Flexible construct of N vacancies and hydrophobic sites on g-C₃N₄ by F doping and their contribution to PFOA degradation in photocatalytic ozonation

N vacancies, hydrophobic sites and electron rich zone were simply regulated by doping F into g-C₃N₄ (CN) to accelerate photocatalytic ozonation of PFOA. Activity of F-CN was superior to that of CN, with 74.3% PFOA removal by F-CN/Vis/O₃ but only 57.1% by CN/Vis/O₃. Experimental results and theory simulations suggested that the photogenerated hole (h_vb⁺) oxidation with the help of N vacancies was vital for PFOA degradation. N vacancies on both CN and F-CN would trap O atom of PFOA and seize electron from α -CF₂ group, which made PFOA more easily to be oxidized. Doping of F narrowed band gap, lowered the valence band position and enhanced the oxidation potential of h_vb⁺. The hydrophobic sites would accelerate the mass transfer of O₃ and PFOA, enhance O₃'s single electron reduction with e_cb^- to generate hydroxyl radicals (•OH) and reduce the recombination of h_vb⁺-e_cb^-. Under the joint function of h_vb⁺, N vacancies and •OH, PFOA degradation in F-CN/Vis/O₃ proceeded through the gradually shortening of perfluoroalky chain and loss of CF₂ unit. The acute and chronic toxicity of generated short-chain perfluorocarboxylic acid toward fish, green algae daphnid were predicted by ECOSAR. And the toxicity change of solutions was examined by luminescent bacteria.