【作者】 徐洁；

【导师】 官宝红；

【作者基本信息】 浙江大学 ， 环境工程， 2019， 硕士

【摘要】 抗生素在制造和使用过程中进入水体环境中,因其生物毒性、生物难降解性而对水体安全构成威胁。头孢类抗生素是使用量最大的抗生素,也是抗生素废水中的典型污染物,对水生生物和人类健康十分有害。在本研究中,以典型的头孢类抗生素——头孢氨苄(CLX)为目标污染物,以二氧化锰为主催化剂、石墨烯为助催化剂,研究复合催化剂催化臭氧氧化去除头孢氨苄的效果,以期开发高效、稳定的催化臭氧氧化处理抗生素废水技术。水热温度和水热时间对二氧化锰的结晶度、形貌有影响,进而影响二氧化锰的催化性能。在140 ℃和12 h的优化条件下,二氧化锰的催化活性最好。当二氧化锰投加量为25 mg/L、臭氧浓度为0.12 mg/L和反应5min时,水中CLX的去除率达到39.1%,是臭氧氧化去除率的3.4倍。利用石墨烯提高催化剂的电子传递效率的性能,合成了复合二氧化锰—石墨烯催化剂(Mn02-GO)催化剂,优化了石墨烯的添加量。在石墨烯添加量为1%wt时,反应5 min后,Mn02-GO催化臭氧氧化降解CLX的效率为50.8%,达到MnO2催化氧化去除CLX效率的1.3倍,但是其催化稳定性不高。为了提高MnO2-GO的稳定性和活性,我们采用杂原子(氮)改性和氨基改性两种方法,进一步优化催化剂设计。氮原子改性能够提高Mn02-NGO的催化效果,反应5 min后,Mn02-NGO催化臭氧氧化降解CLX的效率为57.9%,但是不能够提高Mn02-NGO的稳定性,其原因可能是石墨烯表面的氮原子和金属氧化物的金属原子无法形成稳定的化学键,宏观上无法加强石墨烯和二氧化锰的结合力。氨基改性能够提高MnO2-NH2-GO的催化效果,反应5min后,MnO2-NH2-GO催化臭氧氧化降解CLX的效率为55.5%,同时还能提高Mn02-NH2-GO的稳定性,即使反复使用了 5次,MnO2-NH2-GO催化剂对CLX的催化降解效果只有微小的变化。Mn02-NH2-GO中的二氧化锰与石墨烯结合紧密,反复使用后,二者未见明显的剥离现象。自由基猝灭实验表明,MnO2-NH2-GO催化臭氧氧化CLX过程中,超氧自由基起主导作用。根据磷酸根能够和臭氧分子竞争吸附在催化剂表面酸性位点上的原理,向反应体系投加了磷酸根,导致CLX的降解效率下降38%,证明了Mn02-NH2-GO的催化活性位点为其表面酸性位。催化臭氧氧化反应后,MnO2-NH2-GO表面的锰元素价态发生变化,Mn3+/Mn4+减小,Mn3+失去的电子,电子通过二氧化锰和石墨烯传递到吸附在催化剂表面的臭氧分子,并与臭氧反应产生超氧自由基,降解CLX。研究表明,在降解水中CLX时,复合催化剂的效率Mn02-GO优于MnO2,氮原子改性催化剂Mn02-NGO能够提高催化效率,但是不能提高催化剂的稳定性,而氨基改性的复合催化剂Mn02-NH2-GO同时显著提高催化效率和稳定性。Mn02-NH2-GO催化臭氧氧化能够高效降解水中的CLX,有望推广用于抗生素废水的处理。更多还原

【Abstract】 Antibiotics,which is biologically toxic and difficult to be degraded naturally,may enter into aquatic environment in the process of production or use and then pose a great threat to the water safety.Cephalosporins,which are harmful to aquatic organisms and human health,are the most widely used antibiotics and the typical pollutants in antibiotic wastewater.In this paper,cefalexin(CLX)is selected as the representative of cephalosporin antibiotic pollutants and is subjected to the catalytic ozonation with catalyst composited by manganese dioxide as main catalyst and graphene as supporting catalyst so as to evaluate the catalytic reaction and develop an efficient and stable catalytic ozonation technology for antibiotic wastewater treatment.Hydrothermal temperature and hydrothermal time have effect on the crystallinity and morphology of the synthesized manganese dioxide,thus affecting,the catalytic performance of manganese dioxide.When hydrothermal temperature is 140 ℃ and hydrothermal time is 12 h,the synthesis of manganese dioxide catalytic performance is best.When the dissolved ozone concentration in water is 0.12 mg/L,and the dosage of manganese dioxide is 25 mg/L,the CLX removal rate is 39.1%after 5 min reaction,which is 3.4 times higher than the removal rate of ozone oxidation.Graphene can improve the electron transfer efficiency of the catalyst.Composite manganese dioxide-graphene catalyst(MnO2-GO)is prepared and the amount of graphene added is optimized.The appropriate amount of graphene is 1%wt.After 5 min reaction,the removal rate of CLX with MnO2-GO is 50.8%,which is 1.3 times higher than that of MnO2.However,the catalytic stability of MnO2-GO is poor.In order to improve the stability and performance of the MnO2-GO,we adopt two methods of hetero-atom(nitrogen)modification and amino modification to further optimize the catalyst design.Nitrogen atom modification can improve the catalytic performance of MnO2-NGO.After 5 min reaction,the removal rate of CLX with Mn02-NGO is 57.9%,However,nitrogen atom modification can’t improve the catalytic stability of MnO2-NGO.The reason may be that the nitrogen atoms on the surface of the graphene and metal oxide metal atoms can’t form stable chemical bonds,which is not possible to strengthen the adhesion of graphene and manganese dioxide.Amino modification can improve the catalytic performance of MnO2-NH2-GO.After 5 min reaction,the removal rate of CLX of MnO2-NH2-GO is 55.5%,and the catalytic stability of it increases significantly.Even if the repeated use of the five times,the catalytic degradation effect of CLX of MnO2-NH2-GO is slightly changed.In the MnO2-NH2-GO,it is found that the MnO2 is tightly attached to the graphene surface.After several reactions,MnO2 and graphene are still closely connected.Free radical quenching experiments show that superoxide free radicals played a leading role in the catalytic ozonation of CLX by MnO2-NH2-GO.Phosphate can compete with ozone molecules to adsorb on the acidic site of catalyst surface.With the addition of phosphate,the catalytic degradation efficiency of CLX decreases by 38%,which proves that the active site of MnO2-NH2-GO is its acidic site on the surface.After catalytic ozonation,the valence state of manganese on the surface of MnO2-NH2-GO changes.The Mn3+/Mn4+decreases,and Mn3+loses electrons,which are transferred to the ozone molecules adsorbed on the catalyst surface through manganese dioxide and graphene,and react with ozone to generate superoxide radicals and degrade CLX.The study shows that for catalytic ozonation CLX in water,the efficiency of MnO2-GO catalyst is better than MnO2.Nitrogen-atom modified catalyst MnO2-NGO can improve the catalytic performance,’but it does not help improve the stability of the catalyst,while the amino-modified catalyst MnO2-NH2-GO can significantly improve the catalytic perfomance and stability at the same time.MnO2-NH2-GO catalytic ozonation can efficiently degrade CLX in water,which is expected to be widely used in the treatment of antibiotic wastewater.更多还原