Use of a zeolite-modified electrode for the study of the methylviologen–sodium ion-exchange in zeolite Y

https://doi.org/10.1016/S0022-0728(98)00452-5Get rights and content

Abstract

The electrochemical response of zeolite-modified carbon paste electrodes (ZMCPEs) has been exploited to plot the normalised ion-exchange isotherm of methylviologen and sodium in zeolite Y. Results observed from the proposed methodology agree well with those obtained using the conventional procedure. Selectivity was very high for the large organic divalent cation over sodium species, but the degree of exchange of methylviologen did not exceed 64%. Electrochemistry of ZMCPEs allows the in situ quantitative determination of methylviologen in the zeolite phase, without significant modification in the solution-phase concentrations, so that the ion-exchange isotherm can be plotted very rapidly and without any other chemical analysis.

Introduction

An important intrinsic property of most zeolites is their ability to undergo ion-exchange. Although fundamental ion-exchange equilibria involving alkali metal, alkaline earth, rare earth and ammonium cations were fully characterised a long time ago [1], [2], [3], [4], [5], [6], the applications and uses of natural and synthetic zeolites have attracted much attention and considerable progress in recent years because of their utilisation as ion-exchangers for water softening [7], [8], for the removal and storage of radionuclides [9], [10] as well as the uptake of heavy metals from polluted effluents [11], [12], [13], [14], [15] and the removal of ammonium ions from waste waters [16], [17], [18].

The exchange of ions between zeolite and solution phases can be analysed by calculating distribution coefficients from chemical analyses performed, most often, only on the solution phase (see [19], for example). However, the full characterisation of the ion-exchange equilibrium is best achieved by plotting ion-exchange isotherms [1], [3], [20], [21]. This requires the quantitative analysis of the exchanging cations in both solution and zeolite phases after equilibration [20], [21]. These steps, and especially the analysis of the zeolite phase, are often tedious and time consuming. They are however absolutely necessary, in particular when the zeolite displays a strong affinity for one of the two exchanging cations, because of the small variation (or the low values) of the solution phase concentrations. Some complications with zeolites may arise due to the existence of several different ion exchanging sites and the rigid tridimensional lattice made of pores and channels of molecular dimensions, conferring to zeolites a unique size (and shape) selectivity with volume exclusion effects which could result in incomplete exchange [1], [2], [3], [4], [5], [6], [20], [21].

Recently, zeolite-modified electrodes (ZMEs) have attracted considerable attention from electrochemists [22], [23], [24], [25], [26], [27]. The combination of electrochemical methods with the unusual properties of zeolites (size, shape and size selectivity, ion-exchange capacity, chemical and thermal stability) was exploited in many fields. For example, ZMEs were successfully applied as new selective amperometric sensors [23], [27], [28], [29], [30], [31], [32], [33], [34], by exploiting the ion-exchange between electroactive and non-electroactive cations in zeolite particles located at the electrode surface. The amperometric response of the sensor was directly related to the ion-exchange properties of zeolites [34]. Basically, the electrochemical response of a ZME exchanged with an electroactive cation, Em+, immersed in an electrolyte solution containing a cation C+ (chosen as monovalent for writing convenience), can be explained by the following electron transfer mechanism [35]:Em+(Z)+mC+(S)⇌Em+(S)+mC+(Z)Em+(S)+ne⇌E(mn)+(S)where subscripts S and Z refer to solution and zeolite, respectively. The electroactive species is first exchanged for the electrolyte cation at the electrode  solution interface (Eq. (1)) and then undergoes the charge transfer in the solution phase (Eq. (2)). The voltammetric response of the electrode is therefore strongly affected by the ion-exchange reaction (Eq. (1)). Accordingly, it was recently reported that electrochemistry at ZMEs could be used for the qualitative characterisation of ion-exchange reactions in Ref. [34].

Among other electroactive species, methylviologen (a well-known herbicide whose the electrochemical activity was previously reviewed [35]) was found to give an amperometric response when incorporated in zeolite Y [31], [34], [35], [37], [38], [39]. The electron transfer mechanism responsible for its amperometric response at a zeolite-modified carbon paste electrode (ZMCPE) immersed in a sodium chloride electrolyte solution was demonstrated to proceed according to , [39]. On the other hand, methylviologen is known to be incorporated into the zeolite Y lattice [37], [38], [39], [40], [41]. Due to its large size, methylviologen is excluded from the sodalite cages, being therefore located only in the supercages or in the channels linking the supercages to each other. As a consequence, the kinetics associated with the methylviologen–sodium exchange in zeolite Y is thought to be controlled by the diffusion of the species through the 12-ring apertures of 0.74 nm, and not to any intracrystalline dynamics in interconnected cages of different size (as was the case for the exchange of cations able to reach sites located in pores or channels of various sizes [3]).

The aim of this paper is to provide a new and original way to produce the ion-exchange isotherm of the methylviologen–sodium system under in situ conditions. After having plotted the isotherm following the conventional method [20], we will point out the usefulness of electrochemistry at a zeolite Y modified carbon paste electrode for measuring, in a non destructive way, the equivalent fraction of methylviologen in zeolite Y. Zeolite particles will contact the liquid phase by immersing the ZME into a solution containing the exchanging cations at a constant total normality of 1.0×10−2 N (i.e. concentrations of uniequivalent anions of 10−2 M). A major advantage of this approach is that the solution phase concentrations will be affected neither by the ion-exchange reaction itself nor by the electrochemical determination of the equivalent fraction of methylviologen in zeolite, because of the very high liquid-to-solid ratio, so that the equivalent fractions in solution are not to be measured because they do not change.

