Preparation Of Carbon Nitride-based Composite Photocatalyst And Study On Its Photocatalytic Performance

In order to solve the increasingly serious environmental pollution problem,this paper uses photocatalysis technology,and selects non-metallic semiconductor graphite phase carbon nitride?g-C3N4?with many advantages of visible light catalytic activity,chemical stability and thermal stability as the photocatalyst.However,pure g-C3N4 has a serious impact on its practical application due to the disadvantages of low quantum yield and easy recombination of photogenerated carriers.Therefore,we constructed different heterojunction composite photocatalysts to improve the photocatalytic activity of g-C₃N₄,and used these composite photocatalysts to degrade organic pollutants in water.The main research contents and results are as follows:?1?Cu2O/g-C3N4 p-n heterojunction composite photocatalyst was prepared by in-situ method,and Cu₂O/g-C₃N₄ p-n heterojunction was characterized by a series of characterization methods.Tetracycline?TC?was selected as the target pollutant,and the photocatalytic activity of the composite was evaluated by degrading TC under visible light irradiation.Experiments show that Cu₂O/g-C₃N₄ can remove more than 90%of TC in 90 min,and total organic carbon?TOC?removal rate of TC is as high as 83.4%.Compared with Cu2O and g-C3N4,photocatalytic performance is significantly improved.This is due to the construction of the p-n heterojunction and the internal electric field formed at the interface of the heterojunction,so that the photogenerated carriers are effectively separated and migrated quickly.Through free radical trapping experiments and electron spin resonance?ESR?technology,the active substances in the reaction process were determined to be·O₂^-and h⁺.After five cycles of experiments,the complex still showed high stability and photocatalytic activity.Finally,the photocatalytic degradation mechanism of Cu₂O/g-C₃N₄ p-n heterojunction is discussed.?2?Using ZIF-67 as a template,the cage-like Co9S8?c-Co9S8?was obtained by further processing,and g-C₃N₄ was coated on its surface to construct the c-Co₉S₈/g-C₃N₄?c-CSCN?Z-scheme Composite photocatalyst for degrading tetracycline?tetracycline,oxytetracycline and chlortetracycline?antibiotics under visible light irradiation.High-resolution transmission electron microscopy?HRTEM?and transmission electron microscopy?TEM?analysis show that c-Co₉S₈ and g-C₃N₄ are tightly combined,and the matched energy band structure promotes the transfer of electrons.The photocatalytic activity of the prepared c-CSCN is much higher than that of flake Co₉S₈/g-C₃N₄?s-CSCN?,c-Co₉S₈ and g-C₃N₄,which are 1.5,2.5 and 5.8 times of theirs respectively.At the same time,after five consecutive degradation experiments,c-CSCN still maintains good photocatalytic activity,indicating that c-CSCN Z-scheme photocatalyst has excellent stability.In addition,c-CSCN has a good removal effect on tetracycline on different water substrates,and under direct sunlight outdoors,c-CSCN still shows a good ability to remove tetracycline.Finally,based on free radical trapping experiments,ESR and photodeposition charge flow tracking,the Z-scheme photocatalytic mechanism of c-CSCN hollow heterojunction was proposed.?3?Bi₃Fe_0.5Nb_1.5O₉/g-C₃N₄?BFNO/CN?composite photocatalyst was prepared by electrostatic attraction self-assembly,used for 2,4-dichlorophenol?2,4-DCP?of pesticides and pharmaceutical intermediates Photocatalytic degradation.Because BFNO is ferroelectric,it can generate a spontaneously polarized electric field without applying external stress,driving the rapid separation and migration of photo-generated carriers.With the help of various characterization methods,the morphology,structure,optical and electrical properties of the prepared materials were characterized.Moreover,under visible light irradiation,BFNO/CN showed excellent photocatalytic activity,and the photocatalytic removal rate of 2,4-DCP could reach 83.7%in 2 h.In addition,the continuous degradation experiment still maintained good photocatalytic activity,indicating that it has excellent chemical stability.In addition,through free radical trapping experiments and ESR,it was proved that·O₂^-,h⁺and·OH all contribute to the photocatalytic reaction,and the ranking of the contribution of these three active substances to the degradation reaction is:·O₂^->h⁺>·OH.In addition,BFNO/CN showed excellent photocatalytic activity in different water substrates,and also showed good photocatalytic activity in direct sunlight outdoors,which shows that BFNO/CN has the potential for practical application.Finally,the photocatalytic mechanism of BFNO/CN composite photocatalyst is proposed.