Preparation,characterization and photocatalytic properties of nanoplate Bi<Subscript>2</Subscript>MoO<Subscript>6</Subscript> catalysts

Bismuth molybdate (Bi₂MoO₆) nanoplates have been successfully synthesized by a simple hydrothermal process. The nanoplates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and IR spectroscopy. The effects of hydrothermal temperature and reaction time on the structures and morphologies of the nanoplates were investigated. On the basis of TEM observation of time series samples, a possible formation mechanism of the nanoplates was proposed. Optical absorption experiments revealed that Bi₂MoO₆ nanoplates had absorption in visible-light region, but a blue shift appeared compared with the corresponding bulk materials. Photocatalytic experiments showed that the nanoplates exhibited good photocatalytic activities for degradation of N,N,N′,N′-tetraethylated rhodamine (RhB) under visible-light irradiation (λ > 420 nm).     

Synthesis and property study on Eu(III) complexes of modified poly(N-isopropylacrylamide)

Poly(N-isopropylacrylamide) with aromatic end groups (Ar-PNIPAM) were synthesized by atom transfer radical polymerization of N-isopropylacrylamide in isopropanol using phenyl 2-chloropropionate, (4′-phenyl)phenyl 2-chloropropionate, and (2′,6′-diphenyl)phenyl 2-chloropropionate as initiators and CuCl/tris(2-dimethylaminoethyl)amine (Me₆TREN) as a catalytic system. The resulting polymers had narrow polydispersity index of 1.10–1.14 and molecular weights of 3700–4600 g mol⁻¹. Then, novel functional complexes of Ar-PNIPAM, Europium(III) (Eu(III)), and α-Thenoyltrifluoroacetone (TTA) (Ar-PNIPAM/Eu(III)/TTA) with thermosensitive and fluorescent properties were synthesized and characterized by Fourier transform infrared spectra and fluorescence spectroscopy. Metal Eu(III) was not only bonded to oxygen and nitrogen atoms of polymer chain in PNIPAM, but also bonded to TTA. The maximum emission intensity of the complexes at 613 nm was enhanced about 22, 27, 33 times compared with that of the corresponding Eu(III). The lower critical solution temperatures (LCSTs) of Ar-PNIPAM/Eu(III)/TTA were slightly greater compared with that of PNIPAM. Eu(III) complexes had excellent fluorescence performance, the fluorescence spectrum presented characteristic emission of Eu(III) at 613 nm.     

Influence of substitution of phenyl group by naphthyl in a diphenylthiourea molecule on corrosion inhibition of cold-rolled steel in 0.5 M H2SO4

N,N′-Diphenylthiourea (DPTU) and N-naphthyl-N′-phenylthiourea (NPTU) synthesized in our laboratory, were tested as inhibitors for the corrosion of cold-rolled steel in 0.5 M H₂SO₄ by weight loss and electrochemical measurements. The studies clearly reveal that when we substitutes a phenyl group in N,N′-diphenylthiourea (DPTU) by naphthyl group to obtain N-naphthyl-N′-phenylthiourea (NPTU), the inhibition efficiency increases from 80 to 96% at 2 × 10⁻⁴ M. Polarization curves show that NPTU acts as mixed type inhibitor whereas DPTU predominates as cathodic inhibitor. Changes in impedance parameters (charge transfer resistance, R _t, and double layer capacitance, C _dl) were indicative of adsorption of DPTU and NPTU on the metal surface, leading to the formation of protective films. The degree of the surface coverage of the adsorbed inhibitors is determined by ac impedance technique, and it was found that the adsorption of these inhibitors on the cold-rolled steel surface obeys the Langmuir adsorption isotherm. The effect of the temperature on the corrosion behavior with addition of 10⁻⁴ M of DPTU and NPTU was studied in the temperature range 20–50 °C. Results show that the rate of corrosion of mild steel increased with increasing temperature both in the presence of inhibitors and in their absence. Activation energies in the presence and absence of DPTU and NPTU were obtained by measuring the temperature dependence of the corrosion current. The reactivity of these compounds was analyzed through theoretical calculations based on density functional theory to explain the different efficiency of these compounds as corrosion inhibitors.     

