Characterization and reactivity of cerium loaded MCM-41 for p-chlorobenzoic acid mineralization with ozone

An ozone catalytic oxidation system for the degradation of organic compounds in secondary wastewater from refining and chemical processes

To overcome the low catalytic efficiency, insufficient catalyst strength, and poor ozone circulation in the advanced treatment of secondary wastewater, a hollow cylindrical Fe-Cu-Ce-Mn/Al2O3 catalyst was prepared by the step impregnation method. Compared with the common impregnation method, the step impregnation method produced a more uniform and compact distribution of each metal element, which was more conducive to generating the synergistic effect of various metals; thus, increasing the mineralization rate of organic matter. The hollow cylindrical design ensured the strength of the catalyst and the circulation of ozone. The reduction of the chemical oxygen demand (COD) was compared under different experimental conditions, with the optimal conditions found to be an ozone contact time of 40 min and ozone dosage of 40 mg/L. The average COD, ammonia nitrogen, and ultraviolet absorbance at 254 nm (UV254) removal rates were 36%, 19%, and 20%, respectively. After 3 weeks of continuous experiment, the removal rate was still high. Following analysis by three dimensional fluorescence, GC-MS, and the molecular weight detection of water samples before and after treatment, it was found that the catalyst enhanced the effect of ozone on wastewater treatment, with a significant removal of tryptophan-like aromatic proteins and soluble microbial metabolites, and the removal of most of the small molecular organic matter. In addition, part of the refractory organic matter could be converted into easily degradable organic matter, which greatly improved the biodegradability and mineralization rate of wastewater, and provided good conditions for subsequent treatment.

A comprehensive review on metal based active sites and their interaction with O3 during heterogeneous catalytic ozonation process: Types, regulation and authentication

Heterogeneous catalytic ozonation (HCO) was a promising water purification technology. Designing novel metal-based catalysts and exploring their structural-activity relationship continued to be a hot topic in HCO. Herein, we reviewed the recent development of metal-based catalysts (including monometallic and polymetallic catalysts) in HCO. Regulation of metal based active sites (surface hydroxyl groups, Lewis acid sites, metal redox cycle and surface defect) and their key roles in activating O₃ were explored. Advantage and disadvantage of conventional characterization techniques on monitoring metal active sites were claimed. In situ electrochemical characterization and DFT simulation were recommended as supplement to reveal the metal active species. Though the ambiguous interfacial behaviors of O₃ at these active sites, the existence of interfacial electron migration was beyond doubt. The reported metal-based catalysts mainly served as electron donator for O₃, which resulted in the accumulation of oxidized metal and reduced their activity. Design of polymetallic catalysts could accelerate the interfacial electron migration, but they still faced with the dilemma of sluggish Me^(n+m)+/Meⁿ⁺ redox cycle. Alternative strategies like coupling active metal species with mesoporous silicon materials, regulating surface hydrophobic/hydrophilic properties, polaring surface electron distribution, coupling HCO process with photocatalysis and H₂O₂ were proposed for future research.

Highly stable and efficient calcined γ-Al2O3 catalysts loaded with MnOx-CeOx for the ozonation of oxytetracycline

Catalytic ozonation with supported metal oxides is a promising strategy for addressing refractory pollutants in wastewater. In this study, γ-Al2O3 supported MnOx-CeOx catalysts (MC1, MC2, and MC3) obtained at different calcination temperatures (400 °C, 550 °C, and 700 °C) were applied as effective catalysts for ozonation and explored the feasibility of the treatment of oxytetracycline (OTC) wastewater. Comparatively, the MC2 possessed the highest molar ratios of Mn3+/Mn4+ (1.60) and Ce3+/Ce4+ (0.96), the largest surface area (273.8 m2 g-1) with a petal-shaped structure, and most abundant surface hydroxyls (3.78 mmol g-1). These physicochemical characteristics benefited the surface reaction and resulted in the acceleration of ozone decomposition, electron transfer, and •OH generation, thereby improving the catalyst's adsorption ability and catalytic activity. The combination with MC2 increased the OTC and COD removal of the ozonation process from 59.1% and 29.0% to 94.7% and 83.3% in 25 min, respectively. By employing electron paramagnetic resonance (EPR) and radical quenching experiments, it was verified that •OH species generation promoted the mineralization of OTC. The possible degradation pathways of OTC were investigated through mass spectrometry, and the route consisted of dehydration, deamination, and demethylation. Moreover, during a 12-day continuous experiment, MC2 catalyst exhibited excellent reusability and catalytic stability, with COD removal efficiencies above 80%.

