The Synergy Of Non-thermal Plasma And Photocatalysts G-C₃N₄ On Degradation Of Pharmaceutical Contaminant

Combining non-thermal plasma with photocatalyst to treat organic wastewater is an Advanced Oxidation Technology that combines water treatment technology with Photocatalysis technology.Taking the synergy of dielectric barrier discharge（DBD）and g-C₃N₄ photocatalyst on pharmaceutical wastewater treatment as research objects,this paper constructed the DBD device and studied its performance.Then,the synergy of the DBD and photocatalyst technologies was used to treat simulated pharmaceutical wastewater to investigate their synergistic effect,and this paper also studied the effect of DBD on g-C₃N₄ in aqueous solution.The conclusions of the paper are summarized as the following.1.A gas phase surface DBD reactor with a gas aerator can efficiently degrade pharmaceutical wastewater.This discharge system can remove 82%of ibuprofen（IBP）（initial concentration of 60 mg/L）and 100%of tetracycline（TC）（initial concentration of 200 mg/L）after 25-min treatment.But excessive discharge voltage and aeration intensity could decrease the pharmaceutical removal.To solve the above problems and combine the amplification requirement of the device,design the new-type DBD device by changing the air distribution and aeration design.The efficient degradation of ibuprofen and tetracycline by a new-type gas phase surface DBD device was studied.And the discharge voltage has little effect on the degradation of pollutants,while the aeration intensity has a great impact on the degradation of pollutants.Thus,satisfactory results can be obtained under low voltage conditions which can protect the electrodes and personal safety.This is conducive to the amplification of the new-type gas phase surface DBD device.2.The aqueous O₃ concentration could get saturated within 30 min,but the concentration of H₂O₂ was continuously decreasing within 120 min,and the generation rate of·OH could reach 0.4191 mol/L·min.Under alkaline condition,the concentration of O₃ and H₂O₂ decreases,while the concentration of·OH increases.Photocatalyst g-C₃N₄ was added in the discharge system,which enhanced the degradation of tetracycline and the concentration of H₂O₂ and·OH.However,if the g-C₃N₄ stays in the solution for a long time,the active species would destroy the surface of the photocatalyst.So this reduced the formation rate of H₂O₂.3.In order to study the effect of non-thermal plasma on g-C₃N₄,DBD with double dielectric was used to directly treat g-C₃N₄.It was found that the photocatalytic activities changed periodically when prolonging the discharge time.The short-time contact between them can improve the photocatalytic activities of g-C₃N₄.But when the residence time of g-C₃N₄ in solution is prolonged,the photocatalytic activities will decrease and then increase that ultimately presented a periodic process.DBD would affect the physical and chemical structure of g-C₃N₄ that could lead to the periodic change of the photocatalytic activities of g-C₃N₄.DBD can physically damage g-C₃N₄surface and can oxidize defects of g-C₃N₄ at the same time.Hydroxyl group,carboxyl group,carbonyl group,nitro group and other functional groups are generated on the surface of photocatalyst,and then these functional groups are oxidized to planarize the g-C₃N₄ surface.These physical and chemical effects exfoliated the g-C₃N₄ surface layer by layer.