Novel column reactor design for simultaneous photocatalysis and adsorption of 1-naphthol by FeOOH/peroxymonosulfate: Modelling the kinetics and concentration gradient

This study demonstrated a simultaneous photocatalysis and adsorption of 1-naphthol by peroxymonosulfate (PMS), FeOOH and UV-C in a novel column reactor, which is composed of a submerged UV-C lamp, mixed quartz bead-FeOOH media bed and a continuous supply of oxidant. Around 80 % of 1-naphthol was removed at its optimal condition. The reaction mechanism was found to be pH dependent. At lower pH, photocatalysis and adsorption are favored as the catalyst surface is protonated (≡FeOH₂⁺) to promote PMS activation and 1-naphthol adsorption, and the dissolution of Fe³⁺ enhanced homogeneous activation of PMS. At pH level higher than 8, the reaction becomes retarded due to the deprotonation of catalyst surface and dissociation of 1-naphthol into its conjugate base. Superoxide radical (O₂^•-), singlet oxygen (¹O₂) and sulfate radical (SO₄^•-) were confirmed to contribute to 1-naphthol oxidation. The reactor design was optimized at 20 min retention time. Due to the regeneration of Fe^III/Fe^II sites on FeOOH, the performance of reused catalyst is maintained at 90 % after 5 cycles of reuse. A quadratic regression with R² = 0.929 was used to model the concentration gradient of 1-naphthol along the column at different time intervals.