Modified forward osmosis membranes by two amino-functionalized ZnO nanoparticles: A comparative study

https://doi.org/10.1016/j.cherd.2019.02.019Get rights and content

Highlights

  • ZnO nanoparticles by different amino functionalities are utilized for FOP membranes.

  • The effect of M.ZnO and T.ZnO nanoparticles on FOP performance were investigated.

  • The effect of two nanoparticles on the transport attributes were compared.

  • TFN-T.ZnO membrane demonstrated high water flux due to the amine pendant group.

  • TFN-P.ZnO membrane showed low water flux due to the phenyl groups in MPD monomer.

Abstract

In the current research, the self-synthesized amino functionalized nanoparticles (Zinc oxide nanoparticles modified by1,3-phenylendiamine (M.ZnO) and Triethylenetetramine (T.ZnO)) were synthesized as a new modifier to create thin film nanocomposite membranes for forward osmosis processes (FOP). Prior to efficiency evaluation, the pristine and amino functionalized membranes were characterized utilizing FTIR, FESEM, AFM and contact angle. The FTIR outcomes demonstrated that amine compounds has been successfully attached on the ZnO NPs surface. Comparing to the pristine TFC membrane, the TFN-M.ZnO0.3 membrane (TFC membrane incorporated with 0.3%w M.ZnO) exhibited insignificant increment in water flux and also insignificant decrement in rejection while the TFN-T.ZnO0.3 membrane (TFC membrane incorporated with 0.3%w T.ZnO) exhibited remarkable increment in water flux and insignificant decrement in rejection. Also for Caspian seawater desalination, TFN-M.ZnO0.3 and TFN-T.ZnO0.3 demonstrated water flux of 12.99, and 19.87 L/m2 h respectively. The insignificant increment in flux of TFN-M.ZnO0.3 membrane is associated to the rigid and compact structure of this membrane because of present of MPD monomer in M-ZnO NPs and the remarkably increment in flux of TFN-T.ZnO membrane is associated to the pendant group of TETA that create large free volume in TFN-T.ZnO0.3 membrane. The excellent separation efficiency of the TFN-T.ZnO0.3 membrane in FOP is closely related to the its higher pore sizes, hydrophilicity and porosity as well as low S parameter in comparison to TFN-M.ZnO and bare membranes. Our research provides worth guidelines for producing of amino functionalized TFN membranes for FOP.

Introduction

With the increase of the world’s people, pure water demand for the industrial and domestic needs increase continuously. A viable choice to provide the extra pure water supplies is seawater desalination. In the past two decades, forward osmosis technology (FOT) is under notable scientific interest because it exhibits a promising solution for seawater desalination, environmental challenge and energy storage (Ye et al., 2010; Wang et al., 2012). Despite great potential in generating electric power and fresh water, FOP have not been exerted on a commercialized large-scale due to the limitation of draw solutions (DS) and membrane types (Ray et al., 2016). Particularly, how to create an ideal FOP membrane is a main obstacle. Membranes with two different structures are used for FO process: (i) dense skin asymmetric membranes containing integrated skin-layer on top of a porous sublayer. (ii) Thin film composite (TFC) membranes, consisting at least two layers of ultra-thin active layer and a porous support layer (Mansouri et al., 2018; Zirehpour et al., 2015). A typical TFC FOP membrane contains a top layer (∼100–400 nm thick, frequently made from polyamides layer (PA)) on the surface of a substrate (support layer, sublayer) (Zhou et al., 2014; Peyravi et al., 2014). The sublayer usually consists of polyethersulfone (PES) or polysulfone (PS) cast over a polyester, using a phase inversion processes (PIP). In recent years, TFC membrane have become popular for FOP application due to the their high pure water permeability (PWP) and salt rejection (Mansouri et al., 2018; Zirehpour et al., 2017). The composite and nanocomposite structure of the typical TFC and TFN membranes enable good flexibility in their experimental and commercialized design, as both the PA layer and the bottom sublayer can be tailored singly to optimize the definitive performance (Khajouei et al., 2017a; Esfandian et al., 2017; Khajouei et al., 2017b). PA-TFC FOP membrane which demonstrates a high rejection to salt and good chemical stability has been widely deployed for FOP osmotic power generation and water treatment. However, difficulties, such as membrane fouling insistence and low PWP, are widely exhibit with the existing PA-TFC FOP membranes due to membrane fouling and intensive internal concentration polarization (ICP). To eliminate these matters, PA-TFC FOP membranes are generally undergone chemical modifications on FOP membrane surfaces to increment surface hydrophilicity and therefore membrane antifouling ability (Xu et al., 2017; Xu and Ge, 2018).

