Synergistic degradation of acid orange 7 dye by using non-thermal plasma and g-C3N4/TiO2: Performance, degradation pathways and catalytic mechanism

Abstract

In order to harness the full capability of ultraviolet and visible light in the dielectric barrier discharge induced non-thermal plasma (DBD-NTP) process, g-C3N4/TiO2 catalysts were prepared and utilized in this process. Synergistic degradation of acid orange 7 (AO7) dye by DBD-NTP and g-C3N4/TiO2 was conducted, and the performance, degradation pathways and synergistic catalytic mechanism were investigated. The results showed that the degradation rate of AO7 in the DBD-NTP and g–C3N4–15/TiO2 process increased by 39.1% compared with that in the single DBD-NTP process at 12 min discharge time. At 20 W input power, initial concentration of AO7 was 5 mg/L, catalytic dosage was 0.5 g/L, initial pH value was 10.0 and air flow rate was 52 L/h, the degradation rate of AO7 reached 100.0% after 12 min discharge time. Higher discharge power and initial concentration of AO7 inhibited AO7 degradation, whereas increasing the air flow rate and initial pH value of the solution promoted AO7 degradation. The degradation pathways of AO7 consisted of azo structure destruction, ring opening reaction, hydroxylation, carboxylation and mineralization reaction. The results of radical trapping experiment showed that O2−, h+, OH, O3 and H2O2 were the main reactive species for AO7 degradation in the DBD-NTP and g–C3N4–15/TiO2 process. The Z-scheme photocatalytic mechanism for the g-C3N4/TiO2 catalyst was proposed.