Thin Film Composite (TFC) - MDPI

membranes Review

Important Approaches to Enhance Reverse Osmosis (RO) Thin Film Composite (TFC) Membranes Performance Ahmed Al Mayyahi Department of Chemical Engineering, University of Missouri, Columbia, MO 65211, USA; [email protected] or [email protected] Received: 17 July 2018; Accepted: 9 August 2018; Published: 21 August 2018

Abstract: Thin film composite (TFC) membrane, which consists of polyamide (PA) active film rests on porous support layer, has been the major type of reverse osmosis (RO) membrane since its development by Cadotte in the 1970s, and has been remarkably used to produce clean water for human consumption and domestic utilization. In the past 30 years, different approaches have been exploited to produce the TFC membrane with high water flux, excellent salt rejection, and better chlorine/fouling resistance. In this brief review, we classify the techniques that have been utilized to improve the RO-TFC membrane properties into four categories: (1) Using alternative monomers to prepare the active layer; (2) modification of membrane surface; (3) optimization of polymerization reactions; and (4) incorporation of nanoparticles (NPs) into the membrane PA layer. This review can provide insights to guide future research and further propel the RO TFN membrane. Keywords: nanoparticles (NPs); thin film composite (TFC); interfacial polymerization (IP); surface modification

1. Introduction Because of the rapid growth of the world population and rising water needs, water shortage problems have become dominant [1,2]. In the last century, as the global population quadrupled, the world water demand has increased sevenfold. The problem of water scarcity is not only a problem of appropriate techniques, but also a social and educational problem relying on national and global endeavors as well as on technical solutions [3]. To address water shortage problems, many techniques have been developed including distillation, membrane reverse osmosis (RO), mechanical vapor pressure compression, electrodialysis and nanofiltration processes [4]. Membrane separation processes are gaining global acceptance in both water treatment and desalination due to their simplicity and relatively low cost compared to other treatment technologies [5]. RO membranes can be effectively used to remove salts and other pollutants from brackish water [6]. The water is transferred through the RO membrane by diffusion [7], while the salt is rejected by size exclusion and repulsion electrostatic force between the membrane surface and dissolved ions, which is caused by charge difference [8,9]. For efficient desalination, the membranes must be permeable to water, impermeable to solutes, and capable of tolerating high operating pressures [9]. The first work on RO membranes was initiated by Reid and co-workers [10] in the early 1950s, when they successfully fabricated an active cellulose acetate membrane to remove salt from water. The membrane exhibited efficient desalination (salt rejection: 96%), but water flux through the membrane was significantly low. Researches continued at the University of California, Los Angeles, with the concern of improving water flux without sacrificing salt rejection [11]. In 1961, Sourirajain [12] enhanced membrane flux by increasing cellulous film porosity through using pore-forming monomers.

Membranes 2018, 8, 68; doi:10.3390/membranes8030068

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A major breakthrough in the field of RO is the development of PA thin film composite (TFC) membrane. This membrane consists of two layers, the top is an active PA film prepared by the reaction between m-Phenylenediamine (MPD) and trimesoyl chloride (TMC) on a microporous polysulfone support (PSU), the bottom layer [17,18], as shown in Figure 1. Water flux through the composite depends on the hydrophilicity of the membrane surface and2 ofthe Membranes 2018,membranes 8, 68 23 characteristics of the porous support layer, while salt rejection relies on the surface charges and PA structure [14]. However, cellulose acetate membrane due to its weak Several state-of-the-art reviews has havelimited been applications published to highlight thechemical types ofresistance RO-TFC and low thermal stability [13,14]. Thus, many studies were conducted to produce a membrane with membranes and their performance. For instance, Yin et al. [19] detailed the benefits of incorporating better characteristics. 1979, and coworkers the usechlorine of aromatic polyamide various nanoparticlesInon theBurns membrane's water [15] flux,suggested salt rejection, resistance, and (PA) membrane, which is recognized by its cheap prize and high temperature tolerance, as an antifouling properties. Another review by Xu et al. [20] discussed the influences of sub-layer alternative Thoughgradient water permeability this membrane is less than performance. that of cellulose acetate adjustment[15,16]. on pressure across the by membrane and subsequent Recently, membrane, rejectionthe is higher. Gohil et al.their [21]salt reviewed systematic development of TFC membranes with their structural A major breakthrough in field of RO is the development of PA film additives compositeand (TFC) composition and separation the characteristics, including the effects of thin various IP membrane. This membrane consists of two layers, the top is an active PA film prepared by the reaction reaction parameters. However, until now, there has been no clear classification of the approaches between (MPD) and trimesoyl chloride (TMC)Thus, on a microporous that havem-Phenylenediamine been used to enhance RO-TFC membranes properties. the objective polysulfone of this brief support (PSU), the bottom layer [17,18], as shown in Figure 1. Water flux through composite review is to fill this gap in literature and provide new insights for readers to the improve their membranes depends on the hydrophilicity of the membrane surface and the characteristics of the knowledge in this field. porous support layer, while salt rejection relies on the surface charges and PA structure [14].

Figure 1. Polyamide thin film composite membrane, reproduced with permission from Figure 1. Polyamide thin film composite membrane, reproduced with permission from Khorshidi et Khorshidi et al. [18]. al. [18].

Several state-of-the-art reviews have been published to highlight the types of RO-TFC membranes 2. Using Alternative Monomers to Prepare the Active Layer and their performance. For instance, Yin et al. [19] detailed the benefits of incorporating various Because membrane performance is substantially dependent on aresistance, thin film structure and its nanoparticles on the membrane’s water flux, salt rejection, chlorine and antifouling chemical properties, different monomers have been used to prepare the PA, as shown in Table 1. properties. Another review by Xu et al. [20] discussed the influences of sub-layer adjustment on For example, Li et al. [22] used threeand different isomeric biphenyl acid chlorides pressure gradient across the membrane subsequent performance. Recently, Gohil(mm-BTCE, et al. [21] om-BTCE, op-PTCE) to react, separately, with m-phenylenediamine (MPD) on a porous support. reviewed the systematic development of TFC membranes with their structural composition and Results indicated that theincluding membrane op-PTCE exhibited higher water flux and separation characteristics, theprepared effects offrom various additives and IP reaction parameters. lower salt until rejection, prepared from mm-BTCE and om-BTCE showed waterused flux However, now,while there those has been no clear classification of the approaches that lower have been and higher salt rejection. The reason behind permeability enhancement could be due to the high to enhance RO-TFC membranes properties. Thus, the objective of this brief review is to fill this gap in literature and provide new insights for readers to improve their knowledge in this field. 2. Using Alternative Monomers to Prepare the Active Layer Because membrane performance is substantially dependent on a thin film structure and its chemical properties, different monomers have been used to prepare the PA, as shown in Table 1. For example, Li et al. [22] used three different isomeric biphenyl acid chlorides (mm-BTCE, om-BTCE, op-PTCE) to react, separately, with m-phenylenediamine (MPD) on a porous support. Results indicated that the membrane prepared from op-PTCE exhibited higher water flux and lower salt rejection, while those prepared from mm-BTCE and om-BTCE showed lower water flux and higher salt rejection. The reason behind permeability enhancement could be due to the high density of the carboxylic acid group on the membrane prepared from op-PTCE, which led to better contact with water molecules. On the other hand, the higher salt rejection might be because of the thicker PA layer produced by

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using mm-BTCE and om-BTCE. Another study was reported by Wang et al. [23] in which introducing 3,5 diamino-N-(4-2-aminophenyl)-benzamide (DABA) as a monomer to react with TMC through interfacial polymerization resulted in a more hydrophilic, thinner, and smoother membrane.


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Membranes 2018, 8, xPEER FOR REVIEW PEER REVIEW Membranes 2018, 8, 8, FOR PEER REVIEW Membranes 2018, xx8, FOR Membranes 2018, 8, FOR PEER REVIEW Membranes 2018, x8, PEER REVIEW Membranes 2018, 8, xx FOR FOR PEER REVIEW Membranes 2018, xx PEER REVIEW Membranes 2018, 8,FOR FOR PEER REVIEW

Amine Amine Amine Amine Amine Amine Amine

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Table 1. Reported monomers for synthesis of polyamide composite membranes. monomers for synthesis of polyamide composite membranes. Table 1. Reported TableTable 1. Reported Reported monomers for synthesis synthesis of polyamide polyamide composite membranes. monomers for of composite membranes. Table 1. monomers for synthesis of polyamide composite membranes. 1. Reported Reported monomers forfor synthesis of of polyamide composite membranes. Table 1. 1. Reported monomers synthesis polyamide composite membranes. Table monomers for synthesis of polyamide composite membranes. Table 1. Reported Chemical Structure AcidAcid Chloride Chemical Structure Membrane Performance Chemical Structure Chloride Chemical Chemical Structure Membrane Performance Chemical Structure Acid Chloride Chemical Structure Membrane Performance Chemical Structure Acid Chloride Structure Membrane Performance Chemical Structure Acid Chloride Chemical Structure Membrane Performance Chemical Structure Acid Chloride Chemical Structure Membrane Performance Chemical Structure Acid Chloride Chemical Structure Membrane Performance

Ref. Ref. Ref. Ref. Ref. Ref.

