I. PURPOSE OF A RESEARCH PROPOSAL Arsenic in drinking water has been reported as the most widespread geogenic contaminant in water sources worldwide 1. The World Health Organization (WHO) reports 2 longterm exposure to arsenic from drinkingwater and food can cause cancer, skin lesions, cardiovascular disease and diabetes. WHO’s standard content of arsenic in drinking water is 10 µgL while in Vietnam, the number is 50 µgL 3. Although there is numerous conventional technology available for treating arsenic in water such as oxidation, coagulation – floculation, adsorption and ion exchange, the resulting quality of such technologies does not meet the technical committee of Vietnam (TCVN), and furthermore, the requirement for As concentration tend to reduce to the lower level (10 µgL) from the community due to a higher risk of As exposure 3. Additionally, there are several possible drawbacks such as huge cost, complex operational condition and handling techniques. Modern technology such as nanofiltration (NF) polyamidebased membrane is a promising alternative to the existing removal processes, which show various advantages in terms of operational costs, efficiency, selectivity and energy consumption. In the NF process, the separation performance of the membrane in term of permeability and selectivity is depended on the structure and physicochemical properties of the membrane and thus controlled by the structure of the monomers, concentration of the monomers and reaction conditions. For my knowledge, there is few studies in the fabrication of membrane for As removal. In this work, my purpose is to investigate the separation performance of polyamide based nanofiltration membrane synthesized in laboratory for removing As (V) from water. Following research objectives would facilitate the achievement of this aim: (i). Sucessfully synthesizing NF thinfilm composite (TFC) membrane based polyamide via interfacial polymerization in which I can evaluate the effect of monomer structures on the separation performance of the prepared membrane. (ii). Investigation of the effect influence of the additives on the separation performance
Ho Chi Minh University of Technology Faculty Of Chemical Engineering Office For International Study Programs Thesis Proposal Study on Separation Performance of Polyamide Based Nanofiltration Membrane for Arsenic Removal Submitted by NGUYEN HUU QUANG MINH – ID Number: 1652374 Instructor: MAI THANH PHONG Assoc Prof., Ph.D Ho Chi Minh city, January 2020 TABLE OF CONTENTS I PURPOSE OF A RESEARCH PROPOSAL II OVERVIEW 1 Arsenic .1 Arsenic Contamination in Vietnam Arsenic Removal Techniques 3.1 Oxidation Technique 3.2 Coagulation – Flocculation 3.3 Adsorption and Ion Exchange 3.4 Membrane technology III LITERATURE REVIEW IV METHODOLOGY 10 Materials 10 Membrane preparation .10 Membrane characterization .10 Measurement of the NF separation performance testing 10 Research content 11 5.1 Investigation of the effects of diamine monomers on NF membrane seperation performance .11 5.2 Study on the effects of additives on NF membrane performance 11 V PLAN 12 VI STRUCTURE OF THESIS REPORT .13 REFERENCES 14 ABBREVIATION 15 LIST OF TABLE Table Comparison of main arsenic removal technologies Table Overview of pressure-driven membrane processes Table Schedule for completion of the research 12 I PURPOSE OF A RESEARCH PROPOSAL Arsenic in drinking water has been reported as the most widespread geogenic contaminant in water sources worldwide [1] The World Health Organization (WHO) reports [2] long-term exposure to arsenic from drinking-water and food can cause cancer, skin lesions, cardiovascular disease and diabetes WHO’s standard content of arsenic in drinking water is 10 µg/L while in Vietnam, the number is 50 µg/L [3] Although there is numerous conventional technology available for treating arsenic in water such as oxidation, coagulation – floculation, adsorption and ion exchange, the resulting quality of such technologies does not meet the technical committee of Vietnam (TCVN), and furthermore, the requirement for As concentration tend to reduce to the lower level (10 µg/L) from the community due to a higher risk of As exposure [3] Additionally, there are several possible drawbacks such as huge cost, complex operational condition and handling techniques Modern technology such as nanofiltration (NF) polyamide-based membrane is a promising alternative to the existing removal processes, which show various advantages in terms of operational costs, efficiency, selectivity and energy consumption In the NF process, the separation performance of the membrane in term of permeability and selectivity is depended on the structure and physicochemical properties of the