Reaction kinetics and transformation products of 1-naphthol by Mn oxide-mediated oxidative-coupling reaction

Removal of 1,4-Naphthoquinone by Birnessite-Catalyzed Oxidation: Effect of Phenolic Mediators and the Reaction Pathway

“…Notably, a removal efficiency of 1.7% was observed in the absence of birnessite and reactive mediators, which was ascribed to the adsorption of 1,4-NPQ onto the sample container walls and, possibly, volatilization, whereas a removal efficiency of 9.8% was observed in the presence of birnessite only. Thus, the ability of birnessite to remove 1,4-NPQ by itself is quite low, as reported previously [ 15 ]. However, removal efficiencies of 77.6–100% for 1,4-NPQ were obtained for birnessite in the presence of phenolic mediators, and particularly high values (>99.8%) were achieved for species containing two phenolic groups (i.e., CAT, hydroquinone (HQ), and resorcinol (RES)) or methoxy groups (i.e., 4-methoxyphenol (4-MeP) and 2,6-dimethoxyphenol (2,6-DiMeP) after 24 h. The removal of 1,4-NPQ by birnessite-mediated oxidative reactions was confirmed by comparing the concentrations of Mn ions in the 1,4-NPQ and birnessite reaction samples in the presence and absence of CAT.…”

“…Considering that the efficiency of 1,4-NPQ removal by birnessite-mediated oxidative- transformation in the absence of phenolic mediators was around 9.8% ( Table 1 ), it is suggested that the oxidation of CAT significantly enhanced the removal of 1,4-NPQ via birnessite-catalyzed cross-coupling reactions [ 23 , 35 ]. This result also proves that the 1,4-NPQ generated as an intermediate in the oxidative removal of 1-naphthol by birnessite can be further removed by the birnessite-catalyzed cross-coupling reaction with phenolic mediators [ 15 ].…”

“…The reaction solution was prepared by mixing the 1,4-NPQ standard solution (0.14 mM, pH = 5) with a solution of the phenolic compound (0.6 mM, pH = 5) at a 1:1 ( v / v ) ratio, followed by the immediate injection of birnessite to achieve a loading of 1.0 g L −1 . Here, pH = 5 was selected as a weakly acidic region that can exhibit high reactivity considering the p k a value (4.3–9.9) of the phenolic reaction mediators and the point of zero charge (PZC, 2.4–2.7) of birnessite based on the previous research results [ 15 , 17 ]. For comparison, a reactive mediator-free control sample solution was prepared under the same conditions (0.07 mM 1,4-NPQ, 1.0 g L −1 δ -MnO 2 , pH = 5).…”

“…The pH of the reaction solution was adjusted to 5 using HCl and NaOH. At this pH, the reactivity of birnessite is the most favorable, and this pH also mimics that of natural water bodies (typically 5–8) [ 15 ]. The reaction vessel was completely sealed with a Teflon diaphragm and Al cap, and Al foil was used to block light.…”

“…In particular, ketone- and quinone-based OPAHs exhibit higher toxicity and persistence than the corresponding phenols and carboxylic acids and are, thus, more harmful [ 13 , 14 ]. 1,4-naphthoquinone (1,4-NPQ), a representative quinone-based OPAH (e.g., quinoid PAH) commonly produced by the biochemical degradation of naphthalene- and phenol-containing PAHs [ 15 , 16 ], can bind to macromolecules such as DNA and proteins, making it a potential tumorigenic agent [ 13 ]. However, most studies of the decomposition and removal of PAHs have focused on the removal of the original pollutants (i.e., PAHs), and the subsequent treatment and effects of the oxidative transformation of PAH products remains underexplored.…”