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Bifunctional photocatalytic nanofiltration (NF) membranes are becoming increasingly popular because of their ability to separate and degrade azo compounds (azos) in water. However, several serious drawbacks limit their practical implementation. In this study, a polyamide (PA) layer formed by interfacial polymerization on the polyvinylidene fluoride membrane surface and polydopamine (PDA) were combined with BaTiO 3 /Ti 3 C 2 T x (BT) nanoparticles to prepare photocatalytic BT@PDA (BTPP) membranes, which integrated physical separation and photocatalytic degradation into a single process. By optimizing synthesis conditions, a BTPP membrane with high water permeability (34.0 L·m–2·h–1·bar–1) and Na 2 SO 4 rejection rate (94.7%) was produced. The photocatalytic activity of this membrane was examined by studying the photocatalytic degradation efficiency of several azos. After 180 min of irradiation with a 300 W Xe lamp (λ ≥ 420 nm), the degradation rate of methyl orange (MO) reached 95.3%, while the degradation rates of alizarin yellow GG and methyl red were 92.7% and 83.5%, respectively. The photocatalytic performance of the BTPP membranes for azos degradation was verified by studying the charge transfer process and generation of reactive radical species (·OH and·O 2 –), and possible structures of the main intermediates formed during MO degradation were identified. This work provides new insights into the synthesis and degradation properties of bifunctional photocatalytic NF membranes. [Display omitted] • BaTiO 3 /Ti 3 C2T x (BT) structure with good photocatalytic properties. • Bifunctional photocatalytic BT@dopamine (BTPP) membranes with excellent performance is proposed. • BTPP membranes promote the simultaneous separation and photodegradation of azo compounds. • The degradation of azo compounds by BTPP membranes include ·OH and ·O 2 – active radicals. [ABSTRACT FROM AUTHOR]

The adhesion forces of membrane–humic acid (membrane–HA) and HA–HA were measured by atomic force microscopy (AFM) in conjunction with self-made modified membrane-coated and HA-coated probes, respectively. Normalized flux decline rate and the irreversible fouling index of fouling experiments with HA kept good linear correlations with the AFM force measurements. The extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory was used to explain the influence and regularity of HA solution pH and hydrophilicity of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane interface on membrane fouling behavior. The results of AFM force measurements illustrated that the adhesion force in acidic environment was much stronger than that in alkaline or neutral environment and the adhesion force of PVDF/polyvinylalcohol membrane–HA (PA–HA) was weaker than that of PVDF/polyvinylpyrrolidone membrane–HA (PP–HA). XDLVO theoretical calculated results demonstrated that the polar component of surface tension ( γ AB ) of membrane–foulant could be effectively increased by improving the hydrophilicity of the PVDF UF membrane interface and reducing the solution acidity, which resulted in the decrease of absolute values of the membrane–HA interfacial free energy of adhesion ( Δ G mlf AD ) , the mitigation of the membrane fouling rate and the irreversible fouling degree. The results preliminarily proved that the measurements of microscopic interfacial forces with modified AFM colloidal probes had potential application values in UF membrane fouling behavior. [ABSTRACT FROM AUTHOR]

A self-cleaning surface can effectively solve the accumulation problem of irreversible contamination of ultrafiltration membranes. In this work, a (polyvinylidene fluoride)-g-(polyacrylic acid) (PVDF-g-PAA) ultrafiltration membrane, hereafter denoted as FAS, was prepared by a one-pot method. A superhydrophilic self-cleaning ultrafiltration membrane, hereafter denoted as FASF, was then obtained based on the strong complexation of Fe3+ with the abundant carboxyl groups at the FAS surface, which then mineralized Fe3+ into β-FeOOH nanoparticles and deposited them onto the FAS surface. This deposition was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Bovine serum albumin (BSA) cross-flow filtration experiments confirmed the high ultrafiltration performance of FAS and FASF. FASF exhibited highly efficient degradation of methylene blue (MB) solution under visible light photo-Fenton conditions. The optimum amount of acrylic acid was 6 wt% in the one-pot reaction system, and the alkaline coagulation bath enhanced the wettability of FAS. The β-FeOOH nanoparticle content of the surface-mineralized FASF tended to be saturated after 24 h. β-FeOOH can significantly enhance the hydrophilicity and wettability of FASF and further enhance the antifouling performance of BSA. After four cycles of cleaning operation under visible light photo-Fenton conditions, the flux recovery rate of BSA-contaminated FASF reached 96.2%, and the rejection rate remained stable. FASF had superhydrophilicity, high antifouling, and fast photocatalytic self-cleaning performances, indicating good application prospects in organic wastewater treatment. Image 1 • A superhydrophilic self-cleaning ultrafiltration membrane (FASF) was prepared. • FASF had visible light photo-Fenton reaction activity. • FASF was obtained by Fe3+ mineralization on the surface of PVDF-g-PAA membrane (FAS). • FAS was prepared by graft copolymerization of AA and PVDF through a one-pot method. • FASF had stable antifouling and visible light photo-Fenton self-cleaning performances. [ABSTRACT FROM AUTHOR]

The cross-linked poly(vinyl alcohol) (PVA)/poly(vinylidene fluoride) composite flat sheet membranes were successfully prepared by phase inversion method. Ferric trichloride (FeCl particles were used as cross-linker. PVA is cross-linked during the membrane fabrication. The structures of formed membranes were investigated using scanning electron microscopy and Fourier transform infrared spectroscopy (FTIR). The hydrophilic contact angle, pure water flux, and tensile strength were measured to assess the membrane performance. The antifouling performance of modified membrane for the secondary effluent of urban sewage was evaluated by flux decline, washing recovery rate, fouling resistance analysis, and fractions distribution of different hydrophilicities. FTIR showed that the peak intensity, attributed to -OH groups, decrease gradually with the increase of FeCl3, indicating the formation of a PVA-Fe3+ net work structure. The addition of cross-linking agent FeCl3 confined the compaction of membranes, thus the fouling resistances of membranes were lower and the water flux was higher. When the weight ratio of PVA to FeCl3 was 1/0.09, the modified membranes had the best UF performance and antifouling property. [ABSTRACT FROM AUTHOR]

To obtain a high-performance polyvinylidene fluoride (PVDF) membrane, low-temperature thermally induced phase separation (LT-TIPS) was employed to prepare microporous flat PVDF membranes and hollow-fiber membranes using diluent mixtures of triethylphosphate and diethylene glycol monoethyl ether acetate. The membrane morphology was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that thermally induced phase separation (TIPS) played a more important role than nonsolvent-induced phase separation (NIPS) in determining the cross-sectional morphology of the membranes, and the surface structure was mainly affected by NIPS in a low-temperature (0 °C) coagulation bath. By increasing the temperature of the coagulation bath, different structures of membranes, such as spherulites and cellular and sponge structures, were observed. It is believed that the formation mechanism of these membranes depended on a combined NIPS and TIPS process. Wide-angle X-ray diffraction (XRD) analysis indicated that PVDF crystallized into an α-phase crystal structure for all the membranes tested. In addition, the porosity, tensile strength and filtration performance of the flat membranes were measured. On the basis of the above results, a hollow fiber membrane with highly interconnected pores and high porosity could be prepared employing LT-TIPS. [ABSTRACT FROM AUTHOR]