Enhancing catalytic ozonation activity of MCM-41 via one-step incorporating fluorine and iron: The interfacial reaction induced by hydrophobic sites and Lewis acid sites

Fe-MCM-41 had been widely used as ozonation catalyst, however, the existence of large amount of hydrophilic silanol hindered its interfacial reaction with O₃ and pollutants. To solve this problem, F-Fe-MCM-41 was synthesized by co-doping F and Fe into the framework of MCM-41 to replace silanol with Si-F groups through a one-step hydrothermal method. F introduced hydrophobic sites which contributed to more ibuprofen (IBP) chemisorption on the surface of F-Fe-MCM-41. Moreover, doping F also enhanced the acidity, which accelerated O₃ decomposition into •OH. F-Fe-MCM-41/O₃ exhibited notably activity with 96.6% IBP removal efficiency within 120 min, while only 78.5% and 80.9% in O₃ alone and Fe-MCM-41/O₃, respectively. Surface Lewis acid sites and metal hydroxyl groups were considered as important factors for O₃ activation and •OH generation. F-Fe-MCM-41 exhibited excellent catalytic performance under acidic and alkaline conditions. Comparative experiments revealed that F doping improved the interfacial reaction, especially the interfacial electron transfer, which resulted in the high catalytic activity of F-Fe-MCM-41. F-Fe-MCM-41 possessed good stability and reusability, with only 5.7% decline for IBP removal in five successive cycles. Furthermore, the possible degradation path of IBP was proposed according to DFT calculation and GC-MS analysis.

Reactive Oxygen Species and Catalytic Active Sites in Heterogeneous Catalytic Ozonation for Water Purification

Heterogeneous catalytic ozonation (HCO) processes have been widely studied for water purification. The reaction mechanisms of these processes are very complicated because of the simultaneous involvement of gas, solid, and liquid phases. Although typical reaction mechanisms have been established for HCO, some of them are only appropriate for specific systems. The divergence and deficiency in mechanisms hinders the development of novel active catalysts. This critical review compares the various existing mechanisms and categorizes the catalytic oxidation of HCO into radical-based oxidation and nonradical oxidation processes with an in-depth discussion. The catalytic active sites and adsorption behaviors of O₃ molecules on the catalyst surface are regarded as the key clues for further elucidating the O₃ activation processes, evolution of reactive oxygen species (ROS) or organic oxidation pathways. Moreover, the detection methods of the ROS produced in both types of oxidations and their roles in the destruction of organics are reviewed with discussion of some specific problems among them, including the scavengers selection, experiment results analysis as well as some questionable conclusions. Finally, alternative strategies for the systematic investigation of the HCO mechanism and the prospects for future studies are envisaged.