Ref.

TMCTMC TMC TMC TMC TMC TMC TMC

Itisiswell-known well-known that theinterfacial interfacial polymerization of It is is well-known well-known that the the interfacial polymerization of of ItIt that the polymerization It that interfacial polymerization of is well-known well-known that the interfacial polymerization ofMPD It is well-known that the interfacial polymerization of of It is that the interfacial polymerization It isTFC well-known that the interfacial polymerization of on aaaporous support layer results inin highin water flux MPD and TFC on a porous support layer results [17] MPDand and TFC on porous support layer results in MPD and TFC on porous support layer results [17] MPD and TFC on porous support layer results in [17][17] [17] MPD and TFC onon a porous support layer results in in MPD and TFC aaa porous support layer results [17] MPD and TFC on porous support layer results in [17] and salt rejection high water flux and salt rejection high water flux and salt rejection high water fluxflux and salt rejection high water flux and salt rejection high water and salt rejection high water flux and salt rejection high water flux and salt rejection

BDSA BDSA BDSA BDSA BDSA BDSA BDSA

TMC TMC TMC TMC TMC TMC TMC

Flux increased by more than 100% by using WaterWater Flux increased increased by more more than 100% 100% by using using Water Flux by than by Water Flux increased byby more than 100% byby using Water Flux increased more than 100% using Water Flux increased by more than 100% usingBDSA in the Water Flux increased by more than 100% bybyusing BDSA in the interfacial polymerization. BDSA in the interfacial polymerization. BDSA in the interfacial polymerization. BDSA in the interfacial polymerization. BDSA in the interfacial polymerization. [24] [24] BDSA in the interfacial polymerization. BDSA in the interfacial polymerization. interfacial polymerization. Simultaneously, salt Simultaneously, salt rejection increased from 89rejection to [24][24] [24] Simultaneously, salt rejection rejection increased from 89 89 to to 89 Simultaneously, salt increased from [24] Simultaneously, salt rejection increased from to Simultaneously, salt rejection increased from 89 to Simultaneously, salt rejection increased from 89 to increased from 89salt to 99%. Simultaneously, rejection increased from 89 to 99%. 99%. 99%. 99%. 99%. 99%. 99%.

[24]

S-BAPS S-BAPS S-BAPS S-BAPS S-BAPS S-BAPS S-BAPS S-BAPS

TMC TMC TMC TMC TMC TMC TMC TMC

When compared to the traditional TFC membrane, WhenWhen compared to the theto traditional TFC membrane, membrane, When compared to traditional TFC compared the traditional TFC membrane,this When compared toto the traditional TFC membrane, When compared to the traditional TFC membrane, When compared the traditional TFC membrane, When compared to the traditional TFC membrane, this membrane showed higher water flux, but lower[25] [25] this membrane showed higher water flux, but lower [25] [25] thisthis membrane showed higher water flux, but lower this membrane showed higher water flux, but lower membrane showed higher water flux, but lower [25] membrane showed higher water flux, but lower NaCl rejection this membrane showed higher water flux, but lower [25] this membrane showed higher water flux, but lower [25] NaCl rejection and chlorine resistance. NaCl rejection and chlorine resistance. NaCl rejection andresistance. chlorine resistance. NaCl rejection and chlorine resistance. and chlorine NaCl rejection and chlorine resistance. NaCl rejection and chlorine resistance. NaCl rejection and chlorine resistance.

[25]

BHDTBHDT BHDT BHDT BHDT BHDT BHDT

TMC TMC TMC TMC TMC TMC TMC

This membrane demonstrated chlorine This membrane membrane demonstrated higherhigher chlorine This demonstrated higher chlorine This membrane demonstrated higher chlorine This membrane demonstrated higher chlorine This membrane demonstrated higher chlorine resistance when compared to the normal TFCresistance [26] resistance when compared to the normal TFC [26] when This membrane demonstrated higher chlorine resistance when compared to the normal TFC [26] resistance when compared to to the normal TFC [26] resistance when compared the normal TFC [26] resistance when compared the normal TFC [26] membrane. compared to the normal TFCtomembrane. membrane. membrane. membrane. membrane. membrane.

[26]

TMC TMC TMC TMC TMC TMC TMC TMC

Instudy, this study, the effects of PAMAM content on TFC In this thisIn study, the effects effects of PAMAM PAMAM content on TFC TFC In the of content on this study, the effects of PAMAM content on TFC In In this study, thethe effects of of PAMAM content onon TFC this study, effects PAMAM content TFC In this study, the effects of PAMAM content on TFC membrane performance were studied. NaCl rejection membrane performance were studied. NaCl rejection membrane were studied. NaCl rejection membrane performance were studied. NaCl rejection In this performance study, the effects ofwere PAMAM content onrejection TFC membrane membrane performance were studied. NaCl rejection membrane performance studied. NaCl membrane performance were studied. NaCl rejection was increased when PAMAM concentration was [27] was increased when PAMAM concentration was [27] when waswas increased when PAMAM concentration was [27] performance were studied. NaCl rejection was increased was increased when PAMAM concentration was [27] increased when PAMAM concentration was [27] was increased when PAMAM concentration was [27] was increased when PAMAM concentration was [27] increased from 0.1% to 0.5% (w/v), while water flux increased from 0.1% to 0.5% (w/v), while water flux PAMAM concentration was increased from 0.1% to 0.5% (w/v), increased from 0.1% to 0.5% (w/v), while water flux increased from 0.1% to 0.5% (w/v), while water flux increased from 0.1% to to 0.5% (w/v), while water flux increased from 0.1% 0.5% (w/v), while water flux increased to 0.5% (w/v), while water flux was reduced. was reduced. reduced. while waterfrom flux0.1% was reduced. was was reduced. was reduced. was reduced.

[27]

MPD MPDMPD MPD MPD MPD MPD MPD

PAMAM PAMAM PAMAM PAMAM PAMAM PAMAM PAMAM PAMAM

[17]


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Membranes 2018, 8, x FOR PEER REVIEW Membranes 2018, 8,2018, x FOR Membranes 8, PEER Membranes 2018, 8,xPEER xFOR FORREVIEW PEER REVIEW REVIEW Membranes 2018, 2018, 8, x FOR REVIEW Membranes 8, x PEER FOR PEER REVIEW Membranes 8,8,xxPEER FOR Membranes FORPEER PEERREVIEW REVIEW Membranes 2018, 2018, 8,2018, x FOR REVIEW

Table 1. Cont.

5 of 23 5 of 23 55 of of23 23 5 of 23 5 of 23 of23 23 5 of 2355of

DETA, TETA, DETA,DETA, TETA,TETA, DETA, TETA, or TEPA DETA, TETA, DETA, TETA, or TEPA or TEPA or TEPA DETA, TETA, DETA, TETA, DETA, TETA, DETA, TETA, or TEPA or TEPA TEPA oror TEPA or TEPA or TEPA

TMC TMC TMC TMC TMCTMC TMCTMC TMC

Under operating pressure of 36.52 psi, water fluxes of UnderUnder operating pressure of 36.52 water fluxes of operating pressure of 36.52 psi, of Under operating pressure ofpsi, 36.52 psi, water water fluxes fluxes of TEPA/TMC, TETA/TMC, and DETA/TMC were 51.1 ± Under operating pressure of DETA/TMC 36.52 psi, water fluxes of Under operating pressure of 36.52 psi, water fluxes of±± TEPA/TMC, TETA/TMC, and were 51.1 ± TEPA/TMC, TETA/TMC, and DETA/TMC were 51.1 TEPA/TMC, TETA/TMC, and DETA/TMC were 51.1 Under operating pressure of 36.52 psi, water fluxes 2·h, Under operating of36.52 36.52 psi,water water fluxes of± Under operating of 36.52 psi, water fluxes of±51.1 respectively. On the [28] 4.5, 43.5 ± 0.5, andpressure 33.5 ±pressure 2 L/m Under operating pressure of psi, fluxes ofof TEPA/TMC, TETA/TMC, and DETA/TMC were 51.1 TEPA/TMC, TETA/TMC, and DETA/TMC were 22·h, respectively. respectively. On theOn [28] 4.5, 43.5 ± 43.5 0.5, and 33.5 ± 33.5 233.5 L/m the [28] 4.5, ±± 0.5, and ±±222·h, L/m ·h, respectively. On the [28] 4.5, 43.5TETA/TMC, 0.5, and L/m TEPA/TMC, TETA/TMC, and DETA/TMC were 51.1 ±± TEPA/TMC, TETA/TMC, and DETA/TMC were 51.1 ± 4.5, TEPA/TMC, TETA/TMC, and DETA/TMC were 51.1 TEPA/TMC, and DETA/TMC were 51.1 ± 2 2 SO 4 rejection sequence was: other hand, Na 2 2 ·h, respectively. On the [28] 4.5, 43.5 ±43.5 0.5, 33.5 ±433.5 2 L/m ·h,was: respectively. On the [28] 4.5, ±2and 0.5, and ± 2 L/m SO 4 rejection sequence other hand, Na 22SO was: other hand, Na 22·h, 2 ·sequence SO 4 rejection rejection sequence was: other hand, Na 2 respectively. On the [28] 4.5, 43.5 ± 0.5, and 33.5 ± 2 L/m 43.5 ± 0.5, and 33.5 ± 2 L/m h, respectively. On the other ·h, was: respectively. On the 4.5, ±and 0.5, and ±sequence 2·h, L/m respectively. On the [28] [28] 4.5, 43.5 ±43.5 0.5, 33.5 2rejection DETA/TMC > TEPA/TMC >L/m TETA/TMC. 22SO 44 2rejection other hand, SO±433.5 sequence was: other hand, Na DETA/TMC >Na TEPA/TMC > TETA/TMC. DETA/TMC >>rejection TEPA/TMC >> TETA/TMC. DETA/TMC TEPA/TMC TETA/TMC. hand, SO sequence was: > 22SO sequence was: other hand, Na SO44rejection rejection sequence was: other hand, 4Na 2SO rejection sequence was:DETA/TMC other hand,Na Na DETA/TMC >2 TEPA/TMC > TETA/TMC. DETA/TMC >4 TEPA/TMC > TETA/TMC. TEPA/TMC >>>TETA/TMC. DETA/TMC TEPA/TMC >>TETA/TMC. DETA/TMC TEPA/TMC TETA/TMC. DETA/TMC > TEPA/TMC > TETA/TMC.