membrane and thus controlled by the structure of the monomers, concentration of the monomers and reaction conditions For my knowledge, there is few studies in the fabrication of membrane for As removal In this work, my purpose is to investigate the separation performance of polyamide based nanofiltration membrane synthesized in laboratory for removing As (V) from water Following research objectives would facilitate the achievement of this aim: (i) Sucessfully synthesizing NF thin-film composite (TFC) membrane based polyamide via interfacial polymerization in which I can evaluate the effect of monomer structures on the separation performance of the prepared membrane (ii) Investigation of the effect influence of the additives on the separation performance II OVERVIEW Arsenic Arsenic is a toxic heavy metal which is highly detrimental to ecological systems, and long-term exposure to it, especially in its inorganic form mainly through drinkingwater, is highly dangerous to life as it can cause serious health effects Skin lesions and skin cancer are the most characteristic effects Depending on redox conditions, it is stable in the +5, +3, -3, and oxidation states As(III) is 60 times more toxic than As(V), the pentavalent (+5) or arsenate species are AsO4 -3, HAsO4- and H2AsO4- The trivalent (+3) or the arsenite species include As(OH)4 - , AsO2OH-2 and AsO3-3 The pentavalent arsenic As(V) species are predominant and stable in oxygen-rich aerobic environments, whereas the trivalent arsenite As(III) species are predominant in moderately reducing anaerobic environments such as groundwater [4-5] Arsenic Contamination in Vietnam All Vietnam regions are potentially arsenic contaminated Arsenic has formed in soil, rock and sediments and dissolved into groundwater for thousands of years Arsenic pollution in the Red River Delta is more serious than in the Mekong River Delta Particularly in rural areas of Hanoi such as Thuong Tin, Ung Hoa, Dan Phuong, Thanh Oai and Thanh Tri, the groundwater sources are heavily contaminated with arsenic [3] Survey results of arsenic concentration in groundwater in 345 craft villages in Hanoi city of Hanoi Department of Science and Technology (October 2012) showed that there were 338/345 water samples (97.97%) had Arsenic content is 2-50 times higher than the standard In the Mekong River Delta , 4876 samples of groundwater surveyed have 56% of samples contaminated with arsenic (over 50 µg/L) [3] Arsenic Removal Techniques 3.1 Oxidation Technique Oxidation involves the conversion of soluble arsenite to arsenate This alone does not remove arsenic from the solution, thus, a removal technique, such as adsorption, coagulation, or ion exchange, must follow For anoxic groundwater, oxidation is an important step since arsenite is the prevalent form of arsenic at near neutral pH Aside from atmospheric oxygen, many chemicals, as well as bacteria, have already been used to directly oxidize arsenite in water [6] Atmospheric oxygen, hypochlorite, and permanganate are the most commonly used oxidants Oxidation of arsenite with oxygen is a very slow process, which can take hours or weeks to complete On the other hand, chlorine, ozone, and permanganate, can rapidly oxidize As(III) to As(V) However, despite this enhanced oxidation, interfering substances present in water need to be considered in selecting the proper oxidant as these substances can greatly affect and dictate the kinetics of As(III) oxidation For instance, it was shown that competing anions and organic matter in groundwater greatly affect the use of UV/titanium dioxide (TiO2) in arsenic oxidation Furthermore, this involves a complex treatment, which produces an Asbearing residue that is difficult to dispose Thus, to efficiently remove arsenic from a solution by oxidation, oxidants should be selected carefully Moreover, all cited disadvantages of oxidation alone make it a less competent method for arsenic removal [6] 3.2 Coagulation – Flocculation Coagulation process is traditionally realized by adding ferric or aluminum ions (e.g., FeCl3 and Al2(SO4)3) Fine particles in water first aggregate into coagulates because added ferric or aluminum ions strongly reduce the absolute values of zeta potentials of the particles Then, arsenic ions (arsenate or arsenite) precipitate with the ferric or aluminum ions on the coagulates, and thus concentrate in the coagulates After that, the coagulates are separated from water through filtration, eliminating arsenic from the water [6-7] Flocculation, on the other hand, involves the addition of an anionic flocculant that causes bridging or charge neutralization between the formed larger particles leading to the formation of flocs Finally, solids are