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Despite the widespread presence of hydrogen peroxide (H2O2) in surface water and groundwater systems, little is known about the impact of environmental levels of H2O2 on the redox activity of minerals. Here we demonstrate that environmental concentrations of H2O2 can alter the reactivity of birnessite-type manganese oxide, an earth-abundant functional material, and decrease its oxidative activity in natural systems across a wide range of pH values (4–8). The H2O2-induced reductive dissolution generates Mn(II) that will re-bind to MnO2 surfaces, thereby affecting the surface charge of MnO2. Competition of Bisphenol A (BPA), used as a target compound here, and Mn(II) to interact with reactive surface sites may cause suppression of the oxidative ability of MnO2. This suppressive effect becomes more effective in the presence of oxyanions such as phosphate or silicate at concentrations comparable to those encountered in natural waters. Unlike nitrate, adsorption of phosphate or silicate onto birnessite increased in the presence of Mn(II) added or generated through H2O2-induced reduction of MnO2. This suggests that naturally occurring anions and H2O2 may have synergetic effects on the reactivity of birnessite-type manganese oxide at a range of environmentally relevant H2O2 amounts. As layered structure manganese oxides play a key role in the global carbon cycle as well as pollutant dynamics, the impact of environmental levels of hydrogen peroxide (H2O2/MnO2 molar ratio ≤ 0.3) should be considered in environmental fate and transport models. [ABSTRACT FROM AUTHOR]

Trichloroethylene (TCE) degradation in sand columns has been investigated to evaluate the potential of chelates-enhanced Fenton-like reaction with magnetite as iron source for in situ treatment of TCE-contaminated groundwater. The results showed that successful degradation of TCE in sand columns was obtained by nitrilotriacetic acid (NTA)-assisted Fenton-like reaction of magnetite. Addition of ethylenediaminedisuccinic acid (EDDS) resulted in an inhibitory effect on TCE degradation in sand columns. Similar to EDDS, addition of ethylenediaminetetraacetic acid (EDTA) also led to an inhibition of TCE degradation in sand column with small content of magnetite (0.5 w.t.%), but enhanced TCE degradation in sand column with high content of magnetite (7.0 w.t.%). Additionally, the presence of NTA, EDDS and EDTA greatly decreased H 2 O 2 uptake in sand columns due to the competition between chelates and H 2 O 2 for surface sites on magnetite (and sand). Furthermore, the presented results show that magnetite in sand columns remained stable in a long period operation of 230 days without significant loss of performance in terms of TCE degradation and H 2 O 2 uptake. Moreover, it was found that TCE was degraded mainly to formic acid and chloride ion, and the formation of chlorinated organic intermediates was minimal by this process. [ABSTRACT FROM AUTHOR]

The present study investigated the degradation of trichloroethylene (TCE) in sand suspensions by Fenton-like reaction with magnetite (FeO) in the presence of various chelators at circumneutral pH. The results showed that ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) greatly improved the rate of TCE degradation, while [S,S]-ethylenediaminedisuccinic acid (s,s-EDDS), malonate, citrate, and phytic acid (IP6) have minimal effects on TCE degradation. Quenching tests suggested that TCE was mainly degraded by hydroxyl radical (HO) attack, with about 90% inhibition on TCE degradation by the addition of HO scavenger 2-propanol. The presence of 0.1-0.5% FeO/sand ( w/ w) contributed to 40% increase in TCE degradation rates. In particular, the use of chelators can avoid high concentrations of HO required for the Fenton-like reaction with FeO, and moreover improve the stoichiometric efficiencies of TCE degradation to HO consumption. The suitable concentrations of chelators (EDTA and NTA) and HO were suggested to be 0.5 and 20 mM, respectively. Under the given conditions, degradation rate constants of TCE were obtained at 0.360 h with EDTA and 0.526 h with NTA, respectively. Enhanced degradation of TCE and decreased usage of HO in this investigation suggested that Fenton-like reaction of FeO together with NTA (or EDTA) may be a promising process for remediation of TCE-contaminated groundwater. [ABSTRACT FROM AUTHOR]

