Facile preparation of S/Fe composites as an effective peroxydisulfate activator for RhB degradation

• Sulfur-modified iron oxides were synthesized by facile co-precipitation.
• Neutral pH condition was found as the best pH for RhB degradation.
• The reactivity of iron oxide was greatly enhanced by S-modification.
• S-modification could accelerated electron transfer between iron and persulfate.

A sulfur modified iron oxide composite (S/Fe) was synthesized via facile co-precipitation of ferrous sulfate, sodium thiosulfate and sodium hydroxide followed by air calcination. Characterization results showed that thiosulfate could coordinate with ferrous ions and promote the generation of pyrite to activate PDS. We found that S/Fe composites exhibited a much higher reactivity for PDS activation for RhB degradation than that of non-modified iron oxides. Increasing activator dosage or PDS concentration resulted in increased oxidation efficiency. Neutral pH condition was found to be the best pH for RhB degradation. Different initial pH could significantly influence the radical species generated from PDS activation. Sulfate radical was assumed to be the dominant radical under neutral pH, and conversion of sulfate radicals to hydroxyl radicals occurred at alkaline conditions. The addition of thiosulfate anions into Fe2O3/PDS system would greatly promote RhB removal, but thiosulfate alone was unable to activate PDS for contaminants degradation, indicating that the S-modification may accelerate electron transfer between iron and PDS. In summary, these results show that iron oxides with sulfide modification could be an attractive material for environmental application.