Promoted generation of singlet oxygen by hollow-shell CoS/g-C3N4 catalyst for sulfonamides degradation

Sulfanilamide (SM), which is a representative drug of sulfonamides, is commonly used for the prevention and treatment of bacterial infectious diseases and is extremely difficult to remove from water. Herein, an efficient catalyst (CoS/CN) for sulfanilamide degradation was constructed by CoS self-assembling on ultrathin graphitic carbon nitride (g-C3N4) nanosheets. The prepared hollow-shell CoS/CN catalyst could completely degrade SM within 10 min with a rate constant of 2.49 min−1 through the activation of peroxymonosulfate (PMS). Experiments and theoretical calculations indicated that S2− acted as an electron donor for promoting the generation of Co(II). The combination of g-C3N4 and CoS made the CoS/CN composite have higher conductivity and electron transfer ability than CoS, which promoted the decomposition of PMS to produce reactive oxygen species (ROSs). Singlet oxygen (1O2) was proved as the primary ROSs, and SO4− radicals were generated during the 1O2-dominated degradation process to improve the low mineralization rate. 1O2 and SO4− were derived from the oxidation of PMS and the electron transfer of g-C3N4. The results revealed the synergistic effect of free radicals and non-free radicals during the redox of PMS, and provided theoretical support for the efficient degradation of refractory organics in wastewater.