Anti-fouling behavior of hyperbranched polyglycerol-grafted poly(ether sulfone) hollow fiber membranes for osmotic power generation

Design of Microstructure-Engineered Polymers for Energy and Environmental Conservation

With the ever-growing demand for sustainability, designing polymeric materials using readily accessible feedstocks provides potential solutions to address the challenges in energy and environmental conservation. Complementing the prevailing strategy of varying chemical composition, engineering microstructures of polymer chains by precisely controlling their chain length distribution, main chain regio-/stereoregularity, monomer or segment sequence, and architecture creates a powerful toolbox to rapidly access diversified material properties. In this Perspective, we lay out recent advances in utilizing appropriately designed polymers in a wide range of applications such as plastic recycling, water purification, and solar energy storage and conversion. With decoupled structural parameters, these studies have established various microstructure-function relationships. Given the progress outlined here, we envision that the microstructure-engineering strategy will accelerate the design and optimization of polymeric materials to meet sustainability criteria.

Fluidics for energy harvesting: from nano to milli scales

A large amount of untapped energy sources surrounds us. In this review, we summarize recent works of water-based energy harvesting systems with operation scales ranging from miniature systems to large scale attempts. We focus particularly on the triboelectric energy, which is produced when a liquid and a solid come into contact, and on the osmotic energy, which is released when salt water and fresh water are mixed. For both techniques we display the state of the art understanding (including electrical charge separation, electro-osmotic currents and induced currents) and the developed devices. A critical discussion of present works confirms the significant progress of these water-based energy harvesting systems in all scales. However, further efforts in efficiency and performance amelioration are expected for these technologies to accelerate the industrialization and commercialization procedure.

Dendritic Polymers in Tissue Engineering: Contributions of PAMAM, PPI PEG and PEI to Injury Restoration and Bioactive Scaffold Evolution

The capability of radially polymerized bio-dendrimers and hyperbranched polymers for medical applications is well established. Perhaps the most important implementations are those that involve interactions with the regenerative mechanisms of cells. In general, they are non-toxic or exhibit very low toxicity. Thus, they allow unhindered and, in many cases, faster cell proliferation, a property that renders them ideal materials for tissue engineering scaffolds. Their resemblance to proteins permits the synthesis of derivatives that mimic collagen and elastin or are capable of biomimetic hydroxy apatite production. Due to their distinctive architecture (core, internal branches, terminal groups), dendritic polymers may play many roles. The internal cavities may host cell differentiation genes and antimicrobial protection drugs. Suitable terminal groups may modify the surface chemistry of cells and modulate the external membrane charge promoting cell adhesion and tissue assembly. They may also induce polymer cross-linking for healing implementation in the eyes, skin, and internal organ wounds. The review highlights all the different categories of hard and soft tissues that may be remediated with their contribution. The reader will also be exposed to the incorporation of methods for establishment of biomaterials, functionalization strategies, and the synthetic paths for organizing assemblies from biocompatible building blocks and natural metabolites.

Designing sustainable membrane-based water treatment via fouling control through membrane interface engineering and process developments

Membrane-based water treatment processes have been established as a powerful approach for clean water production. However, despite the significant advances made in terms of rejection and flux, provision of sustainable and energy-efficient water production is restricted by the inevitable issue of membrane fouling, known to be the major contributor to the elevated operating costs due to frequent chemical cleaning, increased transmembrane resistance, and deterioration of permeate flux. This review provides an overview of fouling control strategies in different membrane processes, such as microfiltration, ultrafiltration, membrane bioreactors, and desalination via reverse osmosis and forward osmosis. Insights into the recent advancements are discussed and efforts made in terms of membrane development, modules arrangement, process optimization, feed pretreatment, and fouling monitoring are highlighted to evaluate their overall impact in energy- and cost-effective water treatment. Major findings in four key aspects are presented, including membrane surface modification, modules design, process integration, and fouling monitoring. Among the above mentioned anti-fouling strategies, a large part of research has been focused on membrane surface modifications using a number of anti-fouling materials whereas much less research has been devoted to membrane module advancements and in-situ fouling monitoring and control. At the end, a critical analysis is provided for each anti-fouling strategy and a rationale framework is provided for design of efficient membranes and process for water treatment.

