Concurrent Removal of Selenium and Arsenic from Water Using

Subscriber access provided by GAZI UNIV

Article

Concurrent removal of selenium and arsenic from water using POSS-polyamide thin-film nanocomposite nanofiltration membranes Yingran He, Yupan Tang, and Tai-Shung Chung Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04272 • Publication Date (Web): 28 Nov 2016 Downloaded from http://pubs.acs.org on December 8, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Concurrent removal of selenium and arsenic from water using POSS-polyamide thinfilm nanocomposite nanofiltration membranes

Yingran Hea, Yupan Tangb, Tai Shung Chungb,*,

a

NUS Graduate School for Integrative Science and Engineering, National University of

Singapore, 28 Medical Drive, Singapore 117456, Singapore b

Department of Chemical and Biomolecular Engineering, National University of Singapore,

4 Engineering Drive 4, Singapore 117585, Singapore

*

Corresponding author

Email: [email protected] Tel : (65)-65166645 Fax: (65)-67797936

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 40

Abstract With stringent regulations of toxic ions selenium and arsenic on wastewater discharge, various industries such as coal mining and power generation are demanding more efficient and effective treatment methods to remove these two ions. Since the performance of commercially available thin film composite nanofiltration (NF) membranes reported so far has a great room for improvement, a thin-film nanocomposite (TFN) NF membrane comprising polyhedral oligomeric silsesquioxane (POSS) with high efficiency was developed for the concurrent removal of selenium and arsenic from aqueous solutions. The resultant NF membrane has a mean effective pore diameter of 0.65 nm, molecular weight cutoff of 302 Da and superior pure water permeability of 5.4 LMH/bar with notably high rejections of SeO32-, SeO42- and HAsO42- towards 93.9, 96.5 and 97.4%, respectively. The TFN membranes also exhibit slightly higher rejection performance when a mixed ion solution separation test was conducted. To our best knowledge, this is the first reported NF membrane comprising POSS in the selective layer for the concurrent removal of selenium and arsenic ions. The promising results achieved in this study provide promising methodology for the development of novel NF membranes to remove other multiple toxic ions from waste streams.

Key words: selenium and arsenic removal, nanofiltration, polyhedral oligomeric silsesquioxane (POSS), thin-film nanocomposite (TFN)


Page 3 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.

Introduction

Many industries such as mining, precious metals and coal fired power plants are heavy users of water in numerous countries, putting them on an equal footing, in terms of water needs, with farm irrigation 1. Most of the water that is utilized during processing is for steam generation and cooling. Contaminants such as selenium (Se) and arsenic (As) may be found in many of these effluents with trace amounts of 50 ppb to 500 ppm which negatively impact their disposal 2. Most of plant discharges require highly efficient treatment techniques, particularly for the removal of Se and As contaminants, but little emphasis has, so far, been placed on such discharges.

Se and As are found in waters in the form of oxyanions. Se mainly exists in the Se (IV) (selenite) and Se (VI) (selenate) oxidation state forms. Se is toxic to humans if taken at higher than 400 mg/day 3, and acute exposure may lead to severe respiratory problems and neurological effects 4. Relatively high concentrations of As have been reported both in power-plant discharges and in freshwater supplies. Majority of arsenic found in water are in oxidized (+V oxidation state) and reduced (+III oxidation state) forms; the As(V) form is less harmful than As(III) 5. Protracted contact with As-containing waters is thought to cause arsenicosis, a form of poisoning for humans 6.

Various technologies to reduce Se and As concentrations in water have been used such as precipitation, ion exchange, solvent extraction, reduction/oxidation and adsorption

7–10

.

Though such purification methods are able to remove the elemental contaminants, they are very expensive, require high usage of reagents and huge waste

11

. Consequently, there is

need to develop cheaper and efficient technology for water purification. One particular treatment method that has shown great promise is nanofiltration (NF). NF is a promising



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 40

technology for molecular separation and purification in water treatment. Various dissolved species can be effectively rejected by NF membranes via the size sieving and the Donnan exclusion (electrostatic repulsion) mechanisms

12–16

. Hence, NF has garnered great interests

for the treatment of selenium and arsenic wastewater.

There have been many studies looking at NF application for Se and As removal. Richards et al. used commercialized NF/RO membranes to investigate suitable conditions for selenium removal with a rejection over 85% 17. Elcik et al. employed F270 and NF90 membranes from Dow Chemicals to remove arsenate and arsenite with rejections of about 90%

18

. Another

approach was using a modified polymer for heavy metal removal with a flux of 2 LMH/bar and a HAsO42- rejection of 99%

19

. However, the membranes to remove both selenium and

arsenic simultaneously with high water fluxes and rejections have not been reported so far. In this study we looked at using polyhedral oligomeric silsesquioxane (POSS) as an NF membrane for the simultaneous removal of selenium and arsenic.

POSS was chosen as the nanoparticle for the following unique characteristics: (1) high flexibility to be functionalized, (2) small size of around 1-3 nm

20

and (3) high degree of

compatibility and dispersibility at the molecular level when embedded in diverse polymer matrices

21–23

. POSS has been studied in membrane research for gas separation

pervaporation

27

24–26

and

. In water treatments, POSS was incorporated by Kim et al. to improve

antifouling properties of the membrane as the crosslinker of polyethylene glycol (PEG)

28

.

Dalwani et al. used a POSS ammonium salt as an aqueous monomer and 1, 3, 5benzenetricarbonyltrichloride (TMC) as an organic monomer to prepare a thin POSS – polyamide membrane with good separation performance 29. Duan et al. worked on four kinds of POSS with various functional groups in the selective layer for seawater desalination 30.


Page 5 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Herein, a series of POSS- polyamide TFN membranes were developed via interfacial polymerization between piperazine (PIP) and TMC. The influences of POSS chemistry, thinfilm polymerization scheme, POSS amount and solution pH on membrane performance were systematically investigated. We aim to develop a better thin-film nanocomposite (TFN) NF membrane comprising POSS for the concurrent removal of selenium and arsenic from aqueous solutions. This study may also give remarkable promise to design better NF membranes for waste mining water recycling and toxic ions removal.

2.

