Molecularly Resonant Metamaterials for Broad-Band Electromagnetic Stealth.

Electromagnetic (EM) metamaterial is a composite material with EM stealth properties, which is constructed by artificially reverse engineering metal split resonance rings (SRR). However, the greatest limitation of EM metamaterials is that they can only stealth at a fixed and lower frequency of EM waves, and modern processing techniques still cannot meet the accuracy requirements to fabric nano-size structural unit. Nano-sized and even ultra-small SRR at molecular level are promising arrays to realize the ability of EM stealth function at a higher frequency, although it has proven challenging to synthesize long, straight, connected molecular SRR, and also difficult to arrange those molecular SRR into a strict array. Here, the study overcomes this challenge and demonstrates that the fabric of polypyrrole molecular SRR achieves an ultra-small inner diameter of 2.49 Å and realizes the arrays arrangement at molecular level. Furthermore, the study exploits the EM stealth function and verifies that such arrays of molecular SRR with 2.49 Å have the ability to reach high-performance EM stealth in the range of 106 -1016 Hz. This design concept opens a pathway for developing new metamaterials with broadband EM wave stealth and also serves the wider range of new applications.

Simple Fabrication of Polyvinylidene Fluoride/Graphene Composite Membrane with Good Lipophilicity for Oil Treatment.

Graphene (GE) is an emerging type of two-dimensional functional nanoparticle with a tunable passageway for oil molecules. Herein, polyvinylidene fluoride (PVDF)/GE composite membranes with controllable pore structure were fabricated with a simple non-solvent-induced phase separation method. The change of crystallinity and crystal structure (α, ß, γ, etc.) generated is due to the addition of GE, which benefits the design of a suitable pore structure for oil channels. Meanwhile, the hydrophobicity and thermal stability of the composite membrane were obviously enhanced. With 3 wt % GE, the contact angle was 124.6°, which was increased greatly compared to that of the GE-0 sample. Moreover, the rate of the phase transition process was affected by the concentration of casting solution, temperature, and composition of the coagulation bath. For example, the composite membrane showed better oil-water separation properties when the coagulation bath was dioctyl phthalate. In particular, the oil flux and separation efficiencies were up to 2484.08 L/m2·h and 99.24%, respectively. Consequently, PVDF/GE composite membranes with excellent lipophilicity may have good prospects for oily wastewater treatment.

Fabrication of a novel one-step coating hyper-hydrophobic fluorine-free TiO2 decorated hollow composite membrane for use in longer-term VMD with enhanced flux, rejection, anti-wetting and anti-fouling performances.

Despite recent efforts, there are still significant challenges in preparing hyper-hydrophobic membranes using environmental-friendly materials and simple methods. In this work, using phase separation theory, we prepared a fluorine-free hyper-hydrophobic porous hollow composite membrane using one-step ultrasound dip-coating. Then, fluorine-free modified titanium dioxide, polydimethylsilane and polypropylene was used to construct the porous membrane with a water contact angle of 161°. The distribution of surface elements, morphology, wetting and the scale of titanium on the membranes was characterized using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), the water contact angle and acid-alkali stability, wetting resistance, and so on. The membrane was evaluated for desalination in the presence of organic-pollutants. Under longer-term vacuum membrane distillation, compared with the general polypropylene membrane, the flux of the hyper-hydrophobic membrane increased to 12.17 kg (m2 h)-1, and the rejection rate reached 99.99%. These results indicated that the free-fluorine hyper-hydrophobic membrane could be used for seawater desalination. Finally, our results indicate that the hyper-hydrophobic modified membrane has good potential for use in industrial desalination.

Green preparation of polyvinylidene fluoride loose nanofiltration hollow fiber membranes with multilayer structure for treating textile wastewater.

In this work, polyvinylidene fluoride (PVDF) loose nanofiltration (NF) hollow fiber membranes with multilayer structure were prepared successfully based on a solvent-free process. Graphene oxide (GO) was used to cover the interface pores of the pristine PVDF membranes via vacuum filtration, and polypyrrole (PPy) was polymerized on the surface to further decorate the membrane structure. Interestingly, the modified membranes exhibited a multilayer structure due to synergistic effect of GO and PPy. The structure and property of PVDF loose NF membranes were investigated in detail. After modifying by GO and PPy, the hydrophilicity improved obviously. Moreover, the molecular weight cut off (MWCO) was about 3580 Da, and the smallest pore size of skin layer decreased to 2.5-4 nm. Furthermore, the PVDF loose NF hollow fiber membranes presented a high dye rejection (˃98.5%) for negative dyes, whereas a low salt rejection for NaCl (about 4%), showing a great potential for separating dye/salt accurately. Specifically, there were not any solvent used in all the preparation processes. The work offered a novel strategy for green preparation of loose NF membranes.

