Synergistic mechanism of supported Mn-Ce oxide in catalytic ozonation of nitrofurazone wastewater

Highly efficient mineralization of phenol through catalytic ozonation using urchin-like CuxCe1Oy-BTC catalysts derived from metal-organic frameworks

The efficient mineralization of phenol and its derivatives in wastewater remains a great challenge. In this study, the bimetallic CuCeO2-BTC was screened from a series of MOFs-derived MCeO2-BTC (M = La, Cu, Co, Fe, and Mn) catalysts, and the influence of the Cu/Ce ratio on phenol removal by catalytic ozonation was carefully examined. The results indicate that Cu2Ce1Oy-BTC was the best among the CuxCe1Oy-BTC (x = 0, 1, 2, and 3) catalysts, with a phenol mineralization efficiency reaching close to 100 % within 200 min, approximately 30.1 % higher than CeO2-BTC/O3 and 70.3 % higher than O3 alone. The order of mineralization efficiency of phenol was Cu2Ce1Oy-BTC > Cu3Ce1Oy-BTC > Cu1Ce1Oy-BTC > CeO2-BTC. CeO2-BTC exhibited a broccoli-like morphology, and CuxCe1Oy-BTC (x = 1, 2, and 3) exhibited an urchin-like morphology. Compared with CuxCe1Oy-BTC (x = 0, 1, and 3), Cu2Ce1Oy-BTC exhibited a larger specific surface area and pore volume. This characteristic contributed to the availability of more active sites for phenol degradation. The redox ability was greatly enhanced as well. Besides, the surface of Cu2Ce1Oy-BTC exhibited a higher concentration of Ce3+ species and hydroxyl groups, which facilitated the dissociation of ozone and the generation of active radicals. Based on the results of radical quenching experiments and the intermediates detected by LC-MS, a potential mechanism for phenol degradation in the Cu2Ce1Oy-BTC/O3 system was postulated. This study offers novel perspectives on the advancement of MOFs-derived catalysts for achieving the complete mineralization of phenol in wastewater through catalytic ozonation.

Rare [Cu4I2]2+ cationic cluster-based metal-organic framework and hierarchical porous composites design for effective detection and removal of roxarsone and antibiotics

Fluorescence quenching induced by photoinduced electron transfer (PET) stands as an effective strategy for identifying water pollutants. Herein, a novel (4, 8)-connected three-dimensional framework Cu(I)-MOF ([Cu2I(tpt)]n) with unique 8-connected [Cu4I2]2+ cationic clusters is designed by employing the nitrogen-rich ligand (Htpt = 5-[4(1H-1,2,4-triazol-1-yl)]phenyl-2H-tetrazole). Water-stabilized Cu(I)-MOF exhibits outstanding fluorescence properties, facilitating its application in detecting organic pollutants in water. Benefiting from the fact that the Cu(I)-MOF possesses a higher lowest unoccupied molecular orbitals (LUMO) energy level than that of the analyte, the rapid d-PET can occur, entitling Cu(I)-MOF to a sensitive fluorescence quenching response to roxarsone (ROX), nitrofurazone (NFZ) and nitrofurantoin (NFT) (with detection limits as low as 0.13 µM, 0.15 µM, and 0.13 µM, respectively). The nitrogen-containing sites of melamine foam (MF) are utilized to facilitate the anchoring and growth of Cu-MOF crystals, which enables the preparation of hierarchical microporous - macroporous Cu(I)-MOF/MF composites. The ordered porous structure of Cu(I)-MOF/MF provides cavities and open sites for the efficient removal of ROX (qmax = 210.6 mg∙g-1), NFZ (qmax = 111.5 mg∙g-1) and NFT (qmax = 238.9 mg∙g-1) from water. This characteristic endows the Cu(I)-MOF/MF with rapid and recyclable adsorption capacity. Therefore, this work provides valuable insights to address the problem of detection and removal of pollutants in the aquatic environment.

