Spectrophotometric study of the interaction of toluidine blue with poly (ammonium acrylate) Anouar Ben Fradj a , Ridha lafi a , Lassad Gzara b , Ahmed Hichem Hamzaoui c , Amor Hafiane a, ⁎ a Laboratory of Wastewater Treatment, CERTE, BP 273, Soliman 8020, Tunisia b Center of Excellence in Desalination Technology, King Abdulaziz University, Jeddah, Saudi Arabia c Laboratory of Valorisation of Materials, CNRSM, BP 95, Hammam-Lif 2050, Tunisia abstract article info Article history: Received 27 August 2013 Received in revised form 6 January 2014 Accepted 12 January 2014 Available online 25 January 2014 Keywords: Dye–polyelectrolyte interaction Toluidine blue H-aggregate Thermodynamic parameters Spectrophotometry UV–visible The aim of this work is to study the interaction between Toluidine Blue (TB), a cationic dye, and an anionic poly- electrolyte, poly (ammonium acrylate) (PANH 4 ). The UV–Visible spectroscopy study shows that addition of in- creasing amounts of poly (ammonium acrylate) induces the formation of a metachromatic complex. The stoichiometry of TB–PANH 4 complex evaluated by the molar ratio method is 1:1 and the large hypsochromic ab- sorption shift (73 nm) obtained is attributed to dye H-aggregates. The effects of sodium chloride concentration, pH and Cetyl pyridinium chloride (CPC) concentration, on metachromasy have also been studied. Thermody- namic parameters of interaction ΔG, ΔH and ΔS at different temperatures have been evaluated to determine the stability constant of the complex. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The release of dyes with wide variety of different components from textile activities remains an environmental issue. There are many structural varieties of dyes, such as, azo, diazo, anthraquinone, triphe- nylmethane and phenothiazine. Most of these dyes are toxic and even carcinogenic and this poses a serious hazard to aquatic living organisms [1–4]. The removal of the dye which is considered as pressing task has been done primarily through adsorption using different adsorbents [5–7]. Other techniques involving electrochemical oxidation [8], biolog- ical treatment [9], ozonation [10] etc., are also investigated in the litera- ture. In the context of environmental remediation, polyelectrolytes have been widely investigated in coagulation–flocculation [11–14], and poly- electrolyte enhanced ultrafiltration (PEUF) process [15–18]. To remove dyes from aqueous solutions, we use PEUF as hybrid process which combined ultrafiltration and complexation ability of water soluble poly- mers. But to ensure the efficiency of this method, it is necessary to study in details the nature of the interaction between the dye and the poly- electrolyte [19,20]. On the other hand, it is established that the polyelec- trolyte in aqueous solution affects the absorption spectrum of the dye and therefore the accuracy of its analysis. The observed absorption changes have been attributed to binding of the dye [21–23] with a poly- mer having an opposite charge which enhances dye aggregation at very low concentration. Furthermore the spectral change becomes more complicated in presence of auxiliary chemicals such as NaCl, HCl, NaOH, and CPC. So in the present work we have focused on the effect physico-chemical parameters on the interaction between Toluidine Blue chosen as model dye and poly (ammonium acrylate) as poly- electrolyte. The study will be done by changing the initial concen- tration of the polymer, the pH solution, and the NaCl and surfactant concentrations. 2. Materials and methods 2.1. Chemicals Toluidine blue (C 15 H 16 ClN 3 S), a cationic phenothiazine dye, was purchased from Fluka. Poly (ammonium acrylate), an anionic polyelec- trolyte (PANH 4 ), with molecular weight Mw 30,000 g·mol -1 , was syn- thesized by radical polymerization of ammonium acrylate monomer. The preparation of this polymer is reported elsewhere [24]. The chemi- cal structures of the two compounds are shown in Fig. 1. Chloride acid, sodium chloride, sodium hydroxide and cationic surfactant cetylpyridinium chloride C 16 H 33 Pyr + Cl - (CPC), were provided by Sigma-Aldrich. All the chemicals were used without further purifi- cation. Distilled water was used for all the experiments. 2.2. UV–visible spectroscopy The UV–Visible spectra of different TB solutions were acquired by PerkinElmer Lambda 25 spectrophotometer, with a matched pair of cuvets of 1 cm path length. The temperature was always maintained Journal of Molecular Liquids 194 (2014) 110–114 ⁎ Corresponding author. Tel.: +216 79 325 750; fax: +216 79 325 802. E-mail address: amor.hafiane@certe.rnrt.tn (A. Hafiane). 0167-7322/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molliq.2014.01.008 Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq