Zushun Xu

In situ photoluminescence investigation of doped Alq

We report the photoluminescence (PL) properties measured in situ from vacuum-deposited organic films of tris-(8-hydroxyquinoline) aluminum (Alq) doped with 4-(dicyanomethylene)-2-methyl-6(p-dimethylaminostyryl)-4H-pyran (DCM), where the red emission from the guest molecules is due to Forster energy transfer of excited state energy from host to guest. Both bare DCM-doped Alq (Alq:DCM) and bilayer Alq/Alq:DCM films have been studied, with the thickness of the Alq overlayer continuously varied in the latter case. The PL spectra from the bilayer structure contain no Alq contribution when its thickness is below 2.4 nm. Taking the value as the maximum distance for which the Alq exciton can travel in the film and still transfer its energy to a DCM molecule, the minimum DCM concentration in Alq:DCM necessary to produce red emission only can be estimated at 0.31 wt %. The most efficient red emission appears at the DCM concentration of about 1.7 wt %, at which more than 90% Alq-originated excitons are involved in t...

In situ solution polymerization for preparation of MDI-modified graphene/hyperbranched poly(ether imide) nanocomposites and their properties

Firstly, fully exfoliated graphene oxide (GO) colloidal dispersion in N-methyl-2-pyrrolidone (NMP) with high concentration is obtained by a solvent-exchange method and further used to prepare superior GO-MDI with free isocyanato groups by chemical modification. Then, the yielded GO-MDI is employed to prepare two kinds of MDI-modified graphene/hyperbranched poly(ether imide) (GE-MDI/HBPEI) nanocomposites via in situ random solution co-polycondensation or crosslinking reaction, followed by synchronous thermal imidization and reduction. The chemical modification of GO endows GO-MDI with good solubility in organic solvents to prepare GE-MDI/HBPEI nanocomposites with high filler content. GO-MDI is further used as a multi-functional co-monomer or crosslinker to be introduced into the HBPEI backbone with full compatibility of the guest and host at the molecular level. Finally, the performance tests show that the heat resistance, thermal stability, mechanical strength and modulus, and gas barrier properties of the obtained two kinds of nanocomposites are significantly improved or enhanced compared with pure HBPEI, and the impacts become more and more significant with the increase of GO-MDI content, but their mechanical toughness show trends of increase at first then decrease with the increase of GO-MDI content. Comparisons also show that at the same GO-MDI content, the heat resistance, thermal stability, mechanical strength and modulus of the nanocomposites obtained by in situ random solution co-polycondensation are all superior to those obtained by in situ random solution crosslinking reaction, except the mechanical toughness and gas barrier properties of the former are less than the latter. This effective approach provides a possibility for enriching and developing high performance PEI-based composites with various forms of GE for advanced engineering or functional materials.

Microwave assisted preparation of monodisperse polymeric microspheres and its morphologies and kinetics

The emulsifier-free emulsion polymerization of N-hydroxymethyl acrylamide (NMA), methyl methacrylate (MMA) and styrene (St) was successfully carried out under microwave irradiation, and monodisperse polymeric microspheres were prepared. The experimental results show that the emulsifier-free emulsion polymerization under microwave irradiation has more rapid reaction rate, higher conversion and shorter induction time than the copolymerization with conventional heating. The apparent activation energies are 61.04 and 83.75 kJ/mol, respectively; the microspheres have spherical morphology, and the microspheres prepared by emulsifier-free emulsion polymerization under microwave irradiation are smaller, more uniform than those obtained with conventional heating.

Preparation, characterization, and DNA interaction studies of cationic europium luminescent copolymer

This paper proposed a simple synthetic strategy towards a novel cationic europium luminescent copolymer, poly(METAC-co-NIPAm-co-Eu(AA)3Phen) (PMNEu), and investigation about their complexation ability with DNA. In this approach, first, Eu(AA)3Phen complex monomer containing Eu3+, acrylic acid (AA), and 1,10-phenanthroline (Phen) was synthesized, and subsequently, free radical copolymerization of Eu(AA)3Phen complex monomer with other two functional monomers, [2-(methacryloyloxy) ethyl] trimethylammonium chloride (METAC) and N-isopropylarylamide (NIPAm), was carried out in methanol using azodiisobutyronitrile (AIBN) as the initiator. 1HNMR, GPC, fluorescence spectroscopy, UV–vis spectroscopy, and TEM were used to investigate the chemical structures, molecular weight and molecular weight distribution, fluorescence properties, UV spectra, and morphologies of PMNEu copolymer, respectively. Furthermore, the interaction of PMNEu with DNA was also studied with fluorescence spectroscopy, UV–vis spectroscopy, and agarose gel electrophoresis. These results indicated that PMNEu could interact with DNA via an electrostatic bonding mode and the bonding constant was 2.2 × 105 L/mol. Additionally, TEM observation showed that pure PMNEu formed micelles in water solution, while the size-controllable aggregations of PMNEu with DNA were obtained when PMNEu was mixed with DNA at various concentration ratios. A good biocompability of PMNEu was demonstrated through in vitro cytotoxicity assays.

A multifunctional composite Fe3O4/MOF/L-cysteine for removal, magnetic solid phase extraction and fluorescence sensing of Cd(II)

Fe3O4/MOF (metal organic framework)/L-cysteine was synthesized and applied for the removal of Cd(II) from wastewater. The adsorption kinetics and isotherms were investigated, and the results indicated that the adsorption obeyed the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity was calculated to be 248.24 mg g−1. Fe3O4/MOF/L-cysteine was further applied to determine trace amounts of Cd(II) in real water samples using ICP-AES (inductively coupled plasma-atomic emission spectroscopy) based on magnetic solid-phase extraction (MSPE). The determination limit was 10.6 ng mL−1. Additionally, Fe3O4/MOF/L-cysteine can also be used as a fluorescent sensor for “turn-off” detection of Cd(II), and the detection limit was 0.94 ng mL−1.