Grasping pros and cons of SiO2 proximal to Lewis acidic metal cations in activating H2O2 heterolysis under electric environments

초록

Lewis acidic metals (M6+) cleave H2O2 to evolve center dot OH used for fragmenting aqueous wastes. M6+ species are situated near SiO2 and generate interfacial M6+-SiO2 domains, where M6+ species can avoid aggregation, retain center dot OH productivity with minimal leaching via chelation to the -OH of SiO2, elevate the collisions between M6+ and H2O2 or between center dot OH and aqueous pollutants via confinement, and destabilize contaminants via electron (e-) transfer. The merits of SiO2 stated earlier, however, remain abstract and only partially clarified. Herein, inter-facial Ni6+-SiO2 domains were created on SiO2-modified NiS/Ni9S8 (NiS/Ni9S8-SiO2) to elaborate the afore-mentioned advantages of SiO2 under electric conditions, where it was hypothesized that e-transfer can occur from O2-/di-sulfide (S22-)/poly-sulfide (SN2-) to Ni6+ species. SiO2 was verified to increase the amount of Ni6+ speices for NiS/Ni9S8-SiO2 and reduce their Lewis acidic strengths, which was conducive to lowering the energy barrier required for H2O2 dissection. SiO2 was demonstrated to hardly promote the collisions of Ni6+ with H2O2 because of the hydrogen bonding of H2O2 with SiO2, reduce Ni6+ leaching via e-acceptance from O2-/S22-/SN2-rather than via -OH chelation, while making e-migration from Ni6+ to aqueous organics scarcely compelling.

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