Experimental

2.1. Materials Figure 1 shows the basic chemical structures of POSS, monomers and polymer used in this study

23

. The three POSS particles; namely, Octaammonium POSS (P-8NH3Cl)

POSS Cage Mixture (P-8PEG)

32

, OctaPhenyl POSS (P-8Phenyl)

33

31

, PEG

were purchased from

Hybrid Plastics Inc. (Hattiesburg, MS, USA). The Radel® polyethersulfone polymer (PES) was acquired from Solvay Advanced Polymer (GA, USA) and mixed with N-methyl-2pyrrolidone (NMP, Merck), PEG (Mw= 400 g mol-1, Sigma Aldrich) and deionized (DI) water to prepare casting solutions for the membrane substrate. Piperazine (PIP, SigmaAldrich), 1, 3, 5-benzenetricarbonyltrichloride (TMC, Sigma-Aldrich), and hexane (Fisher Chemicals) were applied to perform interfacial polymerization. Organic solutes, including ethylene glycol (EG), diethylene glycol (DEG), glucose and sucrose from Alfa Aesar, polyethylene glycol and polyethylene oxide at various molecular weights (PEG, Mw= 35,000 and 60,000 g mol-1 and PEO, Mw= 100,000 g mol-1) from Sigma-Aldrich were used to form 200 ppm aqueous solutions for molecular weight cut-off (MWCO) and pore size characterization. The salt transport properties of the membranes were evaluated using NaCl,



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 40

MgCl2, MgSO4 and Na2SO4 while Na2SeO3, Na2SeO4 and Na2HAsO4 were utilized to determine the removal performance of Se and As by the membranes.

2.2. Fabrication of flat sheet substrate The PES polymer was firstly dried in a vacuum oven at 80 oC for 24 hours before use. Then, the dried polymer (20.4 wt%) was dissolved in a mixture, which consists of the pore former PEG 400 (37.7 wt%), solvent NMP (37.7 wt%) and non-solvent DI water (4.2 wt%), at 70 oC under stirring. The resultant solution was degassed overnight before usage. After casting by a knife with a thickness of 150 nm, the whole assembly (i.e., membrane and glass plate) was immediately immersed into a water bath for phase inversion. The resultant membranes were stored in DI water.

2.3. Interfacial polymerization (IP) of thin-film composite (TFC) and TFN membranes The selective layer was prepared by an interfacial polymerization reaction between PIP and TMC. The PES substrate was firstly immersed in a 2 wt% PIP solution for 2 min. Then the membrane was thoroughly dried by the filter paper. A 0.15 wt% TMC/ hexane solution was poured on top of the former support for 1 min. The as-prepared TFC membrane was dried in air for 5 min.

The same procedures were employed to prepare TFN membranes except for the POSS addition. Depending on POSS’s hydrophilicity and hydrophobicity, it was incorporated into the polyamide layer in two ways: (i) adding hydrophobic POSS in the organic phase, and (ii) introducing hydrophilic POSS in the aqueous phase, as illustrated in Figure 2. For method (i), P-8Phenyl was firstly dispersed in the organic solution by ultra-sonication for 15 min at room temperature, followed by the action that the as-mentioned solution was immediately


Page 7 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


deposited onto the membrane surface to react for 1 min. For method (ii), P-8NH3Cl and P8PEG were well dissolved in PIP aqueous solutions respectively.

2.4. Separation performance of membranes Separation performance was achieved by testing the membranes in dead-end cells at room temperature under 10 bar. Pure water permeability (PWP, L m-2 h-1 bar-1, LMH/bar) was measured using DI water while rejection (R, %) was obtained using a series of salt solutions containing either NaCl, MgCl2, MgSO4 or Na2SO4 of 1000 ppm. The membranes were stabilized for 1 h before any measurements were taken. PWP and R are calculated based on the following equations: 𝑃𝑊𝑃 =

𝑅 (%) = 1 −

𝑄 𝐴∆𝑃

(1)

𝐶/ ×100% 𝐶0

(2)

where Q (L/h) is the water flux at the permeate side, ΔP (bars) is the pressure difference between the membrane surface, and A (m2) is the effective filtration area of the membrane. Cp and Cf represent the concentrations of the solute in the permeate and feed. In general, the concentrations for various salts, selenium and arsenic solutions were measured by the conductivity meter (Metrohm AG) and inductively coupled plasma optical emission spectroscopy (ICP-OES) (Optima 7300DV, PerkinElmer), respectively. To ensure reproducibility, five membrane samples were prepared and the average results are reported in this study. The single ion feed concentration is 1000 ppm and the ratio of mixed ions SeO32SeO42- and HAsO42- is 1:1:1.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 40

2.5. Characterizations 2.5.1. Membrane morphology Visualization of the polymeric membranes was done using field emission scanning electron microscopy (FESEM) (JEOL JSM- 6700). The samples were prepared using the similar procedures 34.

2.5.2. Membrane surface charge To measure ζ-potential of the membranes as a function of pH, a SurPASS electrokinetic analyzer (Anton Paar GmbH) was used. During analyses, a 0.01 M NaCl solution was allowed to circulate through the measuring cell with its pH being adjusted via autotitrations with 0.1 M NaOH and 0.1 M HCl 35.

2.5.3. Molecular weight cut off (MWCO) and pore size distribution The pore size distribution of the membranes was characterized using solute transport method described elsewhere

36–39

. Aqueous EG, DEG, glucose, sucrose, PEG and PEO solutions of

200 ppm were used for the measurements. Both residue and filtrate were collected and analyzed using a total organic carbon analyzer (TOC ASI-5000A, Shimazu, Japan). This gave the organic solute concentrations. The MWCO can be determined using the following equation: 𝑑𝑅4 𝑑/ 𝑑 𝑑/

=

1 𝑑/ 2𝜋ln 𝜎/

𝑒𝑥𝑝 −

ln 𝑑/ − ln 𝜇/ 2 ln 𝜎/

>

(3)

>

where mean pore size (𝜇𝑝) was obtained when the solute rejection 𝑅 was 50% and the geometric standard deviation (𝜎𝑝) is calculated as the ratio between 𝑑𝑠 at 𝑅 = 84.13% and 50%. MWCO could be found at 𝑅 = 90%.


