) was utilized here to confirm the success of the polycondensation of monolayered 2DP.

Interfacial synthesis of crystalline two-dimensional cyano-graphdiyne.

A well-defined crystalline cyano-functionalized graphdiyne (CN-GDY) is synthesized at a liquid/liquid interface through alkyne-alkyne coupling reactions. The configurations and nanostructures of CN-GDY were well characterized by TEM, SEM, AFM, XPS, and Raman spectroscopy. HR-TEM and selected area electron diffraction (SAED) in combination with structure simulation firmly revealed a 9-fold stacking mode for CN-GDY.

Sulfur-rich Graphdiyne-Containing Electrochemical Active Tetrathiafulvalene for Highly Efficient Lithium Storage Application.

A sulfur-rich graphdiyne (TTF-GDY) material containing electrochemically active unit of tetrathiafulvalene was successfully synthesized at the liquid/liquid interface under mild conditions. The extended two-dimensional (2D) π-conjugated framework contains large in-plane cavities to accommodate defined sulfur elements and precise sulfur content. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterizations demonstrated that the TTF-GDY adopted the layered structures. X-ray photoelectron spectroscopy (XPS), Raman spectrum, selected area electron diffraction (SAED), crystal modeling, and molecular-mechanics-based calculation further confirmed the proposed framework structure and the expected chemical compositions. Considering the unique structure and sulfur-rich characteristic, we then applied this material as an electrode in lithium battery applications. Due to the unique 2D framework structure, the TTF-GDY exhibited a high specific capacity of 837.6 mAh/g, particularly having a robust long-term stability under the high current density. These results demonstrated that such a sulfur-rich TTF-GDY, as a novel electrochemical material would have great application potential in energy fields.

Fully Conjugated Two-Dimensional sp2 -Carbon Covalent Organic Frameworks as Artificial Photosystem†I with High Efficiency.

The synthesis of fully conjugated sp2 -carbon covalent organic frameworks (COF) is extremely challenging given the difficulty of the formation of very stable carbon-carbon double bonds (-C=C-). Here, we report the successful preparation of a 2D COF (TP-COF) based on triazine as central planar units bridged by sp2 -carbon linkers through the -C=C- condensation reaction. High-resolution-transmission electron microscopy (HRTEM) clearly confirmed the tessellated hexagonal pore structure with a pore center-to-center distance of 2 nm. Powder X-ray diffraction (PXRD) together with structural simulations revealed an AA stacking mode of the obtained layered structure. TP-COF turned out to be an excellent semiconductor material with a LUMO energy of -3.23 eV and a band gap of 2.36 eV. Excitingly, this novel sp2 -carbon conjugated TP-COF exhibited unprecedented coenzyme regeneration efficiency and can significantly boost the coenzyme-assisted synthesis of l-glutamate to a record-breaking 97 % yield within 12 minutes.