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ISSN : 1226-0088(Print)
ISSN : 2288-7253(Online)
Membrane Journal Vol.31 No.5 pp.293-303
DOI : https://doi.org/10.14579/MEMBRANE_JOURNAL.2021.31.5.293

Review on Membranes Containing Silver Nanoparticles with Antibacterial and Antifouling Properties

HanSol Kim*, Rajkumar Patel**, Jong Hak Kim***†
*Bio-Convergence (BC), Integrated Science and Engineering Division (ISED), Underwood International College, Yonsei University, 85 Songdogwahak-ro, Yeonsu-gu, Incheon 21983, South Korea
**Energy and Environmental Science and Engineering (EESE), Integrated Science and Engineering Division (ISED), Underwood International College, Yonsei University, 85 Songdogwahak-ro, Yeonsu-gu, Incheon 21983, South Korea
***Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, South Korea
†Corresponding author(e-mail: jonghak@yonsei.ac.kr; http://orcid.org/0000-0002-5858-1747)
October 11, 2021 ; October 21, 2021 ; October 21, 2021

Abstract


Separation membranes used in water filtration, protein purification or biomedical filtration device frequently undergo membrane fouling for several reasons. The formation of biofilm on the membrane surface by bacteria causes a severe problem for durability of the membrane. For the protein separation, the membrane pores get blocked due to surface hydrophobicity of the membrane. There are several approaches controlling the membrane fouling and one of them is the incorporation of silver nanoparticles. Antibacterial properties of silver nanoparticles are well known and thus widely used in several applications. In this review, we have focused on the membranes where silver nanoparticles or its derivatives are either incorporated in the active layer of thin film composite membranes or uniformly distributed throughout the whole membranes.


silver nanoparticles , antibacterial , biofouling , biofilm

항균 및 방오 특성을 가진 은나노 입자 함유 분리막에 대한 총설

김 한 솔*, 라즈쿠마 파텔**, 김 종 학***†
*연세대학교 언더우드학부 융합과학공학부 바이오융합전공
**연세대학교 언더우드학부 융합과학공학부 에너지환경융합전공
***연세대학교 화공생명공학과

초록


물 여과, 단백질 정제 또는 생체 의학 여과 장치에 사용되는 분리막은 여러 가지 이유로 막 파울링을 거치게 된 다. 박테리아에 의한 막 표면의 바이오필름 형성은 분리막의 내구성에 심각한 문제를 초래한다. 단백질 정제의 경우, 소수성 인 막의 표면으로 인해 막의 기공이 막히게 된다. 분리막의 파울링을 조절하는 방법에는 여러 가지가 있는데, 그 중 하나가 은나노 입자의 도입이다. 은나노 입자의 항균 특성은 잘 알려져 있고 따라서 여러 응용에 사용되고 있다. 본 총설에서는 은나 노 입자 또는 그 유도체가 박막 활성층에 도입되거나 또는 복합막 전체에 균일하게 분포된 분리막에 초점을 두었다.


    1. Introduction

    Membrane separation is an important technology which is applicable for liquid separation, gas separation or separation in biomedical application. Liquid separation process is always associated with the fouling of membrane either by the formation of biofilm on the membrane surface or deposition/blocking of membrane surface by organic contaminants[1-5]. Several works have been carried out on how to reduce the fouling or biofouling for industrial application and academic research.

    Thin film composite (TFC) membranes are generally used for application in reverse osmosis (RO), forward osmosis (FO) and nanofiltration (NF) process. In wastewater treatment or desalination process, the biofouling by the formation of biofilm on the polyamide thin film layer of TFC membrane reduces the efficiency of membrane separation along with the durability of the membrane[6-10]. The crosslink density of the polyamide layer as well as its thickness is another issue that controls the membrane performance. Addition of filler to the active skin layer reduces the crosslink density and the modification of membrane surface enhances the membrane smoothness. This approach enhances the water flux of membrane without compromising the value of salt rejection.