Page 9 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.5.4. Membrane micro-structure Positron annihilation spectroscopy (PAS) is one of the most frequently used analytical methods for characterizing the free volume hole-size and multilayer structure of thin films. In order to control the penetration depth of positrons in the membrane, it is necessary to use a variable-energy positron beam 40,41. The S parameter shows microstructural changes along the membrane depth profile. The R parameter indicates the existence of large pores. The mean penetration depth of positrons Z (nm) can be estimated using the following equation: 𝑍 𝐸B =

40 E.G 𝐸B 𝜌

(4)

where ρ (g/cm3) is the density of the polymer, and E+ (keV) is the positron incident energy.

2.5.5. Adsorption of selenium and arsenic Each membrane of about 100 mg was cut into pieces after freeze drying and immersed into 200 ppm Na2SeO3, Na2SeO4 and Na2HAsO4 solutions, respectively. The mixtures were placed on a roller and the solution concentrations were continuously recorded twice a day, with a total duration of around 60 h. The adsorption values q (mg/g) of Se and As were obtained from the equation below 42 𝑞=

(𝑐J − 𝑐KL ) 𝑉 𝑚

(5)

where c0 and ceq are the initial and equilibrium concentrations (ppm), V is the volume of the mixture (L), and m is the weight of original membrane (g).

3.

Results and discussion

3.1. Characterizations of the membranes Table 1 compares the PWP and salt rejection values of as-prepared TFN membranes consisting of 0.5 wt% P-8Phenyl, P-8NH3Cl and P-8PEG individually. The membrane 9 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 40

comprising 0.5 wt% P-8NH3Cl in the aqueous phase has the highest MgCl2 rejection of 91.7 and the second highest water flux compared to those of membranes containing 0.5 wt% P8Phenyl and P-8PEG in the organic and aqueous phase, respectively. Since P-8Phenyl cannot dissolve fully in hexane that might lead to uneven dispersion of POSS particles in the selective layer, while the larger functional groups of P-8PEG may impose steric effects on the reaction between PIP and TMC. Therefore, P-8NH3Cl was chosen for further studies.

The evolution of membrane morphology from the plain PES substrate to thin-film composite membranes consisting of P-8NH3Cl from 0 to 5 wt% was displayed in Figure 3. The PES asymmetric substrate has a thin sponge-like top layer of ~200 nm and a cross section full of large macrovoids. The top surface is relatively smooth with tiny pores of ∼20 nm in diameter. The finger-like cross section together with the surface pore may help to reduce the transport resistance and, thus, to achieve a high water permeation.

As shown in the left of Figure 3, the grainy structure on the PES substrate apparently increases with an increase in POSS loading. This morphology possibly results from the combination of rapid cross-linking reaction between PIP and TMC monomers, POSS particles and drying. In other words, during interfacial polymerization, the amine saturated substrate is in contact with the TMC organic solution. The amine migrates together with POSS nano-particles by diffusion and convection from the aqueous phase to the interface and reacts with TMC in the organic solvent. The migration and reaction with the participation of POSS nano-particles and then drying may form this grainy structure.

Comparing with the pristine TFC membrane, the TFN membranes exhibit more intense grainy and convex structures with rougher surfaces and this may due to the charges of the the


Page 11 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ammonium chloride groups. Previously, TFN membranes prepared with zeolite-43 or silicabased 44 had shown to have a smoother surface. A possible explanation is the smaller size of POSS (1-3 nm) may influence the formation of the selective layer differently than the large sizes of zeolite and silica (~100nm) which was proposed as “template” effect by Lind et al. 45. In contrast, the small POSS nano-particles could be easily covered with the growing polyamide layer, thus leading to a rougher surface.

Figure 4 displays the surface charge properties of the TFC and TFN membranes as a function of pH. All the membranes exhibit negatively charged which is beneficial to the rejection of negative ions based on the Donnan effect. This phenomenon indicates that, after interfacial polymerization, the unreacted amine from PIP and carboxylic acid from the hydrolysis of acyl chloride of TMC would appear on the membrane surface. As a result, the negative charge characteristic arises from (1) the deprotonation of carboxyl groups (-COOH →-COO-) and (2) the larger steric hindrance of PIP molecules on membranes surface that prevents H+ from attacking the -NH- group to form -NH2+-.

3.2. Effects of POSS loading on NF performance The effects of POSS loading on PWP and salt rejections against NaCl, MgCl2, Na2SO4 and MgSO4 are illustrated in Figure 5. Firstly, the PWP value of the formed TFN membranes marginally drops from 5.5 to 5.4 LMH/bar as the loading increases from 0 to 1 wt %. At the same time, all salt rejections increase slightly.

When the POSS concentration further

increases from 1 to 5 wt %, the PWP value dramatically decreases from 5.4 to 2.7 LMH/bar while the salt rejection almost remains the same. The trend of PWP could be explained as the increase in chain rigidity and the decrease in chain spacing because of the incorporation of



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 40

POSS nano-particles. POSS may also increase the mass transport resistance, perturb the dispersion of nanoparticles in the selective layer and reduce the water uptake.

The overall rejection follows the sequence of R (MgSO4) > R (Na2SO4) > R (MgCl2) > R (NaCl). This sequence can be elucidated by the combined actions of both electrostatic repulsion and size sieving mechanism

46

. The presence of -COO- groups in the TFN

membrane creates a highly negative charge environment that repulses the divalent SO42- more than the monovalent Cl-. Moreover, the radius of hydrated SO42- ions (0.379 nm) is larger than that of hydrated Cl- ions (0.332 nm)

47

which results in the former ion to have more

resistance than Cl- ions when permeating through the membrane.

Figure 6 compares the evolution of the probability density function curves of pore sizes among the PES substrate, thin-film interfacial polymerization membrane, and TFN membrane containing 1wt% POSS, while Table 2 summarize their pore properties such as the mean effective pore diameter, geometric standard deviation and MWCO. The effective pore diameter of the TFN membrane declines from 0.94 nm to 0.65 nm after adding 1% POSS into the membrane, indicating that POSS may serve as a nano-filler that partly tightens the pores in the polyamide layer. As seen in the enlarged panel of Figure 6, the peak shifts to the left, indicating POSS can help decrease the surface pores and narrow down the pore size distribution.

