A new functionalized ultrahigh molecular weight polyethylene-based chelating fiber (UHMWPE-AM) for trace uranium extraction from wastewater was synthesized by preirradiation grafting modification. Adsorption behavior of adsorbent was examined under varying conditions like solution pH, contact time, initial ion concentration and adsorbent dose. The results showed the maximum removal of U(VI) was 99.7% at pH 4. Adsorption isotherm was in agreement with Langmuir isotherm equation with the maximum monolayer adsorption capacity of 16.56 mg/g, and the pseudo-second-order model can well describe the kinetics process. The dominant coordination mechanism of U(VI) on the UHMWPE-AM fibers was ascribed to inner-sphere surface complexation.

Ultra-high molecular weight polyethylene (UHMWPE) fibrous adsorbents with different molar content of amidoxime (MAO) and acrylic acid (MAA) were prepared by graft polymerization of acrylonitrile (AN) and acrylic acid (AA), followed by amidoximation. Uranium adsorption experiments in both artificial and natural seawater were carried out to investigate the effect of MAO and MAA on the uranium adsorption capacity of UHMWPE fibrous adsorbents. Adsorption results showed that the UHMWPE fibrous adsorbent with MAO = 4.27 and MAA = 4.64 mmol/g-ads exhibited better uranium adsorption capacity in both artificial (7.01 mg-U/g-ads) and natural (0.77 mg-U/g-ads) seawater.

Uranium recovery from seawater was investigated in simulated seawater in the laboratory and in natural seawater from the coasts of China with different amidoxime-based (AO) ultrahigh molecular weight polyethylene (UHMWPE) fibers. The capacities of adsorbents AO-UHMWPE-1 and -2 were 4.54 and 2.41 mg U/g-adsorbent, respectively, after 24 h of adsorption in the simulated seawater with 330 ppb U. Their capacities were 2.93 and 1.95 mg U/g-adsorbent, respectively, after 42 days of adsorption in simulated seawater flow-through experiments with 3.3 ppb U. However, because of sediment and marine organism contamination, the capacities were 0.25 and 0.04 mg U/g-adsorbent, respectively, after 68 days of adsorption in natural seawater in Xiamen. The capacity of AO-UHMWPE-7 was 1.41 mg U/g-adsorbent after 15 days of adsorption in natural seawater in Daishan. The average capacity of AO-UHMWPE-7 was 1.50 mg U/g-adsorbent, which was 18 times greater than that for V after 15 days of adsorption in natural seawater in Daishan. Results indicated that there were many factors affecting the adsorption capacity of uranium. In addition to the character of the adsorbent, including degree of grafting, functional group density, and AO conversion ratio, the marine hydrological conditions, such as temperature, flow velocity, turbidity, etc., are also crucially important for uranium extraction from seawater.

ABSTRACTRadiation crosslinked ultrahigh molecular weight polyethylene (X-UHMWPE) powder was prepared by γ-ray irradiation under nitrogen atmosphere with a dose of 50–200 kGy at a dose rate of 7 kGy/h and further annealing in vacuum at 120 °C for 4 h. The crosslinked powder was characterized by FT-IR spectroscopy, gel content, and hot-press molding. Then, X-UHMWPE was added to pristine UHMWPE to prepare a composite with 0–25 wt % filler. The morphology, wear resistance, and tensile property of the composite were investigated. Using X-UHMWPE as a filler could sufficiently improve the wear resistance of the composite. Adding 25 wt % X-UHMWPE (dose: 150 kGy) improved wear resistance by 130% and retained approximately 90% tensile strength and 70% ductility. Wear-resistant and ductile UHMWPE composite may be potentially used for artificial joint replacement and engineering devices. The proposed route is useful in fabricating UHMWPE material with excellent comprehensive performance or functional polymer composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44643.

•A high efficient fibers for Cr(VI) removal was prepared via radiation technique.•Adsorption of Cr(VI) onto this fibrous adsorbent was followed pseudo-second-order.•Maximum adsorbent capacity of Cr(VI) was found to be 295 mg/g.•Cr(VI) was partially reduced to Cr(III) by the nitrogen species of adsorbent.A novel fibrous adsorbent containing amine and quaternary ammonium groups was prepared by radiation-induced graft of glycidyl methacrylate (GMA) onto ultra-high molecular weight polyethylene (UHMWPE) fiber and further modifying with triethylenetetramine (TETA) and glycidyl trimethylammonium chloride (GTA). The ATR-IR spectra and SEM observation demonstrated that amine and quaternary ammonium groups were immobilized onto the surface of UHMWPE fiber. The principal factors affecting the adsorption of Cr(VI) ions have been investigated including pH of the aqueous solution, contact time, temperature and coexisting anions. This novel fibrous adsorbent could effectively adsorb Cr(VI) in the range of pH 1–9, and the maximum adsorption capacity reached 295 mg/g at pH 3 and 25 °C based on the Langmuir isotherm. It was found that adsorption equilibrium could be achieved within 2 h for initial Cr(VI) of 100 mg/L, following the pseudo-second order model. The effect of coexisting anions (including SO42−, H2PO4−, NO3−and Cl−) on the uptake of Cr(VI) was investigated in detail. Additionally, the adsorption saturated fiber could be regenerated by soaking in 0.5 mol/L NaOH solution, and the adsorption performance of this adsorbent could be maintained at 90% after eight cycles of adsorption-desorption. ATR-IR and XPS analysis revealed that Cr(VI) ions were adsorbed on the fiber adsorbent through ion exchange mechanism.

