Effect of MnO₂ Phase Structure on the Oxidative Reactivity toward Bisphenol A Degradation

Abstract

Manganese dioxides (MnO) are among important environmental oxidants in contaminant removal; however, most existing work has only focused on naturally abundant MnO. We herein report the effects of different phase structures of synthetic MnO on their oxidative activity with regard to contaminant degradation. Bisphenol A (BPA), a frequently detected contaminant in the environment, was used as a probe compound. A total of eight MnO with five different phase structures (α-, β-, γ-, δ-, and λ-MnO) were successfully synthesized with different methods. The oxidative reactivity of MnO, as quantified by pseudo-first-order rate constants of BPA oxidation, followed the order of δ-MnO-1 > δ-MnO-2 > α-MnO-1 > α-MnO-2 ≈ γ-MnO > λ-MnO > β-MnO-2 > β-MnO-1. Extensive characterization was then conducted for MnO crystal structure, morphology, surface area, reduction potential, conductivity, and surface Mn oxidation states and oxygen species. The results showed that the MnO oxidative reactivity correlated highly positively with surface Mn(III) content and negatively with surface Mn average oxidation state but correlated poorly with all other properties. This indicates that surface Mn(III) played an important role in MnO oxidative reactivity. For the same MnO phase structure synthesized by different methods, higher surface area, reduction potential, conductivity, or surface adsorbed oxygen led to higher reactivity, suggesting that these properties play a secondary role in the reactivity. These findings provide general guidance for designing active MnO for cost-effective water and wastewater treatment.

Sustained CO2-photoreduction activity and high selectivity over C, Mn-codoped ZnO core-triple shell hollow spheres

“…The presence of Mn is believed to promote catalytic conversions owing to their ability to share electrons with reactant molecules and/or intermediates. [34][35][36][37] Besides, doping gives rise to defect states and impurity levels. They not only reduce the bandgap of the semiconductor, but also improve the light absorptivity of the photocatalyst.…”

MnO2‐Based Materials for Environmental Applications

“…They argue that the antibonding e g 1 electron of Mn 3+ (t 2g 3 e g 1 ) leads to longer and weaker MnO bonds than Mn 4+ . [ 373 ] These weaker MnO bonds are more likely to be destroyed and leading to the instability of MnO 2 . Other researchers hold the opposite view.…”

“…MnO 2 ‐based materials have shown enormous potential applications in the removal of organic pollutants in various wastewater treatment technologies, including adsorption, catalytic ozonation, photocatalytic oxidation, electrocatalytic oxidation, peroxymonosulfate oxidation, catalytic filtration, and energy harvesting galvanic cell technologies. So far, MnO 2 ‐based materials have shown superior performances in the removal of various organic pollutants in water, such as dye (methylene blue, [ 359–361 ] methyl orange, [ 362,363 ] Rhodamine B, [ 309,364 ] Congo red, [ 365 ] acid fuchsin dye, [ 218 ] crystal violet dye, [ 366 ] acid red 73, [ 367 ] neutral red, [ 368 ] and tartrazin yellow [ 369 ] ), phenolic pharmaceuticals (phenol, [ 66,325,342,370–372 ] bisphenol A, [ 99,275,373–378 ] ibuprofen, [ 295 ] tetrabromobisphenol A, [ 379 ] benzophenone‐3, [ 216 ] 2,4‐dichlorophenol, [ 380 ] 4‐chlorophenol, [ 381 ] and 4‐nitrophenol [ 382 ] ), antibiotics (tetracycline, [ 383 ] ceftiofur, [ 243 ] and lomefloxacin [ 243 ] ), as well as ammonia borane, [ 384 ] amides, [ 385 ] lignin, [ 386 ] peroxymonosulfate, [ 237 ] 17 β‐Estradiol, [ 249 ] m ‐aminophenol, [ 387 ] carbamazepine, [ 388 ] dichloroacetic acid, [ 389 ] p ‐arsanilic acid, [ 390 ] phenylarsonic acids, [ 391 ] m ‐cresol, [ 288 ] oxalic acid, [ 392 ] ciprofloxacin, [ 393,394 ] phenanthrene, [ 246 ] norfloxacin, [ 291 ] etc. ( Table 2 ).…”

Identifying the mechanisms of cation inhibition of phenol oxidation by acid birnessite

“…The phenolic compounds used in this study include bisphenol A (BPA), 5-chloro-2-(2,4-dichlorophenoxy) phenol (triclosan), estrone, and 4-methylphenol (p-cresol) (Supplemental Figure S1). Phenolic compounds such as these are found in wastewater effluents that discharge into natural ecosystems (Bina, Mohammadi, Amin, Pourzamani, & Yavari, 2018;Bulloch et al, 2015;Charbonnet, Duan, van Genuchten, & Sedlak, 2018;Grebel et al, 2013Grebel et al, , 2016Huang, Zhong, Dai, Liu, & Zhang, 2018;Lin, Liu, & Gan, 2009b;Luthy & Sedlak, 2017;Montes-Grajales, Fennix-Agudelo, & Miranda-Castro, 2017;Yang, Ok, Kim, Kwon, & Tsang, 2017) and serve to show any differences in cation effects due to phenolic structure (Trainer, Ginder-Vogel, & Remucal, 2020). Cations can inhibit the reaction rate of phenols with manganese oxides (Remucal & Ginder-Vogel, 2014), which has implications for environmental oxidative degradation of phenolic contaminants because cations are ubiquitous in natural systems.…”