•A fluorochemical (FC) coating showed uncommon water wetting in additized fuel.•The coating leveraged coalescence separation of emulsified water from the fuel.•The enhanced separation was due to the interaction between the FC and surfactants.•The unique chemistry of the FC with both soft and hard segments was unfolded.•The discovery opened the door for designing new chemistry for coalescence materials.Emulsified water separation from ultralow sulfur diesel fuel on board a vehicle is critical for modern diesel engine protection. However, such a separation poses great challenges to the commonly used coalescence filter media. These media must be designed to be able to cope with surfactants in the fuel typically by chemical surface modification. In this work, we examined several chemical coatings on glass slide and studied their response to water wetting in both air and diesel fuels containing monoolein, a designated fuel additive for SAE J1488 test standard. It was found that one coating behaved dramatically differently than others. This coating is a fluorochemical (FC) with undisclosed chemistry, which leads to uncommon but favorable water wetting under fuel that further boosts coalescence separation of emulsified water with a commercial stainless steel filter felt. The feature and the chemistry of the coating were then revealed and rationalized with SEM, XPS, FTIR, NMR, GPC-LS and MALDI-TOF MS analyses. Quartz crystal microbalance (QCM) was also used to determine the characteristics of monoolein adsorption on the coatings. The results show that the FC coating chemistry is unique as it provides in one molecule a hard hydrophobic segment and a soft hydrophilic segment, both of which are desired for effective coalescence separation in light of easy capture of small droplets and easy release of gown droplets, even subject to the presence of surfactants in the fuel. Such a chemistry also results in surprisingly intensive adsorption of monoolein. Based on further observation of the relatively faster coalescene of two water droplets under static conditions in fuel on the FC coating surface, it is speculated that the strong adsorption forces the surfactant molecules to be pulled away from the fuel/water interface, thus triggering the subsequent coalescence. It is also postulated that the unique chemistry allows the adsorbed surfactant molecules to re-distribute, leading to the very wetting phenomenon first time observed.An unknown coating chemistry, which presents odd wetting behavior under surfactant-containing fuel oil, was found to benefit coalescence separation of surfactant stabilized water-in-fuel emulsions, and is therefore unfolded to reveal its working mechanism.

•Resin bonded filter media were prepared with in situ generated surface roughness.•Media wettability was fine-tuned by resin solidification control for emulsification.•Media were able to coalesce 3 surfactant-stabilized oil-in-water emulsions.•Separation was surfactant type dependent due to differed adsorption intensity.•Ethanol was identified as an alternative solvent to IPA for resin emulsification.Reported here is a facile resin emulsification method of treating polyurethane enforced filter media by controlling the initial level of solvent volatilization for resin solidification. The treated media are endowed with varying degrees of lipophilicity as determined by their lipophilic to hydrophilic (L/H) values. An optimized treatment condition was pinned for coalescence separation of surfactant-stabilized oil-in-water emulsions using a surfactant free emulsion as the bench mark. The starting separation efficiency was found to depend on the type of surfactant involved in the order of non-ionic surfactant Tween 80 > cationic surfactant cetyl trimethyl ammonium bromide (CTAB) > anionic surfactant sodium dodecyl benzene sulfonate (SDBS). Quartz crystal microbalance (QCM) experiments showed that Tween 80 had the largest adsorption on the polyurethane coating, while least adsorption occurred to SDBS, and mediocre adsorption to CTAB. However, Tween 80 resulted in the lowest time-weighted averaged efficiency as compared to the other surfactants that barely caused any efficiency changes with filtration time. To make the resin emulsification treatment more environmental friendly, more polar solvents were tested, and ethanol was identified as a good alternative to isopropanol.

