Manganese oxides activated peroxymonosulfate for ciprofloxacin removal: Effect of oxygen vacancies and chemical states

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.

Tannic acid-assisted upcycling of Cu from waste printed circuit boards to an efficient peroxymonosulfate catalyst for the degradation of organic pollutants

The recovery of metals from solid waste for use as heterogeneous catalysts to activate peroxymonosulfate (PMS) for organic wastewater treatment is a promising, environmentally friendly and economical strategy. Herein, we present a facile and versatile strategy for upcycling copper (Cu) from waste printed circuit boards (PCBs) to Cu oxides supported on a three-dimensional carbon framework (10PCBs-Cu-TA) with the aid of tannic acid (TA). Compared to the PCBs-Cu synthesized without TA, introducing TA into 10PCBs-Cu-TA reduced Cu leaching, enhanced crystallinity, promoted electron transfer, and increased the number of oxygen vacancies. Moreover, 10PCBs-Cu-TA exhibited superior catalytic activity in activating PMS for the degradation of reactive brilliant blue KN-R, exceeding the activity of 10Cu-TA prepared using commercial Cu(NO3)2·3H2O. This enhanced performance may be attributed to the higher specific surface area and oxygen vacancies of 10PCBs-Cu-TA. The 10PCBs-Cu-TA/PMS system also exhibited broad catalytic universality and adaptability to various contaminants and water matrices. Quenching experiments, electron paramagnetic resonance analysis, and electrochemical measurements indicated that radical and non-radical processes jointly contributed to KN-R degradation. The proposed strategy for upcycling Cu from waste PCBs into functional materials provides novel insights into the utilization of solid waste and the development of PMS activators.

A new multimodal magnetic nanozyme and a reusable peroxymonosulfate oxidation catalyst: Manganese oxide coated-monodisperse-porous and magnetic core-shell microspheres

Monodisperse-porous, polydopamine and manganese oxide coated, core-shell type, magnetic SiO2 (MagSiO2@PDA@MnO2) microspheres 6.4 μm in size were synthesized for the first time, using magnetic, monodisperse-porous SiO2 (MagSiO2) microspheres 6.2 μm in size as the starting material. MagSiO2 microspheres were obtained by a recently developed method namely "staged shape templated hydrolysis and condensation protocol". In the synthesis, MagSiO2 microspheres were consecutively coated by polydopamine (PDA) and then by a MnO2 layer in the aqueous medium. The pore volume and the specific surface area of monodisperse-porous MagSiO2@PDA@MnO2 microspheres were measured as 0.59 cm3 g-1 and 154 m2 g-1, respectively. Their Mn and Fe contents were determined as 66 ± 1 mg g-1 and 165 ± 5 mg g-1 respectively. MagSiO2@PDA@MnO2 microspheres exhibited multimodal enzyme mimetic behavior with highly superior catalase-like, oxidase-like and peroxidase-like activities. The effective production of singlet oxygen (1O2) and superoxide anion (O2-*) radicals in MagSiO2@PDA@MnO2-peroxymonosulfate (PMS) system was demonstrated by ESR spectroscopy. By evaluating this property, MagSiO2@PDA@MnO2 microspheres were tried as a reusable catalyst for dye removal via peroxymonosulfate (PMS) activation in batch experiments for the first time. The degradation runs were made with, rhodamine B (Rh B), methyl orange (MO) and methylene blue (MB) as the pollutant. The core-shell type design allowing the deposition of porous MnO2 layer onto a large surface area provided very fast, instant removals with all dyes, via both physical adsorption and degradation via PMS activation. In the reusability experiments, the removal yields of MO and Rh B decreased 1.8% and 8.9% over five consecutive runs in batch fashion. MagSiO2@PDA@MnO2 microspheres exhibited very good functional and structural stability in consecutive dye degradations. No significant change was observed in Fe content of microspheres while Mn content exhibited a decrease of 7.4% w/w over 5 consecutive degradation runs.