To understand the microstructure of the selective layer, S and R parameters shown in Figure 7 were analyzed using PAS. The S parameter profiles are capable of reflecting the free volume differences of the membranes, while the R identifies the size and intensity of large pores.

48

. The TFN membranes show similar depth profiles of the S parameter where all


Page 13 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


curves initially exhibit a sharp increase and then gradually decrease after reaching the peak. In the case of S parameter, an initial increase was observed which may be owing to the back diffusion and scattering of positroniums near the membrane surface

49

. The subsequent

decrease of the peak suggests the transition from the selective layer to the PES support. All R values drop to smaller values from the surface to the dense selective layer and then sharply rise in the support layer. This is because the selective layer has smaller pores or free volume than the substrate. By comparing the maximum S values at the low incident energy region (i.e., in the selective layer region), the height of the maximum S value gradually drops with an increase in POSS loading, indicating the decrease of free volume with the incorporation of POSS. These results are in consistent with the trend of the reduced water flux of TFN membranes, as shown in Figure 5.

3.3. Selenium and arsenic removal The feasibility of using these TFN membranes for Se and As removal was then assessed. Figure 8 summarizes the membrane rejections of various ions separately as a function of POSS loading. The feed were prepared by directly dissolving the salts of 1000 ppm in DI water without further pH adjustment. The 1% TFN membrane has the highest rejections against all the three ions. The high rejections against these anions can be attributed to the small mean effective pore diameter of the membrane (0.65 nm), which is smaller than the hydrated diameters of these anions

50

. At the same time, the membrane is highly negatively

charged in the whole pH range (Figure 4) so that the Donnan exclusion mechanism plays an additional role in the effective rejection. Consequently, with the combination of both Donnan and size exclusion, the membrane is able to successfully reject various anions.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 40

The higher rejection against Se (VI) is expected because this form of Se is present predominantly as the divalent anionic species of SeO42- (pKa2 = 1.9) in the feed solution. In contrast, Se (IV) may form both HSeO3- and SeO3 2- in the feed solution when pH is higher than 7 because the pK values of their acid reactions are 2.6 and 7.3, respectively, with following dissociation reactions 51: 𝐻> 𝑆𝑒𝑂S ⇌ 𝐻𝑆𝑒𝑂SU + 𝐻B 𝐻𝑆𝑒𝑂SU ⇌ 𝑆𝑒𝑂S>U + 𝐻B

Since HSeO3- is a monovalent species, while SeO3 2- is a bivalent one, the TFN membrane would have a lower rejection against the former than the latter because of the Donnan effect. In addition, the concentration of HSeO3- in the feed solution is higher than that of SeO3 2when the pH value is between 7 and 8 as shown in Figure 10; therefore, the TFN membrane has a lower rejection against Se (IV) (i.e., a combination of HSeO3- and SeO3 2-) than Se (VI) (i.e., SeO42-).

The different rejection rates against SeO42- and HAsO42- can be explained as follows. First, HAsO42- is likely to have a larger hydrated diameter than SeO42- 52. Therefore, SeO42- is able to permeate through the membrane more easily. Second, the higher rejection of HAsO42- may also be attributed to its feed pH because pH is essential for determination of the membrane surface charge and charge density. As the feed pH of the HAsO42- solution is around 8.6 and that of SeO42- is about 7.8, the TFN membrane would display a better rejection with enhanced electrostatic repulsion against HAsO42- than SeO42-.

The rejections of the TFN membranes to the mixed SeO32-, SeO42- and HAsO42- ion solution are also tested, as shown in Figure. 9. The 1% TFN membrane still achieves the highest 14 ACS Paragon Plus Environment

Page 15 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


rejections (>96%) against various ions except for SeO32- (94.1%). Compared to Figure 8, the rejections of three ions in mixed ions solution are faintly higher than those of single ion solutions because a much lower concentration was used in the mixed ions solution (each ion is around 330 ppm). Besides, the pH of the mixed solution is about 8.5 which is higher than those of SeO32- (pH around 7.5) and SeO42- (pH around8.0) single ions solutions. A higher pH can lead to a higher rejection rate for Se ions and that is in accordance with the following Figures 10 and 11. While the pH for the HAsO42- solution is around 8.6 which is close to that of the mixed solution, thus the rejection of As ions does not change much in the mixed ions solution.

The effects of feed pH on membrane rejection and speciation of selenite and selenate were further studied. As illustrated in Figure 10, selenous acid (H2SeO3) is the major ion below pH of 2.6. Then the proportion of monovalent HSeO3- gradually increases and becomes the dominant species between pH 4 and 7. At pH around 8.3, the monovalent HSeO3- and divalent SeO32- ions coexist in equal proportions within the solution. When pH is greater than 8.3, the divalent SeO32− becomes the dominant species. Because of the increased pH and electrostatic repulsion between the membrane and selenite ions, the rejection rate is further enhanced.

Similarly, as shown in Figure 11, the monovalent anion of HSeO4- is the predominant species at pH below 2. It is interesting to note that there is almost no rejection at this extremely acid environment because of the significant decrease in surface charge density of the membrane. However, the proportion of monovalent HSeO4- gradually decreases as the pH value increases. When pH is greater than 4.5, the divalent SeO42− becomes the only existent species within the solution. Therefore, the rejection against selenate grows essentially from 47.1 to 87.1% when



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 40

pH changes from 2.9 to 6.4. As pH further increases from 6.4 to 11.4, the rejection also rises gradually from 87.1 to 97.4% because the TFN membrane becomes more negatively charged. Thus, we can conclude that the feed pH has a substantial effect on selenate and selenite rejections since feed pH influences the surface charge characteristics of the TFN membrane.

Table 3 summarized the separation performance of different commercial and various lab-mad NF membranes reported in recent years. The commercially available membranes have a comparable PWP but lower rejections of the various heavy metals

53

. In contrast, the

previously lab-made membranes generally possess higher heavy metal rejections by maintaining the PWP. Comparing with the previously commercial and lab-made membranes, the newly developed TFN NF membrane shows promising performance.

