Understanding the Thermal Degradation Mechanism of High-Temperature-Resistant Phthalonitrile Foam at Macroscopic and Molecular Levels.

Polymer foam, a special form of polymer, usually demonstrates some unexpected properties that rarely prevail in the bulky polymer. Studying the thermal degradation behavior of a specific polymer foam is important for its rational design, quick identification, objective evaluation, and industrial application. The present study aimed to discover the thermal degradation mechanism of high-temperature-resistant phthalonitrile (PN) foam under an inert gas atmosphere. The macroscopic thermal decomposition of PN foam was carried out at the cost of size/weight loss, resulting in an increasing number of open cells with pyrolyzation debris. Using the TGA/DTG/FTIR/MS technique, it was found that PN foam involves a three-stage thermal degradation mechanism: (I) releasing gases such as H2O, CO2, and NH3 generated from azo-containing intermediate decomposition and these trapped in the closed cells during the foaming process; (II) backbone decomposition from C-N, C-O, and C-C cleavage in the PN aliphatic chain with the generation of H2O, CO2, NH3, CO, CH4, RNH2, HCN, and aromatic gases; and (III) carbonization into a final N-hybrid graphite. The thermal degradation of PN foam was different from that of bulky PN resin. During the entire pyrolysis of PN foam, there was a gas superposition phenomenon since the release of the decomposition volatile was retarded by the closed cells in the PN foam. This research will contribute to the general understanding of the thermal degradation behavior of PN foam at the macroscopic and molecular levels and provide a reference for the identification, determination, and design of PN material.

Design and assembly of Ag-decorated Bi2O3 @ 3D MXene Schottky heterojunction for the highly permeable and multiple-antifouling of fibrous membrane in the purification of complex emulsified oil pollutants.

Membrane separation technology has potential for purifying emulsified oily wastewater. However, the oils, soluble organic substances, and microorganisms can cause complex membrane fouling problems, thereby reducing the separation efficiency and service life. Herein, a highly permeable and multiple-antifouling composite membrane was prepared using porous PAN fibrous mat as support backbone for the assembly of Ag-decorated Bi2O3 @ 3D MXene Schottky heterojunction and hydrophilic TA as the adhesive. The unique arrangement of 3D MXene heterojunction and hydrophilic functionalization effectively broke through the limitation of separation flux and synergistically enhanced the anti-fouling performance of membrane. Such fibrous composite membrane achieved an exceedingly high permeability (2717-3328 L·m-2·h-1) for various emulsified oils, while ensuring excellent oil/water emulsion retention rate (99.59%) and good cycle stability. Meanwhile, the composite membrane displayed favorable photocatalytic degradation performance toward degrading MeB (96.1%) and antibacterial ability. Furthermore, the MD simulation and free radical trapping experiments were carried out to unravel the molecular interactions during the separation process and the photocatalytic mechanism of composite membrane, respectively. Overall, the combination of photocatalytic self-cleaning, anti-oil adhesion, and antibacterial effect renders the membrane high permeability and multiple-antifouling performance, which provides a new strategy for dealing with complex oily wastewater in petrochemical industry.

Bi-functional super-hydrophilic/underwater super-oleophobic 2D lamellar Ti3C2Tx MXene/poly (arylene ether nitrile) fibrous composite membrane for the fast purification of emulsified oil and photodegradation of hazardous organics.

