Antifouling Mechanism Research Articles

Research Progress on Low-Surface-Energy Antifouling Coatings for Ship Hulls: A Review.

The adhesion of marine-fouling organisms to ships significantly increases the hull surface resistance and expedites hull material corrosion. This review delves into the marine biofouling mechanism on marine material surfaces, analyzing the fouling organism adhesion process on hull surfaces and common desorption methods. It highlights the crucial role played by surface energy in antifouling and drag reduction on hulls. The paper primarily concentrates on low-surface-energy antifouling coatings, such as organic silicon and organic fluorine, for ship hull antifouling and drag reduction. Furthermore, it explores the antifouling mechanisms of silicon-based and fluorine-based low-surface-energy antifouling coatings, elucidating their respective advantages and limitations in real-world applications. This review also investigates the antifouling effectiveness of bionic microstructures based on the self-cleaning abilities of natural organisms. It provides a thorough analysis of antifouling and drag reduction theories and preparation methods linked to marine organism surface microstructures, while also clarifying the relationship between microstructure surface antifouling and surface hydrophobicity. Furthermore, it reviews the impact of antibacterial agents, especially antibacterial peptides, on fouling organisms' adhesion to substrate surfaces and compares the differing effects of surface structure and substances on ship surface antifouling. The paper outlines the potential applications and future directions for low-surface-energy antifouling coating technology.

Large-eddy simulation of turbulent channel flows with antifouling-featured bionic microstructures

The large-eddy simulation of a shark skin surface at Reynolds numbers of Reτ=1200, 2400, and 4500 is carried out in a fully turbulent flow channel to investigate the antifouling mechanism of shark skin from the perspective of hydrodynamics. The antifouling properties are validated through the confocal laser scanning microscopy of microorganism settlement and a measurement of the reduction in pollutant mass. A large-eddy simulation database is then analyzed, focusing on mean and turbulent statistics, to explain the flow characteristics of time-varying fields of the flow that surrounds and skims over the shark skin. A phenomenological scenario based on instantaneous visualizations of vortical events using the Q-criterion is put forward to identify the spatiotemporal evolution of turbulent coherent structures in the outer region. Subsequently, the proposed scenario is accessed by analyzing two-point correlation coefficients, the conditional averaging of vortical events, the wall friction coefficient distribution, and the spatiotemporal evolution of vortices. The flow patterns are predominantly driven by the periodic emission of hairpin-type vortices, which form a strong shear layer and exacerbate shear stress and momentum exchange. Furthermore, these vortices are associated with the generation of a bicyclical system involving an unsteady propagation of turbulent fluids, which develops separately near the front and back of each shark scale. These modes elaborate the antifouling mechanism of shark skin. Analysis of the probability density function and the spatiotemporal map reveals that these strong events have high levels of intermittency in time and space, which vitally contributes to the antifouling properties manifested in the evolution of periodic shear friction over different surfaces.

Influence of Light Conditions on the Antibacterial Performance and Mechanism of Waterborne Fluorescent Coatings Based on Waterproof Long Afterglow Phosphors/PDMS Composites.

Marine microbial adhesion is the fundamental cause of large-scale biological fouling. Low surface energy coatings can prevent marine installations from biofouling; nevertheless, their static antifouling abilities are limited in the absence of shear forces produced by seawater. Novel waterborne antifouling coatings inspired by fluorescent coral were reported in this paper. Waterproof long afterglow phosphors (WLAP) were introduced into waterborne silicone elastomers by the physical blending method. The composite coatings store energy during the day, and the various colors of light emitted at night affect the regular physiological activities of marine bacteria. Due to the synergistic effect of fouling-release and fluorescence antifouling, the WLAP/polydimethylsiloxane (PDMS) composite coating showed excellent antifouling abilities. The antibacterial performance of coatings was tested under simulated day-night alternation, continuous light, and constant dark conditions, respectively. The results illustrated that the antibacterial performance of composite coatings under simulated day-night alternation conditions was significantly better than that under continuous light or darkness. The weak lights emitted by the coating can effectively inhibit the adhesion of bacteria. C-SB/PDMS showed the best antibacterial effect, with a bacterial adhesion rate (BAR) of only 3.7%. Constant strong light also affects the normal physiological behavior of bacteria, and the weak light of coatings was covered. The antibacterial ability of coatings primarily relied on their surface properties under continuous dark conditions. The fluorescent effect played a vital role in the synergetic antifouling mechanism. This study enhanced the static antifouling abilities of coatings and provided a new direction for environmentally friendly and long-acting marine antifouling coatings.

