Antibacterial rGO-CuO-Ag film with contact- and release-based inactivation properties.

To reduce the high operational costs of water treatment because of membrane biofouling, next-generation materials are being developed to counteract microbial growth. These modern anti-biofouling strategies are based on new membrane materials or membrane surface modifications. In this study, antimicrobial films comprising rGO, rGO-CuO, rGO-Ag, and rGO-CuO-Ag were synthesized, evaluated, and tested for potential biofouling control using Pseudomonas aeruginosa PAO1 as the model bacterium. The combined rGO-CuO-Ag film displayed enhanced reduction (10-log reduction) in biofouling in comparison to the rGO film (control), followed by the rGO-Ag film (8-log reduction) and rGO-CuO film (0-log reduction). This demonstrated that the use of mixed antimicrobial agents is more effective in reducing biofouling than that of a single agent. The rGO-CuO-Ag film exhibited consistent, controlled, and moderate release of silver (Ag) ions. The release of Ag ions produced a long-lasting antimicrobial effect. These results underscore the potential applications of combined antimicrobial surface-based agents in practice and further research.

Implications of Chemical Reduction Using Hydriodic Acid on the Antimicrobial Properties of Graphene Oxide and Reduced Graphene Oxide Membranes.

The antimicrobial properties of graphene-based membranes such as single-layer graphene oxide (GO) and modified graphene oxide (rGO) on top of cellulose ester membrane are reported in this study. rGO membranes are made from GO by hydriodic acid (HI) vapor treatment. The antibacterial properties are tested after 3 h contact time with selected model bacteria. Complete bacterial cell inactivation is found only after contact with rGO membranes, while no significant bacterial inactivation is found for the control i) GO membrane, ii) the mixed cellulose ester support, and the iii) rGO membrane after additional washing that removes the remaining HI. This indicates that the antimicrobial effect is neither caused by the graphene nor the membrane support. The antimicrobial effect is found to be conclusively linked to the HI eliminating microbial growth, at concentrations from 0.005%. These findings emphasize the importance of caution in the reporting of antimicrobial properties of graphene-based surfaces.

Correlation Between Quorum Sensing Signal Molecules and Pseudomonas aeruginosa's Biofilm Development and Virulency.

Bacteria, when adhered to a substratum, can form biofilms. Nevertheless, many factors dictate biofilm formation and virulence factor production, including a response by the bacteria to their surroundings. This system is referred to as Quorum sensing (QS) also known as cell-cell communication. Pseudomonas aeruginosa is an infection causing agent in immune-compromised patients, it uses acyl-homoserine lactone (AHL) to coordinate its QS systems. In this work, the connection between some members of AHL produced by P. aeruginosa PAO1 and its biofilm development and the production of virulence factor was investigated. It was discovered that N-butanoyl-homoserine lactone (C4-HSL) and N-hexanoyl-L-homoserine lactone (C6-HSL) perform a more consequential and eminent function in the biofilm maturation and virulence factor production while N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL) plays a role in biofilm initiation. Because QS has been reported to be required for biofilm development and pathogenesis of P. aeruginosa, the results of this work have great importance and significance for the design of strategies for the control and prevention of biofilms.

Cleaning efficacy of hydroxypropyl-beta-cyclodextrin for biofouling reduction on reverse osmosis membranes.

In this study, an environmentally friendly compound, hydroxypropyl-beta-cyclodextrin (HP-ß-CD) was applied to clean reverse osmosis (RO) membranes fouled by microorganisms. The cleaning with HP-ß-CD removed the biofilm and resulted in a flux recovery ratio (FRR) of 102%. As cleaning efficiency is sometimes difficult to determine using flux recovery data alone, attached bacterial cells and extracellular polymeric substances (EPS) were quantified after cleaning the biofouled membrane with HP-ß-CD. Membrane surface characterization using scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) and atomic force microscopy (AFM) confirmed the effectiveness of HP-ß-CD in removal of biofilm from the RO membrane surface. Finally, a comparative study was performed to investigate the competitiveness of HP-ß-CD with other known cleaning agents such as sodium dodecyl sulfate (SDS), ethylenediaminetetraacetic acid (EDTA), Tween 20, rhamnolipid, nisin, and surfactin. In all cases, HP-ß-CD was superior.

Fabrication and Performance Evaluation of a Cation Exchange Membrane Using Graphene Oxide/Polyethersulfone Composite Nanofibers.

Ion exchange membranes, especially cation exchange membranes (CEMs), are an important component in membrane-based energy generation and storage because of their ability to transport cations via the electrochemical potential gradient while preventing electron transport. However, developing a CEM with low areal resistance, high permselectivity, and stability remains difficult. In this study, electrospun graphene oxide/polyethersulfone (GO/PES) composite nanofibers were prepared with varying concentrations of GO. To fabricate a CEM, the pores of the electrospun GO/PES nanofiber substrates were filled with a Nafion ionomer. The pore-filled PES nanofiber loaded with 1% GO revealed a noticeable improvement in hydrophilicity, structural morphology, and mechanical properties. The 1% GO/PES pore-filled CEM was compared to a Nafion membrane of a varying thickness and without a nanofiber substrate. The CEM with a nanofiber substrate showed permselectivity of 85.75%, toughness of 111 J/m3, and areal resistance of 3.7 Ω cm2, which were 12.8%, 4.3 times, and 4.0 times better, respectively, than those of the Nafion membrane at the same thickness. The development of a reinforced concrete-like GO/PES nanofiber structure containing stretchable ionomer-enhanced membrane surfaces exhibited suitable areal resistance and reduced the thickness of the composite membrane without compromising the mechanical strength, suggesting its potential application as a cation exchange membrane in electrochemical membrane-based systems.