Synthesis and nonlinear optical properties of novel Y-type polyurethanes with high thermal stability of dipole alignment

2,3-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3′-dimethoxy-4,4′-biphenylenediisocyanate to yield novel Y-type polyurethanes 4–5 containing 2,3-dioxy benzylidenemalononitrile group as a nonlinear optical (NLO)-chromophore, which constituted parts of the polymer backbones. Polyurethanes 4–5 were soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed a thermal stability up to 270 °C in thermogravimetric analysis thermograms and the glass-transition temperatures (T _g) obtained from differential scanning calorimetry thermograms were around 116–135 °C. The second harmonic generation (SHG) coefficients (d ₃₃) of poled polymer films at 106.4 mm⁻¹ fundamental wavelength were around 9.07 × 10⁻¹⁹ C (2.72 × 10⁻⁹ esu). The dipole alignment exhibited high thermal stability up to 10 °C higher than T _g, and there was no SHG decay below 145 °C due to the partial main-chain character of the polymer structure, which was acceptable for nonlinear optical device applications.     

Preparation and optoelectronic properties of N , N ′-diphenyl- N , N ′-bis(3-methylphenyl)-(1,l′-biphenyl)-4,4′-diamine/TiO2 nanostructured hybrids

Organic–inorganic nanostructured hybrids based on N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,l′-biphenyl)-4,4′-diamine (MTPD) and anatase TiO₂ were prepared via layer-by-layer deposition method. The MTPD/TiO₂ hybrids were characterized by UV–Vis absorption spectra, photoconductivity measurements, and surface photovoltage spectra (SPS). Due to the change of the aggregated structure caused by the addition of TiO₂, MTPD showed blue-shifted absorption spectrum. The photosensitivity of MTPD/TiO₂ nanostructured hybrids was increased by two times when compared with that of its single component. Studies on the SPS revealed that the efficient light-induced charge separation and transfer between MTPD and TiO₂ was responsible for the improved photosensitivity. The MTPD/TiO₂ hybrids exhibited high photosensitivity to ultraviolet light with weak intensity and acceptable stability under ultraviolet radiation, which endow the hybrids potential applications in the field of ultraviolet photodetection.     

Thermal expansion coefficient of Y-α′-sialon

A sialon composite composed of Y-α′-sialon and β′-sialon has been fabricated by hot pressing mixtures of Si₃N₄, Y₂O₃ and AlN powders. Thermal expansion coefficients of the Y-α′-sialon and β′-sialon were determined by the high-temperature X-ray diffraction technique. The thermal expansion coefficient of Y-α′-sialon depended on the composition, being minimum at x=0.3 in the formula Y_x(Si_12-4.5x, Al_4.5x)(O_1.5x, N_16-1.5x). The coefficient of β′-sialon increased with increasing lattice constant, that is, the z value in the formula Si_6-zAl_zO_zN_8-z. The thermal expansion coefficient of sialon composites determined by a differential dilatometer increased with increasing amount of Y-α′-sialon. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis and characterization of novel,soluble sulfur-containing copolyimides with high refractive indices

High refractive index, colorless polymers with high temperature resistancy are of great industrial interest. In this study, new sulfur-containing copolyimides with high refractive indices have been synthesized via polycondensation reaction using 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA) as dianhydride monomers, and 4,4′-diaminodiphenyl sulfide (4,4′-SDA) and 2,3,5,6-tetramethyl-1,4-phenylene diamine (4MPD) as well as 3,3′-diaminodiphenyl sulfone (3,3′-DDS) as diamino monomers. The resulting copolyimides are amorphous and soluble in common organic solvents such as dimethylacetamide and N-methylpyrrolidone. They also exhibit very good optical properties such as high transparency (>88% at 589.6 nm) for samples with a thickness of 120–150 μm. Furthermore, higher refractive indices ranging from 1.64 to 1.72 at visible wavelengths compared to currently applied polymer materials, which show refractive indices between 1.5 and 1.6, are found. In addition, the copolyimides synthesized in this study show high thermal stability with glass transition temperatures between 273 and 306 °C.     

