Calcium Modified OMS-2 Promote The Activation Of Peroxymonosulfate For Organic Contaminants Degradation

Advanced oxidation technology based on peroxymonosulfate?PMS?has been widely studied in sewage treatment in recent years.In previous studies,it has been found that manganese oxide octahedral molecular sieve?OMS-2?can effectively activate PMS for the degradation of organic pollutants in wastewater.However,its application is limited due to the low activity under neutral and weakly basic conditions.OMS-2 was modified by calcium and applied to activate PMS for the first time,and Acid Orange 7?AO7?was used as a model to study the performance and mechanism of degradation of pollutants by calcium modified OMS-2 in the presence of PMS.The main contents are as follows:?1?When calcium ions(Ca²⁺)was introduced into OMS-2 + PMS system,the degradation of Acid Orange 7?AO7?was improved under various pH conditions,especially under neutral and weakly basic conditions.For example,when pH was 7,the degradation rate of AO7 increased from 0.0589 min^-1to 0.236 min^-1.It was found that the coordination between Ca2+ and PMS enhanced the oxidation of PMS,which then enhanced the degradation efficiency of AO7 in Ca²⁺+ OMS-2 + PMS system.Through PMS decomposition experiment and inhibitor experiment,we found that there were two main ways to produce active substances: One was the traditional one-electron transfer way to produce free radicals,and the other was non-free-radical two-electron transfer way.?2?The hybrid catalyst CaCO₃/OMS-2 was prepared in situ by a precipitation method.The characterization results indicate that the formation of Ca-O-Mn bonds between CaCO₃ and OMS-2 weakened the bond energy of Mn-O in OMS-2.The CaCO₃/OMS-2 + PMS system possessed high catalytic efficiency for the degradation of AO7,and the degradation reached 93% in 12.5 minutes with a pH of 8.2.The rate of AO7 degradation in CaCO₃/OMS-2 + PMS system was 0.21 min^-1,which was 8.1 and 10 times that of pure OMS-2 and CaCO₃,respectively.After 7 consecutive runs,the reaction rate decreased,however,the decoloration of AO7 could still reach 67% within 12.5 minutes in the 8th cycle.In the CaCO₃/OMS-2 + PMS system,reactive substances such as SO₄^-?,HO?,O₂^-?and ¹O₂were produced,and the main active substance was HO?.?3?Ca₁₀?OH?₂?PO₄?₆/OMS-2?MnHA?hybrid catalyst was prepared in situ by the precipitation method.The characterization results indicate that there were interactions between Ca₁₀?OH?₂?PO₄?6?HA?and OMS-2 in the catalyst.The shift of electrons from HA to OMS-2 increased the electron density of OMS-2 and weakened the bond energy of the Mn-O.The degradation rate of AO7 by MnHA + PMS system was 0.1 min^-1,which was 2.94 times and 10.8 times that of the OMS-2 + PMS and HA + PMS systems,respectively.MnHA had higher catalytic activity in various pH.The hybrid catalyst MnHA still maintain high catalytic activity after 5 consecutive runs,in the 6th reaction the degradation rate of AO7 was 74% after 25 minutes at the 6th reaction.The reactive substances produced in the MnHA + PMS system were SO₄^-?,HO?,O₂^-?and ¹O₂,among which ¹O₂was the main reactive substance.There were two ways of reactive substances produced: one was that PMS obtained an electron from the low-cost manganese and underwent a reduction reaction to produce SO₄^-?and HO?.The other was that the HSO₅^--OMS-2-AO7 complex was formed in the degradation system and electrons transfer from AO7 to PMS via OMS-2 to generate ¹O₂.Based on the above results,The purposes of synergetic activation of PMS to degrade organic pollutants,and broaden the scope of pH application of OMS-2 to activate PMS have been achieved by the modification of OMS-2 with calcium based minerals,which provided new ideas and theoretical basis for the modification of OMS-2 and the study of the activation mechanism of PMS.