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

Novel nanocomposite forward osmosis membranes for treating highly saline and oily wastewater with low fouling, high water flux and high selectivity

This study focuses on the design and synthesis of a new nanocomposite forward osmosis (FO) membrane that is able to separate highly saline and oily wastewater with low fouling, high water flux and high selectivity, in order to battle against global freshwater scarcity. A new design rationale of FO membrane is developed, which highlights that a genuine FO membrane must possess high antifouling capability as the requisite besides high water flux and high selectivity. Guided by this rationale, as-designed new nanocomposite FO membrane consists of a novel antifouling selective layer on top of a three-dimensionally (3D) interconnected porous support layer. Particularly, graphene oxide (GO) nanosheets assisted phase inversion technology is developed to fabricate the 3D interconnected porous support layer, on top of which dip-coating technique is employed to further construct the hydrogel selective layer in ultrathin thickness (~100 nm). The structures and properties of hydrogel selective layer are finely tuned towards both high antifouling capability and high selectivity, wherein the key role of chemical crosslinking is revealed. The best crosslinking agent is identified as glutaraldehyde; the optimum molecular weight of hydrogel is found to be 93 kDa; the optimum concentration of hydrogel solution is 0.25 wt%; the optimum coating time is 20 min; and more importantly, the optimum crosslinking degree is determined as 30%. Based upon all these optimized results, as-synthesized hydrogel FO membrane even with conventional phase inversion constructed support layer can already demonstrate the evident advantages in high selectivity and high antifouling capability, with its water flux/reverse salt flux ratio (JW/JS) 2.4 times higher than that of commercial HTI FO membrane (cellulose triacetate, woven). Furthermore, the support layer is optimized through introducing GO nanosheets to finely adjust the phase inversion process. Here, support layer in highly interconnected porous structure is the key to minimize FO’s intrinsic limitation on water flux i.e. internal concentration polarization (ICP) problem. For the first time, hydrophilic 2D graphitic nanomaterial is demonstrated able to transform the interior pore structure of the support layer from 1D connected to 3D interconnected. Based upon systematic optimization of GO assisted phase inversion process, an entirely new support layer structure with its interior pores highly interconnected in all three dimensions at micrometer scale is created. The formation mechanism of this 3D interconnected porous support layer is attributed to GO induced viscosity difference. Compared with conventional 1D pore connected support layer, this 3D pore interconnected support layer can reduce FO membrane structural parameter (S) by as much as 41.4%, leading to the enhancement in FO water flux (JW) by 72%. Meanwhile, the JW of as-synthesized nanocomposite membrane arrives at 30.5 L m-2 h-1 at FO mode with draw solution of 1.5 M Na2SO4, which is 3.1 times higher than that of HTI membrane under identical operational conditions. Therefore, for the first time, micrometer-scale 3D interconnected porous support layer that is able to break the ICP bottleneck and thus achieve high FO water flux is successfully synthesized with dominant membrane manufacture process (i.e. phase inversion). Most importantly, as-synthesized nanocomposite FO membrane is systematically investigated for its ability to accomplish simultaneous desalination and oil/water separation of highly saline and oily wastewater. FO separation results indicate that this nanocomposite membrane can simultaneously desalinate and deoil hypersaline oil-in-water emulsion with more than three times higher water flux, higher removal efficiencies of both oil and salts (>99.9% for oil and >99.7% for multivalent salt ions), and significantly lower membrane fouling (>80% lower water flux reduction ratio) compared with HTI membrane. The further operation results reveal that this new FO membrane is remarkably superior to HTI membrane in both resistance to salinity induced fouling aggravation and long term antifouling durability. In summary, this is the first study that explores and optimizes the capability of hydrogel macromolecule as a new selective layer for FO membrane. Furthermore, it creates a micrometer-scale 3D interconnected porous nanocomposite support layer to break ICP bottleneck with dominant membrane manufacture process (i.e. phase inversion). Moreover, it also achieves simultaneous desalination and oil/water separation of highly saline and oily wastewater by as-synthesized new FO membrane with low fouling, high water flux and high selectivity. This study points out a new direction for the development of genuine FO membrane and makes a significant impetus to the industrialization of FO technology in order to address global freshwater scarcity.Doctor of Philosophy (IGS

