Modified birnessite MnO2 as efficient Fenton-like catalysts through electron transfer process between the simultaneously surface-activated peroxymonosulfate and pollutants

N-doped biochar-Fe/Mn as a superior peroxymonosulfate activator for enhanced bisphenol a degradation

Emerging contaminants (ECs) are characterized by their widespread environmental distribution and low concentrations, posing significant challenges for their effective removal from source wastewater. To better deal with the problems associated with ECs, we developed a robust Fe-Mn bimetallic catalyst supported on N-doped biochar (FM@NBC-8) for peroxymonosulfate (PMS)-mediated advanced oxidation system, in which bisphenol A (BPA) was investigated as a typical EC. Particularly, complete degradation of BPA in the FM@NBC-8/PMS system was achieved within 5 min, accompanying with a high TOC removal. The degradation rate of BPA with FM@NBC-8 was 143 times that of the initial biochar (BC-8), 20 and 91 times that of single metal-doped catalysts Fe (F@NBC-8) and Mn (M@NBC-8), respectively. The degradation rate of BPA was enhanced to 1.7337 min⁻1 with 0.6 g L⁻1 FM@NBC-8 utilized to activate PMS, achieving a superior performance in BPA degradation compared to most reported results in the literature (0.081∼1.43 min⁻1). The introduction of Fe, Mn, and N elements dramatically enhanced the specific surface area (from 46.285 to 218.541 m2 g⁻1) of the catalyst, thereby enhancing the adsorption capacity of PMS and pollutants on the catalyst. Moreover, the accelerated electron transfer between the catalyst and PMS favored the formation of low-valent metal intermediates (Fe(II)-O-O-SO3- and Mn(II)-O-O-SO3-), responsible for the generation of SO4•-and •OH. And 1O2 was generated mainly via the decomposition of SO5•- in FM@NBC-8/PMS system, thereby collectively enhancing the pollutant degradation. The stability of the catalyst was attributed to the synergistic effects of nitrogen doping and biochar encapsulation, which ensured effective operation of the FM@NBC-8/PMS system across a broad pH range of 3 to 10, while also providing resistance to interference from ubiquitous anions. This study indicates that the bimetal biochar-based materials for catalytic PMS activation have significant potential for practical application in green environmental remediation.

Centrality of phosphate binding modes on metal vanadate in exploiting low-temperature NOX reduction and pyrosulfate dissociation pathways

PO43- guests anchored on metal vanadate hosts are as vital as SO32-/SO42- analogues in wide exploitation for expediting acidic/redox SCR cycles or ABS pyrolysis at low temperatures. This is due to their multiple roles as a provider of Brönsted acidic bonds (BA--H+) and as a dictator of the traits for labile/mobile oxygens (OL/OM) and oxygen vacancies (OV). However, the relationships of BA- (P5+-O2-)/BA--H+ (P5+-O2--H+)/OL/OV/OM feature for the host versus its mono-/bi-dentate PO43- binding mode ( [Formula: see text] / [Formula: see text] ) has never been examined to-date. PO43- guests were thus grafted on MnV2O6 host at 300 °C and 400-500 °C to generate [Formula: see text] -abundant P300 and [Formula: see text] -bountiful P400-P500, respectively. [Formula: see text] species elevated OV hydrophobicity and OM mobility for P300, which were pivotal to enhance its H2O resistance and redox cycle efficiency over P400-P500, respectively. Conversely, [Formula: see text] species outperformed [Formula: see text] counterparts in achieving higher OL nucleophilicity, which was central to reduce the SCR energy barriers and to promote acidic cycle efficiencies for P400-P500. Moreover, P500 had such hydrophobic BA- species that reveal the lowest energy barrier for pyrosulfate (S2O72- of dehydrated ABS) fragmentation among P300-500, thereby unveiling higher ABS resistance than P300-P400 and bi-dentate SO32-/SO42--ample MnV2O6 control with humid, poisonous gases being fed.

Trimetallic MOF-derived Fe-Mn-Sn oxide heterostructure enabling exceptional catalytic degradation of organic pollutants

Developing efficient and environmentally benign heterogeneous catalysts that activate peroxymonosulfate (PMS) for the degradation of persistent organic contaminants remains a challenge. Metal-organic frameworks (MOFs)-derived metal oxide catalysts in advanced oxidation processes (AOPs) have received considerable attention research fraternity. Herein, we report an innovative magnetic trimetallic MOF-derived Fe-Mn-Sn oxide heterostructure (FeMnO@Sn) with adjustable morphology, size and Sn content, prepared through an impregnation-calcination strategy. The formation of a novel magnetic Fe2O3/Fe3O4/Mn3O4 heterostructure induces the generation of abundant Fe2+ and Mn2+ sites on the FeMnO@Sn surface. Meanwhile, the introduction of SnO2 into the Fe2O3/Fe3O4/Mn3O4 heterostructure facilitates the cleavage of the OO bond in adsorbed PMS. The synergy among the different functionalities of each metal oxide plays a vital role in the swift and effective degradation of pollutants. In addition, the uniquely designed catalyst exhibits magnetic properties that facilitate easy recycling and repeated use, thereby meeting environmental protection requirements. Overall, this research highlights the design of heterogeneous catalysts for the effective activation of PMS and provides valuable insights for the advancement of future environmental catalysts.