Research Progress of Natural Products and Their Derivatives in Marine Antifouling.

With the increasing awareness of environmental protection, it is necessary to develop natural product extracts as antifouling (AF) agents for alternatives to toxic biocides or metal-based AF paints to control biofouling. This paper briefly summarizes the latest developments in the natural product extracts and their derivatives or analogues from marine microorganisms to terrestrial plants as AF agents in the last five years. Moreover, this paper discusses the structures-activity relationship of these AF compounds and expands their AF mechanisms. Inspired by the molecular structure of natural products, some derivatives or analogues of natural product extracts and some novel strategies for improving the AF activity of protective coatings have been proposed as guidance for the development of a new generation of environmentally friendly AF agents.

Molecular Dynamics Study of the Antifouling Mechanism of Hydrophilic Polymer Brushes.

We perform all-atom molecular dynamics simulations of the adsorption of amino acid side-chain analogues on polymer brushes. The analogues examined are nonpolar isobutane, polar propionamide, negatively charged propionate ion, and positively charged butylammonium ion. The polymer brushes consist of a sheet of graphene and strongly hydrophilic poly(carboxybetaine methacrylate) (PCBMA) or weakly hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA). The effective interactions between isobutane and polymer chains are repulsive for PCBMA and attractive for PHEMA. Gibbs energy decomposition analysis shows that this is due to the abundance of water in the PCBMA brush, which increases the steric repulsion and decreases the Lennard-Jones attraction. The affinity of the hydrophilic analogues is low for both PCBMA and PHEMA chains, but the balance between the components of the Gibbs energy is different for the two polymers. The simulations are performed at several θ, where θ is the degree of overlap of polymer chains. The antifouling performance against the neutral analogues is better for PCBMA than for PHEMA in the low and high θ regimes. However, in the middle θ regime, the antifouling performance of PHEMA is close to or better than that of PCBMA. This is attributed to the formation of a dense layer of PHEMA on the graphene surface that inhibits direct adsorption of analogue molecules on graphene. The charged analogues do not bind to either the PHEMA or PCBMA brush irrespective of θ.

A robust superhydrophobic-superoleophilic PDMS/Al2O3/CM composite ceramic membrane: Stability, efficient emulsified oil/water separation, and anti-pollution performance

To address the issue of membrane fouling and low separation efficiency of ceramic membrane (CM) commonly encountered in oil/water separation, the implementation of a robust superhydrophobic coating on the surface of CM represents a viable and efficacious strategy. This study presented a facile approach for the fabrication of a durable superhydrophobic-superoleophilic composite coating on the surface of CM by the in-situ growth of needle-shaped alumina (Al2O3) followed by the impregnation of a polydimethylsiloxane (PDMS) coating. Various characterization techniques, such as FESEM, XPS, CLSM, bubble point porometer, contact angle etc. were used to characterize the microstructure, surface composition, pore size distribution, and surface characteristics of the PDMS/Al2O3/CM. The mechanical, chemical, and thermal stability were evaluated by means of sandpaper abrasion, tape peeling, immersion tests including organic solvent, acid, and base solutions, and heat treatment. The separation performance, anti-pollution property, and reusability of the modified CM were evaluated by oil/water mixture and water-in-oil emulsion. And the oil/water separation model and anti-fouling mechanism was also elaborated. The results indicated that a homogeneous needle Al2O3 cluster with a micro/nano dual-scale hierarchical roughness was grown on the surface of the CM, and the further introduction of PDMS gave the modified CM excellent superhydrophobicity with a water contact angle (WCA) of ∼160° and a water rolling angle (WOA) of 7.6°. The PDMS/Al2O3/CM composite membrane exhibited remarkable capability in segregating oil/water mixtures, including emulsified water-in-oil. The separation efficiency remained above 99 %, even after 15 cycles of separation. This study presents a simple technique for fabricating a robust superhydrophobic coating onto the Al2O3-based CM surface, which exhibits the potential for application to other ceramic membrane substrates. And the anticipated outcome of this developing is a broad spectrum of industrial applications for emulsified oil/water purification.

