Functionalizing biochar by Co-pyrolysis shaddock peel with red mud for removing acid orange 7 from water

Biochar modification by metal/metal oxide is promising for improving its adsorption capability for contaminants, especially the anions. However, conventional chemical modifications are complicated and costly. In this study, novel Fe/Fe oxide loaded biochars (RMBCs) were synthesized from a one-step co-pyrolysis of red mud (RM) and shaddock peel (SP), and their potential application for removing anionic azo dye (acid orange 7, AO7) from the aqueous environment was evaluated. Fe from red mud was successfully loaded onto biochars pyrolyzed at 300-800 degrees C, which presented from oxidation form (Fe2O3) to the reduction forms (FeO and Fe-0) with increasing pyrolysis temperature. The RMBC produced at 800 degrees C with RM:SP mass ratio of 1:1 (RMBC800(1:1)) exhibited the best capability for AO7 removal (similar to 32 mg/g), attributed to both adsorption and degradation. The higher surface area of RMBC8001:1 and its greater affinity for AO7 led to the higher adsorption. In addition, RMBC800(1:1)-induced degradation of AO7 was another key mechanism for AO7 removal. The reduction forms of Fe (FeO or Fe-0) in RMBC800(1:1) may provide electrons for breaking down the azo bond in AO7 molecules and result in degradation, which is further enhanced in acid conditions due to the participation of readily release of Fe2+ and the available H+ in AO7 degradation. Furthermore, RMBC800(1:1) can be easily separated from the treated water by using magnetic field, which significantly benefits its separation in wastewater treatment.

Automated summary

In this study, Fe/Fe oxide loaded biochars (RMBCs) were synthesized from red mud and shaddock peel, and their potential for removing anionic azo dye from water was evaluated. The results showed that high pyrolysis temperature and appropriate loading ratio can enhance the adsorption and degradation capability of biochars towards AO7. Additionally, the RMBCs can be easily separated from water using a magnetic field.