Preparation and antifouling performance of low-pressure carbon nanotube membranes based on polydopamine biomimetic modification

In order to investigate the antifouling performance of low-pressure carbon nanotube membranes based on polydopamine (PDA) biomimetic modification, layered multi-walled carbon nanotubes PDA membrane (layered MWCNTs-PDA) and PDA blended MWCNTs membrane (blended PDA/MWCNTs) were prepared. The MWCNTs membranes' antifouling performance and recoverability was significantly improved in filtrating BSA, HA and SA after PDA biomimetic modification, and the total fouling and irreversible fouling were all decreased. Compared with the blended PDA/MWCNTs membrane, the layered MWCNTs-PDA membrane had higher antifouling property as it further improved the electronegativity and hydrophilicity of membrane surface. In addition, denser surface pore size of the layered MWCNTs-PDA membrane can effectively reduce the fouling by trapping foulants on its surface. The combination of PDA biomimetic modification with MWCNTs membrane had a superior antifouling performance and rejection performance in processing NOM and artificial wastewater, and the majority of humic-like foulants could be excluded by the layered MWCNTs-PDA membrane. PDA biomimetic modification alleviated the adhesion of FITC-BSA on the MWCNTs membrane. The layered MWCNTs-PDA membrane especially alleviated the attachment of bacteria and processed excellent antimicrobial ability for bacteria.

Recovery of Natural Polyphenols from Spinach and Orange By-Products by Pressure-Driven Membrane Processes

Spinach and orange by-products are well recognized for their health benefits due to the presence of natural polyphenols with antioxidant activity. Therefore, the demand to produce functional products containing polyphenols recovered from vegetables and fruits has increased in the last decade. This work aims to use the integrated membrane process for the recovery of polyphenols from spinach and orange wastes, implemented on a laboratory scale. The clarification (microfiltration and ultrafiltration, i.e., MF and UF), pre-concentration (nanofiltration, NF), and concentration (reverse osmosis, RO) of the spinach and orange extracts were performed using membrane technology. Membrane experiments were carried out by collecting 1 mL of the permeate stream after increasing the flow rate in 1 mL/min steps. The separation and concentration factors were determined by HPLC-DAD in terms of total polyphenol content and by polyphenol families: hydroxybenzoic acids, hydroxycinnamic acids, and flavonoids. The results show that the transmembrane flux depended on the feed flow rate for MF, UF, NF, and RO techniques. For the spinach and orange matrices, MF (0.22 µm) could be used to remove suspended solids; UF membranes (30 kDa) for clarification; NF membranes (TFCS) to pre-concentrate; and RO membranes (XLE for spinach and BW30 for orange) to concentrate. A treatment sequence is proposed for the two extracts using a selective membrane train (UF, NF, and RO) to obtain polyphenol-rich streams for food, pharmaceutical, and cosmetic applications, and also to recover clean water streams.

Surface characterization of thin-film composite membranes using contact angle technique: Review of quantification strategies and applications

Thin-film composite (TFC) membranes are the most widely used membranes for low-cost and energy-efficient water desalination processes. Proper control over the three influential surface parameters, namely wettability, roughness, and surface charge, is vital in optimizing the TFC membrane surface and permeation properties. More specifically, the surface properties of TFC membranes are often tailored by incorporating novel special wettability materials to increase hydrophilicity and tune surface physicochemical heterogeneity. These essential parameters affect the membrane permeability and antifouling properties. The membrane surface characterization protocols employed to date are rather controversial, and there is no general agreement about the metrics used to evaluate the surface hydrophilicity and physicochemical heterogeneity. In this review, we surveyed and critically evaluated the process that emerged for understanding the membrane surface properties using the simple and economical contact angle analysis technique. Contact angle analysis allows the estimation of surface wettability, surface free energy, surface charge, oleophobicity, contact angle hysteresis, and free energy of interaction; all coordinatively influence the membrane permeation and fouling properties. This review will provide insights into simplifying the evaluation of membrane properties by contact angle analysis that will ultimately expedite the membrane development process by reducing the time and expenses required for the characterization to confirm the success and the impact of any modification.

Polyethyleneimine-assisted co-deposition of polydopamine coating with enhanced stability and efficient secondary modification

The stability and grafting efficiency are important for polydopamine (pDA) coatings used as platforms for secondary grafting.

High-flux polyamide reverse osmosis membranes by surface grafting 4-(2-hydroxyethyl)morpholine

A surface grafted PA RO membrane with 4-(2-hydroxyethyl)morpholine was fabricated to improve water flux.

Manipulating the multifunctionalities of polydopamine to prepare high-flux anti-biofouling composite nanofiltration membranes

An anti-biofouling composite NF membrane was prepared through the rational manipulation of the adhesion, reaction and separation functionalities of PDA.