Maintaining Antibacterial Activity against Biofouling Using a Quaternary Ammonium Membrane Coupling with Electrorepulsion

Antibacterial modification is a chemical-free method to mitigate biofouling, but surface accumulation of bacteria shields antibacterial groups and presents a significant challenge in persistently preventing membrane biofouling. Herein, a great synergistic effect of electrorepulsion and quaternary ammonium (QA) inactivation on maintaining antibacterial activity against biofouling has been investigated using an electrically conductive QA membrane (eQAM), which was fabricated by polymerization of pyrrole with QA compounds. The electrokinetic force between negatively charged Escherichia coli and cathodic eQAM prevented E. coli cells from reaching the membrane surface. More importantly, cathodic eQAM accelerated the detachment of cells from the eQAM surface, particularly for dead cells whose adhesion capacity was impaired by inactivation. The number of dead cells on the eQAM surface was declined by 81.2% while the number of live cells only decreased by 49.9%. Characterization of bacteria accumulation onto the membrane surface using an electrochemical quartz crystal microbalance revealed that the electrorepulsion accounted for the cell detachment rather than inactivation. In addition, QA inactivation mainly contributed to minimizing the cell adhesion capacity. Consequently, the membrane fouling was significantly declined, and the final normalized water flux was promoted higher than 20% with the synergistic effect of electrorepulsion and QA inactivation. This work provides a unique long-lasting strategy to mitigate membrane biofouling.

Volume Overlap Variation within Hyperbranched Polymer Brushes Resolves Topology Effects against Protein Fouling

Hyperbranched polymer brushes with a three-dimensional dendritic structure are used in antifouling applications to obtain bioinert and compact dendritic structures. Though hyperbranched polyglycerol (HPG) is extensively utilized in the antifouling layer, there is still a lack of direct studies on the relationship between the interfacial properties and topology effect of hyperbranched polymer brushes. Here, we established the degree of chain volume overlap (D_v) to characterize the spatial shielding efficiency generated by HPG brushes and investigated the impact mechanism of the variable chain length on the interfacial physicochemical properties. The results revealed the D_v-relevant feature of performance that the most densely packed HPG brushes for a medium-length L_HPG3.07 enable the functional surface to display optimal antifouling performance toward protein adsorption by forming the most effective space barrier and hydrated layer in appropriate molecular weights and graft density. Moreover, we clarified the advance of hyperbranched polymer brushes exhibited in topology effects for imparting surface-enhanced resistance to biofouling relies on the generable higher steric hindrance as compared with linear analogs. This study established a D_v-relevant evaluation model for acquiring an optimized antifouling surface based on the appropriate choice of polymer structure, topology morphologies, and grafting parameters.

Introduction of an antifouling photoelectrode: an effective strategy for a high-performance photoelectrochemical cytosensor

As nonspecific adsorption or biofouling has obvious side effects on the selectivity, it is a great challenge for cytosensors to detect target cells in practical biological samples. In this study, we first propose the design and synthesis of an antifouling photoelectrode. The antifouling photoelectrode not only has the desired photocurrent response, but also possesses an unexpected antifouling capability of resisting nonspecific adsorption of biomolecules. Herein, the PEDOT-HPG/SnS/ZnO-NT antifouling photoelectrode was formed and a robust photoelectrochemical cytosensor with enhanced sensitivity and selectivity has been demonstrated.

Commercial Pressure Retarded Osmosis Systems for Seawater Desalination Plants

The development of renewable energy technologies is of global importance. To realize a sustainable society, fossil-resource-independent technologies, such as solar- and wind-power generation, should be widely adopted. Pressure retarded osmosis (PRO) is one such potential renewable energy technology. PRO requires salt water and fresh water, both of which can be found at seawater desalination plants. The total power generation capacity of PRO, using concentrated seawater and fresh water, is 3 GW. A large amount of energy is required for seawater desalination; therefore, the introduction of renewable energy should be prioritized. Kyowakiden Industry Co., Ltd., has been working on introducing PRO to seawater desalination plants since 2001 and is attracting attention for its ongoing PRO pilot plant with a scale of 460 m³/d, using concentrated seawater and treated sewage water. In this study, we evaluated the feasibility of introducing PRO in existing desalination plants. The feasibility was examined based on technology, operation, and economy. Based on the number of seawater desalination plants in each country and the electricity charges, it was determined whether the introduction of PRO would be viable.

