Improving Polysulfides Adsorption and Redox Kinetics by the Co4 N Nanoparticle/N-Doped Carbon Composites for Lithium-Sulfur Batteries.

Improved conductivity and suppressed dissolution of lithium polysulfides is highly desirable for high-performance lithium-sulfur (Li-S) batteries. Herein, by a facile solvent method followed by nitridation with NH3 , a 2D nitrogen-doped carbon structure is designed with homogeneously embedded Co4 N nanoparticles derived from metal organic framework (MOF), grown on the carbon cloth (MOF-Co4 N). Experimental results and theoretical simulations reveal that Co4 N nanoparticles act as strong chemical adsorption hosts and catalysts that not only improve the cycling performance of Li-S batteries via chemical bonding to trap polysulfides but also improve the rate performance through accelerating the conversion reactions by decreasing the polarization of the electrode. In addition, the high conductive nitrogen-doped carbon matrix ensures fast charge transfer, while the 2D structure offers increased pathways to facilitate ion diffusion. Under the current density of 0.1C, 0.5C, and 3C, MOF-Co4 N delivers reversible specific capacities of 1425, 1049, and 729 mAh g-1 , respectively, and retains 82.5% capacity after 400 cycles at 1C, as compared to the sample without Co4 N (MOF-C) values of 61.3% (200 cycles). The improved cell performance corroborates the validity of the multifunctional design of MOF-Co4 N, which is expected to be a potentially promising cathode host for Li-S batteries.

Process-Tracing Study on the Postassembly Modification of Highly Stable Zirconium Metal-Organic Cages.

Metal-organic cages (MOCs) are discrete molecular assemblies formed by coordination bonds between metal nodes and organic ligands. The application of MOCs has been greatly limited due to their poor stability, especially in aqueous solutions. In this work, we thoroughly investigate the stability of several Zr-MOCs and reveal their excellent stability in aqueous solutions with acidic, neutral, and weak basic conditions. In addition, we present for the first time a process-tracing study on the postassembly modification of one MOC, ZrT-1-NH2, highlighting the excellent stability and versatility of Zr-MOCs as a new type of molecular platform for various applications.

Web-Like Interconnected Carbon Networks from NaCl-Assisted Pyrolysis of ZIF-8 for Highly Efficient Oxygen Reduction Catalysis.

The oxygen reduction reaction (ORR) is under intense research due to its significance in energy storage and conversion processes. Recent studies show that interconnected and hierarchically porous structures can further enhance ORR kinetics as well as catalyst durability, but their preparation can be quite time and/or chemical consuming. Here, a simple approach is reported to prepare such complex structures by pyrolyzing composites containing NaCl and ZIF-8. The templating effect of molten NaCl connects ZIF-8 particles into web-like carbon networks. During ORR activity measurements, it achieves a 0.964 V onset potential and a 38 mV dec-1 Tafel slope, which are comparable to those of the benchmark Pt/C (0.979 V and 40 mV dec-1 ). Due to the metal-free feature, this catalyst exhibits a 16 mV shift in half-wave potential after a 10 000-cycle durability test, which is only 60% of that of Pt/C. The catalyst is also tested in Zn-air batteries and the assemblies are able to work at above 1.2 V for 140 h, which triples the life held by those with Pt/C. This study demonstrates a facile strategy to prepare metal-free ORR catalysts with interconnectivity and hierarchical porosity, and proves their great potentials in ORR catalysis and Zn-air batteries.

Electrocatalysts Derived from Metal-Organic Frameworks for Oxygen Reduction and Evolution Reactions in Aqueous Media.

