Natural surfactant extracted from Sapindus mukurossi as an eco-friendly alternate to synthetic surfactant e a dye surfactant interaction study Sidra-Tul Muntaha, M. Nasiruddin Khan * Department of Chemistry, University of Karachi, Karachi 75270, Pakistan article info Article history: Received 7 April 2014 Received in revised form 29 December 2014 Accepted 8 January 2015 Available online xxx Keywords: Natural surfactant Critical micelle concentration Sodium dodecyl sulfate Conductance Spectrophotometry abstract The comparative study between synthetic and natural surfactants was carried out using spectropho- tometry, conductometric and surface tension measurement. The value of critical micelle concentration for the natural surfactant was determined. The influence of temperature on conductance was observed and the interaction is found favorable at low temperature. The comparative interaction behavior of the surfactants was studied by reacting them individually with an oppositely charged dye. The concentration of both the surfactants was varied from pre to post micellar region to examine spectral changes. It was detected that the variation in the concentration of surfactant leads to the changes in the spectra of dye. The study showed that the initial increase in surfactant concentration leads to the formation of stable ion-pair, but increasing concentration beyond its critical micelle concentration caused the dissolution of dye surfactant aggregates. The surface tension measurement was also performed. The values for equi- librium constant and Gibbs free energy were calculated based on the theoretical model. On the basis of these values, it is stated that the interaction between natural surfactant and dye is thermodynamically favorable and competitive. The use of natural surfactant in place of synthetic surfactant is suggested as an inexpensive, environmental friendly and cleaner substitute. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Amphiphiles that possess surface active properties are known as surfactants. These agents contain both lipophilic and hydrophilic groups in them so they exhibit fascinating and exclusive behavior. Due to the behavior of surfactant, they are widely applicable in industries as a wetting, flocculating and foaming agents, adhesives, penetrators and de-emulsifiers (Mulligan, 2005, 2009; Gharaei- Fathabad, 2011). The widespread use of surfactants in different areas led the foundation of surfactant science. Surfactant science starts getting its recognition as a separate field and also experi- encing advancement day by day. This advancement in the tech- nology of surfactant results in the addition of the huge variety of surfactants. The upgradation of this technology can also impose some serious environmental issues (Chevalier, 2002). Environ- mental concerns on the use of surfactants initiate the interest of the researchers to use alternates to synthetic surfactants. The alter- nates can be natural surfactants. The surfactants that are obtained directly from the natural source are considered as natural surfactants. These surfactants can be obtained either from the source having plant origin or animal origin. During the collection of surfactant from the source, no organic synthesis should have been involved not even as after treatment. Some sort of separation techniques like extraction, filtration, precipitation or distillation should be adopted to acquire the product. The term “natural surfactant” was used by many re- searchers to consider the molecules that are coming indirectly from natural raw materials under this term (Holmberg, 2001; Rybinski, 2001; Salati et al., 2011). In literature, many examples of natural surfactants are reported. Molecule (saponin) derived from the plants belonging to the genus Sapindaceae can be the possible alternative for synthetic surfactants as identified by Roy et al. (1997) and Kommalapati et al. (1997). The other natural surfac- tants like fatty acid esters of sugars and fatty acid esters or amides of amino acids have been suggested to be used as surfactant in the place of synthetic surfactant (Holmberg, 2001; Salati et al., 2011; Johansson and Svensson, 2001). As stated by Holmberg (2001), * Corresponding author. Tel.: þ92 3142134934. E-mail address: nasiruk@uok.edu.pk (M.N. Khan). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro http://dx.doi.org/10.1016/j.jclepro.2015.01.023 0959-6526/© 2015 Elsevier Ltd. All rights reserved. Journal of Cleaner Production xxx (2015) 1e6 Please cite this article in press as: Muntaha, S.-T., Khan, M.N., Natural surfactant extracted from Sapindus mukurossi as an eco-friendly alternate to synthetic surfactant e a dye surfactant interaction study, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.01.023