Preparation Of Molybdenum Carbide/Graphitic Carbon Nitride Heterostructure Photocatalytic Material And Its Performance In Degrading Of Tetracycline

Antibiotic contamination has raised world-wide concerns due to its threats to the organisms in ecosystem and indefinite environmental impacts.The photocatalytic technology has become a promising environmental pollution treatment technology.Photocatalytic degradation of antibiotics from wastewater has aroused tremendous interests due to its high efficiency,stability,and no secondary pollution.Among the as reported numerous photocatalysts,g-C₃N₄,as a novel metal-free visible-light driven photocatalyst,has attracted intensive attention owning to its attractive electronic band structures and remarkable physicochemical stability.But pristine g-C₃N₄ exhibited low level of photocatalytic activity due to the rapid recombination of photo-generated charge carriers,insufficient solar light absorption and relatively low electrical conductivity.On the basis of the above issues,this study modified g-C₃N₄ through heterostructure construction,and detailedly investigated the performance and mechanism of g-C₃N₄ based heterostructure materials for the degradation of tetracycline（TC）.This research provides new insights for the rational design of g-C₃N₄-based photocatalysts,and provides theoretical and technical support for the application of photocatalytic technology for the water pollution treatment.This study is divided into the following 2 parts:In Chapter 3,we constructed a Mo₂C/tubular like g-C₃N₄（Mo₂C/TCN）direct Z-scheme heterostructure photocatalytic system.It maintained the high oxidation and reduction capabilities of the photocatalytic system.The specific hollow tubular structure provided favorable channel for electrons transport,thus realizing highly active and stable photocatalytic degradation of water contaminants.The introduction of Mo₂C improved the efficiency for photon utilization,provided trapping sites for photo-induced electrons and facilitated the separation of electron-hole pair,thus prolonging charge carriers’lifetime,which were in agreement with the results of transient photocurrent response curves,electrochemical impedance spectroscopy,photoluminescence spectra and time-resolved photoluminescence spectra.As a result,the optimized Z-scheme system exhibited impressive visible-light photocatalytic performance.Especially,the Mo₂C/TCN-2 photocatalysts exhibited superior photocatalytic performance for tetracycline degradation with a reaction rate of 0.0391 min^-1,which was 3-times and 9-times higher than those of TCN and pristine g-C₃N₄,respectively.Moreover,in the process of Mo₂C/TCN photocatalytic degradation of TC,·O₂^-and h⁺were the main active species.In Chapter 4,we developed a two-dimensional/two-dimensional Mo₂C/g-C₃N₄ Van der Waals（2D/2D MCN VDW）heterojunction photocatalyst via electrostatic self-assembly method.To investigate the strong electron interaction between 2D/2D VDW heterojunction,we computationally explored the geometric structure,electronic properties,band edge positions,work function,and charge transfer via first-principles calculation.The strong electronic coupling between the VDW forces induced electrons transfer within interlayers and endowed g-C₃N₄ ordered in-plane electron migration.Additionally,the internal electric field between Mo₂C and g-C₃N₄ was established and it synergistically enhanced the photocatalytic overall performance,including the higher separation efficiency of charge carriers,the pronged lifetime of photo-induced charge carriers,the lower electrical resistance and the shorter electrons migration distance.Consequently,the optimal sample（MCN-2）exhibited significant enhancement of photocatalytic activity,the TC was completely decomposed after 60 min of photocatalytic reaction and the apparent rate constant reached up to 0.066 min^-1,which was about 3.8-times higher than that of g-C₃N₄ nanosheets.The trapping electron spin resonance technique and reactive species trapping experiments indicated that the·O₂^-,h⁺and?OH are the major active species and their relative contributions were estimated to be 93.9%,87.9%and80.3%.