Hierarchical Surface Architecture of Hemodialysis Membranes for Eliminating Homocysteine Based on the Multifunctional Role of Pyridoxal 5'-phosphate

Patients with end-stage renal disease are prone to developing a complication of hyperhomocysteinemia, manifesting as an elevation of the homocysteine (Hcy) concentration in human plasma. However, Hcy as a protein-bound toxin is barely removed by conventional hemodialysis membranes. Here, we report a novel hemodialysis membrane by preparing a bioactive coating of pyridoxal 5'-phosphate (PLP) and adding biocompatible hyperbranched polyglycerol (HPG) brushes to achieve Hcy removal. The dip-applied PLP coating, a coenzyme with a role in Hcy metabolism, dramatically promoted a decrease in the Hcy concentration in human plasma. Moreover, the aldehyde group of PLP had an intrinsic chemical reactivity toward the terminal amino group to immobilize the HPG brushes on the hemodialysis membrane surface. The hierarchical PLP-HPG layer-functionalized membranes had a high efficacy for eliminating Hcy, with a concentration from the initial stage of 150 μmol/L reduced to a nearly normal level of 20 μmol/L in simulated dialysis. By analyzing the impact of HPG brushes with various chain lengths, we found that HPG brushes with a medium length enabled the PLP coating with the bioactive function of Hcy conversion to additionally protect Hcy-attacked target cells by providing excellent hydrophilicity and a dense enough chain volume overlap of the hyperbranched architecture. Simultaneously, the densely packed HPG brushes generated a maximal steric and hydration barrier that significantly improved biofouling resistance against blood proteins. The optimally functionalized membranes showed a clearance of 83.1% urea and 49.6% lysozyme and a rejection of 96.0% bovine serum albumin. The diversely functionalized PLP-HPG layers demonstrate a potential route for a more integrated hemodialysis membrane that can cope with the urgent issue of hyperhomocysteinemia in clinical hemodialysis therapy.

Superhydrophobic nanocarbon-based membrane with antibacterial characteristics

To overcome the biofouling challenge which faces membrane water treatment processed, the novel superhydrophobic carbon nanomaterials impregnated on/powder activated carbon (CNMs/PAC) was utilized to successfully design prepare an antimicrobial membrane. The research was conducted following a systematic statistical design of experiments technique considering various parameters of composite membrane fabrication. The impact of these parameters of composite membrane on Staphylococcus aureus growth was investigated. The bacteria growth was analyzed through spectrophotometer and SEM. The effect of CNMs' hydrophobicity on the bacterial colonies revealed a decrease in the abundance of bacterial colonies and an alteration in structure with increasing the hydrophobicity. The results revealed that the optimum preparative conditions for carbon loading CNMs/PAC was 363.04 mg with a polymer concentration of 22.64 g/100 g, and a casting knife thickness of 133.91 μm. These conditions have resulted in decreasing the number of bacteria colonies to about 7.56 CFU. Our results provided a strong evidence on the antibacterial effect and consequently on the antibiofouling potential of CNMs/PAC in membrane.

"Button and Buttonhole" Supramolecular Structure Enables the Self-Healing Behaviors of Functionalized Poly(ether sulfone) Membranes for Osmotic Power Generation

