Behavior And Mechanism Of Cobalt-modified Carbon Nanomaterials With Activated Peroxides For Degradation Of Medicine Contaminants

In recent years,due to the frequent occurrence of public health events,the dosage of medicine has increased sharply.As a kind of broad-spectrum antibiotic,sulfonamides（SAs）are widely used in epidemic cerebrospinal meningitis,respiratory tract infection,and animal feed additives.In addition,a class of broad-spectrum antiviral medicine represented by acyclovir（ACV）is widely used in the treatment of herpes simplex virus,varicella-zoster virus,and so on.These medicines are not fully absorbed by organisms due to the continuous accumulation of dosage and are then discharged into the environment.SAs is one of the antibiotics with the highest detection rate in aquatic environment,and it can maintain its activity in the environment for a long time.Its mineralization rate is very low by biological treatment means.And antibiotic resistance genes persist in the environment and are easily migrated through the food chain.Except for antibiotics,the absorption rate of antiviral medicine in organisms is very low,and most of them are excreted into the environment in the form of their mothers.The transformants formed during natural treatment are more persistent in the environment,such as the transformant carboxy acyclovir of ACV.These transformants have unknown characteristics and toxicity and have a huge impact on the survival of aquatic organisms（fish,shrimp,algae,daphnia,etc.）.The advanced oxidation technology based on peroxides（peroxymonosulfate（PMS）,peracetic acid（PAA））has the advantages of simple operation,high oxidizability,and wide application of p H,and can pass through strong oxidizing free radicals(hydroxyl radical（·OH）,sulfate radical(SO₄^·-),superoxide anion(O₂^·-),organic free radicals（R-O·）and non-free radical active substances（singlet oxygen（¹O₂））mineralize refractory pollutants into small molecular,even CO₂ and H₂O.In many ways of activating PMS and PAA（UV radiation,thermal activation,etc.）.The transition metal activation operation conditions are mild and do not require additional energy input.Co²⁺shows more effective catalytic performance for the activation of PMS and PAA.However,the leaching of Co²⁺inevitably leads to secondary pollution of heavy metal ions in the water,so it is necessary to explore suitable carriers to synergistically activate PMS/PAA with Co to reduce Co loss.Carbon-based materials have attracted widespread attention as catalytic carriers for transition metals due to their high specific surface area,abundant pore structures,and surface functional groups.Through heteroatomic（N,S）doping,the electronic properties of carbon materials can be effectively regulated to enhance their electron-giving ability and promote the transfer of electrons to PMS and PAA.In addition to commonly used carbon-based materials（carbon nanotubes（CNTs）,graphene oxide,and graphite carbon nitride）,carbon-based materials derived from covalent organic framework（COF）with functional design and adjustable pore sizes can constrain the growth of metal nanoparticles,prevent excessive aggregation of metal loads,and also serve as excellent catalytic carriers.In this thesis,two medicine contaminants,sulfamerazine（SMZ）and ACV were selected as pollution models,and two kinds of cobalt-modified carbon-based nanomaterials were prepared:Co nanoparticles encapsulated in nitrogen-doped nanocarbon derived from cobalt-modified covalent organic framework catalyst（Co@COF）and nitrogen-doped carbon nanotubes coated cobalt nanoparticles catalyst（Co@N-CNTs）.Co@COF can effectively activate PMS to achieve efficient degradation of SMZ.Similarly,Co@N-CNTs can activate PAA efficiently and achieve rapid degradation of ACV.The effects of experimental conditions（oxidant loading,catalyst dosage,initial p H of solution）and water substrate（inorganic anions,humic acid）on degradation were also studied.The active species in the system were determined by quenching experiment and electron paramagnetic resonance technique（EPR）,and the possible catalytic mechanism was proposed.The main research content of this thesis is as follows:（1）Co nanoparticles encapsulated in nitrogen-doped nanocarbon derived from cobalt-modified covalent organic framework as peroxymonosulfate activator for sulfamerazine degradation.In this work,new COF materials with high crystallinity and large specific surface areas were used as cobalt-loaded supports.Cobalt nanoparticle-embedded nitrogen-doped carbon porous catalysts（Co@COF）were obtained by high-temperature pyrolysis of the COF materials and cobalt salts.With multiple active sites（Co⁰,pyridine N,and graphitic N）,Co@COF exhibited superior catalytic properties for PMS activation toward the degradation of SMZ.The efficiency of SMZ degradation reached92.4%within 10 min,and the total organic carbon removal rate reached 70.3%within30 min.Using radical quenching experiments and EPR analysis,SO₄^·-,·OH,and ¹O₂were identified in this system,while ¹O₂ was the dominant active species for SMZ removal.The degradation intermediates of SMZ in Co@COF/PMS were monitored by high-performance liquid chromatography-time of flight mass spectrometry（HPLC-QTOF-MS）.（2）Nitrogen-doped carbon nanotubes coated cobalt nanoparticles activated peracetic acid for degradation of acyclovir.In this work,a new type of Co,N co-modified CNTs catalyst（Co@N-CNTs）was fabricated using a carbon layer to coat Co NPs on CNTs.Co@N-CNTs can effectively catalyze PAA to degrade ACV.Under neutral conditions（p H=7）,the removal rate of ACV was 98.25%within 10 minutes.The main active free radicals,CH₃C（O）OO·and CH₃C（O）O·,which degrade ACV in the Co@N-CNTs/PAA system were analyzed by quenching experiments and EPR.The degradation intermediates of ACV were detected by HPLC-QTOF-MS,and the possible degradation mechanism of ACV in the Co@N-CNTs/PAA system was analyzed.