Industrial oily wastewater treatment by microfiltration using silver nanoparticle-incorporated poly (acrylonitrile-styrene) membrane

Membrane filtration exhibit operational limitations such as biofouling, which leads to concentration polarization and reduces permeability and selectivity, despite advantages such as low operating cost, high selectivity, and permeability. In recent years, the antibacterial properties of silver nanoparticles (AgNPs) have been investigated for improving membrane processes; however, the fouling phenomena in presence of AgNPs in the membrane matrix have not been fully discussed. Herein, the antifouling properties of a poly (acrylonitrile-styrene) copolymer incorporated with AgNPs were studied in a microfiltration membrane process. The Creighton method was used to synthesize AgNPs, and the effects of AgNPs on the porosity, morphology, pore size, mechanical strength, permeability, and selectivity of the membranes were investigated. Moreover, to investigate the biofouling of the obtained membranes, microfiltration of industrial oily wastewater was performed at constant pressure over three cycles. Using AgNPs in the membrane matrix resulted in enhanced antifouling properties of the copolymer membrane, which is related to the structure of the AgNPs in the casting solution, as proven by SAXS analysis. The results show that the CFU% for Staphylococcus aureus and E.coli reach 2% and 6%, respectively. Finally, the Derjaguin–Landau–Verwey–Overbeek (DLVO) thermodynamic model was applied to study the antifouling mechanism, correctly predict the separation behavior in the membrane, and design, simulate, and optimize the separation processes in the membrane separation plantsa. The DLVO model could predict the separation behavior in the synthesized membranes, and the poly(acrylonitrile-styrene) copolymer membranes containing AgNPs were proven have promising industrial wastewater treatment applications.

Exploring the low cell adhesion of photoinduced superhydrophilic surfaces for improving the effect of antifouling protective coatings on porous building materials

The susceptibility of building materials to biological colonization is associated with accelerated decay processes, aesthetical alterations and health risks. Thus, preventive measurements involving the use of coatings with passive (bioreceptivity decrease) and active (biocides) antifouling mechanisms are common. Hydrophobic and superhydrophobic coatings that decrease water availability are the most common anti-fouling strategies, although they can promote cell adhesion under the right circumstances and lose effectiveness after the initial biofilm setting.In this work, we explore an innovative alternative strategy to improve the anti-fouling effect of a hydrophobic coating through surface modification to grant low cell-adhesion superhydrophilic properties (while preserving its low water absorption) and its combination with nano-biocides. This is achieved by the incorporation of Ag or CuO-modified TiO2 into an ormosil sol–gel matrix. Irradiation with UV–Vis light activates the superhydrophilic surface while maintaining a decrease in capillary water absorption of >90% and accelerated algal exposure tests showed a markedly lower colonization rate compared to the superhydrophobic surface, owing to the modifications in cell-water-surface interfacial tensions. The nano-biocides showed a dual effect, promoting the transition to superhydrophilic and further decreasing colonization. Furthermore, the superhydrophilic surfaces enhance the biocide effect by promoting the interaction of the nanoparticles with the surrounding media.

A novel catalytic membrane integrated with ozone process for secondary wastewater treatment: Micropollutant removal, membrane fouling control, and its mechanisms

The integration of membrane filtration and catalytic ozonation is increasingly investigated in micro-polluted wastewater treatment, whereas membrane fouling still inhibits its practical application. In the present study, a novel MnCe-catalytic membrane integrated with ozone process (O3/MnCe-CM) was established and applied to remove four micropollutants from the real secondary effluent in continuous operation. Efficient removal of four representative micropollutants with the removal rate ranging from 89.33 % to 99.49 % and superior performance on conventional pollutants, with the DOC, UV254, polysaccharide, and protein reduced by 30 %, 88 %, 32.5 %, and 24 %. The O3/MnCe-CM process had an improved TMP control effect, explicitly reducing the irreversible fouling resistance given a Rir/Rt of 10.17 % which is 42.9 % of that of the O3/CM process. After filtering for 70 days, the TMP only increased by 24.51 kPa. More importantly, the antifouling mechanism was proposed as the combined effects of the decrease of the membrane isoelectric point that elevated its repulsion towards pollutants and the catalytic ozonation that reduced the organic foulants accumulated on the membrane surface and inside the pores. In addition, ozonation in the membrane tank decreased the pollutant load passing through MnCe-CM. In all, the present study provides a novel O3/MnCe-CM process with a promising application perspective.