Developing the multi-functional membranes including oil/water emulsion separation and removal of hazardous organic pollutants is essential to the purification of the complicated wastewater. However, it remains a daunting challenge to combine these intended functions while maintaining high separation efficiency. Herein, we developed a new 2D lamellar MXene/poly (arylene ether nitrile) (PEN) fibrous composite membrane through the self-assembly of TiO2 nanoparticles intercalated MXene nanosheets onto the porous PEN nanofibrous mats and bioinspired polydopamine triggered chemical-crosslinking with polyethyleneimine (PEI). Such nano-intercalation and mussel-inspired crosslinking could effectively regulate the interlayer spacing of the MXene nanosheet skin layer and surface wettability of the composite membrane, which also further contributed to the fast separation and unique bifunctional feature. It was found that the MXene@TiO2/PEN fibrous composite membrane exhibited low oil-adhesion and superhydrophilic (WCA = 0°)/underwater superoleophobic (UOCA > 155°) properties, which could efficiently separate various surfactant-stabilized oil-in-water emulsions under low pressure of 0.04 MPa while keeping good stability (Under 1 M HCl and 2 M NaOH solutions) and recyclability. Interestingly, the fibrous composite membrane achieved favorable permeation flux of 908-1003 Lm-2h-1 (2270-2507.5 Lm-2h-1bar-1) in comparison to other reported MXene based multifunctional composite membranes. Moreover, owing to the synergistic effect of MXene nanosheets and TiO2 nanoparticles, the MXene@TiO2/PEN membrane showed excellent photocatalytic degradation performance for various dyes under visible light, i.e. the photocatalytic degradation efficiency for 15 ppm MB, MO, CV, and MeB solutions achieved 92.31%, 93.50%, 98.06%, and 99.30% within 60 min, respectively. Such 2D MXene bio-functional composite membranes with outstanding oil/water emulsions separation and photocatalytic degradation of dyes pave an avenue for treating complicated oily wastewater.

Controllable preparation of monodisperse alginate microcapsules with oil cores.

Here we report a novel strategy for controllable preparation monodisperse alginate microcapsules with oil cores, where the thickness of the alginate shells, as well as the number and diversity of the oil cores can be tailored precisely. Monodisperse oil-in-water-in-oil (O/W/O) emulsions are generated in a microfluidic device as templates, which contain alginate molecules and a water-soluble calcium complex in the middle aqueous phase. Alginate microcapsules are produced by gelling O/W/O emulsions in oil solution with acetic acid, where the pH decreasing will trigger the calcium ions being released from calcium complex and cross-linking with alginate molecules. Increasing the alginate molecule concentration in emulsion templates affects little on the thickness of the microcapsules but improves their stability in DI water. The strength of alginate microcapsules can be reinforced by post cross-linking in calcium chloride, polyetherimide, or chitosan solution. Typical payloads, such as thyme essential oil, lavender essential oil and W/O emulsions are encapsulated in alginate microcapsules successfully. Furthermore, tailoring the thickness of the alginate shells, as well as the number and the diversity of the oil cores precisely by manipulation the emulsion templates with microfluidics is also demonstrated. The proposed method shows excellent controllability in designing alginate microcapsules with oil cores.

Robust super-hydrophobic/super-oleophilic sandwich-like UIO-66-F4@rGO composites for efficient and multitasking oil/water separation applications.

Super-wetting MOFs@graphene hybrid has shown promising application for oil/water separation, due to high porosity, low density, and controllable wettability, however, achieving excellent stability and recyclability are found to be still challenging. In this study, sandwich-like UIO-66-F4@rGO hybrid was synthesized by immobilization of UIO-66-F4 nanoparticles on rGO matrix, which featured the unique micro/nano hierarchy with hydrophobic characteristics. In order to realize the oil/water separation, as-prepared sandwich-like UIO-66-F4@rGO hybrid was applied as a potential candidate for constructing robust super-hydrophobic/super-oleophilic interfaces by using filter paper (FP) and melamine sponge (MS) as substrates. Typically, the surface modification of substrates can be easily achieved by simple dip-coating method, and interfacial adhesion between substrates and UIO-66-F4@rGO was enhanced by cross-linking of hydroxyl-fluoropolysiloxane (FPSO). Consequently, the super-hydrophobic/oleophilic UIO-66-F4@rGO/FP exhibited high contact angle of 169.3 ± 0.6° and was capable of separating various water-in-oil emulsions effectively. The flux and separation efficiency were 990.45 ± 36.28 Lm-2 h-1 and 99.73 ± 0.19 % driven by gravity, respectively. The super-hydrophobic/super-oleophilic UIO-66-F4@rGO/MS possessed selective oil absorption with absorption capacity of 26∼61 g/g depending on the viscosity of oils and continuous cleaning of oil spill. Furthermore, the UIO-66-F4@rGO composite could tolerate high/low temperature, corrosive solutions, and physical damage, displaying robust and stable super-hydrophobic/super-oleophilic interfaces for treating oily wastewater in harsh environments.

