Unravelling lewis acidic and reductive characters of normal and inverse nickel-cobalt thiospinels in directing catalytic H2O2 cleavage

(Inverse) spinel-typed bimetallic sulfides are fascinating H2O2 scissors because of the inclusion of S2-, which can regenerate metals (Mδ+, δ ≤ 2) used to produce •OH via H2O2 dissection. These sulfides, however, were under-explored regarding compositional, structural, and electronic tunabilities based on the proper selection of metal constituents. Motivated by S-modified Niδ+/Coδ+ promising to H2O2 cleavage, Ni2CoS4, NiCo2S4, NiS/CoS were synthesized and contrasted with regards to their catalytic traits. Ni2CoS4 provided the greatest activity in dissecting H2O2 among the catalysts. Nonetheless, Ni2CoS4 catalyzed H2O2 scission primarily via homogeneous catalysis mediated by leached Niδ+/Coδ+. Conversely, NiCo2S4, NiS, and CoS catalyzed H2O2 cleavage mainly via unleached Niδ+/Coδ+-enabled heterogeneous catalysis. Of significance, NiCo2S4 provided Lewis acidic strength favorable to adsorb H2O2 and desorb •OH compared to NiS and CoS, respectively. Of additional significance, NiCo2S4 provided S2- with lesser energy required to reduce M(δ+1)+ via e- transfer than NiS/CoS. Hence, NiCo2S4 prompted H2O2 scission cycle per unit time better than NiS/CoS, as evidenced by kinetic assessments. NiCo2S4 was also superior to Ni2CoS4 because of the elongated lifespan anticipated as •OH producer, resulting from heterogeneous catalysis with moderate Niδ+/Coδ+ leaching. Furthermore, NiCo2S4 revealed the greatest recyclability and mineralization efficiency in decomposing recalcitrants via •OH-mediated oxidation.