Ultra-low pressure PES ultrafiltration membrane with high-flux and enhanced anti-oil-fouling properties prepared via in-situ polycondensation of polyamic acid

A capillary effect-inspired sponge-structured carboxymethyl cellulose aerogel layer-modified membrane for efficient separation of dye/salt under ultra-low-pressure

In the field of wastewater treatment, the efficient separation of dyes/salts and the high-pressure drive easily results in concentration polarization and membrane contamination. In this study, inspired by the capillary effect of natural sponge structure, an aerogel layer with a bionic three-dimensional mesh porous sponge structure was designed to construct an ultra-low-pressure membrane. With the assistance of tannic acid, the carboxymethyl cellulose (CMC) aerogel layer were constructed on the surface of polyvinylidene fluoride (PVDF) membrane using the layer-by-layer cross-linking and freeze-drying methods. The unique three-dimensional mesh structure of the aerogel provides a capillary effect that accelerates the rapid transport of water molecules. The introduction of polypyrrole (PPy) to the aerogel improves the mechanical properties of the aerogel, helping avoid the collapse during the separation process. Meanwhile, the formed PPy improves the membrane separation performance. The results showed, that under near-zero pressure conditions, the modified membrane had excellent dye/salt separation performance (dye rejection >99 %, salt rejection <10 %) and high flux of pure water (101.3 L·m-2·h-1). Moreover, the membrane also maintained good long-term stability. The study demonstrated the potential of using membrane for dye/salt separation applications by constructing bionic sponge-structured aerogels having capillary effect and good mechanical strength on membrane.

Rapid Construction of Caffeic Acid/p-Phenylenediamine Antifouling Hydrophilic Coating on a PVDF Membrane for Emulsion Separation

The current methods of constructing modification strategies for hydrophilic membranes are time-consuming, complex in operation, and poor in universality, which limit their application on membranes. In this work, inspired by the adhesion properties and versatility of caffeic acid (CA) and p-phenylenediamine (PPDA), a simple, rapid, and universal method was designed for the separation of oil-in-water emulsion by preparing a stable hydrophilic coating separation membrane. The preparation time of the membrane was shortened to 40 min. The developed PVDF-PCA/PPDA membrane showed superhydrophilic and underwater superoleophobic properties. When applied to petroleum ether-in-water emulsion, isooctane-in-water emulsion, and dodecane-in-water emulsion separation, the oil rejection was more than 99.0%. In the circulating separation of 10 g/L soybean oil-in-water emulsion, the oil rejection was more than 99.3%, and the highest flux was 1036 L·m-2·h-1. The prepared PVDF-PCA/PPDA membrane performed well in the separation test of oily wastewater. The proposed strategy is simple and rapid; it may become a universal method for preparing membranes with super strong antifouling properties against viscous oil and accelerate the research progress of membrane separation of oil-in-water emulsions.

A novel PES-C/(GO-COOH/Ce) blended membrane for treating heavy-metal-ion wastewater

A GO-COOH/Ce complex was introduced into a phenolphthalide polythersulfone (PES-C) matrix to prepare a PES-C/(GO-COOH/Ce) blended membrane by nonsolvent-induced phase transformation (NIPS). FT-IR and EDS analysis confirmed that the GO-COOH/Ce complex was successfully incorporated into the PES-C matrix. SEM showed that the blended membrane possessed an asymmetric structure with finger-like pores. The best comprehensive performance was obtained for a PES-C/(GO-COOH/Ce) blended membrane prepared using 0.1 wt.% of the GO-COOH/Ce complex in the casting liquid. The specific results for the blended membrane were as follows: the fluxes of pure water and 0.1 g/L lead nitrate solution were 272 L/m2·h and 214 L/m2·h, respectively; the rejection of bovine serum albumin (BSA) was 99.4%; the rejection of lead ions was 96.2%; the moisture content was 10.9%; the contact angle was 67.1°; the Young's modulus was 35.7 MPa; and the flux recovery ratio was 1.5 times higher than that of the pure PES-C membrane. The antibacterial-zone diameters of the PES-C/(GO-COOH/Ce) blended membrane used against Escherichia coli and Staphylococcus aureus were 2.50 cm and 2.88 cm, respectively. A catalytic cleaning test showed a flux recovery ratio of 63% after washing the PES-C/(GO-COOH/Ce) blended membrane with a 0.2 g/L acetic acid solution for 0.5 h.