Degradation Mechanism Of Polycyclic Aromatic Hydrocarbons By Activated Persulfate With Carbon Nitride Supported Magnetic Materials

Polycyclic aromatic hydrocarbons(PAHs)are naturally and artificially produced and discharged into the environment.They enter into the soil and groundwater through water air exchange and runoff.Polycyclic aromatic hydrocarbons have low availability,high boiling point,strong fat solubility,and are difficult to degrade or remove.Persulfate advanced oxidation is a new technology to remove persistent pollutants from soil and groundwater.Persulfate needs catalyst to activate before oxidizing pollutants.Therefore,the key to efficiently remove pollutants is to select suitable activation materials according to different pollutants and environment conditions.In this study,benzo[a]pyrene(BAP)was used as the target pollutant.Synthesizing a new kind of magnetic material:g-C3N4 supported Fe3O4,NiO(NiO/Fe3O4@g-C3N4)to activate sodium persulfate(PDS),producing non radical pathway to remove benzo[a]pyrene from soil and groundwater.The main results were as follows:(1)The material characterization results show that the material has a lamellar porous structure and a large number of metal oxide nanospheres with a size of about 10-100 nm are loaded on the surface;the crystal structures of g-C3N4,Fe3O4 and NiO are retained in the material;the surface of the material has three characteristic functional groups:Fe-O/Ni-O,C=N/C-N and O-H.Comparing NiO/Fe3O4@g-C3N4 with single g-C3N4,the BET results show that the specific surface area increases from 35.700 m2·g-1 to 48.924 m2·g-1,and the pore size increases from 8.711 nm to 22.427 nm.(2)The results showed that the optimum reaction conditions were 0.5 g·L-1 material concentration,2 mmol·L-1 PDS concentration and pH=7.After 60 min reaction at room temperature,the removal rate of BaP with 5 mg·L-1 concentration was 87.07%.With the increase of temperature,the reaction rate also increases.The reaction is less affected by anions and has strong anti-interference ability.Finally,the magnetic material was recycled by strong magnet,and the removal efficiency was still 67.78%after five consecutive reactions.(3)The mechanism of the reaction was studied by quenching reaction and free radical capture experiment.It was proved that the reaction was indeed a non radical pathway.The reaction pathway was divided into two parts:1.The structural defect of the material(oxygen vacancy VO)activated PDS,which resulted in the dissociation of O-O bond,produced superoxide radical and transformed into singlet oxygen(1O2),which directly participated in the oxidation of pollutants,accounting for 80.51%of the total reaction;2.Through chemical bonding and O-O bond activation,molecules form complexes with materials and participate in oxidation reaction,accounting for 19.49%of the total reaction.(4)The experimental results of contaminated soil showed that comparing with traditional materials(Fe2+,Fe3O4),NiO/Fe3O4@g-C3N4 as PDS activated material has remarkable effect,the degradation rate of BaP reached 55.84%after 60 min at room temperature.Us method can offset the defect of the reaction system,using NiO/Fe3O4@g-C3N4-Us method can activate PDS to remove BAP more efficiently.Under the conditions of 2 wt%material dosage,15 g·L-1 oxidant concentration and 5:1 water soil ratio,the BAP removal rate can reach 93.16%after 60 min.And the reaction system was less disturbed by anions and organic matter(HA)in soil,which could adapt to the complex reaction conditions of soil.