Performance and Mechanism of Catalytic Ozonation Degradation of Salicylic Acid with Waste Aluminum Alloy as Catalyst

The use of waste aluminum alloy metal as an efficient heterogeneous catalyst significantly enhanced the degradation efficiency of salicylic acid (SA), a typical pharmaceutical intermediate, in water by ozonation treatment. In the catalytic ozonation process, the removal ratio of salicylic acid reached 96% in 40 min, whereas the removal ratio with ozone oxidation alone was only 20%, demonstrating a remarkable catalytic effect. Factors such as the catalyst dosage, system pH, ozone dosage, and the initial concentration of salicylic acid all affected the pollutant removal efficiency. Electron paramagnetic resonance (EPR) analysis revealed the generation of active species, including hydroxyl radicals (•OH), superoxide radicals (•O2−), and singlet oxygen (O21) during the catalytic ozonation process. Electrochemical tests indicated that salicylic acid formed coordination complexes with the catalyst, accelerating the oxidative degradation. Liquid chromatography–mass spectrometry (LC-MS) analysis showed that the oxidation of salicylic acid first produced dihydroxybenzoic acid, which decarboxylated to generate phenolic compounds, then underwent ring-opening to form organic acids such as oxalic acid and acetic acid. Ultimately, mineralization resulted in the production of CO2 and H2O, and the toxicity of the treated water was significantly reduced. Importantly, the aluminum alloy catalyst retained excellent stability and recyclability after multiple cycles of ozone oxidation, showing great potential and economic value for practical water-treatment applications.