Effect And Mechanism Of Low-frequency Ultrasound Enhanced Carbon Nanotubes/Permanganate On Removal Of Ciprofloxacin In Water

With the wide application of antibiotic drugs,a large number of undecomposed drugs and metabolites are put into the water,which causing potential harm to aquatic organisms and human beings through the food chain.Ciprofloxacin（CIP）,as a commonly used fluoroquinolone antibiotic,has extensive antibacterial spectrum and strong bactericidal ability,and it has good therapeutic effect on respiratory tract infection and intestinal infection.Moreover,CIP is also frequently detected in effluent from wastewater treatment plants,sewage sludge and surface water.CIP has potential ecotoxicity to the water environment.However,the traditional sewage treatment system is difficult to completely remove CIP.Therefore,it is necessary to develop an efficient,economical and energy-saving method for treating CIP in water.Acoustic chemical oxidation and permanganate advanced oxidation technology are commonly water treatment techniques for removing pollutants,but there are problems such as slow reaction and high energy consumption.Therefore,this study combined several treatments to study the feasibility of low-frequency ultrasound-enhanced carbon nanotube/potassium permanganate system（UCP）for CIP removal.The effects of ultrasonic power（US）,potassium permanganate dosage（KMn O₄,PM）,carbon nanotube dosage（CNTs）,initial p H,temperature and other operating parameters on CIP removal were investigated.The adaptability of UCP system to different water quality was also studied.Finally,The mechanism and reaction path of UCP system on CIP removal were analyzed.The main conclusions are as follows:（1）There were obvious synergistic effects between US and CNTs/PM system.With the increase of US,the CIP removal rate was faster.UCP system can remove CIP efficiently than US,US/PM and US/CNTs systems.The UCP system had good removal effect on sulfamethoxazole,diclofenac,tetracycline hydrochloride and phenol.Moreover,it also had good removal effect on CIP in three kinds of water quality（pure water,tap water and natural water）（>90%）,indicating that UCP system could be used for the removal of pollutants in real water bodies.（2）The dosage of KMn O₄and CNTs were not linearly related to the degradation ratio of CIP.When the dosage of KMn O₄and CNTs were greater than 200μM and 14mg L^-1,respectively,the degradation rate of CIP increased little,therefore,200μM,and14 mg L^-1were selected as the optimal amount for CIP remove.It was beneficial to CIP removal in weak acidity condition.When the solution was strong acid or strong alkaline,the degradation rate of CIP was obviously reduced,the removal rate of CIP was the best（100%）at p H=5.The increase of temperature could promote the removal of CIP in UCP system,which also indicating that the UCP system was an endothermic reaction.（3）The excessive methanol and tert-butanol showed inhibitory effect on the removal of CIP in UCP system,which indicated that hydroxyl radicals were produced in this system.In addition,it was found that there was no significant change in the degradation of CIP through the exposure of N₂and O₂,indicating that there was no singlet oxygen in UCP system.The UV-Vis,X-ray photoelectron,X-ray diffraction spectrum spectroscopy,sodium pyrophosphate effect,manganese dioxide effect experiment,and high-resolution projection electron microscopy showed that the main oxidizing material in UCP system was active intermediate valence manganese,and the yield increased with the increase of CNTs dosage.In addition,the adsorption of CNTs,Mn O₂also contributed to the removal of CIP,which promoted the removal of CIP.In UCP system,there are two main pathways of free radical degradation and non-free radical degradation:the free radical path mainly attacked the quinolone ring,and the non-free radical path mainly attacked the piperazine group.