    In order to overcome the formation of biofilm, various nanoparticles such as gold and copper are immobilized in the membranes. Among them, silver nanoparticles are excellent antibacterial materials and their properties can be enhanced when they are combined with other functional materials[11-15]. It is well known that metal nanoparticles show the antimicrobial properties through the following mechanism; 1) the adhesion to microbial cells, 2) deep penetration inside the cells, 3) the generation of free radicals, 4) the modulation of microbial signal transduction pathways. Nevertheless, leaching of nanoparticles from the membranes is another issue which should be tackled by modifying the membrane surface having good physical/chemical interaction with immobilized nanoparticles.

    This review is mainly divided into two parts; First part is focused on silver nanoparticles containing membranes and the second part is about the membranes containing modified silver nanoparticles or nanoparticles combined with functional materials. Fig. 1 represent the schematic diagram of classification of the membrane and Table 1 represent the summary of membranes analyzed in this review.

    2. Thin Film Composite Membrane

    2.1. Silver nanoparticle

    To avoid the bacterial taint under wet conditions, nanofiber membranes have been proposed for antibacterial activity as filtering implements[16]. Antimicrobial filter was made of electrospun polyacrylonitrile (PAN) nanofibers incorporated with silver nanoparticles (AgNPs) via a wetting procedure. The PAN nanofibers functionalized with silver nanoparticles (PAN-AgNPs) demonstrate antibacterial competence against E.coli and S.aureus. In addition, AgNPs of PAN nanofibers exhibited excellent biostability in mammalian cells. Hence, PAN-AgNPs nanofibers could be used as a probable disinfection filter for biomedical applications. Through the reduction of Ag+ ions, surface-functionalization of electrospun PAN nanofiber membranes with AgNPs was accomplished by a consequent wetting procedure NaOH and AgNO3 solutions. In this circumstance, the resulting PAN-AgNPs nanofiber membranes demonstrated antibacterial performance against both Gram-negative and Gram-positive bacteria. One of the membranes exhibited a good biocompatibility with bodily cells. Hence, PAN-AgNPs showed a considerable potential in the applied usage of antimicrobial filter.

    Using electrospinning, Ag filled in hyperbranched polyethyleneimine/polyestersulfone (HPEI/PES) nanofibrous membranes were developed[17]. The Ag incorporated membranes exhibited a high water flux, and presented antimicrobial characteristics against E.coli, S.aureus, and P.aeruginosa. Hence, the enhanced flux recovery ratio suggests that fouling resistance and growth prevention could further expand. A high water flux was obtained due to the existence of several hydrophilic fibrous networks via a rise in pore capacities. Also, obstruction of attachment and biofilm establishment on the surface of modified membranes was observed, indicating antibacterial properties. A drop in Rt value of fabricated membrane also suggests antifouling properties compared to pure PES. Hence, Ag-HPEI/PES nanofibrous membranes could be a potential usage for water purification. The antibacterial membrane surface is essential for membrane biofouling that is a major aspect of water purification[18]. AgNPs were immobilized on membranes by soaking them in a mixed solution. AgNPs immobilization on the polysulfone ultrafiltration membranes enhanced rejection rate while lowering permeability compared to that of the pure membranes. The AgNPs membranes expressed antibacterial properties which shows an excellent antimicrobial efficacy against bacteria. The silver ion concentration is below the contamination limit of silver ions in drinking water, indicating that the use of AgNPs integrated membranes to treat water poses no threat. Hence, this work suggests a way for manufacturing and immobilizing AgNPs onto various membranes for antimicrobial application. Under the same circumstances, the AgNPs were larger on the surface than on the bulk of membrane, and the surfaces of fibrous membrane offered a more suitable material for growing larger AgNPs than the flat surface. In comparison to pure membranes, AgNPs immobilization on PSF UF membranes enhanced selectivity with higher rejection while decreasing permeability with reduced water flow. It indicates antibacterial properties of AgNPs containing membranes. It is confirmed that AgNPs integrated membranes are safe for the usage in water treatment. Through the phase inversion approach, AgNPs incorporated PES membrane were prepared[19]. After integrating the AgNPs on PES membranes, the hydrophilicity increased, while biofouling, mechanical strength, and roughness were reduced. Antibacterial activity was observed by E.coli in the diffusion, whereas antibiofouling properties were evaluated with different concentrations of AgNPs. Thus, the study presents a method for producing large-scale, self-cleaning membranes.