•HDPE was added to improve the scCO2 foaming of polypropylene.•Radiation cross-linking was employed to improve the scCO2 foaming of PP/HDPE blend.•Tensile strength of irradiated PP/HDPE was improved compared to un-treated PP foam.•Larger foaming temperature window (12 ℃) was achieved for scCO2 foaming of PP/HDPE.A blend of isotactic polypropylene (PP) with high-density polyethylene (HDPE) in different PP/HDPE ratios was irradiated by γ-ray to induce cross-linking and then foamed using supercritical carbon dioxide (scCO2) as a blowing agent. Radiation effect on the melting point and crystallinity were analyzed in detail. The average cell diameter and cell density were compared for PP/HDPE foams prepared under different conditions. The optimum absorbed dose for the scCO2 foaming of PP/HDPE in terms of foaming ability and cell structure was 20 kGy. Tensile measurements showed that the elongation at break and tensile strength at break of the crosslinked PP/HDPE foams were higher than the non-crosslinked ones. Of particular interest was the increase in the foaming temperature window from 4 ℃ for pristine PP to 8–12 ℃ for the radiation crosslinked PP/HDPE blends. This implies much easier handling of scCO2 foaming of crosslinked PP with the addition of HDPE.Download high-res image (642KB)Download full-size image

Anatase nanocrystalline titanium dioxide coatings were produced on ultrahigh molecular weight polyethylene (UHMWPE) fabric by radiation-induced graft polymerization of γ-methacryloxypropyl trimethoxysilane (MAPS) and subsequent cohydrolysis of the graft chains (PMAPS) with tetrabutyl titanate, followed by boiling water treatment for 180 min. The resulting material was coded as UHMWPE-g-PMAPS/TiO2 and characterized by attenuated total reflection infrared spectrometry, differential scanning calorimetry, X-ray diffraction, thermal gravimetry, and ultraviolet absorption spectroscopy, among others. The predominant form of TiO2 in the thin film was anatase. The coating layer was composed of two sublayers: an inner part consisting of an organic–inorganic hybrid layer to prevent photocatalytic degradation of the matrix by TiO2 film, and an outer part consisting of anatase nanocrystalline TiO2 capable of UV absorption. This UHMWPE-g-PMAPS/TiO2 composite exhibited much better thermal resistance than conventional UHMWPE fabric, as reflected by the higher melting point, decreased maximum degradation rate, and higher char yield at 700 °C. Compared with UHMWPE fabric, UHMWPE-g-PMAPS/TiO2 exhibited significantly enhanced UV absorption and excellent duration of UV illumination. Specifically, the UV absorption intensity was 2.4-fold higher than that of UHMWPE fabric; the retention of the break strength of UHMWPE-g-PMAPS/TiO2 reached 92.3% after UV irradiation. This work provides an approach for addressing the issue of self-degradation of TiO2-coated polymeric materials due to the inherent photoactivity of TiO2.Keywords: radiation-induced graft polymerization; sol−gel process; titanium oxide; UHMWPE fabric; UV resistance

•MAPS was graft polymerized onto cotton fabric by γ-ray irradiation inducement.•Anend-capped polysiloxane was immobilized ontografted cotton by chemical method.•Thishybridcottonpresented superhydrophobicity and oil-water separation performance.A new kind of non-fluorine-based organic-inorganic hybrid superhydrophobic cotton fabric was successfully prepared by simultaneous radiation-induced graft polymerization of γ-methacryloxypropyl trimethoxy silane (MAPS) and subsequent end-capping modification with hexamethyldisilazane (HMDS). The chemical structure and surface topography of the pristine and modified cotton fabrics were investigated in detail by ATR-FTIR, XPS, 29Si NMR, SEM and TGA to confirm that the graft reaction and end-capping modification had taken place. The above results demonstrated that the grafting polymerization and following end-capping reaction were completed, and a grafting layer was immobilized onto the surface of the cotton fabric. Surface wettability measurement and oil-water separation showed that the modified cotton surface not only exhibited the superhydrophobicity with a water contact angle of 165°, but also afforded a high efficiency of oil-water separation (96%). In particular, this modified cotton fabric retains superhydrophobicity even after 30 laundering cycles or 400 cycles of abrasion.

The reduction mechanism of Pt4+ ions confined in the channel of multi-walled carbon nanotubes was mainly investigated using X-ray absorption fine structure (XAFS) spectroscopy, with the aid of TEM, Raman, XRD and ICP-AES studies. The XAFS spectra revealed the spontaneous formation of Pt nanoparticles when H2PtCl6 was confined in multi-walled carbon nanotubes (MWCNTs). The Pt L3-edge X-ray absorption near edge structure (XANES) coupled with the C K-edge NEXAFS results indicated that the reduction of Pt4+ from tetravalent to zerovalent was attributed to the electron transfer from MWCNTs. The Fourier transform R-space of the Pt L3-edge XAFS data displayed that the nanoconfinement effect of MWCNTs promoted the formation of Pt nanoparticles. Moreover, the Pt–Pt bond length in confined Pt nanoparticles became shorter than that of Pt in the bulk state. Furthermore, by varying the inner diameter of MWCNTs from 15 nm to 10 nm and 5 nm, the Pt–Pt bond length of nanoconfined Pt nanoparticles decreased gradually. The results clearly revealed that MWCNTs acting as enriched electron donors can continuously reduce the confined Pt ions to Pt nanoparticles, thereby showing a great potential for the design of a new type of confined nanocatalysts.

To shed some light on the uranium extraction mechanism of amidoximate (AO) ligands from uranyl carbonate solution, we present experimental data taken using extended X-ray absorption fine structure at the U L3 edge and theoretical calculation results. The EXAFS data were well simulated and confessedly shows that AO ligands directly substitute the CO32– group in the equatorial plane to form a stable [UO2(CO3)3-x(AO)x](4-x)– complex. Density functional theory calculation indicates that although they have a slightly weaker electrostatic attraction than CO32– ligands, AO ligands display stronger binding capability to uranyl because of the remarkable orbital hybridization between U 5f/6d and (N,O)2p in the uranyl–AO complex. This finding provides strong evidence supporting the substitutional mechanism, which implies that cationic adsorbents are preferred in the further design of higher efficient adsorbents, and furthermore highlights the crucial role of the covalent effect in the extraction process.