Osmotic power generation has emerged as an advanced technology toward water-energy nexus to tackle global water pollution. It provides a sustainable use of salinity gradient from water resources yet encounters major obstacles caused by pressure-retarded osmosis (PRO) membrane fouling. Although membranes with good antifouling properties are widely studied, their antifouling functions are readily lost when scratches or detachments occur through physical damage during operation and chemical degradation by water and corrosive foulants. Consequently, it is important to develop antifouling membranes with autonomous self-healing capabilities. Herein, self-healable functionalized poly(ether sulfone) (PES) antifouling membranes have been fabricated via the sequential conjugation of the zwitterionic random copolymer [poly(1-(1-(1-adamantylcarbonyloxy)methyl)-3-vinylimidazolium bromide-co-1-(3-sulfopropyl)-3-vinylimidazolium-co-vinylamine)] (P(ADVI-co-SBVI-co-VA), abbreviated as PASV copolymer) and linear cyclodextrin polymer (LPCD) on polydopamine-preactivated PES supports. The self-healing behaviors rely on the judiciously designed "button-and-buttonhole" supramolecular network. Specifically, β-cyclodextrins in LPCD and adamantines in PASV act as "buttonholes" and "buttons", respectively. Under physical and chemical damages, the β-cyclodextrin "buttonhole" may sacrificially detach from the adamantine "button" of PASV but then recap another adamantine to restore the protective function. The antifouling and self-healing traits of as-functionalized PES-g-PASV-LPCD membranes were demonstrated by the superior antiprotein behaviors and improved antimicrobial performances on both nonaged and aged samples. In the PRO process, the modified membranes were effective in mitigating organic fouling and exhibited higher power density (79% of the initial value) than the nonmodified ones (47% of the initial value) in municipal wastewater testing. The strategy for engineering inherently healable and antifouling membranes paves a new pathway for the development of sustainable membranes for osmotic power production.

Design of omniphobic interfaces for membrane distillation - A review

Membrane distillation (MD) has a great potential in treating high salinity industrial wastewater due to its unique characteristics. Nevertheless, the implementation of MD for industrial wastewater reclamation must be conducted with precaution because low-surface-tension contaminates in feed solutions may easily wet the membranes. In recent years, omniphobic membranes that exhibit strong repellence towards liquids with a wide range of surface tensions have been proposed as a promising solution to deal with the wetting problem. In this paper, we aim to provide a comprehensive review of omniphobic interfaces and illustrate their fundamental working principles, innovative design approaches and novel applications on membrane distillation. The review may provide insights in designing stable solid-liquid-vapor interfaces and serve as a guidance for the development of robust anti-wetting membranes for industrial wastewater reclamation via membrane distillation.

Antifouling Double-Skinned Forward Osmosis Membranes by Constructing Zwitterionic Brush-Decorated MWCNT Ultrathin Films

Pressure retarded osmosis (PRO) process is hindered by severe fouling occurring within the porous support of the forward osmosis (FO) membranes. We designed a novel double-skinned FO membrane containing a polyamide salt-rejecting layer and a zwitterionic brush-decorated, multiwalled carbon nanotube (MWCNT/PSBMA) foulant-resisting layer on the back side. Our results demonstrated that the coating of the MWCNT/PSBMA layer on the porous polyketone (PK) support imparted enhanced hydrophilicity and smaller membrane pore size, thereby providing excellent resistance toward both protein adhesion and bacterial adsorption. We also further evaluated this resultant double-skinned membrane (i.e., TFC-MWCNT/PSBMA) in dynamic PRO fouling experiments using protein and alginate as model organic foulants. Compared to the pristine TFC-PK and hydrophobic TFC-MWCNT membranes, the TFC-MWCNT/PSBMA membrane exhibited not only the lowest water flux decline but also the highest water flux recovery after simple physical flushing. These results shed light on fabrication of antifouling PRO membranes for water purification purposes.

Calcium-Carboxyl Intrabridging during Interfacial Polymerization: A Novel Strategy to Improve Antifouling Performance of Thin Film Composite Membranes

This study reports a novel intrabridging strategy to improve the antifouling performance of a thin-film composite (TFC) membrane. We demonstrate that the addition of Ca²⁺ during the interfacial polymerization reaction led to the formation of stable Ca²⁺-carboxyl complexes within the polyamide rejection layer. This intrabridging of carboxyl groups by Ca²⁺ effectively sequestrated them, reducing their availability for binding divalent metal ions in the aqueous solution and for forming foulant-metal-membrane interbridges. Membrane fouling and cleaning experiments confirmed improved flux stability and fouling reversibility for the Ca²⁺ modified membranes. The greatly enhanced antifouling performance of these membranes, together with their better surface hydrophilicity and greater water permeability, makes the intrabridging approach highly attractive in overcoming the classical permeability-selectivity-antifouling trade-off. Our findings pave a new direction for synthesizing high-performance TFC membranes.