In this paper, the degradation of three endocrine-disrupting chemicals (EDCs): bisphenol A (BPA), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) by manganite (γ-MnOOH) activated peroxymonosulfate (PMS) was investigated. Preliminary optimisation experiments showed that complete degradation of the three EDCs was achieved after 30 min of reaction using 0.1 g L−1 of γ-MnOOH and 2 mM of PMS. The degradation rate constants were determined to be 0.20, 0.22 and 0.15 min−1 for BPA, E2 and EE2, respectively. Combining radical scavenging approaches, Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analyses, we revealed for the first time that about 40% of EDCs degradation can be attributed to heterogeneous electron transfer reaction involving freshly generated Mn(IV), and 60% to sulfate radical degradation pathway. The influence of various inorganic ions on the γ-MnOOH/PMS system indicated that removal efficiency was slightly affected by chloride and carbonate ions, while nitrate and nitrite ions had negligible impacts. The application of γ-MnOOH/PMS system in real sewage treatment plant water (STPW) showed that degradation rate constants of EDCs decreased to 0.035–0.048 min−1 and complete degradation of the three EDCs after 45 min. This study provides new insights into the reactivity of combined γ-MnOOH and PMS, and opens new ways for the application of Mn-bearing species in wastewater treatment technologies. [Display omitted] • γ-MnOOH/PMS system is able to degrade efficiently EDCs in different water matrix. • A reaction mechanism considering the oxidative species involvement was determined. • Complete removal of EDC was reached in real sewage treatment plant water. • High mineralization efficiency was achieved in STPW. [ABSTRACT FROM AUTHOR]

The key role of trivalent manganese (Mn(III)) species in promoting sulfate radical-based advanced oxidation processes (SR-AOPs) has recently attracted increasing attention. This review provides a comprehensive summary of Mn(III) (oxyhydr)oxide-based catalysts used to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) in water. The crystal structures of different Mn(III) (oxyhydr)oxides (such as α-Mn2O3, γ-MnOOH, and Mn3O4) are first introduced. Then the impact of the catalyst structure and composition on the activation mechanisms are discussed, as well as the effects of solution pH and inorganic ions. In the Mn(III) (oxyhydr)oxide activated SR-AOPs systems, the activation mechanisms of PMS and PDS are different. For example, both radical (such as sulfate and hydroxyl radical) and non-radical (singlet oxygen) were generated by Mn(III) (oxyhydr)oxide activated PMS. In comparison, the activation of PDS by α-Mn2O3 and γ-MnOOH preferred to form the singlet oxygen and catalyst surface activated complex to remove the organic pollutants. Finally, research gaps are discussed to suggest future directions in context of applying radical-based advanced oxidation in wastewater treatment processes. [ABSTRACT FROM AUTHOR]

In this paper, the degradation of three endocrine-disrupting chemicals (EDCs): bisphenol A (BPA), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) by manganite (γ-MnOOH) activated peroxymonosulfate (PMS) was investigated. Preliminary optimisation experiments showed that complete degradation of the three EDCs was achieved after 30 min of reaction using 0.1 g L -1 of γ-MnOOH and 2 mM of PMS. The degradation rate constants were determined to be 0.20, 0.22 and 0.15 min -1 for BPA, E2 and EE2, respectively. Combining radical scavenging approaches, Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analyses, we revealed for the first time that about 40% of EDCs degradation can be attributed to heterogeneous electron transfer reaction involving freshly generated Mn(IV), and 60% to sulfate radical degradation pathway. The influence of various inorganic ions on the γ-MnOOH/PMS system indicated that removal efficiency was slightly affected by chloride and carbonate ions, while nitrate and nitrite ions had negligible impacts. The application of γ-MnOOH/PMS system in real sewage treatment plant water (STPW) showed that degradation rate constants of EDCs decreased to 0.035-0.048 min -1 and complete degradation of the three EDCs after 45 min. This study provides new insights into the reactivity of combined γ-MnOOH and PMS, and opens new ways for the application of Mn-bearing species in wastewater treatment technologies., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Despite the widespread presence of hydrogen peroxide (H 2 O 2 ) in surface water and groundwater systems, little is known about the impact of environmental levels of H 2 O 2 on the redox activity of minerals. Here we demonstrate that environmental concentrations of H 2 O 2 can alter the reactivity of birnessite-type manganese oxide, an earth-abundant functional material, and decrease its oxidative activity in natural systems across a wide range of pH values (4-8). The H 2 O 2 -induced reductive dissolution generates Mn(II) that will re-bind to MnO 2 surfaces, thereby affecting the surface charge of MnO 2 . Competition of Bisphenol A (BPA), used as a target compound here, and Mn(II) to interact with reactive surface sites may cause suppression of the oxidative ability of MnO 2 . This suppressive effect becomes more effective in the presence of oxyanions such as phosphate or silicate at concentrations comparable to those encountered in natural waters. Unlike nitrate, adsorption of phosphate or silicate onto birnessite increased in the presence of Mn(II) added or generated through H 2 O 2 -induced reduction of MnO 2 . This suggests that naturally occurring anions and H 2 O 2 may have synergetic effects on the reactivity of birnessite-type manganese oxide at a range of environmentally relevant H 2 O 2 amounts. As layered structure manganese oxides play a key role in the global carbon cycle as well as pollutant dynamics, the impact of environmental levels of hydrogen peroxide (H 2 O 2 /MnO 2 molar ratio ≤ 0.3) should be considered in environmental fate and transport models.