Generation of reactive oxygen species from oxygen microbubbles in phosphoric acid solution and its application of ferrous iron oxidation.

• O 2 microbubbles have strong oxidizing ability in H 3 PO 4 solutions due to the generation of ROS. • The main ROS specie generated by O 2 microbubbles in H 3 PO 4 solution was determined to be H 2 O 2 • The generation of H 2 O 2 was via a sequential one-electron reduction of O 2 molecule. • The generation of H 2 O 2 was affected by the temperature and H 3 PO 4 concentration. • The activation energy of Fe²⁺ oxidation reaction was significantly reduced due to the strong oxidation effects of ROS generated by the microbubbles. Microbubbles have been widely used in advanced oxidation processes due to the generation of reactive oxygen species (ROS). In this study, the oxidation of ferrous ions in phosphoric acid solutions has been examined, focusing on the advanced oxidation activity of oxygen microbubbles. Ultraviolet spectroscopy was used to determine the species and content of ROS. Electron spin-resonance spectroscopy and radical quenching experiments have confirmed the path of ROS generation. It is concluded that the main ROS in the phosphoric acid solution was H 2 O 2 , and the generation of H 2 O 2 was due to sequential single electron reduction of oxygen molecules. The amount of H 2 O 2 generated was determined to be dependent on the temperature and phosphoric acid concentration, and under the optimal conditions (100 ºC and 7 mol/L H 3 PO 4), 4.23 mmol/L H 2 O 2 was produced from microbubbles. The kinetics analysis with respect to the oxidation of ferrous ions suggested significant reduction of reaction activation energy from greater than 56.1kJ/mol to 43.84 kJ/mol due to the oxidation via ROS, demonstrating that microbubble intensification is a facile and effective advanced oxidation method. [Display omitted] [ABSTRACT FROM AUTHOR]