Ferromanganese oxide-functionalized TiO2 for rapid catalytic ozonation of PPCPs through a coordinated oxidation process with adjusted composition and strengthened generation of reactive oxygen species.

ABSTRACT

Ferromanganese oxide (MFOx) was first utilized to functionalize TiO2 and an MFOx@TiO2 catalyst was developed for catalytic ozonation for rapid attack of pharmaceutical and personal care products (PPCPs) with adjusted reactive oxygen species (ROSs) composition and strengthened ROSs generation. Unlike Al2O3, which strongly relied on adsorption and was significantly influenced by MFOx loading, synergistic catalytical effects of MFOx and TiO2 were observed, and optimal MFOx doping of 2 wt% and MFOx@TiO2 dosage of 500 ppm were obtained for catalyzing ozonation. In ibuprofen (IBP) degradation, MFOx@TiO2-catalyzed ozonation (MFOx@TiO2/O3) obtained 2.0-, 4.7- and 6.9-folds the kobs of TiO2/O3, MFOx/O3 and bare ozonation (B/O3). Stronger O3 decomposition was observed by MFOx@TiO2 over bare TiO2 with the participation of redox pairs Fe(II)/Fe(III) and Mn(II)/Mn(III)/Mn(IV) and increased surface oxygen vacancies (SOVs) from 9.8 % to 33.7 % was detected. The results revealed that Fe(II), Mn(II) and Mn(III) with low valance accelerated Ti(III) generation from Ti(VI), obtaining an unprecedented high Ti(III) composition occupying 35.3 % of the total Ti atoms. Ti(III) catalyzed the direct reduction of SOVs-O2 to •O2-, and it accelerated the formation of Ti(VI)-OH and Ti(VI)-O which catalyzed O3 decomposition into •O2-. •O2- was found to primarily initiate IBP degradation with nucleophilic addition and dominated over 66 % IBP removal. The enhanced •O2- generation further strengthened •OH and 1O2 production. MFOx@TiO2/O3 obtained 17 %, 21 % and 30 % higher TOC removal over TiO2/O3, MFOx/O3 and B/O3, respectively. Acute toxicity tests confirmed the effective toxicity control of organics by MFOx@TiO2/O3 process (inhibition rate 10.9 %). Degradation test of atenolol and sulfamethoxazole confirmed the catalytic effects of MFOx@TiO2. MFOx@TiO2 performed strong resistance to water matrix in application test and showed good stability and reusability. The study proposed an effective catalyst for strengthening the ozonation process on PPCPs degradation and provided an in-depth understanding of the mechanisms and characteristics of the MFOx@TiO2 catalyst and MFOx@TiO2/O3 process.