Adsorptive removal of methylene blue from wastewater using sawdust of Cedrus deodara and its composite with iron oxide nanoparticles: a comparative study

The aim of this study was to prepare a composite of sawdust of Cedrus deodara with iron oxide nanoparticles (CDION) and to use this sawdust and its composite as adsorbents for the removal of methylene blue (MB) from wastewater. Iron oxide nanoparticles (NPs) were prepared by co-precipitation method and both the adsorbents were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) surface area and pore size analysis. These analyses showed successful loading of iron oxide NPs onto the fibrous surface of sawdust in agglomerated form and specific surface area of the nano-composite was found to be 172 m²/g. The BET surface area of uncoated sawdust (CD) was about 6.8 m²/g. The Freundlich adsorption isotherm gave a better fit for CD while the Langmuir adsorption isotherm better described adsorption process on CDION. The maximum adsorption capacities were 406.52 mg/g for CD and 417.70 mg/g for CDION. Maximum dye adsorption occurred above pH 3 for CD and above pH 4 for CDION. Kinetic study showed that adsorption of MB on both adsorbents followed pseudo second order kinetics to a greater extent than pseudo first order. The values of Gibbs free energy change, activation energy, and other thermodynamic parameters for adsorption supported the occurrence of physical adsorption of MB on both adsorbents. The adsorption process was found to occur through film diffusion. Thermodynamic parameters showed that the adsorption process was spontaneous, as indicated by negative Gibbs free energy change values, endothermic and resulted in increase in randomness as enthalpy and entropy changes were positive.