Effective mineralization of p-nitrophenol by catalytic ozonation using Ce-substituted La1‒xCexFeO3 catalyst

In-situ growth of Mn-Ni3S2 on nickel foam for catalytic ozonation of p-nitrophenol

In this study, a new catalyst for catalytic ozonation was obtained by in-situ growth of Mn-Ni3S2 nanosheets on the surface of nickel foam (NF). The full degradation of p-nitrophenol (PNP) was accomplished under optimal conditions in 40 min. The effects of material dosage, ozone dosage, pH and the presence of inorganic anions on the degradation efficiency of PNP were investigated. ESR analysis showed that singlet oxygen (1O2) and superoxide radical (O2•-) are the main contributors of PNP degradation. This study offers a new combination of supported catalysts with high efficiency and easy recovery, which provides a new idea for wastewater treatment.

Effective degradation of quinoline by catalytic ozonation with MnCexOy catalysts: performance and mechanism

Quinoline inevitably remains in the effluent of coking wastewater treatment plants due to its bio-refractory nature, which might cause unfavorable effects on human and ecological environments. In this study, MnCexOy was consciously synthesized by α-MnO2 doped with Ce3+ (Ce:Mn = 1:10) and employed as the ozonation catalyst for quinoline degradation. After that, the removal efficiency and mechanism of quinoline were systematically analyzed by characterizing the physicochemical properties of MnCexOy, investigating free radicals and monitoring the solution pH. Results indicated that the removal rate of quinoline was greatly improved by the prepared MnCexOy catalyst. Specifically, the removal efficiencies of quinoline could be 93.73, 62.57 and 43.76%, corresponding to MnCexOy, α-MnO2 and single ozonation systems, respectively. The radical scavenging tests demonstrated that •OH and •O2- were the dominant reactive oxygen species in the MnCexOy ozonation system. Meanwhile, the contribution levels of •OH and •O2- to quinoline degradation were about 42 and 35%, respectively. The abundant surface hydroxyl groups and oxygen vacancies of the MnCexOy catalyst were two important factors for decomposing molecular O3 into more •OH and •O2-. This study could provide scientific support for the application of the MnCexOy/O3 system in degrading quinoline in bio-treated coking wastewater.

Catalytic Activity of LaFe0.4Ni0.6O3/CeO2 Composites in CO and CH4 Oxidation Depending on Their Preparation Conditions

LaFe_0.4Ni_0.6O₃/CeO₂ (1:1) two-phase composite materials were prepared by mechanochemical (MC) and Pechini routes. The catalytic properties of the composites in methane and CO oxidation reactions strongly depend on their preparation conditions. In low-temperature (<600 °C) catalytic CO oxidation the composites demonstrate a higher activity compared with LaFe_0.4Ni_0.6O₃ perovskite. The highest activity was observed for the composite prepared by mechanical treatment of perovskite and fluorite precursors. There is a correlation between activity and the content of weakly bound surface oxygen species. Catalytic activity in high-temperature (>750 °C) catalytic methane oxidation correlates with the reducibility of samples. The highest activity was observed for the composite prepared by the one-pot Pechini route with higher reducibility of the sample up to 600 °C.

Oxygen-Deficient Engineering for Perovskite Oxides in the Application of AOPs: Regulation, Detection, and Reduction Mechanism

A perovskite catalyst combined with various advanced oxidation processes (AOPs) to treat organic wastewater attracted extensive attention. The physical and chemical catalytic properties of perovskite were largely related to oxygen vacancies (OVs). In this paper, the recent advances in the regulation of OVs in perovskite for enhancing the functionality of the catalyst was reviewed, such as substitution, doping, heat treatment, wet-chemical redox reaction, exsolution, and etching. The techniques of detecting the OVs were also reviewed. An insight was provided into the OVs of perovskite and reduction mechanism in AOPs in this review, which is helpful for the reader to better understand the methods of regulating and detecting OVs in various AOPs.

Porous LaFeO3 perovskite catalysts synthesized by different methods and their high activities for CO oxidation

In this study, spherical α-Fe₂O₃ prepared by the hydrothermal method was used as a template for the first time; LaFeO₃ perovskite catalysts were successfully synthesized by the molten salt method (M-LF-T), sol-gel method (S-LF-T), and co-precipitation method (C-LF-T), respectively. To determine the optimal synthesis method, X-ray diffraction patterns were obtained and showed that single phase LaFeO₃ with good crystallinity was prepared by the molten salt method after calcination at 600 °C for 4 h. SEM and TEM images showed that the M-LF-600 catalyst preserved the spherical structure of α-Fe₂O₃ template. Compared with the catalysts synthesized by the sol-gel method and co-precipitation method, the M-LF-600 catalyst had the highest BET surface area of 16.73 m² g^-1. X-ray photoelectron spectroscopy analysis showed that the M-LF-600 catalyst had the highest surface Fe³⁺/Fe²⁺ molar ratio and the best surface oxygen adsorption capacity. The CO oxidation of the LaFeO₃ catalyst demonstrated that the M-LF-600 catalyst had the best catalytic performance.