Degradation of Sodium Acetate by Catalytic Ozonation Coupled with MnOx/NiOOH-Modified Fly Ash

Fly ash, a type of solid waste generated in power plants, can be utilized as a catalyst carrier to enhance its value-added potential. Common methods often involve using a large amount of alkali for preprocessing, resulting in stable quartz and mullite forming silicate dissolution. This leads to an increased specific surface area and pore structure. In this study, we produced a catalyst composed of MnOx/NiOOH supported on fly ash by directly employing nickel hydroxide and potassium permanganate to generate metal active sites over the fly ash surface while simultaneously creating a larger specific surface area and pore structure. The ozone catalytic oxidation performance of this catalyst was evaluated using sodium acetate as the target organic matter. The experimental results demonstrated that an optimal removal efficiency of 57.5% for sodium acetate was achieved, surpassing even that of MnOx/NiOOH supported catalyst by using γ-Al2O3. After loading of MnOx/NiOOH, an oxygen vacancy is formed on the surface of fly ash, which plays an indirect oxidation effect on sodium acetate due to the transformation of ozone to •O2- and •OH over this oxygen vacancy. The reaction process parameters, including varying concentrations of ozone, sodium acetate, and catalyst dosage, as well as pH value and the quantitative analysis of formed free radicals, were examined in detail. This work demonstrated that fly ash could be used as a viable catalytic material for wastewater treatment and provided a new solution to the added value of fly ash.

Silver nanopopcorns decorated on flexible membrane for SERS detection of nitrofurazone

The synthesis of three-dimensional silver nanopopcorns (Ag NPCs) onto a flexible polycarbonate membrane (PCM) for the detection of nitrofurazone (NFZ) on the fish surface by surface-enhanced Raman spectroscopy (SERS) is presented. The proposed flexible Ag-NPCs/PCM SERS substrate exhibits significant Raman signal intensity enhancement with the measured enhancement factor of 2.36 × 106. This is primarily attributed to the hotspots created on Ag NPCs, including numerous nanoscale protrusions and internal crevices distributed across the surface of Ag NPCs. The detection of NFZ by this flexible SERS substrate demonstrates a low limit of detection (LOD) of 3.7 × 10-9 M and uniform and reproducible Raman signal intensities with a relative standard deviation below 8.34%. It also exhibits excellent stability, retaining 70% of its efficacy even after 10 days of storage. Notably, the practical detection of NFZ in tap water, honey water, and fish surfaces achieves LOD values of 1.35 × 10-8 M, 5.76 × 10-7 M, and 3.61 × 10-8 M, respectively,  which highlights its effectiveness across different sample types. The developed Ag-NPCs/PCM SERS substrate presents promising potential for sensitive SERS detection of toxic substances in real-world samples.

Enhanced ozonation of vanillin catalyzed by highly efficient magnetic MnFe2O4/ZIF-67 catalysts: Synergistic effects and mechanism insights