Easy-handling bamboo-like polypyrrole nanofibrous mats with high adsorption capacity for hexavalent chromium removal.

Development of highly efficient and easy-handling absorbents for heavy metals removal is desirable for the remediation of our existing aquatic system. Herein, we demonstrated the novel bamboo-like polypyrrole nanofibrous mats for the removal of highly toxic hexavalent chromium (Cr(VI)) from aqueous solution. To achieve this target, the V2O5 nanofibrous templates were prepared via non-emulsion electrospinning technique and calcination, followed by in-situ polymerization of pyrrole. Benefiting from the special porous structure, high surface area and abundant adsorption active sites, the resulting bamboo-like polypyrrole nanofibrous mats exhibited a high Cr(VI) adsorption capacity up to 961.5 mg g-1 at room temperature, which can be well maintained for five adsorption/desorption cycles. The adsorption capacity for Cr(VI) can be enhanced with the decrease of pH and adsorption process belonged to the pseudo-second-order model. Furthermore, the adsorption isotherms of bamboo-like polypyrrole nanofibrous mats fitted the Langmuir isotherm model, and the adsorption mechanism of electrostatic attraction between bamboo-like polypyrrole nanofibers and Cr(VI) was presented. More importantly, the flexible and integrated bamboo-like polypyrrole nanofibrous membrane allowed easy handling during application, which is potentially used for heavy metal removal from aqueous solution.

Novel polyvinylidene fluoride nanofiltration membrane blended with functionalized halloysite nanotubes for dye and heavy metal ions removal.

Membrane separation is an effective method for the removal of hazardous materials from wastewater. Halloysite nanotubes (HNTs) were functionalized with 3-aminopropyltriethoxysilane (APTES), and novel polyvinylidene fluoride (PVDF) nanofiltration membranes were prepared by blending with various concentrations of APTES grafted HNTs (A-HNTs). The morphology structure of the membranes were characterized by scanning electron microscope (SEM) and atomic force microscopy (AFM). The contact angle (CA), pure water flux (PWF) and antifouling capacity of membranes were investigated in detail. In addition, the separation performance of membranes were reflected by the removal of dye and heavy metal ions in simulated wastewater. The results revealed that the hydrophilicity of A-HNTs blended PVDF membrane (A-HNTs@PVDF) was enhanced significantly. Owing to the electrostatic interaction between membrane surface and dye molecules, the dye rejection ratio of 3% A-HNTs@PVDF membrane reached 94.9%. The heavy metal ions rejection ratio and adsorption capacity of membrane were also improved with the addition of A-HNTs. More importantly, A-HNTs@PVDF membrane exhibited excellent rejection stability and reuse performances after several times fouling and washing tests. It can be expected that the present work will provide insight into a new method for membrane modification in the field of wastewater treatment.

Controllable synthesis, magnetism and solubility enhancement of graphene nanosheets/magnetite hybrid material by covalent bonding.

Hybrids of Fe(3)O(4) nanoparticles and surface-modified graphene nanosheets (GNs) were synthesized by a two-step process. First, graphene nanosheets were modified by SOCl(2) and 4-aminophenoxyphthalonitrile to introduce nitrile groups on their surface. Second, the nitrile groups of surface-modified graphene nanosheets were reacted with ferric ions on the surface of Fe(3)O(4) with the help of relatively high boiling point solvent ethylene glycol to form a GNs/Fe(3)O(4) hybrid. The covalent attachment of Fe(3)O(4) nanoparticles on the graphene nanosheet surface was confirmed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectrometer (EDS) and scanning electron microscopy (SEM). TEM and HRTEM observations indicated that the sizes of the nanoparticles and their coverage density on GNs could be easily controlled by changing the concentration of the precursor and the weight ratio to GNs. Magnetic measurements showed that magnetization of the hybrid materials is strongly influenced by the reaction conditions. Chemically bonded by phthalocyanine, the solubility of as-synthesized GNs/Fe(3)O(4) hybrid materials was greatly enhanced, which was believed to have potential for applications in the fields of composites, wastewater treatment and biomaterials.