Grasping periodic trend and rate-determining step for S-modified metals of metal sulfides deployable to produce OH via H₂O₂ cleavage

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Iron sulfides are fascinating catalytic phases because these include S-modified Fe<SUP>δ+</SUP> (δ ≤ 2) species functioning as H<SUB>2</SUB>O<SUB>2</SUB> activators to form <SUP> </SUP>OH used for oxidatively degrading aqueous contaminants (e.g., phenol). As an initial step for locating S-modified metal species (M<SUP>δ+</SUP>) that outperform Fe<SUP>δ+</SUP> in catalytic H<SUB>2</SUB>O<SUB>2</SUB> cleavage, hexagonal metal sulfides (MS) were synthesized using Mn, Fe, Co, Ni, and Cu to understand electric potential-assisted H<SUB>2</SUB>O<SUB>2</SUB> scission kinetics on M<SUP>δ+</SUP> species. Ni<SUP>δ+</SUP> species were found to show the greatest <SUP> </SUP>OH productivity among all M<SUP>δ+</SUP> species studied, mainly resulting from the Lewis acidic nature of Ni<SUP>δ+</SUP> species adequate to expedite the liberation of <SUP> </SUP>OH species. This was partially evidenced by H<SUB>2</SUB>O<SUB>2</SUB> activation/phenol degradation runs on M<SUP>δ+</SUP> species, wherein initial H<SUB>2</SUB>O<SUB>2</SUB> activation rate (-r<SUB>H2O2,0</SUB>) or initial phenol degradation rate (-r<SUB>PHENOL,0</SUB>) of Ni<SUP>δ+</SUP> species was 3–9 times those of the other M<SUP>δ+</SUP> species. Ni<SUP>δ+</SUP> species, therefore, were located in the middle of the volcano-shaped curve plotting -r<SUB>H2O2,0</SUB> (or -r<SUB>PHENOL,0</SUB>) versus the type of M<SUP>δ+</SUP>. Kinetic assessment of M<SUP>δ+</SUP> species under fine-tuned reaction environments also showed that regardless of varying H<SUB>2</SUB>O<SUB>2</SUB> concentrations, M<SUP>δ+</SUP> species were found to retain their -r<SUB>H2O2,0</SUB> values in the absence of electric potentials. Conversely, M<SUP>δ+</SUP> species could enhance -r<SUB>PHENOL,0</SUB> values at larger electric potentials, where greater energies were likely exerted on M<SUP>δ+</SUP> species. This indeed corroborated that <SUP> </SUP>OH desorption from M<SUP>δ+</SUP> species was the rate-determining step to direct catalytic H<SUB>2</SUB>O<SUB>2</SUB> scission. In addition to heterogeneous catalytic nature of Ni<SUP>δ+</SUP> species in fragmenting H<SUB>2</SUB>O<SUB>2</SUB>, outstanding H<SUB>2</SUB>O<SUB>2</SUB> scission ability provided by Ni<SUP>δ+</SUP> species could also compensate for their moderate catalytic stability at pH-neutral condition.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Metal sulfides (MS) consisting of S-modified Group IV metals such as Mn, Fe, Co, Ni, and Cu. </LI> <LI> Ni<SUP>δ+</SUP> of NiS (δ ≤ 2) with the greatest initial H<SUB>2</SUB>O<SUB>2</SUB> scission rate to produce <SUP> </SUP>OH (-r<SUB>H2O2, 0</SUB>). </LI> <LI> Ni<SUP>δ+</SUP> of NiS located in the center of a volcano-shaped curve plotting –r<SUB>H2O2,0</SUB> versus M<SUP>δ+</SUP>. </LI> <LI> M<SUP>δ+</SUP> of metal sulfides with the rate-determining step of <SUP> </SUP>OH desorption to direct phenol degradation. </LI> <LI> Ni<SUP>δ+</SUP> of NiS with the greatest initial phenol degradation rate with the moderate recyclability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>