Catalytic ozonation of antibiotics by using Mg(OH)2 nanosheet with dot-sheet hierarchical structure as novel nanoconfined catalyst

Antibiotic pollution has caused important concern for international and national sustainability. Catalytic ozonation is a quick and efficient technique to remove contaminants in aquatic environment. This study firstly developed a nanosheet-growth technique for synthesizing Li-doped Mg(OH)₂ with dot-sheet hierarchical structure as catalyst to ozonize antibiotics. Metronidazole could be totally removed through ozonation catalyzed by Li-doped Mg(OH)₂ in 10 min. Approximately 97% of metronidazole was eliminated in 10 min even the catalyst was used for 4 times. Reaction rate constant of Li-doped Mg(OH)₂ treatment was about 3.45 times that of nano-Mg(OH)₂ treatment, illustrating that the dot-sheet hierarchical structure of Li-doped Mg(OH)₂ exhibited nano-confinement effect on the catalytic ozonation. Approximately 70.4% of metronidazole was mineralized by catalytic ozonation using Li-doped Mg(OH)₂. Temperature of 25 °C was more suitable for catalytic ozonation of metronidazole by Li-doped Mg(OH)₂. Ions generally inhibited the catalytic ozonation of metronidazole while only 0.005 mol L^-1 of Cl^- slightly enhanced the ozonation rate, illustrating complicated mechanisms existed for ozonation of metronidazole catalyzed by Li-doped Mg(OH)₂. The possible mechanisms of the ozonation of metronidazole using Li-doped Mg(OH)₂ included direct ozonation and ozonation catalyzed by radical ·O₂^-, reactive oxygen species ¹O₂ and intermediate (H₂O₂). The synthesized Mg(OH)₂ nanosheet with dot-sheet hierarchical structure is a novel nanoconfined material with excellent reusability and catalytic performance.

Heterogeneous Catalysis of Ozone Using Iron–Manganese Silicate for Degradation of Acrylic Acid

Iron–manganese silicate (IMS) was synthesized by chemical coprecipitation and used as a catalyst for ozonating acrylic acid (AA) in semicontinuous flow mode. The Fe-O-Mn bond, Fe-Si, and Mn-Si binary oxide were formed in IMS on the basis of the results of XRD, FTIR, and XPS analysis. The removal efficiency of AA was highest in the IMS catalytic ozonation processes (98.9% in 15 min) compared with ozonation alone (62.7%), iron silicate (IS) catalytic ozonation (95.6%), and manganese silicate catalytic ozonation (94.8%). Meanwhile, the removal efficiencies of total organic carbon (TOC) were also improved in the IMS catalytic ozonation processes. The IMS showed high stability and ozone utilization. Additionally, H2O2 was formed in the process of IMS catalytic ozonation. Electron paramagnetic resonance (EPR) analysis and radical scavenger experiments confirmed that hydroxyl radicals (•OH) were the dominant oxidants. Cl−, HCO3−, PO43−, Ca2+, and Mg2+ in aqueous solution could adversely affect AA degradation. In the IMS catalytic ozonation of AA, the surface hydroxyl groups and Lewis acid sites played an important role.

Mineral-modulated Co catalyst with enhanced adsorption and dissociation of BH4- for hydrogenation of p-nitrophenol to p-aminophenol

Slow adsorption and dissociation kinetics of NaBH₄ onto the catalyst surface limit the hydrogenation reduction of hazardous p-nitrophenol to worthy p-aminophenol. Herein, we design a mineral-modulated catalyst to facilitate the rate-limiting step. Carbon-coated etched attapulgite (EAtp@C) is obtained by HF treatment. Co/EAtp@C is fabricated via anchoring cobalt nanoparticles (CoNPs) on the carrier EAtp@C. Compared to pure Co, the anchored CoNPs are more electronegative and stable, which provides abundant and stable active sites and accelerates the BH₄^- adsorption and dissociation. Therefore, Co/EAtp@C leads to nearly 100% reduction of p-nitrophenol to p-aminophenol within 8 min and its apparent rate constant K_app (0.69 min^-1) is 4 times higher than that of pure Co. Thermodynamic calculations show a lower activation energy (37.92 kJ mol-1) of Co/EAtp@C catalyst than that of pure Co. Co/EAtp@C also shows magnetic separability and good stability by remaining 98.6% of catalytic conversion rate after six cycles. Significantly, we detect the active species Co-H, and reveal the electron transfer mechanism between catalysts, BH₄^-, and p-nitrophenol by electrochemical method. These results offer a fundamental insight into the catalytic mechanism of p-nitrophenol hydrogenation for rational design of efficient catalysts.

Removal of Paracetamol from Aqueous Solutions by Photocatalytic Ozonation over TiO2-MexOy Thin Films

Analgesics and nonsteroidal anti-inflammatory drugs (NSAIDs) such as paracetamol, diclofenac, and ibuprofen are frequently encountered in surface and ground water, thereby posing a significant risk to aquatic ecosystems. Our study reports the catalytic performances of nanosystems TiO₂-Me_xO_y (Me = Ce, Sn) prepared by the sol-gel method and deposited onto glass slides by a dip-coating approach in the removal of paracetamol from aqueous solutions by catalytic ozonation. The effect of catalyst type and operation parameters on oxidation efficiency was assessed. In addition to improving this process, the present work simplifies it by avoiding the difficult step of catalyst separation. It was found that the thin films were capable of removing all pollutants from target compounds to the oxidation products.