Hao-Cheng Yang

Mussel-inspired modification of a polymer membrane for ultra-high water permeability and oil-in-water emulsion separation

The surface structures and properties of a membrane largely determine its in-service performance during a filtration process. Here we report a facile hydrophilization method via co-deposition of mussel-inspired polydopamine (PDA) and polyethyleneimine (PEI) on a polypropylene microfiltration membrane. The deposition time is greatly shortened and the surface hydrophilicity is significantly improved compared to those membranes decorated only by PDA. The dopamine/PEI deposition solution can be reused several times with negligible effect on the surface hydrophilicity of membranes. Moreover, the PDA/PEI coating endows the membranes with ultra-high water permeability, allowing microfiltration separation of oil-in-water emulsions under atmospheric pressure.

Silica-decorated polypropylene microfiltration membranes with a mussel-inspired intermediate layer for oil-in-water emulsion separation.

Silica-decorated polypropylene microfiltration membranes were fabricated via a facile biomimetic silicification process on the polydopamine/polyethylenimine-modified surfaces. The membranes exhibit superhydrophilicity and underwater superoleophobicity derived from the inherent hydrophilicity and the well-defined micronanocomposite structures of the silica-decorated surfaces. They can be applied in varieties of oil-in-water emulsions separation with high permeate flux (above 1200 L/m(2)h under 0.04 MPa) and oil rejection (above 99%). The membranes also have relatively high oil breakthrough pressure reaching 0.16 MPa due to the microporous structure, showing great potential for practical applications. Furthermore, such mussel-inspired intermediate layer provides us a convenient and powerful tool to fabricate organic-inorganic hybrid membranes for advanced applications.

Janus Membranes: Exploring Duality for Advanced Separation

Janus membranes are an emerging class of materials having opposing properties at an interface. This structure results in selective and often novel transport characteristics. In this Minireview, a definition of the Janus membrane, beyond merely asymmetric materials, is introduced and common fabrication strategies are outlined. Also presented are current and potential applications in directional transport, switchable permeation, and performance optimization with detailed mechanisms.

Surface and interface engineering for organic–inorganic composite membranes

Organic–inorganic composite (OIC) membranes have received great attention over the past decades due to their enhanced performances in many applications. It is well known that surfaces and interfaces play crucial roles in the fabrication and application of the OIC membranes. In this review, we summarize the typical processes used to fabricate the OIC membranes and categorize these membranes as either mixed matrix OIC membranes or interfacial composite OIC membranes, and primarily focus on how the organic–inorganic interfaces influence the membrane formation process and its final structure. Then we reveal how the membrane surfaces and organic–inorganic interfaces in the membrane affect the final performance in certain applications. Through this review, we wish to provide a comprehensive guide to membrane fabrication and regulation, as well as a better understanding of the structure–performance relationships in OIC membranes.

Co-deposition of catechol/polyethyleneimine on porous membranes for efficient decolorization of dye water

Mussel-inspired chemistry has been broadly exploited for multifunctional coatings in the surface modification of applied materials. Polyphenols are ubiquitous in plant tissues and far less expensive than polydopamine for mussel-inspired chemistry. Herein, we report a facile and effective method to modify porous membranes via the co-deposition of catechol (CCh) and polyethyleneimine (PEI). The membrane structures and properties were investigated by ATR/FTIR, XPS, FESEM, zeta potential, water contact angle and pure water flux measurements. The results reveal that the membranes deposited with a CCh–PEI mass ratio of 1:0.25 show excellent hydrophilicity, ultrahigh water permeation flux and distinguished surface charges. These membranes were used to decolorize anionic dye solutions during filtration with superior removal efficiencies of over 99%. Moreover, they have good reusability over repeated operations with a simple regeneration process.

Composite free-standing films of polydopamine/polyethyleneimine grown at the air/water interface

Mussel-inspired free-standing composite films were formed by polymerization of dopamine in the presence of polyethyleneimine at the air/water interface. These films have controllable thickness and asymmetric structure. They can be potentially developed as templates for the fabrication of silver, hydroxyapatite, titania and silica hybrid films.

