Catalyst For Ozonation Research Articles

Catalytic ozonation of three isomeric cresols in the presence of NaCl with nano-mesoporous β-molecular sieves

Catalytic ozonation is one suitable method to efficiently remove pollutants from refractory wastewater which if treated improperly could cause the severe contamination of surface and underground water. In this study, nano-mesoporous β-molecular sieves were synthesized and employed as catalysts for ozonation. These catalysts had large specific surface area, appropriate surface acidity, high thermal stability and chemical stability. Especially, they could be used in the presence of salt which was frequently contained in industrial wastewater. We used three types of cresols (o-, m-, and p- cresol), the typical phenolic pollutants in industrial wastewater, as model target pollutants. Experimental results demonstrated that the catalytic performance of the prepared catalysts was superior to the commercial molecular sieves. High surface area as well as open porous structure of catalysts was believed to enhance the catalytic activity by surface reaction and easy access of reactants to the active sites. The influences of salt (NaCl) concentration and the aqueous pH on the catalytic ozonation of three cresols were discussed respectively in the study. Interestingly, the degradation of three cresols occurred in the order p>m>o at pH=2.0, and the similar result was obtained under alkaline condition. In addition, the conversion of three cresols was highest (more than 95%) at pH=12.0. With the rise of NaCl concentration, the removal rates of three cresols increased at first (0-0.5wt.%) and then decreased (0.5wt.% to 5wt.%). The variation of intermediates during the oxidation of cresols were monitored by GC together with in situ React IR. The degradation mechanism of three cresols was proposed, of which the possibility and feasibility were well certified by frontier molecular orbital theory and atomic charge distribution via density functional theory method.

Ni-Fe layered double hydroxides catalized ozonation of synthetic wastewater containing Bisphenol A and municipal secondary effluent

Ni-Fe Layered Double Hydroxides (Ni-Fe LDHs) was prepared, characterized and used as catalyst in heterogeneous catalytic ozonation of Bisphenol A (BPA) and other organic compounds in secondary effluent. The characterization and ozonation results revealed that the Ni-Fe LDHs possessing a Ni: Fe ratio of 3:1 had the best crystalline and the highest affinity for ozone. Under the optimized conditions, the final TOC and COD removal achieved was 56% and 68%, respectively. BPA in the secondary effluent could be removed completely by Ni3-Fe LDH catalyzed ozonation. The organic compounds removal was mainly attributed to the oxidation by free active radicals such as hydroxyl radicals (OH). In this research the accumulative ·OH in the reaction system was determined to be 28.2 μmol at the reaction time of 60 min. The free active radicals were mostly generated through the electron transfer among different valences of metals on Ni-Fe LDHs surface, and subsequently diffused into bulk solution to oxidize the target organic compounds there.

Catalytic Ozonation by Manganese, Iron and Cerium Oxides on γ-Al2O3 Pellets for the Degradation of Organic Pollutants in Continuous Fixed-Bed Reactor

ABSTRACTHeterogeneous catalytic ozonation is an efficient technology for degrading refractory organic pollutants in water. However, most studied heterogeneous catalysts for catalytic ozonation were powders, which were not practically available for continuous fixed-bed reactor in water treatment. In this work, manganese, iron and cerium oxides on γ-Al2O3 pellets were synthesized and used as heterogeneous catalysts for catalytic ozonation in a continuous fixed-bed reactor. Results showed that all the prepared metal oxides on γ-Al2O3 pellets exhibited facilitated catalytic ozonation for degrading refractory contaminates compared with ozonation alone and catalytic ozonation on pure γ-Al2O3 pellets. The cerium oxides supported on γ-Al2O3 pellets (CeO2/γ-Al2O3) performed best catalytic performance with the COD removal efficiency of 64.3% and TOC removal efficiency of 41.7%. Moreover, the catalytic activity was further enhanced by the synergistic effect of the bimetallic oxides on γ-Al2O3 pellets (CeO2-Fe2O3/γ-Al2O3). This study is expected to help to encourage further research and applications in AOPs based on the success of this work in designing heterogeneous catalysts available for continuous fixed-bed reactor.