In this study, we synthesized magnetic MnFe2O4/ZIF-67 composite catalysts using a straightforward method, yielding catalysts that exhibited outstanding performance in catalyzing the ozonation of vanillin. This exceptional catalytic efficiency arose from the synergistic interplay between MnFe2O4 and ZIF-67. Comprehensive characterization via x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FE-SEM), and energy dispersive spectroscopy (EDS) confirmed that the incorporation of MnFe2O4 promoted the creation of oxygen vacancies, resulting in an increased presence of l adsorbed oxygen (Oads) and the generation of additional ·OH groups on the catalyst surface. Utilizing ZIF-67 as the carrier markedly enhanced the specific surface area of the catalyst, augmenting the exposure of active sites, thus improving the degradation efficiency and reducing the energy consumption. The effects of different experimental parameters (catalyst type, initial vanillin concentration, ozone dosage, initial pH value, and catalyst dosage) were also investigated, and the optimal experimental parameters (300 mg/L1.0-MnFe2O4/ZIF-67, vanillin concentration = 250 mg/L, O3 concentration = 12 mg/min, pH = 7) were obtained. The vanillin removal efficiency of MnFe2O4/ZIF-67 was increased from 74.95% to 99.54% after 30 min of reaction, and the magnetic separation of MnFe2O4/ZIF-67 was easy to be recycled and stable, and the vanillin removal efficiency of MnFe2O4/ZIF-67 was only decreased by about 8.92% after 5 cycles. Additionally, we delved into the synergistic effects and catalytic mechanism of the catalysts through kinetic fitting, reactive oxygen quenching experiments, and electron transfer analysis. This multifaceted approach provides a comprehensive understanding of the enhanced ozonation process catalyzed by MnFe2O4/ZIF-67 composite catalysts, shedding light on their potential applications in advanced oxidation processes. PRACTITIONER POINTS: A stable and recyclable magnetic composite MnFe2O4/ZIF-67 catalyst was synthesized through a simple method. The synergistic effect and catalytic mechanism of the MnFe2O4/ZIF-67 catalyst were comprehensively analyzed and discussed. A kinetic model for the catalytic ozone oxidation of vanillin was introduced, providing valuable insights into the reaction dynamics.

Catalytic ozonation of bisphenol A by Cu/Mn@γ-Al2O3: Performance evaluation and mechanism insight

Herein, an alumina-based bimetallic catalyst (Cu1Mn7@γ-Al2O3) was synthesized for bisphenol A (BPA) degradation in the catalytic ozonation process. The catalytic ozonation system could degrade 93.9% of BPA within 30 min under the conditions of pH = 7.0, 10 mg L-1 O3 concentration, and 24 g L-1 catalyst dosage compared to ozone alone (21.0%). The enhanced BPA degradation efficiency was attributed to the abundant catalytic sites and synergistic effects of Cu and Mn. The results revealed that the synergistic interaction between Cu and Mn effectively accelerated the electron transfer process on the catalyst surface, thus promoting the generation of reactive oxygen species (ROS). Further studies indicated that the BPA degradation in Cu1Mn7@γ-Al2O3/O3 system predominantly followed the ·OH and O2·- oxidation pathway. Based on the density functional theory (DFT) calculations and intermediates detected by LC-MS analysis, two pathways for BPA degradation in the Cu1Mn7@γ-Al2O3/O3 system were proposed. The toxicity estimation illustrated that the toxicity of BPA and its byproducts was effectively reduced in the Cu1Mn7@γ-Al2O3/O3 system. This work provides a new protocol for O3 activation and pollutant elimination through a novel bimetallic catalyst during water purification.

The efficiency and mechanism of excess sludge-based biochar catalyst in catalytic ozonation of landfill leachate

In this study, biochar was produced based on dehydrated excess sludge from the municipal wastewater treatment plant, which was used for catalytic ozonation of pollutants derived from landfill leachate. The necessary catalytic sites in the structure of biochar were originated from the inorganic metals and organic matters in the sludge, which included a large number of functional groups (e.g., C-C, CO, etc.), adsorbed oxygen (Oads accounted for 44.82%) and electron defects (ID/IG=1.01). These active sites could promote the generation of reactive oxygen species (ROS) (e.g., ·OH,·O2-, etc.). The synergistic interaction between the microorganisms in the activated sludge also facilitated the removal rates of pollutants. Proteobacteria, Bacteroidetes, and Deinococcu-Thermus were crucial in the bioreactor. In 16 days of reaction, the removal ratios of NH+4-N and COD were 98.95 ± 0.11% and 90.89 ± 0.47%, respectively. This study not only explains the mechanism of catalytic ozonation of biochar, but also provides a new way of the practical treatment of landfill leachate.

