Journal of Colloid and Interface Science 289 (2005) 42–47 www.elsevier.com/locate/jcis Interaction of Ag(I), Hg(II), and Cu(II) with 1,2-ethanedithiol immobilized on chitosan: Thermochemical data from isothermal calorimetry Eunice F.S. Vieira a,∗ , Antonio R. Cestari a , Elias de B. Santos a , Francisco S. Dias b a Laboratory of Materials and Calorimetry, Departamento de Química/CCET, Universidade Federal de Sergipe, 49100-000, São Cristóvão, Sergipe, Brazil b Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, 60455-760, Fortaleza, Ceará, Brazil Received 21 January 2005; accepted 19 March 2005 Available online 17 May 2005 Abstract The nature of interactions between metal ions Ag(I), Hg(II), Cu(II) and chitosan derivative of 1,2-ethanedithiol, QTDT, was investigated by isothermal calorimetry using the membrane breaking technique. Simultaneous determination of thermal effects, Q int , and amount of cation that interacts, n int , are described. The experimental data have been interpreted in terms of the Langmuir equation to determine the maximum adsorption capacity to form a monolayer, N mon , and the energy of interaction for a saturated monolayer per gram of QTDT, Q mon . With N mon and Q mon , the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of QTDT,  mon H m , was determined. The  mon H m values for Ag(I), Hg(II), and Cu(II) were −60.56, −58.05, and −84.36 kJ mol −1 , respectively. Negative values of G show the spontaneity of the interaction processes. The least entropically favourable processes, i.e., those which present more negative S values, seem to be compensated by the more favourable enthalpic parameter.  2005 Elsevier Inc. All rights reserved. Keywords: Isothermal calorimetry; Interaction of metal ions; Adsorption; Chitosan 1. Introduction Chitosan [poly(N -deacetyl glucosamine)] is a natural polymer that has potential application in several areas of science [1–14]. It is obtained by N -deacetylation of chitin, which is the second-most-abundant naturally occurring polymer found in the exoskeleton of marine crustaceans and the second-most-abundant biopolymer next to cellulose [15]. Chitosan, like most biopolymers, has the property of remov- ing metal ions from wastewater, and such property has been regarded as an area worthy of further investigation. The adsorption of metal ions by certain naturally occur- ring biopolymers and synthetic polymers has gained much * Corresponding author. Fax: +55 79 212 6684. E-mail address: eunice@ufs.br (E.F.S. Vieira). attention. This area of science has been stimulated by some problems of great practical importance such as the adsorp- tion in soil of highly poisoning cations of some heavy el- ements [16–18]. Amongst the range of contaminants that may be found in soils, potentially toxic heavy metals are of particular interest because they show a tendency, under nor- mal circumstances, to accumulate in soils and have a long persistence time because of their interactions with particu- lar soil components. Finally, many of the heavy metals are essential, at low concentrations, for plant, animal, and hu- man health, but, at higher concentrations, they can be toxic. Changes in concentration of heavy metals can be signifi- cantly altered with profiles through a number of biological and chemical processes. Numerous research efforts are being done to develop methods of removing heavy metal ions and attention has to be given to new efficient alternatives such as removal by sorption. Soluble heavy metals can be removed 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.03.043