Fig. 1. (a) UV-vis spectra of 4-FP with different concentrations in aqueous solution. Concentration of residual 4-FP during photolysis under irradiation of different light sources (b) and different incident light wavelengths of xenon lamp as light source (c). Corresponding defluorination (d) and TOC removal (e) efficiencies by photolysis under irradiation of different light sources in (b). (f) Degradation, defluorination, and TOC removal efficiencies of different FAs after 60 min direct photolysis under irradiation of xenon lamp.

Fig. 2. (a) Schematic illustration of the PEC cell for degradation of 4-FP. (b) LSV curves of TiO2 nanopillar photoanode under full spectrum xenon lamp irradiation. (c) Concentration of residual 4-FP by direct photolytic, photocatalytic, electrocatalytic, and photoelectrocatalytic process. (d) Estimating the concentration of ?OH radical by the photoluminescence intensity of TAOH formed in the PEC system. (e) EPR spectra of the samples taken from the PEC system after 15 min full spectrum irradiation at 1.0 VRHE with DMPO as spin-trapping agent. (f) Concentration of residual 4-FP in the PEC system with 0.5 mol L?1 TBA, 50 mmol L?1 Na2EDTA, and 2.5 mmol L?1 TEMPOL as scavengers for ?OH radical, h+, and ?O2- radical, respectively.

Fig. 3. F index (a) and C index (b) of 4-FP degradation in the different degradation processes. (c) Concentration of residual 4-FP as well as corresponding defluorination and TOC removal efficiencies in the PEC system. (d) Schematic illustration of synchronous defluorination-oxidation process for degradation of 4-FP. (e) Concentration of residual 4-FP in the PEC system under irradiation of different light sources.

Fig. 4. (a) HPLC plots of degradation intermediates after different degradation processes. Corresponding mass balances of fluorine (b) and carbon (c) in (a). (Oth. in (b) includes other fluorinated intermediates; FAs in (c) include 4-FP and 4-FC; Aro. in (c) represents defluorinated aromatics, and Oth. in (c) includes other carbon-containing intermediates, such as aliphatics). (d) Plausible coexisting degradation pathways of 4-FP for the synchronous defluorination-oxidation process in the PEC system.

Fig. 5. (a) Concentration of residual 4-FP as a function of time in the PEC system in five consecutive experiments. Effect of initial pH (b) and applied potential (c) on 4-FP degradation in the PEC system. (d) Concentration of residual FAs in the PEC system with an initial concentration of 20 ppm. (e) Corresponding final degradation, defluorination, and TOC removal efficiencies after reaction for 60 min in (d).

Fig. 6. (a) Schematic illustration of the small-scale pilot application system based synchronous defluorination-oxidation process. (b) Performance of the designed system for degradation of 4-FP. Concentration of residual 4-FP (c), the defluorination (d) and TOC removal (e) efficiencies of 4-FP degradation by UVC photolysis, UVA PEC, and tandem system, respectively. Reaction conditions: TiO2 nanopillar photoanode (~50 cm2) and a Ti mesh cathode (~50 cm2) in 0.1 mol L-1 Na2SO4 solution (pH = 6.0) containing 20 ppm 4-FP in a flow rate of 500 mL min-1 (totally 5000 mL for cyclic treatment), at a cell voltage of 3.0 V using a two-electrode setup.