Structural colour using organized microfibrillation in glassy polymer films.

The formation of microscopic cavities and microfibrils at stress hotspots in polymers is typically undesirable and is a contributor to material failure. This type of stress crazing is accelerated by solvents that are typically weak enough not to dissolve the polymer substantially, but which permeate and plasticize the polymer to facilitate the cavity and microfibril formation process1-3. Here we show that microfibril and cavity formation in polymer films can be controlled and harnessed using standing-wave optics to design a periodic stress field within the film4. We can then develop the periodic stress field with a weak solvent to create alternating layers of cavity and microfibril-filled polymers, in a process that we call organized stress microfibrillation. These multi-layered porous structures show structural colour across the full visible spectrum, and the colour can be tuned by varying the temperature and solvent conditions under which the films are developed. By further use of standard lithographic and masking tools, the organized stress microfibrillation process becomes an inkless, large-scale colour printing process generating images at resolutions of up to 14,000 dots per inch on a number of flexible and transparent formats5,6.

Superior Antifouling Capability of Hydrogel Forward Osmosis Membrane for Treating Wastewaters with High Concentration of Organic Foulants.

Wastewaters with high concentrations of organic pollutants pose a great challenge for membrane filtration due to their severe fouling propensity. In this study, a hydrogel forward osmosis (FO) membrane is explored for treating wastewaters of high concentration organic pollutants. This FO membrane has an ultrathin hydrogel selective layer, which is highly hydrophilic (water contact angle as low as 18°) and smooth (surface roughness <5 nm). Investigated with typical organic foulants (protein, alginate, humic acid, and oil) of high concentration (2000-20 000 mg/L), this hydrogel FO membrane exhibits remarkably superior antifouling capability, with its water flux decline ratio lower than a quarter that of commercial FO membrane under identical experimental conditions. The foulants on hydrogel membrane surface can be easily removed by simple physical cleaning without any chemical usage. At the same time, this hydrogel FO membrane achieves ∼2 times higher separation efficiency than commercial FO membrane in terms of specific water flux (JW/JS). The antifouling capability and separation efficiency of this FO membrane can be flexibly tailored during selective layer fabrication process. This study opens a new avenue for the treatment of high-strength organic wastewaters by developing a highly antifouling hydrogel-based FO membrane.

Graphene oxide-fullerene nanocomposite laminates for efficient hydrogen purification.

Graphene oxide (GO) with its unique two-dimensional structure offers an emerging platform for designing advanced gas separation membranes that allow for highly selective transport of hydrogen molecules. Nevertheless, further tuning of the interlayer spacing of GO laminates and its effect on membrane separation efficiency remains to be explored. Here, positively charged fullerene C60 derivatives are electrostatically bonded to the surface of GO sheets in order to manipulate the interlayer spacing between GO nanolaminates. The as-prepared GO-C60 membranes have a high H2 permeance of 3370 GPU (gas permeance units) and an H2/CO2 selectivity of 59. The gas separation selectivity is almost twice that of flat GO membranes because of the role of fullerene.

Structural colour enhanced microfluidics.

Advances in microfluidic technology towards flexibility, transparency, functionality, wearability, scale reduction or complexity enhancement are currently limited by choices in materials and assembly methods. Organized microfibrillation is a method for optically printing well-defined porosity into thin polymer films with ultrahigh resolution. Here we demonstrate this method to create self-enclosed microfluidic devices with a few simple steps, in a number of flexible and transparent formats. Structural colour, a property of organized microfibrillation, becomes an intrinsic feature of these microfluidic devices, enabling in-situ sensing capability. Since the system fluid dynamics are dependent on the internal pore size, capillary flow is shown to become characterized by structural colour, while independent of channel dimension, irrespective of whether devices are printed at the centimetre or micrometre scale. Moreover, the capability of generating and combining different internal porosities enables the OM microfluidics to be used for pore-size based applications, as demonstrated by separation of biomolecular mixtures.

Start-up control for nitrogen removal via nitrite under low temperature conditions for swine wastewater treatment in sequencing batch reactors.

