Heterogeneous Activation Of Peroxymonosulfate By Cobalt-doped MIL-53(Al) For Efficient Tetracycline Degradation In Water

Tetracycline（TC）is widely used in the medical and animal husbandry industries because of its antibacterial effect.However,in recent years,due to the unreasonable disposal of wastewater containing TC,the pollution to the environment and the harm to human beings had become more serious.It is difficult for traditional water treatment methods to remove TC completely,so it is necessary to develop efficient methods to treat TC wastewater.At present,advanced oxidation technology based on sulfate radical(SO₄^·-)has attracted wide attention because of its good catalytic effect.The activation of permonosulfate can produce SO₄^·-and Co²⁺is proved to be the most effective metal ion for activating PMS.However,the presence of Co²⁺in solution as homogeneous ions is toxic to a certain extent.Compared with the homogeneous catalytic system induced by Co²⁺,the heterogeneous catalytic system based on Co-doped MIL-53（Al）is stable for the efficient utilization of Co²⁺and avoiding the Co²⁺leaching.The aim of this work is to synthesize Co-doped MIL-53（Al）by one-step solvent thermal method and use it to activate PMS to remove TC in water.In this study,MIL-53（Al）with different Co doping content was prepared based on the different molar ratios of Co and Al of 10%,15%,20%and 25%.The results of X-ray diffraction（XRD）,field emission scanning electron microscopy（FE-SEM）,Fourier transform infrared spectroscopy（FTIR）,nitrogen adsorption and desorption,X-ray electron spectroscopy（XPS）and inductively coupled plasma mass spectrometry（ICP-MS）indicated that the Co-MIL-53（Al）samples were successfully synthesized.25%Co-MIL-53（Al）with the best TC removal effect presented a cubic strip with an average diameter of 75 nm and a specific surface area of 905.02m²g^-1.The removal effect of TC in 25%Co-MIL-53（Al）/PMS heterogeneous catalytic system is better than that of PMS alone and MIL-53（Al）/PMS system.The higher the doping amount of Co,the better the removal effect.Quenching experiments and electron paramagnetic resonance（EPR）tests showed that Co-MIL-53（Al）activating PMS to degrade TC was mainly due to the action of sulfate radical(SO₄^·-)and singlet oxygen（¹O₂）non-radical.The catalytic performances of Co-MIL-53（Al）/PMS system in conditions of different p H,co-existing substances and water bodies were investigated.Quenching experiments and electron paramagnetic resonance（EPR）showed that the degradation mechanism by Co-MIL-53（Al）activation PMS was mainly attributed to SO₄^·-and singlet oxygen（¹O₂）non-radical.Seven degradation intermediates of TC were identified,and two possible degradation pathways of TC were proposed.Co-MIL-53（AL）/PMS system had a better TC removal effect when the addition dose of PMS was appropriately increased to 30mg,but the effect was decreased when the addition dose was increased to 40mg because of the self-quenching effect of active substances.Co-MIL-53（Al）/PMS system had good stability:this system had good removal effect on TC in the initial p H range of 3-11.80%of TC could still be removed after four cycles of synthetic sample Co-MIL-53（Al）using,and it was almost not affected by the coexisting substances such as humic acid（HA）,NO₃^-,Cl^-and CO₃^2-.Moreover,it still had excellent catalytic performance under actual water conditions（tap water,Xiang River water,pharmaceutical wastewater）.These results indicate that Co-MIL-53（Al）is a promising heterogeneous catalyst for the activation of PMS to degrade TC in water.