The antifouling tris-(8-hydroxyquinoline) aluminum: Titanium dioxide coatings under visible light

Functional antifouling coatings are becoming a direction of developing for marine antifouling coatings. Herein, tris-(8-hydroxyquinoline) aluminum modified with titanium dioxide (AlQ3:TiO2) coatings with photocatalytic antibacterial and fluorescent algae inhibition under visible irradiation were prepared. The AlQ3:TiO2 coatings show high antibacterial activity against E. coli with inhibition efficiencies as high as 97.51 %. Meanwhile, the reactive oxygen species (ROS) and the weak fluorescence produced under visible irradiation have an efficient inhibitory effect on the growth and settlement of algae. Based on the detailed antifouling experiments and electrochemical characterization of the material, a possible antifouling mechanism for AlQ3:TiO2 coatings is proposed.

Influence of an Axial-Electromagnetic Field Treatment Device with a Solenoid Structure on Crystallization Fouling on the Tube Side of a Shell-and-Tube Heat Exchanger.

In this study, the influence of an axial-electromagnetic field treatment device (AEFTD) with a solenoid structure using different electromagnetic frequencies on calcium carbonate (CaCO3) crystallization fouling on the tube side of a shell-and-tube heat exchanger was investigated. The experimental results indicated that the application of the AEFTD could effectively reduce fouling resistance and decelerate the growth rate of CaCO3 fouling. The opposite trend between fouling resistance and the outlet temperature of an experimental fluid indicated that the application of the AEFTD could enhance heat transfer. Meanwhile, the crystal morphologies of the fouling samples were analyzed by means of scanning electron microscopy (SEM). The axial-electromagnetic field favored the formation of vaterite as opposed to calcite. Non-adhesive vaterite did not easily aggregate into clusters and was suspended in bulk to form muddy fouling that could be carried away by turbulent flow. Furthermore, the anti-fouling mechanism of the axial-electromagnetic field is discussed in detail. The anti-fouling effect of the AEFTD on CaCO3 fouling exhibited extreme characteristics in this study. Therefore, the effectiveness of the AEFTD is contingent upon the selection of the electromagnetic parameters.

Revealing the fouling characteristics in membrane-based primary treatment (MPT) of municipal wastewater and the antifouling mechanism of influent conditioning

Membrane-based technology is becoming an attractive option for primary treatment of municipal wastewater (MW) due to its superior organic retention capacity and footprint savings. However, limited understanding of fouling mechanisms still hampered its practical application. This study aims to investigate the fouling characteristics in MPT and analyze anti-fouling mechanisms of influent conditioning. In the meantime, the differences between microfiltration (MF) and ultrafiltration (UF) are also discussed. Dozens of filtration experiments with different membranes (0.1 μm and 100 kDa), MW conditioning methods (coagulation and adsorption) were conducted. Results indicated that a hallmark of MPT is the protective ability of particulate matters present in the raw MW. The irreversible fouling rate was 2–4 times higher in the absence of particulates. Besides, the main irreversible foulant types and the cake growth patterns differed with different pore sizes. As for influent conditioning, coagulation and adsorption collaborate effectively in regulating cake characteristics. Polymeric aluminum chloride reduces the tendency of binding between foulants and membrane, while activated carbon increases the porosity of the cake layer.

