Degradation of a synthetic binary dye mixture using reactive adsorption: Experimental and modeling studies

Simultaneous reactive adsorption of Methylene Blue (MB) and Safranin O (SO) was carried out from a binary aqueous mixture using Fe-GAC/H2O2. Maximum simultaneous removal was found to be 96.2% and 90.2% for MB and SO respectively after 7 h of reactive adsorption using 0.5 g/L Fe-GAC and 20 mM H2O2 optimized doses. Degradation activities of the dyes were accelerated by increasing temperature from 15 to 35 °C. Apparent kinetic reaction rate constant was also increased with increasing temperature and consequently, activation energies of the degradation of individual dyes present in mixture were estimated and found to be 28.59 kJ mol−1 and 32.53 kJ mol−1 for MB and SO respectively. Thermodynamic parameters for MB and SO activation were assessed for the degradation process. Thermodynamic study and ESI-MS analyses revealed that molecule of SO is more difficult to remove than MB. Degradation pathways for MB and SO have been proposed which indicated that the dyes were degraded via demethylation and hydroxylation processes. For pure adsorption of MB and SO, intraparticle diffusion model and extended Freundlich model were found suitable for kinetic and thermodynamic studies, respectively. A film solid pore diffusion model was developed and used to predict the surface mass transfer coefficients (kL), diffusion coefficients (D) for adsorption and reactive adsorption, along with surface reaction rate constants (kR) for reactive adsorption for a binary dye system containing MB and SO. Results from model and experiments were analogous and removal of MB was found to be faster than SO.