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

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

1.

Article Information

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

2. Article link

https://doi.org/10.1016/j.cep.2020.108296

3. Journal Information

Journal Name: Science of the Total Environment 785 (2021) 147328

Research direction involved: Environmental science

4. Author Information: Yuan He a, Liangjie Wang a,b, Zhan Chen a, Bo Shen a, Jinshan Wei a, Ping Zeng b, Xianghua Wen a,⁎

a School of Environment, Tsinghua University, Beijing 100084, China

b State Key Laboratory of Environmental Criteria and Risk Assessment,  Chinese Research Academy of Environmental Sciences, Beijing 100012, China

5. Product models used in the text: 3S-T3-D, 3S-J5000

Key point

Compared with β-MnO2 and γ-MnO2, α-MnO2 has a high degradation activity for IBU and MET in water.

The high activity of α-MnO2 is attributed to its abundant oxygen vacancies and readily reducible adsorbed oxygen.

Oxygen vacancies promote the increase of ozone utilization rate and ROS generation.

All ·OH, ·O2- and 1-O2 play significant roles in the degradation of MET and IBU.

Based on the identified organic intermediate mediators and the reaction sites calculated through the density function theory, the degradation pathway of PPCP was proposed

Introduction

In recent decades, manganese dioxide has been widely regarded as a catalyst for the catalytic ozonation of organic pollutants in wastewater. However, few studies have focused on the structure-activity relationship of MnO2 and the catalytic ozonation mechanism in water. In this study, the oxidative reactivity of three different crystal phases of MnO2 (corresponding to α-MnO2, β-MnO2 and γ-MnO2) to metoprolol (MET) and ibuprofen (IBU) was evaluated. It was found that α -MNO2 contains abundant oxygen vacancies and easily reducible surface-adsorbed oxygen (O2-, O-, OH-), which helps to improve ozone utilization and has high catalytic performance. The degradation efficiency of IBU and MET is 99%. Then α-MnO2 was selected to study the excellent key operating parameters. The results showed that the catalyst dosage was 0.1 g/L, the ozone dosage was 1 mg/min, and the initial pH value was 7. The introduction of α -Mno2 promotes the generation of reactive oxygen species (O2-, O-, OH-), which plays a significant role in the degradation of IBU. Based on the identified organic intermediates and the reaction sites calculated by density functional theory (DFT), the possible degradation pathways of MET and IBU were proposed. This study deepened our understanding of the catalytic ozonation of manganese dioxide and provided a reference for improving process efficiency.

Ozone equipment

2.4. Catalytic ozonation experiments

The catalytic ozonation of MET and IBU were performed in a 500 mL glass reactor equipped with a magnetic stirrer at 25 °C. Both of MET and IBU concentration was 10 mg/L at the beginning. Ozone was generated by an ozone generator (3S-T3-D, Tonglin Technology, China). The inlet ozone concentration was 2.5 mg/L with the flow rate of 200 mL/min.Then ozone was added to the bottom of the glass reactor through an aeration head. 500 mL stock solution was prepared in the glass reactor equipped with magnetic stirrers. 0.2 g/L catalyst was added and mixed with the stock water. During the experiment, 5 mL water samples were taken every 5 min in 30 min and filtered by PTFE filters for further analysis. All the catalytic ozonation experiments were conducted in parallel under the same condition. Ozone concentrations were detected with an ozone detector (3S-J5000, Tonglin Technology, China) for gas and an ozone detector (DOZ30P, Tonglin Technology, China) for liquid phase. The solution pH was adjusted by NaOH or HCl to maintain 7.0 ± 0.5.