Fenton micro-reactor on a bubble: A novel microbubble-triggered simultaneous capture and catalytic oxidation strategy for recalcitrant organic pollutant removal

A novel catalyst-functionalized microbubble system was developed to trigger both of the Fenton reaction and the flotation separation on the gas-liquid interface of bubbles for efficiently removing the recalcitrant organic pollutants from waters. The Fe(II)-functionalized colloidal microbubbles (FCMBs) were featured as large specific surface area, great bubble density and high ·OH activation capacity. Approximately 98.2% and 93.1% of the triphenylmethane and aromatic azo pollutants were removed within 0.5 min, respectively. Particularly, at the lowest Fe(II) dose of 0.2 mmol/L, the FCMB-triggered Fenton still achieved 7.4-20.6% higher removal than the traditional Fenton method at 0.5 min. In addition to the Fenton oxidative degradation mechanism, the FCMBs themselves were able to capture and remove 20.1-36.8% of pollutants from water. Thus, FCMBs served as micro-reactors in terms of: (i) the target molecules and intermediates were adhered and separated by FCMBs; and (ii) the FCMBs enhanced the mass transfer of catalyst and exposed sufficient active sites on the bubble surface for catalytic oxidation reaction. Compared with the traditional Fenton, the present method showed the robust tolerance of pH (4.0-9.5) and salinity (up to 40‰) at decreased Fe(II) doses, and the bio-toxicity of intermediates was obviously lower. The FCMB-triggered pollutant capture and catalytic oxidation technology exhibited a great potency in engineering implementation given the flexible bubble construction, the integration and simplification of treatment unit, as well as the decreased chemical doses.