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 (M^δ+, 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 Ni^δ+/Co^δ+ 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 Ni^δ+/Co^δ+. Conversely, NiCo₂S₄, NiS, and CoS catalyzed H₂O₂ cleavage mainly via unleached Ni^δ+/Co^δ+-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 Ni^δ+/Co^δ+ leaching. Furthermore, NiCo₂S₄ revealed the greatest recyclability and mineralization efficiency in decomposing recalcitrants via ^•OH-mediated oxidation.