Activation Of Peroxymonosulfate By MnO₂/C@CNT Nanocomposite For Degradation Of Tetracycline

With the wide application of tetracycline(TC)in medical treatment,animal husbandry and other fields,tetracycline pollution in water is becoming more and more serious.Traditional water treatment methods can not remove tetracycline completely,so it is necessary to develop an efficient and feasible technology to remove tetracycline in water.In recent years,peroxymonosulfate(PMS)has been widely concerned because of its strong oxidation ability.However,PMS itself reacts slowly with organic pollutants,so it must be activated by some methods.In this study,an acid treated carbon nanotube(o-MWCNT)was used as a template and a simple carbon reduction method was used to prepare a MnO2/C@CNT nanocomposite for activating PMS to degrade TC in water.By changing the ratio of o-MWCNT and potassium permanganate,three kinds of MnO2/C@CNT nanocomposite with different carbon-manganese molar ratios were prepared.The MnO2/C@CNT nanocomposite were characterized by X-ray diffraction(XRD),Fourier infrared spectrometer(FTIR),X-ray electron spectroscopy(XPS),scanning electron microscope(SEM),transmission electron microscope(TEM)and specific surface area and porosity analyzer.The characterization results showed that the MnO2/C@CNT nanocomposite was successfully synthesized,and the MnO2 in the nanocomposite was the ? type with the poor crystallinity.The oxygen-containing groups in o-MWCNT were successfully fixed on the surface of the nanocomposite.MnO2/C@CNT(1:1.75)with the best performance presented a brush-like structure on the whole,with an average diameter of about 110 nm and a specific surface area of 233.573 m2/g.The mechanism of MnO2/C@CNT activating PMS to degrade TC was studied in detail.The main active substances in the MnO2/C@CNT/PMS system are SO4-·and OH·,and SO4-·made a greater contribution to TC degradation.The surface hydroxyl group is the main active site of MnO2/C@CNT,which can fix PMS as a complex on the catalyst surface and activate it through complexation.On the other hand,the oxidation of MnO2/C@CNT also improves with the introduction of PMS,which makes it possible to directly oxidize some TC.The carbon and manganese components of MnO2/C@CNT showed the excellent synergy.The introduction of carbon can effectively increase the number of hydroxyl groups of the catalyst,and also effectively reduce the polarization resistance of the catalyst.In addition,liquid chromatography-mass spectrometry(LC-MS)was used to analyze and detect the intermediate products generated during the process of TC degradation.A total of 11 major intermediate products were detected.Based on these intermediate products,two speculated degradation path of TC in MnO2/C@CNT/PMS system.The effect of catalyst dosage,PMS dosage,initial pH and reaction temperature on the TC degradation in MnO2/C@CNT/PMS system were investigated.The increase of catalyst dosage,PMS dosage and reaction temperature can effectively accelerate the TC degradation.The initial pH had a little effect on the MnO2/C@CNT/PMS system,and MnO2/C@CNT/PMS system can maintain a consistent degradation effect on TC over a wide pH range(3-9).Under the optimal conditions of a reaction temperature of 25?,initial pH=5,0.4 g/L catalyst and 2.0 g/L PMS,the degradation of TC can reach 98.2%within 10 minutes.In addition,the effects of inorganic anions(HCO3-,Cl-and N03)and humic acid(HA),which are common in natural water bodies,on the degradation of TC in the system were also investigated.HCO3 can promote the TC degradation in the system,and Cl-or N03 can inhibit the TC degradation to varying degrees.HA has a serious inhibitory effect on the degradation of TC in the system.