Spectrophotometric study of anionic azo-dye light yellow (X6G) interaction with surfactants and its micellar solubilization in cationic surfactant micelles

Available online at www.sciencedirect.com

Spectrochimica Acta Part A 69 (2008) 1183–1187

Spectrophotometric study of anionic azo-dye light yellow (X6G) interaction with surfactants and its micellar solubilization in cationic surfactant micelles Reza Hosseinzadeh ∗ , Ramin Maleki, Amir Abbas Matin, Yousef Nikkhahi Food & Chemical Analysis Research Lab., Academic Center for Education, Culture and Research, Urmia Branch, Urmia University, Urmia, Iran Received 20 November 2006; accepted 19 June 2007

Abstract Solubilization and interaction of azo-dye light yellow (X6G) at/with cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) was investigated spectrophotometricaly. The effect of cationic micelles on solubilization of anionic azo dye in aqueous micellar solutions of cationic surfactants was studied at pH 7 and 25 ◦ C. The binding of dye to micelles implied a bathochromic shift in dye absorption spectra that indicates dye–surfactant interaction. The results showed that the solubility of dye increased with increasing surfactant concentration, as a consequence of the association between the dye and the micelles. The binding constants, Kb , were obtained from experimental absorption spectra. By using pseudo-phase model, the partition coefficients between the bulk water and surfactant micelles, Kx , were calculated. Gibbs energies of binding and distribution of dye between the bulk water and surfactant micelles were estimated. The results show favorable solubilization of dye in CTAB micelles. © 2007 Elsevier B.V. All rights reserved. Keywords: Absorption spectra; Dyes; Partition coefficient; Binding constant; Solubilization; Surfactant

1. Introduction Micellar systems have received widespread attention over decades and their ability to solubilize organic compounds is of great practical and theoretical importance, as demonstrated in the book edited by Christian and Scamehorn [1–3]. Surfactants are widely used in household and industrial cleaners, cosmetics, research laboratories and as wetting, dispersing and leveling agents for improving dyeing process by increasing solubility, stabilizing the dispersed state and promoting uniform distribution of the dye in the textile [4–6]. Surfactants are composed of a hydrophilic surface and a hydrophobic core in water media. This specific structure

∗

Corresponding author at: Food and Chemical Analysis Research Lab. Academic Center for Education, Culture and Research, Urmia Branch, Urmia University, Urmia, Iran. Fax: +98 441 3445410. E-mail addresses: [email protected], [email protected] (R. Hosseinzadeh). 1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2007.06.022

makes the micelles able to establish chemical interactions with either hydrophilic or lipophilic molecules [7–9]. These aggregates exhibit an interfacial region separating the polar bulk aqueous phase from the hydrocarbon-like interior. As a consequence, micellar solutions consist of a special medium in which hydrophobic, amphiphilic or ionic compounds may be solubilized and reagents may be concentrated or separated in aqueous solution [10]. Micellar solubilization involves the use of micellar surfactant solutions to increase the apparent aqueous solubility of contaminant in a single-phase miscible displacement flood [11]. The phenomenon of solubilization [12] plays an important role in detergency [13], dyeing process in textile industries [6], in pharmaceutical applications [14], to decontaminate groundwater aquifers and in soil clean-up operations (surfactant-enhanced remediation or SER), etc. [15]. Solubilization has been treated as partitioning of additive molecules between a micellar phase and an intermolecular bulk phase [16–18]. The partitioning behavior of additives between the aqueous and the micellar phase is an indication of the hydrophilic–lipophilic balance of the molecules. The interactions between additive-water, additive-

1184

R. Hosseinzadeh et al. / Spectrochimica Acta Part A 69 (2008) 1183–1187

Fig. 1. Molecular structures of light yellow azo dye (X6G) (a), cetyltrimethylammonium bromide (CTAB) (b), and cetylpyridinium chloride (CPC) (c).

micelles and water-micellar phase play a vital role in the partitioning process. The thermodynamic process of the interaction of dye with surfactants and transfer of the dye between micellar and bulk water phases is characterized by free energy changes, binding constant and partition coefficients, respectively. The partition coefficient depends on the structure of the additive and the surfactant that constitutes the micelles. Among the various factors that undoubtedly contribute to the solubilization in micellar systems, hydrophobic contributions are quite significant [16,19]. In our previous work we have reported the interaction of cationic surfactant, cetylpyridinium chloride with three azo dyes [20]. These studies have been done using potentiometric measurements until critical micellar concentration of surfactant. For further understanding about the interaction between azo dye molecules with cationic surfactant micelles and surfactant structure effect on interactions, in this work, interaction of two cationic surfactant micelles with similar hydrophobic tail and different head group, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPC), with anionic azo-dye light yellow (X6G) was investigated (see Fig. 1) using spectroscopic measurements. The absorption spectrophotometry were used to quantify the dye/surfactant binding constants and surfactant/water partition coefficients of dye, by applying the mathematical models that consider partitioning of the dye between the micellar and aqueous pseudo-phases [9,21]. 2. Experimental 2.1. Materials and instruments Cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPC) were obtained from Sigma chemical Co. All the salts (from Merck) were of the highest purity and used without further purification. Light yellow X6G (C.I. Reactive Yellow 2, MW = 872.5 g/mol) textile dye was obtained from Youhao (China). All pH measurements were made at 25 ◦ C, using Metrohm 744 (Switzerland). Absorption spectra were recorded on a Perkin-Elmer Lambda 25, double-beam UV–vis spectrophotometer with 1.0 cm quartz cuvettes and thermostat cell holder for adjusting the temperature (25 ◦ C). All solutions were prepared with double distilled water.

