Novel triangular silver nanoparticle modified membranes for enhanced antifouling performance

Nano-clay modified membranes: A promising green strategy for microalgal antifouling filtration

Membrane fouling is a major challenge which limits the sustainable application of membrane filtration-based microalgal harvesting at industrial level. Membrane fouling leads to increased operational and maintenance costs and represents a major obstacle to microalgal downstream processing. Nano-clays are promising naturally occurring nanoparticles in membrane fabrication due to their low-cost, facile preparation, and their superior properties in terms of surface hydrophilicity, mechanical stability, and resistance against chemicals. The membrane surface modification using nano-clays is a sustainable promising approach to improve membranes mechanical properties and their fouling resistance. However, the positive effects of nano-clay particles on membrane fouling are often limited by aggregation and poor adhesion to the base polymeric matrix. This review surveys the recent efforts to achieve anti-fouling behavior using membrane surface modification with nano-clay fillers. Further, strategies to achieve a better incorporation of nano-clay in the polymer matrix of the membrane are summarised, and the factors that govern the membrane fouling, stability, adhesion, agglomeration and leaching are discussed in depth.

Silver nanoparticles with exceptional near-infrared absorbance for photoenhanced antimicrobial applications

In this work, we outline a simple method for synthesizing decahedral and triangular silver nanoparticles using light to tune particle shape and spectral characteristics. Notably, we were able to generate triangular silver nanoparticles with exceptional absorbance in the near-infrared (NIR) region, with high spectral overlap with the biological window, making them particularly promising for biological applications. We further demonstrate that under complementary LED illumination, these excitable plasmonic particles display exceptional antibacterial properties, several orders of magnitude more potent than similar particles under dark conditions or under illumination that does not match particle absorbance. This work demonstrates the powerful effects that LED lights can have on the antibacterial activity of AgNPs, providing an inexpensive and easily implemented route to unlocking the full potential of AgNPs in photobiological applications.

Conductive MXene ultrafiltration membrane for improved antifouling ability and water quality under electrochemical assistance

Membrane fouling is a major challenge for the membrane separation technique in water treatment. Herein, an MXene ultrafiltration membrane with good electroconductivity and hydrophilicity was prepared and showed excellent fouling resistance under electrochemical assistance. The fluxes under negative potential were 3.4, 2.6 and 2.4 times higher than those without external voltage during treatment of raw water containing bacteria, natural organic matter (NOM), and coexisting bacteria and NOM, respectively. During the treatment of actual surface water with 2.0 V external voltage, the membrane flux was 1.6 times higher than that without external voltage and the TOC removal was improved from 60.7% to 71.2%. The improvement is mainly attributed to the enhanced electrostatic repulsion. The MXene membrane presents good regeneration ability after backwashing under electrochemical assistance with the TOC removal remaining stable at around 70.7%. This work demonstrates that the MXene ultrafiltration membrane under electrochemical assistance possesses excellent antifouling ability and has great potential in advanced water treatment.

Versatile Silver-Nanoparticle-Impregnated Membranes for Water Treatment: A Review

Increased affordability, smaller footprint, and high permeability quality that meets stringent water quality standards have accelerated the uptake of membranes in water treatment. Moreover, low pressure, gravity-based microfiltration (MF) and ultrafiltration (UF) membranes eliminate the use of electricity and pumps. However, MF and UF processes remove contaminants by size exclusion, based on membrane pore size. This limits their application in the removal of smaller matter or even harmful microorganisms. There is a need to enhance the membrane properties to meet needs such as adequate disinfection, flux amelioration, and reduced membrane fouling. To achieve these, the incorporation of nanoparticles with unique properties in membranes has potential. Herein, we review recent developments in the impregnation of polymeric and ceramic microfiltration and ultrafiltration membranes with silver nanoparticles that are applied in water treatment. We critically evaluated the potential of these membranes in enhanced antifouling, increased permeability quality and flux compared to uncoated membranes. Despite the intensive research in this area, most studies have been performed at laboratory scale for short periods of time. There is a need for studies that assess the long-term stability of the nanoparticles and the impact on disinfection and antifouling performance. These challenges are addressed in this study and future directions.

