Effects of a dual functional filler, polyethersulfone-g-carboxymethyl chitosan@MWCNT, for enhanced antifouling and penetration performance of PES composite membranes

Ultrafiltration technology, separating water from impurities by the core membrane, is an effective strategy for treating wastewater to meet the ever-growing requirement of clean and drinking water. However, the similar nature of hydrophobic organic pollutants and the membrane surface leads to severe adsorption and aggregation, resulting unavoidable membrane degradation of penetration and rejection. The present study presents a novel block amphiphilic polymer, polyethersulfone-g-carboxymethyl chitosan@MWCNT (PES-g-CMC@MWCNT), which is synthesized by grafting hydrophobic polyethersulfone to hydrophilic carboxymethyl chitosan in order to suspend CMC in organic solution. A mixture of hydrophilic carboxymethyl chitosan and hydrophobic polymers (polyethersulfone), in which hydrophilic segments are bonded to hydrophobic segments, could provide hydrophilic groups, as well as gather and remain stable on membrane surfaces by their hydrophobic interaction for improved compatibility and durability. The resultant ultrafiltration membranes exhibit high water flux (198.10 L m-2·h-1), suitable hydrophilicity (64.77°), enhanced antifouling property (82.96%), while still maintains excellent rejection of bovine serum albumin (91.75%). There has also been an improvement in membrane cross-sectional morphology, resulting in more regular pores size (47.64 nm) and higher porosity (84.60%). These results indicate that amphiphilic polymer may be able to significantly promote antifouling and permeability of ultrafiltration membranes.

Surface Design of Liquid Separation Membrane through Graft Polymerization: A State of the Art Review

Surface modification of membranes is an effective approach for imparting unique characteristics and additional functionalities to the membranes. Chemical grafting is a commonly used membrane modification technique due to its versatility in tailoring and optimizing the membrane surface with desired functionalities. Various types of polymers can be precisely grafted onto the membrane surface and the operating conditions of grafting can be tailored to further fine-tune the membrane surface properties. This review focuses on the recent strategies in improving the surface design of liquid separation membranes through grafting-from technique, also known as graft polymerization, to improve membrane performance in wastewater treatment and desalination applications. An overview on membrane technology processes such as pressure-driven and osmotically driven membrane processes are first briefly presented. Grafting-from surface chemical modification approaches including chemical initiated, plasma initiated and UV initiated approaches are discussed in terms of their features, advantages and limitations. The innovations in membrane surface modification techniques based on grafting-from techniques are comprehensively reviewed followed by some highlights on the current challenges in this field. It is concluded that grafting-from is a versatile and effective technique to introduce various functional groups to enhance the surface properties and separation performances of liquid separation membranes.

Influence of carbon dioxide plasma treatment on the dry adhesion of vertical aligned carbon nanotube arrays

Vertical aligned carbon nanotube (VACNT) arrays used as dry adhesive materials have broad prospects in the applied fields of space, medicine and electronics. The adhesion of VACNT arrays is believed to be related not only to the nano-array structure and a clean surface, but also to chemical composition. Here, radio-frequency (RF) carbon dioxide (CO₂) plasma treatment is introduced as an effective method for purifying and functionalizing the surface to improve the dry adhesive performance of VACNT arrays. Scanning electron microscopy showed that the VACNT arrays retained the alignment architecture with minimal damage at low power. X-ray photoelectron spectroscopy and contact angle tests revealed that the content of non-polar components (C = C bonds) decreased after treatment, while the content of polar groups (C = O and O-C = O bonds) increased, which changed the surface polarity of the VACNT arrays. Raman analyses and transmission electron microscopy demonstrated that amorphous carbon can be selectively removed with increasing time (0-18 min), but was continuously generated with increasing power (30-90 W). The best adhesive strength of 18 N cm^-2 (increased by 39%) was obtained after CO₂ plasma treating for 10 min at 30 W power, which was attributed to the combined action of purification and polarization.

Surface modification of a PES membrane by corona air plasma-assisted grafting of HB-PEG for separation of oil-in-water emulsions

The main goal of this study is to modify a polyethersulfone (PES) membrane by grafting with hyperbranched polyethylene glycol (HB-PEG) using corona air plasma to intensify the anti-fouling properties of the prepared membrane. The separation efficiency and fouling tendency of the modified membranes were evaluated for the treatment of a synthetic oily wastewater. A mechanism was proposed for the HB-PEG grafting on the surface of the corona treated PES membranes and all steps of the grafting were described in detail. The effects of corona treatment operating conditions on the morphology, surface properties, separation performance and anti-fouling efficiency of the modified PES membranes were investigated. Also, the HB-PEG grafted PES membranes were characterized by FTIR, AFM and contact angle analysis. Finally, the HB-PEG grafting on the surface of the PES membranes altered the surface hydrophilicity and led to the improvement of the anti-fouling property and oil–water permeation flux of all modified membranes without any remarkable changes in oil rejection.

The main goal of this study is to modify a polyethersulfone (PES) membrane by grafting with hyperbranched polyethylene glycol (HB-PEG) using corona air plasma to intensify the anti-fouling properties of the prepared membrane.