Polypyrrole/cadmium sulfide hollow fiber with high performance contaminant removal and photocatalytic activity fabricated by layer-by-layer deposition and fiber-sacrifice template approach.

A recyclable polypyrrole (PPy)/cadmium sulfide (CdS) hollow fiber photocatalyst was innovatively fabricated for solving the loss issue of the current powder-form photocatalyst in slurry system. Core-sheath structure CdS/polyacrylonitrile (PAN) fiber was prepared via successive ionic layer adsorption and reaction (SILAR) method on the surface of PAN fiber. PPy was further deposited on the CdS/PAN fiber by vapor deposition polymerization. After the removal of interior PAN template, PPy/CdS hollow fiber was yielded. The hollow structure of PPy/CdS hollow fiber was confirmed by morphology observation. The resulting PPy/CdS hollow fiber presents low energy band gaps of 1.9 eV, which accounts for enhanced visible light photocatalytic activity after PPy deposition. PPy/CdS hollow fiber shows good dye removal efficiency of 73.06 wt% (dosage of the product as low as 5 mg·10 mL-1), and praiseworthy H2 production rate up to 269.7 µmol·g-1·h-1. PPy/CdS hollow fiber maintained high and sustainable photocatalytic activity compared to CdS/PAN fiber after 8 cycles, indicating that PPy effectively improved the stability of CdS. Here, PPy plays key synergistic role in photocatalysis of PPy/CdS hollow fiber for the promotive and protective effects based on the actual photocatalytic performance and inductively coupled plasma optical emission spectrometer (ICP-OES) results. Compared with nano-sized photocatalysts, the fiber-formed PPy/CdS hollow fiber is highly bulky and easy to recycle. PPy/CdS hollow fiber has great potential for scale-up in industrial application because of its excellent grabbing ability and degradation to contaminants, and ease of disposal.

Graphene-Coated Poly(ethylene terephthalate) Nonwoven Hollow Tube for Continuous and Highly Effective Oil Collection from the Water Surface.

Graphene (GE) has attracted significant attention on account of its unique structure and superior performance, arousing a new research field for materials science. Herein, a novel GE-coated poly(ethylene terephthalate) nonwoven (PGNW) hollow tube (PGNW-T) was fabricated for continuous and highly effective oil collection from the water surface. The PGNW was prepared via a dip-spray coating method, which possessed superhydrophobicity-superoleophilicity and could absorb a variety of oils or organic solvents with the absorption capacity (Q) value of 18-34 times its own weight. Then, PGNW-T was obtained through winding the PGNW on the surface of a porous polypropylene hollow tube. As-prepared PGNW-T was competent for dynamic oil collection with high flux (18 799.94 L/m2 h), outstanding separation efficiency (97.14%), and excellent recyclability (>96% after 10 cycles) from the oil/water mixture. In particular, a miniature device based on as-prepared PGNW-T was developed for continuous thin oil film collection, which could dynamically "catch up" floated oils or organic solvents from the water surface. Finally, our strategy is extremely facile to scale up, showing its huge potential application in practical oil-spill remediation.

Preparation of an electrospun tubular PU/GE nanofiber membrane for high flux oil/water separation.

A simple, tubular structure polyurethane/graphene (PU/GE) nanofiber membrane for continuous oil/water separation was prepared using the following strategies: a polyester (PET) fiber braided tube was used for reinforcement, stearic acid (SA) was used to assist GE dispersion, and a PU solution containing GE was used to cover the outer layer of the PET fiber braided tube using the electrospinning method. Specifically, the PU/GE nanofiber membrane has a multi-branched structure. The tubular braid reinforced (TBR) PU/GE nanofiber membrane was characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), confocal scanning microscopy (CSM) and capillary flow porometry. The contact angle results showed that the TBR PU/GE nanofiber membrane had good hydrophobic and lipophilic properties. The obtained membranes had good oil/water selectivity for oil-water separation (with a separation efficiency up to 99%). In addition, the optimized membrane can be effectively employed to separate a surfactant-stabilized water-in-oil emulsion with a separation efficiency up to 90% and a high permeate flux (137.5 L m-2 h-1). Our TBR PU/GE nanofiber membrane is therefore a desirable material for the highly efficient separation of water-in-oil emulsions, and shows broad application prospects in the field of oil/water separation.