A novel narrow band gap red light-emitting cyanovinylene polymer derived from 3,4-dialkoxy thiophene for optoelectronic applications

A novel donor–acceptor type narrow band gap cyanovinylene poly{3,3′-(3,4-ditetradecyloxythiene-2,5-diyl)bis[2-(thiophen-2-yl)prop-2-enenitrile]} has been designed and synthesized through multistep reactions. All the newly synthesized compounds were characterized by using FTIR and ¹H NMR spectroscopy followed by elemental analyses. The polymer P is found to be thermally stable up to 300 °C under nitrogen atmosphere. The optical and charge-transporting properties of the polymer were investigated by UV–visible, fluorescence emission spectroscopic and cyclic voltammetric studies. The monomer (M) emits intense green-light in solution state and the polymer (P) exhibited intense red-fluorescence both in solution and solid state. The fluorescence quantum yield of the polymer is determined to be 43%. Cyclic voltammetric studies reveal that the polymer possesses good charge carrying property. The electrochemical band-gap is estimated to be 1.8 eV. The studies reveal that the new cyanovinylene polymer P is a promising material for the development of efficient optoelectronic devices.     

Liquid crystalline elastomers based on cyclic cyclosiloxane and mesogenic crosslinking units

Cholesteric liquid crystalline elastomers (LCEs) IP–VIP were graft copolymerized by a one-step hydrosilylation reaction with cyclo(pentamethylhydrogeno)siloxane, a cholesteric liquid crystalline (LC) monomer cholesteryl 3-(4-(undec-10-enoyloxy)phenyl)acrylate and crosslinking LC monomer biphenyl-4,4′-diyl bis(4-(allyloxy)benzoate). The effect of crosslinking mesogens on mesomorphic properties of the chiral LCEs was studied by swelling experiments. All the samples IP–VIP showed cholesteric mesophase when they were heated and cooled. The glass transition temperature (T _g) of elastomers increased slightly with increase of crosslinking mesogens in the polymer systems, but mesophase–isotropic phase transition temperature (T _i) decreased slightly, suggesting that the temperature range of mesophase became narrow with increase of crosslinking mesogens for all the elastomers. In XRD curves, all the samples IP–VIP exhibited diffuse reflections at 2θ ≈ 17° suggesting lack of the smectic-layered packing arrangement, and the intensity of these diffuse diffraction peaks decreases with increase of mesogenic crosslinking units, suggesting that the order between two neighbor LC molecules disturbed by the mesogenic crosslinking agents. The maximum reflection bands shift slightly to long wavelength and become broad at the same temperature, indicating that the helical structure is partially disrupted because of both the constraint of chemical crosslinking agents and the different mesogenic units.     

Uncatalyzed synthesis of polypyrrole with viologen side groups and its chemical properties

A substituted polypyrrole (PPr) with viologen side groups (polymer-1) was obtained from the reaction of N-aminopyrrole with 1-hexyl-1′-(2,4-dinitrophenyl)-4,4′-bipyridinium dihalide (salt-1). A model compound (model-1) was synthesized by the reaction of N-aminopyrrole with N-(2,4-dinitrophenyl)-4-(4-pyridyl)pyridinium chloride (salt-2). UV–vis spectra revealed that polymer-1 had an expanded π-conjugation system along the polymer chain: the polymer showed an onset position of absorption at a wavelength approximately 200 nm longer than the corresponding wavelength of model-1. Polymer-1 received an electrochemical oxidation of the pyrrole ring and reduction of the viologen group within the polymer.     