Engineered polyethersulfone membrane for well-dispersed silver nanoparticle impregnation at high loading: high water permeate flux and biofouling prevention

We present a new method for impregnation of silver nanoparticles (Ag NPs) at high loading on polyethersulfone (PES) membrane's external surface, simultaneously retaining native membrane's porosity - to achieve a high water permeate flux without biofouling. This was possible by PES membrane's surface modification with acrylic acid (AA), finally leading to AA-Ag-PES membrane. AA-Ag-PES had a high (9.04%) Ag-NP loading selectively on membrane surface, as discrete, smaller (mean size: 20 nm) nanoparticles (NPs). In nonfunctionalized Ag-PES, aggregated (mean size: 70 nm) NPs, with lower Ag loading (0.73 wt.%) was obtained, with NP being present both on membrane surface and inside pores. Consequently, AA-Ag-PES could maintain similar water permeability and porosity (10,153.05 Lm^-2 h^-1bar^-1 and 69.98%, respectively), as in native PES (11,368.74 Lm^-2 h^-1bar^-1 and 68.86%, respectively); whereas both parameters dropped significantly for Ag-PES (4,869.66 Lm^-2 h^-1bar^-1 and 49.02%, respectively). AA-Ag-PES also showed least flux reduction (7.7%) due to its anti-biofouling property and high flux recovery after usage and cleaning, compared to native PES and Ag-PES membrane's much higher flux reduction (54.29% and 36.7%, respectively). Hence, discrete NP impregnation, avoiding pore blockage, is key for achieving high water flux and anti-biofouling properties (in AA-Ag-PES), compared to non-functionalized Ag-PES, due to aggregated Ag-NPs inside its pores.

Insight into single-element nobel metal anisotropic silver nanoparticle shape-dependent selective ROS generation and quantification

The biocidal action mechanism of single element noble metal anisotropic nanoparticles has remained a perplexing challenge. Herein, we investigated the photogenerated anisotropic AgNP ROS production kinetics and each ROS species' direct impact on Gram-negative and Gram-positive bacteria. Three shapes (Triangular, Cubes, Rods) of AgNP with excellent morphology were fabricated via plasmon mediated synthesis. The results demonstrated a distinct bactericidal capacity of each NP shape where Ag-Tri outperformed Ag-Cub and Ag-Rod by displaying complete bacterial mutilation at a very low dose of 18 μg mL-1 for the shortest exposure time of 180 min. In contrast, Ag-Cub needed 66.6% higher NP concentration, while Ag-Rod was unable to achieve complete bacterial mutilation. In contrast to O2˙-, (Ag-Tri 69 ± 3.2, Ag-Cub 72 ± 2.9, Ag-Rod 68.5 ± 3.7 μM), the amount of ˙OH production was considerably lower (Ag-Tri 11 ± 1.6, Ag-Cub 10.4 ± 1.9, Ag-Rod 11.3 ± 2.2 μM), while 1O2 remained undetected for all NP shapes. Moreover, antimicrobial activity of selective ROS species revealed O2˙- as a dominant species among ROS. However, O2˙- was not found as a decisive factor in microbial mutilation. SEM images affirmed the significance of the specific geometrical shape and its resultant attachment to bacterial surface to be of paramount significance. The sharp-tip morphology with high-atom density active {111} facets played a pivotal role in physically deteriorating bacterial cells. Ag-Tri morphology in synchronization with ROS species assisted its wedging into the bacterial cell, translating into superior and multifaceted antibacterial performance.

Photothermal bactericidal surfaces: killing bacteria using light instead of biocides

Recent developments of photothermal bactericidal surfaces based on immobilized photothermal agents to kill bacteria through hyperthermia effects are reviewed.