Amino-functionalized synthesis of MnO2-NH2-GO for catalytic ozonation of cephalexin

Catalysts such as MnO2 always play a critical role in catalytic ozonation, which is applied extensively in water treatment for disinfection, odor removal and organic pollutants degradation. To improve the performance of catalytic ozonation, we design and synthesize a catalyst of amino-functionalized hybrid of MnO2 and graphene oxide (MnO2-NH2-GO) with hydrothermal method, and then use it to catalyze the ozonation of cephalexin (CLX), one of β-lactams antibiotics frequently detected as refractory pollutants in aquatic environment. The MnO2-NH2-GO shows much higher catalytic performance than both MnO2 and MnO2-GO in the ozonation of CLX, in which the free radicals of ·O2− play a dominated role and the Mn3+/Mn4+ acting as active sites react with ozone to promote the formation of ·O2− with the help of the enhanced electron transfer facilitated by GO. The MnO2-NH2-GO also shows more stable catalytic performance than MnO2-GO due to the strong covalent bonds bridged by amino to MnO2 and GO to prevent the decoupling of GO from MnO2. This work provides a method to design a smart catalyst for ozonation with high catalytic performance and stability.

Catalytic ozonation benefit from the enhancement of electron transfer by the coupling of g-C3N4 and LaCoO3: Discussion on catalyst fabrication and electron transfer pathway

In this study, the novel design approach of catalyst in catalytic ozonation was proposed to enhance electron transfer in catalytic ozonation, achieving a better performance on micro-pollutants degradation and bromate elimination. The combination of perovskite oxide (LaCoO3, LCO) and graphitic carbon nitride (g-C3N4, CN) was studied to overcome some significant drawbacks of catalytic ozonation with metal oxides catalysts, such as the rate-limiting step between Men+ and Me(n+m)+. Additionally, the in-depth analysis of electron transfer pathway in CN/LCO catalytic ozonation was provided, which provided new insight into the design of highly efficient catalysts for facilitating micro-pollutants degradation and bromate inhibition. CN/LCO was successfully prepared and connected by the formation of -C-O-Co linkages, which exhibited a high activity in the catalytic ozonation for the synchronous degradation of benzotriazole (BZA) and elimination of bromate. Interestingly, being different with the general mechanism of catalytic ozonation, nitrogen vacancies and -C-O-Co bonds were the main active sites in CN/LCO rather than the surface hydroxyl group. With the largest amount of -C-O-Co and more nitrogen defects, CN/LCO exhibited a fast charge transfer along the in-plane direction. Additionally, the fast reduction of Co3+ to Co2+ was found to be initialized by O2•− and single electrons in catalytic ozonation, which resulted in more formation of H2O2 and good inhibition efficiency of bromate. This study not only present the good catalytic ozonation ability for refractory organic micro-pollutants and elimination of bromate using CN/LCO, but also provided insight into electron transfer pathway in the interlayers of CN/LCO, which will be significant for the design of catalyst and to promote charge transfer in catalytic ozonation.

Insights into Heteroatom-Doped Graphene for Catalytic Ozonation: Active Centers, Reactive Oxygen Species Evolution, and Catalytic Mechanism.

To guide the design of novel graphene-based catalysts in catalytic ozonation for micropollutant degradation, the mechanism of catalytic ozonation with heteroatom-doped graphene was clarified. Reduced graphene oxide doped with nitrogen, phosphorus, boron, and sulfur atoms (N-, P-, B-, and S-rGO) were synthesized, and their catalytic ozonation performances were evaluated in the degradation of refractory organics and bromate elimination simultaneously. Doping with heteroatoms, except sulfur, significantly improved the catalytic ozonation activity of graphene. Introducing sulfur atoms destroyed the stability of graphene during ozonation, with the observed partial performance improvement caused by surface adsorption. Degradation pathways for selected refractory organics were proposed based on the intermediates identified using high-resolution Orbitrap mass spectroscopy and gas chromatographic-mass spectroscopy. Three and six new unopened intermediates were identified in benzotriazole and p-chlorobenzoic acid degradation, respectively. Roles of chemical functional groups, doped atoms, free electron, and delocalized π electron of heteroatom-doped graphene in catalytic ozonation were identified, and contributions of these active centers to the formation of reactive oxygen species (ROS), including hydroxyl radicals, superoxide radicals, singlet oxygen, and H2O2, were evaluated. A mechanism for catalytic ozonation by heteroatom-doped graphene was proposed for the first time.