DPA DPA DPA DPA DPADPA DPA DPA DPA DPA

TMC TMC TMC TMC TMCTMC TMC TMC TMC TMC

The polyester bonds of DPA/TMC produced TFC bondsbonds of DPA/TMC produced TFC TFC The polyester of produced The bonds of DPA/TMC DPA/TMC produced TFC The polyester polyester membrane withbonds highbonds chemical stability, while [29] of DPA/TMC produced TFC TFC [29] The polyester of DPA/TMC produced The polyester membrane with high chemical stability, while membrane with high chemical stability, while [29] membrane with high chemical stability, while [29] bonds of DPA/TMC produced TFC The polyester The polyester bonds of DPA/TMC produced TFC membrane bonds of DPA/TMC produced TFC The polyester bonds of DPA/TMC produced TFC The polyester maintaining good performance. membrane with high chemical stability, while [29] [29] membrane with high chemical stability, while maintaining good performance. maintaining good performance. maintaining good performance. with high chemical stability, while maintaining good membrane with high chemical stability, while [29] membrane with high chemical stability, while membrane with high chemical stability, while [29] [29] maintaining good performance. maintaining good performance. performance. maintaining good performance. maintaining good performance. maintaining good performance.

DABA DABADABA DABA DABA DABA DABA DABA DABA DABA

TMC TMC TMC TMC TMC TMCTMC TMC TMCTMC

Results showed that as DABA concentration was Results showed that asthat DABA concentration was was Results showed as concentration Results showed that as DABA DABA concentration was increased, theshowed membrane became more hydrophilic Results showed that as DABA concentration was was [30] Results that as DABA concentration increased, the membrane became more hydrophilic increased, the membrane became more hydrophilic increased, the membrane became more hydrophilic Results showed that as DABA concentration was showed that as DABA concentration was 2·h-250 Results that as DABA concentration wasincreased, [30] [30] Results thatmembrane as DABA concentration was and asResults a showed result, high water flux (55.4 L/m psi) [30] increased, theshowed membrane became more increased, the became more hydrophilic 2hydrophilic 22·h-250 and as a result, high water flux (55.4 L/m ·h-250 psi) and as a result, high water flux (55.4 L/m and as a result, high water flux (55.4 L/m ·h-250 psi) the membrane became more hydrophilic and as apsi) result, [30]high [30] increased, the membrane became more hydrophilic increased, the membrane became more hydrophilic increased, the membrane became more hydrophilic 2 was achieved. 2 2 andachieved. as a result, highL/m water flux (55.4 L/m L/m ·h-250 psi) psi) [30] [30] and as a result, high flux (55.4 ·h-250 2 ·water [30] was water flux (55.4 h-250 psi) was was achieved. was achieved. and as aaresult, flux L/m and as result, highwater water flux(55.4 (55.42achieved. L/m22·h-250 ·h-250 psi) and a result, high high water flux (55.4 L/m ·h-250 psi) psi) wasas achieved. was achieved. was wasachieved. achieved. was achieved.

[23]

MPD MPDMPD MPD MPD MPDMPD MPD MPDMPD

DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO

The developed membrane showed excellent The developed membrane showed excellent The membrane showed excellent The developed developed membrane showed excellent antimicrobial efficiency and showed high water flux and salt [31] developed membrane showed excellent antimicrobial TheThe developed membrane excellent The developed membrane showed excellent antimicrobial efficiency and high water flux and salt [31] [31] antimicrobial efficiency and high water flux and antimicrobial efficiency and high water flux and salt salt [31] The developed membrane showed excellent The developed membrane showed excellent The developed membrane showed excellent rejection. efficiency and high water fluxhigh and water salt rejection. antimicrobial efficiency and high water flux and salt [31] [31] antimicrobial efficiency and flux and salt rejection. rejection. rejection. antimicrobial efficiency and flux and antimicrobial efficiency andhigh highwater water fluxsalt andsalt salt[31] [31] [31] antimicrobial efficiency and high water flux and rejection. rejection. rejection. rejection. rejection.

[30]

MPD MPDMPD MPD MPD MPDMPD MPD MPDMPD

BTAC BTAC BTACBTAC BTAC BTAC BTAC BTAC BTAC BTAC

Membrane surface was highly negatively charged, Membrane surface was highly negatively charged, Membrane surface was negatively charged, Membrane surface was highly highly negatively charged, Membrane surface was negatively charged, smooth, smooth, and surface very thin, which in negatively turn produced high [32] Membrane was highly charged, Membrane surface washighly highly negatively charged, smooth, and very thin, which in turn produced high [32] [32] smooth, and very thin, which in turn produced high smooth, and very thin, which in turn produced high [32] Membrane surface was highly negatively Membrane surface was highly negatively charged, and very thin, which in turn produced highcharged, fouling resistance. Membrane surface was thin, highly negatively charged, fouling resistance. smooth, and very thin, which in turn produced high [32] [32] smooth, and very which in turn produced high fouling resistance. fouling resistance. fouling resistance. smooth, and in turn smooth, andvery verythin, thin,which which inproduced turnproduced produced high[32] [32] [32] smooth, and very thin, which in turn high high fouling resistance. fouling resistance. fouling resistance. fouling resistance. fouling resistance.

[28]

[29]

[31]


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Membranes 2018, 8, xx FOR PEER REVIEW Membranes 2018, 2018, 8,2018, FOR REVIEW Membranes FORPEER PEERREVIEW REVIEW Membranes 8,8,xxPEER FOR Membranes 8, x FOR PEER REVIEW Membranes 2018,2018, 8, x FOR PEER REVIEW

Table 1. Cont.

66 of of 23 2366of of23 23 6 of 23 6 of 23

SMPD SMPD SMPD SMPD SMPD SMPD SMPD

TMC TMCTMC TMC TMC TMC TMC

When SMPS content was the WhenWhen SMPSSMPS content was increased, increased, the molecular molecular When SMPS content wasincreased, increased, themolecular molecular content was the weight of PA was decreased, and it subsequently [33] When SMPS content was increased, the molecularweight When SMPS content was increased, the molecular PA weight of PA was decreased, and it subsequently [33] of When SMPS content was increased, the molecular weight of PA was decreased, and it subsequently [33] weight of PA was decreased, and it subsequently [33] was decreased, and itdecreased subsequently water flux and increased water flux and NaCl rejection. weight of was PA was decreased, and itincreased subsequently [33] increased water flux and decreased NaCl rejection. weight of PA decreased, and it subsequently [33] increased water flux and decreased NaCl rejection. increased water flux and decreased NaCl rejection. decreased NaCl rejection. increased water decreased NaCl rejection. increased water fluxflux andand decreased NaCl rejection.

