Degradation Of Sulfamethoxazole In Water By Dielectric Barrier Discharge Plasma Combined With Bi₂WO₆-rMoS₂ Nanocomposite

Sulfamethoxazole(SMZ)is a synthetic antibacterial drug,which has been widely used in the world.SMZ can be used to prevent and treat infection,and can also be used as a feed additive to promote the growth of food animals.SMZ is classified as a persistent antibiotic because of its low biodegradability and can exist in the environment for a long time.SMZ is frequently detected in wastewater and surface water from many municipal wastewater treatment plants in many countries,usually at ng/L levels.There is ample evidence of adverse effects of SMZ on a variety of aquatic organisms,including bacteria,phytoplankton and zooplankton,even at trace concentrations.Due to the above potential risks,SMZ degradation is a key issue in water treatment.The low-temperature plasma degradation process is generally considered to be a combination of AOPs such as ozonation,ultraviolet pyrolysis,pyrolysis,etc.,which does not need temperature and pressure,is not sensitive to pollutants,and is environmentally friendly,and is currently widely used in environmental governance.In this paper,SMZ was selected as the model pollutant,and hydrothermal method was used to successfully prepare MoS2-supported Bi2WO6(Bi2WO6-rMoS2)composite photocatalyst.The feasibility of dielectric barrier discharge(DBD)combined with Bi2WO6-rMoS2 to degrade SMZ in aqueous solution was studied.Firstly,Bi2WO6,MoS2 and Bi2WO6-rMoS2 catalysts were prepared by hydrothermal method.In order to investigate the properties of composite materials,such as morphology,structure,surface composition and specific surface area,TEM,XRD,XPS,BET and other characterization methods were used to analyze the composites.The results showed that Bi2WO6 was successfully attached to the MOS2 with layered structure.Doped MoS2 has no influence on the crystal structure of Bi2WO6,but it will lead to the increase of the main diffraction peak area and crystallinity of Bi2WO6.Secondly,the effect of operation parameters of DBD synergistic Bi2WO6-rMoS2 catalyst system on SMZ degradation was investigated.Including discharge voltage;initial concentration of solution and initial pH value,mass ratio of MoS2 to Bi2WO6 in composite catalyst and catalyst addition amount,At the same time,the stability of SMZ was investigated by studying the effect of catalyst cycle times on SMZ degradation efficiency.The experimental results show that,within a certain range,increasing discharge voltage is beneficial to improving SMZ degradation efficiency,but it also increases energy consumption and affects energy utilization rate.The lower initial concentration increases the probability of SMZ contact with the active particles,which leads to the improvement of degradation efficiency.Under weakly alkaline conditions,ozone is more likely to form·OH with higher oxidation potential(2.80eV),which is favorable for SMZ degradation.The increase of MoS2 doping will hinder the transmission of ultraviolet light,reduce the light utilization and SMZ degradation efficiency.With the increase of catalyst addition,the yield of active substances and the adsorption capacity of the catalyst also increase,thus improving SMZ degradation efficiency and energy efficiency.The processing capacity of Bi2WO6-rMoS2 catalyst for SMZ decreased slightly after four cycles of treatment,but still remained at a high level,which proved that the composite catalyst has a certain degree of cyclic stability.Subsequently,this paper explored the mechanism of synergistic system to degrade SMZ.In other words,the changes of H2O2 and O3 accumulation concentration,pH and TOC in the dielectric barrier discharge system alone and the cooperative system were investigated.The results showed that the addition of Bi2WO6-rMoS2 catalyst was beneficial to increase the production of H2O2,accelerate the consumption of O3,reduce the solution pH and increase the mineralization rate in the reaction process.Finally,combining the results of the Gaussian theory and the LC-MS test results,the possible intermediates and degradation pathways of SMZ degradation were proposed.Ten intermediates were identified.Four possible degradation pathways were proposed,including hydroxylation of benzene ring,breaking of s-n bond and oxidation of phenyclic amine group.