Facile Approaches of Polymeric Face Masks Reuse and Reinforcements for Micro-Aerosol Droplets and Viruses Filtration: A Review

Since the widespread of severe acute respiratory syndrome of coronavirus 2 (SARS-CoV-2) disease, the utilization of face masks has become omnipresent all over the world. Face masks are believed to contribute to an adequate protection against respiratory infections spread through micro-droplets among the infected person to non-infected others. However, due to the very high demands of face masks, especially the N95-type mask typically worn by medical workers, the public faces a shortage of face masks. Many papers have been published recently that focus on developing new and facile techniques to reuse and reinforce commercially available face masks. For instance, the N95 mask uses a polymer-based (membrane) filter inside, and the filter membrane can be replaced if needed. Another polymer sputtering technique by using a simple cotton candy machine could provide a cheap and robust solution for face mask fabrication. This review discuss the novel approaches of face mask reuse and reinforcement specifically by using membrane-based technology. Tuning the polymeric properties of face masks to enhance filterability and virus inactivity is crucial for future investigation.

Enhanced Fouling Resistance and Antimicrobial Property of Ultrafiltration Membranes Via Polyelectrolyte-Assisted Silver Phosphate Nanoparticle Immobilization

Ultrafiltration (UF) is a low-pressure membrane that yields higher permeate flux and saves significant operating costs compared to high-pressure membranes; however, studies addressing the combined improvement of anti-organic and biofouling properties of UF membranes are lacking. This study investigated the fouling resistance and antimicrobial property of a UF membrane via silver phosphate nanoparticle (AgPNP) embedded polyelectrolyte (PE) functionalization. Negatively charged polyacrylic acid (PAA) and positively charged polyallylamine hydrochloride (PAH) were deposited on the membrane using a fluidic layer-by-layer assembly technique. AgPNPs were immobilized within the crosslinked "bilayers" (BL) of PAH/PAA. The effectiveness of AgPNP immobilization was confirmed by microprofile measurements on membrane surfaces using a solid contact Ag micro-ion-selective electrode. Upon stable and uniform BL formation on the membrane surface, the permeate flux was governed by a combined effect of PAH/PAA-derived hydrophilicity and surface/pore coverage by the BLs "tightening" of the membrane. When fouled by a model organic foulant (humic acid), the functionalized membrane exhibited a lower flux decline and a greater flux recovery due to the electrostatic repulsion imparted by PAA when compared to the unmodified membrane. The functionalization rendered antimicrobial property, as indicated by fewer attachments of bacteria that initiate the formation of biofilms leading to biofouling.

Electrostatically coupled SiO2 nanoparticles/poly (L-DOPA) antifouling coating on a nanofiltration membrane

In this work, the fouling resistance of TFC (thin film composite) nanofiltration membranes have been enhanced using an electrostatically coupled SiO₂ (silica dioxide) nanoparticles/poly(L-DOPA) (3-(3,4-dihydroxyphenyl)-l-alanine) antifouling coating. SiO₂ nanoparticles were synthesized in different size ranges and combined with L-DOPA; and then coated as an anti-fouling layer on the membrane surface by recirculated deposition. Membranes were coated with S-NP (silica nanoparticles) in small (19.8 nm), medium (31.6 nm) and large (110.1 nm) sizes. The zwitterionic compound L-DOPA in the form of self-polymerized poly(L-DOPA) (PDOPA) helped with the attachment of the S-NP to the membrane surface. It was confirmed by AFM (atomic force microscopy) measurement that coating of membranes led to an increase in hydrophilicity and reduction in surface roughness, which in turn led to a 60% reduction in the adhesion force of the foulant on the membrane as compared to the neat membrane. The modified membranes experienced almost no flux decline during the filtration experimental period, whereas the unmodified membrane showed a sharp flux decline. The best coating conditions of silica nanoparticles resulting in enhanced anti-fouling properties were identified. The biofouling film formation on the membranes was evaluated quantitatively using the flow cytometry method. The results indicated that the modified membranes had 50% lower microbial population growth in terms of total event count compared to the neat membrane. Overall, the experimental results have confirmed that the coating of electrostatically coupled SiO₂ nanoparticles and PDOPA (S-NP/PDOPA) on TFC-NF (nanofiltration) membrane surfaces is effective in improving the fouling resistance of the membranes. This result has positive implications for reducing membrane fouling in desalination and industrial wastewater treatment applications.