Investigation On The Preparation And Fluorescent Application Of Micro Nano Graphitic Carbon Nitride

Graphitic carbon nitride materials(g-C₃N₄)with characteristics of the unique energy band structure,excellent physicochemical stability and non-toxicity have shown potential application in the fields of photocatalysis,fluorescence probe,biological imaging and photoelectricity.At present,there is a lack of in-depth research on the photoelectric performance of g-C₃N₄,and it is expected to further explore its other potential applications in the photoelectric field through functional modification strategies.Based on this,this thesis concentrates on graphitic carbon nitride as the research subject,using morphology,element and molecular doping modification strategy,its morphology,electronic structure and performance of band structure are effectively regulated.And the fluorescent applications of the modified graphite phase carbon nitride materials in fluorescent probe,fluorescence regulation,and white light emission are investigated.Bulk g-C₃N₄are synthesized by traditional high temperature thermal polymerization method.On this basis,a simple and green ultrasonic stripping strategy and subsequent filtration process are adopted to regulate the morphology and obtain the g-C₃N₄nanosheets that have relatively uniform size.Compared with bulk g-C₃N₄,the prepared g-C₃N₄nanosheets have excellent optical properties,water dispersion and stability.We constructed a quick and sensitive g-C₃N₄fluorescent probe to detect Fe³⁺in water,and the calculated detection limit is 2.06?M.In addition,the fluorescent probes of g-C₃N₄nanosheets also show a certain degree of reversibility,which meets the requirements of good fluorescence sensing material for the detection of Fe³⁺.The mechanism of fluorescence quenching between g-C₃N₄and Fe³⁺is studied,and it is proposed that the N lone pair electrons in g-C₃N₄nanosheets could be easily transferred to the 3d empty orbital of Fe³⁺for chelation reaction,which promotes its fluorescence quenching.Based on the modification strategy of element doping,g-C₃N₄are modified by adding P atoms.Through a series of characterization of the structure,it is clear that the incorporation of P will replace part of the C lattice position in the g-C₃N₄network structure and form the P–N bonds.The bond length of these formed P–N bonds is larger than the C–N bonds in the structural units,which changes some basic unit structures in the g-C₃N₄layer,resulting in the morphology of g-C₃N₄transform from a large bulk to a small fluffy layer stacking.In addition,the P atom has electron-rich property.After P atoms replacing C atoms to form P–N bonds,the extra lone pair electrons of P will influence the overall electronic properties of g-C₃N₄,effectively adjusting the band structure and reducing the band gap of g-C₃N₄(from 2.64 e V to2.56 e V).Thus,small amplitude control of fluorescence(red-shift from 441 nm to 449nm,and broadening from 49 nm to 65 nm)is achieved.Through the molecular doping strategy,three substances with similar structure(cyanuric acid,melamine and 2,4,6-tiraminopyrimidine)are supramolecular copolymerized upon the(95%)N₂/(5%)H₂reducing gas atmosphere to form N-deficient porous g-C₃N₄.This modification strategy can essentially change the?conjugate network structure and band structure of g-C₃N₄,showing a major breakthrough in the macro performance of g-C₃N₄.The results show that the band gap of g-C₃N₄has been significantly reduced from 2.64 e V to 1.39 e V,and its absorption range has been extended to the whole visible band.Thereby,the fluorescence transition from narrow blue to broadband white range is realized,and the optimal white light coordinate position is(0.297,0.345).The formation mechanism of N defects and porous structure in the sample is described in detail,and it is believed that it comes from the etching of the sample by reducing gas(N₂/H₂)and the escape of gas(NH₃)after the reaction,which plays a crucial role in the regulation of band gap and the expansion of light absorption.In addition,the broadband white light emission mechanism of g-C₃N₄is explored,which is derived from the radiative transition between the N defect energy level and the energy level formed by the?conjugate network of g-C₃N₄.