Kaolinite based catalysts for efficient ozonation of recalcitrant organic chemicals in water

Kaolinite has been widely utilized as a raw material in industrial and agricultural fields. Kaolinite derived materials can be used as catalysts in a catalytic ozonation process (COP) of recalcitrant organic chemicals in wastewater with decreased costs and improved profitability. The silicon (Si), aluminum (Al) and oxygen (O) in layered silicate of kaolinite and amorphous aluminum silicate of metakaolinite contribute to the formation of catalytic active sites. Kaolinite contains surface OH groups, SiO and AlO structures that promote oxidation through the formation of hydroxyl radicals (OHs) mineralizing the pollutant p-nitrophenol. Different metakaolinite has surface SiO and AlO structures that enhance mineralization through surface reaction. Catalytic ozonation of p-nitrophenol using kaolinite and metakaolinite increased the total organic carbon removal (46% and 41%, respectively) relative to single ozonation (32%). Introduction of Mn into kaolinite and metakaolinite further accelerate OH generation, improving the catalytic activity. Among the catalysts, the highest activity was observed using Mn loaded kaolinite (TOC removal 66%). Its enhanced activity may be mainly attributed to cooperative interactions from the distributed Mn oxides (Mn2+, Mn3+, and Mn4+) and surface OH groups. This study introduces the potential application of kaolinite and metakaolinite for the treatment of recalcitrant chemical wastewaters in catalytic ozonation processes.

The role of surface hydroxyl concentration on calcinated alumina in catalytic ozonation.

Alumina has been used as a catalyst for ozonation, surface hydroxyl on which is regarded as the active center for ozone attack, but the influences of hydroxyl generation are still vague. Here, we prepared alumina with different hydroxyl concentrations by adjusting calcination temperatures, of which the catalytic activity was evaluated with the mineralization degree of phenol, and then revealed the active sites of hydroxyl generation with characterization of XRD, Py-IR, and NH3-TPD. The results show that the greater the hydroxyl concentration, the higher the catalytic activity, demonstrating that surface hydroxyl contributes to its catalytic activity. The effect of calcination temperatures on hydroxyl concentration and catalytic activity is in accordance with the amount of weak Lewis acid sites on the surface of alumina, illustrating the surface hydroxyl derived from the decomposition of water adsorbed on weak Lewis acid sites. However, the catalytic performance of the alumina decreases slowly in a long-term reaction owing to the active center reduction resulted from the coverage by organic acids from phenol degradation. The present work reveals the influences of hydroxyl generation which are beneficial for adjusting surface hydroxyl regarded as active site for ozone attack and the reason of catalyst deactivation, which provides guideline for the rational design of catalyst.

Graphite Felt Supported MgO Catalytic Ozonation of Bisphenol A

ABSTRACTGraphite felt supported magnesium oxide (MgO/GF) catalyst was prepared by the equal volume impregnation method. Bisphenol A (BPA) was chosen as the target contaminant to be degraded by different ozone-based processes. The results of X-ray powder diffraction/scanning electron microscopy showed that MgO was uniformly loaded on graphite felt. The results showed that the removal percentages of BPA and COD by MgO/GF catalytic ozonation in 9 min could reach 88.2 and 42.1, respectively, but only 48.2 and 10.5 by O3 under the same conditions. The catalytic activity of the MgO/GF catalyst was relatively stable in 5 recycling tests. The mechanism study deduced that the high activity of MgO/GF in ozonation of BPA resulted from effective mitigation of pH change of the solution. The results show that MgO/GF is a potential catalyst in ozonation of refractory chemicals.