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.Published versio

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.Published versio

Fine-tuning selective layer architecture of hydrogel membrane towards high separation performances for engineered osmosis

Ultrathin and/or ultrasmooth selective layer is one of the paramount goals in membrane realm for maximizing separation efficiency and/or minimizing fouling tendency. Towards this goal, the architecture of hydrogel selective layer is finely tuned for the first time for improving engineered osmosis (EO) membrane performance. Through delicately controlling synthesis parameters, ultrathin selective layer as thin as 30 nm, and ultrasmooth selective layer with sub-1 nm roughness (the smoothest EO membrane in literature) are successfully synthesized respectively. Analysis of reverse osmosis (RO) experimental results reveals hydrogel layer resistance to water permeation is linearly reduced by 1.40 × 1013 m−1 as the layer is tailored thinner per 10 nm, which leads to the remarkable enhancement of water permeability by ~10 times from 0.49 L m−2 h−1 bar−1 of 500 nm thickness to 4.75 L m−2 h−1 bar−1 of 30 nm thickness. Pressure-retarded osmosis (PRO) and forward osmosis (FO) tests indicate 45-nm-thick hydrogel layer achieves the maximum separation efficiency in terms of specific water flux (JW/JS). Moreover, the mechanism for tuning hydrogel layer architecture is discussed on the basis of microscopic characterizations. This study sheds new light on ultrathin and ultrasmooth selective layer for promoting EO membrane to smartly tackle different kinds of wastewater

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.Published versio

Structural colour enhanced microfluidics

マイクロ流体デバイスの製造に革新をもたらす新手法. 京都大学プレスリリース. 2022-05-19.New process revolutionizes microfluidic fabrication. 京都大学プレスリリース. 2022-05-19.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

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 (<i>J</i>_W/<i>J</i>_S). 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

Nanodiamond mediated interfacial polymerization for high performance nanofiltration membrane

Introducing nanomaterial in interfacial polymerization (IP) system for nanofiltration (NF) membrane synthesis has witnessed a remarkable performance enhancement thus drawing intensive attention. However, the underlying mechanism for nanomaterial induced performance enhancement is still unclear due to the lack of study on nanoparticle dispersity and architecture at polymerization interface. Using nanodiamond (ND) as the example, this study demonstrates nanoparticle undergoes aggregation preferably at the reaction interface and the architecture of ND particles has a direct impact on membrane structure and performance. Through proactively controlling the aggregation extent while employing these ND clusters as the nano-template, the feature morphology of NF membrane is transformed from nodules to ridges at the nanoscale. Such transformation generates a significant augmentation of effective membrane area, leading to the increase of water permeance by 70%. With a low amount of nanodiamond addition (<0.1 wt%), the NF membrane can achieve a high water permeance of 150 L m−2 h−1 MPa−1 with ~98% rejection of Na2SO4. Moreover, the introduction of nanodiamond makes the nanofiltration membrane more hydrophilic, with water contact angle decreased from 50° to 35°. The comparison with contemporary nanofiller studies indicates our nanodiamond strategy yields some of the best performance enhancement

Overcoming humidity-induced swelling of graphene oxide-based hydrogen membranes using charge-compensating nanodiamonds

Graphene oxide (GO) can form ultrapermeable and ultraselective membranes that are promising for various gas separation applications, including hydrogen purification. However, GO films lose their attractive separation properties in humid conditions. Here we show that incorporating positively charged nanodiamonds (ND+s) into GO nanolaminates leads to humidity-resistant, yet high-performing, membranes. While native GO membranes fail at a single run, the GO/ND+ composite retains up to ~90% of GO’s H2 selectivity against CO2 after several cycles under an aggressive humidity test. The addition of negatively charged ND to GO brought no such stabilization, suggesting that charge compensation acts as the main mechanism conferring humidity resistance, where ND+s neutralize the negative charge GO sheets. We observed a similar but inferior stabilization effect when positively charged polyhedral oligomeric silsesquioxane replaces ND+. The demonstrated material platform offers a solution for separating H2 gas from its usually humid mixtures generated from fossil fuel sources or water splitting