Synthesis and Characterization of a New Copolymer Consisting of Polyamide 1210 and Reactive Phosphorus-Nitrogen Flame-Retardant.

The thermal stability and reactivity of organophosphorus flame-retardants play a critical role in synthesizing copolymerized flame-retardant polyamides. Herein, this work successfully synthesizes a flame-retardant CEPPA-DDA salt (CDS) with both good thermal stability and high reactivity by reacting 2-carboxyethyl phenyl phosphonic acid (CEPPA) with 1,12-dodecanediamine (DDA). Flame-retardant polyamide 1210 (FRPA) is further prepared by copolymerizing the CDS, DDA, and sebacic acid (SEA). The test results show that the introduction of CDS can significantly improve the flame-retardant properties of FRPA. Specifically, the flame-retardant polyamide 1210 (FRPA-7) with 7 wt% CDS addition can reach V-0 grade according to UL-94 standard, accompanying limiting oxygen index value of 30.2% and tensile strength of 38.62 MPa. Compared with pure polyamide 1210, the peak heat release rate and total heat release rate of FRPA-7 reduce by 24.11% and 9.40%, respectively. This study provides a simple strategy to prepare flame-retardant polyamides with high flame retardancy and good mechanical properties, which are expected to show great potentials in future industrial applications.

Mechanism Study of the Polymerization of Polyamide 56: Reaction Kinetics and Process Parameters.

Polyamide 56 (PA56) has gained significant attention in the academic field due to its remarkable mechanical and thermal properties as a highly efficient and versatile biobased material. Its superior moisture absorption property also makes it a unique advantage in the realm of fiber textiles. However, despite extensive investigations on PA56's molecular and aggregate state structure, as well as processing modifications, little attention has been paid to its polymerization mechanism. Herein, the influence of temperature and time on PA56's polycondensation reaction is detailed studied by end-group titration and carbon nuclear magnetic resonance (NMR) techniques. The reaction kinetics equations for the pre-polymerization and vacuum melt-polymerization stages of PA56 are established, and possible side reactions during the polycondensation process are analyzed. By optimizing the reaction process based on kinetic characteristics, PA56 resin with superior comprehensive properties (melting temperature of 252.6 °C, degradation temperature of 371.6 °C, and tensile strength of 75 MPa) is obtained. The findings provide theoretical support for the industrial production of high-quality biobased PA56.

A One-Pot Polymerization for Concurrently Inducing Predominant Helicity in Optically Inactive Helical Polymer and Constructing Graphene-Based Chiral Hybrid Foams.

Synthetic chiral helical polymers have achieved impressive progress in past few decades. Unfortunately, how to construct chiral helical polymer-derived functional materials still remains highly challenging. The present contribution reports an unprecedented, one-step strategy for judiciously combining chiral helical polymer with graphene to construct chiral hybrid foams. Graphene oxide (GO), ascorbic acid (L-AA), Rh catalyst, and an achiral acetylenic monomer bearing phenylboronic acid group are mixed in an aqueous dispersion. Under mild conditions, the monomer underwent polymerization; meanwhile GO transforms into reduced graphene oxide (RGO) which in situ self-assembles to construct a 3D porous structure. Herein, L-AA simultaneously plays double roles: 1) working as a chiral source for the monomer to undergo helix-sense-selective polymerization or transferring its chirality to the polymer chains via forming borate structure; and 2) working as a reducing agent for reducing GO. The preparation strategy combines four processes into one single step: monomer polymerization, chirality transfer, reduction of GO, and RGO's self-assembly. The eventually obtained chiral hybrid foams demonstrate advantages of porous structure, chirality, and reversible borate functional groups. The established preparation strategy promises a potent platform for conveniently constructing advanced chiral polymeric materials and even chiral hybrids starting from achiral monomers.

Immobilization of horseradish peroxidase on electrospun magnetic nanofibers for phenol removal.