3.4. Selenium and arsenic adsorption The static adsorption of selenium and arsenic ions on both pristine TFC and 1% TFN membranes was investigated with the data shown in Figure. 12. For the pristine TMC membrane, the adsorption of SeO32- and SeO42- ions are below 3 mg/g and that of HAsO42- is below 1.5 mg/g. The optimal pH for absorption is around 2-4 54. When selenium and arsenic salts dissolve in water, the pH values of their solutions are around 9.0 and 8.6, respectively. In the alkaline solution, electrostatic interactions become enhanced and the SeO32-, SeO42and HAsO42- were repelled by the negative charged membrane

55

. When 1% POSS was

blended into the membrane, the adsorption amounts of two selenium ions drop dramatically to less than 0.6 mg/g and that of arsenic ions reduces to 0.25 mg/g. The decreases in adsorption are possibly credited to larger POSS molecules on the membrane surface that deter the interaction between ions and membranes, leading to less ions adsorbed

56

. These


Page 17 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


results confirm that the high rejections against Se and As ions are mainly due to the separation instead of adsorption.

4.

Conclusions

By incorporating 1 wt% P-8NH3Cl during the film polymerization of PIP and TMC, we have developed a TFN NF membrane with a remarkable water permeability of 5.4 LMH/bar and impressive rejections of 93.9%, 96.5% and 97.4% against SeO32-, SeO42- and 97.4% and HAsO42- ions, respectively. The TFN membranes also exhibit slightly higher rejection performance when a mixed ion solution is used as the feed. Experimental results suggest that both POSS loading and feed pH play important roles on selenium and arsenic removal. The newly developed P-8NH3Cl TFN membrane may show promising potential to fabricate next generation NF membranes for toxic ion removal applications.

AUTHOR INFORMATION Corresponding Author *Telephone: +65-6166645. Fax: +65-67791936. E-mail [email protected] Notes The authors declare no completing financial interest.

ACKNOWLEDGEMENTS The authors would like to thank Ms. J. Gao, Ms. Y. Zhang, Ms. Y Cui, Dr. G Han and Mr. Z.W. Thong for their kind help and suggestions.

References (1)

Yang, L.; Shahrivari, Z.; Liu, P. K. T.; Sahimi, M.; Tsotsis, T. T. Removal of Trace 17 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 40

Levels of Arsenic and Selenium from Aqueous Solutions by Calcined and Uncalcined Layered Double Hydroxides (LDH). Ind. Eng. Chem. Res. 2005, 44 (17), 6804. (2)

Moore, L.; Mahmoudkhani, A. Methods for Removing Arsenic From Aqueous Systems. Proc. Tailingd Mine Waste 2011, 1.

(3)

Gorchev, H. G.; Ozolins, G. WHO Guidelines for Drinking-Water Quality. WHO Chron. 2011, 38 (3), 104.

(4)

Howarth, A. J.; Katz, M. J.; Wang, T. C.; Platero-Prats, A. E.; Chapman, K. W.; Hupp, J. T.; Farha, O. K. High Efficiency Adsorption and Removal of Selenate and Selenite from Water Using Metal-Organic Frameworks. J. Am. Chem. Soc. 2015, 137 (23), 7488.

(5)

Padungthon, S.; German, M.; Wiriyathamcharoen, S.; SenGupta, A. K. Polymeric Anion Exchanger Supported Hydrated Zr(IV) Oxide Nanoparticles: A Reusable Hybrid Sorbent for Selective Trace Arsenic Removal. React. Funct. Polym. 2015, 93, 84.

(6)

Hokkanen, S.; Repo, E.; Lou, S.; Sillanpaa, M. Removal of arsenic(V) by Magnetic Nanoparticle Activated Microfibrillated Cellulose. Chem. Eng. J. 2015, 260 (January 2015), 886.

(7)

Chen, S.; Zhu, S.; Lu, D. Solidified Floating Organic Drop Microextraction for Speciation of Selenium and Its Distribution in Selenium-Rich Tea Leaves and Tea Infusion by Electrothermal Vapourisation Inductively Coupled Plasma Mass Spectrometry. Food Chem. 2015, 169, 156.

(8)

Chandra, V.; Park, J.; Chun, Y.; Lee, J. W.; Hwang, I. C.; Kim, K. S. WaterDispersible Magnetite-Reduced Graphene Oxide Composites for Arsenic Removal. ACS Nano 2010, 4 (7), 3979.

(9)

Awual, M. R.; Yaita, T.; Suzuki, S.; Shiwaku, H. Ultimate Selenium (IV) Monitoring


Page 19 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and Removal from Water Using a New Class of Organic Ligand Based Composite Adsorbent. J. Hazard. Mater. 2015, 291, 111. (10)

Ahoranta, S. H.; Kokko, M. E.; Papirio, S.; Özkaya, B.; Puhakka, J. A. Arsenic Removal from Acidic Solutions with Biogenic Ferric Precipitates. J. Hazard. Mater. 2016, 306, 124.

(11)

Kim, J.; Benjamin, M. M. Modeling a Novel Ion Exchange Process for Arsenic and Nitrate Removal. Water Res. 2004, 38 (8), 2053.

(12)

Shao, L.; Cheng, X. Q.; Liu, Y.; Quan, S.; Ma, J.; Zhao, S. Z.; Wang, K. Y. Newly Developed Nanofiltration (NF) Composite Membranes by Interfacial Polymerization for Safranin O and Aniline Blue Removal. J. Memb. Sci. 2013, 430, 96.

(13)

Gu, H.; Huang, Y.; Zhang, X.; Wang, Q.; Zhu, J.; Shao, L.; Haldolaarachchige, N.; Young,

D.

P.;

Wei,

S.;

Guo,

Z.

Magnetoresistive

Polyaniline-Magnetite

Nanocomposites with Negative Dielectrical Properties. Polymer (Guildf). 2012, 53 (3), 801. (14)

Zhu, W. P.; Gao, J.; Sun, S. P.; Zhang, S.; Chung, T. S. Poly(amidoamine) Dendrimer (PAMAM) Grafted on Thin Film Composite (TFC) Nanofiltration (NF) Hollow Fiber Membranes for Heavy Metal Removal. J. Memb. Sci. 2015, 487, 117.

