Degradation of phenanthrene in sulfate radical based oxidative environment by nZVI-PDA functionalized rGO catalyst

The ability of SO4 center dot- based advanced oxidation processes activated by nano zero-valent iron (nZVI) on reduced graphene oxide (rGO) functionalized by polydopamine (PDA) (nZVI-PDA@rGO) in degradation of phenanthrene (PHE) was investigated under various environmental conditions. The results showed that, compared with nZVI, the catalytic degradation of PHE was enhanced after anchoring nZVI on the PDA@rGO nanosheet in the activation of sodium persulfate (SPS) and peroxymonosulfate (PMS). The maximum PHE removal efficiency reached 95.9% and 98.7% in the nZVI-PDA@rGO/SPS (50 mg L-1/0.3 mM) and nZVI-PDA@rGO/PMS (50 mg L-1/0.0375 mM) systems, respectively. The effects of pH, anions and humic acid (HA) on the PHE degradation were tested in the nZVI-PDA@rGO coupling with PMS or SPS system. The higher PHE removal could be maintained in the nZVI-PDA@rGO/SPS system at pH up to 7.74 and in the nZVI-PDA@rGO/PMS system at pH up to 7.86, respectively. Cl- had a positive effect on PHE removal in both SPS and PMS systems, while a negative effect was observed in the presence of SO42-, NO3- and HCO3- (HCO3- > SO42- > NO3-). In addition, the PHE removal was inhibited significantly after addition of 50 mg L-1 HA. The radical scavenger tests were carried out to identify the dominant reactive oxygen species (ROSs), which demonstrated that SO4 center dot- and HO center dot were the two primary ROSs responsible for the PHE removal. The intermediate products were identified by LC-MS and the degradation pathway of PHE was proposed.