Electrochemical energy conversion and storage devices such as fuel cells and metal-air batteries have been extensively studied in recent decades for their excellent conversion efficiency, high energy capacity, and low environmental impact. However, sluggish kinetics of the oxygen-related reactions at air cathodes, i.e., oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are still worth improving. Noble metals such as platinum (Pt), iridium (Ir), ruthenium (Ru) and their oxides are considered as the benchmark ORR and OER electrocatalysts, but they are expensive and prone to be poisoned due to the fuel crossover effect, and may suffer from agglomeration and leaching after long-term usage. To mitigate these limits, it is highly desirable to design alternative ORR/OER electrocatalysts with prominent performance. Metal-organic frameworks (MOFs) are a class of porous crystalline materials consisting metal ions/clusters coordinated by organic ligands. Their crystalline structure, tunable pore size and high surface area afford them wide opportunities as catalytic materials. This Review covers MOF-derived ORR/OER catalysts in electrochemical energy conversion, with a focus on the different strategies of material design and preparation, such as composition control and nanostructure fabrication, to improve the activity and durability of MOF-derived electrocatalysts.

A Modulated Hydrothermal (MHT) Approach for the Facile Synthesis of UiO-66-Type MOFs.

Developing a general and economically viable approach for the large-scale synthesis of water-stable metal-organic frameworks (MOFs) with repeatable quality remains the key step for their massive production and commercialization. We herein report a green (aqueous solutions), mild (100 °C, 1 atm), and scalable (can be up to kilograms) modulated hydrothermal (MHT) synthesis of UiO-66, an iconic MOF that has been widely studied recently for its high water stability. More importantly, the MHT synthetic approach can be applied to synthesize other water-stable MOFs with structures identical to UiO-66, such as UiO-66-(F)4, UiO-66-(OCH2CH3)2, and UiO-66-(COOH)4, which cannot be obtained via the traditional solvothermal method. Their performance in postcombustion CO2 capture has also been evaluated. Our MHT approach has clearly depicted a roadmap for the facile synthesis of zirconium-based water stable MOFs to facilitate their massive production and commercialization.

NiFe nanosheets as urea oxidation reaction electrocatalysts for urea removal and energy-saving hydrogen production.

The preparation of high-performance electrocatalysts is a breakthrough to solve the increasingly prominent problems of environmental degradation and energy depletion. Urea oxidation reaction (UOR) plays a vital role in treating urea-rich wastewater and assisting hydrogen production with low energy consumption. To alleviate the sluggish intrinsic reaction kinetic barrier of six-electron transfer involved in UOR, we develop a NiFe ultra-thin two-dimensional nanosheet array supported on nickel foam as UOR electrocatalyst by one-step hydrothermal method. Benefiting from the in-situ synthesis strategy, abundant mesoporous structure, and the electronic structure change of Ni after the introduction of Fe, NiFe nanosheets (NiFe NSs) exhibit remarkable UOR catalytic activity and excellent long-term stability. Moreover, we assemble a two-electrode electrolytic cell with NiFe NSs/NF as the anode. The results show that the cell voltage of urea assisted water electrolysis for hydrogen production decreased by 15.2% rather than the regular water splitting, as well as that the urea concentration in electrolyte is degraded 55.6% after electrolysis for 36 h at 1.70 V. This work indicates a feasibility verification for the electrocatalytic removal of urea in wastewater treatment, and an efficient and energy-saving method for urea-assisted electrolytic hydrogen production based on NiFe nanosheets.

Recent advances in the synthesis and applications of graphene-polypeptide nanocomposites.

The combination of peptides and graphene-derived materials provides a new way to prepare graphene-based nanocomposites with unique structures, properties, and functions. The modification of graphene with different polypeptides not only improves the biocompatibility and biological recognition ability of graphene-based materials, but also greatly expands their application fields. In this work, we summarize different interactions between graphene and polypeptides, and the synthesis methods of novel functional graphene-polypeptide nanocomposites based on the interactions in recent years (from 2016 to present). In addition, the potential applications of graphene-peptide hybrid nanocomposites in biomedicine, tissue engineering, biosensors, environmental science engineering, optoelectronic materials, and energy storage are introduced. We hope that this review will help readers to understand the methods and mechanisms of the modification of graphene surfaces with biomolecules, and promote readers to understand the synthesis and applications of graphene-based nanocomposites. This work may provide hints and references for the development of peptide sequence design, and biomedical and functional materials, and will help in designing and synthesizing novel graphene-based nanomaterials with unique properties and suitable for various applications in the future.