removed afterwards through filtration or sedimentation [6] A review of these ferric or aluminum ions along with their distinct advantages and disadvantages is shown in Table [7] Table Comparison of main arsenic removal technologies Ions Advantages - Durable powder chemicals are available Aluminum - Low capital cost and simple in coagulatio operation n - Effective over a wider range of pH Ferric coagulatio n 3.3 Disadvantages - Produces toxic sludges - Low removal of arsenic - Pre-oxidation may be required - Common chemicals are available - Medium removal of - More efficient than alum As(III) coagulation on weigh basis - Sedimentation and filtration needed Removal (%) 90 94.5 Adsorption and Ion Exchange Adsorption is a process that uses solids as medium for the removal of substances from gaseous or liquid solutions Basically, substances are separated from one phase followed by their accumulation at the surface of another This process is driven mainly by van der Waals forces and electrostatic forces between the adsorbate molecules and the adsorbent surface atoms This makes it important to characterize first the adsorbent surface properties (e.g., surface area, polarity) before being used for adsorption [6] Adsorption has been reported as the most widely used technique for arsenic removal due to its several advantages including relatively high arsenic removal efficiencies, easy operation, and handling, cost-effectiveness, and no sludge production However, adsorption of arsenic strongly depends on the system’s concentration and pH Additionally, contaminated water does not only contain arsenic, it is always accompanied by other ions (E.g., phosphate and silicate), competing for the adsorption sites Moreover, The effectiveness of adsorption in arsenic removal can also be hindered by the type of adsorbent itself In addtition, Most conventional adsorbents have irregular pore structures and low specific surface areas, leading to low adsorption capacities Lack of selectivity, relatively weak interactions with metallic ions, and regeneration difficulties can also confine the ability of these sorbents in lowering arsenic concentrations to levels below maximum concentration level [6] 3.4 Membrane technology 3.4.1 General review of membrane technology A membrane is an interphase between two adjacent phases acting as a selective barrier, regulating the transport of substances between the two compartments In membrane processes, a membrane separates two phases The membrane allows transport of one or few components more readily than that of other components The driving force for transport can be either a pressure gradient, a temperature gradient, a concentration gradient or an electrical potential gradient [6] Typically, membranes are synthetic materials with billions of pores acting as selective barriers, which not allow some constituents of the water to pass through Generally, there are two categories of pressure-driven membrane filtrations (as shown in Table 2): (i) low-pressure membrane processes, such as microfiltration (MF) and ultrafiltration (UF); and (ii) high-pressure membrane processes, such as reverse osmosis (RO) and nanofiltration (NF) [6] Table Overview of pressure-driven membrane processes Parameter Permeability (1/h·m2 ·bar) Pressure (bar) Pore size (nm) MF UF RO NF >1000 10 – 1000 1.5 – 30 0.05 – 1.5 0.1 – 100 – 10,000 0.1 – – 100 – 20 0.5 – – 120 < 0.5 MF alone cannot be used to remove dissolved arsenic species from arseniccontaminated water Thus, the particle size of arsenic-bearing species must be increased prior to MF; the most popular processes for this being coagulation and flocculation However, the pH of the water and the presence of other ions are major factors affecting the efficiency of this arsenic immobilization This can be a disadvantage of this technique especially since arsenate is negatively charged in this pH range, it can bind by surface complexation resulting in efficient arsenate removal Therefore, complete oxidation of arsenite to arsenate is needed for this technique to be effective [6] As MF, UF alone is not an effective technique for the treatment of arseniccontaminated water due to large membrane pores Arsenic removal was reported to decrease with decreasing pH Moreover, despite the effective removal of arsenic, the concentration of the surfactant in the effluent is so high that it needs to be further treated with powdered activated carbon before being discharged to the environment [6] Both NF and RO are suitable for the removal from water of dissolved compounds with a molecular weight above 300 g/mol These techniques can significantly reduce the dissolved arsenic level in water given that the feed is free from suspended