MPD MPDMPD MPD MPD MPD MPD

mm-PETC mm-PETC mm-PETC mm-PETC mm-PETC mm-PETC mm-PETC

2·h and NaCl Under 290 flux 2·hNaCl ·h and Under 290 psi, psi, water flux was was 37.1 L/m 222·h and NaCl rejection Under 290water psi,water water flux37.1 wasL/m 37.12L/m L/m Under 290 psi, water flux was 37.1 L/m Under 290 psi, flux was 37.1 ·hand andNaCl NaCl 2·h rejection was 98.4% NaCl Under 290 psi, water flux was 37.1 L/m 2 rejection was 98.4% NaCl Under 290 psi, water flux was 37.1 L/m ·h andand rejection was 98.4% rejection was 98.4% was 98.4% rejection 98.4% rejection waswas 98.4%


om-PETC om-PETC om-PETC om-PETC om-PETC om-PETC om-PETC

2·h and NaCl [34] [34] [34] Under 290 flux L/m 2·h [34] ·h and Under 290 psi, psi, water flux was was 50 L/m 222·h and NaCl Under 290water psi,water water flux50 was 502L/m L/m and 290 psi, water flux was 50 L/m Under 290 psi, flux was 50 ·hNaCl andNaCl NaCl rejection Under 2 [34] rejection was 97.8% ·h and NaCl Under 290 psi, water flux was 50 L/m 2 [34] rejection was 97.8% Under 290 psi, water flux was 50 L/m ·h and NaCl rejection was 97.8% was 97.8% rejection was 97.8% rejection 97.8% rejection waswas 97.8%


op-PETC op-PETC op-PETC op-PETC op-PETC op-PETC op-PETC

2·h and NaCl Under 290 flux 2·hNaCl ·h and Under 290 psi, psi, water flux was was 45.2 L/m 222·h and NaCl rejection Under 290water psi,water water flux45.2 wasL/m 45.22L/m L/m 290 psi, water flux was 45.2 L/m Under 290 psi, flux was 45.2 ·hand andNaCl NaCl Under 2·h and NaCl rejection was 97.2% Under 290 psi, water flux was 45.2 2·h and rejection was 97.2% NaCl Under 290 psi, water flux was 45.2 L/mL/m rejection was 97.2% was 97.2% rejection was 97.2% rejection 97.2% rejection waswas 97.2%

MPD MPDMPD MPD MPD MPD

ICIC ICIC ICIC ICIC ICICICIC

MPD MPDMPD MPD MPD MPD

CFIC CFICCFIC CFIC CFIC CFIC

Under operating pressure of psi, flux Under operating pressure of 232 232of psi, water flux was was 63 Under operating pressure of 232water psi,water water flux63 was63 63 Under operating pressure 232 psi, flux was 22·h and NaCl rejection was 98.2%. In addition, the L/m Under operating pressure of 232 psi, water flux 63 2 L/m ·h and rejection was 98.2%. In addition, thewas 22·h Under operating pressure of 232 psi, water flux was 63the L/m ·hNaCl andNaCl NaCl rejection was 98.2%. In addition, the L/m and rejection was 98.2%. In addition, 2·hshowed membrane significant resistance L/m and NaCl rejection was 98.2%. In addition, 2·h and membrane showed significant resistance against L/mmembrane NaCl rejection was 98.2%. Inagainst addition, the the membrane showed significant resistance against showed significant resistance against chlorine. membrane showed significant resistance against chlorine. membrane showed significant resistance against chlorine. chlorine. [35] chlorine. [35] [35] chlorine. [35] Under operating pressure of 232 psi, water flux was Under operating pressure of 232 psi, water flux was Under operating pressure of 232 psi, water flux was Under operating pressure of 232 psi, water flux was [35] [35] 2 around 43.3 L/m and rejection was around Under operating of 232 psi, flux 2pressure around 43.3 L/m ·h and NaCl rejection waswater around 22·h Under operating pressure ofNaCl 232 psi, water fluxaround waswas around 43.32·h L/m ·hNaCl and NaCl rejection was around around 43.3 L/m and rejection was 2·h 98.6%. In addition, the membrane showed significant around 43.3 L/m and NaCl rejection was around 2·h 98.6%. In addition, the membrane showed significant around 43.3 L/m and NaCl rejection was around 98.6%. In addition, the membrane showed significant 98.6%. In addition, the membrane showed significant resistance chlorine. 98.6%. In addition, the membrane showed significant resistance against chlorine. 98.6%. Inagainst addition, thechlorine. membrane showed significant resistance against chlorine. resistance against resistance against chlorine. resistance against chlorine.

[32]

[22]

MPD MPDMPD MPD

and UnderUnder 290 psi, water flux was L/m 2·hNaCl and NaCl psi, water flux50 was 50·h L/m rejection was290 97.8% rejection was 97.8% rejection was 97.8% rejection was 97.8%

om-PETC om-PETC om-PETC om-PETC

[34]


MPD MPDMPD MPD

7 of 23

op-PETC op-PETC op-PETC op-PETC

Table 1. Cont.

MPDMPD MPDMPD MPD

ICIC ICICICIC ICIC ICIC

MPD MPDMPD

CFICCFIC CFIC CFICCFIC

MPD MPD Membranes 2018, 8, x FOR PEER REVIEW Membranes 2018, FOR PEER REVIEW Membranes 2018, xxFOR PEER REVIEW Membranes 2018,8,8, 8, FOR PEER Membranes 8, xxPEER FORREVIEW PEER REVIEW REVIEW Membranes 2018, 8,2018, x FOR

2·h and NaCl Under 290 psi, water flux was 45.2 L/m 2·h and NaCl 290water psi, water flux45.2 wasL/m 45.22·h L/m and UnderUnder 290 psi, flux was 2·hNaCl and NaCl Under 290 psi, water flux was 45.2 L/m rejection was 97.2% rejection was 97.2% rejection was 97.2% rejection was 97.2%

Under operating pressure of 232 psi, water flux was 63 Under operating pressure 232water psi, water flux63 was 63 Under operating pressure of 232of psi, flux was Under operating pressure of 232 psi, water flux was63 63L/m2 ·h operating pressure of 232 psi, water flux was L/m22Under ·h and NaCl rejection was 98.2%. In addition, the 2·h and NaCl rejection was 98.2%. In addition, the L/m L/m ·h and rejection was 98.2%. In addition, the the 2·hNaCl L/m and NaCl rejection wasIn 98.2%. In addition, and NaCl rejection was 98.2%. addition, the membrane membrane showed significant resistance against membrane showed significant resistance against membrane showed significant resistance against membrane showed significant resistance against showed significant resistance against chlorine. chlorine. chlorine. chlorine. chlorine. [35] [35] [35] [33] [35] Under operating pressure of 232 psi, water flux was operating pressure 232water psi, water flux was UnderUnder operating pressure of 232of psi, flux was Under operating pressure of 232 psi, water flux was 2 around 43.3 L/m ·h and rejection was around 2·hNaCl around 43.32·h L/m and NaCl rejection wasflux around Under of 232 psi, water was around around 43.3operating L/m and NaCl rejection was around 2pressure around 43.3 L/m ·h and NaCl rejection was around 98.6%. In addition, the membrane showed significant 2 98.6%. In addition, the membrane significant 43.3 L/m ·h and NaCl rejection wasshowed around 98.6%. In addition, 98.6%. In addition, the membrane showed significant 98.6%. In addition, the membrane showed significant 7 of 2377ofof23 23 resistance against chlorine. 23 the membrane showed significant resistance against chlorine.77 of resistance against chlorine. resistance against chlorine. resistance against chlorine. 7 of 23 of 23

HFA-MDA HFA-MDA HFA-MDA HFA-MDA HFA-MDA HFA-MDA HFA-MDA

TMC TMC TMC TMCTMC TMC TMC

Under operating pressure of 400 psi, NaCl rejection Under operating pressure of 400 psi, NaClrejection rejection Under operating pressure of 400 psi, NaCl Under operating pressure of 400 psi, rejection was 85% at low pH 4, but increased to 96.1% at pH 10. Under operating pressure of 400 psi, NaCl NaCl rejection Under operating pressure of 400 psi, NaCl rejection was 85% at low pH 4, but increased to 96.1% pH 10. 85% at was 85% atatlow pH 4,4,but increased to 96.1% atat pH 10. Under operating pressure of 400 psi, NaCl rejection was was 85% low pH but increased to 96.1% at pH 2 2 ·h and 80 L/m ·h at pH 4 and [36] Water flux was 48 L/m was 85% at low pH 4, but increased to 96.1% at pH 10. 10. 2·h and 80 2·hat was 85% at low pH 4, but increased to 96.1% pH 10. 2 2 L/m at pH 4 and [36] Water flux was 48 L/m low pH 4, but increased to 96.1% at pH 10. Water flux was[36] 2·hand 2·hat ·h 80 L/m ·h pH 44and Water flux was 48 L/m and 80 L/m at pH and [36] Water flux was 48 L/m 2the 2·h pH 10, respectively. Besides, membrane showed ·h and 80 L/m at pH 4 and [36] Water flux was 48 L/m 2 2 2 2 ·h and 80 L/m ·h at pH 4 and [36] Water flux was 48 L/m 48 L/m · h and 80 L/m · h at pH 4 and pH 10, respectively. pH 10, respectively. Besides, the membrane showed pH 10, respectively. Besides, the membrane showed pH 10, respectively. Besides, the membrane showed significant chlorine resistance. pH 10, respectively. Besides, the membrane showed Besides, thechlorine membrane showed significant chlorine resistance. pH 10, respectively. Besides, the membrane showed significant chlorine resistance. significant resistance. significant chlorine resistance. significant chlorine resistance. significant chlorine resistance.