Section snippets

Apparatus

Electrochemical experiments were performed at 25°C in an undivided 50 ml three electrode cell. Solutions were purged by bubbling pure nitrogen during 15 min before measurements. Working electrodes were home-made carbon paste electrodes (unmodified or zeolite-modified, see section 2.3.). The counter-electrode was made of a platinum wire, and the saturated calomel (model TR 100, Radiometer) and Ag  AgCl (Metrohm) reference electrodes were used, respectively for cyclic voltammetry and square wave

The MV2+/Na+ ion-exchange equilibrium

The MV2+/Na+ ion-exchange of zeolite Y can be represented by the following equilibrium (Eq. (3)):2 Na+(Z)+MV2+(S)⇋2 Na+(S)+MV2+(Z)where subscripts Z and S refer to zeolite and solution phases, respectively. The isotherm corresponding to the exchange is expressed as MVZ=f(MVS) at a constant total ion concentration where MVZ and MVS are the equivalent fractions of methylviologen in the zeolite and in solution, respectively.

The exchange isotherm is shown in Fig. 1. The main features of Fig. 1 are

Conclusions

By using a zeolite-modified carbon paste electrode, it has been shown that cyclic voltammetry is a good tool for the quantitative characterisation of the binary MV2+and Na+ ion-exchange in zeolite Y. Good correlation was found between the normalised isotherms plotted either following the conventional method or using the proposed methodology. The resort to electrochemistry at zeolite-modified electrodes is attractive because it provides a rapid quantification of the normalised equivalent

References (55)

  • R.P Townsend

    Stud. Surf. Sci. Catal.

    (1991)
  • M Loizidou et al.

    Zeolites

    (1987)
  • M Pansini et al.

    Microporous Mater.

    (1996)
  • A Neveu et al.

    Water Res.

    (1985)
  • R Cintoli et al.

    Water Sci. Technol.

    (1995)
  • J Lehto et al.

    React. Polym.

    (1995)
  • D.R Rolison et al.

    Talanta

    (1991)
  • F Bedioui

    Coord. Chem. Rev.

    (1995)
  • J Wang et al.

    Anal. Chim. Acta

    (1988)
  • J Wang et al.

    J. Electroanal. Chem.

    (1996)
  • C Bing et al.

    Talanta

    (1996)
  • A Walcarius et al.

    Anal. Chim. Acta

    (1997)
  • H.A Gemborys et al.

    J. Electroanal. Chem.

    (1986)
  • A Walcarius et al.

    Electrochim. Acta

    (1993)
  • A Walcarius et al.

    Electrochim. Acta

    (1993)
  • A Walcarius et al.

    J. Electroanal. Chem.

    (1996)
  • M.A Keane

    Microporour Mater.

    (1995)
  • A Walcarius et al.

    J. Electroanal. Chem.

    (1997)
  • A Walcarius et al.

    Anal. Chim. Acta

    (1998)
  • B Ballarin et al.

    J. Electroanal. Chem.

    (1998)
  • F Hellferrich

    Ion-exchange

    (1962)
  • H.S Sherry

    Molecular Sieve Zeolites

  • D.W. Breck, Zeolites Molecular Sieves, Structure, Chemistry and Use, Wiley, NY, 1974 (original edition); R.E. Krieger,...
  • R.P Townsend

    Pure Appl. Chem.

    (1986)
  • A Dyer

    An Introduction to Zeolite Molecular Sieves

    (1988)
  • L.V.C Rees
  • M Baacke et al.
  • Cited by (32)

    • Sunlight assisted synthesis of silver nanoparticles in zeolite matrix and study of its application on electrochemical detection of dopamine and uric acid in urine samples

      2016, Materials Science and Engineering C
      Citation Excerpt :

      ZMEs are widely used in ion-exchange [16], electrocatalysis and electroanalytical devices with better sensitivity [17], high thermal and chemical stability [18]. Nowadays, the ZMEs were accomplished in various routes through copper doped zeolite expanded graphite epoxy electrode [19], iron-ion doped natrolite zeolite-MWCNT modified GCE [20], Ag-doped zeolite expanded graphite-epoxy composite electrode [21], methylviologen supported on zeolite Y modified electrode [22], graphite-zeolite modified electrode [23], mesoporous carbon [24], cytochrome c immobilized on NaY zeolite [25], methylene blue incorporated into mordenite zeolite [26] bismuth modified zeolite doped CPE [27], NiCo2/O4/nano-ZSM-5 nanocomposite [28] and Ru-red incorporated zeolite modified CPE [29]. Dopamine (DA) is usually coexisting with uric acid (UA) in biological fluids which are playing an important role in human metabolism [30].

    • Zeolite Y film as a versatile material for electrochemical sensors

      2016, Materials Letters
      Citation Excerpt :

      For molecular sensor electrodes, it is a crucial to modify the conducting substrate with zeolite crystallites. Various designs and preparation methods for the modification of zeolite-based electrodes have been proposed: (i) formation of a zeolite-polymer composite [15–18], (ii) dispersion of zeolite particles into a conductive composite matrix [19–21], and (iii) chemical bonding of zeolite onto a substrate [22,23]. However, these zeolite-modified electrodes often develop cracks that is resulted in direct contact of the molecules with the pristine electrode and are, therefore, not suitable for practical application as sensors for the detection of specific molecules.

    View all citing articles on Scopus
    View full text