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A-Mn 2 O 3 nanocatalyst possess efficient catalytic properties for PS activation and exhibits remarkable performance for the degradation of organic contaminants via singlet oxygen. In this study, the catalytic activation of persulfate (PS) via metal oxides was investigated, and the A-Mn 2 O 3 nanocatalyst was found to have the highest efficiency among other PS activators for the degradation of organic contaminants. Additionally, A-Mn 2 O 3 exhibited a remarkable efficiency in activating PS for the degradation of phenol compared to both B-Mn 2 O 3 and C-Mn 2 O 3. This was attributed to the longer bonds between edge-sharing MnO 6 octahedra, the unique structure, the high content surface –OH groups, and the average oxidation states. This indicated that all these properties played an important role in an efficient PS activation. Electron paramagnetic resonance (EPR) spectroscopy, scavenger tests, and chemical probes were conducted to investigate the reactive oxygen species (ROS). Singlet oxygen (1O 2) was determined to be the main ROS generated from PS activation. A plausible mechanism study was proposed, which involved inner-sphere interactions. An electron transfer of the Mn species facilitated the decomposition of PS to generate HO 2 • /O 2 • − radicals, which were utilized as a precursor for 1O 2 generation via direct oxidation or the recombination of HO 2 • /O 2 • −. Finally, the phenol and Sulfachloropyridazine (SCP) degradation pathways were proposed by 1O 2 over the A-Mn 2 O 3 /PS system according to HPLC and LC-MS results. [ABSTRACT FROM AUTHOR]

[Display omitted] • MnO-H containing a large number of oxygen vacancies (OVs) was synthesized. • MnO-H exhibits better catalytic performance than MnO-N and MnO-C. • OVs improve catalytic performance for rapid acetaminophen (ACE) degradation. • MnO-H activates peroxymonosulfate and triggers an electron transfer pathway. • ACE is primarily removed via an electron transfer pathway. Understanding the role of oxygen vacancies (OVs) in endowing catalytic activity is important for the design of efficient catalysts for advanced oxidation processes. In this study, we prepared MnO catalysts with different amounts of OVs under an atmosphere of H 2 (MnO-H) and N 2 (MnO-N) and investigated their acetaminophen (ACE) degradation efficiency via peroxymonosulfate (PMS) activation. MnO-H exhibited the best degradation performance because of its numerous OVs, compared with that of MnO-N and the commercial MnO. Data analysis revealed that ACE degradation proceeded via electron transfer. Density functional theory calculations confirmed that compared with the other catalysts, MnO-H/PMS with more OVs had higher catalytic activity, higher adsorption energy, lower work function, and higher electron transformation. The MnO-H/PMS system was stable at pH 3.0–9.0 and showed good recyclability. We believe that our findings will provide deeper insights into the role of OVs and encourage the use of less toxic metal oxides as catalysts in the selective degradation of organic pollutants in water bodies. [ABSTRACT FROM AUTHOR]

• The generation of Mn(III) and Mn(II) is crucial for peroxymonosulfate activation; • Multiple reactive species including radicals and non-radical were involved; • The formation of BrO 3 − is inhibited in α-MnO 2 nanowires/peroxymonosulfate process; • Sixteen intermediates were detected during the degradation of atrazine. In this study, a series of Mn based catalysts with different oxidative states, crystal structures and morphologies was applied to activate peroxymonosulfate (PMS) for the degradation of atrazine (ATZ). Among them, α-MnO 2 nanowires (Mn-1) demonstrated the highest efficiency. The structure-performance relationship study revealed that the generation of Mn(III) along with the transformation of lattice oxygen to surface hydroxyl groups played the dominant role in controlling the efficiency, and Mn-1 are prone to undergo electron transfer to achieve the transition from Mn(IV) to Mn(III) or even Mn(II). Both radical (sulfate radical (SO 4 •−) and hydroxyl radical (•OH)) and non-radical species (1O 2) contributed to ATZ degradation and accordingly inhibit the formation of toxic BrO 3 − from Br−. Sixteen intermediates were identified in proposed degradation pathways. The toxicity tests, the consistent performance with coexisting anions and humic acid in water matrix, and the satisfying reusability implied the sustainable application of Mn-1/PMS in future. [ABSTRACT FROM AUTHOR]

