Removal Of Bisphenol A Via Activation Of Peroxymonosulfate With Ni-based Catalysts

Bisphenol A(BPA),as an environmental hormone,is detected in all kinds of water environment.Therefore,it is urgent to find a suitable method to remove BPA from water.Recently,advanced oxidation technology has been widely studied as an efficient method to remove organic pollutants from water.At the same time,peroxymonosulfate-based advanced oxidation technology has been widely concerned because of its high removal efficiency and no secondary pollution.In addition,the Ni-based catalysts with high activation performance for peroxymonosulfate can replace the traditional Co-based catalysts and reduce the preparation cost of the catalysts.Therefore,it is significant to explore Ni-based catalysts with high stability,low metal leaching and high catalytic activity.In this paper,four novel Ni-based catalysts were prepared and the mechanism of permonosulfate activation was studied.The main works include the following aspects:Firstly,NiO-ZnO composite oxide catalysts were prepared by homogeneous precipitation method.BPA degradation experiment was used to evaluate the performance of NiO-ZnO nanoparticles for PMS activation.The Ni/Zn molar ratio and calcination temperature were optimized.The NiO-ZnO catalyst calcined at 550℃ with Ni/Zn molar ratio of 15:85 was selected for further study(Ni15Zn85-550).The characterizations(XPS,HRTEM,FTIR,CO2-TPD,NH3-TPD,etc.)show that Ni15Zn85-550 was a typical mesoporous material with a large number of oxygen vacancies on the surface.DFT calculations show that the existence of oxygen vacancies regulates the surface charge distribution of the catalyst,which is conducive to the adsorption and activation of PMS.Then,the catalyst dosage,PMS concentration,initial solution pH,initial BPA concentration and reaction temperature were optimized by single factor control method.The optimum process conditions are as follows:BPA=10 mg.L-1,PMS=0.10 mM,Ni15Zn85-500=30 mg·L-1,initial pH=6.5,reaction temperature 303 K.Under these conditions,the removal efficiency of BPA and TOC were 95.26%and 67.11%,respectively.In addition,the presence of coexisting inorganic anions has a great influence on the degradation of BPA in the system.At the same time,the catalyst life cycle tests shows that the prepared Ni15Zn85550 had poor stability and lifetime due to the loss of metal active sites under acidic conditions.Quenching test and electron paramagnetic resonance(EPR)show that the main reactive oxygen species(ROS)in Ni15Zn85-550/PMS system are surface-bond SO4·-,surface-bond·OH and 1O2.The analysis of intermediates indicates that BPA had three degradation pathways:Oxidation of hydroxyl groups on aromatic rings,ring opening reaction of aromatic rings and coupling of the two substances.Although the NiO-ZnO nanoparticle catalyst prepared in the previous chapter has strong PMS activation performance,the high metal leaching could lead to secondary heavy metal pollution in water(c(Zn)=3.77 mg·L-1).Therefore,the further development of Ni-based catalysts with high PMS activation efficiency and low metal leaching has become the focus of this chapter.The g-C3N4 supported NiCx nano-cluster catalyst(NiCx-CN)was synthesized by one-step pyrolysis method and used to activate PMS to degrade BPA in water.Firstly,the prepared NiCx-CN catalysts were characterized by XPS,HRTEM,FTIR,CO2-TPD,NH3-TPD,etc.The results show that NiCx-CN is a typical mesoporous heterojunction catalyst with good electron transport properties.DFT calculations display that the heterojunction structure formed by g-C3N4 and NiCx leads to electron rearrangement in the catalyst system.It results in the formation of charge accumulation centers and charge loss centers on the surface of the catalyst.The acidic sites as charge loss centers are favorable for the adsorption and activation of PMS.In addition,DFT calculations also illustrate that when PMS is adsorbed on the surface of NiCx-CN,some electrons tend to transfer from the catalyst to PMS,thus stretching the peroxide bond in PMS.In general,the longer peroxide bond is beneficial to the decomposition and transformation of PMS.Then,the catalyst dosage,PMS concentration,initial solution pH,initial BPA concentration and reaction temperature were optimized by single factor control method.The optimum process conditions are as follows:BPA=5 mg·L-1,PMS=0.163 mM,Ni15Zn85-500=200 mg·L-1,initial pH=6.5,and reaction temperature 303 K.In addition,the presence of coexisting inorganic anions has a great influence on the degradation of BPA.At the same time,the recycle