Study On The Efficiency And Mechanism Of Peroxymonosulfate Activation For Rhodamine B Degradation By Copper-based Catalyst

With the rapid development of industry,Rhodamine B（Rh B）has been continuously detected in the environmental.Due to the high toxicity and carcinogenicity of Rh B,its low concentration in the water is harmful to the environment and humans.Advanced Oxidation Process（AOPs）can degrade and mineralize the organic pollutants by utilizing Reactive oxygen species（ROS）,with achieving the purpose of water purifying.Among many AOPs,the AOPs based on peroxymonosulfate（PMS）have unique advantages in the efficient removal of organic pollutants due to their low energy consumption,mild reaction conditions and high ROS utilization rate.As a promising nanomaterial,transition metal catalyst has been widely used in PMS-based AOPs.However,the role of specific sites and synergistic effect among components in the transition metal catalyst,and in-depth understanding of PMS activation mechanism have not been fully studied.Therefore,a series of Cu Co Fe oxide catalysts,Ba modified Cu Mg oxide catalysts and carbon nitride supported Cu Mg oxide composite catalysts were prepared by sol-gel method combined with high temperature calcination.The catalysts with the best catalytic performance（0.5CCF-500-6,Cu Mg10Ba-750-2 and CM/g-C₃N₄）were selected to construct the PMS-based AOPs for rapid Rh B removal.In addition,a series of characterization techniques and experiments were used to clarify the role of special sites and the synergistic effect among components,and to explore the activation mechanism of PMS.The main research results were as followed:（1）The optimal reaction conditions of Rh B degradation were obtained by optimizing the reaction parameters,and it was[PMS]=2.0 m M,[0.5CCF-500-6]=0.50 g/L and[Rh B]=10.0 mg/L.Under the optimal reaction conditions,the removal efficiency of Rh B in0.5CCF-500-6/PMS and Co Fe₂O₄/PMS systems was 99.70%and 74.91%respectively within15 min.This result indicated that Cu site could improve the catalytic performance of0.5CCF-500-6.Based on the result of X-ray photoelectron spectroscopy and electrochemical analysis,this could be ascribed to more Co and Fe species with low valence generated on the0.5CCF-500-6 surface and faster electron transfers occurred by Cu site.（2）The optimal reaction conditions of Rh B degradation were obtained by optimizing the reaction parameters,and it was[PMS]=2.0 m M,[Cu Mg10Ba-750-2]=0.50 g/L and[Rh B]=10.0 mg/L.Under the optimal reaction conditions,the removal efficiency of Rh B in Cu Mg10Ba-750-2/PMS system was 98.56%within 5 min,while that in Cu Mg/PMS system was 3.12%.This indicated that Ba site played an important role in improving the catalytic performance of Cu Mg10Ba-750-2.The characterization results showed that Ba site could enhance the catalytic performance of Cu Mg10Ba-750-2 by increasing its particle dispersion,specific surface area and pore volume,and accelerating its electron transfers.（3）The optimal reaction conditions of Rh B degradation were obtained by optimizing the reaction parameters,and it was[PMS]=1.0 m M,[CM/g-C₃N₄]=0.30 g/L and[Rh B]=10.0mg/L.Within 5 min,the removal efficiency of Rh B in CM/g-C₃N₄/PMS system was 99.63%,which was much higher than that in CM/PMS system（19.03%）and g-C₃N₄/PMS system（28.01%）,indicating that the synergistic effect of CM and g-C₃N₄was beneficial to improve their catalytic performance.The characterization results showed that the synergistic effect of Mg O and g-C₃N₄could not only reduce the agglomeration of particle,increase the specific surface area and pore volume,provide more reaction sites,but also accelerate the electron transfers,thus improving the catalytic performance of CM/g-C₃N₄.（4）The results of mechanism studies showed that metal species,surface hydroxyl groups and g-C₃N₄were the reaction sites for PMS activation,and surface hydroxyl groups were critical for the formation of surface-bound reactive species（SBRS）.Cu site and the synergistic effect between Mg O with g-C₃N₄resulted in more surface hydroxyl groups generated on the surface of catalyst,which accelerated the formation of SBRS.In the process of PMS activation,Cu could not only cooperate with Co and Fe species to activate PMS,but also accelerate the regeneration of Co²⁺and Fe²⁺.Moreover,the addition of Ba site accelerated the generation of Cu⁺,facilitating the activation of PMS.Among many ROS,¹O₂was the main ROS of three systems,and the self-reaction of SO₅^·-was its main source.This paper revealed the role of Cu and Ba sites as well as the synergistic effect of metal oxide and carbon nitride.In addition,the activation mechanism of PMS was clarified,and the formation and main source of ¹O₂were also analyzed in depth.These results provide references for improving the catalytic performance of transition metal catalytsts by metal site or supporter composite and also for their PMS activation mechanism.