Ultraviolet light-activated peroxymonosulfate (UV/PMS) system for humic acid mineralization: Effects of ionic matrix and feasible application in seawater reverse osmosis desalination.

The use of membrane-based technology has evolved into an important strategy for supplying freshwater from seawater and wastewater to overcome the problems of water scarcity around the world. However, the presence of natural organic matter (NOM), including humic substances affects the performance of the process. Here, we present a systematic report on the mineralization of humic acid (HA), as a model for NOM, in high concentration of salts using the ultraviolet light-activated peroxymonosulfate (UV/PMS) system as a potential alternative for HA elimination during membrane-based seawater desalination and water treatment processes. Effects of various parameters such as PMS concentration, solution type, pH, anions, and anion-cation matrix on HA mineralization were assessed. The results show that 100%, 78% and 58% of HA (2 mg/L TOC) were mineralized with rate constants of 0.085 min-1, 0.0073 min-1, and 0.0041 min-1 after 180 min reaction time at pH 7 when 0.5 mM PMS was used in deionized water, sodium chloride solution (35,000 ppm) and synthetic seawater, respectively. The reduced efficiency under saline conditions was attributed to the presence of anions in the system that acted as sulfate and hydroxyl radicals' scavengers. Furthermore, the safety of the treated synthetic seawater was evaluated by analyzing the residual transformed products. Overall, pretreatment with the UV/PMS system mitigated fouling on the RO membrane.

Antiviral Nanomaterials for Designing Mixed Matrix Membranes.

Membranes are helpful tools to prevent airborne and waterborne pathogenic microorganisms, including viruses and bacteria. A membrane filter can physically separate pathogens from air or water. Moreover, incorporating antiviral and antibacterial nanoparticles into the matrix of membrane filters can render composite structures capable of killing pathogenic viruses and bacteria. Such membranes incorporated with antiviral and antibacterial nanoparticles have a great potential for being applied in various application scenarios. Therefore, in this perspective article, we attempt to explore the fundamental mechanisms and recent progress of designing antiviral membrane filters, challenges to be addressed, and outlook.

Antimicrobial mechanism of reduced graphene oxide-copper oxide (rGO-CuO) nanocomposite films: The case of Pseudomonas aeruginosa PAO1.

The antimicrobial properties of two-dimensional materials such as graphene-based surfaces are vital for environmental and biomedical applications. Here, the improvement of the antibacterial property of reduced graphene oxide by the preparation of rGO-CuO nanocomposite films was reported. The rGO-CuO nanocomposites were synthesized via a simple hydrothermal method, and the nanocomposite films were fabricated by filtering through a polytetrafluoroethylene (PTFE) filter with the assistance of a vacuum filtration unit. After characterization of the nanocomposite films, the antibacterial properties were tested against Pseudomonas aeruginosa PAO1. The fabricated rGO-CuO nanocomposite films exhibited excellent antibacterial activity, leading to complete bacterial inactivation upon contact. The antibacterial properties were closely linked to the reactive oxygen species (ROS) independent pathway rather than the ROS-dependent pathway. This work provides an insight into the antibacterial mechanisms of reduced GO and copper oxide composite film for water treatment systems and the potential application of these nanocomposites in biomedicine.

Recent Progress in One- and Two-Dimensional Nanomaterial-Based Electro-Responsive Membranes: Versatile and Smart Applications from Fouling Mitigation to Tuning Mass Transport.

Membrane technologies are playing an ever-important role in the field of water treatment since water reuse and desalination were put in place as alternative water resources to alleviate the global water crisis. Recently, membranes are becoming more versatile and powerful with upgraded electroconductive capabilities, owing to the development of novel materials (e.g., carbon nanotubes and graphene) with dual properties for assembling into membranes and exerting electrochemical activities. Novel nanomaterial-based electrically responsive membranes have been employed with promising results for mitigating membrane fouling, enhancing membrane separation performance and self-cleaning ability, controlling membrane wettability, etc. In this article, recent progress in novel-nanomaterial-based electrically responsive membranes for application in the field of water purification are provided. Thereafter, several critical drawbacks and future outlooks are discussed.

High-flux ultrafiltration membrane with open porous hydrophilic structure using dual pore formers.

This work investigated the synergistic effect of polyvinylpyrrolidone (PVP) and hydroxypropyl-beta-cyclodextrin (HP-ß-CD) as dual pore forming agents on the properties and performance of polysulfone (PSf) ultrafiltration membranes. A fixed concentration of PVP and varying concentrations of HP-ß-CD were used to prepare the membranes using the phase inversion technique. The results showed that the inclusion of these additives in the dope solution increased its thermodynamic instability and promoted instantaneous demixing. Overall, an increase was observed in the hydrophilicity, open porous structure and mechanical strength of the membranes. Cross-flow filtration tests demonstrated that the pure water permeability of the fabricated membrane was 891 LMH bar-1, about 4.37 times higher than the pristine membrane, while bovine serum albumin (BSA) rejection was relatively constant (about 93%) for all the fabricated membranes. This work proposed that the addition of HP-ß-CD and PVP as dual pore formers can produce a viable ultrafiltration membrane with improved water permeability without a middle ground on rejection potential.