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Abstract This work provides a new and simple method to improve the performance of polyamide reverse osmosis membrane, including selectivity properties and antifouling ability. Herein, quaternary ammonium groups have been immobilized on polyamide membrane surface by grafting and self-polymerization reaction of epoxy group in 2,3-epoxypropyl trimethyl ammonium chloride with tris(dimethylaminomethyl)phenol as curing catalyst. The surface properties of the modified membrane, such as surface charge, hydrophilicity and roughness have been characterized in detail and compared with virgin PA membrane. This novel modification method mainly achieves three advances in terms of membrane performance and fabricating technique. On one hand, the positively charged quaternary ammonium group immobilized on membrane surface can prevent cationic surfactant absorbing to improve fouling-resistance, due to the electric repulsion effect. On the other hand, self-polymerization reaction based on epoxy group occurred on polyamide surface can fill up the aggregate pore or reduce the pore size in polyamide, resulting in the increase of salt rejection. More importantly, the membrane modification process is very simple and efficient, which adapts to fabricate RO membrane with high performance on industrial production line completely. Highlights • Positively charged TFC membranes have been fabricated by immobilizing quaternary ammonium group on PA surface. • NaCl rejection of the TFC membrane can increase from 98.50% to 99.72% after modification. • Modified TFC membrane shows much more improved fouling-resistance ability to cation surfactant than virgin PA membrane. [ABSTRACT FROM AUTHOR]

Abstract: Based on the molecular structure feature and bioadhesion phenomenon, dopamine was selected to prepare composite membranes. The amine and phenol groups in dopamine, and the catechol groups of polydopamine all could react with acyl chloride groups of trimesoyl chloride (TMC) forming a dense thin film onto porous PES ultrafiltration substrate. The interaction between the thin film and the substrate of the composite membrane was enhanced due to the bioadhesion of polydopamine. The dopamine/TMC composite membranes were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and water contact angle measurement. The preparation parameters of dopamine/TMC composite membranes including pH value of water phase, reaction time, reaction temperature, and monomer concentrations were investigated, respectively. The separation performance of dopamine/TMC composite membranes was in the nanofiltration range. The composite membranes exhibited long-term structural stability in ethanol and chemical stability in sodium hypochlorite solution. Compared with the others in enhancing the structural stability, the bioadhesion method was simple and time-saving. [Copyright &y& Elsevier]

Abstract: This study presents a novel and versatile approach to robustly bind TiO2 nanoparticles on thin film composite (TFC) membranes by using polydopamine, which is capable to self-polymerize on membranes as well as on the surfaces of nanoparticles. The traditional self-assembly method is used as a reference. The binding performance of both methods is investigated by rinsing and wiping tests and evaluated by scanning electronic microscopy (SEM). In addition, the effects of the concentration of TiO2 nanoparticles in the suspension as well as the polymerization time of dopamine on the binding performance are studied. It was observed that, for the same modification and rinsing conditions, the polydopamine method is able to bind significantly more TiO2 on the membrane surface. According to the wiping test, the quantity of nanoparticles embedded in the polydopamine layer does not change. However, the traditional self-assembly method cannot stand the wiping force and no nanoparticles are left after wiping. The interesting hydrophilicity and the filtration performance of each modification step is further investigated. The polydopamine significantly increases the water contact angle of the polyamide thin film composite (TFC) membranes. The membranes modified by the traditional self-assembly method exhibit a significant flux loss compared to the original membranes. On the contrary, the polydopamine method can keep the membrane performance. Thus, this procedure can be considered as a novel and versatile method to bind TiO2 nanoparticles on TFC membranes, and it can be easily adapted for a variety of membranes to bind nanomaterials without a complex surface pretreatment. [Copyright &y& Elsevier]

Abstract: Based on the self-polymerization and strong adhesion characteristic of dopamine in wet conditions, the hydrophobic polyethylene (PE) porous membranes were surface-modified via simply immersing them into dopamine aqueous solution for 24h. Subsequently, heparin was immobilized covalently onto the resultant membrane by the coupling between heparin and reactive polydopamine layer. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were utilized to determine the chemical compositions of membrane surface, which confirmed the successful introduction of polydopamine and immobilization of heparin molecules. Scanning electronic microscopy (SEM) and atomic force microscopy (AFM) were employed to investigate the changes in surface morphologies after surface modification. The data of water contact angle measurements indicated that the hydrophilicity of PE membranes was remarkably improved after polydopamine coating and heparin immobilization. The results of in vitro hemocompatibility test proved that surface heparinization significantly suppressed the adhesion of platelet and enhanced the anticoagulation ability of PE membranes. This work offered a convenient approach to improve the permeability and biocompatibility of inert PE porous membranes for their biomedical and blood-contacting applications. [ABSTRACT FROM AUTHOR]