Modification of a hydrophobic-ligand-containing porous sheet using tri-n-octylphosphine oxide, and its adsorption/elution of bismuth ions

https://doi.org/10.1016/j.reactfunctpolym.2010.10.008Get rights and content

Abstract

A neutral extractant, tri-n-octylphosphine oxide (TOPO), was used to chemically modify a porous sheet, with a final density of 1.0 mmol/g. First, glycidyl methacrylate (GMA) was graft-polymerized onto a porous polyethylene sheet with an average pore diameter, porosity, and thickness of 1.2 μm, 75%, and 2.0 mm, respectively. Second, an octadecane thiol group was introduced into the poly-GMA graft chain. Third, TOPO was deposited on the graft chain via a hydrophobic interaction. Bismuth chloride solution (BiCl3 in 0.15 M HNO3) was forced through the pores of the TOPO-modified porous sheet. The equilibrium binding capacity for bismuth was 0.19 mmol/g. Bismuth ions bound to TOPO were quantitatively eluted with 11 M HNO3.

Introduction

Extractants developed for liquid–liquid extraction in nuclear chemistry are useful for the recovery of rare-metal ions dissolved in liquids [1], [2]. However, the use of such extractants in liquid–liquid extraction is disadvantageous from environmental and economical viewpoints. Solid-phase extraction (SPE) is advantageous over liquid–liquid extraction in that no waste solvents are produced [3], [4], [5], [6], [7], [8], [9], [10]. To advance SPE technology, solids as supporting materials must be prepared that can serve as scaffolds for the extractants while preserving the extractant’s ability to recover rare-metal ions.

Extractants can be classified as acidic, basic, or neutral. Because most extractants contain many normal or branched alkyl chains, they are attached to the supporting materials via the hydrophobic interaction between the hydrophobic part of the extractant and the hydrophobic domain of the supporting material. In addition, the use of acidic and basic extractants to modify supporting materials is enhanced by an electrostatic interaction that occurs only during deposition.

We developed a hydrophobic polymer chain grafted onto a porous hollow-fiber membrane with an inner diameter of 2 mm and a thickness of 0.5 mm [11], [12], [13], [14], [15]. The hydrophobic groups of the polymer chain include octyl (C8) and octadecyl (C18) groups. The representative extractants bis(2-ethylhexyl)phosphate (HDEHP), tri-n-octylphosphine oxide (TOPO), and N-methyl-N,N-dioctyloctan-1-ammonium chloride (Aliquat 336) were used to modify porous hollow-fiber membranes that were then used to capture ionic yttrium [12], [13], bismuth [11], and palladium [14] species, respectively. However, a more suitable shape for the fabrication of the SPE module and a simpler scheme for the modification of the trunk polymers are desirable for practical use. Recently, a porous sheet instead of a porous hollow-fiber membrane has been proposed as a novel supporting matrix [16]. This porous sheet can be easily fabricated into a bed simply by cutting it into disks.

TOPO, a neutral extractant, is difficult to deposit onto supporting materials at a sufficiently high density because it does not have a charged group in its chemical structure. The phosphoryl oxygen in TOPO coordinates directly to metal ions [17]. Sawaki et al. [11] prepared a novel supporting material consisting of a double-layer polymer chain, i.e., the upper part of a diol group and the lower part of a hydrophobic group along the polymer chain, for modification using TOPO. TOPO deposited at a density of 0.65 mmol/g captured bismuth ions during the permeation of a bismuth solution through the TOPO-modified porous hollow-fiber membrane. However, the relatively low permeability of the TOPO-modified porous hollow-fiber membrane was a drawback.

This study had three objectives: (1) to prepare a TOPO-modified porous sheet by radiation-induced graft polymerization and subsequent chemical modifications, (2) to adsorb and elute bismuth ions using the resultant porous sheet, and (3) to compare the metal-ion-binding performances of a TOPO-modified porous sheet and a TOPO-modified porous hollow-fiber membrane.