An ultrahigh molecular weight polyethylene (UHMWPE) fibrous adsorbent with amidoxime (AO) groups, denoted as AO-UHMWPE, was prepared by preirradiation-induced graft copolymerization of acrylonitrile (AN) and acrylic acid (AA) on UHMWPE fibers, followed by amidoximation. The chemical structure, thermal stability, and mechanical strength were evaluated by means of Fourier transform infrared spectrometry, thermogravimetric analysis, and tensile tests, respectively. The adsorption behaviors of the AO-UHMWPE fiber were studied by batch adsorption in 331 ppb uranium solution, and flow-though adsorption experiments in simulated and natural seawater. It was found that the adsorption conditions (i.e., contact time and manner, temperature, and uranyl ion initial concentration) significantly influence the amount of uranyl ions binding to the AO-UHMWPE fibers. The adsorption of uranium in the batch adsorption experiment was 4.54 g-U/kg-ad in the presence of massive amounts of interference ions.

Amidoximated nylon-66 fiber containing double amidoxime groups per repeating unit (coded as PA66-g-PGMA-IDPAO) for the purpose of removing low uranium concentrations (1–25 mg/L) from aqueous solutions and application in simulated nuclear industry effluents was prepared by a simultaneous radiation-induced emulsion graft polymerization method. It was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and single fiber tensile strength tester. Batch adsorption experiments were conducted to investigate the effect of initial pH, sorption isotherm, adsorption kinetics, and thermodynamics. It was found that the optimum initial pH is 5.0. The sorption isotherm followed the Langmuir isotherm. The adsorption kinetics fit the pseudo-second-order model. The thermodynamics parameters revealed that the adsorption process was spontaneous and endothermic. The sorption test performed in a simulated nuclear industry effluent demonstrated a high adsorption efficiency (about 91.3%) and selectivity for uranium.

•The affinity of amidoximate (AO−) for uranyl is similar to that of CO32−, but stronger than that of carboxyl (AA−).•The dissociated H+ from HAA is conducive for the uranium extraction process from seawater.•The host structures have a strong impact on the interaction between uranyl and the ligand-based host architectures.Amidoxime-based polyethylene fiber plays an important role in sequestering uranium from seawater. Co-grafting carboxyl groups with amidoxime onto polyethylene fibers can enhance the uranium sorption efficiency. This work aims to theoretically understand the complexation of uranyl with amidoxime-, carboxyl- and mixed amidoxime/carboxyl-based host architectures within a polyethylene fiber. Using density functional theory method, we examined the geometrical structures, the electronic structures and the thermodynamic stabilities of various substitution complexes, as well as the effect of host structure on these complexes. The results showed that the affinity of amidoximate (AO−) for uranyl is similar to that of CO32−, but stronger than that of carboxyl (AA−). For the uranyl complexes with separate mixed amidoximate/carboxyl, the U–O(AO−), U–N(AO−) and U–O(AA−) bonds show the decreasing order of covalent character. However, for the uranyl complexes with mixed amidoximate/carboxyl-based host architectures, the covalent character of U–O(AO−), U–O(AA−) and U–N(AO−) bonds decrease in sequence. HAA is thermodynamically more favorable to react with UO2(CO3)34− forming a complex than HAO, which is due to the higher dissociation ability of HAA compared to HAO. The dissociated H+ from HAA is conducive for the dissociation of UO2(CO3)34−, which is possibly the origin of the synergistic effects between HAO and HAA in the uranium extraction process from seawater. The host structures have a strong impact on the interaction between uranyl and the amidoxime-, carboxyl- and mixed amidoxime/carboxyl-based host architectures. Comparing all the host architectures, those with –(CH2)4– and –(CH2)3– as linkages are more appropriate for uranyl together with one CO32− group.The host architectures with –(CH2)4– as linkages are more appropriate for uranyl, followed by –(CH2)3–.

•TR-EPR and transient absorption spectra of MeAQ− in [bmim][PF6] were recorded.•CIDEP signal was changed to net absorption at longer delay times in [bmim][PF6].•Lifetime of transient radical in [bmim][PF6] was longer than that in acetonitrile.•Various factors have an influence on photoinduced electron transfer in [bmim][PF6].Photoinduced electron transfer between 2-methylanthraquinone (MeAQ) and triethylamine (TEA) in a room-temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), was investigated by comparing the time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy and the transient absorption spectroscopy. The results of TR-EPR spectroscopy, in which MeAQ was 8 mmol L−1 and TEA was 150 mmol L−1, indicated that the transient radical would exist longer time in [bmim][PF6] than in acetonitrile. At the delay time of 8 μs after laser excitation, the TR-EPR signal transformed from an emissive peak into an absorptive peak when the experiment was performed in [bmim][PF6]. The results of the transient absorption spectroscopy, in which MeAQ was 0.1 mmol L−1 and TEA was 2.2 mmol L−1, showed that the efficiency and the rate of the photoinduced electron transfer reaction in [bmim][PF6] were obviously lower than that in acetonitrile. It was concluded that various factors, such as concentration, viscosity and local structural transformation of the solution, have an influence on the process of photoinduced electron transfer in [bmim][PF6].

When room-temperature ionic liquids (IL) are used as an electrolyte, their transport behaviors are still under heavy debate due to their complicated ion-associations. In this article, we conducted molecular dynamics simulations to study the molecular scale ion associations from the very dilute 1-butyl-3-methylimidazolium iodide/water solution to the pure IL. It revealed that ions are localized in a multicoordinated ion cage structure with nanoseconds in concentrated IL solutions. Dynamics analyses indicate that the transport of this solution can be depicted by the Debye–Hückel model only in dilute IL/water electrolyte. The velocity and rotational correlation functions showed that the lifetime of translational and rotational motions are at the level of picoseconds and nanoseconds, respectively, because of the ion cage effect. The lifetime of ion association demonstrated that the recombination of association ions was prevalent in IL solutions. It means that the dipolar or stable contact ion-pairs model may not be suitable for depicting the IL transport.

A temperature-dependent X-ray absorption fine structure (XAFS) study was performed to investigate structural changes in the 1-hexyl-3-methylimidazolium bromine (C6mimBr) ionic liquid (IL) confined within the channels of multiwalled carbon nanotubes (MWCNTs). The XAFS spectra at room temperature confirmed the charge transfer from the bromine anion of the encapsulated IL to the MWCNTs. R-space analysis at ambient temperature revealed the reduced distance between the anions and cations in the confined IL compared with that in the bulk state. Interfacial-induced solidification and nanoconfinement in MWCNTs induced the self-assembly of ions in the confined IL to form a layered arrangement near the inner surface of MWCNTs. In situ XAFS analysis revealed that with increasing temperature charge transferred from MWCNTs to Br anions because of the damage from the conjugative effect between Br and MWCNTs and the relatively strong electronegativity of Br atoms. R-space analysis also showed gradual reduction in distance between cations and anions with increasing temperature. This finding indicated that the anion moved toward the ring planar, and ions rearranged from the layered to the near-planar structure. Raman and XRD experiments confirmed the structural transformation of the confined IL at increased temperature.

