Mechanism of Synergistic Effect on Electron Transfer over Co-Ce/MCM-48 during Ozonation of Pharmaceuticals in Water

Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2- and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment.

Enhancing water purification through F and Zn-modified Fe-MCM-41 catalytic ozonation

Due to its low interfacial electron migration ability and highly hydrophilic, Fe-MCM-41 (FeM) had poor activity and stability during catalytic ozonation. To this end, the secondary metal Zn and Si-F group were introduced into the framework of FeM to create surface potential difference and hydrophobic sites. Comparative characterizations showed that there existed rich acid sites with great potential difference on F-Fe-Zn-MCM-41 (FFeZnM). Additionally, because of the existence of hydrophobic and electron-withdrawing Si-F unit, the electron migration ability, hydrophobicity and acidity of FFeZnM were enhanced. The greater O3 mass transfer was induced by Si-F group and O3 was directly activated at Fe and Zn Lewis acid sites into •OH, •O2- and 1O2. With •OH acting as main species, FFeZnM/O3 achieved the superior IBP removal (93.4%, 30 min) and TOC removal (46.6%, 120 min) over those of sole O3 and F-FeM/O3 processes, respectively. HCO3-, Cl-, NO3- and SO42- hindered IBP degradation by FFeZnM/O3, but high concentration humic acid (HA) exhibited promotion by forming HA-IBP complex. IBP degradation by FFeZnM/O3 was enhanced with tap water, river water, and effluent from the secondary sedimentation tank of the sewage plant acting as medium. This study proposed an innovative approach to catalyst design for catalytic ozonation.

Single-atom Pt-CeO2/Co3O4 catalyst with ultra-low Pt loading and high performance for toluene removal

The design and manufacture of high activity and thermal stability catalysts with minimal precious metal loading is essential for deep degradation of volatile organic compounds (VOCs). In this paper, a novel single-atom Pt-CeO₂/Co₃O₄ catalyst with ultra-low Pt loading capacity (0.06 wt%, denoted as 0.06Pt-SA) was fabricated via one-step co-precipitation method. The 0.06Pt-SA exhibited excellent toluene degradation activity of T₉₀ = 169 °C, matched with the nanoparticle Pt-supported CeO₂/Co₃O₄ catalyst with more than six times higher Pt loading (0.41 wt%, denoted as 0.41Pt-NP). Moreover, the ultra-long durability (toluene conversion remains 99% after 120 h stability test) and excellent toluene degradation ability in a wide space speed range of 0.06Pt-SA were superior to that of 0.41Pt-NP catalyst. The excellent performance was derived from the strong metal-support interaction (SMSI) between the single atomic Pt and the carrier, which induced more Pt⁰ and Ce³⁺ for oxygen activation and more Co³⁺ for toluene removal. The in situdiffuse reflectance infrared spectroscopy (DRIFTS) experiments confirmed that the conversion of intermediates was accelerated in the reaction process, thereby promoting the toluene degradation. Our results should inspire the exploitation of noble single-atomic modification strategy for developing the low cost and high performance VOCs catalyst.

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.

The degradation of printing and dyeing wastewater by manganese-based catalysts

Printing and dyeing wastewater generally has high pH, high turbidity, poor biodegradability, complex composition, and high chroma, which make it one of the most difficult industrial wastewaters to treat. Herein, heterogeneous ozone oxidation technology is applied to oxidize and degrade printing and dyeing wastewater. A metal oxide catalyst supported on activated carbon (γ-MnO₂/AC) was prepared by hydrothermal synthetic method and shown to enable synergistic catalysis involving MnO₂ metal sites and N/C sites. A simulated methyl orange solution was used to determine the effects of various preparation and operation parameters. The results confirmed that the γ-MnO₂/AC catalyst exhibited good chemical oxygen demand (COD) removal and reusability. Additionally, γ-MnO₂/AC demonstrated excellent degradation of the secondary biochemical effluent of printing and dyeing wastewater (COD removal = 72.45% within 120 min). The γ-MnO₂/AC catalyst was fully characterized, and the mechanism governing its catalytic ozone oxidation process was investigated experimentally.

Using biochar to strengthen the removal of antibiotic resistance genes: Performance and mechanism

In this study, the excess activated sludge was used for pyrolysis to produce biochar with Ce modification. The removal process and mechanism of ampicillin resistance gene (ARG_Amp) by biochar was investigated. The results showed that when pyrolyzing the excess sludge at 400 °C, the organic components in the sludge could be partially pyrolyzed and complexed with Ce. By accepting electrons from phenol or quinone, persistent free radicals (PFRs) were formed on the surface of biochar. On the optimized conditions with the initial ARG_Amp concentration of 41.43 mg/L, the removal ratios of ARG_Amp by adsorption, PFRs, hydroxyl free radicals (·OH) by adding H₂O₂ were 28.37%, 8.26%, and 27.56%. No melted DNA was detected in the treated samples. The oxidation process by PFRs and ·OH can directly destroy the ARG_Amp structure. The phosphodiester bond in the base stacking structure and the phosphate bond in the nucleotide are the possible action sites of PFRs. Treated ARG_Amp products were in the form of base pair residues or short-chain double helix structures. ·OH can be added to the bases of nucleotide molecules to form highly active free radical adducts. They can initiate molecular dehydrogenation and intermolecular proton transfer, resulting in oxidation of the base to the scission of the phosphate sugar backbone.

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.