Preparation of boronate affinity controllable-oriented polysaccharides magnetic molecularly imprinted polymer and its application for membrane flux improvement

In this study, researchers successfully developed a novel Magnetic Molecularly Imprinted Polymer of Boronate Affinity Controllable-Oriented Dextran (MMIP-Dextran) to enhance membrane flux by selectively adsorbing polysaccharide-type substances. The structure and components of the MMIP-Dextran were thoroughly investigated using various techniques such as Transmission Electron Microscopy (TEM), Vibrating Sample Magnetometer (VSM), Brunauer-Emmett Teller (BET), Fourier Transform Infrared (FT-IR), and Thermogravimetric Analysis (TGA). Batch experiments were conducted to assess the adsorption performance and mechanisms. Results showed that the MMIP-Dextran exhibited a high adsorption capacity of 31.2 mg g−1 and good specific recognition performance (imprinting factor, IF=2.83) for the Dextran template. Furthermore, the MMIP-Dextran had a superior polysaccharide adsorption capacity of 22.10 mg g−1 compared to the Non-Imprinted Polymer (NIP) in soluble microbial products (SMPs) derived from a bioreactor, showing a 2.45-fold improvement. Meanwhile, the Specific Filtration Resistance (SFR) tests indicated that the membrane flux improvement by MMIP-Dextran (15.2 %) is 2.1 times better than NIP (7.2 %). Adsorption kinetics and thermodynamics analyses revealed that the spontaneous adsorption process was predominantly governed by chemically rate-limiting steps. Density Functional Theory (DFT) analysis further revealed that the spatial configuration transformation of the Boric Acid Ligand (BAL) played a crucial role in the adsorption/desorption process. Overall, this study offers a promising approach to promoting the permeate flux of membrane and provides a deeper understanding of the antifouling mechanism using MMIPs.

Thin-Film Nanocomposite Membranes with Nature-Inspired MOFs Incorporated for Removing Fluoroquinolone Antibiotics

A nanofiltration membrane functionalized with metal-organic frameworks (MOFs) is promising to enhance micropollutant removal and realize wastewater reclamation. However, the current MOF-based nanofiltration membranes still suffer from severe fouling problems with an indefinable mechanism when used for antibiotic wastewater treatment. Hence, we report a nature-inspired MOF-based thin-film nanocomposite (TFN-CU) membrane to explore its rejection and antifouling behavior. Compared with unmodified membranes, the optimal TFN-CU5 membrane (with 5 mg·mL-1 C-UiO-66-NH2) had high water permeance (17.66 ± 1.19 L·m-2·h-1·bar-1), exceptional rejection for norfloxacin (97.92 ± 2.28%) and ofloxacin (95.36 ± 1.03%), and excellent long-term stability for treating synthetic secondary effluent with antibiotic rejection over 90%. Furthermore, it also showed superior antifouling capability (flux recovery up to 95.86 ± 1.28%) in bovine serum albumin (BSA) filtration after fouling cycles. Deriving from the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach, the antifouling mechanism between BSA and the TFN-CU5 membrane was mainly attributed to the inhibited adhesion forces because the growing short-ranged acid-base interaction caused repulsive interfacial interactions. It is further revealed that BSA fouling behavior is slightly retarded under an alkaline environment, while strengthened in the presence of calcium ions and humic acid, as well as high ionic strength. In short, the nature-inspired MOF-based TFN membranes possess exceptional rejection and organic fouling resistance, giving insights into the design of antifouling membranes during antibiotic wastewater reclamation.

Why does SLIPS inhibit P.aeruginosa initial adhesion in static condition?

Slippery liquid-infused porous surfaces (SLIPSs) have distinguished themselves in inhibiting bacteria attachment and biofilm development in static conditions. However, underlying antifouling mechanisms, especially from gene level in bioinformatics, is still lacking. In this work, we investigated the initial attachment difference of Pseudomonas aeruginosa PAO1 on polydimethylsiloxane (PDMS) surface and the infused silicone slippery surface (i-PDMS). RNA sequencing (RNA-seq) was used to investigate the differences in the expression of PAO1 gene on elastomer surface during initial adhesion before and after oil injection. Compared with PDMS, bacterial attachment on i-PDMS was remarkably decreased 98.0 ± 0.7 % within 10 mins. And the antifouling ability of i-PDMS significantly outperformed PDMS throughout the entire culture period of PAO1 (14 days) in static conditions. RNA-seq reveals that the down-regulated PA1382 of PAO1 in bulk near the i-PDMS surfaces may inhibit bacterial initial adhesion. PA1382 gene encodes type II secretion outer membranes (OM) secretin, also known as type II secretion system (T2SS) protein GspD, which is involved in regulating the opening or closing of exoprotein channels, influencing bacterial adhesion and biofilm formation by controlling the secretion of toxins or effectors. Our findings provide a deeper understanding of the mechanism by which SLIPS inhibits initial bacterial adhesion.

