Elsevier

Journal of Hazardous Materials

Volume 368, 15 April 2019, Pages 292-299
Journal of Hazardous Materials

Fabrication of a novel polyvinylidene fluoride membrane via binding SiO2 nanoparticles and a copper ferrocyanide layer onto a membrane surface for selective removal of cesium

https://doi.org/10.1016/j.jhazmat.2019.01.065Get rights and content

Highlights

  • A novel PVDF membrane with selected properties for Cs was fabricated.

  • The SiO2 and CuFC NPs are irreversibly fixed on the membrane surface.

  • CuFC/SiO2/PVDF membrane exhibits great flux and high stability.

  • Composite membrane owns high selectivity with the co-existing ions and organics.

  • Competitive adsorption and Donnan’ effect govern the rejection of Cs.

Abstract

A novel polyvinylidene fluoride (PVDF) membrane was fabricated through chemical binding SiO2 nanoparticles (NPs) and copper ferrocyanide (CuFC) layers onto a membrane surface simultaneously to improve the removal efficiency of Cs. The results indicated that the SiO2 NPs were strongly deposited onto the membrane surface, and the CuFC layer was firmly attached on the surface of SiO2 NPs and the membrane. CuFC/SiO2/PVDF membrane remained stable after the acidic solution and sonication stress treatments. CuFC/SiO2/PVDF membrane showed good permeate flux and high selectivity on removal of Cs, and adsorbing capacity reached 1440.4 mg m−2 for Cs. The membrane remained high rejections of Cs in a wide pH, and could be regenerated well by H2O2 and N2H4. Selective adsorption and electrostatic interaction govern the rejection of Cs. The coexisting cations decreased the rejection of Cs mainly in accordance to the order of cations’ hydration radii as K+ > Na+ > Ca2+ > Mg2+. In addition, the rejection of Cs could still reach 99.4% in 8 h in the filtration of humic acid solution and natural surface water. The membrane could removal of Cs from water effectively by directly rapid filtration, suggesting it can be applied as promising technology for radioactive wastewater treatment.

Introduction

Increasing industrial activities accelerate the release of radionuclides [1,2]. Cesium (137Cs) is the most hazardous and abundant radionuclide in the aqueous environment, due to its high energy gamma ray emission (661.9 keV) and relatively long half-life (30.1 years) [3]. In the past years, several methods have been studied for removing Cs from aqueous solution which includes precipitation, solvent extraction, adsorption/ion exchange and membrane technology [[4], [5], [6], [7]]. Membrane technology is increasing as pretreatment in desalination and used in wastewater treatment containing Cs because it offers significant advantages compared with conventional removal methods [5,8,9]. In our previous studies, reverse osmosis (RO) membrane has demonstrated good capabilities in removing of Cs, but the RO membrane is limited by membrane fouling and high energy consumption [9,10]. Low pressure membranes (LPMs) have been applied widely in the world from a cost-benefit perspective due to that their filtration pressures were just one tenth of RO membranes [11,12]. However, it is difficult to remove Cs by LPMs through mechanical filtration, and the membranes are no selective [13,14]. As a result, now LPMs filtration systems Cs has to be eliminated by including adsorbents in the solution upstream of the membrane or by utilizing an accessional processing unit [5,[15], [16], [17]].

Transition metal ferrocyanides have been reported to be one of the most promising adsorbents due to their superb high selectivity and large adsorption capacities for Cs, thereby being extensively studied in the last decade [[18], [19], [20], [21], [22]]. Among the transition metal ferrocyanides, copper ferrocyanide (CuFC) was demonstrated as an efficient and environmentally friendly Cs scavenger [19,[23], [24], [25]]. CuFC had strong affinities to Cs, which was less affected by the coexisting cations and solution pH [[26], [27], [28]]. In generally, as fine powers, the CuFC crystals are difficult to use directly in the filtration of Cs separated from aqueous solution [29]. The excellent performances of CuFC and the development of modification technology unprecedentedly promote the development of novel CuFC composite membranes with actual value. The substrate membrane prevents CuFC from leaching into the treated water and also mechanically supports the CuFC layer. By simultaneously taking advantage of the CuFC layer and membrane substrate, the composite membrane can be an effective material with great potential for use in radioactive wastewater remediation. CuFC has been directly precipitated into the pore of membrane, which had the low stability and decreased the flux, resulting in low selectivity of Cs [30,31]. Recently, the CuFC crystals have been impregnated to various materials such as silica, zeolite and magnetic nanoparticles (NPs), in order to improve the mechanical properties of the absorbent [28,32,33]. To improve the bonding strength and mitigate membrane pore blocking caused by the CuFC particles deposition, the hydrophilic silica (SiO2) layer was introduced into the CuFC composite membrane. Polyvinylidene fluoride (PVDF) with outstanding mechanical strength, good thermal stability, and high chemical resistance has been widely applied as a LPMs material for industrial process [[34], [35], [36]]. Some literatures on embedding SiO2 NPs onto PVDF membranes have indicated the membrane flux and hydrophilicity were highly improved [35,37]. On the other hand, CuFC type particles could coat onto SiO2 through chemical bonding, and present a high selectivity to Cs [28,38,39]. To the best of our knowledge, no study has developed the CuFC-coated NPs onto the membrane surface synchronously with tight binding for property improvement.

