Yanlei Su

Efficient Wastewater Treatment by Membranes through Constructing Tunable Antifouling Membrane Surfaces

In the present study, a facile in situ approach for constructing tunable amphiphilic or hydrophilic antifouling membrane surfaces was demonstrated by exquisitely manipulating the microphase separation and surface segregation behavior of the tailor-made ternary amphiphilic block copolymers during the commonly utilized wet phase inversion membrane-formation process. Under dead-end filtration for oily wastewater treatment, the membrane with amphiphilic surface exhibited over 99.5% retention ratio of chemical oxygen demand (COD) without appreciable membrane fouling: the water permeation flux was slightly decreased during operation (total flux decline was 6.8%) and almost completely recovered to the initial value (flux recovery ratio was more than 99.0%) after simple hydraulic washing. While for the proteins-containing wastewater treatment, the membrane with hydrophilic surface exhibited about 52.6% COD retention ratio and superior antifouling performance: only 17.0% total flux decline and also more than 99.0% flux recovery ratio. Hopefully, the present approach can be developed as a competitive platform technology for the preparation of robust and versatile antifouling membrane, leading to the high process efficiency of wastewater treatments.

Antifouling, High-Flux Nanofiltration Membranes Enabled by Dual Functional Polydopamine

A facile method for fabricating antifouling and high-flux nanofiltration (NF) membranes was developed based on bioinspired polydopamine (PDA). Polyethersulfone (PES) ultrafiltration membrane as the support was first deposited a thin PDA layer and then chemically modified by a new kind of fluorinated polyamine via Michael addition reaction between fluorinated polyamine and quinone groups of PDA. PDA coating significantly reduced the pore sizes of the PES support membrane and endowed the NF membrane with high separation performance (flux about 46.1 L/(m(2) h) under 0.1 MPa, molecular weight cutoff of about 780 Da). The grafted fluorinated polyamine on the PDA layer could form low free energy microdomains to impede the accumulation/coalescence of foulants and lower the adhesion force between foulants and the membrane, rendering the membrane surface with prominent fouling-release property. When foulant solutions (including bovine serum albumin, oil and humic acid) were filtered, the resultant NF membrane exhibited excellent antifouling properties (the minimal value of total flux decline ratio was ∼8.9%, and the flux recovery ratio reached 98.6%). It is also found that the structural stability of the NF membrane could be significantly enhanced due to the covalent bond and other intermolecular interactions between the PDA layer and the PES support.

Protein fouling resistant membrane prepared by amphiphilic pegylated polyethersulfone.

A mild and facile grafting of poly(ether glycol) methyl ether methacrylate (PEGMA) monomers onto polyethersulfone (PES) was carried out. Then, the PES-g-PEGMA membranes with integrally anisotropic morphology were fabricated through the coupling of non-solvent induced phase inversion and surface segregation. Compared with PES control membrane, the surface hydrophilicity of PES-g-PEGMA membranes was remarkably enhanced due to the drastic enrichment of poly(ethylene glycol) (PEG) segments on the membrane surface; protein adsorption was significantly inhibited due to the hydrogen bonding interactions between hydrophilic groups and water molecules. Ultrafiltration experiments were used to assess the permeability and protein fouling resistance of the PES-g-PEGMA membranes. It was found that the PES-g-PEGMA membranes with higher surface coverage of PEG segments displayed stronger antibiofouling property. Moreover, the stable antibiofouling property for PES-g-PEGMA membranes was acquired due to covalent bonding interactions between hydrophilic PEGMA side chains and PES main chains.

Free-Standing Graphene Oxide-Palygorskite Nanohybrid Membrane for Oil/Water Separation.

