Calotropis procera an effective adsorbent for removal of Congo red dye: isotherm and kinetics modelling

Abstract

From environmental point of view, the removal of effluents from aquatic systems caused by presence of synthetic dyes is extremely important. Oven dried leaf powder solid waste of low-cost bioadsorbent Calotropis procera, has been tested for the removal of azo dye, Congo red (CR) from aqueous solution. Adsorption of CR onto this natural adsorbent has been characterized with X-ray fluorescence, X-ray diffraction, scanning electron microscopy and Fourier transformer infrared. The effects of different parameter such as; contact time, initial dye concentration, adsorbent amount, pH, temperature, electrolyte, surfactant concentration and desorption have been studied. The adsorption has been represented with Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich isotherm models. The maximum adsorption capacity of CR onto bioadsorbent has been found to be 25.77 mg g− 1. The adsorption process has been followed the Weber–Morris Intra-particle diffusion model with the involvement of pseudo second order and Elovich models. The calculated values of thermodynamic parameters such as ΔH and ΔS for uptake of CR have been found to be 35.26 kJ mol− 1 and 120.11 J mol− 1K− 1 respectively. Negative values of ΔG indicate the spontaneous nature of the adsorption process. The results indicate that C. procera has high potential application towards removal of CR dye due to its high adsorption capacity.