Bisphenol A Bisphenol Bisphenol AA Bisphenol A Bisphenol A Bisphenol A Bisphenol A

TMC TMC TMCTMC TMC TMC TMC

This membrane showed significant fouling resistance This membrane showed significant fouling resistance [37] This membrane showed significant fouling resistance This membrane showed significant fouling resistance membrane showed significant fouling resistance [37] alongThis with high showed water flux and salt fouling rejection. This membrane showed significant fouling resistancealong [37] [37] This membrane significant resistance along with high water flux and salt rejection. along with high water flux and salt rejection. with high water flux and salt rejection. along with high water flux and salt rejection. [37] [37] along with high water flux and salt rejection. along with high water flux and salt rejection.

[35]

TMBPA TMBPA TMBPA TMBPA TMBPA TMBPA TMBPA

TMC TMCTMC TMC TMC TMC TMC

Under operating pressure of 130 psi, water flux was Under operating pressure 130 psi, water flux was Under operating pressure ofof 130 psi, water flux was psi, water flux was Under operating pressure of 130 psi, water flux 2·h and membrane good 66.7 L/m Under operating pressure of 130 psi, water flux was was[38] 22 ·hthe Under operating pressure of 130showed psi, water flux was 2·h 66.7 L/m and ·h and the membrane showed good [38] 66.7 L/m 2 and the membrane showed good [38] 66.7 L/m and the membrane showed good [38] 66.7 L/m 2·h antifouling properties. ·h and the membrane showed good 66.7 L/m 2 antifouling properties. ·h and the membrane showed good [38] [38] 66.7 L/m antifouling properties. antifouling properties. antifouling properties. antifouling properties. antifouling properties.

[36]

[34]


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One challenge facing RO TFC membrane durability is the degradation of the PA layer by chlorination [37]. Liu et al. [33] used three different polyacyl chlorides including 5-isocyanato-isophtahloyl chloride (ICIC), 5-chloroformyloxy-isophthaloyl chloride (CFIC), and TMC to prepare the TFC membrane with high chlorine tolerance. Results showed that the membrane prepared from MPD-CFIC and MPD-TMC possessed better chlorine stability when compared to MPD-ICIC membrane. It has been pointed out that the urea bond (NHCONH-) in MPD-ICIC could be easily attacked by chlorine. Recently, a composite membrane with high chlorine resistance has prepared through interfacial polymerization of hexafluoroalcohol (HFA)-aromatic diamine and trimesoyl chloride (TMC) [34]. The steric and electron withdrawing properties of HFA groups mitigated the probability of chlorine attack on the benzene rings or amide groups in the PA layer. In term of fouling resistance, Hilal et al. [35,36] prepared composite membranes with improved antifouling properties by interfacial polymerization of bisphenol A (BPA) and trimesoyl chloride (TMC). This was attributed to the strong repulsion force between the negatively-charged bisphenol and organic foulants. 3. Modification of Membrane Surface It was found that membrane performance is greatly affected by the treating steps that follow the synthesis process [38–42]. Chemical surface modifications are one of the promising post-treatment techniques that have been widely used to enhance TFC membrane surface properties. For example, Mickols and coworkers [43] used ethylenediamine and ethanolamine to increase membrane hydrophilicity. Their study showed that increasing the hydrogen bonding at the PA layer could enhance the interaction between water molecules and membrane surface, resulting in high water flux. Another study by Kuehne et al. [44] demonstrated that soaking the membrane in a solution containing glycerol promoted surface wettability and a 70% increase in water flux was obtained. Wilf et al. [45] coated poly(vinyl alcohol) on TFC membrane surface to enhance fouling resistance and membrane durability. The modified membrane demonstrated better resistance against organic fouling when compared with the normal TFC membrane. Moreover, the membrane showed good permeability and long-term stability. The enhanced fouling resistance was ascribed to the lower rate of organics adsorption on the coated membrane. Coatings of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) have also exhibited enhanced chlorine resistance according to Kang et al. [46]. Additionally, Sakar et al. [47] used dendrimer-based coatings to reduce fouling effects. Recently, Ngo et al. [48] used redox initiated graft polymerization to coat TFC membrane with hydrophilic poly(acrylic acid). The coated membrane had lower roughness than the virgin one, and subsequently better fouling resistance and water flux was achieved. Wu et al. [49,50] used gas plasma treatment to modify the TFC membrane. More carboxylic groups were introduced onto the surface by oxygen gaseous plasma treatment, which resulted in high water flux. On the other hand, argon plasma treatment improved chlorine resistance by introducing more amide groups onto the membrane surface. In addition, Lin et al. [51] demonstrated that the antifouling properties of the TFC membrane could be improved by using atmospheric gas plasma treatment. This kind of treatment created a polymeric brush at membrane surface which was capable of mitigating the attachment of organic foulant, Figure 2. However, plasma-induced grafting is a promising approach to produce a membrane with significant performance; however, it has not been thoroughly investigated and further research in this area is required.

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Figure 2. A schematic illustration of the nano-structured RO membrane, showing the antifouling polymeric brush, reproduced with permission from Lin et al. [51], with copyright permission from Figure 2. Society A schematic illustration of the nano-structured RO membrane, showing the antifouling ©2010 Royal of Chemistry. polymeric brush, reproduced with permission from Lin et al. [53], with copyright permission from ©2010 Royal Society of Chemistry.

Bing et al. [52] used redox initiation to enhance TFC membrane performance, especially chlorine resistance. Immersing the membrane in potassium persulfate (K2 S2 O8 ) solution initiated the interfacial Bing et al. [54] used redox initiation to enhance TFC membrane performance, especially crosslinking between the active film and PSU support, producing a thinner PA layer with more chlorine resistance. Immersing the membrane in potassium persulfate (K2S2O8) solution initiated the functional groups and denser cross linking. Reducing PA thickness led to enhanced water flux, as the interfacial crosslinking between the active film and PSU support, producing a thinner PA layer with water spent a shorter time to penetrate the membrane. On the other hand, increasing the crosslinking more functional groups and denser cross linking. Reducing PA thickness led to enhanced water improved salt rejection by narrowing the passages for salt transportation. Moreover, the crosslinking flux, as the water spent a shorter time to penetrate the membrane. On the other hand, increasing the reduced the N-chlorination sites on the membrane surface and hence, improved chlorine resistance. crosslinking improved salt rejection by narrowing the passages for salt transportation. Moreover, crosslinking the N-chlorination 4. the Optimization of reduced Polymerization Reactions sites on the membrane surface and hence, improved chlorine resistance. A major area of intense research is the optimization of interfacial polymerization reaction mechanisms such as kinetics, solvent solubility, reactant diffusion coefficient, reaction time, polymer molecular weight 4. Optimization of Polymerization Reactions range, and characteristics of micro-porous support [53–56]. Tomaschke et al. [57] found that mixing A major of intense research is the optimization of interfacial polymerization reaction amine salts with area the casting solution formed a cross-linked membrane with an improved rejection. mechanisms such as kinetics, solvent solubility, reactant diffusion coefficient, reaction time, Chau et al. [58] added N,N-dimethyleformamide into a casting solution that introduced more carboxylic polymergroups molecular weight and characteristics micro-porous [55–58]. Tomaschke functional to PA layer,range, and eventually increased of water flux. Kwaksupport et al. [59] used dimethyl et al. [59] found that mixing amine salts with the casting solution formed a cross-linked sulfoxide as an additive to modify the aromatic PA thin-film layer. The quantitative analysis of themembrane surface with an improved rejection. Chau et al. [60] added N,N-dimethyleformamide into a casting solution morphology showed correlation between water permeability and both surface area and surface roughness; that introduced more carboxylic functional groups to PA layer, and eventually increased water flux. the flux improved with increasing roughness and surface area without a significant loss of salt rejection. Kwak et al. [61] used dimethyl sulfoxide as an additive to modify the aromatic PA thin-film layer. Other researches showed that the addition of ethers, sulphur compounds, and alcohol- or water-soluble The quantitative analysis ofproduce the surface morphology showed correlation between water polymers to casting solution could high permeability without jeopardizing salt rejection [60–62]. permeability and both surface area and surface roughness; the flux improved with increasing Instead of modifying the casting solution, Michol et al. [63,64] succeeded in adding a complexing roughness and surface area without a significant loss of salt rejection. Other researches showed that agent (phosphate containing compound) to the poly functional acyl halide prior to the substantial the addition of ethers, sulphur compounds, and alcohol- or water-soluble polymers to casting reaction between functional acyl halide and poly functional amide. It was thought that the addition solution could produce high permeability without jeopardizing salt rejection [62–64]. of a complexing agent resulted in the formation of “association” with a polyfunctional acyl halide Instead of modifying the casting solution, Michol et al. [65,66] succeeded in adding a monomer capable of reducing the hydrolysis of acyl halide functional groups and permitting sufficient complexing agent (phosphate containing compound) to the poly functional acyl halide prior to the subsequent reaction with amine functional groups, thus resulting in a significant enhancement in substantial reaction between functional acyl halide and poly functional amide. It was thought that membrane performance. the addition of a complexing agent resulted in the formation of “association” with a polyfunctional Another alternative approach for optimizing the polymerization reaction is to introduce acyl halide monomer capable of reducing the hydrolysis of acyl halide functional groups and surface-modified macromolecules (active additives) to acyl halide solution. This approach depends on the concept that the macromolecules may transfer to the PA film surface during the polymerization