Graphene oxide (GO) is an emerging kind of building block for advanced membranes with tunable passageway for water molecules. To synergistically manipulate the channel and surface structures/properties of GO-based membranes, the different building blocks are combined and the specific interfacial interactions are designed in this study. With vacuum-assisted filtration self-assembly, palygorskite nanorods are intercalated into adjacent GO nanosheets, and GO nanosheets are assembled into laminate structures through π-π stacking and cation cross-linking. The palygorskite nanorods in the free-standing GOP nanohybrid membranes take a 3-fold role, rendering enlarged mass transfer channels, elevating hydration capacity, and creating hierarchical nanostructures of membrane surfaces. Accordingly, the permeate fluxes from 267 L/(m(2) h) for GO membrane to 1867 L/(m(2) h) for GOP membrane. The hydration capacity and hierarchical nanostructures synergistically endow GOP membranes with underwater superoleophobic and low oil-adhesive water/membrane interfaces. Moreover, by rationally imparting chemical and physical joint defense mechanisms, the GOP membranes exhibit outstanding separation performance and antifouling properties for various oil-in-water emulsion systems (with different concentration, pH, or oil species). The high water permeability, high separation efficiency, as well as superior anti-oil-fouling properties of GOP membranes enlighten the great prospects of graphene-based nanostructured materials in water purification and wastewater treatment.

Zwitterionic materials for antifouling membrane surface construction.

UNLABELLED Membrane separation processes are often perplexed by severe and ubiquitous membrane fouling. Zwitterionic materials, keeping electric neutrality with equivalent positive and negative charged groups, are well known for their superior antifouling properties and have been broadly utilized to construct antifouling surfaces for medical devices, biosensors and marine coatings applications. In recent years, zwitterionic materials have been more and more frequently utilized for constructing antifouling membrane surfaces. In this review, the antifouling mechanisms of zwitterionic materials as well as their biomimetic prototypes in cell membranes will be discussed, followed by the survey of common approaches to incorporate zwitterionic materials onto membrane surfaces including surface grafting, surface segregation, biomimetic adhesion, surface coating and so on. The potential applications of these antifouling membranes are also embedded. Finally, we will present a brief perspective on the future development of zwitterionic materials modified antifouling membranes. STATEMENT OF SIGNIFICANCE Membrane fouling is a severe problem hampering the application of membrane separation technology. The properties of membrane surfaces play a critical role in membrane fouling and antifouling behavior/performance. Antifouling membrane surface construction has evolved as a hot research issue for the development of membrane processes. Zwitterionic modification of membrane surfaces has been recognized as an effective strategy to resist membrane fouling. This review summarizes the antifouling mechanisms of zwitterionic materials inspired by cell membranes as well as the popular approaches to incorporate them onto membrane surfaces. It can help form a comprehensive knowledge about the principles and methods of modifying membrane surfaces with zwitterionic materials. Finally, we propose the possible future research directions of zwitterionic materials modified antifouling membranes.

Coordination-enabled synergistic surface segregation for fabrication of multi-defense mechanism membranes

The antifouling mechanism lies at the heart of a number of surface-governed applications ranging from biomedical implants and devices, marine coatings, to membrane separations. However, the multi-defense mechanism has not been ingeniously employed to design and fabricate high-performance antifouling membranes. In this study, a coordination chemistry-enabled approach is explored to manipulate the synergistic surface segregation of amphiphilic copolymers and hydrophilic inorganic nanoparticles during the membrane formation process, thus constructing membrane surfaces with an optimally integrated fouling-resistant mechanism and fouling-release mechanism. Moreover, the metal–organic coordination interaction ensures the stable coexistence of copolymers and inorganic nanoparticles on the membrane surface, as well as the high mechanical strength of membranes. Consequently, the membranes display superior antifouling properties and long-term stability in oil/water emulsion separation.

Probing molecular-level surface structures of polyethersulfone/pluronic F127 blends using sum-frequency generation vibrational spectroscopy.

