The Preparation Of Graphitic Carbon Nitride Functional Materials And Its Application For The Degradation Of Organic Pollutants In Advanced Oxidation Process

Refractory organic pollutant poses severe threat to the global ecological environment and human health due to their persistency and bio-toxicity.How to effectively eliminate recalcitrant organic pollutants from wastewater and water environment has long been a major challenge for our society.In this respect,advanced oxidation processes(AOPs)are very effective,with advantages of facicle operation and high degradation efficiency.However,the usually high cost and energy consumption of AOPs restrict their widespread application.In this study,novel low-cost graphitic carbon nitride(g-C3N4)materials were prepared and used as heterogeneous catalysts for photochemical or sulfate radicals(SO4’-)-based AOPs to degrade refractory organic pollutants.First,mesoporous g-C3N4 nanospheres(MCNS)was synthesized from cyanamide precursor by using a hard template synthesis method.The obtained MCNS were used for photocatalytic degradation of bisphenol A(BPA),exhibiting excellent photocatalytic activity and stability.The chemical structure,composition and energy band structure of the MCNS were characterized to decipher the mechanisms of photocatalytic activity enhancement relative to its bulk counterparts.The following mechanisms were proposed:(1)The greatly improved specific surface area of MCNS not only facilitated mass transfer in catalysis but also resulted in more exposed active sites for producing photogenerated carriers.(2)Due the narrow band gap of MCNS,photo-generated electrons could easily jump from the valence band to the conduction band at minimal energy input,which further increased the quantity of available photogenerated carriers.In the mean time,light absorption in the visible-light region was also enhanced with the narrow band gap(3)The use of cyanamide as precursor resulted in more amino or cyanamide defects at surface terminations of MCNS,which favor more efficient electron transfer and hinder the recombination of photoinduced charge carriers.Therefore,the MCNS show great potential for sustainable photocatalytic pollutant degradation by using solar energy as the driving force.Despite of the sustainable nature of the above photocatalytic AOP,photo-generated holes or hydroxl radicals have limited degradation ability and selectivity for pollutants.Therefore,we further explored SO4·--based AOP by using g-C3N4 catalysts.To this end,we immobilized spinel cobalt-ferrite(CoFe2O4)particles on graphitic carbon nitride nanosheets(CNS)via a low-cost,one-step solvothermal method.The CoFe2O4-CNS composite showed significantly raised catalytic activity for peroxymonosulfate(PMS)activation and sulfonamide degradation compared to the bare CoFe2O4 NPs.In addition,the CoFe2O4-CNS couldbe more efficiently separated under magnetic field and resuspended due its larger sizes and no agglomeration.A stable activity of the nanocomposite catalyst during repeated use was also demonstrated.The mechanisms of its high acitivity and stability were elucidated:on one hand,the introduction of CNS allowed an improved dispersion of the CoFe2O4 particles and thus more exposed active sites of(?)CoII and(?)FeII.On the other hand,the regeneration of(?)CoII and(?)FeII was reinforced by graphitic N on the zigzag edges of CNS.Our results imply high potential of CoFe2O4-CNS as a low-cost,efficient heterogeneous catalysts for sustainable water treatment and environmental remediation applications.