Investigation On The Synthesis And Properties Of Carbon Encapsulated Iron/Iron Carbide Nanoparticles

Carbon-encapsulated magnetic nanoparticles(CEMNPs),which combine the performance advantages of the carbon shells and magnetic metal cores,can be used as a new-type and recyclable adsorbent in water treatment.But at present,there are still some problems in the synthesis of CEMNPs,such as imperfect morphology and structure,low purity,poor magnetic properties and adsorption effect,which affect their practical application.Therefore,it is of great significance to further investigate the synthesis process and upgrade the comprehensive performances of CEMNPs.In view of the performance requirements of CEMNPs as adsorbing material,Fe/Fe₃C@C magnetic nanoparticles were synthesized by freeze-drying and chemical vapor deposition(CVD)in this paper.The effects of acetylene/argon ratio,synthesis time,catalyst content and synthesis temperature on the synthesis process of Fe/Fe₃C@C were studied.The formation mechanism of Fe/Fe₃C@C was analyzed.The adsorption properties of the material for methylene blue(MB)were discussed.These provide the experimental and theoretical basis for the research of treating polluted water by using them as a high performance adsorbent.Based on the preparation of ferric citrate/sodium chloride(Na Cl)composite powder by freeze-drying technology,Fe/Fe₃C@C nanoparticles were synthesized by CVD process using acetylene as carbon source.The effects of related process parameters on the morphology,structure and properties of Fe/Fe₃C@C were investigated.The results show that the Na Cl carrier can be removed by washing with water and centrifugation,thereby the high-purity Fe/Fe₃C@C can be obtained.Fe/Fe₃C@C particles exhibit the poor dispersion and larger particle size with the increase of acetylene/argon ratio.The particle size and thermal oxidation stability show an upward trend as the synthesis time is prolonged.The graphitization degree of the carbon encapsulations significantly decreases with the increased Fe catalyst content.In the range of 300?450?,the samples change from CEMNPs to carbon nanofibers(CNFs),along with the enhanced graphitization degree and thermal oxidation stability as the temperature increases.In addition,the saturation magnetization(M_s)of Fe/Fe₃C@C closely relates to the carbon content.The key factors affecting the coercive force(H_c)are the thickness of carbon layer and particle size of Fe/Fe₃C cores.Under the conditions of acetylene/argon ratio of 1:10,synthesis time of 60min,catalyst content of 5 wt.%,and synthesis temperature of 400?,the obtained“flower-like”Fe/Fe₃C@C exhibit good dispersion,high graphitization degree and thermal oxidation stability,which also possess porous surface structure,large specific surface area,and high M_s and H_c values.The adsorption properties of Fe/Fe₃C@C for MB in water were investigated.The results show that,Fe/Fe₃C@C exhibit a good adsorption effect toward MB and possess effective separation ability under magnetic field.The equilibrium adsorption of the material conforms to Langmuir and Freundlich models,and the adsorption process conforms to the pseudo-second-order kinetic model.The“flower-like”Fe/Fe₃C@C particles exhibit the good adsorption performance with a high saturated adsorption capacity(theoretical value of90.14 mg/g)and fast adsorption efficiency(reaching equilibrium within 40 min).