Comparative study on pollutant degradation by different advanced oxidation processes using Fe-doped TiO2-loaded reduced graphene oxide catalysts

To enhance the removal efficiency of refractory organic pollutants in high-salinity wastewater, three types of advanced oxidation processes (AOPs), i.e., photocatalysis, Fenton catalysis, and photocatalysis coupled with Fenton catalysis, were used to degrade tetracycline (TC) and rhodamine B (RhB) in sodium sulfate solution (15 %). Different Fe-doped TiO 2 -loaded reduced graphene oxide materials prepared by adsorption-layer nanoreactor synthesis were employed as catalysts in AOPs. The differences in the mechanism of the three types of AOPs for TC and RhB degradation were explored. The results showed that Fe doping can improve the degradation performance of catalysts in these AOPs, both in freshwater and saline water. Salt ions strongly inhibited pollutant degradation in both the photocatalytic degradation and Fenton catalysis process. The synergistic photocatalytic Fenton system can resist the interference of salt ions, thus effectively degrading both TC and RhB. The removal rates of TC and RhB reached 75.21   % and 84.11   % in 3   h, respectively. In the combined photocatalytic Fenton system, the active species were mainly photogenerated holes (h + ), but some ·OH and ·O 2 − radicals also participated in the decomposition of pollutants. For the two molecules, density functional theory calculations revealed the different atomic sites that were attacked by h + and ·OH. Salt ions surrounded electrophilic atoms with large f − values in the molecule, thus hindering the h + attack on these atoms. In contrast, salt ions did not affect the atom with the largest f 0 . More h + and ·OH were generated in the photocatalytic Fenton system, effectively reducing the interference of salt ions with pollutant degradation.