A novel metal-free nitrogen doped carbon material was synthesized by post doping of nitrogen (different amounts of melamine) into carbon substrate derived from glucose, at 550 °C under nitrogen protection. Despite the optimized catalyst has a low nitrogen content of 2.16%, it could effectively activate PMS and exhibited an excellent catalytic performance for phenol degradation with an exceptionally low activation energy. Experiments showed the degradation rates of phenol by the catalyst upon N-doped was 29 times higher than that by carbon substrate, and the reaction pathway of PMS activated transformed from free-radical pathway of carbon substrate to non-radical process. Further, all experimental and theoretical investigations demonstrated the critical role of pyrrolic –N in carbonaceous material to the PMS activation for the first time, which attracts the electrophilic species of PMS and drives the electron transfer towards PMS, thereby the performance of the catalysis was enhanced. The catalytic process performed on various aromatic compounds with different substituents showed a selective degradation dependent on ionization potential (IP). The simple and economical preparation method and the efficiency of the catalyst developed in the study make the activation toward PMS a viable approach for a practical large-scale industrial application. Image 1 [ABSTRACT FROM AUTHOR]

The development of green and efficient heterogeneous catalysts for permanganate (Mn(VII)) activation remains unexplored. Given the different roles of crystal structures of MnO 2 in many applications, it is of great significance to investigate the reactivity of MnO 2 with different phases for Mn(VII) activation. In this study, it was found that the first-order rate constants for phenol degradation in the presence of 100 μM Mn(VII) follow an order of α-MnO 2 (0.0884 min−1) > δ-MnO 2 (0.0746 min−1) > β-MnO 2 (0.0417 min−1) > γ-MnO 2 (0.0396 min−1). The fact is in line with Mn(VII) adsorption, which can be related closely to the surface area, pore diameter, and isoelectric points of the catalysts. Other phenolic contaminants such as parachlorophenol and bisphenol A were also degraded efficiently by the Mn(VII)/α-MnO 2 system. After coordination with surface Mn species in MnO 2 , the Mn–O bond of Mn(VII) is stretched with an increase in electron transfer reactivity and a decrease in oxygen atom transfer ability. A surface-promoted electron transfer process is then proposed for phenol degradation by the system. A good adaptability and reusability of the Mn(VII)/α-MnO 2 system were observed. The influence of several parameters and comparisons with other catalysts were also studied. This work provides insights into the phase-dependent reactivity of MnO 2 catalysts for Mn(VII) activation and pollutant degradation. [Display omitted] • MnO 2 structures affected Mn(VII) adsorption and phenol degradation. • The high surface areas, pore diameters, and isoelectric points were important. • The OAT reactivity of adsorped Mn(VII) decreased and ET reactivity increased. • Direct ET mechanism played a significant role in phenol degradation. • The MnO 2 catalyst showed good reusability during successive runs. [ABSTRACT FROM AUTHOR]

The development of new strategies to improve the removal of organic pollutants with permanganate (KMnO 4) is a hot topic in water treatment. While Mn oxides have been extensively used in Advanced Oxidation Processes through an electron transfer mechanism, the field of KMnO 4 activation remains relatively unexplored. Interestingly, this study has discovered that Mn oxides with high oxidation states including γ-MnOOH, α-Mn 2 O 3 and α-MnO 2 , exhibited excellent performance to degrade phenols and antibiotics in the presence of KMnO 4. The MnO 4 - species initially formed stable complexes with the surface Mn(III/IV) species and showed an increased oxidation potential and electron transfer reactivity, caused by the electron-withdrawing capacity of the Mn species acting as Lewis acids. Conversely, for MnO and γ-Mn 3 O 4 with Mn(II) species, they reacted with KMnO 4 to produce cMnO 2 with very low activity for phenol degradation. The direct electron transfer mechanism in α-MnO 2 /KMnO 4 system was further confirmed through the inhibiting effect of acetonitrile and the galvanic oxidation process. Moreover, the adaptability and reusability of α-MnO 2 in complicated waters indicated its potential for application in water treatment. Overall, the findings shed light on the development of Mn-based catalysts for organic pollutants degradation via KMnO 4 activation and understanding of the surface-promoted mechanism. [Display omitted] • Mn oxides with high oxidation states exhibited higher activity for KMnO 4 activation. • Mn(II) species in MnO reacted with KMnO 4 to produce cMnO 2. • KMnO 4 can form stable complexes with the surface Mn(III/IV) species. • The oxidation potential and ET reactivity of adsorbed KMnO 4 increased. • Direct ET mechanism played a significant role in phenol degradation. [ABSTRACT FROM AUTHOR]