(15)

Chang, Y.; Liao, S. C.; Higuchi, A.; Ruaan, R. C.; Chu, C. W.; Chen, W. Y. A Highly Stable Nonbiofouling Surface with Well-Packed Grafted Zwitterionic Polysulfobetaine for Plasma Protein Repulsion. Langmuir 2008, 24 (10), 5453.

(16)

Sin, M.-C.; Chen, S.-H.; Chang, Y. Hemocompatibility of Zwitterionic Interfaces and Membranes. Polym. J. 2014, 46 (8), 436.

(17)

Richards, L. A.; Richards, B. S.; Schafer, A. I. Renewable Energy Powered Membrane Technology: Salt and Inorganic Contaminant Removal by Nanofiltration/reverse Osmosis. J. Memb. Sci. 2011, 369 (1–2), 188.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(18)

Page 20 of 40

Elcik, H.; Celik, S. O.; Cakmakci, M.; Özkaya, B. Performance of Nanofiltration and Reverse Osmosis Membranes for Arsenic Removal from Drinking Water. Desalin. Water Treat. 2015, 1.

(19)

Gao, J.; Sun, S. P.; Zhu, W. P.; Chung, T. S. Chelating Polymer Modified P84 Nanofiltration (NF) Hollow Fiber Membranes for High Efficient Heavy Metal Removal. Water Res. 2014, 63, 252.

(20)

Freger, V. Nanoscale Heterogeneity of Polyamide Membranes Formed by Interfacial Polymerization. Langmuir 2003, 19 (11), 4791.

(21)

Paul, D. R.; Robeson, L. M. Polymer Nanotechnology: Nanocomposites. Polymer (Guildf). 2008, 49 (15), 3187.

(22)

Huang, J. chao; He, C. bin; Xiao, Y.; Mya, K. Y.; Dai, J.; Siow, Y. P. Polyimide/POSS Nanocomposites: Interfacial Interaction, Thermal Properties and Mechanical Properties. Polymer (Guildf). 2003, 44 (16), 4491.

(23)

Ayandele, E.; Sarkar, B.; Alexandridis, P. Polyhedral Oligomeric Silsesquioxane (POSS)-Containing Polymer Nanocomposites. Nanomaterials 2012, 2 (4), 445.

(24)

Iyer, P.; Iyer, G.; Coleman, M. Gas Transport Properties of Polyimide-POSS Nanocomposites. J. Memb. Sci. 2010, 358 (1–2), 26.

(25)

Li, Y.; Chung, T. S. Molecular-Level Mixed Matrix Membranes Comprising Pebax® and POSS for Hydrogen Purification via Preferential CO2 Removal. Int. J. Hydrogen Energy 2010, 35 (19), 10560.

(26)

Chua, M. L.; Shao, L.; Low, B. T.; Xiao, Y.; Chung, T. S. Polyetheramine-Polyhedral Oligomeric Silsesquioxane Organic-Inorganic Hybrid Membranes for CO2/H2 and CO2/N2 Separation. J. Memb. Sci. 2011, 385–386 (1), 40.

(27)

Le, N. L.; Wang, Y.; Chung, T. S. Pebax/POSS Mixed Matrix Membranes for Ethanol Recovery from Aqueous Solutions via Pervaporation. J. Memb. Sci. 2011, 379 (1–2),


Page 21 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


174. (28)

Kim, D. G.; Kang, H.; Han, S.; Lee, J.-C. The Increase of Antifouling Properties of Ultrafiltration Membrane Coated by Star-Shaped Polymers. J. Mater. Chem. 2012, 22 (17), 8654.

(29)

Dalwani, M.; Zheng, J.; Hempenius, M.; Hill, A.; Wessling, M.; Benes, N. E. UltraThin Hybrid Polyhedral Silsesquioxane-Polyamide Films with Potentially Unlimited 2D Dimensions. J. Mater. Chem. 2012, 22, 14835.

(30)

Duan, J.; Litwiller, E.; Pinnau, I. Preparation and Water Desalination Properties of POSS-Polyamide Nanocomposite Reverse Osmosis Membranes. J. Memb. Sci. 2015, 473, 157.

(31)

Carroll, J. B.; Frankamp, B. L.; Srivastava, S.; Rotello, V. M. Electrostatic SelfAssembly of Structured Gold Nanoparticle/polyhedral Oligomeric Silsesquioxane (POSS) Nanocomposites. J. Mater. Chem. 2004, 14 (4), 690.

(32)

PEG POSS, http://hybridplastics.com/product/pg1190-Peg-Poss-Cage-Mixture/.

(33)

P-8Pheynl, http://hybridplastics.com/product/ms0840-Octaphenyl-Poss/.

(34)

Zhang, D. Y.; Liu, J.; Shi, Y. S.; Wang, Y.; Liu, H. F.; Hu, Q. L.; Su, L.; Zhu, J. Antifouling Polyimide Membrane with Surface-Bound Silver Particles. J. Memb. Sci. 2016, 516, 83.

(35)

Tang, Y. P.; Yuwen, S.; Chung, T. S.; Weber, M.; Staudt, C.; Maletzko, C. Synthesis of Hyperbranched Polymers towards Efficient Boron Reclamation via a Hybrid Ultrafiltration Process. J. Memb. Sci. 2016, 510, 112.

(36)

Wang, K. Y.; Chung, T. S. The Characterization of Flat Composite Nanofiltration Membranes and Their Applications in the Separation of Cephalexin. J. Memb. Sci. 2005, 247 (1–2), 37.

(37)

Van Der Bruggen, B.; Vandecasteele, C. Modelling of the Retention of Uncharged



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 40

Molecules with Nanofiltration. Water Res. 2002, 36 (5), 1360. (38)

Aimar, P.; Meireles, M.; Sanchez, V. A Contribution to the Translation of Retention Curves into Pore Size Distributions for Sieving Membranes. J. Memb. Sci. 1990, 54 (3), 321.

