In-situ photoelectrocatalytical formation of sulfate radicals on BiPO4 modified carbon paper electrode in sodium sulfate electrolyte for high efficient degradation of pefloxacin

In recent years, advanced oxidation processes (AOP) based on sulfate free radicals (SO 4 − ·) have attracted considerable attention due to the excellent advantages of SO 4 − · compared with hydroxyl radical (·OH). However, SO 4 − · generally produced by activating extra persulphates, which causes high cost and risk of secondary pollution. In this work, BiPO 4 modified carbon paper electrode (BiPO 4 /CP) successfully fabricated via simple method can be used as a photocatalyst to effectively activate sulfate originally existed in wastewater to generated sulfate radicals in-situ without adding any extrinsic chemical oxidants. Pefloxacin (PFX) was degraded effectively on BiPO 4 /CP with the help of applied potential. CP with large surface area and high electrical conductivity as an excellent support for BiPO 4 is beneficial to improve the reutilization, electron transfer and photocatalytic performance of BiPO 4 . Moreover, BiPO 4 with large bandgap has sufficient redox capacity to produce not only ·OH, superoxide radical (·O 2 − ), but also SO 4 − ·, which is crucial for photocatalytic pollutant degradation. Detailed characterizations give strong evidences of the successful fabrication of photocatalyst, thermodynamic feasibility of SO 4 − · in-situ formation, the generation of free radicals, and the possible mechanism. Consequently, under the optimal conditions (pH=5.6, +1.0 V (vs.SCE), [SO 4 2− ]=10 mM, 61 μW cm −2 UV light irradiation, 33 mg BiPO 4 loaded on CP), the degradation efficiency of PFX (10 mg/L) was 87.8% in 120 min, which was 5.1 ad 8.2 times higher than that in photocatalytic and electrocatalytic system and 3.3 times higher than that without SO 4 2− . Meanwhile, BiPO 4 /CP maintains high level of degradation efficiency of PFX after 6 cycles under the optimal conditions.