Fluorometry detection for trypsin via inner filter effect between cytochrome C and in-situ formed fluorescent thiochrome.

A fluorometry assay for trypsin sensitive determination has been presented. The fluorescence of the system at 370/445 nm is derived from thiochrome obtained by in-situ oxidation of thiamine. Based on the inner filter effect, cytochrome C (Cyt C) can quench the fluorescence at 445 nm effectively. Cyt C is specifically hydrolyzed by trypsin through an enzymatic reaction, giving rise to the enhancement of the fluorescence intensity. The change value of fluorescence intensity is proportional to trypsin concentration, which is successfully used for trypsin quantitative detection. This method exhibits good repeatability and selectivity with a detection limit of 0.15 µg mL-1 and a quantification limit of 0.50 µg mL-1 for trypsin sensing. Moreover, it is applied to detect trypsin in practical serum and urine samples with accurate results. The proposed assay is not only a promising candidate for trypsin determination in practical application but also a potentially valuable tool in urine comprehensive analysis and disease diagnosis.

In Situ Formation of Micropore-Rich Titanium Dioxide from Metal-Organic Framework Templates.

Phase and porosity control in titanium dioxide (TiO2) is essential for the optimization of its photocatalytic activity. However, concurrent control over these two parameters remains challenging. Here, a novel metal-organic framework templating strategy is demonstrated for the preparation of highly microporous anatase TiO2. In situ encapsulation of Ti precursor in ZIF-8 cavities, followed by hydrolysis and etching, produces anatase TiO2 with a high Brunauer-Emmett-Teller surface area of 335 m2·g-1 and a micropore surface area ratio of 48%. Photocatalytic hydrogen generation catalyzed by the porous TiO2 can reach a rate of 2459 µmol·g-1·h-1. The measured photocatalytic activity is found to be positively correlated to the surface area, highlighting the importance of porosity control in heterogeneous photocatalysts.

Hydrazone-based covalent organic frameworks for Lewis acid catalysis.

Hydrazone-based covalent organic frameworks (COFs) are rich in functional groups but have very limited variety and applications. Herein, two hydroxy-rich hydrazone-based COFs are synthesized in pure water and postsynthetically incorporated with CoII, exhibiting Lewis acid catalytic activity towards cyanosilylation of various aldehydes with size selectivity.

Reversed thermo-switchable molecular sieving membranes composed of two-dimensional metal-organic nanosheets for gas separation.

It is highly desirable to reduce the membrane thickness in order to maximize the throughput and break the trade-off limitation for membrane-based gas separation. Two-dimensional membranes composed of atomic-thick graphene or graphene oxide nanosheets have gas transport pathways that are at least three orders of magnitude higher than the membrane thickness, leading to reduced gas permeation flux and impaired separation throughput. Here we present nm-thick molecular sieving membranes composed of porous two-dimensional metal-organic nanosheets. These membranes possess pore openings parallel to gas concentration gradient allowing high gas permeation flux and high selectivity, which are proven by both experiment and molecular dynamics simulation. Furthermore, the gas transport pathways of these membranes exhibit a reversed thermo-switchable feature, which is attributed to the molecular flexibility of the building metal-organic nanosheets.

Ultrathin two-dimensional porous organic nanosheets with molecular rotors for chemical sensing.