Polydopamine-Coated Porous Substrates as a Platform for Mineralized β-FeOOH Nanorods with Photocatalysis under Sunlight

Immobilization of photo-Fenton catalysts on porous materials is crucial to the efficiency and stability for water purification. Here we report polydopamine (PDA)-coated porous substrates as a platform for in situ mineralizing β-FeOOH nanorods with enhanced photocatalytic performance under sunlight. The PDA coating plays multiple roles as an adhesive interface, a medium inducing mineral generation, and an electron transfer layer. The mineralized β-FeOOH nanorods perfectly wrap various porous substrates and are stable on the substrates that have a PDA coating. The immobilized β-FeOOH nanorods have been shown to be efficient for degrading dyes in water via a photo-Fenton reaction. The degradation efficiency reaches approximately 100% in 60 min when the reaction was carried out with H2O2 under visible light, and it remains higher than 90% after five cycles. We demonstrate that the PDA coating promotes electron transfer to reduce the electron-hole recombination rate. As a result, the β-FeOOH nanorods wrapped on the PDA-coated substrates show enhanced photocatalytic performance under direct sunlight in the presence of H2O2. Moreover, this versatile platform using porous materials as the substrate is useful in fabricating β-FeOOH nanorods-based membrane reactor for wastewater treatment.

Highly Stable, Protein-Resistant Surfaces via the Layer-by-Layer Assembly of Poly(sulfobetaine methacrylate) and Tannic Acid

Zwitterionic materials have received great attention because of the non-fouling property. As a result of the electric neutrality of zwitterionic polymers, their layer-by-layer (LBL) assembly is generally conducted under specific conditions, such as very low pH values or ionic strength. The formed multilayers are unstable at high pH or in a high ionic strength environment. Therefore, the formation of highly stable multilayers of zwitterionic polymers via the LBL assembly process is still challenging. Here, we report the LBL assembly of poly(sulfobetaine methacrylate) (PSBMA) with a polyphenol, tannic acid (TA), for protein-resistant surfaces. The assembly process was monitored by a quartz crystal microbalance (QCM) and variable-angle spectroscopic ellipsometry (VASE), which confirms the formation of thin multilayer films. We found that the (TA/PSBMA)n multilayers are stable over a wide pH range of 4-10 and in saline, such as 1 M NaCl or urea solution. The surface morphology and chemical composition were characterized by specular reflectance Fourier transform infrared spectroscopy (FTIR/SR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Furthermore, (TA/PSBMA)n multilayers show high hydrophilicity, with a water contact angle lower than 15°. A QCM was used to record the dynamic protein adsorption process. Adsorption amounts of bovine serum albumin (BSA), lysozyme (Lys), and hemoglobin (Hgb) on (TA/PSBMA)20 multilayers decreased to 0.42, 52.9, and 37.9 ng/cm(2) from 328, 357, and 509 ng/cm(2) on a bare gold chip surface, respectively. In addition, the protein-resistance property depends upon the outmost layer. This work provides new insights into the LBL assembly of zwitterionic polymers.

Janus Membranes with Opposing Surface Wettability Enabling Oil-to-Water and Water-to-Oil Emulsification

A Janus membrane with opposing wettability was first reported with both function of water-to-oil and oil-to-water emulsification. This membrane is conveniently fabricated by single-surface deposition of polydopamine/polyethylenimine (PDA/PEI). The asymmetric wettability can also reduce the transmembrane resistance during the process, indicating an economical and promising strategy to prepare various emulsions. This research opens a novel avenue for exploring and understanding the Janus membrane, and provides a perspective to design the asymmetric membrane structures with promoted performance in conventional membrane processes.

Composite nanofiltration membranes via the co-deposition and cross-linking of catechol/polyethylenimine

High performance nanofiltration (NF) membranes are facilely fabricated via the co-deposition of catechol (CCh) and polyethylenimine (PEI) on the surface of a polysulfone (PSf) ultrafiltration membrane, with subsequent cross-linking by glutaraldehyde (GA). The surface properties of the studied membranes have been investigated in detail by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning election microscopy, atomic force microscopy, zeta potential, and water contact angle. The NF performance of the membranes are dependent on the CCh/PEI ratio, co-deposition time and cross-linking condition. Results reveal that the optimum membrane yields a rejection of 88% and a permeation flux of 25 L m−2 h−1 when filtrating the 1000 mg L−1 MgCl2 solution at 0.6 MPa. And the negatively charged membrane surface is related to the following salt rejection sequence: MgSO4 > Na2SO4 > MgCl2 > CaCl2 > NaCl. Meanwhile, the membranes show excellent operation stability during a 240 h consistent filtration test.