Application of Heterogeneous Catalytic Ozonation for Refractory Organics in Wastewater

Catalytic ozonation is believed to belong to advanced oxidation processes (AOPs). Over the past decades, heterogeneous catalytic ozonation has received remarkable attention as an effective process for the degradation of refractory organics in wastewater, which can overcome some disadvantages of ozonation alone. Metal oxides, metals, and metal oxides supported on oxides, minerals modified with metals, and carbon materials are widely used as catalysts in heterogeneous catalytic ozonation processes due to their excellent catalytic ability. An understanding of the application can provide theoretical support for selecting suitable catalysts aimed at different kinds of wastewater to obtain higher pollutant removal efficiency. Therefore, the main objective of this review article is to provide a summary of the accomplishments concerning catalytic ozonation to point to the major directions for choosing the catalysts in catalytic ozonation in the future.

Enhanced catalytic ozonation towards oxalic acid degradation over novel copper doped manganese oxide octahedral molecular sieves nanorods.

A series of copper doped manganese oxide octahedral molecular sieves (Cu-OMSx-T) with different Cu/Mn ratios and hydrothermal temperatures were successfully synthesized and used for catalytic ozonation towards oxalic acid (OA) degradation. The as-prepared Cu-OMSx-T composites were comprehensively investigated by BET, FT-IR, XPS and etc. characterizations. The results indicated that the Cu doping would increase the specific surface area, change chemical bonds, and promote the transformation of multivalent metals and the generation of oxygen vacancies. It was noteworthy that the hydrothermal temperature played an important role in the morphology of Cu-OMSx-T composites and the Cu/Mn molar ratios greatly influenced the catalytic activities. Amongst, the Cu-OMS0.5-140 achieved the optimum catalytic activity with 97.3% of OA degradation efficiency and 98.8% of mineralization rate in 30 min at pH 6.0. Moreover, hydroxyl radical and superoxide radical were identified as the major reactive radicals and the catalytic mechanism for OA degradation enhancement was also elucidated. In addition, the Cu-OMS0.5-140 exhibited great stability and reusability with high OA mineralization rate (>90%) and low metal release after five times recycle. Overall, the results indicated that the synthesized Cu-OMS0.5-140 is an efficient, stable, and recyclable ozonation catalyst, and could be a promising alternative material for water purification.

Synthesis and characterization of magnetic manganese ferrites

This research work explored the synthesis and characterization of magnetic manganese ferrites using a simple combustion method. The purpose of creating the magnetic manganese ferrites was for their planned use as ozonation catalysts. Their magnetic properties allow for their recovery from the treatment system. Magnetic manganese ferrites were prepared by mixing manganese nitrate and iron nitrate in a stoichiometric ratio of 1:2. Polyvinyl alcohol was added to the mixed metal salt solution and the ratio of PVA: total nitrate salt added was varied from 1:1 up to 1:2 by weight. The resulting particles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), tunneling electron microscope (TEM), and Ultraviolet–Visible spectroscopy (UV/Vis).

Catalytic Ozonation of Sulfonamide, Fluoroquinolone, and Tetracycline Antibiotics Using Nano-Magnesium Hydroxide from Natural Bischofite

Huge amounts of natural bischofite (MgCl2∙6H2O) resulting from the mining process of salt lakes often cannot be utilized effectively and are discarded; techniques for reutilization of the discarded bischofite as magnesium resources are limited. The nano-magnesium hydroxide (nano-Mg(OH)2) synthesized from natural bischofite was firstly used as catalyst for ozonation of antibiotics including sulfathiazole (ST), ofloxacin (OFL), and tetracycline (TC). Rapid ozonation of ST, OFL, and TC was achieved using nano-Mg(OH)2 as catalyst. The removal rate constant of OFL in the catalytic ozonation treatment (kOFL = 0.512 min−1) was nearly 2.1 times higher than the single ozonation (kOFL = 0.249 min−1). The removal rate constant of ST and TC increased by 23.5% and 32.8% from 0.298 min−1 and 0.384 min−1 to 0.368 min−1 and 0.510 min−1, respectively, when the catalyst was added into the reaction system. The removal rate constant of ST sharply increased from 0.259 to 0.604 min−1 when the reaction temperature increased from 15 to 35 °C while those of OFL and TC changes slightly. The removal efficiency sharply decreased when the initial concentration of ST, OFL, and TC increased from 10 to 500 mg L−1. Both anions and cations could inhibit the removal of ST, OFL, and TC at relatively higher concentrations. The prepared nano-Mg(OH)2 catalyst could maintain its catalytic activity in the repeated use process. High removal efficiency of typical antibiotics and heavy metals free indicated that nano-Mg(OH)2 from natural bischofite is a promising ozonation catalyst in terms of antibiotics removal.

