Structural Regulation Of Graphitic Carbon Nitride And Enhanced Degradation Of Imidacloprid By Activated Persulfate

Water pollution caused by pesticide residues has seriously threatened the safety of aquatic animals and human health.Imidacloprid（IMD）,as one of neonicotinoid pesticides,has a very stable molecular structure and is difficult to decompose naturally in the environment.Advanced oxidation of persulfate coupled with photocatalysis has been widely used in the treatment of refractory organic wastewater.Graphite phase carbon nitride（g-C₃N₄）is widely used in photocatalytic activation of persulfate to degrade various organic pollutants in water due to its green,stable and easy synthesis characteristics.However,the application of g-C₃N₄ prepared by traditional thermal polymerization is limited due to the shortcomings of limited exposed active sites,low utilization rate of visible light and easy recombination of photogenerated charge.In this study,g-C₃N₄ with different morphologies was prepared through the strategy of morphology control,and persulfate（PMS）was activated under visible light to achieve the degradation of IMD pesticide,and the influence of different factors on the degradation effect of IMD was considered.The main research contents include the following two aspects:1.Amino functionalized g-C₃N₄ ultra-thin nanosheets（NHCN）with high specific surface area were prepared by a stepwise collaborative treatment method of hydrochloric acid assisted hydrothermal shear and ammonia intercalation hot stripping.The pristine g-C₃N₄（PCN）has a thick stacked structure due to the strong interlayer interaction,and it is difficult to obtain ultra-thin homogeneous nanosheets by single peeling method.The amino functionalized ultra-thin g-C₃N₄ nanosheets obtained by the two-step collaborative peeling method have larger specific surface area of g-C₃N₄,exposing more active sites.The photogenic carrier migration and diffusion are promoted.The photocatalytic activation of persulfate for the degradation of IMD showed that compared with g-C₃N₄（HCN）prepared by hydrochloric acid assisted hydrothermal method and g-C₃N₄（NCN）prepared by ammonia intercalation thermal stripping method,g-C₃N₄ prepared by two-step synergic method showed the best degradation activity of IMD.At the same time,the effects of different factors（catalytic dose,PMS amount,IMD concentration,inorganic anion and natural organic matter）on the degradation of IMD in vis/NHCN/PMS system were considered.·O₂^-,¹O₂and h⁺were identified by quenching and EPR,and the degradation pathway of IMD was predicted by high resolution liquid-mass spectrometry.2.Ultra-thin g-C₃N₄ tube（HTCN）modified with nitrogen defects was prepared by hydrogen thermal stripping.Morphology control and defect modification can significantly improve the photocatalytic performance.Through the degradation performance analysis,the prepared catalyst showed enhanced catalytic activity and excellent ability to activate PMS.In vis/PMS system,HTCN achieved complete degradation of IMD within 20 min.The degradation rates were 9.83 and 3.53 times higher than those of the original massive g-C₃N₄（PCN）and ordinary tubular g-C₃N₄（TCN）,respectively.The excellent degradation performance of HTCN is attributed to its significantly increased surface area（192.33 m²/g）exposing more active sites.The ultra-thin tube wall structure shortens the migration distance of photogenerated carrier to the catalyst surface,promotes the mass transfer and improves the photogenerated charge separation ability.The EPR results show that HTCN has a nitrogen defect and more unpaired electrons.The results of DFT calculation show that the position of nitrogen vacancy is the location of bridging nitrogen.The introduced nitrogen vacancy can act as an electron trapping center and inhibit photogenic charge recombination.It also acts as the active site to promote persulfate activation.The ultrathin structure and modification of nitrogen vacancy can adjust the band structure,and form a higher reduction potential to activate PMS to generate active substances with higher oxidation capacity,thus realizing the efficient degradation of IMD.Quenching experiments and ESR show that O₂^-,¹O₂ and h⁺are the main active substances in the degradation process,and play an important role in the degradation process.