Comparative adsorption studies of indigo carmine dye on chitin and chitosan.
The adsorption of indigo carmine dye onto chitin and chitosan from aqueous solutions was followed in a batch system. The ability of these materials to adsorb indigo carmine dye from aqueous solution was followed through a series of adsorption isotherms adjusted to a modified Langmuir equation. The maximum number of moles adsorbed was 1.24 +/- 0.16 x 10(-5) and 1.54 +/- 0.03 x 10(-4) mol g(-1) for chitin and chitosan, respectively. The same interactions were calorimetrically followed and the thermodynamic data showed exothermic enthalpic values of -40.12 +/- 3.52 and -29.25 +/- 1.93 kJ mol(-1) for chitin and chitosan, respectively. Gibbs free energies for the two adsorption processes of indigo carmine dye presented a positive value for chitin and a negative one for chitosan, reflecting that dye/surface interactions are thermodynamic favorable for chitosan and nonspontaneous for chitin at 298.15 K. The interaction processes were accompanied by an increase of entropy value for chitosan (90 +/- 6 J mol(-1)K(-1)) and a decrease for chitin (-145 +/- 13 J mol(-1)K(-1)). Thus, dye/chitosan interaction showed favorable enthalpic and entropic processes, reflecting thermodynamic stability of the formed complex, while dye/chitin interaction showed an exothermic enthalpic value and a highly nonfavorable entropic effect, resulting in a nonspontaneous thermodynamic system.
Instituto de Química, Universidade de Brasília, Caixa Postal 4478, 70919-970 Brasília, Distrito Federal, Brazil. agsprado@unb.br
Alexandre G S
AG
Prado
Jocilene D
JD
Torres
Elaine A
EA
Faria
Sílvia C L
SC
Dias
D000327:Adsorption; D002240:Carbohydrate Sequence; D002686:Chitin / Q000737:chemistry*; D048271:Chitosan / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry; D007203:Indigo Carmine / Q000737:chemistry* / Q000493:pharmacokinetics; D008969:Molecular Sequence Data; D015394:Molecular Structure; D013499:Surface Properties
D004396:Coloring Agents; D002686:Chitin; D048271:Chitosan; D007203:Indigo Carmine