Yolk-porous shell nanospheres from siliver-decorated titanium dioxide and silicon dioxide as an enhanced visible-light photocatalyst with guaranteed shielding for organic carrier.

A nagging problem for the decompostion of photocatalyst organic carrier can be expected to be resolved by shielding effect from our yolk-porous shell nanospheres. The nanospheres were synthesized by a facile strategy: polyporrole (PPy) and silver were deposited together on TiO2 by chemical oxidative polymerization; then PPy/Ag-coated TiO2 nanoparticles were encapsulated in silicon dioxide (SiO2) shell with polyethylene glycol (PEG) as a pore-forming agent via sol-gel method based on hydrolysis of tetraethyl orthosilicate (TEOS). After removing intermediary PPy between yolk and shell by calcination and washing off PEG in shell, yolk-porous shell (SiO2@void@Ag/TiO2) nanospheres were formed. The voids in SiO2@void@Ag/TiO2 can serve as photocatalytic reactors. The channels in porous shell at outer layer provide passages for light transmission, dye molecule accessing and degradants out. More importantly, the euphotic and porous shell exhibited an impressive protection to organic carrier, lest unfavorable decomposition occurred. Yolk-porous shell nanospheres showed commendable performance with >99.5% of dye removal efficiency under 3 h visible light irradiation, higher than pristine TiO2 and Ag/TiO2 nanoparticles, due to the synergy effect of robust adsorption capacity and photocatalysis. Our work could provide a good strategy for developing novel carrier-based photocatalysts for environmental remediation application, which can be readily extended to the combination of other nanophotocatalysts and organic carriers for enhancing sustainable photocatalytic performance.

Pretreatment of water-based seed coating wastewater by combined coagulation and sponge-iron-catalyzed ozonation technology.

Coagulation-sedimentation combined with sponge iron/ozone (CS-SFe/O3) technology was applied to pretreat water-based seed coating wastewater (WSCW) from pesticide manufacturing. Coagulation with polyferric sulfate at a dosage of 1.5 g L-1 and a pH of 8.0 was effective, with color and chemical oxygen demand (COD) removal rates of 96.8 and 83.4%, respectively. SFe/O3 treatment further reduced the organic content in the effluents, especially concerning the degradation of aromatic pollutants, as demonstrated via ultraviolet-visible spectrophotometry (UV-vis), excitation-emission matrix (EEM) fluorescence spectrometry, and gas chromatography-mass spectrometry (GC/MS) analyses. The residual color and COD values of the effluent were 581.0 times and 640.0 mg L-1, respectively, under optimal conditions (ozone concentration of 0.48 mg L-1, SFe dosage of 20.0 g L-1, initial pH of 9.0, and reaction time of 30 min). Organic pollutants were also degraded by the high amounts of HO, which may have been generated via the transformation of ozone into HO on the SFe's surface and in the solution. Meanwhile, the biochemical oxygen demand (BOD5)/COD ratio of the WSCW increased, which indicates that the biodegradability improved significantly. The amount of iron leached from SFe particles was 4.5 mg L-1, which shows that the SFe catalyst has good stability. The operating cost of the combined CS-SFe/O3 technology was estimated at approximately 2.79 USD t-1. The results of this study suggest that the application of the combined CS-SFe/O3 technology in WSCW pretreatment can be beneficial for removing suspended solids, degrading recalcitrant pollutants, and enhancing biodegradability for the subsequent bioprocessing treatment.

Poly(vinylidene Fluoride-Hexafluoropropylene) Porous Membrane with Controllable Structure and Applications in Efficient Oil/Water Separation.

Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) porous membranes are fabricated via thermally induced phase separation (TIPS) with mixed diluent (dibutyl phthalate (DBP)/dioctyl phthalate (DOP)). The effects of mixed diluent are discussed in detail in term of morphology, mean pore size, selective wettability, etc. The results show that the membrane structure changes from spherulitic to bicontinuous with the change of DBP/DOP ratio. It is also found that the degree of crystallization decreases with the decrease of DBP/DOP ratio in mixed diluent. When liquid-liquid (L-L) phase separation precedes solid-liquid (S-L) phase separation, the obtained membranes have outstanding hydrophobicity and lipophilicity, excellent mechanical property. Additionally, the PVDF-HFP hybrid membranes are prepared with silica (SiO2) particles and the effect of SiO2 content on structure and properties is discussed. It is found that the PVDF-HFP hybrid membrane with 2 wt % SiO2 (M3-S2) has better properties and higher filtration rate and separation efficiency for surfactant-stabilized water-in-oil emulsion separation. Moreover, the membrane M3-S2 also exhibits excellent antifouling performance for long-running.