In this study, Fe3O4/polyacrylonitrile (PAN) magnetic nanofibers (MNFs) were fabricated by electrospinning method to immobilize the horseradish peroxidase (HRP), making which a complex platform for phenol removal application. Results indicated that, the average diameter of MNFs was about 200-400 nm and the maximum saturation magnetic induction was 19.03 emu/g. Compared with the free HRP, the modified HRP showed no change in optimum pH, but showed higher catalytic activity. Moreover, HRP immobilized MNFs (H-MNFs) with 40% Fe3O4 nanoparticles loading had the lowest HRP loading, but had the highest relative activity, because of the magnetic synergy with the presence of MNPs. Subsequently, the 40% H-MNFs was used for the remediation of phenol wastewater, achieved the removal efficiency of phenol to 85% in the first round use, and remained 52% of efficiency after 5 recycles using. It was expected that the H-MNFs could be a potential application in wastewater treatment such as phenol removal.

Self-assembly of various silver nanocrystals on PmPD/PAN nanofibers as a high-performance 3D SERS substrate.

We report a facile method to synthesise flexible 3D surface-enhanced Raman scattering (SERS) substrates, using poly-m-phenylenediamine/polyacrylonitrile (PmPD/PAN) nanofiber mats as templates to self-assemble citrate-stabilized Ag nanocrystals (AgNCs), such as Ag nanoparticles (AgNPs), Ag nanotriangles (AgNTs) or Ag nanodisks (AgNDs). The SERS performances of AgNC@2D and AgNC@3D substrates were compared using 4-MBA as the probe molecule. The effect of the extinction wavelength as well as the density and morphology of the AgNCs on the SERS enhancement effect was explored. The results suggest that the 3D AgNT@PmPD/PAN nanofiber mat exhibits the highest SERS sensitivity and the lowest relative standard deviation (RSD) value. The detection limit of 4-MBA is as low as 10(-8) M, making the nanofiber mat a promising candidate for the SERS detection of chemical molecules. In addition, this study provides a simple route for the fabrication of SERS substrates with different types of noble metals and materials with strong SERS enhancement performance.

Zinc Ion-crosslinked polycarbonate/heparin composite coatings for biodegradable Zn-alloy stent applications.

Zinc and its alloys are the best candidates for biodegradable cardiovascular stents due to their good corrosion rate and biocompatibility in vasculature. However, the cytotoxicity caused by the rapid release of zinc ions during the initial degradation stage and the lack of an anticoagulant function are huge challenges for their practical clinical applications. In this work, we developed a zinc ion-crosslinked polycarbonate/heparin composite coating via electrophoretic deposition (EPD) to improve the biocompatibility and provide anticoagulant functions for Zn-alloy stents. Both electrochemical tests and in vitro immersion tests demonstrated an enhanced corrosion resistance and lower Zn ion release rate of the coated Zn alloys. Enhanced adhesion and proliferation of endothelial cells on coated Zn alloys were also observed, indicating faster reendothelialization than that on bare Zn alloys. Moreover, the surface erosion of the composite coating led to the uniform and long-term release of heparin, which remarkably inhibited the adhesion and activation of platelets, and may have endowed the coated Zn-alloy stents with long-term anticoagulant functions.

Facile fabrication of biodegradable endothelium-mimicking coatings on bioabsorbable zinc-alloy stents by one-step electrophoretic deposition.

The zinc-alloy stent is one of the best potential candidates for bioabsorbable metal stents because of its appropriate corrosion rate aligned to the duration of the healing process of the surrounding vessel tissues. However, excessive release of zinc ions, causing cytotoxicity of endothelial cells, and insufficient surface bio-functions of Zn-alloy stents lead to considerable challenge in their application. Herein, one-step electrophoretic deposition was employed to apply a hybrid coating of polycarbonate, tannic acid, and copper ions with tailored functions on Zn-alloy stents to enhance their corrosion resistance and provide an endothelium-mimicking surface. Specifically, the synthesized amino-functionalized aliphatic polycarbonates endowed the hybrid coating with specific surface-erosion properties, resulting in superior corrosion resistance and long-term stability in degradation tests both in vitro and in vivo. The immobilized copper ions enabled the catalytic generation of nitric oxide and promoted the adhesion and proliferation of endothelial cells on zinc alloy. The added tannic acid firmly chelated the copper ions and formed durable phenolic-copper-amine crosslinked networks by electrostatic interaction, resulting in long-term stability of the hybrid coating during the 21 day dynamic immersion test. Tannic acid exerted a synergistic antibacterial effect with copper ions as well as a reduction in the inflammatory response to the zinc substrate. In addition, the hybrid coating improved the in vitro hemocompatibility of zinc alloys. By adjusting the amount of chelated copper in the coating system, the biological function of the corresponding coatings can be controlled, providing a facile surface treatment strategy to promote the progress of zinc-alloy stents in clinical applications.