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permitting sufficient subsequent reaction with amine functional groups, thus resulting in a significant enhancement in membrane performance. Another alternative approach for optimizing the polymerization reaction is to introduce Membranes 2018, 8, 68 10 of 23 surface-modified macromolecules (active additives) to acyl halide solution. This approach depends on the concept that the macromolecules may transfer to the PA film surface during the polymerization andproperties change surface properties of membrane whilst bulk properties and change surface of membrane whilst maintaining bulk maintaining properties unaltered [65,66]. unaltered [67,68]. Arafat al.using foundpoly(ethylene that by using poly(ethylene as an active additive in the Arafat et al. found thatetby glycol) as an glycol) active additive in the interfacial interfacial polymerization, the water flux and salt rejection were significantly increased [69]. polymerization, the water flux and salt rejection were significantly increased [67]. 5. Incorporation Incorporation of of Nanoparticles Nanoparticles (NPs) (NPs) into into Membrane MembranePA PALayer Layer 5. A new new class of incorporation of of nanoparticles (NPs) intointo the A of membrane membranehas hasbeen beenformed formedbybythe the incorporation nanoparticles (NPs) toptop layer of of conventional thin film the layer conventional thin filmcomposite compositemembrane membrane(fabrication (fabricationprocess process Figure Figure 3). Table 22 summarizedthe theperformance performanceofofRO ROthin thinfilm filmnanocomposite nanocomposite (TFN) membranes that were reported summarized (TFN) membranes that were reported in in literatures and the next section discusses the most important studies. literatures and the next section discusses the most important studies.

Figure thethe IP IP process, reproduced withwith permission fromfrom Yin et al. et [19], Figure3.3.TFN TFNmembrane membranefabrication fabricationbyby process, reproduced permission Yin al. with permission from © 2014©Elsevier. [19], copyright with copyright permission from 2014 Elsevier.


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Table 2. Summary of important fillers used to modify TFC membranes. Nanofiller

PA Layer Monomers

Substrate

Performance of TFN 1012

1012

Ref. mPa−1 ·s−1

Zeolite NaA

MPD-TMC

PSU

Water flux was increased from 2.5 × to 3.9 × without compromising salt rejection (94%) by increasing the concentration of nanoparticles from 0 to 0.4 wt.%.

[60]

Zeolite NaAAaA

MPD:TEA-TMC

PSU

Both AgA-TFN and NaA-TFN membranes exhibited higher water flux than that of TFC membrane. No change in salt rejection was observed. Both membranes showed enhanced antimicrobial properties.

[61]

Different sized zeolite

MPD:TEA:SLS:IPA-TMC

PSU

The membrane embedded with smaller zeolite NPs produced higher water flux than the membrane with larger zeolite NPs.

[62]

Silica

MPD-TMC

PSU

By increasing silica concentration, the thermal properties of the membrane were considerably enhanced.

[68]

[69]

MWCNTs

MPD-TMC

PSU

Under filtration pressure of 225 psi, both water flux and salt rejection were decreased from 18 to 12 L/m2 ·h and 98 to 92.2 wt.%, respectively, by increasing the concentration of MWCNTs from 0 to 1 wt.%. On the other hand, the membrane demonstrated significant chlorine resistance.

Zeolite -LTA

MPD-TMC-post Treatment

PSU

NaCl rejection and water flux were 99.4 wt.% and 42 L/m·h, respectively, and had a filtration pressure of 300 psi.

[70]

F-Silica

MPD-TMC

PSU

When NPs concentration was 0.4 wt.%, the membrane showed high thermal stability.

[71]

F-MWCNTs

MPD-TMC

PSU

The membrane showed high dyes and brilliant blue rejection (91%)

[72]

Metal alkokxide

MPD: SLS-TMC

PSU

Water flux was encreased by approximately 2-fold when compared with the virgin membrane.

[73]

Zeolite NaX

MPD-TMC

PES

Under filtration pressure of 175 psi, the water flux was increased from 8.01 to 29.76 L/m2 ·h by increasing the content of NPs from 0 to 0.2 wt.% without jeopordizing NaCl rejection (above 90%). Also, the membrane showed good thermal stability.

[74]

iLSMM

MPD-TMC

PSU

Under filtration presure of 300 psi, the optimized water flux was 42 L/m2 ·h and the NaCl rejection was 97%. Besides, the membrane showed good antifouling properties.

[75]

MCM-41

MPD-TMC

PSU

Under filtration pressure of 300 psi, Water flux was increased from 28 to 46 L/m2 ·h by increasing the concentration of NPs from 0 to 0.1 wt.%, while NaCl rejection was maintained (97 wt.%).

[76]

APQZ

MPD-TMC

PSU

Water flux was increased from 16 to 40 L/m2 ·h by increasing the concentration of NP from 0 to 0.1 wt.%. In addition, the membrane showed good mechanical stability.

[77]


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Table 2. Cont. Zwitterion-CNT

MPD-TMC

PES

Under 530 psi, the optimized water flux was 48.46 L/m2 ·h, and NaCl rejection was 98.6%.

[78]

Carboxylic MWNTs

MPD-TMC

PES

Under 100 psi, the optimized water flux was 40 L/m2 ·h. Moreover, the membrane showed good mechanical stability.

[79]

Zeolite (Silicate-1)

MPD-TMC

PSU

The membrane showed higher chemical stability than the one with NaX-Zeolite NPs.

[80]

L/m2 ·h)

Zeolite-NaA

MPD-TMC

PSU

Under 232 psi, good water flux was achieved (46.5 by adding the NPs in organic phase and high salt rejection (97%) by adding the NPs in aqueous phase.

[81]

Aminated Zeolite

MPD:aPES:TEA-TMC

PSU

Under 797 psi, adding PES and TEA to MPD-nanoparticle solution increased water flux from 23.2 to 37.8 L/m2 ·h without compromising salt rejection (98%). Moreover, the membrane showed good chlorine resistance.

[82]

Zeolite-A

MPD-TMC

PSU

The membrnae showed significant fouling resistance.

[83] L/m2 ·h

Mesoporous SiO2

MPD-TMC

PSU

Under 232 psi, water flux was increased from 19 to 53 by increasing the concentration of NPs from 0 to 0.1 wt.%, while NaCl rejection remained (97%).

[84]

HBP-g-silica

MPD: aPES-TMC

PSU

Under 797.7 psi, the optimized water flux was 34.4 L/m2 ·h, while the salt rejection was 97.7%. And, the membrane showed better chlorine resistance.

[85]

Aluminosilicate CNTs

MPD-TMC

PSU

Under 232 psi, the optimized water flux was 23 L/m2 ·h, while NaCl rejection was 97.5%.

[86]

F-MWCNTs

MPD-TMC

PSU

Under 232 psi, the optimized water flux was 28.05 L/m2 ·h, while salt rejection was 90%. In addition, the membrane showed better antifouling and antioxidant properties.

[87]

HNTs

MPD-TMC

PSU

Under 217.5 psi, water flux was increased from 18 to 36.1 L/m2 ·h by increasing the concentration of NPs from 0 to 0.1% without sacrificing NaCl rejection (93%). Besides, the membrane had enhanced fouling properties.

[88]

OA-SiO2

MPD-TMC

PSU

The OA modified-silica PA membrane produced higher salt rejection (98%) when compared to the unmodified silica PA membrane (95%).

[89]

Clay

MPD-TMC

PSU

Under 232 psi, water flux was increased from 36.6 to 51 L/m2 ·h by adding 0.1 wt.% NPs without compromising NaCl rejection (around 99%). Also, the membrane exhibited significant antifouling properties.

[90]

GO-TiO2

MPD-TMC

PSU

Under 217.5 psi, both water flux and salt rejection were increased from 34 to 51 L/m2 ·h and 97 to 99%, respectively, by adding 0.02 wt.% NPs. Besides, the membrane demonstrated robust chlorine resistance.

[91]


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Table 2. Cont.

HN2 -TNTs

MPD-TMC

PSU

Under 217.5 psi, both water flux and NaCl rejection were increased from 19 to 36 L/m2 ·h and 94 to 96%, respectively, by adding 0.05 wt.% NPs. Moreover, the membrane showed good fouling resistance.

[92]

[93]

GO

MPD-TMC

PSU

Under 217 psi, the optimized water flux was 22 L/m2 ·h, while NaCl rejection was above 80%. Moreover, the modified membrane exhibited excellent fouling resistance against BSA and HA.

Al-ZnO

MPD-TMC

PSU

Under 225 psi, the optimized water flux was 32 L/m2 ·h, while NaCl rejection was 98%.

