Preparation Of Wool Keratin Based Single Atom Catalysts And Its Application In Fenton Reaction

As a new heterogeneous catalyst,single-atom catalysts have great advantages in performance and economic benefits.The excellent catalytic performance of single-atom catalysts is mainly due to their clear active sites,uniform atomic dispersion and adjustable coordination environment.The economic benefits of single-atom catalysts are attributed to the high specific surface area of active centers and nearly 100%atomic utilization.However,isolated metal atom sites are sensitive to the coordination environment,and subtle changes of the coordination environment will significantly affect the electronic structure of the active center.Therefore,it is particularly important to explore the influence of coordination environment on catalytic activity.In this study,the research background,reaction mechanism and research progress of Fenton reaction in the treatment of printing and dyeing wastewater are introduced in detail.A variety of metal monatomic catalysts were prepared by co-impregnation and high temperature annealing using wool keratin as the carrier material of the catalyst.The main research contents of this paper are summarized as follows:Firstly,single-atom catalysts with wool keratin and silk protein as carrier materials were prepared with Fe as active metal,named Fe SA/NCS and Fe SA/NC.Combined with the difference of sulfur in wool keratin and silk protein,the regulation of sulfur coordination on catalytic performance in the use of single-atom catalysts was explored.High-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)images can clearly distinguish the isolated and dispersed single metal atoms on heteroatom doped carbon nanosheets,which proved the successful synthesis of single-atom catalysts.X-ray photoelectron spectroscopy(XPS)curves showed that the introduction of S element was conducive to inhibit the electron transfer from Fe to N,and in order to improve the content of Fe²⁺in Fe SA/NCS samples and made Fe SA/NCS produce more hydroxyl radicals in Fenton reaction.The degradation tests of methylene blue(MB),rhodamine B(Rh B)and phenol showed that the Fe SA/NCS samples with more S element had the best degradation activity.After 30 minutes of illumination,the degradation rate of MB by Fe SA/NCS was97.8%,while the degradation rate of silk fibroin-based nitrogen doped carbon loaded Fe single atom(FE SA/NC)without S element was only 23.1%.The complete degradation time of MB in Fe SA/NC samples was more than 130 minutes,which was much lower than that in Fe SA/NCS samples.Secondly,by changing the preparation conditions and reaction environment,the effects of catalyst synthesis temperature,H₂O₂ addition,catalyst addition and substrate p H value on the reaction performance were studied.Fe-SACs-900 almost degraded MB dye substrate within 30 min of illumination,while the complete degradation times of Fe-SACs-800 and Fe-SACs-1000 were 60 min and 80 min,respectively.This was mainly due to the reduction of Zn Cl₂ to Zn during carbonization and evaporation at 900°C,resulted in a large number of microporous structures on the catalyst surface.When the synthesis temperature was800°C,the catalyst surface was a non-porous two-dimensional nano sheet structure,indicated that Zn was not completely removed,so the specific surface area of the catalyst was inhibited and the activity was reduced.In addition,when the synthesis temperature rose to 1000°C,it would not only make the metal atomize and agglomerate easily,but also improve the crystallinity of carbon-based materials,in order to cover the active center of the catalyst,so that it cannot give full play to its activity.The p H value of substrate solution has always been one of the important factors affecting Fenton reaction.In this study,when the p H value was neutral,it had a better oxidative degradation rate.Within 30 minutes of the beginning of the reaction,the degradation rate of MB reached 97.6%.When the solution was alkaline or strongly acidic,it was not conducive to the Fenton reaction.Finally,single-atom catalysts with metal Co and Mn as active centers were successfully prepared,and it was proved that wool keratin can be used as a carrier material with excellent performance.HAADF-STEM images can also distinguish the uniformly dispersed single metal atoms on Co SA/NCS and Mn SA/NCS samples.However,compared with Fe single-atom catalysts dominated by Fenton reaction,the oxidation performance of oxidation active molecules generated by Fenton-like reaction with Co and Mn as active metals is weak and the degradation performance will decline.Co SA/NCS and Mn SA/NCS samples needed photoreaction for 120 min and 100 min respectively to completely degrade the MB substrate.