Improving the contamination resistance of membranes is one of the most effective ways to address the short service life of membranes. While preparing the membrane system structure, doping nanoparticles into the polymer matrix is beneficial to the preparation of high-performance membranes. To develop a new structure for membrane contamination protection, in this study, a novel asymmetric polyamide 66 composite ultrafiltration (UF) membrane was fabricated by incorporating different masses (ranging from zero to 0.5 wt.%) of graphene oxide (GO) into the polyamide 66 microporous substrate, using formic acid and propylene carbonate as solvents. The effects of GO doping on the morphology, microporous structure and surface of ultrafiltration membranes were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), integrated thermal analysis (DSC) and contact angle (CA). In addition, pure water flux, bovine serum albumin (BSA) rejection and contamination resistance were measured to evaluate the filtration performance of different membranes. The overall performance of all the modified membranes was improved compared to pure membranes. The results of contact angle and permeation experiments showed that the addition of GO improved the hydrophilicity of the membrane, but reduced the permeability of the membrane. The minimum flux was only 3.5 L/m2·h, but the rejection rate was 92.5%. Most noteworthy was the fact that GO further enhanced the anti-pollution performance of the membranes and achieved a remarkable performance of 91.32% when the GO content was 0.5 wt.%, which was 1.36 times higher than that of the pure membrane. Therefore, optimal performance was achieved. Furthermore, the UF membrane made of composite substrate offers a promising solution for the development of long-life ultrafiltration membranes with better stability, high-cost efficiency and adequate chemical durability.

Polyamide 66 microporous membranes were prepared by cold non-solvent-induced phase separation using polyamide 66-formic acid-propylene carbonate as a ternary membrane-forming system. The formed membranes exhibited a special bicontinuous structure consisting of interglued spherical crystals or interlocked bundles of microcrystalline aggregates. The variation of the microporous structure under the influence of preparation conditions, solvent, aging time, and polymer concentration affects the comprehensive performance of the membranes. For example, the cold-induced operation and the use of different membrane-forming solvents contributed to the crystallization of polyamide 66, resulting in an increased contact angle of polyamide 66 membranes, obtaining a high resistance to contamination of up to 73.5%. Moreover, the formed membranes still have high mechanical strength.

In this paper, we report for the first time the successful formation of a covalent cross-linking structure between polyacrylic acid and polyamide 66 in an electrospun nanofiber membrane by the facilitated amidation reaction using N-Hydroxy-succinimide (NHS) and N-(3-Dimethylaminopropyl)-N’-ethyl-carbodiimide hydrochloride (EDC). The structure and properties of the fiber membrane are characterized using scanning electron microscopy, wide field X-ray diffraction and differential scanning calorimetry. The results show that the presence of the cross-linked structure not only affects the construction of the nanofiber network framework but also influences the pore size distribution and size of the fiber membrane surface, which in turn affects its retention of contaminants and water absorption performance. After modification, the cross-linked membranes exhibited a significant retention performance of up to 77% for methyl tert-butyl ether (MTBE) with a reduced pure water flux. Furthermore, after crosslinking, the fiber membrane has been strongly enhanced with more stable pH response behavior.

With the development of industry, more and more oily wastewater is discharged into the water, which brings great harm to the ecological environment and human health. Membrane separation technology is a very promising technology for oily wastewater treatment. In this experiment, a 1:1 mixed solution of formic acid and dichloromethane (FA/DCM) was used as a solvent to prepare a PA66 microfiltration membrane by evaporation method, and nano-SiO2 was used to modify the PA66 with the determined formula. The apparent morphology, hydrophilicity and mechanical properties of the membrane were characterized by scanning electron microscopy, contact angle test and tensile test, and the effect of treating oily wastewater by microfiltration membrane before and after modification was analyzed. The results show that the mechanical strength and hydrophilicity of the microfiltration membrane are improved after modification by SiO2, and the sewage treatment effect is better. The removal rates of unmodified microfiltration membrane to total suspended solids, chemical oxygen demand and oil concentration are 55%~96%, 50%~85% and 55%~92%; the removal rates of modified microfiltration membrane to total suspended solids, chemical oxygen demand and oil concentration are 98%~99%, 91%~95% and 95%~99%.

For most work on separation membrane for oily wastewater, heavy metals in oily wastewater may pollute the environment. Novel α-zirconium-phosphate-nanoparticle/polyacrylonitrile (α-ZrP-NP/PAN) mixed matrix membranes (MMMs) were prepared for effective oily wastewater treatment. The α-ZrP-NP contributed abundant –OH groups to the MMMs and enhanced their hydrophilicity. Meanwhile, the surface of the MMMs carried enhanced negative charges due to the α-ZrP-NP in the pH range of 3–10. Scanning electron microscopic analysis of the MMM morphology revealed that the macrovoid structure enhanced, the surface pore size, and the number of pores increased. The MMMs achieved a considerably improved flux and recovery rate of 175.91 L/m2·h and 75.66%, respectively, indicating improvements in filtration efficiency and anti-fouling performance. The purification effect (oil and COD removal rate) of the MMMs on oily wastewater remains above 90%, which reflects the decent purification ability of the membrane on oily wastewater. The removal rate of Pb2+, a representative heavy metal ion, reached 94.82%. The regeneration efficiency of the MMM contaminated with lead ions was more than 90%. These results demonstrated the tremendous potential of the treatment of heavy-metal-containing oily wastewater using the fabricated MMMs.