    Diverse mixed matrix asymmetric polymeric membranes (SM1-SM6) were assembled with antimicrobial drug and different concentration of AgNPs. SM1 had the least amount of rejection. SM2 had a higher rate of bacterial rejection, which is related to E.coli’s drug sensitivity. Bacterial inhibition was enhanced in all other membranes when AgNP concentration increased. SM6 demonstrated the highest bacterial depletion. Hence, fabricated PES membrane mixed with AgNPs could be effective for antibiofouling and cleaning membranes. In another study, low pressure plasma was applied to insert amine functionalities into the polyamide surface of TFC membranes[20]. AFM and SEM were employed to examine the structural changes that occurred after polymerization, and roughness of the surface got reduced. Fig. 2 represent the FTIR spectra of the membranes.

    Furthermore, the increased attachment of silver to the surface membrane validated the metal affinity, which was accompanied by enhanced antibacterial properties with the growth inhibition of E.coli. Hence, plasma polymerization is a feasible method for creating functional amine-enriched TFC polyamide surfaces. Plasma polymerization revealed the viability of amine functionality cohering to the polyamide layer in a TFC membrane. With increasing time of polymerization, rising value of the surface isoelectric point was constant with enriching amine components, which clearly depicted the optimal pH conditions for amine full membranes. Silver nanoparticles with improved metal bindings on amine groups verified antibacterial properties of the membranes. After immobilization of silver, polydopamine (PDA) coated on the PES membrane to increase the wettability and antimicrobial characteristic[ 21]. There are four different membrane samples. PES with higher amount of pore generating PVP increased E.coli rejection compared to the pristine PES. The PDA coating helped to form extra protecting layer that decreased pore size, resulting in a greater rejection rate than prior membranes. The Ag/PDA/PES and PVP membrane showed a complete eradication of E.coli, indicating the best antimicrobial property and the highest humic acid rejection rate of 99.33 % among all modified membranes. Thus, among the fabricated membranes, Ag-immobilized PDA-coated PES composite membrane completely eradicated E.coli cell, showing excellent bacteriostatic and antibacterial characteristics. The PDA coating attached to silver particles lowered the rate of silver leaching to reach below the maximum contamination limit in drinking water quality regulations. Admitting that biofouling could be solved with zwitterion complexes and antibacterial nanoparticles, Yi et al. investigated the influence of zwitterion type and their interlinking with AgNPs on diverse conditions[22]. The zwitterions helped to increase AgNPs concentration, which led to enhance antibacterial and antifouling characteristics without affecting nanofiltration properties. Fig 3 represents the schematic diagram of membrane formation.

    When compared to SO3- zwitterions, COO- zwitterions were more suitable for Ag metallization and mineralization, and confirmed it by using DFT to identify Gibbs free energy of the binding between ions and zwitterions. Zwitterion grafting increased the degree of metallization and mineralization on the surface. Also, COO- based zwitterions exhibited strong interconnection between silver ions and COO- zwitterion and more stable bonding between those particles on the TFC membrane. Various tests confirmed that COO- based zwitterions showed both stability and antibacterial property, and enhanced antifouling properties were attained for both mineralization and metallization on zwitterion membranes while maintaining NF efficacy.