Antifouling induced by surface wettability of poly(dimethyl siloxane) and its nanocomposites

Abstract Antifouling technologies have attracted considerable attention in recent years, as numerous fouling phenomena pertaining to inorganic, organic, bio-, and composite foulants substantially affect daily life. Poly(dimethyl siloxane) (PDMS) has several practical applications; however, it possesses limited resistance to inorganic, organic, or biofoulants such as proteins or bacteria. Among the antifouling strategies reported thus far, antifouling induced by surface wettability (AFISW) is an exceptional strategy with considerable potential. It presents numerous advantages such as a physical working mechanism, eco-friendliness, and facile material fabrication process. To achieve AFISW, PDMS can be modified with several nanomaterials to tune its surface wettability to meet antifouling requirements. This article presents a systematic review of the existing research on AFISW in PDMS to achieve improved antifouling performance. Specifically, we first provide a background on fouling, focusing on the different types of fouling and antifouling mechanisms. Then, we provide a comprehensive review of AFISW based on four types of surface wettability, namely, superhydrophilicity, hydrophilicity, hydrophobicity, and superhydrophobicity. Finally, we discuss suitable AFISW strategies for different types of fouling mechanisms based on PDMS and its nanocomposites. This review will help researchers design and fabricate various polymeric materials and their nanocomposites with tailored surface wettability for AFISW applications.

Mechanistic insights into simultaneous reversible and irreversible membrane fouling control in a vibrating anaerobic membrane bioreactor for sustainable municipal wastewater treatment

Vibrating membrane (VM) technology has shown low energy demands for in-situ antifouling enhancement in aerobic membrane bioreactors, and is expected to have greater potential for sustainable wastewater treatment applied in anaerobic membrane bioreactors (AnMBRs). However, it remains unclear how VM improves antifouling performance in AnMBRs and how the membrane fouling orignates, develops and diminishes in comparison to the conventional in-situ biogas scouring. This study reported the successful adoption of VM as a effective antifouling strategy for the vibrating AnMBR (V-AnMBR) in long-term (514 days) municipal wastewater treatment. The V-AnMBR showed superior performance, achieving 61.8%–89.4% longer filtration time, 0.68%–1.04% more organics removal and 10.7%–30.6% higher methane yields compared to the conventional biogas-scouring AnMBR (C-AnMBR). Both AnMBRs showed that membrane foulant layer (FL) was dominated in the order of colloid(FL) > EPS(FL) > SMP(FL), which could be reduced by VM to lower 10.7%–11.5% of the reversible fouling and 21.4%–26.9% of the irreversible fouling compared to biogas scouring. Furthermore, VM minimized the breakdowns of biomass typically caused by biogas scouring and reduced the release of fouling contributors from the mixed liquor, including the half of reductions of biopolymers and aromatic proteins. This work offers in-depth explanations of how membrane fouling develops in AnMBRs treating municipal wastewater, and elucidates the mechanisms of how VM achieves dual benefits on preventing foulant self-development and reducing membrane fouling contributors. Such mechanistic insights into fouling development and membrane fouling contributors would advance the understandings of antifouling mechanisms and guide next-generation sustainable AnMBR technology for mainstream wastewater treatment.

Antimicrobial Nanoparticles Mediated Prevention and Control of Membrane Biofouling in Water and Wastewater Treatment: Current Trends and Future Perspectives.