Highly efficient catalytic ozonation degradation of levofloxacin by facile hydrogenation-modified red mud wastes

Iron-rich red mud (RM) is a potential catalyst. However, as industrial waste, is strongly alkaline, low effectiveness, and safety concerns are problems that cannot be ignored, it is urgent to mine out a reasonable disposal and utilization technology for the waste. In this study, an effective catalyst (H-RM) was obtained by facile hydrogenation heating modification of red mud. Then above-prepared H-RM was applied in the catalytic ozonation degradation of levofloxacin (LEV). The H-RM exhibited more remarkable catalytic activities than the RM in terms of LEV degradation, and the optimal efficiency can reach over 90% within 50 min. The mechanism experiment proved that the concentration of dissolved ozone and hydroxyl radical (•OH) significantly increased, which enhanced the oxidation effect. Hydroxyl radical played a dominant role in the degradation of LEV. In the safety test, it is concluded that the concentration of total hexavalent chromium (total Cr(Ⅵ)) in the H-RM catalyst decreases and the leaching concentration of water-soluble Cr(Ⅵ) in aqueous solution is low. The results indicated that the hydrogenation technique is an available Cr (Ⅵ) detoxification method for RM. Moreover, the H-RM has excellent catalytic stability, which is beneficial to recycling and maintains high activity. This research provides an effective means to fulfill the reuse of industrial waste as an alternative to standard raw materials, and comprehensive utilization of the waste to attain the purpose of treating pollution with wastes.

Degradation of Sodium Acetate by Catalytic Ozonation Coupled with a Mn-Functionalized Fly Ash: Reaction Parameters and Mechanism

Supported ozone catalysts usually take alumina, activated carbon, mesoporous molecular sieve, graphene, etc. as the carrier for loading metal oxide via the impregnation method, sol-gel method and precipitation method. In this work, a Mn-modified fly ash catalyst was synthesized to reduce the consumption and high unit price of traditional catalyst carriers like alumina. As a solid waste discharged from coal-fired power plants fueled by coal, fly ash also has porous spherical fine particles with constant surface area and activity, abd is expected to be applied as the main component in the synthesis of ozone catalyst. After the pretreatment process and modification with MnOx, the obtained Mn-modified fly ash exhibited stronger specific surface area and porosity combined with considerable ozone catalytic performance. We used sodium acetate as the contaminant probe, which is difficult to directly decompose with ozone as the end product of ozone oxidation, to evaluate the performance of this Mn-modified fly. It was found that ozone molecules can be transformed to generate ·OH, ·O2- and 1O2 for the further oxidation of sodium acetate. The oxygen vacancy produced via Mn modification plays a crucial role in the adsorption and excitation of ozone. This work demonstrates that fly ash, as an industrial waste, can be synthesized as a potential industrial catalyst with stable physical and chemical properties, a simple preparation method and low costs.

Enhanced Catalytic Ozonation by Mn-Ce Oxide-Loaded Al2O3 Catalyst for Ciprofloxacin Degradation

Catalytic ozonation is an effective and promising advanced oxidation technology for organic pollutant removal. Herein, CexMn_1-xO₂ metal oxides loaded on Al₂O₃ catalysts (Mn-Ce/Al₂O₃) were synthesized for catalytic ozonation of the wastewater containing ciprofloxacin. The morphology, crystal structure, and specific surface area of the prepared catalyst were characterized. The characteristics of the Mn-Ce/Al₂O₃ catalyst revealed that the loaded MnO₂ could interfere with the formed CeO₂ crystals and then produced complex CexMn_1-xO₂ oxides. Compared with an ozone-alone system (47.4%), the ciprofloxacin degradation efficiency in the Mn-Ce/Al₂O₃ catalytic ozonation system elevated to 85.1% within 60 min. The ciprofloxacin degradation kinetic rate over the Mn-Ce/Al₂O₃ catalyst is 3.0 times that of the ozone-alone system. The synergetic corporation of redox pairs between Mn(III)/Mn(IV) and Ce(III)/Ce(IV) in the Mn-Ce/Al₂O₃ catalyst could accelerate ozone decomposition to generate active oxygen species and further significantly improve the mineralization efficiency of ciprofloxacin. The work demonstrates the great potential of developing dual-site ozone catalysts for advanced treatment of wastewater.