The development of efficient and eco-friendly Mn-based hybrids for the degradation of biorefractory organic pollutants via peroxymonosulfate (PMS) activation is highly desired. In this study, a novel graphite nanosheet (GNs)-based Fe-Mn bimetallic oxide (Fe doped birnessite MnO 2 , FeMn/GNs) was synthesized under mild conditions. Compared with monometallic Fe or Mn oxide on GNs, FeMn/GNs exhibited a higher surface area, decreased Mn oxidation states, stronger interaction with GNs, and more active sites for PMS adsorption. Among different Fe/Mn ratios, Fe 2 Mn 1 /GNs showed the optimum performance for bisphenol A (BPA) degradation with the first-order rate constant of 0.22 min−1, which was about 8.5 and 12.9 times higher than that of Mn/GNs and Fe/GNs, respectively. Different from the pollutant-catalyst-PMS electron transfer mechanism for Mn/GNs, the direct two-electron transfer in FeMn/GNs+PMS system, was mainly processed between the simultaneously activated BPA and PMS. This was probably based on the double adsorption sites of Fe and Mn species on the same catalyst: PMS was adsorbed by Fe species through hydroxyl groups, while BPA was mainly coordinated with Mn species due to the layered structure and hydrophobicity of the Mn oxide. This study is expected to provide the rational design of efficient Mn-based hybrids for PMS activation. [Display omitted] • A novel FeMn/GNs composite was synthesized under mild conditions. • The influence of Fe and GNs on the structure of δ-MnO 2 was discussed. • The strong interactions improved the performance of PMS activation. • Direct electron transfer mechanim plays a significant role in BPA degradation. • The process was mainly through the simultaneous activated PMS and BPA. [ABSTRACT FROM AUTHOR]

[Display omitted] • The MnG hybrid was prepared by a simple redox method at room temperature. • The catalyst possessed excellent characters such as high surface area and defects. • The synergistic effects between OMS-2 and graphite nanosheets were discussed. • The catalyst showed high activity for AO7 degradation via PMS activation. • Direct electron transfer process played a significant role in the MnG/PMS system. The abundant and low-cost manganese oxides have attracted increasing interest in peroxymonosulfate (PMS) activation. Nevertheless, the low zeta potentials and surface area of the catalysts lead to weak adsorptions of PMS and pollutants under neutral and basic conditions, and thus the low degradation efficiency. Herein, a promising hybrid from graphite nanosheets (GNs) and cryptomelane-type manganese octahedral molecular sieves (OMS-2) was developed by a simple redox method at room temperature. The catalysts possessed a high surface area and a great number of surface defects, which enhanced the adsorption of PMS; while the introduction of GNs increased the capacity of pollutants adsorption and the rate of electron transfer. Compared with pure OMS-2 and other catalysts, the hybrid catalyst showed a much higher performance for acid orange 7 degradation at pH 8.2 with a first-order rate constant of 0.414 min−1, due to the above synergistic effects between OMS-2 and GNs. Based on quenching experiments, PMS decomposition and degradation of pollutants with different oxidation potentials, a direct electron transfer process through Mn-O-PMS complexes was identified to contribute the degradation. Moreover, a galvanic oxidation system was set up to further confirm the occurrence of the mechanism. Overall, this work provides an important step in developing Mn-based hybrids for organic pollutants degradation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mullite YMn 2 O 5 with abundance surface labile oxygen species was prepared. • The catalyst shows high activity for BPA degradation via PMS activation. • The degradation rate is linearly dependent on the ratio of labile oxygen species. • Direct electron transfer process plays a significant role in BPA degradation. • Possible degradation pathway of BPA was proposed. The development of efficient and eco-friendly Mn-based catalysts for peroxymonosulfate (PMS) activation and revealing the mechanism are highly desired for pollutants removal in wastewater. In this study, a ternary mullite oxide YMn 2 O 5 (YMO) was synthesized for bisphenol A (BPA) degradation in the presence of PMS for the first time. Combined with XPS, EPR and TG, abundant surface labile oxygen species (O lab) with a ratio of 39.7% were identified in the mullite materials, which was higher than that for α-, β-, γ- and δ-MnO 2. YMO also exhibited higher interfacial conductivity and stronger interactions among the catalyst, PMS and BPA than other MnO 2. Superior performance in BPA degradation was observed with YMO, and O lab was suggested as the main active sites, for the normalized first-order rate constant was linearly dependent on the ratio of the oxygen species. Chemical quenching experiments, EPR and open circuit potential suggested that the degradation of BPA was mainly caused by the direct electron transfer process through the reactive O lab -PMS complexes. The influence of YMO concentration, PMS concentration, solution pH, different anions and reaction temperature was thoroughly studied. Moreover, the intermediates were identified and the possible degradation pathways were proposed. This work demonstrated that mullite oxide YMO with enriched O lab species can be used as eco-friendly catalysts for efficient PMS activation to remove recalcitrant organic compounds in wastewater. [ABSTRACT FROM AUTHOR]