Preparation And Properties Of Graphitic Carbon Nitride Supported Iron-based Fenton Catalysts

With the development of society and economy,the problems of water shortage and water pollution are becoming more and more serious.As a kind of advanced oxidation processes,Fenton reaction is widely used to degrade various organic pollutants due to its low cost,simple operation,mild reaction conditions and high efficiency.However,the traditional homogeneous Fenton reaction has many problems such as low utilization efficiency of H₂O₂,operation under acidic conditions,a large amount of iron sludge generated after reaction and the difficulty in recycling of the catalyst.The heterogeneous Fenton reaction solves some problems of the homogeneous one,for example,it can be carried out under neutral conditions and the catalyst can be recycled,but the activity of the catalyst is still lower than the homogeneous Fenton reagent,and the active metal species are easily lost.Therefore,the development of heterogeneous Fenton catalysts with high activity and high stability has become one of the important goals in the field of water treatment.Iron-doped g-C₃N₄ materials?Fe/g-C₃N₄?were prepared by one-step calcination of ferric chloride and dicyandiamide.The composite exhibits excellent Fenton catalytic activity under visible light irradiation,and methylene blue?50 mg/L?can be completely removed within 30minutes.However,the performance of Fe/g-C₃N₄ was greatly reduced after three dark Fenton reaction cycles,and the removal rate of methylene blue was reduced from 100%to 46%in 50minutes.Through XPS spectra analysis of the catalysts,it was found that the Fe²⁺/Fe³⁺ratio in the Fe/g-C₃N₄ catalyst remained unchanged during the photo Fenton reaction cycle.By contrast,the Fe²⁺/Fe³⁺ratio gradually decreases during the dark Fenton reaction cycle.Transient photocurrent spectra and AC impedance spectra indicate that the introduction of Fe promotes the charge separation and transfer of g-C₃N₄.Therefore,the reason why visible light promotes the activity and stability of Fenton reaction can be explained by the fact that Fe³⁺can capture the photo-generated electrons generated by g-C₃N₄ under visible light irradiation.Then Fe³⁺is reduced to Fe²⁺,which continuously promotes the regeneration of the active center Fe²⁺and thus maintains the catalytic activity in the photo Fenton reaction.A series of Fe-Ce/g-C₃N₄ composites with different ratios of Fe/Ce were prepared by calcining the mixture of Fe-based metal organic framework?Fe-MOF?,Ce-based metal organic framework?Ce-MOF?and melamine.The composite exhibits excellent Fenton catalytic activity and stability for degrading high concentration organic pollutants.The ratio of Fe/Ce has important effect on the Fenton reaction activity.The catalyst with Fe/Ce ratio of3:1 shows the best catalytic activity,which could remove 100%of methylene blue?200 mg/L?within 50 min.The reaction time could be further shortened to 40 min when introducing visible light into the reaction system.The excellent Fenton reaction performance can be attributed to:?1?The in situ generation of g-C₃N₄ as support can well stabilize and disperse Fe and Ce cations;?2?The synergistic effect between Fe and Ce and the photocatalysis of g-C₃N₄promotes the regeneration of Fe²⁺,leading to the production of more hydroxyl radicals to degrade the organic pollutants.