Applications of vacancy defect engineering in persulfate activation: Performance and internal mechanism

The vacancy defects in heterogeneous catalysts have received extensive attention for persulfate (PS) activation. Vacancy defects can tune the electronic structure of metal oxides and generate unsaturated coordination sites. Meanwhile, the adsorption energy of reactants on catalyst surface is optimized. Thereby, the reaction energy barrier between catalysts and PS decreases, which could promote catalytic activation and accelerate pollutants degradation. Nowadays, oxygen vacancy (OV), nitrogen vacancy (NV), sulfur vacancy (SV), selenium vacancy (SeV) and titanium vacancy (TiV) have been widely studied with great potential for water remediation. So far, no review was reported regarding the vacancy activated persulfate systems. This paper summarized the types, preparation, mechanism and applications of vacancy in PS systems systematically. In addition, we put forward possible development of vacancy engineering in PS activation systems. It is expected that this review will contribute to the controllable synthesis and applications of vacancies in catalysts for PS activation and contaminants removal.

Mechanistic insight into the degradation of ciprofloxacin in water by hydroxyl radicals

Ciprofloxacin (CIP), an effective antibacterial drug, is widely used to treat bacterial infections in humans and animals. However, drug pollution from residues and the development of resistant genes may pose serious ecological risks. Among the known methods of CIP degradation, advanced oxidation technology initiated by hydroxyl radicals exhibits great potential. However, an in-depth study of the degradation mechanism is difficult because of the limitations of the testing methods. In this study, CIP oxidation by hydroxyl radicals was evaluated using density functional theory (DFT), and the thermodynamics, kinetics, and toxicity were investigated. The results show that CIP oxidation occurs mainly through the piperazine ring, benzene ring, and CC. High reactivity is achieved in the initial reactions, where only five reactions are not thermodynamically spontaneous. Reactions involving direct hydrogen abstraction by oxygen in this system are superior to the indirect reactions. Some theoretically predicted products, such as P6 and P11, are consistent with those reported in previous experiments, indicating that the theoretical study can provide supplementary information about the oxidation paths. The branching ratios for the hydrogen atom abstraction and addition reactions were 37. 45% and 62.55%, respectively. Finally, this reaction system is completely nontoxic based on toxicity assessment.

Novel construction of the catalyst from red mud by the pyrolysis reduction of glucose for the peroxymonosulfate-induced degradation of m-cresol

Red mud of low cost is regarded as a promising alternative to heterogeneous catalysts for activating peroxymonosulfate (PMS) to degrade m-cresol. Improper valence states of metal oxides and coated active substances in red mud greatly hampered its wide application. To solve this problem, the modified red mud (WRMG/700) was prepared by the pyrolysis reduction of glucose in N₂ atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectrum (XPS) analysis confirmed the production of Fe₃O₄, MnO and NiO in red mud and their gathering on the surface of particles. WRMG/700 exhibited the excellent performance toward PMS activation for the m-cresol degradation with 99.02% degradation efficiency and a pH-independent catalytic activity between initial pH 3-8. The removal efficiency of COD increased with the reaction time under the optimized degradation conditions. The free radical scavenging experiments and electron paramagnetic resonance (EPR) test confirmed ¹O₂ played a dominant role during m-cresol degradation in the WRMG/700/PMS system, implying m-cresol degradation was a non-radical oxidation process. Accordingly, the possible reaction mechanism was proposed. WRMG/700 retained its activation performance even after five recycles. This study showed a low cost and simple operation process for m-cresol elimination.

A Review of Sulfate Radical-Based and Singlet Oxygen-Based Advanced Oxidation Technologies: Recent Advances and Prospects

In recent years, advanced oxidation process (AOPs) based on sulfate radical (SO4●−) and singlet oxygen (1O2) has attracted a lot of attention because of its characteristics of rapid reaction, efficient treatment, safety and stability, and easy operation. SO4●− and 1O2 mainly comes from the activation reaction of peroxymonosulfate (PMS) or persulfate (PS), which represent the oxidation reactions involving radicals and non-radicals, respectively. The degradation effects of target pollutants will be different due to the type of oxidant, reaction system, activation methods, operating conditions, and other factors. In this paper, according to the characteristics of PMS and PS, the activation methods and mechanisms in these oxidation processes, respectively dominated by SO4●− and 1O2, are systematically introduced. The research progress of PMS and PS activation for the degradation of organic pollutants in recent years is reviewed, and the existing problems and future research directions are pointed out. It is expected to provide ideas for further research and practical application of advanced oxidation processes dominated by SO4●− and 1O2.