The electric double layer structure and differential capacitance of single crystalline Au(100) electrodes in the ionic liquid 1-butyl-3-methyl-imidazolium hexafluorophosphate are investigated using molecular dynamics simulations. Results show strong adsorption on the electrode surface. The potential of zero charge (pzc) and maxima of differential capacitance are strongly dependent on the adsorption layer structure. At potentials near the pzc, cations and anions adjacent to the electrode surface are coadsorbed on the same screening layer. This strong adsorption layer results in overscreening effects on the compact layer and induces both a bell-shaped differential capacitance curve and a positive pzc. Moreover, the potential required for transition from overscreening to overcrowding is about 4.0 V. This transition potential may be attributed to the higher interaction energy between the Au(100) electrode and ions compared with the binding energy in our cation–anion system.Keywords: adsorption; electric double layer; ionic liquid; molecular dynamics simulation

•Crystallite size of crosslinked PTFE was investigated using SAXS at the first time.•Crystallite size of crosslinked PTFE became smaller with an increase of doses.•Crystallite size will become smaller due to the restriction of molecule mobility.•Crystallite size shrinking of crosslinked PTFE was further confirmed by DSC and SEM.The crystal structure of crosslinked polytetrafluoroethylene (XPTFE) and its morphological variations as compared with pure PTFE were investigated using differential scanning calorimetry, synchrotron small angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). The XPTFE samples were obtained by irradiating PTFE at the melt state using different radiation doses. Results showed that the melting temperature of the XPTFE decreases with the increase in radiation dose. The crystal melting enthalpy increases under low-dose irradiation. The scattering intensity decreases with the increase in radiation dose, which indicates the decrease in crystal size. Based on the SAXS patterns, the XPTFE crystallite size is smaller than the PTFE crystallite size. The difference in crystal sizes is more pronounced for XPTFE obtained under high radiation doses. This finding is confirmed by the SEM images of the XPTFE fractured surfaces. These results provide a reasonable explanation for the improved transparency and the relatively low crystallinity and high wear resistance of XPTFE compared with PTFE.SAXS curves of PTFE (a), XPTFE-150 (b), XPTFE-500 (c), XPTFE-1000 (d), XPTFE-3000 and (e), Scattering intensity decreased with an increase of dose in Fig. It indicates that the content of lamellae decreases as the radiation increases.

[Bmim]2PtCl4 (Bmim: 1-butyl-3-methylimidazolium) ionic liquid was confined in porous SiO2 nanoparticles ([Bmim]2PtCl4@SiO2) with an average pore size of 7.1 nm. The structure of [Bmim]2PtCl4@SiO2 was investigated through X-ray diffraction and X-ray absorption fine structure (XAFS). The average coordination numbers of Pt species in [Bmim]2PtCl4 and [Bmim]2PtCl4@SiO2 were 4.0 and 5.0, respectively. Parts of Pt2+ in [Bmim]2PtCl4@SiO2 were oxidized to form high-valence Pt4+. The possible forms and structures of Pt in the ionic liquid were analyzed according to the coordination number. XAFS analysis and density functional theory calculations imply the favorable formation of dimer (i.e., Pt2Cl82–) in [Bmim]2PtCl4@SiO2, in which two bridge Cl atoms were connected to two Pt atoms. In addition, Pt2Cl82– contained mixed-valence platinum (Pt2+ and Pt4+). The results of differential scanning calorimetry also showed that the melting point of this nanoconfined ionic liquid increased.

[Emim]Br ionic liquid was confined in porous SiO2 nanoparticles. It is shown that the confinement in the nanopores leads to a compression of molecular size and an increase in the melting point. The pore size of SiO2 is a key factor in tuning the anion-cation distance and the melting point of the confined ionic liquids.

An amidoxime-based ultra-high molecular weight polyethylene (UHMWPE) fibrous adsorbent was successfully prepared by γ-irradiation-induced graft copolymerization of acrylonitrile (AN) and acrylic acid (AA), followed by amidoximation. The grafting of AN and AA on the UHMWPE fiber and the amidoximation of the grafted fiber were confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The mechanical property of the original and modified UHMWPE fibers was compared by single-filament strength test. The adsorption property of the UHMWPE fibrous adsorbent was evaluated by adsorption test in uranyl nitrate solution and seawater. The surface of the modified UHMWPE fibers was covered by the grafting layer and became rough. The tensile strength of the amidoxime-based UHMWPE fibrous adsorbent was influenced by the absorbed dose and hydrochloric acid elution, but was independent of the grafting yield and amidoximation. The uranium adsorption amount of the amidoxime-based UHMWPE fibrous adsorbent after immersing in seawater for 42 days was 2.3 mg-U/g.

This study investigates the effect FeCl3 on the radiation stability of the ionic liquid, 1-butyl-3-methylimidazolium chloride (BmimCl) over a wide dose range of 0 to 1000 kGy under γ-ray radiation. The ionic liquid species, BmimFeCl4, was formed by adding FeCl3 into BmimCl. The results showed that the presence of FeCl4− significantly improved the radiation resistance of BmimCl, wherein the effect was more pronounced at higher FeCl4− content. Meanwhile, under irradiation, Fe(II) was generated from Fe(III), which was reduced by solvated electron. In addition, the concentration of Fe(II) increased with low level of absorbed dose, but leveled off at higher doses. Moreover, the radiation yield of the solvated electrons of BmimCl was further estimated at approximately 0.358±0.01 μmol/J in BmimCl-7 mol% FeCl3 system.