This study explores a novel and facile approach to fabricate a highly selective PVDF composite membrane for Cs via post fabrication tethering of hydrophilic SiO2 and CuFC NPs on the membrane surface. A tight chemical bond for binding SiO2 NPs (surface-tailored with amine functional groups) on the membrane surface was formed by the introduction of Hydroxyl groups onto the PVDF membrane surface by chemical processes. Afterward, the fixed SiO2 NPs were covalently bond to CuFC NPs in the presence of copper chloride and potassium ferrocyanide. The CuFC-functionalized composite membranes were sufficiently characterized, and the effect of competitive ions and organic matter on Cs removal in both synthetic and nature water were investigated.

Section snippets

Materials

Isotope of cesium nitrate (CsNO3) was obtained from Acros and used as the surrogate for 137Cs due to their similar chemical characteristics. Copper chloride (CuCl2), potassium ferrocyanide (K3[Fe(CN)6]•3H2O), hexane, and trimesoyl chloride (TMC, 98%) were supplied by Sigma-Aldrich. SiO2 NPs modified with amino groups (300 nm, w/v: 2.5%) and tetrabutylammonium fluoride (TBAF, 98%) were purchased from Aladdin industrial corporation (Shanghai, China). Humic acid (HA) was provided by Sinopharm

Characterization of the modified membranes

To form reactive groups (−COCl) and loading amino-modified SiO2 NPs onto membrane surface, the pristine PVDF membrane was pretreated in KOH solution and TMC hexane media, respectively [34]. Afterward, the CuFC was further spiked onto the SiO2 NPs of the membrane surface. The detailed modification processes are shown in Fig. 1.

The pristine PVDF membrane was conduct by KOH to promote the production of unsaturated double bonds using for nucleophilic addition process to inducing the hydroxyl group.

Conclusions

  • 1

    One highly selective PVDF membrane for Cs removal was firstly prepared via a facile and effective strategy binding SiO2 and CuFC onto the PVDF membrane surface synchronously. And, a covalent bond tightly bound CuFC NPs onto the SiO2 surface. The obtained functionalized membrane exhibited a relatively high permeate flux and selectivity for Cs, and it can bind up to 1440.4 mg m−2 for Cs.

  • 2

    The CuFC/SiO2/PVDF membrane proved to have high stability in a wide pH and physical stress, and shown the

Acknowledgements

This study was financially supported by the Major Science and Technology Program for Water Pollution Control and Treatment of China (2015ZX07406006) and the National Natural Science Foundation of China (Grant No.41603109, Grant No. 21677015and Grant No.51238006).

References (46)

  • D. Rana et al.

    Radioactive decontamination of water by membrane processes - a review

    Desalination

    (2013)
  • C.-P. Zhang et al.

    Research on the treatment of liquid waste containing cesium by an adsorption-microfiltration process with potassium zinc hexacyanoferrate

    J. Hazard. Mater.

    (2009)
  • D. Ding et al.

    Selective removal of cesium by ammonium molybdophosphate-polyacrylonitrile bead and membrane

    J. Hazard. Mater.

    (2017)
  • X. Liu et al.

    Adsorption removal of cesium from drinking waters: a mini review on use of biosorbents and other adsorbents

    Bioresour. Technol.

    (2014)
  • A. Nilchi et al.

    Adsorption of cesium on copper hexacyanoferrate-PAN composite ion exchanger from aqueous solution

    Chem. Eng. J.

    (2011)
  • H. Kim et al.

    Rapid removal of radioactive cesium by polyacrylonitrile nanofibers containing Prussian blue

    J. Hazard. Mater.

    (2018)
  • E. Cho et al.

    Chemically bound Prussian blue in sodium alginate hydrogel for enhanced removal of Cs ions

    J. Hazard. Mater.

    (2018)
  • H. Kim et al.

    Photocatalytic enhancement of cesium removal by Prussian blue-deposited TiO2

    J. Hazard. Mater.

    (2018)
  • F. Han et al.

    Removal of cesium from simulated liquid waste with countercurrent two-stage adsorption followed by microfiltration

    J. Hazard. Mater.

    (2012)
  • R. Chen et al.

    Selective removal of cesium ions from wastewater using copper hexacyanoferrate nanofilms in an electrochemical system

    Electrochim. Acta

    (2013)
  • H.-M. Yang et al.

    Sodium-copper hexacyanoferrate-functionalized magnetic nanoclusters for the highly efficient magnetic removal of radioactive caesium from seawater

    Water Res.

    (2017)
  • T. Sangvanich et al.

    Selective capture of cesium and thallium from natural waters and simulated wastes with copper ferrocyanide functionalized mesoporous silica

    J. Hazard. Mater.

    (2010)
  • C. Su

    Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: a review of recent literature

    J. Hazard. Mater.

    (2017)
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