Surface grafting techniques on the improvement of membrane bioreactor: State-of-the-art advances

Membrane bioreactor (MBR) is regarded as the state-of-the-art technology in separation processes. Surface modification techniques play a critical role in improving the conventional membrane system which is mostly hydrophobic in nature. The hydrophobic nature of membranes is known to cause fouling, resulting in high maintenance costs and shorter lifespan of MBR. Thus, surface grafting aims to improve the hydrophilicity of bio-based membrane systems. This review describes the major surface grafting techniques currently used in membranes, including photo induced grafting, plasma treatment and plasma induced grafting, radiation induced grafting, thermal induced grafting and ozone induced grafting. The advantages and disadvantages of each method is discussed along with their parametric studies. The potential applications of MBR are very promising, but some integral membrane properties could be a major challenge that hinders its wider reach. The fouling issue could be resolved with the surface grafting techniques to achieve better performance of MBRs.

Plasma Modification and Synthesis of Membrane Materials-A Mechanistic Review

Although commercial membranes are well established materials for water desalination and wastewater treatment, modification on commercial membranes is still necessary to deliver high-performance with enhanced flux and/or selectivity and fouling resistance. A modification method with plasma techniques has been extensively applied for high-performance membrane production. The paper presents a mechanistic review on the impact of plasma gas and polymerization, at either low pressure or atmospheric pressure on the material properties and performance of the modified membranes. At first, plasma conditions at low-pressure such as plasma power, gas or monomer flow rate, reactor pressure, and treatment duration which affect the chemical structure, surface hydrophilicity, morphology, as well as performance of the membranes have been discussed. The underlying mechanisms of plasma gas and polymerization have been highlighted. Thereafter, the recent research in plasma techniques toward membrane modification at atmospheric environment has been critically evaluated. The research focuses of future plasma-related membrane modification, and fabrication studies have been predicted to closely relate with the implementation of the atmospheric-pressure processes at the large-scale.

Excimer laser channel creation in polyethersulfone hollow fibers for compartmentalized in vitro neuronal cell culture scaffolds

Hollow fiber scaffolds that compartmentalize axonal processes from their cell bodies can enable neuronal cultures with directed neurite outgrowth within a three-dimensional (3-D) space for controlling neuronal cell networking in vitro. Controllable 3-D neuronal networks in vitro could provide tools for studying neurobiological events. In order to create such a scaffold, polyethersulfone (PES) microporous hollow fibers were ablated with a KrF excimer laser to generate specifically designed channels for directing neurite outgrowth into the luminal compartments of the fibers. Excimer laser modification is demonstrated as a reproducible method to generate 5microm diameter channels within PES hollow fiber walls that allow compartmentalization of neuronal cell bodies from their axons. Laser modification of counterpart flat sheet PES membranes with peak surface fluences of 1.2Jcm(-2) results in increased hydrophobicity and laminin adsorption on the surface compared with the unmodified PES surface. This is correlated to enhanced PC12 cell adhesion with increasing fluence onto laser-modified PES membrane surfaces coated with laminin when compared with unmodified surfaces. Adult rat neural progenitor cells differentiated on PES fibers with laser-created channels resulted in spontaneous cell process growth into the channels of the scaffold wall while preventing entrance of cell bodies. Therefore, laser-modified PES fibers serve as scaffolds with channels conducive to directing neuronal cell process growth. These hollow fiber scaffolds can potentially be used in combination with perfusion and oxygenation hollow fiber membrane sets to construct a hollow fiber-based 3-D bioreactor for controlling and studying in vitro neuronal networking in three dimensions between compartmentalized cultures.

Surface modification of polypropylene microporous membrane to improve its antifouling characteristics in an SMBR: N2 plasma treatment

Fouling is the major obstacle in membrane processes applied in water and wastewater treatment. The polypropylene hollow fiber microporous membranes (PPHFMMs) were surface modified by N(2) low-temperature plasma treatment to improve the antifouling characteristics. Morphological changes on the membrane surface were characterized by field emission scanning electron microscopy (FE-SEM). The change of surface wettability was monitored by contact angle measurements. The static water contact angle of the modified membrane reduced obviously; the relative pure water flux of the modified membranes increased with the increase of plasma treatment time. To assess the relation between plasma treatment and membrane fouling in a submerged membrane bioreactor (SMBR), filtration of activated sludge was carried out by using synthetic wastewater. After continuous operation in the SMBR for about 90 h, flux recoveries for the N(2) plasma-treated PPHFMM for 8 min were 62.9% and 67.8% higher than those of the virgin membrane after water and NaOH cleaning. The irreversible fouling resistance decreased after plasma treatment.

Enhancement of the flux for polypropylene hollow fiber membrane in a submerged membrane-bioreactor by surface modification

To improve its limiting flux and antifouling characteristics in a submerged membrane-bioreactor (SMBR) for wastewater treatment, polypropylene hollow fiber microporous membrane (PPHFMM) was surface-modified by the plasma-induced immobilization of poly (N-vinyl-2-pyrrolidone) (PVP) and the plasma treatment with different gases respectively. Attenuated total reflection-Fourier transform infrared spectroscopy (FT-IR/ATR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscope (FE-SEM) were used to characterize the structural and morphological changes on the membrane surface. Water contact angle was measured by the sessile drop method. It was found that the water contact angle was 128.8, 72.3, 62.7, 74.4, 79.1, 86.3, and 71.3 degrees for the nascent, PVP-immobilized, air, O2, Ar, CO2 and H2O plasma treated PPHFMM, respectively. The SMBR was operated at fixed transmembrane pressure to determine the limiting flux for the PPHFMM before and after surface modification. Results showed that the limiting flux appeared to be 103, 159, 117, 133, 136, 121 and 152 L/(m(2)x h) for the nascent, PVP-immobilized, air, 02, Ar, CO2 and H2O plasma treated PPHFMM, respectively. After continuous operation for about 50 h in the SMBR, the antifouling characteristics were improved to some extent.