Surface Grafting of Reverse Osmosis Membrane with Chlorhexidine Using Biopolymer Alginate Dialdehyde as a Facile Green Platform for In Situ Biofouling Control

From Antibacterial to Antibiofilm Targeting: An Emerging Paradigm Shift in the Development of Quaternary Ammonium Compounds (QACs)

In a previous development stage, mostly individual antibacterial activity was a target in the optimization of biologically active compounds and antiseptic agents. Although this targeting is still valuable, a new trend has appeared since the discovery of superhigh resistance of bacterial cells upon their aggregation into groups. Indeed, it is now well established that the great majority of pathogenic germs are found in the environment as surface-associated microbial communities called biofilms. The protective properties of biofilms and microbial resistance, even to high concentrations of biocides, cause many chronic infections in medical settings and lead to serious economic losses in various areas. A paradigm shift from individual bacterial targeting to also affecting more complex cellular frameworks is taking place and involves multiple strategies for combating biofilms with compounds that are effective at different stages of microbiome formation. Quaternary ammonium compounds (QACs) play a key role in many of these treatments and prophylactic techniques on the basis of both the use of individual antibacterial agents and combination technologies. In this review, we summarize the literature data on the effectiveness of using commercially available and newly synthesized QACs, as well as synergistic treatment techniques based on them. As an important focus, techniques for developing and applying antimicrobial coatings that prevent the formation of biofilms on various surfaces over time are discussed. The information analyzed in this review will be useful to researchers and engineers working in many fields, including the development of a new generation of applied materials; understanding biofilm surface growth; and conducting research in medical, pharmaceutical, and materials sciences. Although regular studies of antibacterial activity are still widely conducted, a promising new trend is also to evaluate antibiofilm activity in a comprehensive study in order to meet the current requirements for the development of highly needed practical applications.

Effects of Ethyl Lauroyl Arginate (LAE) on Biofilm Detachment: Shear Rate, Concentration, and Dosing Time

Biofilm formation is one of the main obstacles in membrane treatment. The non-oxidizing biocide ethyl lauroyl arginate (LAE) is promising for mitigating biofilm development on membrane surfaces. However, the operating conditions of LAE and their impact on biofilm detachment are not comprehensively understood. In this study, a real-time in vitro flow cell system was utilized to observe biofilm dispersal caused by the shear rate, concentration, and treatment time of LAE. This confirmed that the biofilm was significantly reduced to 68.2% at a shear rate of 3.42 s−1 due to the increased physical lifting force. LAE exhibited two different mechanisms for bacterial inactivation and biofilm dispersal. Biofilms treated with LAE at sub-growth inhibitory concentrations for a longer time could effectively detach the biofilm formed on the surface of the glass slides, which can be attributed to the increased motility of microorganisms. However, a high concentration (i.e., bactericidal concentration) of LAE should be seriously considered because of the inactivated sessile bacteria and their residual debris remaining on the surface. This study sheds light on the effect of LAE on biofilm detachment and provides insights into biofouling mitigation during the membrane process.

Robust In Situ Fouling Control toward Thin-Film Composite Reverse Osmosis Membrane via One-Step Deposition of a Ternary Homogeneous Metal-Organic Hybrid Layer

Membrane fouling is one of the persistent headaches for water desalination because of the significant detriment to membrane performance and operating cost control. It is a great challenge to overcome such crisis in a facile and robust manner. This work was dedicated to customizing an antifouling thin-film composite (TFC) reverse osmosis (RO) membrane with a polydopamine (PDA)/β-alanine (βAla)/Cu²⁺ ternary homogeneous metal-organic hybrid coating. The metal ions were evenly distributed in a continuous organic network via polydentate coordination. The incorporation of βAla enabled a substantial promotion of the Cu²⁺ loading capacity on the membrane surface. The involved one-step codeposition protocol made the surface engineering practically accessible. The deposition time was optimized to afford an uncompromising permselectivity of the membrane. This novel trinity was a smart blend of anti-adhesive and bactericidal factors, and each component in the all-in-one layer performed its own function. The hydrophilic PDA/βAla phase induced weak deposition propensity of organic foulant and bacteria onto the modified membrane, as elucidated by water flux variation, foulants adhesion profile, and interfacial interaction energy. Meanwhile, the Cu²⁺-loaded surface strongly inactivated the attached bacteria to further alleviate biofouling. Excellent sustainability and stability implied the reliable performance of such trinity-coated membrane in practical service. Given the simplicity and robustness, this work opened a promising avenue for in situ fouling control of TFC RO membranes during water desalination.

