While metal is the most common conductive constituent element in the preparation of metamaterials, one-dimensional conductive carbon nanotubes (CNTs) provide alternative building blocks. Here alumina (Al2O3) nanocomposites with multi-walled carbon nanotubes (MWCNTs) uniformly dispersed in the alumina matrix were prepared by hot-pressing sintering. As the MWCNT content increased, the formed conductive MWCNT networks led to the occurrence of the percolation phenomenon and a change of the conductive mechanism. Two different types of negative permittivity (i.e., resonance-induced and plasma-like) were observed in the composites. The resonance-induced negative permittivity behavior in the composite with a low nanotube content was ascribed to the induced electric dipole generated from the isolated MWCNTs. The frequency dispersions of such negative permittivity can be fitted well by the Lorentz model, while the observed plasma-like negative permittivity behavior in the composites with MWCNT content exceeding the percolation threshold could be well explained by the low frequency plasmonic state generated from conductive nanotube networks using the Drude model. This work is favorable to revealing the generation mechanism of negative permittivity behavior and will greatly facilitate the practical applications of metamaterials.

Herein, we report the characterization of highly fluorescent citric-acid derived carbon dots (CACDs) synthesized by hydrothermal treatment of citric acid and diethylenetriamine below 200 °C. After being purified using a gel permeation chromatography cleanup system, the complexity and chemical composition of the CACDs were evaluated by liquid chromatography coupled with high-resolution Fourier transform ion cyclotron resonance mass spectrometry. The fluorophores consisted of five-membered ring fused 2-pyridones identified as the photoluminescence origin. M06-2X density functional calculations, surface tension and morphological studies suggested DETA@5CA serves as the main building block to fabricate supramolecular aggregates. Then we proposed that the dimeric and trimeric fluorophores coupled with DETA@5CA led to “dot” topologies in the CACDs solution under the effect of hydrogen bonding. In aqueous solution, the CACDs exhibited narrowly dispersed optical properties and a high fluorescent quantum yield (∼98%). Moreover, the supramolecular interaction induced CACDs have high sensitivity under various ambient conditions, such as pH, organic solvents and metal ions.

•The Knoevenagel condensations catalyzed by the novel Nmm-based ionic liquids show higher tolerance for diverse substrates.•The purification is easy and applicable for the large-scale synthesis.•The catalyst is recyclable.A series of novel N-methyl morpholine (Nmm) based ionic liquids with 1,2-propanediol group were synthesized and used as catalysts for Knoevenagel condensation at room temperature in water. Under the effect of the catalyst, various aldehydes or aliphatic ketones could react with a wide range of activated methylene compounds well, including malononitrile, alkyl cyanoacetate, cyanoacetamide, β-diketone, barbituric acid, 2-arylacetonitrile and thiazolidinedione. Furthermore, most of the products could be separated just by filtrating and washing with water. Additionally, the catalyst is recyclable and applicable for the large-scale synthesis.Download high-res image (144KB)Download full-size image

A domino reaction of phthalhydrazide and vinylketone in the presence of phosphotungstic acid was successfully established, and 3D turbine-type tetrasubstituted 1H-indazolo[1,2-b]phthalazinedione derivatives were conveniently obtained with moderate to excellent yields (up to 95%). The highly efficient catalytic system exhibited broad substrate scopes under mild conditions. A 78% yield of the desired product was obtained when the reaction was conducted on a multi-gram scale.

A simple and practical thio-Michael addition of α,β-unsaturated amides catalyzed by Nmm-based ionic liquids with a 1,2-propanediol group has been developed. All the α,β-unsaturated amides without substituents at the carbon end could smoothly react with sulfur-nucleophiles in water. Meanwhile for thio-Michael addition of α,β-unsaturated amides with substituents at the carbon end, the relevant product could also be obtained successfully under solvent-free conditions at 55 °C. Furthermore, the IL-catalyst is recyclable and applicable for gram-scale synthesis.

Epoxy nanocomposites reinforced with polypyrrole functionalized nano-magnetite (Fe3O4–PPy) showed significantly enhanced electromagnetic wave absorption performance and flame retardancy. The Fe3O4–PPy nanocomposites were prepared by the surface initiated polymerization method. The epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites possess a minimum reflection loss (RL) value of −35.7 dB, which is much lower than that of either epoxy/(7.5 wt%)PPy nanocomposites with a minimum RL value of −11.0 dB or epoxy/(30.0 wt%)Fe3O4 with a minimum RL value of −17.8 dB at the same thickness (1.7 mm). Meanwhile, the bandwidth of epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites for RL < −10 dB and RL < −20 dB is 4.0 GHz and 0.8 GHz, respectively. The increased interface area, eddy current loss and anisotropic energy are essentially important to achieve higher reflection loss and broader absorption bandwidth for epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites. Moreover, the significantly reduced flammability was observed in the epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites compared with pure epoxy. The total heat release of epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites decreased from 25.5 kJ g−1 of pure epoxy to just 12.3 kJ g−1. The tensile strength of the epoxy nanocomposites was reported as well. These new nanocomposites with an enhanced electromagnetic wave absorption property and flame retardancy possess great potential for safer electromagnetic wave absorbers in the electronic industry to satisfy stringent industrial standards.

Degradable bioelastomers represent a useful class of biomaterials. In this paper, a novel biodegradable network of elastomeric polyesters, poly((1,2-propanediol-sebacate)-citrate) (PPSC), was synthesized by condensation of 1,2-propanediol, sebacic acid and citric acid without any catalyst. An oligomeric diol of 1,2-propanediol-sebacate was first synthesized by carrying out a controlled condensation reaction between 1,2-propanediol and sebacic acid, and then a pre-polymer was synthesized by condensation of the diol and citric acid, whereat the pre-polymer was post-polymerized and simultaneously crosslinked in mold at 120 °C. A series of PPSC polymers were prepared at different post-polymerization times and different monomers' ratio. Tg confirms that PPSC is totally amorphous at 37 °C. The mechanical properties of PPSC testified that the new polymers are typical elastomers with low hardness and large elongation. The different post-polymerization times and monomers' ratio had strong influence on the degradation rates and mechanical performances. The material was expected to be useful for drug controlled delivery, tissue engineering scaffold and other biomedical applications.

Epoxy nanocomposites reinforced with polypyrrole functionalized nano-magnetite (Fe3O4–PPy) showed significantly enhanced electromagnetic wave absorption performance and flame retardancy. The Fe3O4–PPy nanocomposites were prepared by the surface initiated polymerization method. The epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites possess a minimum reflection loss (RL) value of −35.7 dB, which is much lower than that of either epoxy/(7.5 wt%)PPy nanocomposites with a minimum RL value of −11.0 dB or epoxy/(30.0 wt%)Fe3O4 with a minimum RL value of −17.8 dB at the same thickness (1.7 mm). Meanwhile, the bandwidth of epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites for RL < −10 dB and RL < −20 dB is 4.0 GHz and 0.8 GHz, respectively. The increased interface area, eddy current loss and anisotropic energy are essentially important to achieve higher reflection loss and broader absorption bandwidth for epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites. Moreover, the significantly reduced flammability was observed in the epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites compared with pure epoxy. The total heat release of epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites decreased from 25.5 kJ g−1 of pure epoxy to just 12.3 kJ g−1. The tensile strength of the epoxy nanocomposites was reported as well. These new nanocomposites with an enhanced electromagnetic wave absorption property and flame retardancy possess great potential for safer electromagnetic wave absorbers in the electronic industry to satisfy stringent industrial standards.