Adsorption studies of cationic dyes onto Ashoka (Saraca asoca) leaf powder

In present study, batch adsorption experiments were carried out using ashoka leaf powder (ALP), a low cost, locally available biomaterial as an adsorbent for the removal of cationic dyes such as methylene blue, malachite green, rhodamine B and brilliant green from aqueous solution. The ALP was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM). Effect of various physico-chemical parameters such as pH, ionic strength, adsorbent dose, contact time, initial dye concentration and temperature were investigated and optimal experimental conditions were ascertained. Available models like Lagergren's pseudo-first order kinetics, Ho's pseudo-second order kinetics and intraparticle diffusion were used to evaluate the kinetics and the mechanism of the adsorption. The Langmuir, Freundlich, Temkin and Scatchard isotherm models were tested to represent the equilibrium data and the constants of the isotherms were determined by using the experimental data. Thermodynamic parameters such as change in Gibb's free energy (ΔG°), change in enthalpy (ΔH°) and change in entropy (ΔS°) were calculated to predict the nature of adsorption process.

► Saraca asoca leaf powder has been fruitfully employed for the removal of hazardous cationic dyes from aqueous solution. ► Adsorption followed pseudo-second order and intraparticle diffusion model. ► Freundlich isotherm model was found to be best fit and Temkin isotherm model was least fit in adsorption equilibrium data. ► Thermodynamic data showed that the adsorption process was spontaneous and feasible in nature and exothermic. ► Quantitative recovery of the dye and adsorbent was done.