Graphitic carbon nitride (g-C3N4) nanosheets functionalized composite membrane with self-cleaning and antibacterial performance

Membrane fouling significantly impedes membrane performance and thus short lifespan of the membrane. Membranes that functionalized with photocatalytic activity are deemed as an effective and novel approach to settle membrane fouling. The membranes with self-cleaning and antibacterial performance were fabricated via facilely filtering g-C₃N₄ nanosheets onto polyacrylonitrile (PAN) porous substrates. The g-C₃N₄ nanosheets were exfoliated by acid etching and ultrasound treatment, and the exfoliated nanosheets was verified by Fourier transform infrared spectra, Atomic force microscopy and X-ray diffraction. The g-C₃N₄ nanosheets functionalized composite membranes have a water permeability of 11.70 L m^-2 h^-1 bar^-1 and a good antibacterial activity. In addition, the membranes could be restored their original permeability and their surfaces were close to initial color even after three cycles rejecting dyes and post treatment under irradiation with visible light. Besides, the degradable and antimicrobial mechanisms of the membranes were investigated respectively. These g-C3N4 nanosheets composite membranes with self-cleaning and antimicrobial properties have a potential feasibility in water treatment, and provide an alternative method for fabricating self-cleaning membranes.

Diblock Polymer Brush (PHEAA- b-PFMA): Microphase Separation Behavior and Anti-Protein Adsorption Performance

In this paper, a series of amphiphilic diblock polymers of poly(hydroxyethylacrylamide)- b-poly(1H,1H-pentafluoropropyl methacrylate) (PHEAA- b-PFMA) were grafted from silicon wafer via surface-initiated atom transfer radical polymerization (SI-ATRP). Surface wettability and chemical compositions of the modified surfaces were characterized by contact angle goniometer and X-ray photoelectron spectroscopy (XPS) respectively. Molecular weight and polydispersity of each block were measured using gel permeation chromatography (GPC). The topography and the microphase separation behavior of PHEAA- b-PFMA surfaces were investigated by atomic force microscope (AFM). The results show that only when the grafting density (σ) and thickness of PHEAA brush were in the range of 0.9-1.3 (chain/nm²) and 6.6-15.1 nm, respectively, and the ratio of PFMA/PHEAA varied from 89/42 to 89/94, could the diblock copolymer phase separate into nanostructures. Further, the antiprotein adsorption performance of the modified surfaces against BSA, fibrinogen, and lysozyme was studied. The results indicated the modified surfaces could reduce the protein adsorption compared to the pristine silicon wafer. For Fibrinogen, the antiadsorption effect of PHEAA- b-PFMA-modified surfaces with microphase segregation was better than that of corresponding PHEAA modified surfaces. The results provide further evidence that surface composition and microphase segregation of fluorinated moieties of block copolymer brushes significantly impact protein adsorption behaviors.

Improved Anti-Biofouling Performance of Thin -Film Composite Forward-Osmosis Membranes Containing Passive and Active Moieties

Forward osmosis (FO) has gained increasing attention in desalination, wastewater treatment, and power generation. However, biofouling remains a major obstacle for the sustainable development of the FO process. Both passive and active strategies have been developed to mitigate membrane biofouling. A comprehensive understanding of different strategies and mechanisms has fundamental significance for the antifouling membrane development. In this study, thin-film composite (TFC) FO membranes were modified with polydopamine (PDA) coating as a passive antibacterial moiety and silver nanoparticles (Ag NPs) as an active antibacterial moiety. Their anti-biofouling performances were investigated both in static and dynamic conditions. In static exposure, the PDA-coated membranes exhibited great passive anti-adhesive property, and the Ag-NP-generated membranes presented both of excellent passive anti-adhesive properties and active antibacterial performance. While in dynamic cross-flow running conditions, Ag NPs effectively mitigated the membrane water flux decline due to their inhibition of biofilm growth, the PDA coating failed because of its inability to inactivate the attached bacteria growth. Moreover, Ag NPs were stable and active on membrane surfaces after 24 h of cross-flow operation. These findings provide new insights into the performances and mechanisms of passive and active moieties in the FO process.

