Degradation of 2,4-dinitrotoluene by iron sulfide/manganese sulfide–biochar composites in the presence of persulfate and hydrogen peroxide

BACKGROUND

Iron sulfide/manganese sulfide (FeS/MnS)–biochar composites were synthesized and their effectiveness at removing 2,4-dinitrotoluene (DNT) from water was evaluated. It was hypothesized that FeS/MnS–biochar composites have large surface areas for DNT sorption and reduction, and the capacity to promote persulfate- and hydrogen peroxide (H₂O₂)-mediated DNT oxidation.

RESULTS

Compared to removal by biochar alone, the removal of DNT by 2 and 50wt.% FeS–biochar composites (1 g dosage) was enhanced via sorption and reduction by 37% and 48%, respectively. As the biochar increased the pH, however, the FeS–biochar composite was not as effective as FeS alone at removing DNT, indicating that an acidic medium may be necessary for the reductive removal of DNT by the FeS–biochar composite. In contrast, MnS and MnS–biochar composite were not as effective at reducing DNT as FeS and the FeS–biochar composite. FeS–biochar composites demonstrated good catalytic efficacy and enhanced persulfate- and H₂O₂-mediated DNT oxidation. The 50 wt% FeS–biochar composite (5 g dosage) removed 93% and 100% of DNT in the presence of persulfate/H₂O₂ (3 mmol L⁻¹), respectively, under the given conditions. Both the Fe²⁺ in the FeS and the carbon in the FeS–biochar composites contributed to the catalytic enhancement of the DNT oxidation. Radical quenching tests and electron paramagnetic resonance spectroscopic analysis revealed that sulfate (SO₄⁻∙) and hydroxyl (OH∙) radicals are dominant radical species to account for the enhancement of DNT oxidation. In contrast, neither Mn²⁺ nor S²⁻ in MnS and MnS–biochar composite worked as a catalyst to enhance the DNT oxidation by persulfate/H₂O₂.

CONCLUSION

The results of the present study indicate that FeS and FeS–biochar composites are promising as sorbents, reductants, and catalysts for the remediation of environmental DNT contamination. © 2025 Society of Chemical Industry (SCI).