Preparation Of Ni@C Microspheres/Ndoped Carbon Nanotubes Composites For Activating Peroxymonosulfate

Peroxymonosulfate（PMS）activation can generate strong oxidative sulfate radicals(SO₄^·-)that possess higher redox potential,longer half-life period,and wider range of p H applications than those of hydroxyl radical（·OH）,and thus the PMS based advanced oxidation process has long been regarded as the wastewater treatment technology with great application promise.Catalytic decomposition is the most economical strategy of PMS activation.However,traditional homogeneous catalysts gradually fade out of people’s attention due to their inherent drawbacks,such as secondary pollution,difficulty in regeneration,and so on.In contrast,heterogeneous catalysts are arousing more and more research interests,benefiting from their advantages of easy separation and recycling.As a kind of burgeoning nonmetallic heterogeneous catalyst,carbon nanotubes（CNTs）display desirable activation performance of PMS,especially in the presence of heteroatoms（such as N,P,S,etc.）,and their catalytic activity increases exponentially.In order to solve the problems of complex preparation procedures,low doping amount,and difficult recovery of hetero-atom doped carbon nanotubes,Ni@C microspheres/N-doped CNTs composites（Ni@C@NCNTs）are prepared through an in-situ growth strategy,and their catalytic efficiency and mechanisms in the degradation process of Bisphenol A by PMS activation are systematically investigated.In-situ surface growth of NCNTs is realized through providing melamine vapor into the matrix of Ni@C microspheres in a high-temperature inert gas atmosphere.The content of NCNTs in these composites can be effectively controlled by regulating the weight ratios（n）of melamine to Ni@C microspheres.With the increase of n,there are more and more NCNTs can be found on the surface of Ni@C microspheres.Besides,the content of doped N in Ni@C@NCNTs-n and their specific surface area also be promoted.It is analyzed that the resultant composite Ni@C@NCNTs-5 exhibited optimal catalytic performance,the degradation process for 25 ppm of Bisphenol A completed within 15 minutes.The results of XPS indicate that the total content of doped N is 8.06%,of which the graphited N accounts for 26.71%.Nitrogen adsorption and desorption results show that the specific surface area and pore volume of Ni@C@NCNTS-5 are 96.9 m²/g and the 0.337 cm³/g,respectively.High concentration of nitrogen doping sites and high specific surface area are responsible for the optimal catalytic performance.The degradation rate of Ni@C@NCNTs-5 for Bisphenol A solution of the equivalent concentration in actual water is more than 85%,and the degradation efficiency is more than 60%in the system with anion concentration of 10 m M.In addition,the degradation efficiencies for dye pollutants such as rhodamine B,methyl orange can also reach up to more than 60%.ICP results show that the concentration of Ni²⁺in the solution after reaction is 3.26 ppm.Finally,free radical quenching tests and EPR are employed to identify the reactive oxygen species（ROS）.The results indicate that the main ROS in the degradation process dominated by non-radical processes is ¹O₂,and SO₄^·-and·OH play an auxiliary role.A series of composites Ni@C@NCNTs-t（t is the temperature of in-situ growth of CNTs）are prepared by adjusting the calcination temperature.The proportion of graphited N in total N content can be effectively controlled through changing the value of t.When t=750,the resultant composite（Ni@C@NCNTs-750）displays optimized performance for catalytic degradation of Bisphenol A in the presence of PMS,and the degradation process is completed within 5 minutes.XPS results indicate that the total content of N in Ni@C@NCNTs-750 is 8.01%,of which the graphited N accounts for 32.88%.Nitrogen adsorption and desorption results show that the specific surface area of Ni@C@NCNTs-750 reaches up to 92.4 m²/g.Ni@C@NCNTs-750 possesses stronger adaptability in actual water and different anionic environments,and its degradation rate increases by about 10%,when degrading pollutants of the same concentration.By comparing the infrared spectrum of samples before and after degradation,it can be concluded that the excellent degradation performance of composite for Bisphenol A absolutely results from PMS.