Kinetic and thermodynamic studies for cesium removal from low-level liquid radioactive waste using impregnated polymeric material

A novel polymeric impregnated material was prepared by loading 4,4′(5′)di-t-butylbenzo-18-crown-6 (DtBB18C6) onto poly(acrylamide-acrylic acid-acrylonitrile)-N,N′-methylenediacrylamide [P(AM-AA-AN)-DAM]. The sorption of ¹³⁷Cs onto P(AM-AA-AN)-DAM/DtBB18C6 was studied using batch equilibrium technique with respect to the pH, contact time, and temperature. The applicability to treatment of low-level liquid radioactive waste was examined. The free energy (ΔG ⁰), enthalpy (ΔH ⁰), and entropy (ΔS ⁰) of the sorption were calculated. These parameters showed that the sorption of ¹³⁷Cs onto P(AM-AA-AN)-DAM/DtBB18C6 was spontaneous and endothermic in nature. The Lagergren first-order, pseudo-second-order, and homogeneous particle diffusion models were tested kinetically to describe the reaction mechanism. The experimental data were fitted well by the pseudo-second-order kinetic model.     

Liquid–crystal azopolyamides with high thermal stability and inherent viscosity

In order to get novel photochromic fiber-forming polyamides with liquid crystal (LC), high inherent viscosity and thermal stability properties, two linear azobenzene polyaramides were synthesized by alternative polycondensation reactions of trans-azobenzene-4,4′-dicarbonyl chloride with various diamine monomers without any substituents under low temperature. As expected, the resulting polyamides exhibit high degree of crystallinity (the highest value reaches 52%), inherent viscosity (the highest value reaches 4.26 dL/g), and thermal stability (≤5% weight loss at 350 °C) due to intensively intermolecular hydrogen bonding and extremely symmetric and rigid molecular structures, which were identified by FT-IR spectroscopy and elemental analysis. Moreover, important liquid crystal and photoisomerization properties for optical devices and photochromics fibers spinning are also observed in N,N-dimethylacetamide (DMAc) solutions due to the regular rigid structure and intermolecular hydrogen bonding. The synthesized azo polyamides are suitable for fiber spinning and can be applied in fields of potential optical techniques and novel anti-ultraviolet and photochromic fibers industry at wide temperature ranges.     

Promoted NIR-II Fluorescence by Heteroatom-Inserted Rigid-Planar Cores for Monitoring Cell Therapy of Acute Lung Injury

Fluorophores with emission in the second near-infrared (NIR-II) window have displayed salient advantages for biomedical applications. However, exploration of new luminogens with high NIR-II fluorescent brightness is still challenging. Herein, based on the “ring-fusion” strategy, a series of heteroatom-inserted rigid-planar cores is proposed to achieve the bathochromic NIR-II fluorophores with aggregation-induced emission (AIE) performance. Interestingly, one of the representative fluorophores, 4,4′-(5,5′-([1,2,5]thiadiazolo[3,4-i]dithieno[2,3-a:3′,2′-c]phenazine-8,12-diyl)bis(4-octylthiophene-5,2-diyl))bis(N,N-diphenylaniline) (TTQiT), enjoys a maximum emission beyond 1100 nm because of the efficiently narrowed energy bandgap by electron-rich sulfur-atom-inserted core, which is verified by theoretical calculation. Taking advantage of the bright NIR-II emission of TTQiT nanoparticles, the desirable in vivo NIR-II imaging with high signal-to-background ratios is successfully performed and a long-term stem cell tracking in the detection of acute lung injury is further realized. Therefore, it is anticipated that this work will provide a promising molecular engineering strategy to enrich the scope of NIR-II fluorophores for catering to diverse demands in biomedical applications.     