Molecular rotors have played an important role in recent materials chemistry. Although several studies on functional materials containing molecular rotors have been reported for fluorescence sensing, this concept has yet to be realized in two-dimensional (2D) materials. Here we report the preparation of all-carbon, π-conjugated 2D porous organic nanosheets, named NUS-24, which contain flexible tetraphenylethylene (TPE) units as the molecular rotors. NUS-24 nanosheets exhibit high stability, large lateral size, and ultrathin thickness (2-5 nm). The dynamic TPE rotors exposed on the surface of NUS-24 nanosheets can be restricted in the aggregated state with different water fractions, which is reminiscent of the aggregation-induced emission mechanism, thereby leading to the size-selective turn-on fluorescence by volatile organic compounds. Significantly, the ultrathin 2D nanosheets and its composite membranes show much higher sensitivity and selectivity toward Fe3+ ions and nitro-containing compounds sensing, suggesting their potential applications in explosive detection and environmental monitoring.

Improving Water-Treatment Performance of Zirconium Metal-Organic Framework Membranes by Postsynthetic Defect Healing.

Microporous metal-organic frameworks (MOFs) as building materials for molecular sieving membranes offer unique opportunities to tuning the pore size and chemical property. The recently reported polycrystalline Zr-MOF membranes have greatly expanded their applications from gas separation to water treatment. However, Zr-MOFs are notoriously known for their intrinsic defects caused by ligand/cluster missing, which may greatly affect the molecular sieving property of Zr-MOF membranes. Herein, we present the mitigation of ligand-missing defects in polycrystalline UiO-66(Zr)-(OH)2 membranes by postsynthetic defect healing (PSDH), which can help in increasing the membranes' Na+ rejection rate by 74.9%. Intriguingly, the membranes also exhibit excellent hydrothermal stability in aqueous solutions (>600 h). Our study proves the feasibility of PSDH in improving the performance of polycrystalline Zr-MOF membranes for water-treatment applications.

Fabrication of Highly Stable and Efficient PtCu Alloy Nanoparticles on Highly Porous Carbon for Direct Methanol Fuel Cells.

Boosting the durability of Pt nanoparticles by controlling the composition and morphology is extremely important for fuel cells commercialization. We deposit the Pt-Cu alloy nanoparticles over high surface area carbon in different metallic molar ratios and optimize the conditions to achieve desired material. The novel bimetallic electro-catalyst {Pt-Cu/PC-950 (15:15%)} offers exceptional electrocatalytic activity when tested for both oxygen reduction reaction and methanol oxidation reactions. A high mass activity of 0.043 mA/µgPt (based on Pt mass) is recorded for ORR. An outstanding longevity of this electro-catalyst is noticed when compared to 20 wt % Pt loaded either on PC-950 or commercial carbon. The high surface area carbon support offers enhanced activity and prevents the nanoparticles from agglomeration, migration, and dissolution as evident by TEM analysis.

Highly Porous Carbon Derived from MOF-5 as a Support of ORR Electrocatalysts for Fuel Cells.

The development of highly competent electrocatalysts for the sluggish oxygen reduction reaction (ORR) at cathodes of proton-exchange membrane fuel cells (PEMFCs) is extremely important for their long-term operation and wide applications. Herein, we present highly efficient ORR electrocatalysts based on Pt/Ni bimetallic nanoparticles dispersed on highly porous carbon obtained via pyrolysis of a metal-organic framework MOF-5. In comparison to the commercial Pt/C (20%), the electrocatalyst Pt-Ni/PC 950 (15:15%) in this study exhibits a pronounced positive shift of 90 mV in Eonset. In addition, it also demonstrates excellent long-term stability and durability during the 500-cycle continue-oxygen-supply (COS) accelerating durability tests (ADTs). The significantly improved activity and stability of Pt-Ni/PC 950 (15:15%) can be attributed to the Pt electron interaction with Ni and carbon support as has been proved in X-ray and microscopic analysis.

Fe/Fe3 C/N-Doped Carbon Materials from Metal-Organic Framework Composites as Highly Efficient Oxygen Reduction Reaction Electrocatalysts.