solids and that arsenic is preferably present as arsenate [6] 3.4.2 NF versus RO NF membranes have low molecular weight cut-offs (200 - 1000 Da) and smaller pore size (∼1 nm) They also have a surface electrostatic charge which gives them great selectivity towards ions or charged molecules More specifically, NF membrane can be used to remove small neutral organic molecules while surface electrostatic properties allowed monovalent ions to be reasonably well transmitted with multivalent ions mostly retained NF membrane's operating pressure ranged from to 20 bars, which was much lower than RO membranes [8] Indeed, RO cannot be used for partial and or selective demineralization NF is more suitable for directly producing drinking water and the post treatment can be simplified The argument, that NF membranes are more selective was also presented It was clearly shown that NF selectivity for monovalent ions is higher than RO [9] Moreover, NF offers several advantages, such as low operation pressure, high flux, high retention of multivalent anion salt and organic molecular above 300, relatively low investment, low operation and maintenance cost Furthermore, NF membranes available in the market show a wide range of properties and thus this variation affects the membrane performances Additionally, NF membranes properties can be characterized in terms of the hydrophobicity, membrane roughness, membrane charge, membrane molar weight cut-off, retention properties and permeability Modeling can also be used to analyze and to predict the membranes performances [10-11] To sum up, it can be confidently stated that a competing membrane process for arsenic removal in the near future is NF Therefore, an adequate understanding of the arsenic treatment using NF is necessary III LITERATURE REVIEW The separation performance of polyamide membrane is influence by many factors such as: monomers structure, monomers concentration, reaction time, pre-treatment, additives Therefore, the control of the preparation condition is the key to produce the polyamide-based NF membrane which is suitable for individual purpose Mai Thanh Phong et al [12] has synthesized NF thin-film composite (TFC) via polymerization between piperazine (PIP) in water and trimesoyl chloride (TMC) in hexane onto polyacrylonitrile (PAN) supporting substrate The effect of PIP and TMC concentration on separation process has been studied The characteristic peaks are assigned to the amide II band (C – N – H) and and amide I band (N – C = O) of the PA thin film, and also the carboxylic groups, which is the result of the hydrolysis of unreacted acyl chloride The results showed that the cross-linking degree enhanced as increasing TMC concentration in the range from 0.05 wt.% to 0.15 wt.% With the TMC concentration higher than 0.15 wt.%, the ratio of I(COOH ) /I (CONH ) exhibited an opposite trend It indicated that the IP reaction was improved with the increase in TMC concentration The interfacial polymerization occurred at the organic side of the interface of water and organic solvents which can be controlled by the diffusion of m-phenylenediamine (MPD) and TMC Therefore, an increase in either MPD or TMC concentrations might enhance the driving force for diffusion of monomers to the reaction region to form rapidly a dense thin-film and thereby limited the growth of thickness of the membrane However, increasing TMC concentration may induce a deficiency in the available MPD at the organic side of the interface It would lead to an increase of a linear structural fraction with carboxylic acid functional groups, associated with a more hydrophilic surface in the organic [12] By increasing PIP concentration, the diffusion of PIP to the reaction side of the interface was accelerated Consequently, the reaction rate is faster and a dense PA film with high extent of cross-linking was formed The dense film also plays as a role of a barrier, which prevents and blocks the diffusion of PIP to the organic side of the interface for reacting with TMC Therefore, the obtained membrane became thinner, denser, and more hydrophobic It can be seen from the results that the PA membrane produced with the TMC concentration of 0.15 wt.% and the PIP concentration of 2.0 wt.