Nano-zerovalent manganese/biochar composite for the adsorptive and oxidative removal of Congo-red dye from aqueous solutions

Congo-red (CR), a precursor of textile products and a contaminant of great concern, has contaminated aquatic environments. Here, we explored the synthesis of mesoporous nano-zerovalent manganese (nZVMn) and Phoenix dactylifera leaves biochar (PBC) composite for the removal of CR from water. The nZVMn/PBC adsorbed 117.647 mg/g of CR versus 25.316 mg/g by PBC at [CR](0) = 20 mg/L and [PBC](0) = [nZVMn/PBC](0) = 500 mg/L. Variation of [nZVMn/PBC](0), [CR](0) and pH influenced the adsorption of CR. Freundlich adsorption isotherm and pseudo-first-order kinetic models best fitted CR adsorption. The H2O2 coupling with nZVMn/PBC promoted removal of CR possibly due to the formation of hydroxyl radical ((OH)-O-center dot) and caused 95 % removal of CR versus 77 % by nZVMn/PBC alone. The (OH)-O-center dot scavengers inhibited the removal of CR. The nZVMn/PBC showed a good reusability and efficient removal of CR up to the seventh cycle of treatment. Results reveal that nZVMn improved performance, thermal stability and reusability of biochar. Degradation products from (OH)-O-center dot-mediated degradation of CR were studied by ultraperformance liquid chromatography with mass spectrometric detector to establish degradation pathways. The ion-chromatographic analysis showed the formation of non-toxic inorganic acetate product, which suggests high potential of the newly fabricated adsorbent in the removal of CR.

Automated summary

The composite of nZVMn and PBC showed higher adsorption capacity for CR compared to PBC alone, and the addition of H2O2 further enhanced the removal efficiency. The study also revealed the formation of non-toxic inorganic acetate products during the degradation process, indicating the potential of the new adsorbent for CR removal.