A series of Fe/Fe3 C-containing N-doped porous carbon materials (Fe/NC) were prepared by pyrolyzing composites that contained a metal-organic framework (MIL-88c-Fe) with dicyandiamide. The Fe/NC obtained at 800 °C (Fe/NC800) showed comparable onset potential and kinetics to that of the commercial Pt/C catalyst in catalyzing the oxygen reduction reaction (ORR). Further measurements suggested that it has better durability and much higher methanol tolerance than Pt/C. Acid leaching was performed to reveal the critical role of Fe-containing sites in ORR catalysis.

Improving the hydrogen selectivity of graphene oxide membranes by reducing non-selective pores with intergrown ZIF-8 crystals.

We report the intergrowth of ZIF-8 crystals on ultrathin graphene oxide (GO) membranes, which helps to reduce the non-selective pores of pristine GO membranes leading to gas selectivities as high as 406, 155, and 335 for H2/CO2, H2/N2, and H2/CH4 mixtures, respectively.

Synthesis of a Sulfonated Two-Dimensional Covalent Organic Framework as an Efficient Solid Acid Catalyst for Biobased Chemical Conversion.

Because of limited framework stability tolerance, de novo synthesis of sulfonated covalent organic frameworks (COFs) remains challenging and unexplored. Herein, a sulfonated two-dimensional crystalline COF, termed TFP-DABA, was synthesized directly from 1,3,5-triformylphloroglucinol and 2,5-diaminobenzenesulfonic acid through a previously reported Schiff base condensation reaction, followed by irreversible enol-to-keto tautomerization, which strengthened its structural stability. TFP-DABA is a highly efficient solid acid catalyst for fructose conversion with remarkable yields (97 % for 5-hydroxymethylfurfural and 65 % for 2,5-diformylfuran), good chemoselectivity, and good recyclability. The present study sheds light on the de novo synthesis of sulfonated COFs as novel solid acid catalysts for biobased chemical conversion.

A nitrogen-doped graphene/carbon nanotube nanocomposite with synergistically enhanced electrochemical activity.

A new kind of nitrogen-doped graphene/carbon nanotube nanocomposite can be synthesized by a facile hydrothermal process under mild conditions, which exhibits synergistically enhanced electrochemical activity for the oxygen reduction reaction. This research provides a new route to access a metal-free electrocatalyst with high activity under mild conditions.

PinX1 regulation of telomerase activity and apoptosis in nasopharyngeal carcinoma cells.

BACKGROUND: Human interacting protein X1 (PinX1) has been identified as a critical telomerase inhibitor and proposed to be a putative tumor suppressor gene. Loss of PinX1 has been found in a large variety of malignancies, however, its function in inhibiting telomerase activity of tumor cells is not well documented. Here we show that PinX1 is essential for down-regulation telomerase activity of nasopharyngeal carcinoma. METHODS: Expression vectors of human PinX1 (pEGFP-C3-PinX1) and its small interfering RNA (PinX1-FAM-siRNA) were constructed and transfected into NPC. Their effects on mRNA of telomerase catalytic subunit (hTERT), telomerase activity, cell proliferation, cell migration, wound healing, cell cycles and apoptosis were examined using semi-quantitative RT-PCR, stretch PCR, MTT assay, Transwell, scratch assay and flow cytometry, respectively. RESULTS: Transfection of pEGFP-C3-PinX1 and PinX1-FAM-siRNA increased and reduced PinX1 mRNA by 1.6-fold and 70%, respectively. Over-expression of PinX1 decreased hTERT mRNA by 21%, reduced telomerase activity, inhibited cell growth, migration and wound healing ability, arrested cells in G0/G1 phase, and increased apoptotic index. In contrast, down-regulation of PinX1 did not alter the above characteristics. CONCLUSIONS: PinX1 may play important roles in NPC proliferation, migration and apoptosis and has application potential in tumor-targeted gene therapy.