Advanced Anti-Fouling Membranes for Osmotic Power Generation from Wastewater via Pressure Retarded Osmosis (PRO)

A facile and versatile approach was demonstrated for the fabrication of low-fouling pressure retarded osmosis (PRO) membranes for osmotic power generation from highly polluted wastewater. A water-soluble zwitterionic random copolymer with superior hydrophilicity and unique chemistry was molecularly designed and synthesized via a single-step free-radical polymerization between 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-aminoethyl methacrylate hydrochloride (AEMA). The P[MPC- co-AEMA] copolymer was then chemically grafted onto the surface of PES/Torlon hollow fibers via amino groups coupling of poly(AEMA) with the polyimide structures of Torlon, leaving the zwitterions of poly(MPC) in the feed solution. Because of the outstanding hydrophilicity, unique cationic and anionic groups, and electrical neutrality of the zwitterionic brush, the newly developed membrane showed great resistances to both inorganic scaling and organic fouling in PRO operations. When using a real wastewater brine comprising multifoulants as the feed, the P[MPC- co-AEMA] modified membrane exhibits a much lower flux decline of 37% at Δ P = 0 bar after 24-h tests and a smaller power density decrease of 28% at Δ P = 15 bar within 12-h tests, compared to 61% and 42% respectively for the unmodified one. In addition to the low fouling tendency, the modified membrane shows outstanding performance stability and fouling reversibility, where the flux is almost fully recovered by physical backwash of water at 15 bar for 0.5 h. This study provides valuable insights and strategies for the design and fabrication of effective antifouling materials and membranes for PRO osmotic power generation.

Antifouling enhancement of polyimide membrane by grafting DEDA-PS zwitterions

In order to improve the water flux and antifouling property of polyimide (PI) membrane, zwitterions are grafted on PI membrane surface via a two-step modification route by reactions with N,N-diethylethylenediamine (DEDA) and 1,3-propane sultone (PS) sequentially. The reaction mechanism and physicochemical properties of membranes are confirmed via various characterization techniques. The anti-biofouling performance of the zwitterion-grafted PI membranes is evaluated by bacterial suspension immersion tests in Escherichia coli (E. coli) and staphylococcus aureus (S. aureus) solutions. The antifouling property is assessed via the filtration test using the bovine serum albumin (BSA) and dodecyl trimethyl ammonium bromide (DTAB) aqueous feed solutions. The effect of the reaction time with DEDA in the zwitterion-grafted process on the antifouling property is further investigated systematically. The results show that both the anti-biofouling and antifouling performances of zwitterion-grafted PI membranes are significantly improved.

Novel Dimensionally Controlled Nanopore Forming Template in Forward Osmosis Membranes

To lower the unfavorable internal concentration polarization effect in forward osmosis (FO) membranes, support layers of highly porous interconnected structures with specifically large surface-to-volume ratios are indispensable. Herein, zinc oxide (ZnO) has been introduced as a new template to manipulate the porous structure of poly(ether sulfone) (PES) support layer. The ZnO can be readily synthesized as desired in different dimensionally controlled nanostructures. The performance of the FO membrane was initially ameliorated in terms of permeability and selectivity through simple incorporation of ZnO nanostructures in the PES support layer. The PES support layer was blended with appropriate amounts of ZnO nanostructures, casted on a glass plate, and subsequently acid washed to leach out the embedded ZnO nanostructures. Different nanoporous structures were achieved when ZnO of different nanostructures was used to modify the PES support layer. The experimental results indicated that the permeability of FO membranes could be simply improved by incorporation of ZnO nanostructures in PES support layer. Higher hydrophilicity and formation of suitable internal pores were mainly responsible for such observation. Although surface hydrophilicity of the support layers was reduced after being acid washed, water permeation through the membrane was intensified due to the formation of interconnected porous structure.