Removal of basic yellow dye from aqueous solution by sorption on green alga Caulerpa scalpelliformis

Dynamic batch experiments were carried out for the biosorption of basic yellow dye on to the green macroalgae Caulerpa scalpelliformis. The factors affecting the sorption process such as the initial concentration of the dye and pH of the solution, the adsorbent dosage and the time of contact were studied. The sorption kinetics followed pseudo-second order kinetic model. The Caulerpa species exhibited a maximum uptake of 27 mg of dye per gram of seaweed. The Boyd's plot confirmed the external mass transfer as the rate-limiting step. The average effective diffusion coefficient was found to be 2.47 × 10−4 cm2/s. Sorption equilibrium studies demonstrated that the biosorption followed Freundlich isotherm model, which implies a heterogeneous sorption phenomenon. Various thermodynamic parameters such as enthalpy of sorption ΔH°, free energy change ΔG° and entropy ΔS° were estimated. The negative value of ΔH° and negative values of ΔG° show the sorption process is exothermic and spontaneous. The negative value of entropy ΔS° shows the decreased randomness at the solid-liquid interface during the sorption of dyes onto green seaweed.