tests of catalyst diaplay that the NiCxCN has poor reusability due to less metal active sites.Additionally,according to a series of quenching experiments,EPR and PMSO degradation experiments,it is proved that the NiCx-CN/PMS system contains a pollutant mediated pathway dominated by high valence Ni&+=O species and a non-radical pathway with 1O2 as ROS.Besides,the pollutant mediated pathway dominated by Ni&+=O species was the main degradation pathway in NiCx-CN/PMS system.The analysis of intermediates shows that there were three degradation pathways of BPA.To solve the problem that the catalyst has poor lifetime due to the loss of metal active sites.A type of N-doped carbon nanotubes coated Ni nanoparticles(Ni-N-CNT)was synthesized in situ.Firstly,the calcination temperature was optimized.Ni-N-CNT catalyst calcined at 900℃ was selected for characterizations(XPS,HRTEM,FTIR,CO2-TPD,NH3-TPD,etc.).The results illustrate that the prepared Ni-N-CNT-900 is a kind of heterojunction catalyst with bamboo like carbon nanotubes coated with Ni metal nanoparticles.DFT calculations display that N doping is beneficial to the regulation of the surface charge distribution of the catalyst,resulting in different acid/basic sites.At the same time,the surface of the catalyst doped with graphitic N has the best charge transfer performance,which is beneficial to the activation of PMS.Then,the catalyst dosage,PMS concentration,initial pH and reaction temperature were optimized by single factor control method.The optimum process conditions are as follows:BPA=20 mg·L-1,PMS=0.244 mM,Ni-N-CNT-900=250 mg·L-1,initial pH=2-11,and reaction temperature 303 K.Under these conditions,the removal efficiency of BPA and TOC were 100%and 32.78%,respectively.In addition,Ni-N-CNT-900/PMS process also has strong anion resistance.At the same time,recycle tests of catalyst display that the prepared Ni-N-CNT-900 catalyst has satisfactory stability and lifetime.Additionally,1O2 is the main ROS in Ni-N-CNT900/PMS system,which is confirmed by quenching test and EPR.The analysis of intermediates shows that there are two degradation pathways of BPA:(ⅰ)oxidation of benzene ring or hydroxyl group and(ⅱ)β-cleavage of isopropyl group between benzene rings.Metal Ni nanoparticles and Ni3ZnC0.7 alloy nanoparticles coated with N-doped graphite(NiZn-N-G)were prepared by derivatization of metal organic frameworks(MOF).The investigation of calcination temperature showes that with the increase of calcination temperature,the graphitization degree and adsorption performance of the prepared catalyst are greatly improved.It is beneficial to improve the electron transfer performance of the catalyst and the enrichment of trace pollutants.In addition,the higher the calcination temperature,the stronger the magnetic properties of the catalyst,which is beneficial to the recovery and utilization of the catalyst.Therefore,the characterizations of NiZn-N-G calcined at 900℃(XPS,HRTEM,FTIR,C02-TPD,NH3-TPD,etc.)was tested.The results display that the successful doping of N element and graphitization can improve the electron transfer ability of the catalyst.The presence of acid/basic sites is beneficial to the adsorption and activation of PMS.In addition,DFT results illustrate that coating graphite or N-doped graphite on the surface of metal nanoparticles can not only reduce the work function of catalyst surface and enhance the electron transfer between catalyst and adsorbate,but also effectively control the surface charge distribution and create more sites for the adsorption and activation of PMS.Meanwhile,the different coating degree of graphite or N-doped graphite on metal nanoparticles will also lead to the change of adsorption energy between PMS and catalyst.Appropriate adsorption energy is beneficial to the charge transfer between PMS and catalyst.The catalyst dosage,PMS concentration,initial pH and reaction temperature were optimized by single factor control method.The optimum process conditions are as follows:BPA=20 mg·L-1,PMS=0.244 Mm,NiZn-N-G-900=200 mg·L1,initial pH=2-11 and reaction temperature 303 K.In addition,the discussion of coexisting inorganic anions indicates that NiZn-N-G-900/PMS process has strong anion resistance.Meanwhile,the recycle tests of catalyst show that the prepared NiZn-N-G-900 catalyst has satisfactory stability and lifetime.Besides,the results of quenching experiments and EPR indicate that the main ROS in NiZn-N-G-900/PMS system was 1O2.The analysis of the intermediates indicates that NiZn-N-G-900/PMS system has the same BPA degradation pathway as Ni-N-CNT-900/PMS system.