Efficient adsorptive removal of methyl green using Fe3O4/sawdust/MWCNT: Explaining sigmoidal behavior

Abstract

The 4R concept (reduce, reuse, recycle and repurpose) in water management necessitates innovative adsorption techniques that utilize sustainable and natural materials. This study investigates the use of natural sawdust embedded in magnetic iron oxide to treat wastewater. The performance of the newly synthesized FeO/sawdust adsorbent was also compared to the native FeO and FeO/MWCNT. Methyl Green (MG) was used as a model pollutant due to its wide use and potential toxicity. The new adsorbents demonstrated a high removal efficiency that exceeds 97 % under ambient conditions. The study investigates the effect of pH on adsorption, revealing a significant shift in removal efficiency as pH increases, with an optimal pH of around 7. The pH dependence is explained based on the point-of-zero-charge of the FeO adsorbent and the structure of the dye. The thermodynamic parameters (Δ°, Δ°, and Δ°) of adsorption were determined through a temperature study. The adsorption equilibrium was found to be endothermic, therefore preferring elevated temperatures. Because the adsorption data of the study exhibited S-shaped-like curves, sigmoidal models were used to describe the adsorption isotherms. This provided new insights into the competitive adsorption mechanisms acting on the heterogeneous FeO/sawdust surfaces. The kinetics study indicates rapid and efficient adsorption with pseudo-second-order reaction. The half-life of the reaction was as low as 4.8 min. The findings suggest a rapid, highly efficient and sustainable method to remove organic pollutants from wastewater.