Global wastewater pollution issues demands developing innovative and cost-efficient techniques for wastewater treatment. The current study reports application of different metal oxide (iron, copper, zinc) doped carbon-based materials such as activated carbon (AC), groundnut shell (GS), cotton stalk (CS) and biochar (BC) for the removal of methylene blue (MB). Iron oxide-doped AC exhibited significantly higher adsorption capacity (-32 mg/g) with all the other metal oxide-doped AC having the adsorption capacity below -10 mg/g. Adsorption of MB on FeCS followed the Freundlich isotherm, suggesting multilayer adsorption on the heterogeneous active sites. Kinetic models indicated dominant chemisorption mechanisms, aligning well with the pseudo-second-order model. Higher adsorption capacity under alkaline pH conditions is attributed to the prevalence of negative charges on the surface. The presence of ultrasound further intensified the adsorption behavior resulting in a maximum removal efficiency of -90 % within 10 min. An optimum adsorbent loading of 0.5 g/L was determined for effective removal of MB. FeCS adsorbent displayed stable performance over multiple cycles, affirming its reliability for reuse. These results shed light on the practical application of biochars derived from large scale pyrolysis process for the wastewater remediation.
