| Tetracycline antibiotics are one of the top ten antibiotics that induce resistance genes.They are widespread in the water environment and seriously threaten human health and ecological safety.Photocatalysis is a green and efficient water environmental remediation technology under mild conditions.As an organic semiconductor,graphitic phase carbon nitride(g-C3N4)has attracted much attention in photocatalysis because of its abundant source of synthetic raw materials,good stability,response to visible light,and easy structural modification.However,deficiencies such as narrow visible light response range,low specific surface area,and easy compounding of photogenerated electrons and holes lead to poor photocatalytic degradation performance of g-C3N4.Based on the structure-property relationship,gC3N4 photocatalyst with high catalytic activity was developed by adjusting the composition and morphology of precursors and then applied to the degradation of tetracycline hydrochloride.The primary studies and conclusions are as follows.(1)HDMP-doped and cyano-defects co-modified g-C3N4(HDMP-CD-CN)was synthesized by a co-condensation reaction under air using dicyandiamide,NaHCO3,and 4,6-dimethyl-2-hydroxypyrimidine(HDMP)as precursors.The characterization results show that the HDMP molecule was grafted into the g-C3N4 structure,and NaHCO3 led to the formation of cyano-defects.HDMP,as an electron acceptor,forms a donor-acceptor system with the heptazine unit,and the cyano-defects are the site for capturing photogenerated electrons.The two work together to promote intramolecular charge transfer,thus inhibiting the recombination of photogenerated carriers,making it easier to be captured and participate in redox reactions.The decomposition rate of tetracycline hydrochloride by HDMP-CD-CN in visible light was significantly higher,with a reaction rate constant of 0.0406 min-1,which was 3.8 times higher than that of the bulk phase g-C3N4.Free radical trapping experiments demonstrate that the main active species are superoxide radicals(·O2-)and holes(h+).(2)Flaked g-C3N4(HFDCN)was synthesized by hydrothermal and freeze-drying of dicyandiamide as a precursor,then calcination under Ar.The characterization results reveal that the hydrothermal and freeze-drying processes lead to lamellar structures that increase the specific surface area of HFDCN and enhance the n→π*electron leap by distorting the planar symmetric structure of g-C3N4.In addition,the distorted structure confers a stronger electron-feeding ability to HFDCN,allowing for faster electron transfer to PMS(Peroxymonosulfate,HSO5-)molecules while improving the efficiency of photogenerated electron and hole separation,thus enhancing the synergistic effect between photocatalysis and activated PMS.HFDCN degraded 91.0%of tetracycline hydrochloride in the Vis-SR-AOP system,and the addition of Cl-,HCO3-,CO32-and HA,as well as an increase in pH,had a promotive effect on the degradation.The main reactive species are·O2-,h+,and singlet oxygen(1O2). |
