Enhanced activation of sulfite by a mixture of zero-valent Fe-Mn bimetallic nanoparticles and biochar for degradation of sulfamethazine in water

Due to the inherent disadvantages of homogeneous transition metal-activated sulfite system, such as narrow pH range, slow Fe3+/Fe2+ circulation and low electron transfer efficiency, the heterogeneous system of zero-valent Fe-Mn bimetallic nanoparticles (ZVFMB) physically mixed with biochar (BC) to activate sulfite(S(IV)) was developed to improve the removal of sulfamethazine (SMT). The results showed that the heterogeneous ZVFMB-BC/S(IV) system could rapidly degrade 92% of SMT within 15 min, because of the formation of a large number of active radicals, mainly hydroxyl radicals (62.2%). Through in-depth discussion, we found that due to the obvious defect structure (ID/IG = 2.05) and abundant phenolic hydroxyl groups on the surface of biochar, biochar was fully qualified for the roles of electron shuttle and electron donor, which were verified by various characterization methods such as FTIR, Raman and linear sweep voltammetry (LSV). Startlingly, it was worth mentioning that biochar can be activated in situ in the oxidation process to form micropores and increase the surface area and pore volume, which facilitated the rapid degradation of SMT. Moreover, this system also shows excellent performance in other water bodies, such as simulated groundwater under neutral or weak acidic conditions and water bodies with other pollutants (e.g., SBD, CBZ, ATZ). All in all, compared to the traditional Fe/Mn ions activated sulfite system, this system has a wide range of pH tolerance, high electron transfer efficiency and excellent degradation rate, showing great potential for application in the degradation of organic pollutants.