Low-peroxide-consumption fenton-like systems: The future of advanced oxidation processes

Conventional heterogeneous Fenton-like systems employing different peroxides have been developed for water/wastewater remediation. However, a large population of peroxides consumed during various Fenton-like systems with low utilization efficiency and associated secondary contamination have become the bottlenecks for their actual applications. Recent strategies for lowering the peroxide consumptions to develop economic Fenton-like systems are primarily devoted to the effective radical generation and subsequent high-efficiency radical utilization through catalysts/systems engineering, leveraging emerging nonradical oxidation pathways with higher selectivity and longer life of the reactive intermediate, as well as reactor designs for promoting the mass transfer and peroxides decomposition to improve the yield of radicals/nonradicals. However, a comparative review summarizing the mechanisms and pathways of these strategies has not yet been published. In this review, we endeavor to showcase the designated systems achieving the reduction of peroxides while ensuring high catalytic activity from the perspective of the above strategic mechanisms. An in-depth understanding of these aspects will help elucidate the key mechanisms for achieving economic peroxide consumption. Finally, the existing problems of these strategies are put forward, and new ideas and research directions for lowering peroxide consumption are proposed to promote the application of various Fenton-like systems in actual wastewater purification.

Roles of BOCu sites and graphite nitrogen on persulfate non-radical activation for tetracycline degradation

The activation of peroxymonosulfate (PMS) by carbon-based catalysts is deemed to be a promising method for the degradation of refractory organic contaminants in wastewater. Herein, a Cu-doping strategy in B and N co-doped carbon nanotubes with highly dispersed BOCu sites and graphite nitrogen were successfully synthesized for activating PMS to degradate tetracycline. The best removal rate of tetracycline within 60 min (97.63 %) was obtained by the 1.5 % Cu-BNC and the degradation rate was increased by 17.9 times. The enhanced catalyst activity was attributed to the promoting the cycle of the Cu(I)/Cu(II) redox pair by the formed BOCu sites, and the accelerating the electron transfer process by the adsorption of graphitic N for PMS. The non-free radical pathway including 1O2 and electron transfer played a dominant role in the 1.5 % Cu-BNC/PMS system. The degradation intermediates of TC were identified and three possible degradation pathways were proposed. Further toxicity analysis of the intermediates showed that the 1.5 % Cu-BNC/PMS system had a significant effect on weakening and reducing the biological toxicity and mutagenicity of TC. Moreover, it presented an excellent degradation performance in raw natural water. In general, the proposed regulation of carbon-based catalysts via the coordination-driven effect provides ideas for efficient wastewater treatment.

Non-radical oxidation driven by iron-based materials without energy assistance in wastewater treatment

Chemical oxidation is extensively utilized to mitigate the impact of organic pollutants in wastewater. The non-radical oxidation driven by iron-based materials is noted for its environmental friendliness and resistance to wastewater matrix, and it is a promising approach for practical wastewater treatment. However, the complexity of heterogeneous systems and the diversity of evolutionary pathways make the mechanisms of non-radical oxidation driven by iron-based materials elusive. This work provides a systematic review of various non-radical oxidation systems driven by iron-based materials, including singlet oxygen (1O2), reactive iron species (RFeS), and interfacial electron transfer. The unique mechanisms by which iron-based materials activate different oxidants (ozone, hydrogen peroxide, persulfate, periodate, and peracetic acid) to produce non-radical oxidation are described. The roles of active sites and the unique structures of iron-based materials in facilitating non-radical oxidation are discussed. Commonly employed identification methods in wastewater treatment are compared, such as quenching, chemical probes, spectroscopy, mass spectrometry, and electrochemical testing. According to the process of iron-based materials driving non-radical oxidation to remove organic pollutants, the driving factors at different stages are summarized. Finally, challenges and countermeasures are proposed in terms of mechanism exploration, detection methods and practical applications of non-radical oxidation driven by iron-based materials. This work provides valuable insights for understanding and developing non-radical oxidation systems.

Oxidative polymerization versus degradation of organic pollutants in heterogeneous catalytic persulfate chemistry

Catalytic polymerization pathways in advanced oxidation processes (AOPs) have recently drawn much attention for organic pollutant elimination owing to the rapid removal kinetics, high selectivity, and recovery of organic carbon from wastewater. This work presents a review on the polymerization regimes in AOPs and their applications in wastewater decontamination. The review mainly highlights three critical issues in polymerization reactions induced by persulfate activation (Poly-PS-AOPs), including heterogeneous catalysts, persulfate activation pathways, and properties of organic substrates. The dominant influencing factors on the selection of catalysts, activation regimes of reactive oxygen species, and polymerization processes of organic substrates are discussed in detail. Moreover, we systematically demonstrate the merits and challenges of Poly-PS-AOPs upon pollutant degradation and polymer synthesis. We particularly highlight that Poly-PS-AOPs technology could be promising in the treatment of industrial wastewater containing heterocyclic organics and the synthesis of polymers and polymer-functionalized materials for advanced environmental and energy applications.

Permanganate activation with Mn oxides at different oxidation states: Insight into the surface-promoted electron transfer mechanism

The development of new strategies to improve the removal of organic pollutants with permanganate (KMnO₄) 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 KMnO₄ activation remains relatively unexplored. Interestingly, this study has discovered that Mn oxides with high oxidation states including γ-MnOOH, α-Mn₂O₃ and α-MnO₂, exhibited excellent performance to degrade phenols and antibiotics in the presence of KMnO₄. The MnO₄^- 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-Mn₃O₄ with Mn(II) species, they reacted with KMnO₄ to produce cMnO₂ with very low activity for phenol degradation. The direct electron transfer mechanism in α-MnO₂/KMnO₄ system was further confirmed through the inhibiting effect of acetonitrile and the galvanic oxidation process. Moreover, the adaptability and reusability of α-MnO₂ 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 KMnO₄ activation and understanding of the surface-promoted mechanism.