•Thiourea was grafted to PVDF resin through Michael addition reaction.•Thick membranes were fabricated using the resin and pore size was tailored.•Membranes used as membrane chromatography successfully adsorbed Au(III).•Pore size distribution affected the performance of membrane chromatography.•A new mathematical model considering pore polydispersity was proposed.Thick and hydrophilic microporous poly(vinylidene fluoride) (PVDF) affinity membranes were prepared for low-concentration gold separation by grafting thiourea on alkali treated PVDF resin. The modified polymer was easily cast into membranes by non-solvent induced phase separation through two coagulation processes, and the addition of N-methyl-2pyrrolidone into the second coagulation bath improved the pore size distribution effectively. The grafted polymer and membrane were characterized by FTIR, Raman, 1H NMR, XPS, SEM and pore size distribution measurement. Static adsorption of Au (III) with the membranes followed pseudo-second order kinetics and Langmuir isotherm. Dynamic adsorption was investigated by using stacked membranes in the form of a membrane chromatography. The results showed that increasing the number of membrane layers improved the membrane bed utilization, which was attributed to the increased adsorption sites and a combined effect of reduced average membrane pore size and narrowed pore size distribution (PSD). The effect of PSD on performance of the membrane chromatography was further separated from that of the mean pore size, and it was shown that narrower PSD indeed was favorable. A new mathematical model based on dispersive mass transfer through the membrane pores and incorporating PSD was established. The model was found to be able to predict the membrane breakthrough behavior very well. Finally, the elution performance of gold laden membrane was studied, and an optimized formulation of the eluent consisting of thiourea and HCl was determined.Download high-res image (69KB)Download full-size image

•A spiral wound module of electrospun chitosan nanofiber membranes was fabricated.•Superhydrophilic surface of the membrane brings about high flux and low pressure drop.•Loading capacity was dependent on flow rate and nanofiber deposition density.•The module exhibited high adsorption capacity and selectivity for Cr (VI).•The module had advantages over NF in light of rejection, flux and ease of operation.A re-generable spiral wound module of affinitive electrospun chitosan nanofiber membranes was fabricated, and the feasibility of the module for treating Cr (VI) contaminated water was studied. The effect of flow rate, initial Cr (VI) concentration, chitosan nanofiber deposition density, and other metal ions on Cr (VI) adsorption was investigated in detail. It was found that the loading capacity of the module was dependent on flow rate and nanofiber deposition density, but independent on initial Cr (VI) concentration. Lower flow rate led to higher adsorption capacity. The maximum adsorption capacity obtained with 2 g/m2 nanofiber membranes in the module was 20.5 mg/g at 10% breakthrough. The module could also adsorb Cu (II), Cd (II) and Pb (II) ions separately but showed good selectivity to Cr (VI) when these metal ions were coexistent. The dynamic adsorption behavior of the module was better fitted by Dose-Response model. Furthermore, the separation of Cr (VI) by commercial nanofiltration (NF) membranes was examined and compared with the spiral wound nanofiber membranes constructed in this work. The result showed the latter had several advantages over the former in terms of rejection, flux and ease of operation.

•Microwave irradiation was applied to produce nano-TiO2/cellulose composite fibers.•100 nm raspberry-like TiO2 composed of 10 nm primary particles were formed.•Composites fabricated by in situ TiO2 growth outperformed due to large surface area.•Composites with hierarchical surface structure lead to rapid adsorption of Pb2+.•The adsorption was due to electrostatic interaction and the fibers were reusable.Cellulose fibers were used as substrates to induce the formation of nano-TiO2 via heterogeneous titanium oxysulfate hydrolysis under microwave irradiation. The microwave provided fast heating for the one-pot reaction at 90 °C and contributed to the generation of 10 nm anatase TiO2 nanoparticles. These spherical particles further fused into 100 nm raspberry-like mesoporous TiO2 agglomerates uniformly distributed on the cellulose surface. The composite material was able to adsorb Pb2+ very rapidly from simulated wastewater with a maximum capacity of 42.5 mg/g. The adsorption, characterized by pseudo-second order kinetics and Freundlich isotherm, was attributed to the reaction between the hydroxyl groups of TiO2 and Pb2+ to form PbO bond, as indicated by XPS analysis. The adsorbent can be easily regenerated for a number of times without significant reduction in adsorption performances.

