Using supercritical CO2 in the preparation of metal-organic frameworks: Investigating effects on crystallisation

In this report, we explore the use of supercritical CO2 (scCO2) in the synthesis of well-known metal-organic frameworks (MOFs) including Zn-MOF-74 and UiO-66, as well as on the preparation of [Cu24(OH-mBDC)24]n metal-organic polyhedra (MOPs) and two new MOF structures {[Zn2(L1)(DPE)]∙4H2O}n and {[Zn3(L1)3(4,4’-azopy)]∙7.5H2O}n, where BTC = benzene-1,3,5-tricarboxylate, BDC = benzene-1,4-dicarboxylate, L1 = 4-carboxy-phenylene- methyleneamino-4-benzoate, DPE = 1,2-di(4-pyridyl)ethylene, 4.4’-azopy = 4,4’- azopyridine, and compare the results versus traditional solvothermal preparations at low temperatures (i.e., 40 °Ϲ). The objective of the work was to see if the same or different products would result from the ssCO2 route versus the solvothermal method. We were interested to see which method produced the highest yield, the cleanest product and what types of morphology resulted. While there was no evidence of additional meso- or macroporosity in these MOFs/MOPs nor any significant improvements in product yields through the addition of scCO2 to these systems, it was shown that the use of scCO2 can have an effect on crystallinity, crystal size and morphology

Luminescent Boron Quinolate Block Copolymers via RAFT Polymerization

The preparation of well-defined luminescent organoboron quinolate block copolymers via sequential RAFT polymerization is reported. Boron-containing block copolymers with PS, P­(St-<i>alt</i>-MAh), and PNIPAM as the second block were successfully synthesized. The photophysical properties of the block copolymers were studied by UV–vis and fluorescence spectroscopy. Independent of the second block, the boron quinolate block copolymers that contain the parent 8-hydroxyquinolato ligand (PM1-<i>b</i>-PS, PM1-<i>b</i>-PNIPAM, PM1-<i>b</i>-P­(St-<i>alt</i>-MAh)) are green luminescent, whereas a polymer with 5-(4-dimethylaminophenyl)-8-hydroxyquinolate as the ligand (PM2-<i>b</i>-PS) shows red luminescence. The P­(St-<i>alt</i>-MAh)-based block copolymer was further modified with photoactive azobenzene groups. The self-assembly behavior of the amphiphilic block copolymers was studied by transmission electron microscopy (TEM) and dynamic light scattering (DLS). In water, PM1-<i>b</i>-PNIPAM forms spherical micelles. The azobenzene-modified P­(St-<i>alt</i>-AbMA)-<i>b</i>-PM1 exhibits a solvent-dependent self-assembly behavior in basic solutions, and large spindle-shaped aggregates and spherical micelles were observed

Electron-Deficient Triarylborane Block Copolymers: Synthesis by Controlled Free Radical Polymerization and Application in the Detection of Fluoride Ions

Luminescent triarylborane homo and block copolymers with well-defined chain architectures were synthesized via reversible addition–fragmentation chain transfer polymerization of a vinyl-functionalized borane monomer. The Lewis acid properties of the polymers were exploited in the luminescent detection of fluoride ions. A dual-responsive fluoride sensor was developed by taking advantage of the reversible self-assembly of a PNIPAM-based amphiphilic block copolymer. Anion detection in aqueous solution was realized by introducing positively charged pyridinium moieties along the polymer chain

Interconnected Nanoflake Network Derived from a Natural Resource for High-Performance Lithium-Ion Batteries

Numerous natural resources have a highly interconnected network with developed porous structure, so enabling directional and fast matrix transport. Such structures are appealing for the design of efficient anode materials for lithium-ion batteries, although they can be challenging to prepare. Inspired by nature, a novel synthesis route from biomass is proposed by using readily available auricularia as retractable support and carbon coating precursor to soak up metal salt solution. Using the swelling properties of the auricularia with the complexation of metal ions, a nitrogen-containing MnO@C nanoflake network has been easily synthesized with fast electrochemical reaction dynamics and a superior lithium storage performance. A subsequent carbonization results in the in situ synthesis of MnO nanoparticles throughout the porous carbon flake network. When evaluated as an anode material for lithium-ion batteries, an excellent reversible capacity is achieved of 868 mA h g^–1 at 0.2 A g^–1 over 300 cycles and 668 mA h g^–1 at 1 A g^–1 over 500 cycles, indicating a high tolerance to the volume expansion. The approach investigated opens up new avenues for the design of high performance electrodes with highly cross-linked nanoflake structures, which may have great application prospects

Grafted Copolymerization Modification of Hemicellulose Directly in the Alkaline Peroxide Mechanical Pulping (APMP) Effluent and Its Surface Sizing Effects on Corrugated Paper

