Interaction and band structure-determined inhibition of negative Cr (VI) and positive Fe (III) for antibiotic photodegradation by nitrogen-doped dissolved black carbon.

The influences of the positive Fe and the negative CrO on the tetracycline (TC) photodegradation by N-doped dissolved black carbon (NDBC) have been investigated in this work. A series of samples (NDBC300, NDBC400 and NDBC500) have been extracted from the corresponding biochar. NDBC400 has the best photodegradation performance (79%) for TC under visible light irradiation. Adding CrO and Fe can reduces TC photodegradation efficiency into 37% and 53%, respectively. This maybe from that CrO has stronger interaction with NDBC400 than Fe since it can quench more fluorescence intensity of NDBC400 than Fe. Furthermore, CrO can reduce the steady-state concentration of NDBC400*, O and •OH, whereas Fecan just reduce the steady-state concentration of NDBC400* and increase the concentration of •OH. This may explain why CrO has stronger inhibit performance of TC photodegradation by NDBC400 than Fe. The band structures of NDBC400, NDBC400-Fe and NDBC400-CrO are constructed. And the VB of NDBC400-Fe has a stronger ability to produce •OH than NDBC400. In summary, coupling interaction and band structure characterization of NDBC400, NDBC400-Fe and NDBC400-CrO can explain well why CrO has stronger inhibition effect than Fe and Fe can increase the concentration of •OH. This work provides a deep insight for the photochemical behavior of dissolved black carbon and the transformation behavior of the co-existed metal ions and antibiotics.