State of Art and Perspectives in Catalytic Ozonation for Removal of Organic Pollutants in Water: Influence of Process and Operational Parameters

The number of organic pollutants detected in water and wastewater is continuously increasing thus causing additional concerns about their impact on public and environmental health. Therefore, catalytic processes have gained interest as they can produce radicals able to degrade recalcitrant micropollutants. Specifically, catalytic ozonation has received considerable attention due to its ability to achieve advanced treatment performances at reduced ozone doses. This study surveys and summarizes the application of catalytic ozonation in water and wastewater treatment, paying attention to both homogeneous and heterogeneous catalysts. This review integrates bibliometric analysis using VOS viewer with systematic paper reviews, to obtain detailed summary tables where process and operational parameters relevant to catalytic ozonation are reported. New insights emerging from heterogeneous and homogenous catalytic ozonation applied to water and wastewater treatment for the removal of organic pollutants in water have emerged and are discussed in this paper. Finally, the activities of a variety of heterogeneous catalysts have been assessed using their chemical–physical parameters such as point of zero charge (PZC), pKa, and pH, which can determine the effect of the catalysts (positive or negative) on catalytic ozonation processes.

Advanced catalytic ozonation for degradation of pharmaceutical pollutants-A review

Various chemical treatment techniques are involved in removing refractory organic compounds from water and wastewater using the oxidation reaction of hydroxyl radicals (^•OH). The use of catalysts in advanced catalytic ozonation is likely to improve the decomposition of molecular ozone to generate highly active free radicals that facilitate the rapid and efficient mineralization and degradation of numerous organics. For the degradation of toxic organic pollutants in wastewater, the advanced catalytic ozonation process has been widely applied in recent years. Low utilization efficiency of ozone and ineffective mineralization of organic contaminants by ozone can be remedied with advanced catalytic ozonation. Advanced catalytic ozonation has gained popularity because of these merits. However, homogeneous catalytic ozonation has the disadvantage of producing secondary contaminants from the addition of metallic ions. Heterogeneous catalytic ozonation can overcome this drawback by utilizing metals, metallic oxides, and carbon materials as a catalyst of efficacy and stability. This review discusses various aspects of catalytic ozonation in wastewater treatment of pharmaceutical pollutants, application of catalytic ozonation process in typical wastewater, and prospects in advancing the techniques in heterogeneous catalytic ozonation.

Engineering of Mn3O4@Ag microspheres assembled from nanosheets for superior O3 decomposition

A topochemical transformation route was designed for synthesis of Mn3O4 nanospheres using β-MnOOH as the precursor. Ag nanoparticles were doped via an in situ redox reaction to obtain Mn3O4@Ag-NF, which displayed an enhanced performance for O3 elimination.

Catalytic ozonation for metoprolol and ibuprofen removal over different MnO2 nanocrystals: Efficiency, transformation and mechanism

Manganese dioxide has been widely recognized as catalyst in catalytic ozonation for organic pollutants removal from wastewater in recent decades. However, few studies focus on the structure-activity relationship of MnO₂ and catalytic ozonation mechanism in water. In the present study, the oxidative reactivity of three different crystal phases of MnO₂ corresponding to α-MnO₂, β-MnO₂ and γ-MnO₂ towards metoprolol (MET) and ibuprofen (IBU) were evaluated. α-MnO₂ was found to contain the most abundant oxygen vacancy and readily reducible surface adsorbed oxygen (O^2-, O^-, OH^-), which facilitated an increase of ozone utilization and the highest catalytic performance with 99% degradation efficiency for IBU and MET. α-MnO₂ was then selected to investigate the optimum key operating parameters with a result of catalyst dosage 0.1 g/L, ozone dosage 1 mg/min and an initial pH 7. The introduction of α-MnO₂ promoted reactive oxygen species (O^2-, O^-, OH^-) generation which played significant roles in IBU degradation. Probable degradation pathways of MET and IBU were proposed according to the organic intermediates identified and the reaction sites based on density function theory (DFT) calculations. The present study deepened our understanding on the MnO₂ catalyzed ozonation and provided reference to enhance the process efficiency.

Enhanced catalytic ozonation of ibuprofen using a 3D structured catalyst with MnO2 nanosheets on carbon microfibers

Heterogeneous catalytic ozonation is an effective approach to degrade refractory organic pollutants in water. However, ozonation catalysts with combined merits of high activity, good reusability and low cost for practical industrial applications are still rare. This study aims to develop an efficient, stable and economic ozonation catalyst for the degradation of Ibuprofen, a pharmaceutical compound frequently detected as a refractory pollutant in treated wastewaters. The novel three-dimensional network-structured catalyst, comprising of δ-MnO₂ nanosheets grown on woven carbon microfibers (MnO₂ nanosheets/carbon microfiber), was synthesized via a facile hydrothermal approach. Catalytic ozonation performance of Ibuprofen removal in water using the new catalyst proves a significant enhancement, where Ibuprofen removal efficiency of close to 90% was achieved with a catalyst loading of 1% (w/v). In contrast, conventional ozonation was only able to achieve 65% removal efficiency under the same operating condition. The enhanced performance with the new catalyst could be attributed to its significantly increased available surface active sites and improved mass transfer of reaction media, as a result of the special surface and structure properties of this new three-dimensional network-structured catalyst. Moreover, the new catalyst displays excellent stability and reusability for ibuprofen degradation over successive reaction cycles. The facile synthesis method and low-cost materials render the new catalyst high potential for industrial scaling up. With the combined advantages of high efficiency, high stability, and low cost, this study sheds new light for industrial applications of ozonation catalysts.

Catalytic ozonation for water and wastewater treatment: Recent advances and perspective

Ozonation process has been widely applied in water and wastewater treatment, such as for disinfection, for degradation of toxic organic pollutants. However, the utilization efficiency of ozone is low and the mineralization of organic pollutants by ozone oxidation is ineffective, and some toxic disinfection byproducts (DBPs) may be formed during ozonation process. Catalytic ozonation process can overcome these problems to some extent, which has received increasing attention in recent years. During catalytic ozonation, catalysts can promote O₃ decomposition and generate active free radicals, which can enhance the degradation and mineralization of organic pollutants. In this paper, the history of ozonation application in water treatment was briefly reviewed. The properties of the ozone molecule, the ozonation types and several ozone-based water treatment processes were briefly introduced. Various catalysts for catalytic ozonation, including homogeneous and heterogeneous catalysts, such as metal ions, metal oxidizes, carbon-based materials and their possible catalytic mechanisms were analyzed and summarized in detail. Furthermore, some inconsistent results of previous research on catalytic ozonation were analyzed and discussed. The application of catalytic oxidation for the degradation of toxic organic pollutants, including phenols, pesticides, dyes, pharmaceuticals and others, was summarized. Finally, several key aspects of catalytic ozonation, such as pH effect, the catalyst performance, the catalytic mechanism were proposed, to which more attention should be paid in future study.

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.

Modified hierarchical birnessite-type manganese oxide nanomaterials for CO catalytic oxidation

Hierarchical birnessite-type manganese oxide catalysts modified by transition metal (cobalt, cerium, copper, and nickel) cations were synthesized via a facile hydrothermal reaction.