Fast mineralization of acetaminophen by highly dispersed Ag-g-C3N4 hybrid assisted photocatalytic ozonation

Highly dispersed Ag-g-C3N4 hybrid was synthesized successfully by a simple calcination method in present study. The samples were characterized by TEM, XRD, XPS, BET and UV–vis DRS. The results indicate that Ag element are existent as metallic silver and highly dispersed in the matrix of g-C3N4 nanosheet. It was used as active catalyst for photocatalytic ozonation of acetaminophen (ACE) (solar light/Ag-g-C3N4/O3). The results showed that the apparent rate constant of mineralize ACE by solar light/4% Ag-g-C3N4/O3 during 120 min is almost 2 times as large as that with solar light/g-C3N4/O3. The mechanism of photocatalytic ozonation with 4% Ag-g-C3N4 was further confirmed. In this system, Ag acts as not only a good photo-generated electron acceptor for photocatalysis but also a beneficial decomposition center for ozone. Subsequently, holes and hydroxyl radicals both make contribution to the mineralization of ACE in solar light/4% Ag-g-C3N4/O3 process. A superior synergistic effect was observed in mineralization of ACE according to the synergy index of 5.3. Furthermore, Effects of various pH values and silver contents on the ACE mineralization were evaluated. The pathway of ACE degradation in photocatalytic ozonation system with 4% Ag-g-C3N4 was also proposed.

Continuous-flow ozonation over modified ceramsite: implications for the degradation of cation red x-GRL.

Catalytic ozonation has been widely used for refractory dye wastewater treatment due to highly reactive HO·. In this study, a kind of low-cost and environmental-friendly modified ceramsite sphere derived from pyrite cinder, silty clay and kaolin was prepared as ozonation catalyst. The degradation performances of cation red x-GRL were performed under a continuous mode. Being close to the practical treatment, continuous-flow ozonation study is vital for applying heterogeneous catalytic ozonation in wastewater treatment at a large industrial scale. Results showed that the absorption capacity of this modified ceramsite towards cation red x-GRL was confirmed to be slight. The mineralization efficiency was high, accounting for 48.0% of 200 mg/L cation red x-GRL at a constant flow rate of 0.18 L/min (hydraulic retention time = 16 min), while only 7.8% during ozonation alone. Furthermore, this novel catalytic ozonation can maintain high mineralization efficiency in a wide range of pH (3-10), which was ascribed to the synergistic catalytic performance of various oxides. The reaction mechanism is ascribed to the promotion of ·OH production from O3 molecules' decomposition. Moreover, ozone utilization efficiency at hydraulic retention time of 16 min during catalytic ozonation was 2.0 times as high as that during ozonation alone.

The Selectivity of Different Sized Catalysts on DOM Fractional Removal during the Catalytic Ozonation of Municipal Sewage

Dissolved organic matter (DOM) is a typical kind of pollutant with a complex composition, and different advanced treatments demonstrate different abilities toward its fractional removal. Hence, it is necessary to analyze the fraction of DOM that remains when using advanced treatments. In this paper, ozonation was used to deal with the biological effluents and comparisons of the catalytic ozonation with different particle sizes of γ-Al2O3 were made. The results of these comparisons indicated that the catalysts were active in improving the removal of DOM and γ-Al2O3 with different particle sizes can selectively remove DOM. The result of fluorescence showed that a decrease in the catalyst particle size contributes to a significant decrease in the fluorescence intensity, except for tryptophan-like substances. Meanwhile, DOM fractions with large molecular weights could be decomposed into small molecules by ozonation, resulting in increased hydrophilicity. However, the use of a catalyst in ozonation increased the removal of hydrophilic components. Additionally, a smaller catalyst particle size increased the removal of hydrophilic components. The results of catalyst analysis implied that the surface hydroxyl groups of catalyst γ-Al2O3 and the diffusion of DOM in the catalyst γ-Al2O3 played important roles in the ozonation catalytic process for the removal of DOM.

