Yunze Wang

A pH-responsive PVDF membrane with superwetting properties for the separation of oil and water

Responsive materials with surfaces that have controllable oil wettability under water offer considerable potential in advanced applications. We have developed an economical and convenient method for constructing a superwetting polyvinylidene fluoride (PVDF) membrane, giving super-hydrophobicity under oil and super-oleophobicity under water. The membrane has been achieved by incorporating pH-responsive N,N-dimethylaminoethylmethacrylate (DMAEMA) hydrogels into PVDF using a combination of in situ polymerization and conventional phase separation. In pure or acidic water the poly-DMAEMA chains modify wettability by the protonation or deprotonation of their tertiary amine side-groups, affecting the wettability of the membrane under water. In addition, this responsive membrane has been utilized for the separation of surfactant-stabilized water-in-oil and oil-in-water emulsions. High flux and separation efficiency can be obtained, together with excellent antifouling properties, suggesting that the membranes will find wide application in the separation of oil and water systems.

Investigation of the heat resistance, wettability and hemocompatibility of a polylactide membrane via surface crosslinking induced crystallization

Polylactide (PLA) has attracted much attention as a sustainable and environmentally friendly material. However, the poor heat resistance restricts its potential application as a porous membrane. Herein, a PLA membrane with excellent heat resistance, hydrophilicity and hemocompatibility was developed via a surface crosslinking induced crystallization strategy, which involved two key reactions, namely, copolymerization of N-vinyl-2-pyrrolidone (NVP) and triethoxyvinylsilane (VTES) and the subsequent hydrolysis condensation on the surface of the PLA membrane. Attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were applied to analyse the surface chemistry and crystallization evolution, which confirmed that the P(VP-VTES) copolymer was hydrothermally crosslinked and induced the crystallization of the PLA membrane. The surface crystallization significantly improved the heat resistance and preserved membrane morphology, which was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and the dimension shrinkage. The modified PLA membrane with χc ∼ 37% remained almost unchanged dimensions and morphology even after annealing at 100 °C for 5 min. The improved hemocompatibility was verified by the prolonged clotting time and recalcification time, which was consistent with the enhanced hydrophilicity. All results showed that surface crosslinking induced crystallization strategy simultaneously improved the heat resistance and hemocompatibility, indicating a promising method for preparing robust and compatible PLA membranes.

Enhanced catalytic degradation of 4-NP using a superhydrophilic PVDF membrane decorated with Au nanoparticles

Poly(vinylidene fluoride) (PVDF) membranes have been widely applied to treat wastewater, however, the removal of toxic aromatic phenolic compounds remains a technical challenge due to the serious adsorption fouling and difficult degradation. Herein, we aimed to design a superhydrophilic PVDF membrane decorated with Au nanoparticles, which enhanced the rapid degradation of p-nitrophenol (4-NP). The superhydrophilic PVDF membrane with a micro/nano structured surface was decorated with Au nanoparticles via poly(dopamine) (PDA) as a spacer. The influences of membrane affinity (e.g. Hydrophilic Membrane (HM), micro/nano structured superhydrophilic membrane (MSiM), and micro/nano structured superhydrophobic membrane (MSoM)) on PDA deposition and the subsequent Au decoration were comprehensively investigated. The synthesized Au nanoparticles were characterized using transmission electron microscopy (TEM) and UV-vis absorption spectra. The morphology and composition was evaluated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Static catalytic experiments demonstrated that MSiM degraded over 90% of 4-NP in 5 minutes with a kinetic reaction rate constant of 47.84 × 10−2 min−1 and high stability over 6 cycles. A membrane catalytic reactor (MCR) was designed to realize the continuous catalytic degradation of 4-NP with a kinetic reaction rate constant of 7 × 10−2 min−1.

APTES assisted surface heparinization of polylactide porous membranes for improved hemocompatibility

Surface heparinization is considered an efficient strategy to improve the hemocompatibility of polymeric membranes. We aim to realize the feasible surface heparinization of polylactide (PLA) membranes by means of a colourless 3-aminopropyltriethoxysilane (APTES) functionalized platform. APTES conjugated heparin (Hep–APTES) was first synthesized through the amidation reaction and then anchored onto PLA membrane via surface attachment, condensation, multilayer formation. The surface chemistry was confirmed by Fourier Transform Infrared-Attenuated Total Reflectance (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS). The influences of heparinization time and micro-swelling agent (DMAc) on the heparin density, stability and sustained-release were investigated. The hydrophilicity, flux and morphology were also studied by contact angle, pure water flux and Scanning Electron Microscope (SEM). The hemocompatibility was evaluated by the activated partial thromboplastin time (APTT), prothrombin time (PT), the content of fibrinogen (FIB), platelet and Bovine Serum Albumin (BSA) adsorption respectively. All results demonstrated that APTES assisted surface heparinization provided a feasible and efficient strategy to improve the hemocompatibility of PLA membrane.

