Carbon-Cobalt Composite Catalyst For Peroxymonosulfate-Driven Catalytic Oxidation Of Organic Pollutants In Water And Its Mechanism

Peroxymonosulfate（PMS）has attracted more attention as an emerging oxidant in advanced oxidation processes（AOPs）,due to that it is applicable at a wide p H range and easy to transport and store.The carbon-cobalt composite catalysts maintain excellent catalytic activity for PMS activation while they can be readily separated from the liquid phase and are less harmful to the environment,therefore they are expected for degradation of organic pollutants.To develop efficient carbon-cobalt composite catalysts,it is important to further study structure-property relationship.In this dissertation,the mechanism and methods of PMS activation were summarized,besides,the progress of catalysts for PMS activation to remove organic pollutants was reviewed.To avoid the inhibition of interfering species on PMS activation over carbon-cobalt composite catalysts,radical-based CoFe₂O₄/reduced graphene oxide aerogel（CFGA）and nonradial-based magnetic nitrogen-doped porous carbon were synthesized and characterized.The degradation of organic pollutants via PMS activation over porous composite catalysts was investigated and the relationship between their structure and catalytic performance was clarified.The current study not only provided a strategy for designing highly efficient carbon-cobalt composite catalysts on PMS activation,but also presented new insight into the mechanism of PMS heterogeneous activation.The main innovations and conclusions are shown as follows:（1）Graphene aerogel was used as a carrier for CoFe₂O₄ nanoparticles to achieve efficient activation of PMS and the relationship between their structure and catalytic performance was clarified.Compared with the traditional powdered carrier,the aerogel carrier had a macroscopic block structure,which could avoid the problem of easy sedimentation and accumulation of the powdered catalyst in water,but had excellent recyclability.The abundant pore structure and huge specific surface area of aerogel were conducive to the orderly dispersion and mass transfer.In terms of the degradation of pollutants by PMS activation,complete removal of phenol under CFGA/PMS system was achieved in 60 min,higher than that of CoFe₂O₄ NPs（80.7%）.The phenol removal was up to 83%in the regenerated CFGA/PMS system,while regenerated CoFe₂O₄ NPs still showed poor reusability（only 32.9%phenol removal was achieved in the second run）,indicating the better reusability of CFGA.Meanwhile,the existing Cl^-had a promoted effect on phenol removal while HA barely prohibited phenol removal.It was found that the Co atoms were active centers for the generation of radicals.（2）The magnetic nitrogen-doped porous carbon catalyst was synthesized from metal framework materials and graphene oxide.The structure and active sites of the catalyst were adjusted by the addition of graphene oxide.It was proved that graphite nitrogen was the main active center.In addition,the relationship between their structure and catalytic performance was clarified.The metal elements in MOFs could not only catalyze the carbonization during the synthesis,but also provided good recyclability for the catalyst.By adding GO contents into the system,forming of compact graphene-based porous structure and improvement of graphitization degree were achieved,which led to a better distribution of the active sites and better electron transfer ability,thus great catalytic performance was achieved.For example,magnetic nitrogen-doped porous carbon with an addition of 1%GO showed the best performance in PMS activation for phenol degradation（97.1%phenol degradation efficiency and 76.9%TOC removal efficiency in 10 min）.It was revealed that the electron transfer pathway was the main mechanism for degradation of organic pollutants by PMS activation and graphitic nitrogen was the main active center.This system had great tolerances to the influence of unfavorable environmental factors,such as Cl^-and HA,so it had great potential in pollutants treatment in the complex water matrix.