Enhancement of Copper Catalyst Stability for Catalytic Ozonation in Water Treatment Using ALD Overcoating.

Atomic layer deposition (ALD) of alumina overcoating can significantly enhance the stability of copper oxide-based catalysts for catalytic ozonation of organic compounds in advanced water/wastewater treatment. The catalyst leaching was reduced by about 90% while high (up to 98%) activity was demonstrated in terms of total organic carbon (TOC) removal. Synchrotron X-ray absorption spectroscopy results indicated that the Al2O3 protecting layer passivated the under-coordinated copper sites, which were likely to be responsible for leaching.

A new nano-ZnO/perlite as an efficient catalyst for catalytic ozonation of azo dye

A new nano-ZnO/perlite as an efficient catalyst for catalytic ozonation of azo dye

Catalytic Ozonation using Iron-Doped Water Treatment Sludge as a Catalyst for Treatment of Phenol in Synthetic Wastewater

In this study, iron (Fe)-doped water treatment sludge, designated as Fe/WTS, was prepared by a hydrothermal method using phosphoric acid and impregnation with ferric nitrate. The results from X-ray diffraction (XRD) confirmed the presence of Fe loaded on the WTS support, while Brunauer-Emmett-Teller (BET) analysis indicated an increase of specific surface area of the WTS from 37.37 m2/g to 118.51 m2/g after acid modification. The Fe/WTS was successfully used as a catalyst in catalytic ozonation for degradation of phenol in synthetic wastewater. Factors affecting phenol removal efficiency including reaction time, pH, catalyst dosage, and Fe content were investigated. At the optimum condition, i.e., reaction time of 120 min, pH of 11, catalyst dosage of 1 g/L, and Fe content of 2% (w/w), the removal efficiency of phenol was 99.16% which was higher than that of sole ozonation (44.61%). The results of kinetic analyses indicated that the reactions of catalytic ozonation in the presence of Fe/WTS and WTS catalysts followed pseudo-first order kinetic model with rate constants of 0.0362 and 0.0065 min-1, respectively, while that of sole ozone was 0.0046 min-1. This finding presented the potential use of Fe/WTS as a novel catalyst for catalytic ozonation.

Oxygen functionalized graphitic carbon nitride as an efficient metal-free ozonation catalyst for atrazine removal: Performance and mechanism

The oxygen functionalized graphitic carbon nitride (O@g-C3N4) composite was synthesized by a facile hydrogen peroxide hydrothermal approach in this study. It is the first report about the investigation and application of O@g-C3N4 as the metal-free catalyst for catalytic ozonation of atrazine (ATZ) in aqueous solution. The composition, structure, and morphology of obtained O@g-C3N4 were characterized by BET, XRD, FT-IR, SEM, TEM, and XPS, respectively. It was noted that O@g-C3N4 appeared as flower cluster or short rod-like structures with hierarchical edges, which was remarkably different from the laminated g-C3N4. The characterization results revealed that the doping O atoms into g-C3N4 framework via CO, CO, or/and NO bonds would modulate the configuration and physicochemical properties of g-C3N4, and meanwhile create nitrogen vacancies and new active sites to enhance the catalytic performance. The O@g-C3N4 exhibited superior catalytic ozonation activity with an improvement of 29.76% on ATZ degradation efficiency and more than 3.36 times of pseudo-first-order rate constant (0.6279 min−1) was achieved in O3/O@g-C3N4 process compared to single ozonation. Meanwhile, the feasibility of O@g-C3N4 for practical application was further evaluated at different catalyst dosages, initial ATZ concentrations, solution pHs, and natural organic matters. According to electron spin resonance and radical scavenger experiments, both superoxide radical and •OH were identified as the major reactive oxygen species in O3/O@g-C3N4 process. Moreover, the O@g-C3N4 showed excellent stability and reusability over multiple reaction cycles without obvious activity loss. The results indicated that O@g-C3N4 was demonstrated to be a highly efficient, stable, and recoverable catalyst, presenting the great potential in contributing to a new paradigm for designing environmental-friendly and highly efficient ozonation catalysts for water treatment.