Dramatic enhancement effects of l-cysteine on the degradation of sulfadiazine in Fe3+/CaO2 system

Excessive sulfonamides accumulated in soil and groundwater seriously menace the ecological environment and human health. The performance of a Fenton-like system applying Fe³⁺ and calcium peroxide (CaO₂) in the presence of l-cysteine(l-cys) for sulfadiazine (SDZ) degradation was investigated. Compared with other chelating agents such as citric acid, butyric acid and Ethylenediaminetetraacetic acid, l-cys could effectively promote the SDZ removal in Fe³⁺/CaO₂ system. With the addition of 0.5 mM l-cys, the SDZ degradation increased from 2.14% to 66.53% in 60 min. High concentration of HCO₃^- inhibited the degradation of SDZ while slightly negative effects on SDZ degradation were observed in the presence of Cl^- or humic acid (HA) in l-cys/Fe³⁺/CaO₂ system. Electron paramagnetic resonance (EPR) analysis and radicals scavenge tests affirmed the generation of OH and O₂- in l-cys/Fe³⁺/CaO₂ system. Possible degradation pathway of SDZ was speculated and the toxicity of SDZ intermediates was further evaluated. l-cys could enhance the reduction of Fe³⁺ to Fe²⁺ and reduced the Fe³⁺ precipitation due to the l-cys could form stable complexes with Fe³⁺. l-cys/Fe³⁺/CaO₂ system exhibited high mineralization ability. Overall, these results indicated that l-cys is a promising chelating agent for sulfadiazine wastewater treatment.

Catalytic Ozonation of Recalcitrant Organic Chemicals in Water Using Vanadium Oxides Loaded ZSM-5 Zeolites

The discharge of wastewater having recalcitrant chemical compositions can have significant and adverse environmental effects. The present study investigates the application of a catalytic ozonation treatment for the removal of recalcitrant organic chemicals (ROCs) from the water. Novel catalytic materials using vanadium (V) oxides deposited onto the surface of NaZSM-5 zeolites (V/ZSM) were found to be highly efficient for this purpose. The highly-dispersed V oxides (V4+ and V5+) and Si-OH-Al framework structures were determined to promote the surface reaction and generation of hydroxyl radicals. The constructed V1/ZSM450 (0.7 wt% of V loading and 450°C of calcination) exhibited the highest activity among the developed catalyst compositions. The V1/ZSM450-COP increased the mineralization rate of nitrobenzene and benzoic acid by 50 and 41% in comparison to single ozonation. This study demonstrates the enhanced potential of V/ZSM catalysts used with catalytic ozonation process (COP) for the treatment of chemical wastewaters.

Synthesis of manganese incorporated hierarchical mesoporous silica nanosphere with fibrous morphology by facile one-pot approach for efficient catalytic ozonation

Manganese incorporated fibrous silica nanosphere (MnOx-0.013/KCC-1) was synthesized by one step hydrothermal method for the first time and its catalytic activity for ozonation of oxalic acid was studied. For comparison, manganese loaded MCM-41 (MnOx-0.013/MCM-41) was prepared by impregnation method. Various characterizations showed that the morphological, structural and textural properties of MnOx-0.013/KCC-1 were well preserved. Ozonation and catalytic ozonation by MnOx-0.013/KCC-1 and MnOx-0.013/MCM-41 led to 4, 85 and 60% reduction in TOC respectively. Furthermore, 0.05 and 1.2mgL(-1) leaching of Mn was detected from MnOx-0.013/KCC-1 and MnOx-0.013/MCM-41, which are approximately 2.0 and 42.0% of the total Mn present in MnOx-0.013/KCC-1 and MnOx-0.013/MCM-41 respectively. The high catalytic activity was attributed to the generation of hydroxyl radical. Surface hydroxyl groups investigated by using phosphates and ATR-FTIR were believed to be the active sites. Our proposed method of synthesis can be generalized for the synthesis of other metal oxides incorporated fibrous silica for environmental catalysis and other catalytic reactions.

Low-temperature NOx(x = 1, 2) removal with ˙OH radicals from catalytic ozonation over a RGO–CeO2nanocomposite: the highly promotional effect of oxygen vacancies

CeO₂grown on a reduced graphene oxide nanocomposite (RGO–CeO₂) was successfully synthesized by a facile alkaline hydrothermal method with the addition of ethylene glycol.