[94]

MCM-48-SiO2

MPD-TMC

PSU

Under 232 psi, the optimized water flux was 68 L/m2 ·h. And, NaCl rejection was around 97%.

[95]

GO

MPD-TMC

PSU

Under 300 psi, water flux was increased from 39 to 60 L/m2 ·h by increasing NPs concentrations from 0 to 0.015 wt.%, while NaCl rejection was above 93%.

[96]

[97]

ZnO

MPD-TMC

PSU

Under 300 psi, water flux was increased from 60 to 85 L/m2 ·h by increasing the concentration of ZnO from 0 to 0.1 wt.%. Under UV irradiation the membrane showed super water flux (120 L/m2 ·h). In addition, the membrane showed excellent fouling resistance.

MOFs

MPD-TMC

PSU

Under operation pressure of 300 psi, water flux and NaCl rejection were 85 L/m2 ·h and 98.5%, respectively.

[98]

[99] [100]

Graphene quantum dots

PIP-TMC

PES

Under operation pressure of 0.2 Mpa, water flux was 120 L/m2 ·h, 6.8-times higher than that of the virgin membrane. Moreover, the membrane showed excellent fouling resistance.

ZIF-8

MPD-TMC

PSU

53% enhancement in water flux was achieved. NaCl rejection was 99.4%. L/m2 ·h)

TiO2

MPD-TMC

PES

The addition of TiO2 resulted in higher water flux (24.3 as compasred with the virgin TFC (21.5 L/m2 ·h), while membrane selectivity was preserved (97%). Additionally, by increasing feed solution temeprature from 25 to 65 ◦ C, further enhancement in water flux was achieved.

CQDs

PIP-TMC

PSU

The addition of carbon quantum dots led to significant incerease in permeate flux (from 18 to 42.1 L/m2 ·h) without jeopordizing Na2 SO4 rejection (93%). Moreover, the fouling capacity of membrane was enhanced.

[102]

Na+ functionalized CQDs

MPD-TMC

PES

Impresive water flux (104 L/m2 ·h), high rejection of SeO3 2 (97.5%), and excellent fouling resistance were achieved when quantum dots concentration was 0.05 wt.%.

[103]

SiO2

MPD-TMC

PSU

Water flux was increased from 30 to 50 L/m2 ·h by increassing NPs concentration from 0 to 0.1 wt.% along with slight increase in salt rejection (from 92 to 95%).

[104]

Ziconiumv (IV)-carboxylate MOFs

MPD-TMC

PSU-PVP-LiCl

52% increase in water flux was achieved without comprimising NaCl rejection (95.5%).

[105]

[101]


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Jeong and Huang [60] reported that adding NaA zeolite NPs into the PA could result in an increase in water permeability without decreasing salt rejection. It was claimed that the superior hydrophilicity, high negative surface charge, and internal pores of zeolite nanomaterial facilitated water absorption and movement across the membrane, while maintaining high salt rejection via Donnan exclusion. Lind et al. [62] studied the influence of zeolite crystal size on the apparent structure, morphology, interface, and permeability of zeolite-PA TFN membranes. The existence of zeolite NPs resulted in higher permeability, greater negative surface charge, and thicker PA when compared with the raw membrane. The smaller NPs produced greater permeability, while the larger NPs produced more favorable surface properties. This study implied that the size of NPs may be considered an additional “degree of freedom” in designing the nanostructured membranes. Recently, Mayyahi [106] used quantum dots as an ultra-small filler to modify the TFN. Both water flux and salt rejection were increased upon the addition of QDs. Another study by Fathizadeh et al. [74] showed that increasing MPD and TMC concentrations to 3% w/v and 0.15% w/v, respectively, during TFN preparation in the presence of zeolite NPs formed a membrane with superior water flux but declined NaCl rejection. The low solute rejection was attributed to the poor dispersion of nanoparticles in the high molecular weight PA layer. The aggregation of NPs could have generated micro-holes in the PA, which allowed the brackish water to pass through. The reported results suggested that the relation between NPs and IP condition is another important factor that needs to be addressed. In addition to zeolite, different NPs such as nano-silica [68,71,104], multiwall carbon nanotubes [69,72], zwitterion functionalized-carbon nanotubes [78], Titanium dioxide (TiO2 ) [101,107], and clay nano-sheets [90] have been used to modify the composite membranes. All these researches showed that imparting NPs to the PA could enhance membrane performance in terms of permeate flux, salt rejection, chlorine resistance, and antifouling properties. For instant, Barona et al. [86] found that incorporating aluminosilicate single-wall carbon nanotubes (SWNTs) into the membrane surface resulted in a significant increase in water flux without affecting salt rejection. The functional groups on SWCNTs secured excellent dispersion of fillers in the PA and, as a result, enhanced the overall performance. A remarkable enhancement in membrane performance was achieved in another study by Jun et al. [76] upon the addition of MCM-41 silica NPs without compromising salt rejection. The high water permeability was ascribed to the enhanced membrane hydrophilicity as well as the pores in the NPs that imparted extra channels for water transportation. It is known that PA composite membranes are very sensitive to chlorine. As the PA layer touches the chlorinated water, the amine groups oxidize by chlorine and decompose in water, leading to deteriorated separation performance [108]. Park et al. [69] used acid functionalized MWCNTs to improve the chlorine resistance. When MWCNTs were incorporated into the PA active layer, the membrane showed enhanced anti-chlorine properties. This could be ascribed to the reaction between the functional groups in carbon nanotubes and the amine groups in PA structure, which as a result formed a barrier above the PA that reduced membrane chlorine exposure. Another study by Kim et al. [85] showed that attaching hyper branched polyamide modified silica NPs onto PA layer could protect the membrane from chlorine attack. The extra amino groups presented by the functionalized silica NPs were the main target for chlorine and subsequently lessened membrane surface exposure, as shown in Figure 4. It seems that all researchers followed the same strategy to produce a membrane with high chlorine resistance, which generates a protection layer on the membrane surface; however, this could not provide long term efficiency as the barrier might be finally degraded and the chlorine reaches the membrane surface [82,87,109].


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Figure chlorine attack, reproduced withwith permission fromfrom Kim Kim et al. et [85], Figure4.4.Protection Protectionsequence sequenceagainst against chlorine attack, reproduced permission al. with permission from © 2013©Elsevier. [87], copyright with copyright permission from 2013 Elsevier.

Membranefouling foulingis generally is generally known the accumulation of unwanted materials on Membrane known as theas accumulation of unwanted materials on membrane membrane surfaces [112]. and micro-biological fouling of TFN membranes aresubstantial among the surfaces [110]. Organic andOrganic micro-biological fouling of TFN membranes are among the substantial reasons that lead to membrane performance declination [113]. Hence, many studies are reasons that lead to membrane performance declination [111]. Hence, many studies are devoted devoted toadevelop a TFC with desired fouling resistance withoutoff” “trading any ofproperties the other to develop TFC with desired fouling resistance without “trading any ofoff” the other propertiespermeability including and permeability and rejection efficiency. Kimthat et incorporating al. [114] showed that including rejection efficiency. Kim et al. [112] showed hydrophilic incorporating hydrophilic filler into the PA layer could increase membrane resistance against filler into the PA layer could increase membrane resistance against organic fouling. The results organic fouling. demonstrated that between there was a reverse relationship between demonstrated that The thereresults was a reverse relationship hydrophilicity and organic foulants hydrophilicity and organic foulants accumulation. This could be ascribed to the weak interaction accumulation. This could be ascribed to the weak interaction between organic foulants and hydrophilic between Another organic foulants hydrophilic surfaces. that Another study by et al. [77] exhibited that surfaces. study byand Rana et al. [75] exhibited an increase in Rana membrane’s negative surface an increase membrane's negative surface charge could repulsive enhance fouling resistance, due to the charge couldinenhance fouling resistance, due to the strong force between the membrane strong repulsive force between the membrane and negatively charged foulants. Lee et al. used and negatively charged foulants. Lee et al. [113] used Ag nanoparticles as fillers in the PA to[115] mitigate Ag nanoparticles as fillers the PA to mitigate accumulation on the surface. Results bacterial accumulation on the in surface. Results showedbacterial that the Ag-TFN membrane has better resistance showedbacterial that the fouling. Ag-TFNItmembrane resistance against bacterial fouling. It and is believed that against is believedhas thatbetter Ag nanoparticles disturb the permeability respiration Ag nanoparticles disturb the permeability and respiration functions of the bacterial cell, and functions of the bacterial cell, and eventually destroy the DNA [114–116]. eventually DNA [116–118]. Kim etdestroy al. usedthe a new approach to prepare hybrid TFC by the self-assembly between titanium Kim et al. used a new approach to groups prepare[117]. hybrid TFC by the self-assembly titanium oxide NPs and PA’s carboxylic functional Results indicated that the UVbetween irradiation of the oxide NPs and PA's carboxylic functional groups [119]. Results indicated that the UV irradiation of membrane could reduce E-coli content on the surface and this was attributed to the ability of TiO2 to the membrane could reduce E-coli content onunder the surface and this attributed the ability of form different hydroxyl and peroxide radicals the influence of was UV light. Thesetoactive radicals TiO 2 to form different hydroxyl and peroxide radicals under the influence of UV light. These active were capable of destroying the bacterial cells. Ben-Sasson et al. [116] used electrostatic attraction to radicals were (Cu) capable of destroying bacterial cells.surface. Ben-Sasson et indicated al. [118] used electrostatic attach copper nanoparticles to thethe TFC membrane Results that the presence attraction to charged attach copper (Cu) the TFC membrane of surface. Results indicated that of positively Cu-NPs didnanoparticles not affect the to overall hydrophilicity the membrane, but reduced the presence of positively charged Cu-NPs did not affect the overall hydrophilicity of the the growth of bacterial cells. The SEM images of the membrane’s surface exhibited that the bacterial membrane, but reduced the growth of bacterial cells. Thecould SEM be images of the surface cells were damaged when contacted with Cu-NPs. This ascribed to membrane’s the high toxicity of exhibited that the bacterial cells were damaged when contacted with Cu-NPs. This could be Cu that led to bacterial DNA damage. Choi et al. [118] used “layer-by-layer assembly” to attach ascribed to the high toxicity of Cu that led to bacterial DNA damage. Choi et al. [120] used graphene oxide (GO) and aminated-graphene oxide (AGO) to TFC membrane surface, as shown in “layer-by-layer assembly” attachenhanced grapheneresistance oxide (GO) and aminated-graphene (AGO) to Figure 5. The resultant TFC to showed against organic fouling and oxide chlorine attack, TFC membrane surface, as shown in Figure 5. The resultant TFC showed enhanced resistance while preserving water flux and NaCl rejection. Hu and Mi [119] succeeded in using layer-by-layer against organic fouling GO andNPs chlorine attack, preserving water flux and NaClwith rejection. Hu and deposition” to connect to the PA. Inwhile this case, GO-NPs formed linkages membrane’s Mi [121] succeeded in using layer-by-layer deposition” to connect GO NPs to the PA. In this case, GO-NPs formed linkages with membrane's functional groups. The newly developed membrane exhibited superior water flux and excellent dye rejection. The disadvantage of the “surface located