(39)

Singh, S.; Khulbe, K. C.; Matsuura, T.; Ramamurthy, P. Membrane Characterization by Solute Transport and Atomic Force Microscopy. J. Memb. Sci. 1998, 142 (1), 111.

(40)

Zhang, S.; Wang, K. Y.; Chung, T. S.; Chen, H.; Jean, Y. C.; Amy, G. WellConstructed Cellulose Acetate Membranes for Forward Osmosis: Minimized Internal Concentration Polarization with an Ultra-Thin Selective Layer. J. Memb. Sci. 2010, 360 (1–2), 522.

(41)

Y. P. Tang, N. Widjojo, T.S. Chung, M. Weber, C. M. Nanometric Thin Skinned DualLayer Hollow Fiber Membranes for Dehydration of Isopropanol. IFAC Proc. Vol. 2013, 59 (8), 2943.

(42)

Montazer-Rahmati, M. M.; Rabbani, P.; Abdolali, A.; Keshtkar, A. R. Kinetics and Equilibrium Studies on Biosorption of Cadmium, Lead, and Nickel Ions from Aqueous Solutions by Intact and Chemically Modified Brown Algae. J. Hazard. Mater. 2011, 185 (1), 401.

(43)

Jeong, B.; Hoek, E. M. V; Yan, Y.; Subramani, A.; Huang, X.; Hurwitz, G.; Ghosh, A. K.; Jawor, A. Interfacial Polymerization of Thin Film Nanocomposites : A New Concept for Reverse Osmosis Membranes. J. Memb. Sci. 2007, 294, 1.

(44)

Jadav, G. L.; Singh, P. S. Synthesis of Novel Silica-Polyamide Nanocomposite Membrane with Enhanced Properties. J. Memb. Sci. 2009, 328 (1–2), 257.

(45)

Lind, M. L.; Ghosh, A. K.; Jawor, A.; Huang, X.; Hou, W.; Yang, Y.; Hoek, E. M. V. Influence of Zeolite Crystal Size on Zeolite-Polyamide Thin Film Nanocomposite Membranes. Langmuir 2009, 25 (17), 10139.


Page 23 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(46)

Zhang, Y.; Zhang, S.; Chung, T. S. Nanometric Graphene Oxide Framework Membranes with Enhanced Heavy Metal Removal via Nanofiltration. Environ. Sci. Technol. 2015, 49 (16), 10235.

(47)

Nightingale, R. Phenomenological Theory of Ion Solvation . Effective Radii of Hydrated Ions. J. Phys. Chem. 1959, 63, 1381.

(48)

Tang, Y. P.; Paul, D. R.; Chung, T. S. Free-Standing Graphene Oxide Thin Films Assembled by a Pressurized Ultrafiltration Method for Dehydration of Ethanol. J. Memb. Sci. 2014, 458, 199.

(49)

Chen, H.; Hung, W.-S.; Lo, C.-H.; Huang, S.-H.; Cheng, M.-L.; Liu, G.; Lee, K.-R.; Lai, J.-Y.; Sun, Y.-M.; Hu, C.-C.; et al. Free-Volume Depth Profile of Polymeric Membranes Studied by Positron Annihilation Spectroscopy: Layer Structure from Interfacial Polymerization. Macromolecules 2007, 40 (21), 7542.

(50)

Zhu, W. P.; Sun, S. P.; Gao, J.; Fu, F. J.; Chung, T. S. Dual-Layer Polybenzimidazole/polyethersulfone (PBI/PES) Nanofiltration (NF) Hollow Fiber Membranes for Heavy Metals Removal from Wastewater. J. Memb. Sci. 2014, 456, 117.

(51)

Elrashidi, M. A.; Adriano, D. C.; Workman, S. M.; Lindsay, W. L. Chemical Equilibria of Selenium in Soils: A Theoretical development1. Soil Science. 1987, pp 141–152.

(52)

Thong, Z.; Han, G.; Cui, Y.; Gao, J.; Chung, T. S.; Chan, S. Y.; Wei, S. Novel Nanofiltration Membranes Consisting of a Sulfonated Pentablock Copolymer Rejection Layer for Heavy Metal Removal. Environ. Sci. Technol. 2014, 48 (23), 13880.

(53)

Al-Rashdi, B. A. M.; Johnson, D. J.; Hilal, N. Removal of Heavy Metal Ions by Nanofiltration. Desalination 2013, 315 (November 2016), 2.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 40

(54) Lounsbury, A. W.; Yamani, J. S.; Johnston, C. P.; Larese-Casanova, P.; Zimmerman, J. B. The Role of Counter Ions in Nano-Hematite Synthesis: Implications for Surface Area and Selenium Adsorption Capacity. J. Hazard. Mater. 2016, 310, 117. (55)

Bao, Y.; Yan, X.; Du, W.; Xie, X.; Pan, Z.; Zhou, J.; Li, L. Application of AmineFunctionalized MCM-41 Modified Ultrafiltration Membrane to Remove Chromium (VI) and Copper (II). Chem. Eng. J. 2015, 281, 460.

(56)

Xiao, W.; Yan, B.; Zeng, H.; Liu, Q. Dendrimer Functionalized Graphene Oxide for Selenium Removal. Carbon N. Y. 2016, 105, 655.


Page 25 of 40


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Concurrent removal of selenium and arsenic from water using POSS-polyamide thin-film nanocomposite nanofiltration membranes

Yingran He, Yupan Tang, Tai Shung Chung

ACS Paragon Plus Environment

Page 26 of 40

Page 27 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


Polyethersulfone (PES)

Piperazine (PIP) P‐8Phenyl: R=

P‐8NH3Cl: R=

NH3Cl

P‐8PEG: R= ‐ CH2CH2 (OCH2CH2)m OCH3, m= ~13.3

1, 3, 5‐Benzenetricarbonyl chloride (TMC)

Figure 1: Chemical structures of POSS, monomers and polymer used in this study [25].