% exhibited a good separation performance with permeation flux of 64 Lm-2h-1 and As(V) rejection of 95%, respectively [12] S Veríssimo et al [13] investigated the influence on membrane performance of the use of different piperazine derivatives Composite membranes were prepared by interfacial polymerization of PIP, N,N′-diaminopiperazine (DAP), 1,4-bis(3aminopropyl)-piperazine (DAPP) and N-(2-aminoethyl)-piperazine (EAP) with TMC separately Their nanofiltration performance was evaluated with solutions of NaCl, MgSO4 and Na2SO4 (3g/l and pH 6) at 10×105 Pa The surface charge was investigated by zeta-potential measurements and the morphological studies by atomic force microscopy (AFM) and scanning electron microscopy (SEM) [13] The PIP–TMC membranes presented an average water permeability of 6.6 × 10-5 l (m-2h-1Pa-1) and the average rejection to the divalent salts MgSO4 (93%) and Na2SO4 (95%) was higher than to the monovalent salt NaCl (40%) The membranes have slight acidic property and have a negatively charged surface at the pH The morphological studies revealed a somewhat rough surface [13] The DAP–TMC membranes gave the highest average water permeability, around 8.8 × 10-5 l (m-2h-1Pa-1) The average salt rejections for NaCl, MgSO4 and Na2SO4 were 21, 72 and 89%, respectively The membranes also showed some acidic property and were negatively charged at pH The membranes surface was very flat and had a very thin film [13] The DAPP–TMC membranes have an average water permeability of 3.2 × 10-5 l (m-2h-1Pa-1) and different average salt rejections to NaCl (57%), MgSO4 (75%) and Na2SO4 (35%) The membranes surface is amphoteric and at pH is positively charged A smooth surface characterizes the membranes [13] The EAP–TMC membranes presented an average water permeability of 3.1 × 10-5 l (m-2h-1Pa-1) and the average rejection to the divalent salts MgSO4 (90%) and Na2SO4 (92%) was higher than to the monovalent salt NaCl (31%) The membranes have amphoteric surface and are negatively charged at pH The membranes surface was flat and had a very thin film [13] Overall, DAP – TMC has the highest average water permeability The average salt rejection of divalent salts is higher than the monovalent one except DAPP – TMC PIP – TMC showed the rough surface while the surface of the rest ones are flat Asim K Ghosh et al [14] reported on the attempt to correlate MPD–TMC reaction and curing conditions to RO membrane separation performance (water flux, salt rejection), film structure and interfacial characteristics (hydrophilicity, roughness) Polyamide composite membranes are formed by immersing the polysulfone support membrane in an aqueous solution of MPD for 15s The gas is applied to the wetted membrane surface until the surface appears dull and dry The MPD saturated support membrane is then immersed into the organic solution of TMC for 15 s, which results in formation of an ultra-thin polyamide film over the polysulfone support The resulting composite membranes are heat cured at 50oC for 10 (unless otherwise specified), washed thoroughly with deionized (DI) water, and stored in DI water filled lightproof containers at 5oC When additives triethylamine (TEA) and Camphorsulfonic acid (CSA) are employed, g of TEA and g of CSA are added to 75–80 mL of DI water under vigorous stirring After complete dissolution of the TEA–CSA mixture, DI water is added to provide a total solution volume of 100 mL Finally, g of MPD is added to the 100 mL TEA–CSA aqueous solution The use of additives in monomer solutions can influence the rate and extent of interfacial polymerization as well as the extent of crosslinking Properties of polyamide films formed with TEA–CSA added to the aqueous-MPD reaction solution The results represent average changes in pure water permeability, salt permeability, contact angle, and surface roughness relative to the membrane formed without TEA– CSA in the same solvent In all the cases, pure water permeability dramatically increases, salt rejection is practically unchanged, contact angle is slightly reduced, and roughness is significantly reduced by TEA–CSA addition Membrane surface features appear more nodular when TEA–CSA is present compared to the ridge-and-valley morphology of membranes formed without TEA–CSA On SEM and transmission electron microscopy (TEM) images, the nodular morphology is measurably smoother than the ridge-and-valley morphology according to AFM surface roughness analyses Cross-section TEM images of hexane and isopar based membranes prepared with TEA–CSA looked thinner and smoother than without TEA–CSA membranes Three novel polyacyl chloride monomers: 2,4,4′,6-biphenyl tetraacyl chloride (BTAC), 2,3′,4,5′,6-biphenyl pentaacyl chloride (BPAC) and 2,2′,4,4′,6,6′-biphenyl hexaacyl chloride (BHAC) were successfully synthesized by Tunyu Wang et al [15] TFC RO membranes were prepared by using TMC, BTAC, BPAC as well as BHAC to interfacial react with m-phenylenediamine (MPDA) on the polysulfone support through interfacial polymerization respectively, for the purpose of investigating the effects of the polyacyl chloride functionality on the RO membrane properties TFC RO membranes were prepared through interfacial polymerization