2.2. Methods Stock solutions of 5 × 10−6 mol dm−3 X6G were prepared by dissolving the certain amount of dye in distilled water. Stock solution of 1 × 10−1 mol dm−3 of CTAB and CPC surfactants were prepared by dissolving an appropriate amount of the surfactants in water. The variation of absorbance of dye solution by increasing of surfactants concentrations was recorded at maximum absorption wavelength using water as a blank. Dye/surfactant binding constants and micelle/water partition coefficients were determined from the absorbances of a series of solutions containing a fixed concentration of dye (Cdye = 5 × 10−6 mol dm−3 ) and increasing concentration of surfactants. 3. Results and discussions From the dye absorption spectra, the addition of surfactant (stock concentrations of surfactants were 1 × 10−1 mol dm−3 ) shows bathochromic shift of the higher wavelength maximum when surfactant is present. This shift indicate that dye interact with CTAB and CPC molecules. Also the increase in absorbance with increasing surfactant concentration is regarded to be caused by penetration of the dye molecules into the micelles as observed in other cases [22–29]. It is well known that a solute can be arranged in various ways in the micelle. Spatial position of a solubilized molecule in a micelle will depend on its polarity: non-polar molecules will be solubilized in the micellar core and substances with intermediate polarity will be distributed along the surfactant molecules in certain intermediate positions [30]. Solubilized molecule may pass completely inside the hydrophobic core or penetrate a particular depth into the surface layer (solute can be adsorbed on the surface of the micelle or, in the case of molecules containing polar substituents, be oriented with the polar portion of the molecule situated in the surface layer and the non-polar portion directed into the micelle). According to the X6G dye molecular structure, it can be seen that the anionic molecule has hydrophobic centers that make it suitable for both electrostatic and hydrophobic interactions with CTAB and CPC cationic surfactants. It seems that at first, electrostatic interaction between oppositely charged dye and surfactant molecules of micelles have a major role for consequent hydrophobic interac-

R. Hosseinzadeh et al. / Spectrochimica Acta Part A 69 (2008) 1183–1187

1185

Table 1 The values of binding constant, partition coefficient and related Gibbs energies for interaction and solubilization of light yellow dye ([X6G] = 5 × 10−6 mol dm−3 ) with/in CPC and CTAB micelles Surfactant

Kb

G◦b (kJ/mol)

Kx

G◦x (kJ/mol)

CPC CTAB

148 348

−12.38 −14.49

11,100 27,028

−23.08 −25.28

so Eqs. (1) and (2) can be established: Dye + Surfactant  [Complex]

(1)

[Complex] [Dye][Surfactant]

(2)

Kb = Fig. 2. Visible absorption spectra of light yellow ([X6G] = 5 × 10−6 mol dm−3 ) at various concentrations of CPC.

where Kb is binding constant, by assuming [Complex] = Cb : Kb =

tions and dye penetration and distribution between micelle and water phases. As mentioned above, Figs. 2 and 3 directly indicate the solubilization of dye in CPC micelles. Although the dye molecules are incorporated in the micelles, their chromophores are still oriented near the surface and hence absorb light more favorably than in the aqueous balk solution [29]. More hydrophobic dyes displayed a higher increase in A than less hydrophobic dyes. Results show that light yellow azo dye (X6G) interact with CTAB micelles better than CPC micelles and distribute in CTAB micelles more favorable than in CPC micelles (see results in Table 1). 3.1. Determination of binding constant The values of the binding constants Kb were obtained according to the methods described previously [31–33]. According to this fact that the binding of surfactant to dye is an equilibrium,

Cb (CDye − Cb )(CSurfactant − Cb )

(3)

where CDye and CSurfactant are the analytical concentrations of dye and surfactant in solution, respectively. According to the Beer–Lambert law: A0 εDye l

(4)

A − A0 εb l

(5)