We blended Pluronic F127 into polyethersulfone (PES) to improve surface properties of PES, which has been extensively used in biomaterial and other applications. The molecular surface structures of PES/Pluronic F127 blends have been investigated by sum-frequency generation (SFG) vibrational spectroscopy. The molecular orientation of surface functional groups of PES changed significantly when blended with a small amount of Pluornic F127. Pluronic F127 on the blend surface also exhibited different features upon contacting with water. The entanglement of PES chains with Pluronic F127 molecules rendered the blends with long-term surface stability in water in contrast to the situation where a layer of Pluronic F127 adsorbed on the PES surface. Atomic force microscopy (AFM) and quartz crystal microbalance (QCM) measurements were included to determine the relative amount of protein that adsorbed to the blend surfaces. The results showed a decreased protein adsorption amount with increasing Pluronic F127 bulk concentration. The correlations between polymer surface properties and detailed molecular structures obtained by SFG would provide insight into the designing and developing of biomedical polymers and functional membranes with improved fouling-resistant properties.

Fabrication of antifouling polymer–inorganic hybrid membranes through the synergy of biomimetic mineralization and nonsolvent induced phase separation

Membrane-based technology is regarded as the most promising approach for oil/water separation, but suffers from severe membrane fouling. Hybrid membranes may have great opportunities in dealing with fouling problems due to their hierarchical structures and multiple functionalities. In this study, novel kinds of hybrid membranes with both inorganic hydrophilic microdomains and organic low surface free energy (LSFE) microdomains are fabricated through the synergy of in situ biomimetic mineralization and nonsolvent induced phase separation. The as-prepared hybrid membrane exhibits a homogeneous dispersion of nanoparticles, higher mechanical strength, underwater superoleophobicity and surface heterogeneity. Owing to its concomitant collaborative fouling-resistant mechanism and fouling-release mechanism, it is difficult for oil foulants to approach or attach to the membrane surface, and consequently the membranes display significantly enhanced antifouling properties and separation performance. Particularly, the permeation flux decline approaches zero during oil-in-water emulsion filtration. This study may endeavor to provide a facile and generic strategy to manipulate the structure–property relationship of membranes for efficient water treatment processes.

Improved antifouling property of PVDF membranes by incorporating an amphiphilic block-like copolymer for oil/water emulsion separation

An amphiphilic block-like copolymer bearing hydrophobic poly(butyl methacrylate) (PBMA), hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (PEGMA) and low surface energy poly(hexafluorobutyl methacrylate) (PHFBM) segments was synthesized by free radical polymerization. The copolymer was then used as an additive to fabricate antifouling polyvinylidene difluoride (PVDF) membranes by the non-solvent induced phase separation (NIPS) method. During the membrane preparation process, the low surface energy PHFBM segments were dragged to the membrane surfaces by the surface segregated hydrophilic PEGMA segments. The presence of the PHFBM segments on the membrane surfaces significantly enhanced the antifouling property of the PVDF membranes during oil/water emulsion filtration. The total flux decline (Rt) was drastically decreased to 10.6% and the flux recovery ratio (FRR) was 99.4%. In addition, the influences of different operating conditions (including agitating speed, operating pressure and oil concentration) on the antifouling property were extensively investigated. The fluxes were nearly completely recovered after simple hydraulic cleaning even under a low agitating speed, high operating pressure and high oil concentration.

Green coating by coordination of tannic acid and iron ions for antioxidant nanofiltration membranes

A novel green coating method was proposed to prepare composite nanofiltration (NF) membranes without using organic solutions or toxic reagents in the formation of the active layer compared with traditional interfacial polymerization. Tannic acid (TA) and iron(III) chloride (FeCl3) were chosen as the two reactive monomers dissolved in the aqueous phase. The stable metal–polyphenol complex coating was formed via the coordination reaction between TA and iron ions (FeIII) upon porous support. Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and water contact angle were used to characterize the chemical features of the prepared TA–FeIII/polyethersulfone (PES) composite NF membranes. Scanning electron microscope (SEM) and atomic force microscopy (AFM) were utilized to observe the surface morphologies. The effects of reactive monomer concentration and reaction time on the permeability of water and rejection of dyes and inorganic salts were investigated, respectively. The TA–FeIII/PES composite NF membranes possessed good structural stability and oxidation resistance ability.