In order to understand the effect of surface chemical groups on the immobilized species, Au-containing imidazolium-based ionic liquid (IL) [Bmim][AuCl4] was intentionally immobilized on polystyrene (PS) submicrospheres (d ∼300 nm) with a very small surface area (4–10 m2/g), which possess carboxyl-moiety (COONa or COOH) on the surface. The behavior of immobilized [Bmim][AuCl4] on the two types of submicrospheres was investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD). It was revealed that the melting points (Tm) of [Bmim][AuCl4] that had been immobilized on PS-COONa and PS-COOH submicrospheres were decreased by 2.7 and 4.1°C, respectively. The interaction mechanism between the IL and submicrosphere surface moieties was further analyzed by X-ray absorption fine structure (XAFS) analysis. The data indicated that the coordination environment of Au species changed markedly when [Bmim] [AuCl4] was immobilized on the surfaces of PS-COONa and PS-COOH submicrospheres, as illustrated by the decrease in white line peak intensity. The effect of surface COOH groups on Tm depression and the white line peak intensity of the XANES spectrum is more pronounced than that of COONa groups, most likely due to the possible hydrogen bond formation between the COOH group and [Bmim]+.

•PS/PE alloy foam was prepared by supercritical carbon dioxide foaming method.•The addition of SEBS copolymer remarkably improved the cell morphology of the PS/PE alloy foams.•A non-destructive X-ray microtomography (XMT) was employed to observe the cell morphology of the PS/PE alloy foams.Non-destructive X-ray microtomography at a third generation synchrotron facility was applied to analyze the cell morphology of microcellular polystyrene (PS)/polyethylene (PE) alloy foams. This method, differing from the observation of cross section of cell by SEM, enables one to observe a complete cell structure in the polymer foam. PS/PE foams were prepared using a supercritical CO2 foaming process. A styrene–ethylene–butylene–styrene (SEBS) copolymer was used as the compatibilizer of PS and PE to improve the cell morphology. The effects of PS/PE composition and foaming conditions (temperature and pressure) on the cell structure of foams were investigated in detail. The optimal SEBS content for the foaming of PS/PE (70:30) alloys was found to be 5 wt%. The cell size and cell density were also dependent on the foaming temperature and the saturation pressure.

Phase behaviors of the liquids in nanospaces are of particular interest to understand the thermodynamics of the liquid on the nanoscale and for their applications that involve the confined systems. However, in many cases, the inconsistent observations of melting point variation for confined liquids are often revealed by different groups. Ionic liquids are a special kind of liquid. Here, by using the merits of the nonvolatile nature of ionic liquids, we realized the encapsulation of ionic liquids inside of mesopores silica oxide nanoparticles with a complete removal of compressed gas under high-vacuum condition; the completely confined ionic liquid formed a crystalline-like phase. It was found that compressed gas plays an important role in changing the melting point of the confined ionic liquid.Keywords: compressed gas; ionic liquid; melting point; nanoconfinement; phases transition;

In this work, we demonstrate for the first time that hydrophobic ILs can be strikingly tuned to be hydrophilic under a strong external electric field, with the use of nonequilibrium molecular dynamics (MD) simulations and atomic force microscopy (AFM) experiments. With increase of the electric field strength, the cation–anion and water–water interactions are both attenuated. The cations and anions gradually evolve from an IL interface to a water medium, leading to surprisingly hydrophilicity with high intersolvent mixing. This novel hydrophilic mixing process can be reversibly tuned to phase separation by reversing the electric field. These simulations suggest that the driving force of this hydrophobic–hydrophilic transition derived from a different tuning effect for the cations and the anions.

In this paper, the melting process of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) crystals confined in carbon nanotubes were investigated using molecular dynamics simulation. The confined ions formed a “shell-chain” structure within the nanopore. Our results revealed that this “shell-chain” structure possessed long-range crystalline order at low temperature and initiated melting at approximately 500 K, which well fit with experimental observations of ionic liquids in carbon nanotubes. This melting process was also confirmed by the potential energy profile of the confined ions. It was found that below 500 K, the ions within the nanopores were almost frozen around their positions. As the temperature increased above 500 K, the average number of hydrogen bonds for each confined anion began to decline linearly. This decline led to a dramatic change in the packing arrangement of the confined ions, followed by a steep rise in the ionic diffusivity.

A detailed study was explored to compare the transient absorption spectra of the neat 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) with its solution in water or acetonitrile. It was concluded that the excited triplet state 3[bmim]+* was produced after 266 nm laser irradiation, and then the neutral radical [bmim] and the cation radical [bmim] 2+ were formed through two possible paths. The transient absorption spectra of the neat [bmim][BF4] and its solution were similar but the reaction kinetics were different due to their different local structures such as dimeric or cluster. The energy transfer between excited [bmim][BF4] and β-carotene further affirmed the existence of 3[bmim]+*. And the reaction that the hydrated electron captured by [bmim]+ to produce [bmim] in solution was observed.Graphical abstract.Highlights► The transient absorption spectra of neat [bmim][BF4] and its solution were recorded. ► Due to the different local structure, their transient absorption spectra were similar but not identical. ► 3[bmim]+*, [bmim]2+ and [bmim] were produced after laser photolysis of [bmim][BF4]. ► Photoinduced processes such as energy transfer and electron capture by [bmim]+ were observed.

Four kinds of imidazolium-based ionic liquids (ILs) were immobilized onto the surface of nano-SiOx particles (d∼ 20 nm) by grinding in an agate mortar to produce a series of weight ratios of ionic liquid to nanoparticles. The physicochemical properties of immobilized ILs were investigated by differential scanning calorimetry, powder X-ray diffraction and Raman spectroscopy. It was found that the melting points (Tm) of the immobilized ILs depressed significantly in comparison with the bulk ionic liquids. The Tm depressions are 10, 12, 13 and 41 °C for [EMIM][PF6], [PMIM][PF6], [PHMIM][BF4] and [EMIM][I], respectively, for a loading amount of 35 wt% ionic liquid. The Tm depression of [EMIM][PF6] was independent of the weight proportion of immobilized ionic liquid up to 50 wt%, indicating that nano-SiOx has a large capacity for immobilized ILs. The Tm depression of [EMIM][I] is particularly significant because the H-bonding interactions of iodine anions with surface silanol groups of nano-SiOx particles is much weaker than that of fluorine anions with silanol groups of other investigated ionic liquids.

