Elsevier

Journal of Membrane Science

Volumes 570–571, 15 January 2019, Pages 314-321
Journal of Membrane Science

Fabrication of a novel and green thin-film composite membrane containing nanovoids for water purification

https://doi.org/10.1016/j.memsci.2018.10.057Get rights and content

Highlights

  • A nanovoids-enhanced TFC membrane was prepared.

  • Systematic characterization results confirmed the complete removal of CuNPs.

  • The nanovoids containing TFC membrane achieved 4-fold water flux than that of CuNPs loaded membrane.

  • The nanovoids-enhanced TFC membrane showed linear relationship between water flux and applied pressure.

Abstract

Thin film nanocomposite (TFN) membranes, which incorporate nanomaterials in a crosslinked polyamide matrix, often show enhanced separation properties thanks to the additional pores or channels offered by these materials. In this study, we deliberately created nanovoids in the dense polyamide rejection layer by acid-etching copper nanoparticles (CuNPs) contained in a TFN membrane. Systematic membrane characterization confirmed the complete removal of CuNPs using 1% HNO3, which formed nanovoids of approximately 10 nm in size. The water flux of the etched membrane TFC-Cu50X was nearly quadrupled compared to that of the CuNPs loaded membrane TFC-Cu50. This significantly improved water flux can be ascribed to the enhanced water transport through these nano-sized voids. The nanovoids-enhanced approach provides new possibilities for synthesizing high performance membranes.

Introduction

Thin-film nanocomposite (TFN) membranes, which incorporate nanomaterials in a salt-rejecting polyamide (PA) layer, have attracted tremendous attention in the past decade [1], [2], [3]. Compared to thin-film composite (TFC) membranes, TFN can dramatically improve membrane water permeability (e.g., up to 200% enhancement), while maintaining similar salt rejection [1]. Notably, the embedded nanomaterials with micro or mesopores, such as zeolite [4], [5], mesoporous silica [6], [7], metal-organic-framework (MOF) [8] and carbon nanotubes [9] could further enhance membrane water permeability compared to their solid counterparts. The higher water flux can be ascribed to the preferential water pathway in the nanovoids of these porous nanomaterials [6]. Despite the enhanced membrane separation performance, conventional TFN membranes still have some obstacles, such as potential leaching [10] and nanomaterials toxicity [11].

The improved porosity of polyamide rejection layer can significantly improve membrane separation performance [12], [13]. As an alternative approach to conventional TFN, Livingston and co-workers [14] applied microporous monomers for interfacial polymerization, resulting in the formation of a microporous cross-linked rejection layer that showed excellent permeability and selectivity compared to commercial membranes. In a more recent study [13], we reported series of approaches to generate nanovoids in the polyamide rejection layer by the formation of nanosized gas bubbles (e.g., by the addition of bicarbonate or ultrasound application) during the interfacial polymerization. These nanovoids significantly increased both membrane water permeability and salt rejection. Several studies also highlighted the importance of the microporous structure of membrane rejection layer [15], [16], [17], [18], [19], [20].

In this study, we report a facile method to fabricate novel high performance TFC membranes, where nanovoids were generated through the etching of nanoparticles incorporated in the PA-Polysulfone(PSF) interface. Specifically, we first synthesized copper nanoparticles (CuNPs) loaded TFN membranes, followed by their removal using an HNO3 solution to create an “arch-like” polyamide morphology. We hypothesize that these nanovoids could significantly decrease the membrane hydraulic resistance, thus greatly enhancing water permeability. This work provides a novel insight into the fabrication of a high performance nanovoids-enhanced TFC membrane.

Section snippets

Materials and reagents

Chemicals for the preparation of membrane substrates and interfacial polymerization, including polysulfone (PSF, Mw 35,000), N,N-dimethylformamide (DMF, anhydrous 99.8%), m-Phenylenediamine (MPD, flakes, 99%) and hexane (HPLC grade, 95%) were all obtained from Sigma-Aldrich. Trimesoyl chloride (TMC, 99%) was purchased from J&K Scientific Ltd. Cupric sulfate-anhydrous (CuSO4, AR, Dieckmann, Hong Kong) and sodium borohydride (NaBH4, 98%, Sigma-Aldrich) were used to generate CuNPs in situ on

Membrane characterization

Fig. 2 presents the SEM micrographs (plan view) of the control (PSF) and CuSO4/NaBH4 modified polysulfone (PSF-Cu) substrates. The control polysulfone substrate had a relatively flat surface with a root-mean-square (Rq) roughness of 9.3 ± 1.8 nm. With the increased concentration of the applied CuSO4 and NaBH4 solution, the surface roughness of the modified substrate increased up to 14.9 ± 3.4 nm (Supplementary material, Fig. A1). Elemental analysis of EDS (inserts of Fig. 2) further confirmed

Acknowledgement

This study receives financial support from the Seed Funding for Strategic Interdisciplinary Research Scheme, the University of Hong Kong.

References (48)

  • F.A. Pacheco et al.

    Characterization of isolated polyamide thin films of RO and NF membranes using novel TEM techniques

    J. Membr. Sci.

    (2010)
  • S. Xiong et al.

    Thin film composite membranes containing intrinsic CD cavities in the selective layer

    J. Membr. Sci.

    (2018)
  • X.-H. Ma et al.

    A facile preparation of novel positively charged MOF/chitosan nanofiltration membranes

    J. Membr. Sci.

    (2017)
  • M. Ben-Sasson et al.

    In situ surface functionalization of reverse osmosis membranes with biocidal copper nanoparticles

    Desalination

    (2016)
  • Z. Yang et al.

    A novel thin-film nano-templated composite membrane with in situ silver nanoparticles loading: separation performance enhancement and implications

    J. Membr. Sci.

    (2017)
  • G.M. Geise et al.

    Water permeability and water/salt selectivity tradeoff in polymers for desalination

    J. Membr. Sci.

    (2011)
  • A.K. Ghosh et al.

    Impacts of reaction and curing conditions on polyamide composite reverse osmosis membrane properties

    J. Membr. Sci.

    (2008)
  • L.-x. Dong et al.

    A thin-film nanocomposite nanofiltration membrane prepared on a support with in situ embedded zeolite nanoparticles

    Sep. Purif. Technol.

    (2016)
  • S. Xiong et al.

    Novel thin film composite forward osmosis membrane of enhanced water flux and anti-fouling property with N-[3-(trimethoxysilyl) propyl] ethylenediamine incorporated

    J. Membr. Sci.

    (2016)
  • X. Zhang et al.

    Improved performance of thin-film composite membrane with PVDF/PFSA substrate for forward osmosis process

    J. Membr. Sci.

    (2017)
  • Y. Zhao et al.

    Synthesis of robust and high-performance aquaporin-based biomimetic membranes by interfacial polymerization-membrane preparation and RO performance characterization

    J. Membr. Sci.

    (2012)
  • Y.-y. Zhao et al.

    Role of membrane and compound properties in affecting the rejection of pharmaceuticals by different RO/NF membranes

    Front. Environ. Sci. En.

    (2017)
  • J. Yin et al.

    Graphene oxide (GO) enhanced polyamide (PA) thin-film nanocomposite (TFN) membrane for water purification

    Desalination

    (2016)
  • S. Qi et al.

    Aquaporin-based biomimetic reverse osmosis membranes: stability and long term performance

    J. Membr. Sci.

    (2016)
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