To achieve nitrification/denitrification via nitrite (NO2-N) successfully under low temperature conditions, aerobic duration (AD) control and free ammonia (FA) control strategies were carried out in the start-up period of real swine wastewater treatment by two sequencing batch reactors (SBRs) operated in parallel. Over the entire 270 days of operation, NO2-N/ (NO2-N + NO3-N) accumulation in each reactor finally reached 73.3 % (AD control) and 80.4 % (FA control) respectively, when the temperature decreased from 25 °C to 12 °C. Meanwhile, the chemical oxygen demand (COD) and total nitrogen (TN) removal ratios were 92.1 % and 95.1 % respectively under AD control, and 92.2 % and 95.0 % under the FA control strategy. The satisfactory performance indicated that both strategies could help activated sludge to counteract the influence of low temperature well, reflecting the fact that the microbial communities in both reactors were not overly affected. Psychrophiles belonging to Bacteroidetes, γ-Proteobacteria, and Firmicutes were dominant and identified by construction of 16 s rRNA and amoA gene clone libraries. Although microbial community formation was influenced by decreasing temperature, the different strategies led to differences in community shift approaches and structures, particularly in terms of ammonia oxidizing bacteria (AOB). Some of the genera were washed out in AD control, while operational taxonomic units (OTUs) identified as Nitrosomonas eutropha and N. nitrosa could noticeably increase and quickly outcompete others under the FA control strategy.

Efficient Oil/Water Separation Membrane Derived from Super-Flexible and Superhydrophilic Core-Shell Organic/Inorganic Nanofibrous Architectures.

To address the worldwide oil and water separation issue, a novel approach was inspired by natural phenomena to synthesize superhydrophilic and underwater superoleophobic organic/inorganic nanofibrous membranes via a scale up fabrication approach. The synthesized membranes possess a delicate organic core of PVDF-HFP and an inorganic shell of a CuO nanosheet structure, which endows super-flexible properties owing to the merits of PVDF-HFP backbones, and superhydrophilic functions contributed by the extremely rough surface of a CuO nanosheet anchored on flexible PVDF-HFP. Such an organic core and inorganic shell architecture not only functionalizes membrane performance in terms of antifouling, high flux, and low energy consumption, but also extends the lifespan by enhancing its mechanical strength and alkaline resistance to broaden its applicability. The resultant membrane exhibits good oil/water separation efficiency higher than 99.7%, as well as excellent anti-fouling properties for various oil/water mixtures. Considering the intrinsic structural innovation and its integrated advantages, this core-shell nanofibrous membrane is believed to be promising for oil/water separation, and this facile approach is also easy for scaled up manufacturing of functional organic/inorganic nanofibrous membranes with insightful benefits for industrial wastewater treatment, sensors, energy production, and many other related areas.

A new nano-engineered hierarchical membrane for concurrent removal of surfactant and oil from oil-in-water nanoemulsion.

Surfactant stabilized oil-in-water nanoemulsions pose a severe threat to both the environment and human health. Recent development of membrane filtration technology has enabled efficient oil removal from oil/water nanoemulsion, however, the concurrent removal of surfactant and oil remains unsolved because the existing filtration membranes still suffer from low surfactant removal rate and serious surfactant-induced fouling issue. In this study, to realize the concurrent removal of surfactant and oil from nanoemulsion, a novel hierarchically-structured membrane is designed with a nanostructured selective layer on top of a microstructured support layer. The physical and chemical properties of the overall membrane, including wettability, surface roughness, electric charge, thickness and structures, are delicately tailored through a nano-engineered fabrication process, that is, graphene oxide (GO) nanosheet assisted phase inversion coupled with surface functionalization. Compared with the membrane fabricated by conventional phase inversion, this novel membrane has four times higher water flux, significantly higher rejections of both oil (~99.9%) and surfactant (as high as 93.5%), and two thirds lower fouling ratio when treating surfactant stabilized oil-in-water nanoemulsion. Due to its excellent performances and facile fabrication process, this nano-engineered membrane is expected to have wide practical applications in the oil/water separation fields of environmental protection and water purification.

A new nanocomposite forward osmosis membrane custom-designed for treating shale gas wastewater.

Managing the wastewater discharged from oil and shale gas fields is a big challenge, because this kind of wastewater is normally polluted by high contents of both oils and salts. Conventional pressure-driven membranes experience little success for treating this wastewater because of either severe membrane fouling or incapability of desalination. In this study, we designed a new nanocomposite forward osmosis (FO) membrane for accomplishing simultaneous oil/water separation and desalination. This nanocomposite FO membrane is composed of an oil-repelling and salt-rejecting hydrogel selective layer on top of a graphene oxide (GO) nanosheets infused polymeric support layer. The hydrogel selective layer demonstrates strong underwater oleophobicity that leads to superior anti-fouling capability under various oil/water emulsions, and the infused GO in support layer can significantly mitigate internal concentration polarization (ICP) through reducing FO membrane structural parameter by as much as 20%. Compared with commercial FO membrane, this new FO membrane demonstrates more than three times higher water flux, higher removals for oil and salts (>99.9% for oil and >99.7% for multivalent ions) and significantly lower fouling tendency when investigated with simulated shale gas wastewater. These combined merits will endorse this new FO membrane with wide applications in treating highly saline and oily wastewaters.