In comparison to the composite membranes utilized for NFP and ROP, the attributes of the sublayer are more significant in FO application. During FOP, both top layer and sublayer of TFC FOP membranes are simultaneously contacted with feed solution (FS) and DS. In this case, sublayer is as significant as the top layer (Sirinupong et al., 2018). The dense and thick sublayer provides a large insistence against the diffusion of the DS to the back side of the PA layer which contributed to the ICP, thereby adversely affecting the PWP of the TFC membranes (Xu and Ge, 2018). Unlike external concentration polarization (ECP) phenomenon, ICP phenomenon cannot be limited by changing turbulence or cross-flow rate (Roy et al., 2016). Membrane structure parameter is generally taken as a straight sign of the degree of ICP phenomenon, which is determined by the sublayer tortuosity, porosity and thickness. Thus the sublayer should be very porous and thin with low tortuosity to enhance mass transfer, and yet has sufficient chemical, thermal and mechanical stability to withstand industrial operations (Akther et al., 2015; Tian et al., 2017). Hydrophilic modification of the support layer has been considered the main procedure of ICP phenomenon mitigation. It is known that a hydrophilic support layer not only enhances the transportation of solute and water molecules, but also improves the support layer wettability. Enhanced overall porosity as well as reduced tortuosity can be provided by decreasing air entrapment in the sublayer pores; and a smaller S value results. The faster transport of solute and water molecules together with the smaller S contributes to a lower ICP phenomenon and higher pure water permeability (PWP). In terms of engineering aspect, the use of a technique that no needs to add some modification steps in the membrane production line is very important. Adding modifying agent into the dope solution of support membrane is one of the practical way for the membrane manufacturer suppliers. However, it requires more research and survey in view of trade and industry to be feasible in the membrane companies. The hydrophilization of FOP membrane sublayer is an important research area in the membrane science (Morales-Torres et al., 2016; Darabi et al., 2017). One approach to increase the hydrophilicity of PES membranes is by blending a filler or surface modifier of hydrophilic nature (Darabi et al., 2017), such as halloysite nanotube (HNTs) (Ghanbari et al., 2016), silica (SiO2) (Tian et al., 2017), multi-walled carbon nanotubes (Morales-Torres et al., 2016), titanium dioxide (TiO2) (Emadzadeh et al., 2014), and graphene oxide (GO) (Mansouri et al., 2018). Incorporating oxygen-containing surface groups in polymeric membranes increases their surface hydrophilicity and, as result, increases their dispersion in specific polymers and solvents, which may affect the FOP membrane properties (Morales-Torres et al., 2016). Sirinupong et al. (2018) used (TiO2)/(GO) in PS substrate. The nanocomposite sublayer exhibited an increment in porosity and a decline in the S value. Also for the FO test the TFN membrane demonstrated greater PWF with a little increment in reverse salt flux (RSF). In a subsequent study (Tian et al., 2017), Tian et al incorporated SiO2 nanoparticles (NPs) in polyetherimide nanofibrous support layer for TFN membranes fabrication. Results illustrated that the TFN membrane with the 1.6% SiO2 loading had the maximum support layer porosity, the smallest structural value, and the highest PWF.

Developing support layer of TFC FOP membranes encouraged us to produce self-synthesized NPs into sublayer matrix in lieu of using commercially NPs for FOP membrane fabrication. In the present work, we try to attain new modifier agent (through surface modification of ZnO NPs by two different aliphatic and aromatic amines) to use by this technique. It is related that the Zinc oxide (ZnO) NPs are a promising nanofiller due to their environmentally friendly mechanical and chemical stability, non-toxic nature and low cost (Feng et al., 2014). The attendance of multiple hydroxyl groups at the ZnO NPs surface has made ZnO NPs superhydrophilic and also easily reacted with silane compounds (3-Glycidyloxypropyl) trimethoxysilane (GTMS)). GTMS-ZnO NPs were exposed to reaction of ring-opening epoxy groups by amine functional groups. These amino-functionalized ZnO NPs not only modify the reaction speed between amine and organic monomers but also might affect the morphology of PA layers, and eventually the separation efficiency of the TFC membrane (Emadzadeh et al., 2015; Shen et al., 2017). Since the actual membrane efficiency for seawater desalination is significant for industrial applications. So, in this article we describe a novel FOP membranes for seawater desalination. Furthermore for the first time, we recommend two new types of ZnO NPs modified by 1,3-phenylendiamine (MPD) and Triethylenetetramine (TETA) amino-functionalized groups (encoded to M.ZnO and T.ZnO) as a potential nanofiller into PES polymer matrix for developing FOP sublayers. The purposes of the current work are to (i) investigate the effect of amine in the ZnO NPs on the transport attributes and morphology of the sublayers; (ii) investigate the effect of M.ZnO and T.ZnO NPs content in membrane sublayers on FOP performance; (iii) Compare the effect of M.ZnO and T.ZnO NPs on the transport attributes and FOP membranes performance; and (iv) fabrication of TFN FOP membrane with low S parameter and high PWF. This paper may open up novel insights to design advanced FOP membranes for seawater desalination and water reuse.

Section snippets

M.ZnO and T.ZnO NPs synthesis

For synthesizing the ZnO NPs, solution (1) and (2) were prepared according to the following procedure: solution (1) 29.75 g Zn (NO3)2·6H2O (Merck) dissolved in 1 L deionized water (DI water), and solution (2) 12.72 g Na2CO3 (Merck) dissolved in 1 L DI water. After that 200 mL of solution (1) and 200 mL of solution (2) were mixed together under stirring. The solution was centrifuged and then rinsed with DI water. The producing powders were rinsed with acetone (Merck, ≥99.5%) and dried at 373 K

ZnO.T and ZnO.M NPs

During the synthesizing of ZnO NPs through precipitation procedure, using Zn(NO3)2·6H2O as a main method causes to create OH group upon the ZnO NPs for the next modification step. The ZnO NPs were grafted with GTMS silane compounds by reaction between OH groups of ZnO NPs and methoxy groups of GTMS. This leads to graft GTMS with free head of epoxide group on the ZnO NPs. Ring-opening reaction of the epoxy group was accomplished by a reaction between the grafted ZnO NPs with amine groups of MPD

Conclusion

In current research, new TFN membranes synthesized by ZnO NPs with amino functionalized groups (M.ZnO and T.ZnO). The FTIR spectra shows that the GTMS and amine compounds has been successfully attached on the ZnO NPs surface. In addition, FESEM and EDX results demonstrated that the M.ZnO and T.ZnO NPs existed within the sublayers matrix and improved its attributes in terms of hydrophilicity, tortuosity, porosity, S value and perm-selectivity. Experimental outcomes represented that the PWF was

Acknowledgment

The authors acknowledge the funding support of Babol Noshirvani University of Technology through Grant program No. BNUT/389026/97.

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