of trimesoyl chloride (TMC), BTAC, BPAC, and BHAC with MPDA respectively The results reveal that the functionality of the acid chloride monomer strongly influences the properties of the RO membrane As the functionality of the acid chloride monomer increased, the resulting membrane skin layer became more negatively charged, thinner and smoother In addition, all the four membranes exhibited close salt rejection rates according to the RO separation performance tests However, with the increase of acid chloride functionality the permeate flux of the resulting RO membrane became lower, due to a combination of the increase in the carboxylic acid groups on the membrane surface, lower mobility of the crosslinked polyamide chains and lower surface roughness In-Chul Kim et al [16] perform the experiment on the effect of alkyl phosphate additives during interfacial polymerization Polyamide membranes were prepared by interfacial polymerization on a polysulfone (PSF) UF membrane The PSF membrane was dipped into an aqueous solution containing MPD, TEA (2–3 wt.%), dimethyl sulfoxide (1 wt.%), 2-ethyl-1,3-hexane diol (0.2–0.3 wt.%), and CSA (1–2 wt.%) in DI water, after which the excess solution was removed by squeezing with a soft rubbery roller after The PSF membrane was then immersed in a solution of 0.1 wt.% TMC and different concentrations of tributyl phosphate (TBP) or triphenyl phosphate (TPP) in isoparaffin After of reaction, the membrane was dried in air for The membrane was rinsed with a 0.2 wt.% Na2CO3 solution In order to demonstrate the effect of the additives in an organic solution on the membrane performance, the concentrations of TBP and TPP were varied under the same condition to that of the aqueous solution The water flux and NaCl rejection of the membranes with additives of TBP and TPP in the TMC organic solution at different concentrations For the membranes using TBP as an additive in the organic solution, an increase in the water flux was observed with no significant loss of salt rejection when the amount of TBP in the organic solution was increased up to 0.9 wt % However, it was found that with the increase in TPP concentration in the TMC organic solution, the water flux was slightly decreased without loss of salt rejection TBP as an additive has much better performance than TPP due to the complex formation between TBP and TMC in an organic solution [16] Both membranes show a unique ridge-and-valley structure With the addition of TBP into the TMC organic solution, the surface morphology of the membrane prepared without TBP addition was changed The addition of TBP in the TMC organic solution during interfacial polymerization tends to increase the ridge portion of the polyamide TFC membrane Most of the ridge film covers the valley film The AFM image of the membrane with no TBP addition shows a ridge-and-valley structure The membrane with the addition of 0.6 wt.% TBP in the TMC organic solution indicates that the surface of the TFC polyamide film has a broad ridge and a loose structure compared to the membrane without TBP addition [16] ShanShan Guan et al [17] investigated the effect of additives on the performance and morphology of sulfonated copoly (phthalazinone biphenyl ether sulfone) (SPPBES) composite nanofiltration membranes SPPBES composite membranes were prepared from SPPBES coating solutions containing different additives The effect of the additives including glycol, glycerol and hydroquinone in the SPPBES solutions on membrane performance and morphology were studied For all of SPPBES composite membranes, the salt rejection increased in the order: R(MgCl2) < R(NaCl) ≤ R(MgSO4 ) < R(Na2 SO4 ) The rejection of SPPBES membranes prepared from these additives decreased as follows: glycol > glycerol > hydroquinone The SPPBES composite membrane prepared from glycerol as the additive had the highest flux, while composite membrane prepared from hydroquinone as the additive showed the lowest flux Smooth composite membrane surfaces were obtained when glycol and glycerol were used as additives, and they were no significant difference The most important properties of the TFC membranes are permeability and selectivity, which are basically determined by the physicochemical properties of the upper polyamide layer such as surface roughness, hydrophilicity, charge performance as well as skin layer thickness Factors affecting these physicochemical properties include: support membrane structure and chemistry, monomer structures and concentration, catalysts and other additives in the aqueous solution and/or in the organic solution during the interfacial polymerization, reaction and curing conditions, and other post-treatments Among all these factors, the