A polytetrafluoroethylene (PTFE) sheet was cross-linked by electron beam irradiation at 335 ± 5 °C in a nitrogen gas atmosphere. With increasing dose, the cross-linked PTFE (X-PTFE) sheet became transparent, and the melting point and the heat of crystallization decreased gradually. The tribological behavior of the X-PTFE sheet was investigated on a ring-on-ring tribometer and a block-on-ring friction tester under dry friction conditions. It was shown that the friction coefficient of X-PTFE increased with the absorbed dose, and that the increase was about 5% for cross-linking at a dose of 3000 kGy. The substantial improvement of the wear resistance of X-PTFE is of particular interest. The wear resistance of X-PTFE was improved by three orders of magnitude at a dose of 150 kGy. Scanning electron microscopy (SEM) analysis revealed that, after the tribological test, the ground surface of the virgin PTFE sheet was smooth, and the debris was in the form of flakes; while the worn surface of X-PTFE was rough, and the abraded debris was in the form of a fine powder. The three-dimensional network of X-PTFE is responsible for its excellent wear resistance behavior.

Applications of ionic liquids (ILs) in electrified interfaces and electrochemical systems require insight into the molecular-level structure and properties of the interfacial ILs. Using atomistic molecular dynamics (MD) simulations, we show here that a new double-layer stacking formation of the [Bmim][PF6] IL can be triggered by the surface negative charge. We also found that the double-layer formation induced by the surface charge thoroughly extended into the bulk phase, implying a strong unscreened ion effect in our IL system. Further study indicated that the double-layer formation in the bulk phase was due to a rapid structural transition. Different IL formations, including the conventional adsorption layer and the double-layer formation, can be achieved in sequence by increasing the surface negative charge. Moreover, the diffusion ability of the new double-layer formation in the bulk phase is much lower when compared to that observed in its original uncharged condition. The structure and properties of the ILs formation may be attributed to the tail−tail aggregation hypothesis of the nonpolar domain in the IL.

Confinement can induce unusual behavior in the properties of matter. Using atomistic molecular dynamics simulations, we report here a liquid-to-solid transition of a bilayer of ionic liquid 1,3-dimethylimidazolium chloride ([Dmim][Cl]) confined between graphite walls in order to mimic the phase transition of an ionic liquid confined to hydrophobic nanospace. It was found that the ionic liquid bilayer undergoes a clear and drastic phase transition at a wall distance of about 1.1 nm, forming a new high-melting-point solid phase with different hydrogen bonding networks. In the new phase, each cation is surrounded by the three nearest-neighbor anions, and each anion is also encircled by the three nearest-neighbor cations. Strong π−π stacking interactions are found between the cations of the bilayer solid. The anions can be formed into a hexagonal ring around the cations. The new bilayer solid is a high-melting-point crystal possessing a melting point of 825−850 K, which is higher than that of the bulk crystal by more than 400 K.

The components and structures of ionic liquid ChCl−ZnCl2 in different ChCl:ZnCl2 ratios were investigated using XAFS (X-ray absorption fine structure) technique. The average coordination number and distance of Zn species at different x(ZnCl2) (mole fraction of ZnCl2 when synthesizing) were calculated. It is shown that x(ZnCl2) has a regular influence on the coordination number of Zn species, due to the change of anion forms and structures in the ChCl−ZnCl2 ionic liquid. The possible forms and structures of Zn species in the ionic liquids were analyzed according to the coordination number. XAFS and DSC (differential scanning calorimetry) analysis imply that besides ZnCl3− and Zn2Cl5− anions, the Cl−Zn−Cl ion pair is a main species in the ionic liquid at higher x(ZnCl2). This newly discovered Zn species has substantial influence on the properties of the ionic liquid. From the analysis of the coordination numbers and coordination distance, a new mechanism of interactions between Ch+ cation and Cl−Zn−Cl ion pairs or Cl− is proposed.

A natural pigment, riboflavin (RF), was successful in immobilizing to the multiwalled carbon nanotubes (MWNTs) as antennae by a noncovalent approach. 1H NMR analysis indicated their π−π stacking interaction by the proton shift at the isoalloxazine ring of RF. Subsequently, time-resolved spectroscopic experiments were carried out to monitor the photoinduced charge separation states in the riboflavin/carbon nanotubes (RF/MWNTs) superstructures. It was found that charge separation was accessible in the superstructures with 355 nm laser excitation. The recombination of charge separation states was observed to be an obvious two-step process. A fast decay with a lifetime of ∼ 40 ns was attributed to the recombination of surface-immobilized RF radicals and localized electrons in MWNTs. Another relative longer process with a lifetime of ∼ 3.0 μs was assigned to the storage electron in MWNTs and thus retarded the recombination of charge separation states.

Molecular dynamics simulations were performed to study the phase behavior of a monolayer of room temperature ionic liquid 1,3-dimethylimidazolium chloride ([Dmim][Cl]) confined between two graphite walls at 425 K. These simulations predict a first-order freezing transition from a liquid monolayer to a solid monolayer induced by varying the distance between the parallel graphite walls (H = ∼0.65−0.95 nm). The resulting monolayer solid consisting of a hydrogen-bonded network structure is very different from bulk crystalline [Dmim][Cl]. The phase transition can be induced only at a molecular surface density of ρ = 1.9/nm2.

A detailed investigation was carried out on the foaming of cross-linked low-density polyethylene (x-LDPE) sheets with CO2 as a blowing agent on a batch scale. The x-LDPE sheets were produced through two different sequences, i.e., part formation after irradiation (Sequence A), and irradiation after part formation (Sequence B). The foaming behavior of x-LDPE samples prepared by both Sequence A and B was compared in terms of cell size distribution, cell size, cell density and volume expansion ratio. The optimum radiation dose for the foaming of x-LDPE was found to be 50 kGy. At a foaming temperature of 100 °C, the cell size of x-LDPE foam was less than 10 μm, and the maximal value of cell density reached 1011 cells/cm3. The SA and SB series of x-LDPE foams both had a microcellular structure. It may be possible to realize a continuous manufacture process for x-LDPE foam with the Sequence A.Two series of microcellular cross-linked polyethylene foams were produced by a radiation and scCO2 approach. The cell morphology of LDPE foams was compared in detail. The two series of foams revealed a reverse pattern of cell structure (cell size distribution, cell size and cell density) with increasing radiation dose. The optimum radiation dose of 50 kGy for the foaming of x-LDPE was found. Irradiation led to a wider foaming temperature range of LDPE.

