Thermodynamics of adsorption of food colours

Abstract

Thermodynamics of adsorption of two synthetic food colours, Tartrazine and Brilliant blue, was investigated. The adsorbent used was activated carbon, produced from saw dust waste. For each of the food colours, equilibrium studies were carried out at different temperatures (308 K, 318 K, 328 K and 338 K). The Langmuir adsorption model was employed for equilibrium studies. Amount of colour adsorbed per gram of adsorbent, at equilibrium, was influenced by molecular size of adsorbate and temperature. Adsorption at the tartrazine-adsorbent interface was exothermic, while that at the brilliant blue-adsorbent interface was endothermic. Adsorption of tartrazine was associated with a negative entropy change, while there was increased degree of disorderliness at the brilliant blue-adsorbent interface. Each of the adsorbate-adsorbent systems was associated with positive change in Gibbs free energy, within the range of temperature employed in this work.