Theoretical investigation on the low-energy isomer identification, structural evolution, stability, and electronic properties of Al10-xBex (x = 1-9) nanoalloys.

Numerous isomeric equilibrium structures have been identified for the Al10-xBex (x = 1-9) nanoalloy clusters by using the stochastic search procedure in combination with density functional theory calculations. The relative stability and various electronic properties of the lowest-energy Al10-xBex (x = 0-10) clusters have been systematically studied by using the B3LYP and CCSD(T) methods with the aug-cc-pVDZ basis set. The evolution of the binding energies, the second difference in energy, HOMO-LUMO gaps, vertical detachment energies, vertical ionization potentials, vertical electron affinities, and hardness with the increasing number of Be atoms in the most stable Al10-xBex (x = 0-10) clusters demonstrates that the global minimum of Al8Be2 cluster possesses a special stability. Thus, the electronic structure of the lowest-energy Al8Be2 cluster has been also detected in detail. In addition, it is found that the polarizabilities gradually decrease with increasing number of Be atoms, and the charges always transfer from Al to Be atoms in these nanoalloy clusters. We hope this work could provide helpful insight into the composition-dependent electronic properties of BeAl alloy at the nanoscale, serving as powerful guidelines for future experimental research.

Polyacrylonitrile/polypyrrole core/shell nanofiber mat for the removal of hexavalent chromium from aqueous solution.

Polyacrylonitrile/polypyrrole (PAN/PPy) core-shell structure nanofibers were prepared via electrospinning followed by in situ polymerization of pyrrole monomer for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. Attenuated total reflections Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) results confirmed the presence of the polypyrrole (PPy) layer on the surface of PAN nanofibers. The morphology and structure of the core-shell PAN/PPy nanofibers were studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), and the core-shell structure can be clearly proved from the SEM and TEM images. Adsorption results indicated that the adsorption capacity increased with the initial solution pH decreased. The adsorption equilibrium reached within 30 and 90 min as the initial solution concentration increased from 100 to 200mg/L, and the process can be described using the pseudo-second-order model. Isotherm data fitted well to the Langmuir isotherm model. Thermodynamic study revealed that the adsorption process is endothermic and spontaneous in nature. Desorption results showed that the adsorption capacity can remain up to 80% after 5 times usage. The adsorption mechanism was also studied by XPS.

In situ controlled growth of well-dispersed gold nanoparticles in TiO2 nanotube arrays as recyclable substrates for surface-enhanced Raman scattering.

In this paper, well-aligned Au-decorated TiO(2) nanotube arrays with high surface-enhanced Raman scattering (SERS) enhancement were prepared using a facile in situ reduction and controlled growth approach. The gold nanoparticles are well-dispersed and assembled on the mouth surface and the inside of the TiO(2) nanotubes without clogging. The structure and optical properties of the Au-decorated TiO(2) nanotube arrays have been characterized. The Au-decorated TiO(2) nanotube arrays were employed as SERS-active substrates, which exhibit good performance due to long-range coupling between Au nanoparticles, and TiO(2)-assisted enhanced charge-transfer from Au to Rh6G. The SERS activity of the substrates strongly depends on the crystallite size and level of aggregation. The substrates display significant fluorescence quenching ability and uniform SERS responses throughout the whole surface area. Particularly, good recyclability is shown. The photocatalytic property of Au-decorated TiO(2) nanotube array was exploited to recycle the substrate through UV light photocatalytic purification. The experimental results showed that the substrate is featured by high reproducibility and can be used as a highly efficient SERS substrate for multiple detection of different chemical and biological molecules.