In situ reduced graphene oxide-based polyurethane sponge hollow tube for continuous oil removal from water surface.

Graphene oxide (GO) was prepared by using the natural graphite as raw materials via the modified Hummers' method and ultrasonic stripping method. GO was reduced online after its anchoring on the surface of polyurethane sponges by a dip-coating method, then in situ reduced graphene oxide-based polyurethane (IRGOPU) sponges were fabricated. The characterizations of IRGOPU sponges were investigated using Field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and contact angle measurement. The IRGOPU sponges had an adsorption capacity for a broad range of oils up to 21.7 ~ 55 g/g. A simulation experiment of large-scale oil spill using a simple IRGOPU sponge hollow tube component was designed. The process of continuous oil removal from water surface was quick and effective, and the oil/water separation efficiency could be up to 99.6%. The results indicated that the IRGOPU sponge hollow tube may be an optimum candidate for the oil/water separation of large-scale oil spill.

Preparation of PSF/FEP mixed matrix membrane with super hydrophobic surface for efficient water-in-oil emulsion separation.

Polysulfone (PSF)/fluorinated ethylene propylene (FEP) mixed matrix membranes (MMMs) with super hydrophobic surface were successfully fabricated via non-solvent induced phase separation (NIPS) method. The effects of FEP content on the morphology, roughness, wettability, pore size, and mechanical property of PSF/FEP MMMs were characterized by scanning electron microscope, confocal microscopy, contact angle goniometer, mercury porosimetry, and tensile testing instrument, respectively. When the FEP content was 9 wt%, the average roughness of M-4 reached 0.712 µm. Meanwhile, the water contact angle (CA) and the water sliding angle (SA) was 153.3° and 6.1°, respectively. M-4 showed super hydrophobicity with a micro- and nanoscale structure surface. Then, M-4 was used for separating of water-in-oil emulsion, showing high separation efficiency for water-in-kerosene and water-in-diesel emulsions of 99.79% and 99.47%, respectively. The flux and separation efficiency changed slightly after 10 cycles. Therefore, this study indicated that the obtained PSF/FEP MMM with super hydrophobic surface could be used for efficient water-in-oil emulsion separation.

A study on fabrication of PVDF-HFP/PTFE blend membranes with controllable and bicontinuous structure for highly effective water-in-oil emulsion separation.

In this study, poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP)/polytetrafluoroethylene (PTFE) blend membranes for water-in-oil emulsion separation were prepared via a thermally induced phase separation (TIPS) method using dibutyl phthalate (DBP) and dioctyl phthalate (DOP) as a mixed diluent. The effects of PTFE content on the obtained membranes' structure and properties were studied. The results showed that the surface structure of the obtained membranes without addition of PTFE particles was denser and the surface pores got smaller. The porosity, pore size and hydrophobicity obviously increased with the increase in PTFE content. However, the breaking elongation and breaking strength decreased with the increase of PTFE content. When the PTFE content was 10 wt%, the obtained membrane showed the highest separation efficiency for different kinds of water-in-oil emulsions. In addition, the antifouling performance of the obtained membranes was also studied for many times of reuse. This paper introduces an effective and facile method to prepare hydrophobic-oleophilic membranes for water-in-oil emulsion separation.

Evaluation of polypropylene and poly (butylmethacrylate-co-hydroxyethylmethacrylate) nonwoven material as oil absorbent.

Polypropylene (PP) and poly(butylmethacrylate-co-hydroxyethylmethacrylate) (PBMA-co-HEMA) nonwoven materials as oil absorbents have been fabricated for the first time via melt blown method. As-prepared nonwovens were investigated in terms of mass per unit area, density, air permeability, contact angle, and morphology observations for fiber diameter distribution and single fiber surface by a field emission scanning electron microscope. The nonwovens are demonstrated as fast and efficient absorbents for various kinds of oils with oil absorbency up to seven to ten times their own weight. The nonwovens show excellent water repulsion but superoleophilic properties. The measured contact angles for water and toluene are more than 127° and ca. 0°, respectively. The addition of PBMA-co-HEMA makes the nonwoven surface more hydrophobic while conserving superoleophilicity. Compared with PP nonwoven, broad diameter distribution of the blend nonwoven is attributed to poor melt fluidity of PBMA-co-HEMA. In terms of single fiber, coarse surface and the presence of point-like convexities lead to the fibers being more readily wetted by oil. More interesting, oil-water separation and oil recovery can be easily carried out by filter and absorption-desorption process, the recovered materials contained hardly any oil droplet and could be reused for next cycles.