CDye = Cb =

where A0 and A are the absorbance of dye at maximum absorption wavelength in the absence and presence of surfactant, respectively. εDye and εb are the molar extinction coefficients of dye and the complex, respectively. l is the light path of the cuvette (1 cm). By displacing CDye and Cb in Eq. (3) by Eqs. (4) and (5), Eq. (6) can be deduced: εDye εDye A0 1 = + A − A0 εb εb K Csurfactant

(6)

Plot of 1/(A − A0 ) versus 1/Csurfactant is linear and the binding constant (Kb ) can be estimated from the ratio of the intercept to the slope. Fig. 4 shows the plot of 1/(A − A0 ) versus 1/Csurfactant , at specified experimental conditions for dye–CPC micelles, similar plot has been obtained for dye–CTAB micelles interactions. 3.2. Determination of partition coefficient Absorbance values obtained at λmax , can be also used for the calculation of partition coefficient, Kx , defined according to the pseudo-phase model as Kx = Fig. 3. The differential absorbance change of 5 × 10−6 mol dm−3 light yellow with concentration of CPC at related maximum absorption wavelength.

m XDye w XDye

(7)

m and Xw are the mole fractions of dye in micellar where XDye Dye and aqueous phase, respectively. They are related with concen-

1186

R. Hosseinzadeh et al. / Spectrochimica Acta Part A 69 (2008) 1183–1187

Fig. 4. The plot of 1/(A − A0 ) vs. 1/CSurfactant for dye–CPC interactions, where A0 is the initial absorption band of pure light yellow dye and A is the recorded absorption at different surfactant concentrations.

trations of species in the solubilization system: m XDye

=

w XDye =

m CDye m + Cm CDye surfactant w CDye w + Cw CDye surfactant + nw

(8)

(9)

w m and Csurfactant represent concentrations of where Csurfactant surfactant in micellar and monomeric states, and nw = 55.5 mol dm−3 is the molarity of water. Under the present w + Cw experimental conditions CDye surfactant nw , if we express KS = Kx /nw , we get the equation:

KS =

m /(C m + C m CDye Dye surfactant ) w CDye

m CDye

CDye

A A∞

G◦b = −RT ln Kb

(14)

From Eq. (15), the standard free energy change of the transfer of dye from bulk water phase to micellar phase can be obtained G◦x = μ0m − μ0m = −RT ln Kx

(15)

The values of G◦b , G◦x and related equilibrium constants (K) are summarized in Table 1.

(11)

4. Conclusion

At a certain CDye , f is equal to zero in the non-micellar region up to CMC and increases with increasing the concentration of surfactant above CMC. As Csurfactant increases up to infinity, f approaches unity since all added dye should be solubilized in micelles. The fraction f can be directly calculated from the experimental data using Eq. (12): f =

plot of 1/A versus 1/(CDye + Csurfactant − CMC) for light yellow solubilization in CPC micelles, similar plot has been obtained for dye solubilization in CTAB micelles (results summarized at Table 1). The Gibbs energy of binding can be obtained by the following equations:

(10)

The fraction f of the associated dye may be defined as f =

Fig. 5. Relation between 1/(A − A0 ) and 1/(Cdye + CSurfactant − CMC) for light yellow dye (C = 5 × 10−6 M) and CPC surfactant interactions.

(12)

where A = A − Aw and A∞ = A∞ − Aw , A∞ being the absorbance of dye completely bound to surfactant. By using Eqs. (11) and (12), Eq. (10) can be written in linear form: 1 1 1 = (13) + ∞ ∞ A A KS A (CDye + CSurfactant − CMC) KS and Kx (KS = Kx /nw ) is obtained from the slope of the plot of 1/A versus 1/(CDye + Csurfactant − CMC). Fig. 5 shows the

It has been expected that the interaction between light yellow dye (X6G) and cationic CTAB micelles would be the strongest than CPC micelles. This is supported with diminishing of A increasing by increasing CPC surfactant concentration. As mentioned before this diminish, in A increasing, indicate that dye interact with CPC micelles weekly in comparison with CTAB micelles and consequently dye solubilization in CTAB micelles has been done better than CPC micelles. Due to this fact that both CTAB and CPC surfactants have same hydrophobic hydrocarbon tail and differ only at the hydrophilic cationic charge head groups, so it would be clear that charged head group of surfactants have great effect on dye–surfactant interactions and dye micellar solubilization. Although the hydrophobic tail has major role in dye micellar solubilization, the initial electrostatic interactions is essential in these interaction. In the here CPC week interaction, in comparison to CTAB strong interaction, is due to the specific effect of aromatic cationic head group of the CPC versus quaternary ammonium cationic head group of CTAB micelles in surfactant interaction with X6G anionic dye.

R. Hosseinzadeh et al. / Spectrochimica Acta Part A 69 (2008) 1183–1187

Acknowledgement Financial supports of the Jahad-E-Daneshgahi of Urmia are gratefully appreciated.

