A Facile Microwave-assisted Fabrication Of Functional Carbon Nitride Nano-materials And Their Application

Graphitic carbon nitride nano-materials,because of its unique physical and chemical properties,such as low environmental toxicity,high quantum yield,good chemical resistance and excellent biocompatibility,was applied in many fields such as bioimaging,biosensing and ion detection,has received the widespread attention and research.In this paper,fluorescence carbon nitride quantum dots and fluorescence carbon nitride nanosheets with high quantum yield were prepared from citric acid and urea.The synthesis condition,structural characteristic,and detection of metal ions were studied.（1）The carbon nitride quantum dots（CNQDs）were prepared using citric acid and urea as the precursors by microwave-assisted method.The product was characterized by multiple analytical techniques including transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,fluorescence spectra,UV-Vis spectra,and Fourier transform infrared spectroscopy（FT-IR）.The as-prepared CNQDs exhibited excellent fluorescence property.The fluorescence quantum yield could reach 27.1%.Mercuric ions exhibited good fluorescence quenching selectivity to the CNQDs,and this was exploited to design a method for fluorometric determination of Hg²⁺.We also performed the growth experiments using green beans as a model to investigate their biocompatibility and cytotoxicity preliminary.（2）The carbon nitride nanosheets（CNNSs）were prepared using citric acid and urea as the precursors by a facile one-pot microwave-assisted solvothermal method at relatively low temperature in a short time.The obtained CNNSs were characterized by multiple analytical techniques including transmission electron microscopy（TEM）,atomic force microscope（AFM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,solid-state nuclear magnetic resonance（NMR）and Fourier transform infrared spectroscopy（FTIR）.The CNNSs with a quantum yield of 38.9%could serve as an effective fluorescent probe for free chlorine with a detection limit of 0.195μM.The quenching rate was quick（less than 1 min）,and the linear response range of free chlorine was from 0 to 100μM.This method has promising potential applications in the detection of free chlorine in real water samples.（3）High performance liquid chromatography（HPLC）with ultraviolet and fluorescence detectors was used for the component analysis of the products derived from citric acid and urea.The effect of chromatographic conditions on the separation was investigated.The effect of reaction conditions on the luminescence properties of the products was studied,and then the fluorescence mechanism of functional carbon nitride was explored.