Transformation of bisphenol AF and bisphenol S by manganese dioxide and effect of iodide

In this work, transformation of bisphenol A (BPA) alternatives bisphenol AF (BPAF) and bisphenol S (BPS) by manganese dioxide (MnO₂) and the effect of iodide (I^-) during these processes were investigated in comparison with BPA for the first time. These three bisphenols showed appreciable reactivity towards MnO₂ with the half-lives of their loss following the order of BPA < BPAF < BPS under similar conditions, and a higher transformation efficiency was generally obtained at a lower pH. The presence of I^- apparently accelerated the transformation of BPAF and BPS by MnO₂ at pH ≤ 7 but negligibly affected BPA transformation over the pH range of 5-9. This discrepancy could be well explained by the relative contribution of hypoiodous acid (HOI) in situ formed from I^- oxidation by MnO₂. Polymers, hydroxylated derivatives, and bond-cleavage products were detected from BPAF and BPS treated by MnO₂, where a series of reactions of BPAF/BPS radicals formed from one-electron oxidation of BPAF/BPS were likely involved, similar to the case of BPA reported in literature. A group of iodinated aromatic products were additionally identified from BPAF/BPS treated by MnO₂ in the presence of I^- (e.g., iodinated BPAF/BPS and iodinated BPAF/BPS dimers), and they could be further transformed. This study suggests that naturally occurring manganese oxides play a significant role in the attenuation of bisphenols released into the environment and the presence of I^- can display a great effect on their transformation.

Oxidative transformation of emerging organic contaminants by aqueous permanganate: Kinetics, products, toxicity changes, and effects of manganese products

Permanganate (Mn(VII)) has been widely studied for removal of emerging organic contaminants (EOCs) in water treatment and in situ chemical oxidation process. Studies on the reactive intermediate manganese products (e.g., Mn(III) and manganese dioxide (MnO₂)) generated from Mn(VII) reduction by EOCs in recent decades shed new light on Mn(VII) oxidation process. The present work summarizes the latest research findings on Mn(VII) reactions with a wide range of EOCs (including phenols, olefins, and amines) in detailed aspects of reaction kinetics, oxidation products, and toxicity changes, along with special emphasis on the impacts of intermediate manganese products (mainly Mn(III) and MnO₂) in-situ formed. Mn(VII) shows appreciable reactivities towards EOCs with apparent second-order rate constants (k_app) generally decrease in the order of olefins (k_app = 0.3 - 2.1 × 10⁴ M^-1s^-1) > phenols (k_app = 0.03 - 460 M^-1s^-1) > amines (k_app = 3.5 × 10^-3 - 305.3 M^-1s^-1) at neutral pH. Phenolic benzene ring (for phenols), (conjugated) double bond (for olefins), primary amine group and the N-containing heterocyclic ring (for amines) are the most reactive sites towards Mn(VII) oxidation, leading to the formation of products with different structures (e.g., hydroxylated, aldehyde, carbonyl, quinone-like, polymeric, ring-opening, nitroso/nitro and C-N cleavage products). Destruction of functional groups of EOCs (e.g., benzene ring, (conjugated) double bond, and N-containing heterocyclic) by Mn(VII) tends to decrease solution toxicity, while oxidation products with higher toxicity than parent EOCs (e.g., quinone-like products in the case of phenolic EOCs) are sometimes formed. Mn(III) stabilized by model or unknown ligands remarkably accelerates phenolic EOCs oxidation by Mn(VII) under acidic to neutral conditions, while MnO₂ enhances the oxidation efficiency of phenolic and amine EOCs by Mn(VII) at acidic pH. The intermediate manganese products participate in Mn(VII) oxidation process most likely as both oxidants and catalysts with their generation/stability/reactivity affecting by the presence of NOM, ligand, cations, and anions in water matrices. This work presents the state-of-the-art findings on Mn(VII) oxidation of EOCs, especially highlights the significant roles of manganese products, which advances our understanding on Mn(VII) oxidation and its application in future water treatment processes.

Plasmonic photocatalytic nanocomposite of in-situ synthesized MnO2 nanoparticles on cellulosic fabric with structural color

The textile industry produces 20 % of the industrial water pollution containing toxic substances mostly dyes. Reducing material consumption and developing more efficient and scalable textile waste-water treatment methods such as photocatalytic degradation is essential. In this work, manganese dioxide nanoparticles (MnO2 NPs) were synthesized on the cotton fabric via a facile in-situ process. The preparation process was optimized for the highest photocatalytic activity under sunlight and color change originating from the plasmonic structural color of the nanoparticles. This promotes the photocatalytic activity by delocalization of the hot electrons while demonstrating the best washing and light fastness by using the least chemicals, and energy in a short time. In this way, the fabric was colored without any dye and possessed robust photocatalytic activity. Further, no dye-containing waste-water is made, and also accomplished to degrade dyes in a few hours under sunlight which is substantial for sustainable development. The treated fabrics indicated favorable mechanical properties, enhanced thermal stability, and perfect biocompatibility.

Oxidation of methylparaben (MeP) and p‑hydroxybenzoic acid (p-HBA) by manganese dioxide (MnO2) and effects of iodide: Efficiency, products, and toxicity

It is reported that methylparaben (MeP, a widely used phenolic preservative) and its major metabolite p‑hydroxybenzoic acid (p-HBA) display estrogenic activity and are frequently detected in various environmental settings. Naturally occurring manganese dioxide (MnO₂) plays an important role in attenuation of contaminants released into the environment, and the presence of iodide (I^-) may affect these processes. In this work, it was found that both MeP and p-HBA displayed considerable reactivity towards MnO₂ with their half-lives increased with decreasing MnO₂ concentrations or increasing pH. The presence of I^- obviously accelerated the transformation efficiency of MeP and p-HBA by MnO₂ with stronger enhancement at higher I^- concentrations or lower pH. Dimeric products (e.g., dimeric MeP or p-HBA) were generated from MeP/p-HBA treated by MnO₂, and iodinated aromatic products (e.g., mono-/di-iodinated MeP/p-HBA) were additionally identified in the presence of I^-. Higher concentrations of these iodinated aromatic products were generally formed at higher I^- or lower MnO₂ concentrations or lower pH. Ecotoxicity analysis showed that dimeric and iodinated aromatic products were more eco-toxic than parent MeP/p-HBA. This work shows that MnO₂ may greatly affect the fate of MeP and p-HBA released into the environment, and the presence of I^- can significantly affect these processes.