In-situ fabrication of novel flower like MoS2/CoTiO3 nanorod heterostructures for the recyclable degradation of ciprofloxacin and bisphenol A under sunlight

Effectual degradation of toxic water contaminants is a crucial step in water purification and designing an efficient semiconductor based hybrid structure photocatalyst is a good approach to achieve this. Benefiting from the combination of semiconductors, a series of novel visible-light active flower-like MoS₂/CoTiO₃ nanorod heterostructures with excellent morphological contact interface were prepared through a facile in-situ hydrothermal process. These heterostructures were well characterized and demonstrated high photocatalytic performance for ciprofloxacin (CIP) and bisphenol A (BPA) under sunlight irradiation. Compared to pristine CoTiO₃ and MoS₂, the optimal catalyst (5 wt% MoS₂/CoTiO₃) presented 39.97 and 22.32 times higher activity for CIP degradation and 26.85 and 15.66 times higher activity for BPA degradation, respectively. This improved activity can be accounted for the effective interfacial contact which promotes the efficient charge carriers separation and reduce its recombination. The catalyst exhibited decent stability and was potentially reused for five cycles without significant loss in activity. Furthermore, based on active species scavenging experiments the plausible photodegradation mechanism is discussed in detail.

Efficient degradation of clofibric acid by heterogeneous catalytic ozonation using CoFe2O4 catalyst in water

CoFe₂O₄ (Cobalt ferrite, CF) nanoparticles were prepared, well characterized and applied as efficient solid catalyst in catalytic ozonation, named CF/O₃ process, for the removal of emerging organic contaminants (EOCs). The degradation and mineralization of clofibric acid (CA) in CF/O₃ process were dramatically enhanced in comparison with those under the O₃ system. Surface hydroxyl groups (HGs) were considered as an important factor for ozone decomposition and the reactive oxygen species (ROS) on the catalyst surface were mainly responsible for CA elimination. The contribution and formation of ROS, including hydroxyl radicals (^•OH), especially superoxide radicals (O₂^•-), singlet oxygen (¹O₂), and hydrogen peroxide (H₂O₂) were evaluated, and a rational mechanism was elucidated accordingly. Probable degradation pathway of CA was proposed according to the organic intermediates identified. The acute toxicity of the treated solution increased during the first 15 min and then declined rapidly and nearly disappeared as the reaction proceeded. In addition, acceptable catalytic performance of CF/O₃ can be obtained for the treatment of other EOCs and the treatment of natural surface water spiked with CA. This work presents an efficient and promising catalytic ozonation technique for the elimination of EOCs in complex water matrices.

Clinoptilolite mediated activation of peroxymonosulfate through spherical dispersion and oriented array of NiFe2O4: Upgrading synergy and performance

Inspired by the features of both transition metal oxide and natural clinoptilolite (flaky structure with suitable pore diameter and open skeleton structure), we adopted a robust strategy by immobilization of nickel ferrite nanoparticles (NiFe₂O₄) on the clinoptilolite surface via typical citric acid combustion method. The hybrid catalyst exhibited enhanced peroxymonosulfate (PMS) activation efficiency and bisphenol A (BPA) degradation performance. Calculated by effective equivalent of NiFe₂O₄, it is found that the reaction rate constant (k) of NiFe₂O₄/clinoptilolite/PMS system (0.1859 min^-1) was 11.9 times higher than that of bare NiFe₂O₄/PMS system (0.0156 min^-1), which demonstrated that catalyst would be conjugated to PMS or contaminant efficiently and renders the rapid degradation and mineralization in the presence of clinoptilolite. After comprehensive characterization analysis and DFT simulations, natural mineral carrier effect (i.e. decreased crystalline size, increased oxygen vacancy content, etc.), abundant surface-bonded and structural hydroxyl groups as well as effective bonding with iron or nickel ions charged for the potential activation mechanism of PMS by NiFe₂O₄/clinoptilolite composite. And it is indicated that not only ^•OH and SO₄^•-, but also ¹O₂ was involved into series reactions. Overall, this study put forward a green and promising technology for high-toxic wastewater treatment.

Catalytic ozonation of bio-treated coking wastewater in continuous pilot- and full-scale system: Efficiency, catalyst deactivation and in-situ regeneration

In this study, the performance of catalytic ozonation in the treatment of bio-treated coking wastewater (BCW) using pilot- and full-scale systems was investigated. Additionally, the removal efficiency of organic pollutants from BCW, the deactivation mechanism of Mn_xCe_1-xO₂/γ-Al₂O₃, and backflushing optimization for in-situ catalyst regeneration, which have not been previously investigated, were analysed. Results of the 12-month pilot scale experiments showed that catalytic ozonation resulted in the effective removal of organic pollutants when backflushing was applied as an in-situ catalyst regeneration strategy. The effluent chemical oxygen demand (COD) content decreased from 150 to 78 mg L^-1, and remained below a discharge limitation of 80 mg L^-1, and the stable COD removal efficiencies (from 56.0% to 47.9%) indicated that catalyst deactivation, which primarily resulted from the deposition of inorganic salts on the surface of the catalyst that limited interaction between ozone and active sites and/or prevented electrons transfer, was primarily inhibited by backflushing. The catalyst regeneration via in-situ air- and water-backflushing was attributed to the scrubbing, collision, and/or the loosing effect. Additionally, in the full-scale experiment, the catalytic ozonation process with in-situ alternative backflushing exhibited a stable COD removal efficiency (above 45.6%) for 885 days when water- and air-flushing strengths of 10 L m^-2 s^-1 and 15 L m^-2 s^-1, respectively, were applied with a 7-day regeneration interval. Therefore, the results of this study provide new insights into catalytic ozonation and support its engineering application in BCW treatment.

Catalytic NO reduction by CO over ceria–cobalt oxide catalysts

The effectiveness of the tandem catalysts was verified by a combination of Co₉₈Ce₂ for low temperature reactions and Co₁₅Ce₈₅ for high temperature reactions.