Membranes2018, 2018,8,8,x xFOR FORPEER PEERREVIEW REVIEW Membranes

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functional groups. The newly developed membrane exhibited superior water flux and excellent nanocomposite membrane” theof loss nanoparticles during filtration,especially especiallythose those attached dye rejection. The disadvantage theofof “surface locatedduring nanocomposite membrane” is the loss of nanocomposite membrane” isisthe loss nanoparticles filtration, attached by electrostatic forces. The depletion of nanoparticles reduces the efficiency of the membrane and nanoparticles especially those attached by electrostatic forces. depletion of by electrostaticduring forces. filtration, The depletion of nanoparticles reduces the efficiency of theThe membrane and may expose nanoparticles to the permeated water causing a threat to people’s health. As a result, nanoparticles reduces the efficiency of the membrane and may exposetonanoparticles to theAspermeated may expose nanoparticles to the permeated water causing a threat people’s health. a result, Yin and and co-workers. [122] used cyseteamine “bridging agent” attach silver (Ag) (Ag) water causing a threat to[122] people’s health. As a result, co-workers. [120] used cyseteamine as a Yin co-workers. used cyseteamine asasYin aa and “bridging agent” toto attach silver nanoparticles to the membrane surface, as shown in Figure 6. Results indicated that the modified “bridging agent” to attach silversurface, (Ag) nanoparticles the membrane as shown Figure 6. nanoparticles to the membrane as shown intoFigure 6. Resultssurface, indicated that theinmodified membrane hasstable stable Agmodified NPs,superior superior antimicrobial properties, highpermeability, permeability,and andgood good Results indicated that the membrane has stable properties, Ag NPs, superior antimicrobial properties, membrane has Ag NPs, antimicrobial high separation efficiency. Recently, Mayyahi [123] showed that UV irradiation of TFN membrane which high permeability, andRecently, good separation Recently, [121] showed UV irradiation separation efficiency. Mayyahiefficiency. [123] showed that Mayyahi UV irradiation of TFNthat membrane which impregnated withTiO TiO2 could 2 could resultininrobust robust antibacterial properties. of TFN membrane which impregnated with TiO in robust antibacterial properties. impregnated with result antibacterial properties. 2 could result

Figure 5.Layer-by-layer Layer-by-layer depositionofofpositively-charged positively-charged GOand and aminated-GOnanosheets nanosheets onthe the Figure Figure 5. 5. Layer-by-layerdeposition deposition of positively-chargedGO GO andaminated-GO aminated-GO nanosheetson on the membrane surface; reproduced with permission from Choi et al. [121], with copyright permission membrane reproducedwith withpermission permissionfrom fromChoi Choi et al. [121], copyright permission membrane surface; surface; reproduced et al. [118], withwith copyright permission from from©©2013, 2013,American AmericanChemical ChemicalSociety. Society. from © 2013, American Chemical Society.

Figure Schematic illustration of attaching Ag-NPs on the TFC membrane surface; reproduced with Figure6.6.6.Schematic Schematicillustration illustrationof ofattaching attachingAg-NPs Ag-NPson onthe theTFC TFCmembrane membranesurface; surface;reproduced reproducedwith with Figure permission from Yin et al. [120], with copyright permission from © 2013 Elsevier. permission from Yin et al. [122], with copyright permission from © 2013 Elsevier. permission from Yin et al. [122], with copyright permission from © 2013 Elsevier.

Conclusions 6.6.Conclusions tremendousdevelopment developmentininTFN TFNmembranes membranesfor forwater waterpurification purificationhas hasbeen beenachieved achieved AAtremendous includingproducing producingaamembrane membranewith withsuper superwater waterflux, flux,high highsalt saltrejection, rejection,and andexcellent excellentfouling fouling including


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6. Conclusions A tremendous development in TFN membranes for water purification has been achieved including producing a membrane with super water flux, high salt rejection, and excellent fouling and chorine resistance via using innovative approaches such as imparting the favored properties of nanoparticles to the membrane surface, optimizing the membrane fabrication process, modifying the materials that are required to synthesis the membrane, and changing membrane surface properties by post-treatment. However, researchers have failed to find an alternative to the PA barrier layer or to suggest a new support layer. We do agree that PA atop PSU/PES showed robust efficiency in RO and other water treatments applications, but these membranes have been used since 1970 and scholars have successfully addressed almost all the challenges facing the progress of such membranes. Forthcoming researches should be dedicated to suggest a new reverse osmosis membrane rather than developing the existing one. Funding: This research received no external funding. Conflicts of Interest: The author declares no conflict of interest.

Abbreviations AGO Ag Al-ZnO BDSA BHAC BHDT BPA CFIC CNT CQDs Cu DABA DMF DMSO DETA DPA F-MWCNTs F-silica GO HBP-g-silica HNTs ICIC IP iLSMM MOFs MPD mm-BTEC MWCNTs NPs OA-SiO2 om-BTEC MOFs op-BTEC PA PAMAM

Aminated-graphene oxide Silver Aluminum doped zinc oxide 2,20 -benzidinedisulfonic acid 2,20 ,4,40 ,6,60 -biphenyl hexaacyl chloride Bis-2,6-N,N-(2-hydroxyethyl) diaminotoluene Bisphenol 5-chloroformyloxy-isophthaloyl chloride Carbon nanotube Carbon quantum dots Copper Triamine 3,5-diamino-N-(4-aminophenyl)-benzamide N,N-dimethylformamide 2,4,6-pyridinetricarboxylic acid chloride Diethylenetriamine Dopamine Functionalized multi wall carbon nanotubes Functionalized silica Graphene oxide Hyper-branched aromatic polyamide-grafted silica Halloysite nanotubes 5-isocyanato-isophtahloyl chloride Interfacial polymerization In-situ hydrophilic surface modifying macromolecules Metal–organic frameworks m-phenylenediamine 3,30 ,5,50 -biphenyl tetraacyl chloride Multiwall carbon nanotubes Nanoparticles Oleic acid modified silica 2,20 ,4,40 -biphenyl tetraacyl chloride Metal–organic framework 2,20 ,5,50 -biphenyl tetraacyl chloride Polyamide Ethylenediamine cored poly(amidoamine)


PDMAEMA PSU RO SiO2 SMPD SWCNTs TFC TFN TiO2 TMC TETA TEPA TNTs UV ZIF ZnO

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Poly(N,N-dimethylaminoethyl methacrylate) Polysulfone Reverse osmosis Silicon dioxide Sulfonated m-phenylenediamine Single-wall carbon nanotubes Thin film composite Thin film nanocomposite Titanium dioxide Trimesoyl chloride Triethylenetetramine Tetraethylenepentamine Titanate nanotubes Ultraviolet Zeolitic imidazolate framework Zinc oxide

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