In this work, the graft copolymerization of acrylamide (AM) and methacryloyloxy ethyl trimethyl ammonium chloride (DMC) with the hemicellulose in the alkaline peroxide mechanical pulping (APMP) effluent was investigated using the Fenton agent (FeSO₄/H₂O₂) as an initiator. The effects of the reaction conditions on the characteristics of the graft copolymers were studied. On the basis of the graft copolymer characterization, the optimum conditions were as follows: total active ingredient concentration 31%, reactive temperature 50 °C, amount of the initiator 0.4%, ratio of H₂O₂ to FeSO₄ 1:1, molar ratio of DMC to AM 1.5:20 and optimum percentages of <i>C</i>, <i>G</i>, GE, and viscosity are 65%, 246%, 98%, and 5020 cP, respectively. Structure elucidation of the graft copolymer was obtained by ¹H NMR spectroscopy and FT-IR. Gel-permeation chromatography (GPC) was employed to determine the molecular mass and molecular mass distribution of hemicellulose and graft copolymer. The thermal degradation properties of hemicellulose and the graft copolymers were measured by thermo gravimetric analysis (TGA). The graft copolymer was subsequently used as a corrugated paper surface sizing agent, which can significantly improve the physical strength and water resistance of corrugated paper

Grafted Copolymerization Modification of Hemicellulose Directly in the Alkaline Peroxide Mechanical Pulping (APMP) Effluent and Its Surface Sizing Effects on Corrugated Paper

In this work, the graft copolymerization of acrylamide (AM) and methacryloyloxy ethyl trimethyl ammonium chloride (DMC) with the hemicellulose in the alkaline peroxide mechanical pulping (APMP) effluent was investigated using the Fenton agent (FeSO₄/H₂O₂) as an initiator. The effects of the reaction conditions on the characteristics of the graft copolymers were studied. On the basis of the graft copolymer characterization, the optimum conditions were as follows: total active ingredient concentration 31%, reactive temperature 50 °C, amount of the initiator 0.4%, ratio of H₂O₂ to FeSO₄ 1:1, molar ratio of DMC to AM 1.5:20 and optimum percentages of <i>C</i>, <i>G</i>, GE, and viscosity are 65%, 246%, 98%, and 5020 cP, respectively. Structure elucidation of the graft copolymer was obtained by ¹H NMR spectroscopy and FT-IR. Gel-permeation chromatography (GPC) was employed to determine the molecular mass and molecular mass distribution of hemicellulose and graft copolymer. The thermal degradation properties of hemicellulose and the graft copolymers were measured by thermo gravimetric analysis (TGA). The graft copolymer was subsequently used as a corrugated paper surface sizing agent, which can significantly improve the physical strength and water resistance of corrugated paper

Giant Enhancement of Defect-Bound Exciton Luminescence and Suppression of Band-Edge Luminescence in Monolayer WSe₂–Ag Plasmonic Hybrid Structures

We have investigated how the photoluminescence (PL) of WSe₂ is modified when coupled to Ag plasmonic structures at low temperature. Chemical vapor deposition (CVD) grown monolayer WSe₂ flakes were transferred onto a Ag film and a Ag nanotriangle array that had a 1.5 nm Al₂O₃ capping layer. Using low-temperature (7.5 K) micro-PL mapping, we simultaneously observed enhancement of the defect-bound exciton emission and quenching of the band edge exciton emission when the WSe₂ was on a plasmonic structure. The enhancement of the defect-bound exciton emission was significant with enhancement factors of up to ∼200 for WSe₂ on the nanotriangle array when compared to WSe₂ on a 1.5 nm Al₂O₃ capped Si substrate with a 300 nm SiO₂ layer. The giant enhancement of the luminescence from the defect-bound excitons is understood in terms of the Purcell effect and increased light absorption. In contrast, the surprising result of luminescence quenching of the bright exciton state on the same plasmonic nanostructure is due to a rather unique electronic structure of WSe₂: the existence of a dark state below the bright exciton state

Decay and nutrient dynamics of coarse woody debris in the Qinling Mountains, China

<div><p>As an ecological unit, coarse woody debris (CWD) plays an essential role in productivity, nutrient cycling, carbon sequestration, community regeneration and biodiversity. However, thus far, the information on quantification the decomposition and nutrient content of CWD in forest ecosystems remains considerably limited. In this study, we conducted a long-term (1996–2013) study on decay and nutrient dynamics of CWD for evaluating accurately the ecological value of CWD on the Huoditang Experimental Forest Farm in the Qinling Mountains, China. The results demonstrated that there was a strong correlation between forest biomass and CWD mass. The single exponential decay model well fit the CWD density loss at this site, and as the CWD decomposed, the CWD density decreased significantly. Annual temperature and precipitation were all significantly correlated with the annual mass decay rate. The K contents and the C/N ratio of the CWD decreased as the CWD decayed, but the C, N, P, Ca and Mg contents increased. We observed a significant CWD decay effect on the soil C, N and Mg contents, especially the soil C content. The soil N, P, K, Ca and Mg contents exhibited large fluctuations, but the variation had no obvious regularity and changed with different decay times. The results showed that CWD was a critical component of nutrient cycling in forest ecosystems. Further research is needed to determine the effect of diameter, plant tissue components, secondary wood compounds, and decomposer organisms on the CWD decay rates in the Qinling Mountains, which will be beneficial to clarifying the role of CWD in carbon cycles of forest ecosystems.</p></div