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

PES substrate

Page 28 of 40

P‐8Phenyl TMC in the organic phase

Interfacial polymerization: adding POSS in different phases

PIP in the aqueous phase

TFN membrane

P‐8NH3Cl

P‐8PEG

Figure 2. Two routes to add POSS particles during the interfacial polymerization [33-35]. ACS Paragon Plus Environment

Page 29 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


Surface Surface

Cross ‐ section

500 nm

50 µm

PES substrate 500 nm

Pristine TFC 500 nm

50 µm

500 nm

500 nm

50 µm

500 nm

0.5% TFN

Figure 3. Surface and crosssection morphology of TFC and P-8NH3Cl TFN membranes.



TFC 0.5% TFN 1% TFN 3% TFN 5% TFN

0

-40

-potential (mV)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 30 of 40

-80

-120

-160

-200 2

4

6

8

10

12

pH

Figure 4. ζ-potential as a function of pH of TFC membranes.


Page 31 of 40

100

8

7

6

80 MgCl2

PWP

NaCl MgSO4

5

60

Na2SO4 40

Rejection (%)

PWP (LMH bar -1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


4 20

3

0

2 0

1

2

3

4

5

POSS concentration (w/v %)

Figure 5. Effects of P-8NH3Cl loading on PWP and salt rejection of the TFN membranes.



3.0

Probability density function (nm-1)

3.0

Probability density function (nm-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 32 of 40

2.5

2.0

1.5

1.0

PES substrate TFC 1% TFN

2.5

2.0

1.5

1.0

0.5

0.0 0

1

2

3

0.5

0.0 0

5

10

15

20

25

Pore Diameter, dp (nm)

Figure 6 . Probability density function curves of the PES substrate, TFC and 1% TFN membranes. ACS Paragon Plus Environment

Page 33 of 40

0.475

0.54

Selective dense layer

Pristine TFC 0.5% TFN 1% TFN 3% TFN 5% TFN

0.52

0.470 0.50

R

0.465

S

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


0.48

Pristine TFC 0.5% TFN 1% TFN 3% TFN 5% TFN

0.460

0.455

0.46

0.44

0.42

0

5

10

15

20

25

30

0

Positron Incident Energy (keV)

5

10

15

20

Positron Incident Energy (keV)

Figure 7. S and R parameters vs. positron incident energy (or depth) for the TFN membranes with different P-8NH3Cl loadings.


25

30


100

SeO32SeO42HAsO42-

95

Rejection (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 34 of 40

90

85

80

75 0

1

2

3

4

5

Loading of POSS (w/v%)

Figure 8. Effect of P-8NH3Cl loading on selenium and arsenic removal by the TFN membranes. (All salt concentrations were 1000 ppm, the feed solutions were prepared by directly dissolving the salts in deionized water without pH adjustment).


Page 35 of 40

SeO32- and SeO42-

100

HAsO4298

Rejection (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


96

94

92

90

88 0

1

2

3

4

5

Loading of POSS (w/v%)

Figure 9. Effect of P-8NH3Cl loading on the removal of mixed selenium and arsenic ions by the TFN membranes. (The mixed ions ratio in the solution is 1:1:1. The feed solutions were prepared by directly dissolving the salts in deionized water without the pH adjustment). ACS Paragon Plus Environment


HSeO-3

100

80

80

SeO23 H2SeO3

60

60

40

40

20

20

0 0

2

4

6

8

10

12

new-calculation

100

% Se

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 36 of 40

0 14

pH

Figure 10. Speciation of selenite ions and rejection by the TFN membrane as a function of feed pH. (The TFN membrane contains 1 wt% P-8NH3Cl. The feed concentration was 1000 ppm).


SeO24

HSeO-4

100

% Se

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


100

80

80

60

60

40

40

20

20

Rejection (%)

Page 37 of 40

H2SeO4 0 0

2

4

6

8

10

12

0 14

pH

Figure 11. Speciation of selenate ions and rejection by the TFN membrane as a function of feed pH. (The TFN membrane contains 1 wt% P-8NH3Cl. The feed concentration was 1000 ppm)



SeO32SeO42HAsO42-

3.0

2.5

Adsorption (mg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 38 of 40

2.0

1.5

1.0

0.5

0.0

Pristine TFC

1% TFN

Membrane types

Figure 12. Adsorption of selenium and arsenic on pristine TFC and 1% TFN membranes.


Page 39 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


Table 1. Membrane performance of three kinds of TFN membranes with different POSS structures at the loading of 0.5 wt%.

POSS type

PWP (LMH/bar)

R (MgCl2) (%)

R (NaCl) (%)

P‐8Phenyl

6.1±0.4

84.5±1.2

23.7±1.5

P‐8NH3Cl

5.5±0.2

91.7±0.8

29.8±1.1

P‐8PEG

5.1±0.1

88.9±0.7

31.2±1.4

Table 2. Mean effective pore diameter (µp), geometric standard deviation (σp) and molecular weight cut-off (MWCO) of the membranes. Spinning parameter

µp (nm)

σp

MWCO(Da)

Substrate

13.64

1.17

67300

Pristine TFC

0.94

1.29

652

1% TFN

0.65

1.51

302



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 40 of 40

Table 3. Benchmarking of NF membranes for selenium and arsenic removal Membrane

PWP (LMH/bar)

Ion

Testing condition Rejection(%)

SeO42NF

90 a

4

20 ppm, 10 bar As (V)

BW

1.35

As (V) SeO42-

20 ppm, 10 bar

20 ppm, 10 bar

Chelating polymer-modified P84

2

HAsO42-

1000 ppm, 10 bar

PAMAM grafted hollow fibre

3.6

HAsO42-

NF 270 a

5.1

As (III)

As (V)

17

>99

19

1000 ppm, 10 bar

>99

14

1000 ppm, 4 bar

90±2.1

53

93.9±0.6 1000 ppm, 10 bar

HAsO42a

90.0±3.8 64.2±4.7

SeO32SeO42-

17 78.9±5.1

2.43

5.4±0.3

18

29.8±1.1

TFC-S a

Lab-made membrane

89.5±1.9 94.1±1.9

SeO4230 a

Reference

The commercial membranes


96.5±1.1 97.4±1.9

This work

Concurrent Removal of Selenium and Arsenic from Water Using

Recommend Documents