Synthesis, thermal, photoluminescent, and electroluminescent properties of a novel quaternary Eu(III) complex containing a carbazole hole-transporting functional group

A novel quaternary Eu(III) complex containing a carbazole fragment as hole-transporting functional group was synthesized, and its thermal stability, photoluminescent (PL), electroluminescent (EL) properties were studied. Its glass transition temperature (T _g) was 131 °C and 5% weight loss temperature was 325 °C. In studies of its EL properties, two devices with the Eu(III) complex as red light-emitting materials were fabricated and measured. Device 1: ITO/NPB (40 nm)/Eu(III) complex (30 nm)/Alq₃ (30 nm)/LiF (0.7 nm)/Al (100 nm), NPB was N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine as the hole-transporting layer, Alq₃ was tris(8-hydroxyquinoline) aluminum as the electron-transporting layer. Device 1 gave two emission bands of the Eu(III) complex and Alq₃ with the maximum luminance of 437 cd/m² at 17.34 V, and its turn-on voltage was 10 V. In device 2, an electron-transporting/hole-locking layer of BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, 30 nm) was added between the Eu(III) complex and Alq₃ layers, only a sharp red emission band of the Eu(III) complex was given with the maximum luminance of 186 cd/m² at 20.08 V, and its turn-on voltage was 12 V.     

Reaction sintering and the α-Si3N4/β′-sialon transformation for compositions in the system Si-Al-O-N

The reaction sintering of three powder compositions corresponding to points near theβ′-phase line in the region of z=0.75 has been studied using apparatus which allowed the continuous monitoring of the densification kinetics. The powder compositions were prepared from mixtures ofα-Si₃N₄, Al₂O₃ and AIN, and the weight changes in the compacts could be kept to less than ∼ 1% over a two hour period. The densification rate is sensitive to small changes in powder composition and decreases markedly as theβ∼'-sialon phase is approached from the oxygen-side. Theα-Si₃N₄ toβ′-sialon conversion rate, on the other hand, is almost independent of the powder composition. The sintering and transformation kinetic data, combined with surface area measurements and observations on the microstructure of the sintered compacts, indicate that the sintering behaviour is controlled by at least two processes, namely the vapour phase transport of material and a solution-diffusion-reprecipitation process involving a grain boundary liquid phase. Both processes result in the conversion ofα-Si₃N₄ toβ′-sialon and result in microstructural coarsening but only the second process leads to overall densification in the powder compact.     

Study on the moisture absorption of pyridine containing polyurethane for moisture-responsive shape memory effects

Supramolecular polymers are attractive in recent years. In this article, a series of pyridine containing polyurethanes (PUPys) with various pyridine contents and various MDI-BDO contents were synthesized from 1,6-hexamethylene diisocyanate (HDI), 1,4-butanediol (BDO), N,N-bis(2-hydroxylethyl) isonicotinamine (BINA) and diphenylmethane diisocyanate (MDI). Thereafter, the moisture absorption of PUPys was mainly investigated systematically from the effect of temperature, relative humidity (RH), pyridine content, MDI-BDO content, the mechanism, and the kinetic of moisture absorption. Results show that the moisture absorption process of PUPys matches with Fick’s second law in the initial stage. The moisture absorption is dependent on the content of N,N-bis(2-hydroxylethyl) isonicotinamine (BINA), e.g., the moisture absorption decreases with the increase of MDI-BDO content as well as the decrease of BINA content. In addition, the moisture absorption increases with the increase of temperature and relative humidity (RH). Accordingly, the moisture absorption process of PUPy45 at RH = 65% and T = 25° can be expressed with the equation: lnM _t  = 8.88–2975(1/T) + 0.5lnt. On the basis of the moisture absorption, the shape recovery process of PUPys film under the moisture condition support that PUPys show excellent moisture-responsive shape memory effects.     