Robust poly(lactic acid) membranes improved by polysulfone-g-poly(lactic acid) copolymers for hemodialysis

Poly(lactic acid) (PLA) is a sustainable membrane candidate for liquid separation and purification. However, the inherent brittleness restrains its practical application, especially for a porous membrane with thin thickness and high porosity. We aim to prepare PLA membranes with controlled pore structure and dialysis performance with improved mechanical and thermal stability by incorporating polysulfone-graft-poly(lactic acid) (PSf-g-PLA) copolymer. Different from the common rubbery elastomer, the brush-like PSf-g-PLA copolymer with a rigid backbone chain and soft side chains was elaborately synthesized to toughen and modify PLA membranes via a phase inversion process. 1H NMR, FTIR and GPC were conducted to determine the structure and molecular weight of the PSf-g-PLA. The influences of chloromethylation substitution and the content of copolymer on the membrane microstructure, the mechanical and thermal stability, and the dialysis performance were investigated in detail. It was demonstrated that the modified PLA membrane exhibited a pure water flux of 54 L m−2 h−1, 95% rejection to BSA, and 65% and 18% clearance of urea and lysozyme, respectively. Besides, both mechanical and thermal stability of the modified PLA membrane were improved by incorporating brush-like PSf-g-PLA.

Surface PEGylation on PLA membranes via micro-swelling and crosslinking for improved biocompatibility/hemocompatibility

Poly(lactic acid) (PLA) has attracted growing attention as a sustainable and environmentally benign membrane material. The good biocompatibility/hemocompatibility is essential for hemodialysis membranes. To circumvent the inadequate hydrophilicity/biocompatibility/hemocompatibility, we have developed a feasible strategy that enables the persistent PEGylation on PLA membranes via micro-swelling and subsequent UV-initiated crosslinking of poly(ethylene glycol)diacrylate (PEGDA). The content of DMSO and PEGDA in the reaction solution was crucial to control the surface PEGylation kinetics. Besides, the influence of PEGylation on membrane chemistry, morphology, hydrophilicity, water flux and dynamic fouling resistance to BSA was investigated. It was demonstrated that the biocompatibility/hemocompatibility was significantly improved by the surface PEGylation in terms of reduced BSA adsorption, extended APTT and alleviative platelet adhesion.

Investigation of abnormal thermoresponsive PVDF membranes on casting solution, membrane morphology and filtration performance

An interesting PVDF membrane with unusual thermoresponsive behavior was prepared by the incorporation of P(OEGMA-co-VTMOS). The P(OEGMA-co-VTMOS) copolymer was first in situ synthesized in a PVDF/triethyl phosphate (TEP) casting solution. A P(OEGMA-co-VTMOS) network was assembled in the PVDF membrane through hydrolysis and condensation during phase inversion. PVDF/P(OEGMA-co-VTMOS) in organic solvent demonstrated a typical LCST around 35 °C, reflecting the reversible transition of the coil-to-globule conformation. Microphase separation was responsible for the appearance of turbidity of the casting solution. FTIR, XPS, TGA and SEM confirmed the surface enrichment of the copolymer, especially in the membrane bottom. The hydrophilicity and protein anti adsorption were improved despite the temperature variation. In particular, AFM in aqueous media was conducted to determine the reversible morphology and water channel variation under heating and cooling. Different from common thermoresponsive membranes, the so-modified PVDF membranes exhibit a reversible abnormal change of pure water flux and BSA rejection with temperature. The intriguing thermoresponsive behavior and mechanism of the modified PVDF membrane was thoroughly investigated from the aspects of PVDF/TEP casting solution, membrane morphology in aqueous media and water/BSA filtration performance.

Large mesoporous carbons decorated with silver and gold nanoparticles by a self-assembly method: enhanced electrocatalytic activity for H2O2 electroreduction and sodium nitrite electrooxidation

We report here the synthesis of silver and gold nanoparticles onto poly (diallyldimethyl ammoniumchloride, PDDA)-functionalized large mesoporous carbon (LMC) by a simple self-assembly method. Characterization of these nanocomposites by transmission electronic microscopy and electrochemical techniques is described. The gold nanoparticle-decorated PDDA-functionalized LMC (AuNPs/PDDA–LMC) showed an enhanced electrocatalytic response toward sodium nitrite oxidation with a wider linear range and higher sensitivity that is even comparable with Pt-based sensors. The silver nanoparticle-decorated PDDA-functionalized LMC (AgNPs/PDDA–LMC) exhibited a remarkable catalytic performance toward H2O2 reduction. At an applied potential of −0.4 V, the designed sensor had a low detection limit of 6.5 μM and wide linear response range from 20 μM to 9.62 mM with a fast response time of less than 2 s. The easy fabrication and excellent electrocatalytic capability of the LMC-based metal nanoparticle hybrids can be expected to be applied in the detection of other compounds.