    2.2. Modified silver nanoparticles

    Ali et al. reported embedding of silver incorporated with graphene oxide (GO-Ag) into PSF membrane to induce antibacterial and antifouling properties[23]. The membrane with antibacterial characteristic was tested with Escherichia coli and Staphylococcus aureus; whereas the membrane with antifouling property was investigated on ultrafilteration of bovine serum albumin (BSA). The results showed that GO-Ag with PSF membrane prevented biofilm growth, adhesion, expansion of bacterial species. The result showed that a higher value of BSA flux for PFS/GO-Ag membrane compared to the normal PFS membrane, verifying that GO-Ag helped to enhance the penetration with its increased hydrophilicity. In addition, PFS/GO-Ag membrane showed higher feed flow reversal (FFR) value than that of PFS membrane. This confirms that the antifouling occurs in PFS/GO-Ag composite membrane. Through the ultrafiltration for PSF membrane, all fouling mechanisms were observed in the data. However, blocking and cake formation appliances predominated UF progresses. Thus, the results from the experiment substantiated that GO-Ag could possibly help in antifouling and antimicrobial membrane. In the preparation of Ag@ZnO-Oleic acid nanoparticles with thin film nanocomposite membranes, the interfacial polymerization occurred in trimesolyl chloride (TMC) solutions[ 24]. The results demonstrated that adding Ag with ZnO-OAc nanoparticles into the polyamide layer enhanced physiochemical characteristics of TFN membranes. This membrane showed a greater salt rejection, a lower flux drop rate, and a higher flux recovery ratio compared to the free TFC membrane. It also showed antimicrobial activity against E.coli and S.aureus. During interfacial polymerization, Ag with ZnO-OAc nanoparticles were integrated into the PA layer of membranes. Compared with the neat polymer membranes, the thin film nanocomposite membrane showed a higher salt rejection, a lower flux decline rate in BSA solution, and higher flux recovery rate. Almost all the E.coli and S.aureus were killed with Ag@ZnO-OAc nanoparticles membrane. This membrane could demonstrate significant prospect for water treatment due to their high stability, enhanced fouling resistance, and antimicrobial efficacy.

    The silver-zinc oxide (Ag-ZnO) with polyamide thin film composite (PA-TFC) membrane was evaluated by ATR-FTIR for PA functional groups and contact angle for hydrophilicity on the surface[25]. The synthetic process of TFC membrane is represented in Fig. 4.

    The SEM images for zinc incorporated silver nanoparticles are represented in Fig. 5. The inclusion of Ag-ZnO nanoparticles into the PA-TFC membrane enhanced its permeability, fouling resistance, rejection, and hydrophilicity. The contact angle decreased for PA-TFC and Ag-ZnO/PA-TFC membrane. In addition, PA-TFC recorded a high flux recovery compared to the pure membrane. These indicate that PA-TFC intensified antifouling tendency. Ag-ZnO nanocomposite was integrated into the PA-TFC through interfacial polymerization. This modified membrane revealed its increased hydrophilicity compared to the measurements of contact angles in the neat membranes. Enhancement in hydrophilicity led to express delicate penetration and rejection against 2,4-DCP and 2-CP. Higher flux recoveries also show good antifouling properties of the membrane, and a constant release of silver indicates a long-standing reversible fouling membrane.

    Hybrid nanostructures (HNS) coated with metal/metal oxide-carbon nanotubes were utilized to create thin film nanocomposite membranes for purification purposes[ 26]. Four different metal and metal oxide nanoparticles were formed on the surface of nanotubes, and the HNS were further coated with polydopamine. PES substrate was coated with carbon nanotube containing metal/metal oxide and polydopamine (PDA). Polyamide thin film was formed by interfacial polymerization on the top of PDA layer. The modified membrane outperformed the TFC membrane regarding on permeation properties, while retaining selectivity against both divalent and monovalent salt solutions. The study closely investigated the fabricated HNS for several characterization techniques. Almost double the pure water flux was attained without influencing the permeability and selectivity performance compared to that of neat polymer membrane. The interlayer thickness was found to be dependent on the construction of a defect-free and mechanically balanced polyamide layer on HNS. Hence, the coated HNS and modified TFC membranes, demonstrated their plausibility for nanofiltration membranes.

    Palygorskite (Pal; formula: (Mg,Al)2Si4O10(OH)·4H2O) is a hydrophilic mineral with high factor ratio that allows nanoparticles to stick to their surface[27]. Silver nanoparticles incorporated with the membrane enhanced the antibacterial capacity. The study synthesized Pal coated with polydopamine, and formed Pal/Ag nanocomposite which had a rough surface on PA layer that advanced the membrane permeability. Also, Pal’s unique tubular morphology assist rapid permeation of water molecules. Thus, the fabricated membrane increased permeate flux and maintained the stable rate of salt rejection compared to those of the TFC. Reverse osmosis membrane was prepared by incorporating the Pal/Ag nanocomposite into PA layer. Pal/Ag nanocomposite productively improved the hydrophilicity of the surface, which makes the membrane to enhance its water permeability whereas retaining the rate of salt rejection. The fabricated membrane also exhibited antimicrobial property against E.coli. Thus, the activity shown by the reverse osmosis membrane was enhanced by the addition of Pal/Ag nanocomposite, and reveals a favorable anticipation in the desalination.