Section snippets

Materials

A porous sheet made of high-density polyethylene, which was supplied by INOAC CORPORATION, was used as a trunk polymer for grafting. This porous sheet had a thickness of 2.0 mm, a porosity of 75%, and an average pore diameter of 1.2 μm. Glycidyl methacrylate (GMA) was purchased from Nakalai Tesque Co. and used without further purification. 1-Octadecane thiol (C18SH) was acquired from Sigma–Aldrich Co. Tri-n-octylphosphine oxide (TOPO) was purchased from Tokyo Kasei Co. Other chemicals were of

Deposition of TOPO onto a porous sheet

The C18S sheet was immersed in various concentrations of TOPO dissolved in ethanol. The dependence of the amount of TOPO deposited onto the C18S sheet on the TOPO concentration during the modification and the pure water flux of the resultant TOPO-modified porous sheets are shown in Fig. 2. The amount of TOPO deposited increased with increasing TOPO concentrations, whereas the pure water flux decreased with increasing TOPO concentrations. The pure water flux of 27 m/h at 0.1 MPa and 298 K at a TOPO

Conclusions

Electron-beam-induced graft polymerization is applicable to the modification of a porous sheet over the entire surface for the deposition of extractants. An epoxy-group-containing vinyl monomer was appended uniformly across the porous sheet. Subsequently, a 1-octadecyl group (C18H37single bond) was introduced into the polymer chain grafted onto the porous sheet. TOPO, which contains octyl groups, was deposited onto the 1-octadecyl group. The resultant TOPO-modified porous sheet had a higher binding rate

References (22)

  • E.P. Horwitz et al.

    Anal. Chim. Acta

    (1995)
  • E.P. Horwitz et al.

    Anal. Chim. Acta

    (1992)
  • V. Camel

    Solid-phase extraction

  • V. Camel

    Spectrochim. Acta B

    (2003)
  • E.P. Horwitz et al.

    Anal. Chim. Acta

    (1993)
  • R. Navarro et al.

    React. Funct. Polym.

    (2008)
  • B. Burghoff et al.

    React. Funct. Polym.

    (2009)
  • N. Kabay et al.

    React. Funct. Polym.

    (2010)
  • S. Domon et al.

    J. Membr. Sci.

    (2005)
  • S. Asai et al.

    J. Chromatogr. A

    (2005)
  • S. Asai et al.

    J. Membr. Sci.

    (2006)
  • Cited by (8)

    • High-resolution separation of neodymium and dysprosium ions utilizing extractant-impregnated graft-type particles

      2018, Journal of Chromatography A
      Citation Excerpt :

      To reduce the distance from metal ion binding sites to the convection flow, we selected porous materials with small pores, 0.3–1.2 μm in diameter, as a substrate. Utilizing electron-beam-induced graft polymerization (EIGP), a hydrophobic polymer brush was appended to the porous materials, and extractants were impregnated via hydrophobic interactions [6,10]. We selected EIGP from various chemical modification methods of porous materials because it easily provides stable covalent modification and functionalizable surfaces.

    • Extraction of lead, copper, and bismuth with mixtures of N,N-di(1-methylheptyl) acetamide and neutral organophosphorus extractants

      2013, Separation and Purification Technology
      Citation Excerpt :

      Therefore, the separation of these metals has received considerable attention. Solvent extraction [1–11], cloud point extraction [12], dispersive liquid–liquid microextraction [13], supported liquid membranes [14], and adsorption [15–20] have found their applications in this field. As a branch of solvent extraction, synergistic extraction has become a common method for the separation of metal ions [22].

    • Metal adsorbent for alkaline etching aqua solutions of Si wafer

      2012, Radiation Physics and Chemistry
      Citation Excerpt :

      Precursor monomer, glycidyl methacrylate, was selected for grafting. This monomer was used to be grafted in organic solvents such as methanol (Tanaka et al., 2010) and dimethyl sulfoxide (Yamashiro et al., 2007) since it is not soluble well in water. Recently, it was found that the grafting proceeded effectively using water and emulsifier of this monomer (Seko et al., 2007).

    • Innovative polymeric adsorbents: Radiation-induced graft polymerization

      2018, Innovative Polymeric Adsorbents: Radiation-Induced Graft Polymerization
    View all citing articles on Scopus
    View full text