inherent chemistry of the monomers employed in the polymerization has been proven to play a major role as confirmed from various studies over the past decades In addition, it is common in practice to use combinations of additives to influence monomer solubility, diffusivity, hydrolysis, or protonation or to scavenge inhibitory reaction byproducts NF is a pressure-driven membrane process that lies between UF and RO, it were consider “low-pressure RO membrane” thus, some of the study on RO could also be considered for better understanding about NF membrane [8] For instance, the work of Tunyu Wang et al [15] on the effect of monomers on RO membrane for salt rejection or the experiment of Asim K Ghosh et al [14] on evaluating the addition TEA – CSA to the aqueous MPD solution using RO membrane The studies demonstrate that the physicochemical properties such as flux and rejection of the membrane are mainly affected during the interfacial polymerization Among all the factors, monomers play a central role involving monomers’ structure, monomers’ concentration, concentration ratio between monomers, reaction time and reaction temperature, type of solvent, post-heat treatment Additives, on the other hand, are able to influence monomer solubility, diffusivity, hydrolysis, or protonation or to scavenge inhibitory reaction byproducts Most nanofiltration membranes are composite and have a polyamide thin film prepared by interfacial polymerization Their characteristics and performance are mainly determined by the thin film and consequently by the monomers used for its preparation For example, In S Veríssimo et al [14] work, different thin films were prepared with small structural differences to help understanding how the amines structure influences the membranes nanofiltration performance, surface charge and morphology The results show different average water permeability of the samples which was correlated with hydrophobic/hydrophilic character of the monomers by use of the octanol–water partition coefficient The research on MPD/TMC concentration of Mai Thanh Phong et al [12] also show that an increase in either MPD or TMC concentrations increase the driving force for diffusion of monomers quickly However, increasing TMC concentration would lead to an increase of a linear structural fraction with carboxylic acid functional groups, associated with a more hydrophilic surface due to the deficiency in the available MPD at the organic side The study on addtives such as TPP and TBP has been performed by In-Chul Kim et al [16], it was found different additives lead to different performance due to the complex formation between additives and TMC in an organic solution In conclusion, the need of studying on NF membrane performance in order to apply NF membrane process on arsenic treatment process in water is necessarry since most of the researchs contribute towards the performance of monomers structure and additives on RO membrane polymerization and a large number of research on NF membrane is for desalination process purpose only IV METHODOLOGY Materials Polyacrylonitrile (PAN) porous support substrate was provided by DowFilmtec (USA) PIP, ethylenediamine (EDA), MPD, triethylenetetramine (TETA) and TMC with the purity of 99% was received from Sigma-Aldrich (USA) Deionized (DI) water and hexane (99%) were used as solvents for the synthesis of polyamide membrane Arsenate (Na2AsHSO4) was purchased from Merck (Germany) Additives such as sodium dodecyl sulfate (SDS), triethylamine (TEA) and triphenyl stannyl acetate (TPTA) received from Merck (Germany) Other chemicals are reagents with high purity (98%) using during synthesis and membrane testy process Membrane preparation PA thin film was hand-cast on the PAN substrate through interfacial polymerization PA based TFC membrane was formed by immersing the PAN support membrane in a PIP aqueous solution for Excess PIP solution was removed from the support membrane surface using a tissue The PIP saturated support membrane was then immersed into the TMC-hexane solution for min, which resulted in the formation of an ultra-thin polyamide film over the PSF support The derived membrane was vertically held for before it was immersed in a 200 ppm NaClO for and then dipped in 1,000 ppm Na2S2O5 solution for 30 s The membrane was finally dipped in DI water for Before the obtained membrane can be used for the experiments, it was immersed in a DI water container with the water replaced regularly Membrane characterization Attenuated total reflectance Fourier transform infrared (ATR- FTIR) spectroscopy was employed to analysis the functional groups of the membranes The water contact angle will be used to represent the hydrophilicity of