Thermodynamic and Kinetic Studies of Methylene Blue Degradation Using Reactive Adsorption and Its Comparison with Adsorption

Granular activated carbon doped with iron (Fe-GAC) was prepared and methylene blue (MB) removal efficiency was tested using reactive adsorption (Fe-GAC/H2O2) and adsorption (Fe-GAC). The color removal efficiencies of Fe-GAC/H2O2 and Fe-GAC were found to be 94% and 25%, respectively, in 3 h at 30 degrees C. The higher MB removal was achieved because of hydroxyl radical-induced oxidative degradation in the presence of Fe-GAC/H2O2 at natural pH. MB removal rate using reactive adsorption (0.015 min(-1)) was much faster than adsorption (0.004 min(-1)). Thermodynamic parameters revealed that enthalpy change was approximately one-third for reactive adsorption as that for adsorption, indicating reactive adsorption to be superior. Electrospray ionization-mass spectrometry (ESI-MS) analysis showed that reactive degradation of MB molecule followed demethylation and hydroxylation processes. The process of reactive adsorption was further investigated by identifying compounds using desorption from spent Fe-GAC through ESI-MS. Recovery and identification of such degraded compounds may be commercially attractive. An oxidative degradation pathway and a reactive adsorption scheme have been proposed.