Global water scarcity and water pollution necessitate wastewater reclamation for further use. As an alternative to conventional techniques, membrane technology is extensively used as an advanced method for water purification and wastewater treatment due to its selectivity, permeability, and efficient removal of pollutants. However, microbial biofouling is a major threat that deteriorates membrane performance and imparts operational challenges. It is a natural phenomenon caused by the undesirable colonization of microbes on membrane surfaces. The economic penalties associated with this menace are enormous. The traditional preventive measures are dominated by biocides, toxic chemicals, cleaners and antifouling surfaces, which are costly and often cause secondary pollution. Recent focus is thus being directed to promote inputs from nanotechnology to control and mitigate this major threat. Different anti-microbial nanomaterials can be effectively used to prevent the adhesion of microbes onto the membrane surfaces and eliminate microbial biofilms, to provide an economical and eco-friendly solution to biofouling. This review addresses the formation of microbial biofilms and biofouling in membrane operations. The potential of nanocomposite membranes in alleviating this problem and the challenges in commercialization are discussed. The antifouling mechanisms are also highlighted, which are not widely elucidated.

Insights into boosting SiC membrane superhydrophobic-superoleophilic property and oil purification performance by hierarchical structure control

Engineering of superhydrophobic-superoleophilic (SHB-SOL) ceramic membrane surface with hierarchical structures remains challenging and the relation between physicochemical structure-dependent wettability and separation performance lacks investigation. Herein, SHB-SOL SiC ceramic membranes with different hierarchical micro-nano structures were fabricated by ZnO nanoflower (NF) deposition and silane grafting. Three SiC ceramic membranes with different pore sizes were purposefully used as the pristine, these membranes displayed similar geometric structures in different scales. The modified SiC membrane surface becomes stronger in SHB-SOL property as the pore size decreases and the optimal membrane possessing the lowest pore size presented a water contact angle of 172.46° and a water sliding angle of 5°. When used for pure oil or oily mixture separation, all the SHB-SOL SiC membranes exhibited enhanced oil fluxes compared with their pristine forms. At a pressure of 0.5 bar, the optimal membrane could completely reject water droplets and graphite solids (D50 =4.8 µm) for the oil-water-solid mixture containing 0.05 wt% water and 0.05 wt% graphite, showing a stable oil (hexane) flux of 1383.8 L·m−2·h−1. This work also reveals the effects of the hierarchical structures on the SHB-SOL property formation and the resulting antifouling mechanism, which offers novel insights into boosting ceramic membranes with desired surface wettability for enhanced separation performance.

Ficus religiosa-inspired microstructure-controlled low surface energy coatings with long-term antifouling effect

In general, antifouling coatings based on structural design mostly use the most basic shapes such as cuboids as repeating units. In this study, four kinds of complex surface micro-structured coatings inspired by natural bifacial leaf Ficus religiosa were obtained and applied to the field of marine antifouling coatings. Based on the antifouling mechanism of surface microstructure, SiO2 @PDMS(polydimethylsiloxane)-based Ficus religiosa-like coatings (Gxy, x = D or Z, y = A or I) were prepared by the blending method and the biological template method using the same positive and negative film materials. The antifouling performances of the coatings were evaluated by mussel attachment experiments and diatom attachment experiments. Compared with pure PDMS, the anti-mussel adhesion rate of SiO2@PDMS can be as high as 73.08 %. After 8-day diatom attachment experiments, the SiO2 @PDMS-based and adaxial side-structured negative film (GDI) showed an excellent antifouling performance compared with non-structured sample, and the anti-diatom adhesion rate was 17.96. In addition, a series of surface-modified micro-structured SiO2 @PDMS-based coatings (MGxy, x = D or Z, y = A or I) were prepared from the perspective of low surface energy. The surface energy of MGxy is between 19.62 and 29.95 mJ/m2, and the surface energy after diatom attachment experiment is between 13.51 and 22.23 mJ/m2. The structure, hydrolysis-condensation modification, hydrolysate and the effect of structure on hydrolysate were analyzed by the results of diatom attachment experiment. The importance of structure and the complementary effect of structure and modification on antifouling performance were explained again. Among them, the modified SiO2 @PDMS-based and abaxial side-structured positive film (MGZA) showed the best anti-diatom performance. After 8 days diatom attachment experiment, the anti-diatom adhesion rate of MGZA was as high as 90.78 %. Moreover, the newly discovered microstructural units on GDI and MGZA were parameterized. The results of this study provide insights for further research and long-term application of bionic microstructure and surface modification in the field of antifouling.