Here we report transient spectral red-shift and transient absorption enhancement of p-benzoquinone radical in the presence of CdSe quantum dots after 355 nm pulse laser excitation. The spectral shift was caused by surface-bound p-benzoquinone molecules while the transient absorption increase was due to interfacial electron transfer from CdSe quantum dots to p-benzoquinone molecules. In contrast, spectral shift and absorption increase were much less significant for anthraquinone in the presence of CdSe quantum dots due to their weak adsorption abilities.

Poly(methyl methacrylate) (PMMA) microspheres with a nonporous skin and open cellular core structure were obtained by supercritical carbon dioxide foaming via a pressure quench method. The microspheres were characterized by particle size analyzer, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Effects of foaming conditions such as CO2 pressure, temperature, and cell growth time on the particle size, size distribution, and morphology of the PMMA microspheres were investigated in detail. It was found that higher foaming temperature and higher pressure resulted in an increase of particle size. However, a longer cell growth time caused a decrease in size of the foamed PMMA microspheres.

Gamma-radiation induced degradation of polytetrafluoroethylene (PTFE) in 60 wt.% dispersion was studied in the dose range of 20–200 kGy and the change in property of PTFE was characterized by differential scanning calorimetry (DSC), photon cross correlation spectroscopy (PCCS), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR spectroscopy and X-ray photoelectron spectroscope (XPS). It was found that the mean particle size of PTFE reduces from 250 nm of the control to 170 nm at 100 kGy, as confirmed by dynamic laser scattering and SEM. The crystallinity degree of PTFE increased at 20 kGy but remained unvaried at higher dose level. G-value of scission, G(s), was determined to be 0.46 μmol/J.Gamma-radiation induced degradation of polytetrafluoroethylene (PTFE) in 60 wt.% dispersion was studied in the dose range of 20–200 kGy and the mean particle size of PTFE was found to decrease with dose, as measured by PCCS and SEM.

Thiourea chitosan was prepared by the reaction of chitosan with ammonium thiocyanate in ethanol. Thiourea chitosan was characterized by FT-IR, 13C NMR, and elemental analysis; XPS confirmed that in thiourea chitosan–Ag+ complex, S atoms coordinated to silver ions and were the major electron donors; O atoms also coordinated to silver ions and they were another electron donors next to S atoms. N atoms did not take part in coordination. Thiourea chitosan–Ag+ complex overcomes the instability of Ag+. Antimicrobial activities of the complex was evaluated against six species of bacteria and molds. The complex showed a wide spectrum of antimicrobial activities, whose MIC values against bacteria were 20 times lower than those of chitosan, 100 times lower than those of sodium diacetate and 200 times lower than those of sodium benzoate, respectively; the complex has a better antibacterial activity than antifungal activity.

•UHMWPE powder was irradiated by γ ray and EB in air with difference in dose rate.•Radiation oxidation was studied and compared experimentally and theoretically.•The dose rate has great effect on thickness of oxidation layer in UHMWPE powder.Oxidation is an important effect of irradiation on polyethylene in air. In this work, oxidation of ultra-high molecular weight polyethylene (UHMWPE) powder (ca. 110 μm in diameter) induced by gamma rays (γ ray) and electron beams (EB) in air resulted in some large differences in properties, such as oxidative scission due to dose rate differences. However, other properties, such as surface wettability and thermal stability were not that greatly affected. The dose-rates used were 0.0019 kGy/s from a cobalt-60 gamma source and 92 kGy/s from an electron beam. The chemical structure, oxidation level, surface wettability and thermal stability of irradiated UHMWPE were analyzed by FT-IR, XPS, TGA and the static contact angle. Hydrophilic carboxyl and carbonyl groups were present on the surface of irradiated UHMWPE after irradiation in air, resulting in a decrease in the contact angle. After irradiation at 300 kGy, the gel content of the γ ray-irradiated UHMWPE samples decreased to almost zero, while that of EB irradiated UHMWPE decreased to 57%. For UHMWPE powder irradiated by gamma rays at lower doses, radiation-induced oxidation was complete and consistent with a simple theoretic estimation. Surface wettability was primarily affected by surface oxidation, and the oxidation level of UHMWPE could be easily predicted.Download full-size image

Methyl acrylate (MA) monomer was grafted onto ultra-high molecular weight polyethylene (UHMWPE) fibers by γ-ray pre-irradiation induced graft polymerization. The grafting of MA on UHMWPE fiber was confirmed by thermogravimetric analysis and Fourier-transform infrared spectroscopy. The degree of grafting (DG) increased with an increase in absorbed dose and reached a significantly high value (approximately 200%) at 100 kGy. Scanning electron microscopy analysis revealed that the surface of the UHMWPE-g-PMA fibers was covered by the MA grafting layer and became rough. The monoclinic crystalline and orientated intermediate phases were disordered by the grafting chains such that degree of orientation declined gradually with increasing DG. The tensile strength of UHMWPE-g-PMA fiber decreased with increasing dose but was independent of DG, whereas the fiber modulus declined with DG. UHMWPE-g-PMA fiber that possesses desirable mechanical properties could be obtained at a dose of less than 10 kGy.Highlights► Methyl acrylate was grafted on UHMWPE fiber by radiation graft polymerization. ► High dose led to an increase in grafting yield and reaction rate. ► Grafting chains disordered the monoclinic crystalline and intermediate phase. ► Tensile strength of modified fiber decreased with an increase in dose. ► Modulus of modified fiber decreased with an increase in grafting yield.