the TFC membrane surface Membrane samples were prepared for scanning electron microscope (SEM) for characterizing the surface morphology and cross section 10 The roughness of the membrane surface will be analysed by atomic force microscopy (AFM) Measurement of the NF separation performance testing The NF membrane was evaluated by filtering a solution at 150 ppb using a cross-flow system Firstly, the NF membrane was used for deionized water in hours at P = 250 psi After the flux of the membrane reaches a stable value, replace deionized water with a solution of 150 ppb As (V) and operate at P = 150 psi After 30 minutes, the water flux is measured and the permeate water flow rate is sampled to be measured by internal concentration polarization (ICP) to determine As concentration in the product flow The measurement result is the result of replicate experiments Water flux J ( L m−2 h−1 ) can be determined from permeate water flow rate as equation (1): J= QP Am ×t (1) Where QP is the permeate water flow rate, Am is the effective membrane area (0.0024 m2) and t is the filtration time The As(V) concentrations in the feed and permeate solutions were used to calculate the observed arsenic rejection Xs (%) as shown in equation (2): ( X s= 1− ) C P , As ×100 % C F , As (2) Where CP,As and CF,As are the arsenic concentration in feed and permeate sides, respectively Research content 5.1 Investigation of the effects of diamine monomers on NF membrane seperation performance Composite membranes were prepared by interfacial polymerization of PIP, MPD and EDA with TMC separately Polyamide composite membranes are formed by immersing for minutes The concentration of each monomer and TMC is fixed at wt.% and 0.15 wt.%, respectively The membrane characterization is described in study at section IV and the separation performance testing is demonstrated in study At section IV 5.2 11 Study on the effects of additives on NF membrane performance The diamine-based NF membrane has the most suitable water flux (J) and arsenic rejection (Xs) that achieved in study 5.1 at section IV will be prepared with varied concentration from 0.02 wt.% To 0.30 wt.% V PLAN This section presents my schedule and qualifications for completing the proposed research This research culminates in a formal report, which will be completed by May 25th, 2020 To reach this goal, I will follow the schedule presented in Table Most of my time will be spent performing the process to find key results, and presenting those results to the thesis report Table Schedule for completion of the research Month (2020) February March April May Week Activities Material preparation Membrane preparation Analyze different type of monomers Performe experiment on impact of additives Analyze membrane morphology 12 10 11 12 13 14 16 17 18 Review Statistical analysis of data Report writing 13 VI STRUCTURE OF THESIS REPORT This section presents my expected structure of my thesis report for obtaining the objectives discussed in the previous section ACKNOWLEDGEMENT TABLE OF CONTENT LIST OF FIGURES LIST OF TABLES ABBREVIATION ABSTRACT Chapter I INTRODUCTION Chapter II OVERVIEW II.1 Arsenic II.2 Arsenic Contamination in Vietnam II.3 Arsenic removal techniques II.3.1 Oxidation Techniques II.3.2 Coagulation – Flocculation II.3.3 Adsorption and Ion Exchange II.3.4 Membrane technology (MF,UF,RO and NF) II.4 NF membrane Chapter III SYNTHETIC LITERATURE REVIEW Chapter IV MATERIAL AND METHODS IV.1 Membrane material IV.2 Membrane preparation IV.3 Monomer and solvent characterization IV.4 Membrane characterization IV.5 Method Chapter V RESULTS VI.1 Properties of membranes formed in different organic solvents VI.2 Properties of membranes formed with additives PIP,MPD and EDA VI.3 Properties and morphology of NF membranes formed at different temperatures Chapter VI DISCUSSTION AND CONCLUSION REFERENCES 14 REFERENCES 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MF MPD MPDA NF PAN PIP PSF RO SEM SPPBES TBP TEA TEM TFC TMC TPP UF 16 World Health Organization Atomic force microscopy Attenuated total reflection - fourier-transform infrared 2,2′,4,4′,6,6′-biphenyl hexaacyl chloride 2,3′,4,5′,6-biphenyl pentaacyl chloride 2,4,4′,6-biphenyl tetraacyl chloride Camphorsulfonic acid N,N’’ – Diaminopiperazine 1,4-Bis(3-aminopropyl)-piperazine Deionized N-(2-Aminoethyl)-piperazine Ethylenediamine Microfiltration m-phenylenediamine m-phenylenediamine Nanofiltration Polyacrylonitrile Piperazine Polysulfone Reverse osmosis Scanning electron microscopy Sulfonated copoly (phthalazinone biphenyl ether sulfone) Tributyl phosphate Triethylamine Transmission electron microscopy Thin-film composite Trimesoylchloride (TMC) Triphenyl phosphate Ultrafiltration 17