Investigation On Covalent Modification Of Graphitic Carbon Nitride And Photocatalytic Application For Elimination Of Antibacterial Drug

The human health and ecological equilibrium are harmed by the antibacterial drug residuals（ADs）in environment.The effective elimination of ADs cannot be achieved through the conventional approaches.The advanced oxidation processes（AOPs）have the disadvantages of energy consuming,high cost and introducing secondary pollutants.To accomplish energy conservation,emission reduction and carbon neutrality,the solar driven photocatalysis is considered as one of the most potential technologies.The photocatalysts are critical for photocatalysis.The high cost and secondary pollution risk of traditional photocatalysts e.g.transition metal oxide and sulfide limit their practical applications.As one kind of photocatalyst,graphitic carbon nitride（g-C₃N₄）has received numerous attentions from researchers for environmental and energy application because it is metal-free,environmental-friendly and highly stability.However,the as-prepared g-C₃N₄has low specific surface area,high rate of photo-induced carrier recombination and insufficient absorption of visible light,etc.As a result,modification of g-C₃N₄ is regarded as important approaches to improve its photocatalytic activity.In this thesis,as the initial photocatalyst,two-dimensional（2D）g-C₃N₄ nanosheets（CNNS）was studied for the moxifloxacin（MOX）elimination.Based on the CNNS,covalent modification was carried out with groups of different electron effect,which were expected to have improved photocatalytic activity.Our studies could be summarized as follows.CNNS was synthesized with a method of ammonium chloride assisted chemical blowing.Compared to the bulk g-C₃N₄（BCN）,the CNNS had similar physicochemical properties,but possessed much larger surface area and pore volume,and higher separation efficiency of photo-generated charges.Therefore,the photocatalytic activity of CNNS towards MOX elimination was much better than that of BCN.The main reactive oxygen species（ROS）was superoxide radical（?O₂^-）.The plausible photocatalytic mechanism of MOX elimination with CNNS was proposed on the basis of band structure and other tests.The effectiveness of photocatalytic elimination MOX with CNNS was confirmed by the degradation pathways proposing,the chemical structure analysis,antibacterial activity and environmental toxicity tests of degradation intermediates.The potential practical application of CNNS was confirmed according to the tests of photocatalyst reusability and practical scenarios.In this thesis,the covalent modified strategies of CNNS could be summarized as follows.（1）As an electron-withdrawing group,dodecyl benzene sulfonyl group was grafted to the terminal amino group of CNNS to synthesize CGS.（2）As an electron-donating group,para-methoxy benzoyl group was grafted to the terminal amino group of CNNS to synthesize CGM.（3）Para-methoxy benzoyl group was grafted to the terminal amino group of CGS to synthesize CGSM,dodecyl benzene sulfonyl group was grafted to the terminal amino group of CGM to synthesize CGMS.The characterizations demonstrated that the CGS and CGM maintained the main characteristics of g-C₃N₄,and the corresponding functional groups were grafted onto CNNS with covalent bond.The band structures of the CGS and CGM were adjusted to decrease the redox potential of conduction band（CB）.The reducing capacity of photogenerated electron（e^-）was enhanced.The amount of?O₂^-as the main ROS was increased,and the photo-induced hole（h⁺）was also involved in the photocatalysis.Besides,the hydroxyl radical（?OH）was involved in photocatalysis for CGM.The plausible photocatalytic mechanisms of MOX elimination with CGS and CGM were proposed on the basis of band structure and other tests.The effectiveness of photocatalytic elimination MOX with CGS and CGM were confirmed by the degradation pathways proposing,the chemical structure analysis,antibacterial activity and environmental toxicity tests of degradation intermediates.The potential practical application of CGS and CGM were confirmed according to the tests of photocatalyst reusability and practical scenarios.Compared with the CNNS,CGS and CGM,the CGSM and CGMS maintained the crystal phase of g-C₃N₄ but the band-gap energy（E_g）and the steady-state fluorescence intensity were decreased.Compared with the CNNS,the improved photocatalytic ability of CGSM and CGMS could be attributed to the decreased recombination rate of photo-induced carriers,increased absorption of visible light and adjusted band structure.The?O₂^-and h⁺were involved in photocatalysis for CGSM and CGMS.The effectiveness of photocatalytic elimination MOX with CGMS was suggested by the antibacterial activity tests of the photocatalytic degradation intermediates.The reusability of CGMS was confirmed.The potential practical application of CGSM and CGMS were confirmed according to the practical scenarios.In this thesis,firstly,the CNNS was prepared by the strategy of morphological controlling.Then,the CGS and CGM were prepared by the strategy of covalent modification with dodecyl benzene sulfonyl group（an electron-withdrawing group）and para-methoxy benzoyl group（an electron-donating group）,respectively.In addition,the CGMS and CGSM were fabricated by the strategy of simultaneous covalent modification with dodecyl benzene sulfonyl group and para-methoxy benzoyl group.The essential structures and properties of materials were characterized,the evidences of successful modification were also obtained.The photocatalytic degradation activities of MOX were studied,the expectation of improving photocatalytic reaction capacities were achieved.The different materials had different ROS,h⁺and electronic structures.The plausible photocatalytic reaction mechanisms of different materials were proposed.The potential practical applications of materials were implied based on the evaluation of photocatalytic reaction paths and degradation products and the tests of photocatalytic reaction activities in several real scenarios.