    Zhang et al. reported a unique technique to form the membranes with silver-polyethylene glycol PEGylated dendrimer nanocomposite coating that showed best antifouling among other membranes with different functional groups[28]. Further, the bonding between the amine-functionalized surface and the tip was determined by AFM force measurements, and revealed that the electrostatic interactions between the aminefabricated membrane are intense, deriving an accumulation of proteins on the surface. Hence, the adhesive force for PEG and silver nanoparticle modified membranes are minimal, explaining that membranes have less protein fouling. The study developed different functionalities on the surface membranes, and among those, the silver-PEGylated dendrimer nanocomposite membrane was the most efficient within antifouling properties. In contrast to the pristine membrane, the amine-modified membrane demonstrated a decline in fouling due to the improved hydrophilicity and high toxicity in poly(amido amine) (PAMAM). Lastly, it was found that the electrostatic connections between the amine-fabricated membrane were high while the adhesion force for PEG and silver nanoparticle incorporated membranes was weak followed by a decrease in protein fouling. The development of anti-biofouling membrane is essential to reduce biofouling.

    Liu et al. grafted the biogenic silver nanoparticles (BioAg0-6) on the surface of polyamide nanofiltration membrane[29]. BioAg0-6 grafted membrane (TFC-S-BioAg) enhanced hydrophilicity and water flux of TFC membranes. Through the silver leaching properties of grafted BioAg0-6 had a better stability than chemical AgNPs. Also, TFC-S-BioAg showed more effective and durable antimicrobial properties. Thus, TFC-S-BioAg could be a plausible membrane to mitigate biofouling. Biogenic AgNPs and chemical AgNPs were grafted onto the surface of PA TFC nanofiltration membrane. Both showed increased hydrophilicity, water flux, and remained suitable rate of salt rejection. In contrast, TFC-S-BioAg exhibited better stability and antimicrobial ability compared to TFC-S-ChemAg. Hence, TFC-S-BioAg could be an effective tool to reduce biofouling. Xu et al. designed a new multifunctional thin film nanocomposite nanofiltration membrane by bonding cellulose nanocrystal and silver (CNC/Ag) nanocomposites into a PA layer to solve biofouling issue[30]. CNC/Ag TFN nanofiltration membrane showed a high water permeability and a high rate of sodium sulfate rejection. Moreover, this membrane showed antibacterial activity and antifouling with high flux recovery ratio. Thus, this membrane could be a potential nanofiltration membranes for water treatment. Thin film nanocomposite NF membranes embedded with CNC/AG nanocomposites are synthesized, and recorded a high flux and rejection rate compared to the pristine membranes. Also, these membranes exhibited excellent antimicrobial, reverse fouling properties of the membrane, and silver stability on the membrane surface.

    The researchers synthesized polyvinyl chloride (PVC) fiber ultrafiltration membranes with pure and manufactured silver nanoparticles and found that silver nanoparticles modification enhanced the dispersal throughout the membranes[31]. The PVC membrane incorporated with Ag showed higher hydrophilicity, pristine water flow, and greater stability than PVC/Ag membranes with the same nanoparticle concentration. In addition, antibacterial tests indicated that PVC/incorporated Ag membranes had larger inhibition areas than PVC/Ag membranes. PVC based hollow fiber ultrafiltration membranes with different variables of pure and fabricated silver nanoparticles were investigated throughout the study. The result exhibited that the silver nanoparticles were evenly spread-out the membranes compared to pure particles. The PVC/Ag/silica membranes have lower hydrophilicity and higher water flux than those of PVC/Ag membranes. Thus, PVC/Ag/ silica membrane showed higher antifouling, antibacterial properties and chemical oxygen demand (COD) removal compared to the other membranes. These results depict that PVC membranes with fabricated silver nanoparticles hold excellent antifouling and antimicrobial properties that could be used in industrial applications. Yang et al. reported the formation of nanochannels around the silver nanoparticles is responsible for hydrolysis of trimesolyl chloride monomers and thus the cessation of interfacial polymerization around hydrophilic particles[32]. Fig 6 represent the schematic of membrane fabrication.