[14] [15] [16] [17] [18]

References [1] H. Hoiland, M.I. Gjerde, C. Mo, E. Lie, Colloid Surf. A 183 (2001) 651. [2] H. Hoffmann, W. Ulbricht, in: H.-J. Hinz (Ed.), Thermodynamic Data for Biochemistry and Biotechnology, Springer, Heidelberg, 1986. [3] S.D. Christian, J.F. Scamehorn, Solubilization in Surfactant Aggregates, Marcel Dekker, New York, 1995. [4] A.R. Tehrani Bagha, H. Bahrami, B. Movassagh, M. Arami, F.M. Menger, Dyes Pigm. 72 (2007) 331. [5] E.O. Goddard, in: E.D. Goddard, K.P. Ananthapadamanabham (Eds.), Interactions of Surfactants with Polymer and Proteins, CRC Press, Boca Raton, FL, 1993. [6] S.M. Ghoreishi, M. Shabani Nooshabadi, Dyes Pigm. 65 (2005) 117. [7] P.C. Hiemenz, in: J.J. Lagowski (Ed.), Principles of Colloid and Surface Chemistry, 2nd ed., Marcel Dekker, New York, 1986. [8] I.V. Berezin, K. Martinek, A.K. Yatsimirskii, Russ. Chem. Rev. 42 (1973) 787. [9] O. Cudina, K. Karljikovic-Rajic, I. Ruvarac-Bugarcic, I. Jankovic, Colloid Surf. A. 256 (2005) 225. [10] C.O. Rangel-Yagui, H.W. Ling Hsu, A. Pessoa-Jr, L. Costa Tavares, Braz. J. Pharm. Sci. 41 (2005) 237. [11] K. Fujio, T. Mitsui, H. Kurumizawa, Y. Tanaka, Y. Uzu, Colloid Polym. Sci. 282 (2004) 223. [12] P.H. Elworthy, A.T. Florence, C.B. Macfarlane, Solubilization by SurfaceActive-Agents, Chapman & Hall, London, 1968. [13] J.C. Lim, C.A. Millar, Langmuir 7 (1991) 2021.

[19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33]

1187

E. Nurnberg, W. Pohler, Prog. Colloid Polym. Sci. 69 (1984) 48. I. Xiarchos, D. Doulia, J. Hazard. Mater. 136 (2006) 882. C.A. Bunton, L. Sepulveda, J. Phys. Chem. 83 (1979) 680. G.A. Smith, S.D. Christian, E.E. Tucker, J.E. Scamhorn, J. Colloid Interf. Sci. 130 (1989) 254. R.S. Tsai, W. Fan, N. El Tayer, P.A. Carrupt, B. Testa, L.B. Kier, J. Am. Chem. Soc. 115 (1993) 9632. C. Hirose, L. Sepulveda, J. Phys. Chem. 85 (1981) 3689. R. Hosseinzadeh, A.K. Bordbar, A.A. Matin, R. Maleki, J. Braz. Chem. Soc. 18 (2007) 359. O. Cudina, I. Jankovic, M. Comor, S. Vladimirov, J. Colloid Interf. Sci. 301 (2006) 692. K. Naeem, S.S. Shah, S.W.H. Shah, G.M. Laghari, Monatshefte fur Chemie 131 (2000) 761. S.S. Shah, K. Naeem, S.W.H. Shah, H. Hussian, Colloid Surf. A 148 (1999) 299. S.S. Shah, G.M. Laghari, K. Naeem, S.W.H. Shah, Colloid Surf. A 134 (1998) 111. S.S. Shah, G.M. Laghari, K. Naeem, Thin Solid Film 346 (1999) 145. S.S. Shah, K. Naeem, S.W.H. Shah, G.M. Laghari, Colloid Surf. A 168 (2000) 77. S.S. Shah, R. Ahmad, S.W.H. Shah, K.M. Asif, K. Naeem, Colloid Surf. A 137 (1998) 301. H. Kawamura, M. Manabe, Y. Miyamoto, Y. Fujita, S. Tokunga, J. Phys. Chem. 93 (1989) 5536. Y. Miyashita, S. Hayano, Bull. Chem. Soc. Jpn. 54 (1981) 3249. C.O. Rangel-Yagui, A. Pessoa-Jr, L. Costa Tavares, J. Pharm. Pharmaceut. Sci. 8 (2005) 147. C.D. Kanakis, P.A. Tarantilis, M.G. Polissiou, S. Diamantoglou, H.A. Tajmir-Riahi, J. Mol. Struct. 798 (2006) 69. J.J. Stephanos, J. Inorg. Biochem. 62 (1996) 155. L. Sepulveda, J. Colloid Interf. Sci. 46 (1974) 372.