•Thin chitosan membranes with symmetric and interconnected pore structure were prepared by an easy immersion-precipitation method using silica as porogen.•Cu(II) adsorption onto the membrane has pseudo-second order kinetics and Toth isotherm.•The performance of the adsorber was thickness dependent but flow rate independent.•The regeneration of the adsorber is simple and easy for multiple-use.•BDST and Thomas models derived for packed columns are also applicable to the membrane adsorber.Thin chitosan membranes with symmetric and interconnected pore structure were prepared using silica as porogen, and their physical properties including pore structure, pore size distribution, porosity and water affinity were analyzed. The membrane showed a maximum Cu(II) adsorption capacity of 87.5 mg/g in static adsorption, and the adsorption fitted pseudo-second order kinetics and Toth adsorption isotherm. The membranes were then stacked in layers as an adsorber to remove small concentration Cu(II) from water dynamically. At feed concentration of 5 mg/L, the adsorber could retain Cu(II) effectively when its thickness reached over 200 μm, and the performance was further improved by using more membranes layers. Within a certain limit, the adsorber showed a ‘flow-independent’ loading behavior, an indication of fast mass transfer inside the membrane. The adsorption process was correlated well with bed depth service time (BDST) model, Thomas model and Yoon and Nelson model, and the adsorber was also found to be regenerable and re-usable.

Coalescence separation of oil dispersions of various hydrometallurgical extractants and solvents was studied using in-house-developed fibrous media that showed good separation performance toward four out of six common extraction reagents suspended in water as small oil droplets. The separation was affected by oil/water interfacial tension and their density difference. Further, using kerosene as the model oil, the separation was performed on a flatsheet bench to investigate the effect of other factors including the media thickness, influent oil concentration, and media face velocity. Media with larger thickness resulted in better separation and, correspondingly, higher pressure drop. The influent oil concentration and media face velocity were mutual constraints to the separation efficiency. When the oil concentration was low, the time-weighted average separation efficiency stayed the same or increased with the velocity; when it was high, the opposite trend prevailed.

•75 nm diameter chitosan nanofibers electrospun produced.•Enhanced Cr(VI) adsorption delivered by chitosan nanofibers.•Nanofiber's adsorption by diffusion limited due to fiber packing.•Most Cr(VI) co-anions had little or no effect on the adsorption except for SO42−.•Amino and hydroxyl groups of chitosan were both engaged in the adsorption.Stacked chitosan nanofibers with an average diameter of 75 nm were successfully produced by electrospinning using 5 wt% chitosan in acetic acid as the spinning solution. The fibers were then cross-linked with glutaraldehyde to remove chromium [Cr(VI)] from water via static adsorption. It was found that the adsorption correlated well with pseudo-second order kinetic model, and followed a mixed isotherm of Freundlich and Langmuir. The maximum nanofibers adsorption capacity was 131.58 mg/g, more than doubled that of chitosan powders. Common co-ions such as Cl−, NO3−, Na+, Ca2+ and Mg2+ had little or no effect on the adsorption but SO42− was an exception. Fourier transform infrared spectroscopy and X-ray photoelectron spectrophotometer analyses indicated that both amino and hydroxyl groups of chitosan were engaged in the adsorption.

•Nonwoven filter mats were fabricated and enforced with resin binders.•Unique roughening treatment was applied to the mats.•Treated mats showed excellent coalescing separation of 4 oil-in-water emulsions.•Mats pre-saturated with oils still performed well.•Good separation was attributed to balanced mat surface wettability.Oily wastewater is a major problem in industries that can cause severe environmental pollution without proper treatment. In this paper, an easily fabricated, robust and durable nonwoven fibrous filter mat was prepared for coalescence filtration of four kinds of oil-in-water emulsions, namely hexadecane/water, octane/water, soybean oil/water and engine oil/water. An aromatic thermoplastic polyurethane resin (TPU) was selected to bind the fibers together for structure integrity of the mat. Special roughening treatment to the mat was conducted to deliver the required wettability for effective coalescence separation of these emulsions. The filter mat thus prepared reached a tensile strength of 2.99 MPa, 20 times stronger than that of the pristine mat. The mat surface was made both hydrophilic and superoleophilic, allowing it to have separation efficiency as high as 99.61% in a single pass flow. Moreover, even pre-saturated with oil, the mat remained effective in separation and permitted high flow, proving its high caliber for potential industrial applications.

Commercial stainless steel felt was endowed with LBL self-assembly of dual size nano-SiO2 particles to have a hierarchical micro/nano surface structure. The pore size of the felt was tailored at the same time by tuning the assembling cycles. Chemical vapor deposition (CVD) of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) at two concentration levels was applied to the roughened felt to render it both hydrophobic/superhydrophobic and oleophobic. The felt thus prepared was wettable by oil underwater, which allowed it to be effective as a coalescing material for separating 4 kinds of oil-in-water emulsions. The nanometer-thick POTS coating was durable for months. The coalescence separation efficiency was found to be dependent on both pore size and surface wettability of the felt in air. It was less sensitive to pore size change when the surface was more hydrophobic and oleophobic (amphiphobic). When the pore size was kept constant, more amphiphobic felt was less efficient for separation. When the surface turned superhydrophobic, the separation became better as the pore size was reduced. These findings provide new insights for designing better coalescence materials, especially when the effects of surface wettability and pore size are intermingled.

Controlled assembly of nanoscale building units to form special micro-/nanostructures is of interest for achieving desired properties in many practical applications. The raspberry- or strawberry-like hierarchical structure with multi-level dimensions is one example of special surface wettability design. In this work, a series of coatings with hierarchical nanostructure and dual roughness are constructed on sintered stainless steel mesh and stainless steel fiber felt via layer-by-layer self-assembly of SiO2 nanoparticles having different sizes. The surface is then chemically treated to obtain the wetting properties needed for intended separation of oil from water. The surface morphology of the coatings is observed using scanning electron microscopy and atomic force microscopy. The surface wetting properties are investigated by measuring the coatings' water and oil contact angle in air and under water. The results show that the stainless steel mesh with such coatings has superhydrophobicity, and thus can efficiently separate regular oil–water mixtures. Furthermore, the stainless steel fiber felt treated with similar coatings can also separate oil-in-water emulsions through the non-sieving coalescence mechanism, achieving an oil–water separation efficiency as high as 99.4%.

•Spindle TiO2 nanocrystals were in situ synthesized on cellulose fibers (CF).•Cellulose acted as a template to direct TiO2 crystal growth with orientation.•Minute amount of spindle TiO2 enhanced Pb2+ adsorption capacity.•Dynamic adsorption with TiO2/CF membrane outperformed CF membrane significantly.TiO2/cellulose nanocomposite was synthesized by in situ generation of titanium dioxide (TiO2) nanocrystals on cellulose fibers (CF) via facile hydrolysis of TiOSO4. Cellulose was intended as a scaffold to immobilize TiO2 nanoparticles (NPs), but turned out surprisingly to be also a chemical template that directed the crystal growth. As a result, spindle rutile TiO2 crystals were nicely formed on the surface of cellulose. These crystals were further controlled to disperse uniformly without agglomeration for better use of their surface area to adsorb heavy metals. The TiO2/CF composite showed enhanced adsorption capacity, good regenerability and selectivity for lead (Pb2+) removal. In addition, the composite fibers were readily fabricated into a nonwoven filter bed through which dynamic filtration experiment was conducted. A 12-fold increase in filtered bed volume was achieved for TiO2/CF bed compared with pure CF bed before breakthrough took place. This work provides a green pathway for fabricating low cost, high efficiency and engineering application possible nanosorbents for water decontamination.

Controlled assembly of nanoscale building units to form special micro-/nanostructures is of interest for achieving desired properties in many practical applications. The raspberry- or strawberry-like hierarchical structure with multi-level dimensions is one example of special surface wettability design. In this work, a series of coatings with hierarchical nanostructure and dual roughness are constructed on sintered stainless steel mesh and stainless steel fiber felt via layer-by-layer self-assembly of SiO2 nanoparticles having different sizes. The surface is then chemically treated to obtain the wetting properties needed for intended separation of oil from water. The surface morphology of the coatings is observed using scanning electron microscopy and atomic force microscopy. The surface wetting properties are investigated by measuring the coatings' water and oil contact angle in air and under water. The results show that the stainless steel mesh with such coatings has superhydrophobicity, and thus can efficiently separate regular oil–water mixtures. Furthermore, the stainless steel fiber felt treated with similar coatings can also separate oil-in-water emulsions through the non-sieving coalescence mechanism, achieving an oil–water separation efficiency as high as 99.4%.