Resolving the Tribo-catalytic reaction mechanism for biochar regulated Zinc Oxide and its application in protein transformation

The utilization of mechanical energy to control water pollutants under dark conditions is currently a point of study focus. Herein, biochar -zinc oxide (BC-ZnO) composites with various structures were synthesized by co-pyrolysis of cotton and ZnO at different temperature and used for tribo-catalytic reaction. The introduction of BC can improve charge transmission and separation efficiency. Ultraviolet photoelectron spectra (UPS) and density functional theory (DFT) calculation prove the addition of BC can reduce work function of ZnO, and enhance its electron-donating ability. Specially, suitable adsorption amount is the key factor to improve the tribo-catalytic performance. When the pyrolysis temperature is 600 °C, BC-ZnO has the best degradation efficiency, which can degrade 90% Rhodamine B (RhB) in 75 min, while ZnO can degrade only 38%. On this basis, using bovine serum albumin (BSA) as a model, the effect of tribo-catalytic reaction on controlling proteins in water was studied by fluorescence excitation-emission matrix spectroscopy (3D EEM) and infrared microscope, and the transformation of proteins was further analyzed. This study provides a new strategy to improve the tribo-catalytic performance of ZnO, and explores its application prospects of biological wastewater control.

Smart Self-Cleaning Membrane via the Blending of an Upper Critical Solution Temperature Diblock Copolymer with PVDF

Poly(2,2,2-trifluoroethyl methacrylate)-b-poly(imidazoled glycidyl methacrylate-co-diethylene glycol methyl ether methacrylate) (PTFEMA-b-P(iGMA-co-MEO₂MA)) containing an upper critical solution temperature (UCST) polymer chain was prepared and blended with poly(vinylidene fluoride) (PVDF) to produce a thermoresponsive membrane with smart self-cleaning performance. The successful preparation of the membrane was demonstrated by attenuated total reflection-Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy characterization. The membrane shows UCST performance, and its flux changes with the filtrate temperature as the UCST polymer chain stretches out and contracts in response to various temperatures. In addition, the UCST polymer chain can disrupt the foulant and push it away from the membrane when the temperature is above the UCST and thus enables membranes to exhibit a smart self-cleaning behavior. To the best of our knowledge, this work is the first report of a smart self-cleaning membrane based on the blending of a diblock copolymer containing a UCST polymer chain with PVDF.

Fabrication of self-assembled 0D-2D Bi2MoO6-g-C3N4 photocatalytic composite membrane based on PDA intermediate coating with visible light self-cleaning performance

A Self-cleaning surface can efficaciously solve the problem of irreversible contamination buildup on filtration membranes. Photocatalytic membranes were fabricated via vacuum assisted layer-by-layer (LBL) self-assembly of 0D-2D Bi₂MoO₆-g-C₃N₄ on a PDA coated thin-film composite PVDF substrate by Schiff base reaction. The rejection rate of the simulated polysaccharide was more than 90%, and that of the simulated protein was more than 80%. The combination of the membrane and the photocatalyst promoted the degradation of tetracycline hydrochloride by the composite membrane to 67.85% when original membranes had minor effect. Under visible light, reversible radiation pollutants (R_r) gradually replaced irreversible pollutants (R_ir) as the main pollutants. The flux recovery ratio (FRR) of 0D-2D Bi₂MoO₆-g-C₃N₄/PVDF membrane was 85% after being irradiated with visible light for 30 min. The flux recovery rate of contaminated photocatalytic membrane remained 75%, and the rejection was maintained in a stable range after four cycles of the cleaning operation under visible light. The results indicated that the excellent photocatalytic performance of 0D-2D Bi₂MoO₆-g-C₃N₄ photocatalysis material and the increase of multi-dimensional functional layer morphology on pollutant contact area improved the mechanical stability, interception performance and self-cleaning performance of the composite membrane. This work not only builds a new type of composite coating membranes, but also help us to further understand the relationship between the dimensions of photocatalytic materials and the improvement of photocatalytic membrane performance.

Preparation of Multipurpose Polyvinylidene Fluoride Membranes via a Spray-Coating Strategy Using Waterborne Polymers

As reported herein, the waterborne polymers poly(glycidyl methacrylate-co-poly(ethylene glycol) methyl ether methacrylate) P(GMA-co-mPEGMA) and polyethyleneimine (PEI) were used to prepare multipurpose polyvinylidene fluoride (PVDF) membranes via a direct spray-coating method. P(GMA-co-mPEGMA) and PEI were alternately sprayed onto the PVDF membrane to yield stable cross-linked copolymer coatings. The successful coating of polymers onto the membrane surface was verified by scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy characterization. The coated membrane exhibited oil rejection rates that exceeded 99.0% for oil water mixture separation and 98.0% for oil/water emulsion separation. The flux recovery ratio reached 96.7% after bovine serum albumin filtration and washing with water. The removal efficiencies of the coated membrane M3 for Congo red, methyl orange, methylene blue, and crystal violet, Pb(II), Cu(II), and Cd(II) were 82.4, 83.9, 6.3, 26.8, 90.6, 91.3, and 86.2%, respectively. Thus, it can be used for the removal of dyes and heavy metal ions from wastewater. The antibacterial activities of the coated membranes were also confirmed by the inhibition zone tests and confocal laser scanning microscopy analysis. In addition, the cross-linking strategy provides the coated membranes with excellent durability and repeatability. More importantly, the use of water as the solvent can ensure that the application of these membrane coatings proceeds via a very safe and environmentally friendly coating process.