Iron manganese Oxide Modified Multi-walled Carbon Nanotube as Efficient Adsorbent for Removal of Organic Dyes: Performance, Kinetics and Mechanism Studies

In this study, iron manganese composite oxide (FeMnO x ) were integrated with multi-walled carbon nanotube (MWCNTs) to synthesize an effective adsorbent for acid orange (AO) and basic violet (BV), two widely used organic dyestuffs belonging to anionic and cationic, respectively. Among all the composites evaluated, the FeMnO x -MWCNTs with Fe–Mn ratios of 1:1 and load ratio of 45% achieved superior adsorption capacity than others, and was selected as the best adsorbent. The Characterization data indicated that the physicochemical properties and structural characteristics of FeMnO x -MWCNTs have changed obviously after modification, with larger specific surface area and richer groups. The maximum adsorption capacity of AO (403.23 mg/g) and BV (165.29 mg/g) could be attained under optimal conditions: 300 min, 0.05 g adsorbent dosage, 100 mg/L dyes and pH 2.0 (for AO) or pH 10.0 (for BV). Moreover, the adsorption kinetics of the two dyes were both well fitted the pseudo-second-order kinetics model, and the adsorption isotherms agreed well with the Freundlich model for AO while Langmuir model for BV. Moreover, the FeMnO x -MWCNTs with optimal FeMnO x content showed relatively higher final adsorption amount and faster adsorption rate, thus better fitting with the kinetics. A mechanism was proposed that physical adsorption is the dominator during the process. The results indicated that the introduction of FeMnO x into the MWCNTs significantly enhanced the dye removal efficiency, providing a promising method for the improvement of carbon nanometer adsorbents. Graphic Abstract The selected graph can not only express the synthetic methods of FeMnO x -MWCNTs by chemical coprecipitation, but also presented the adsorption process and mechanism of AO and BV, which showed the purposes of this work simultaneously.