Frequency-dependent dielectric and electric modulus properties of Li–Ni–Sm–Fe–O spinel embedded in conducting polymer

Conducting polymeric nanocomposite containing Li–Ni–Sm–Fe–O spinel was synthesized by the chemical oxidizing of aniline in the presence of LiNi_0.5Sm_0.08Fe_1.92O₄ particles. The dielectric and electric modulus properties of the as-prepared samples were investigated over a frequency range from 10⁶ to 10⁹ Hz. The dielectric constant (ε′), dielectric loss (ε″) and dissipation factor (tan δ) for all samples presented relatively high values at low frequency and were found to decrease with the frequency. The values of ε′, ε″ and tan δ of the nanocomposite were lower than that of the pristine PANI. Electric modulus analysis had been carried out to understand the electrical relaxation process. The dielectric relaxation time for the nanocomposite became longer due to the introduction of LiNi_0.5Sm_0.08Fe_1.92O₄ particles lowering the crystallinity of PANI.     

Effect of the chemical structure of aromatic polyimides on their thermal aging,relaxation behavior and mechanical properties

This article examines the effects of structural changes and thermal aging treatments on the relaxation processes and mechanical properties of three polyimides differing for their molecular structure i.e. PMDA-ODA, 6FDA-ODA, and 6FDA-6FpDA. These polyimides were obtained by thermal imidization of their polyamic acid precursors, which were synthesized from the respective dianhydrides [pyromellitic anhydride (PMDA), hexahydrofluoroisopropylidene diphthalic anhydride (6FDA)], and diamines [4,4′-diaminodiphenyl ether (ODA), 4,4′-(hexafluoroisopropylidene) dianiline (6FpDA)]. After the curing process, the polyimides were thermally aged at a fixed temperature for various times Dynamic mechanical measurements performed in a multi-frequency mode, were used to determine the glass-rubber and sub-glass transitions, as well as the activation energy of the β transition. It was found that the T _g decreased in the order PMDA-ODA > 6FDA-6FpDA > 6FDA-ODA as a result of an increased chain rigidity and molecular packing induced by charge transfer interactions during the thermal imidization process. The β sub-glass transition showed two relaxation processes identified as β′ and β′′. The β′ process was attributed to the local motion of the diamine constituents while the β′′ process was caused by the local motion of the dianhydride moiety. The cooperativity of these molecular motions was also assessed via the Starkweather method. The thermal aging enhanced the state of aggregation of polyimide chains and thus the T _g and the sub-glass transition properties. This effect was particularly marked for the PMDA-ODA polyimide. Also the mechanical properties were significantly affected by chemical structure and aging treatments. For non-aged samples the more influenced parameter was the elongation at break, which decreased in the order PMDA-ODA > 6FDA-ODA > 6FDA-6FpDA. The aging enhanced the elastic modulus and the tensile strength and reduced the elongation at break.     

Fluorinated polyimide–silica films with low permittivity and low dielectric loss

A sol–gel process was used to prepare polyimide–silica hybrid films from the fluorinated polyimide precursors (6FDA-ODA) and tetraethylorthosilicate (TEOS) in N,N-dimethyl acetamide. The hybrid film was then treated with hydrofluoric acid to remove the dispersed silica particles, leaving inside the film pores with diameters ranged from 80 nm to 1 μm, which depended on the size of the silica particles. The chemical structures and morphology of the hybrid and porous films were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The synthesized porous fluorinated polyimide films show low relative dielectric permittivity of 1.9, rendering them promising for microelectronic packaging materials.     

Crystallization of Mg-containing phases in β′-Si-Al-O-N ceramics

The microstructures ofβ′-Si-Al-O-N ceramics of base composition Si₄Al₂O₂N₆ with large MgO additive (6 to 7 wt %) have been compared in the hot-pressed and sintered conditions. In both ceramics Mg shows only a small solubility inβ′ crystals and is mainly segregated in a “matrix” phase. In hot-pressed materials this is an Mg-Al-silicate glass whereas in sintered materials, inhomogeneities in composition and internal cavities are believed to catalyse its crystallization as the spinel phase (MgAl₂O₄ with partial Si substitution). A minor phase in sintered ceramics is the 15R “polytype” of the AlN structure.