    These nanochannels tripled the water permeability of the membrane up to 50 L m-2 h-1, and showed increased salt rejection. These properties enhanced the size exclusion, improved Donnan exclusion, and re- pressed hydrophobic interaction. Thus, the formation of nanochannels could be the potential design to help the desalination. The study successfully showed that hydrophilic silver nanoparticles triggered the creation of nanochannels in TFC membranes. This increased the permeability of the water and the rejection of salt. In contrast, the integration of hydrophobic nanofillers showed a reduction in water permeability. Without nanochannels around the nanofillers, water transport would be halted within the increase in resistance. Thus, nanofillers can improve the solute rejection by providing more even loading of particles. Lastly, incorporating hydrophilic nanofillers into an organic phase has a less constant impact, resulting in a decrease in water permeability.

    3. Conclusions

    Membrane fouling is an inherent problem in liquid separation membrane. Wastewater treatment and desalination of sea water are severely affected by the formation of biofilm on the surface of TFC membrane which affected the membrane performance. Another cause of membrane fouling is the property of the membrane surface. These limitations are overcome by the incorporation of silver nanoparticles either on the surface or in whole membrane. In order to enhance the attachment of these nanoparticles onto the membrane surface, it is modified with various functional groups. The antibacterial property is enhanced by simultaneous incorporating other functional moieties along with silver nanoparticles that have synergistic effect of killing bacteria. In particular, the modified nanoparticles prevented biofilm growth, adhesion, expansion of bacterial species, resulting in increased hydrophilicity and feed flow reversal (FFR) value.

    Figures

    MEMBRANE_JOURNAL-31-5-293_F1.gif

    Schematic representation of the membranes containing silver nanoparticles.

    MEMBRANE_JOURNAL-31-5-293_F2.gif

    ATR-FTIR peak profile for absorption bands noted after plasma polymerization: (a) peaks at 1,724 to 1,666 cm–1 for PSf and (b) at 1,716 cm–1 to 1,666 cm–1 for TFC. (c) SIR-Map homogeneity analysis with integration of peak 1,666 cm–1 (Reproduced with permission from Reis et al., 20, Copyright 2015, American Chemical Society).

    MEMBRANE_JOURNAL-31-5-293_F3.gif

    (a) Thin film composite membranes comprising selective layers of polyamide (yellow) and porous support (gray), (b) membrane functionalized with zwitterions (green), followed by (c) Ag ions (silver) deposition via immersion in AgNO3 solution. These membranes were immersed in different solutions to obtain (d) metallized membranes that contain Ag nanoparticles (purple) and (e) mineralized membranes that contain AgCl nanoparticles (black). (Reproduced with permission from Yi et al., 22, Copyright 2019, American Chemical Society).

    MEMBRANE_JOURNAL-31-5-293_F4.gif

    Synthesis reaction of PA-TFC from trimesoyl chloride and pepirazine (Reproduced with permission from Kotlhao et al., 25, Copyright 2019, MDPI).

    MEMBRANE_JOURNAL-31-5-293_F5.gif

    SEM images of (a) Ag, (b) ZnO nanoparticles, and (c) Ag-ZnO nanocomposites (Reproduced with permission from Kotlhao et al., 25, Copyright 2019, MDPI).

    MEMBRANE_JOURNAL-31-5-293_F6.gif

    (a) Schematic diagram of the mechanism of AgNPs induced nanochannels in the polyamide layer for efficient water transport. (b) Schematic diagram of membrane fabrication. A polysulfone substrate was soaked by 50 mL of AgNO3 solution and 50 mL of NaBH4 solution, respectively, to generate the AgNPs. Then, the interfacial polymerization reaction between 1% MPD and 0.2% TMC was performed on this AgNPs loaded substrate to obtain the final AgNPs incorporated TFN membranes (Reproduced with permission from Yang et al., 32, Copyright 2019, American Chemical Society).

    Tables

    Summary of the Membranes Containing Silver Nanoparticles in the Literature

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