Enhanced oxidation of arsenite to arsenate using tunable K+ concentration in the OMS-2 tunnel

Application of manganese oxide-based materials for arsenic removal: A review

In the context of growing arsenic (As) contamination in the world, there is an urgent need for an effective treatment approach to remove As from the environment. Industrial wastewater is one of the primary sources of As contamination, which poses significant risks to both microorganisms and human health, as the presence of As can disrupt the vital processes and synthesis of crucial macromolecules in living organisms. The global apprehension regarding As presence in aquatic environments persists as a key environmental issue. This review summarizes the recent advances and progress in the design, strategy, and synthesis method of various manganese-based adsorbent materials for As removal. Occurrence, removal, oxidation mechanism of As(III), As adsorption on manganese oxide (MnOx)-based materials, and influence of co-existing solutes are also discussed. Furthermore, the existing knowledge gaps of MnOx-based adsorbent materials and future research directions are proposed. This review provides a reference for the application of MnOx-based adsorbent materials to As removal.

Promoting the mechanism of OMS-2 for gas adsorption in different K+ concentrations

Adsorption performances between the OMS-2 catalyst and CH4 and O2 molecules are enhanced with increasing tunnel K+ concentration.

Abiotic oxidation of arsenite in natural and engineered systems: Mechanisms and related controversies over the last two decades (1999-2020)

Abiotic oxidation of toxic As(III) to As(V) is being deemed as a necessary step for the overall arsenic decontamination in both natural and engineered systems. Direct oxidation of As(III) by chemical oxidants, such as ozone, permanganate, ferrate, chlorine and chloramine, or naturally occurring minerals like Mn, Fe oxides, seems straightforward. Both O₂ and H₂O₂ are ineffective for arsenite oxidation, but they can be activated by reducing substances like Fe²⁺, Fe⁰ to increase the oxidation rates. Photo-induced oxidation of As(III) has been demonstrated effective in Fe complexes or minerals, NO₃^-/NO₂^-, dissolved organic matter (DOM), peroxygens and TiO₂ systems. Although a variety of oxidation methods have been developed over the past two decades, there remain many scientific and technical challenges that must be overcome before the rapid progress in basic knowledge can be translated into environmental benefits. To better understand the trends in the existing data and to identify the knowledge gaps, this review describes in detail the complicated mechanisms for As(III) oxidation by various methods and emphasizes on the conflicting data and explanation. Some prevailing concerns and challenges in the sphere of As(III) oxidation are also pointed out so as to appeal to researchers for further investigations.

Simultaneous introduction of K+ and Rb+ into OMS-2 tunnels as an available strategy for substantially increasing the catalytic activity for benzene elimination

OMS-2 is one of the most promising catalysts for carcinogenic benzene elimination, and single-type alkali metals are typically introduced into the OMS-2 tunnels to modify its catalytic activity. Here, we reported a novel approach for significantly increasing the catalytic activity of OMS-2 via the simultaneous introduction of K⁺ and Rb⁺ into the tunnels. The catalytic results demonstrated that K⁺ and Rb⁺ codoped OMS-2 showed catalytic activity for benzene oxidation that exceeded those of K⁺ and Rb⁺ single-doped OMS-2, as evidenced by enormous decreases (△T₅₀ = 106 °C and △T₉₀ > 132 °C) in catalytic temperatures T₅₀ and T₉₀ (which correspond to benzene conversion percentages of 50% and 90%, respectively). The origin of the effect of K⁺ and Rb⁺ codoping on the catalytic activity of OMS-2 was experimentally and theoretically investigated via ¹⁸O₂ isotope labeling, CO temperature-programmed reduction, and density functional theory calculation. The higher catalytic activity of K⁺ and Rb⁺ codoped OMS-2 was attributed to its higher lattice oxygen activity as well as its higher oxygen vacancy defect concentrations compared to the single-doped OMS-2 cases.