Singlet oxygen-dominated activation of peroxymonosulfate by 3D hierarchical MnO2 nanostructures for degradation of organic pollutants in water: Surface defect and catalytic mechanism

One material, two functions: A dual-mechanistic approach for the removal of persistent and mobile organic micropollutants from drinking water

Organic micropollutants (OMP), especially those that are more persistent and mobile due to their physico-chemical properties, are resistant to common water treatment techniques and might reach drinking water. Considering the wide range and different physico-chemical properties of persistent and mobile (PM) substances, the strategic integration of synergistic processes appears as a promising solution for the removal of persistent and mobile substances. In this study, the development of a dual-functional material is explored for synergistic adsorption and catalysis, presenting a dual-mechanistic approach for removing potentially persistent and mobile substances from drinking water. The material was fabricated using waste materials (coffee and aluminum wastes) and tested for removing 23 selected OMP. The results demonstrate that the dual-functional material can both adsorb some target OMP and activate persulfate to oxidize OMP by generating reactive oxygen species (ROS). Recycling of the material in repeated cycles revealed removal of several OMP even in 5th cycle, using 0.5 g/L of the synthesized material, 0.5 mM persulfate and 1 h contact time. Quenching experiments indicated that singlet oxygen (1O2) is the dominant ROS in the proposed system, implying that it is a non-radical advanced oxidation process.

Metal ion-modulated synthesis of γ-MnO2 nanosheet for catalytic oxidative degradation of clomiprazole

Two-dimensional non-layered oxide nanosheets exhibit exceptional catalytic properties, offering significant potential for environmental applications. In this study, we report the development of a novel Fe-doped γ-MnO2 material with a hierarchical microsphere morphology, achieved through a metal ion regulation strategy. Unlike conventional sea urchin-like γ-MnO2, Fe doping induced a transformation to a two-dimensional non-layered structure composed of nanosheets, significantly increasing the specific surface area and exposing more active sites. The Fe-doped γ-MnO2 catalysts were evaluated for the degradation of chlorimiprazole (CBZ), a persistent pollutant, using a sulfate radical-based advanced oxidation process. Among the synthesized catalysts, NF-0.25Fe exhibited superior performance, achieving 93% CBZ removal within 16 min under near-neutral conditions. This exceptional activity was attributed to the optimized morphology, higher low-valence Mn content, and enhanced surface-active oxygen species. Systematic investigations revealed that the catalyst dosage, PMS concentration, and pH critically influenced the catalytic efficiency. This work demonstrates the potential of metal ion modulation in tailoring the structural and catalytic properties of transition metal oxides. The insights gained here provide a robust foundation for designing advanced nanomaterials for environmental remediation and other catalytic applications.

Preparation of Heterogeneous Fenton Catalysts Cu-Doped MnO2 for Enhanced Degradation of Dyes in Wastewater

Herein, a series of heterogeneous Fenton catalysts, Cu doped MnO2 (CDM), with different Cu/Mn molar ratios were prepared via a hydrothermal reaction. Meanwhile, detailed characterizations were used to study the structures of CDM, and it is amazing that the morphology of CDM changed from nanowires to nanoflowers with an increasing amount of Cu doped. Apart from this, both the specific surface area and oxygen vacancy increased obviously with the increasing Cu/Mn molar ratio. Then, the degradation of different dyes was utilized to evaluate the catalytic activity of different CDM with H2O2 used as the oxidizing agent, and the 50%-CDM with the highest content of Cu doped displayed the best catalytic activity. Herein, the degradation efficiency (D%) of Congo red (CR) solution with low concentration (60 mg/L) reached 100% in 3 min, while the D% of CR solution with a high concentration (300 mg/L) reached 99.4% after 5 min with a higher dosage of H2O2. Additionally, the 50%-CDM also displayed excellent reusability, for which the D% values were still higher than 90% after the 14th cycles. Based on the structure characteristics and mechanism analysis, the excellent catalytic capacity of 50%-CDM was due to the combined influence of large specific surface area and abundant oxygen vacancy. Thus, a promising heterogeneous Fenton catalyst was developed in this study, which proved the treatment efficiency of actual dye wastewater.

Z-scheme MnO2/Mn3O4 heterojunctions with efficient peroxymonosulfate activation for organic pollutant removal

The exploration of efficient heterogeneous catalysts for persistent organic pollutant removal is extremely attractive. In the present work, MnO2/Mn3O4 photo-Fenton catalysts were designed by a facile hydrothermal route to activate peroxymonosulfate (PMS) under visible light irradiation for organic pollutant degradation. The optimized MnO2/Mn3O4 heterojunction shows excellent Rhodamine B (RhB) removal efficiency, whose apparent kinetic constant is 11.9 and 5.36 times as high as the MnO2 and Mn3O4. Meanwhile, there is a neglectable attenuation in catalytic performance after 5 recycling runs. Based on the active species trapping experiments, the non-radical process contributes more than the radical process during RhB degradation. Moreover, factors including the dosage of PMS, initial RhB concentration, initial pH, the presence of various anions, different organic pollutants, and water sources are investigated. Systematical characterizations reveal that the enlarged specific surface areas and the efficient charge separation aroused from the Z-scheme mechanism are attributed to the enhanced photo-Fenton performance. The present work contributes to the construction of the Mn-based photo-Fenton catalyst with efficient PMS activation capacity for environmental remediation.