To investigate the radiation effect on polyacrylonitrile (PAN) fibers as well as on the preoxidation process, PAN fibers were irradiated by γ-rays at room temperature at 50–500 kGy in vacuum and then were thermally oxidized in air. Gel fraction determination indicated that γ irradiation led to the predominant crosslinking of PAN fibers, with G values (the number of event per 100 eV absorbed) of G(X)=0.28 and G(S)=0.16 for chain crosslinking and scission, respectively. It was found that irradiation caused a slight change in the crystal structure and tensile strength at low dose. Radiation led to a reduction of the onset temperature of cyclization reaction and moderated the exothermic behavior. The density of the PAN fibers after thermal oxidation was used to evaluate the preoxidation extent. It was proven that radiation could significantly accelerate the preoxidation process and consequently shortened the preoxidation time. Radiation crosslinking may have potential application in the production of PAN-based carbon fibers.Highlights► PAN fiber was irradiated in vacuum to induce crosslinking at room temperature. ► Radiation crosslinking regulated the exothermic cyclization behavior of PAN fiber. ► Radiation had little effect on crystalline structure and orientation of PAN fiber. ► The decrease in tensile strength was insignificant due to crosslinking. ► The preoxidation process of PAN fiber was greatly accelerated by irradiation.

Free radicals in vacuum, air and oxygen atmospheres were studied using electron spin resonance (ESR). Mainly two types of radicals, namely alkyl radicals and polyimine radicals, are formed in polyacrylonitrile (PAN) fibers after γ-ray irradiation. The G value of the radical formation was calculated to be 2.1 (number of radicals per 100 eV absorbed) in air at room temperature based on the ESR measurements. The radical stability and decay behaviors at room temperature and elevated temperatures were also investigated under different atmospheres. The alkyl radicals were found to be rather stable when stored in vacuum at room temperature, but they decayed via reaction with oxygen when stored in air. The alkyl radicals disappeared completely after a thermal treatment at 110 °C in vacuum, but only 15% of the polyimine radicals decayed; this indicates that polyimine radicals are more stable compared to the alkyl radicals due to their lower mobility.Highlights► Radicals formed by radiation were assigned to polyimine and alkyl radicals. ► G-value of radicals was measured to be 2.1 per 100 eV. ► The radicals were found to be extremely stable in vacuum at room temperature. ► Effect of oxygen on radical decay under various conditions was studied.

•Radiation cross-linking improved the foaming of atactic polypropylene by SC CO2.•Radiation effects on the cell structure of foamed PP were investigated in detail.•Irradiation of atactic PP led to a wider temperature window for the SC CO2 foaming.Atactic polypropylene (PP) samples with melt flow indices (MFI) of 7.0 g/10 min were irradiated and then foamed with supercritical carbon dioxide (scCO2). A detailed investigation was carried out to understand the effect of radiation on the scCO2 foaming of polypropylene. Variations in the molecular weight, branching degree, crystallinity, and melting and crystallization temperatures of irradiated PP were investigated. The cell diameter, cell density, volume expansion ratio and foaming rate were analyzed in detail under different conditions. It was found that the cell structure of PP foam became more uniform and the foaming temperature window increased to 10 °C. This compares favorably to the 4 °C observed with pristine atactic PP. The best cell morphology was observed at a dose of 30 kGy. The corresponding average diameter and cell density were 16.4μm and 5.7×107 cells/cm3, respectively.

Photoinduced chemical reactions of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) were studied by laser photolysis at a wavelength of 266 nm. Excited triplet state 3[bmim]+* was observed, radical cation [bmim]2+ and neutral [bmim]* radical via photoionization were also formed. Energy transfer from 3[bmim]+* to β-carotene was confirmed. Oxidation via one electron transfer from TMPD to 3[bmim]+* was also observed and the rate constant was determined to be 1.2 × 105 L·mol−1·s−1. The reaction of [bmim][PF6] with hydrated electron (eaq−) was confirmed by laser photolysis in aqueous solution.

The reduction mechanism of Pt4+ ions confined in the channel of multi-walled carbon nanotubes was mainly investigated using X-ray absorption fine structure (XAFS) spectroscopy, with the aid of TEM, Raman, XRD and ICP-AES studies. The XAFS spectra revealed the spontaneous formation of Pt nanoparticles when H2PtCl6 was confined in multi-walled carbon nanotubes (MWCNTs). The Pt L3-edge X-ray absorption near edge structure (XANES) coupled with the C K-edge NEXAFS results indicated that the reduction of Pt4+ from tetravalent to zerovalent was attributed to the electron transfer from MWCNTs. The Fourier transform R-space of the Pt L3-edge XAFS data displayed that the nanoconfinement effect of MWCNTs promoted the formation of Pt nanoparticles. Moreover, the Pt–Pt bond length in confined Pt nanoparticles became shorter than that of Pt in the bulk state. Furthermore, by varying the inner diameter of MWCNTs from 15 nm to 10 nm and 5 nm, the Pt–Pt bond length of nanoconfined Pt nanoparticles decreased gradually. The results clearly revealed that MWCNTs acting as enriched electron donors can continuously reduce the confined Pt ions to Pt nanoparticles, thereby showing a great potential for the design of a new type of confined nanocatalysts.

Four kinds of imidazolium-based ionic liquids (ILs) were immobilized onto the surface of nano-SiOx particles (d∼ 20 nm) by grinding in an agate mortar to produce a series of weight ratios of ionic liquid to nanoparticles. The physicochemical properties of immobilized ILs were investigated by differential scanning calorimetry, powder X-ray diffraction and Raman spectroscopy. It was found that the melting points (Tm) of the immobilized ILs depressed significantly in comparison with the bulk ionic liquids. The Tm depressions are 10, 12, 13 and 41 °C for [EMIM][PF6], [PMIM][PF6], [PHMIM][BF4] and [EMIM][I], respectively, for a loading amount of 35 wt% ionic liquid. The Tm depression of [EMIM][PF6] was independent of the weight proportion of immobilized ionic liquid up to 50 wt%, indicating that nano-SiOx has a large capacity for immobilized ILs. The Tm depression of [EMIM][I] is particularly significant because the H-bonding interactions of iodine anions with surface silanol groups of nano-SiOx particles is much weaker than that of fluorine anions with silanol groups of other investigated ionic liquids.