Synthesis Of Graphitic Carbon Nitride Nanosheets Composites And Theirs Application In Sensor

Graphiticcarbonnitridenanosheets（CNNS）,two-dimensionallayer nanostructures,due to fantastic water solubility,high fluorescence quantum yield,good stability,excellent biocompatibility and non-toxic,it has been widely studied.In this paper,we have prepared CNNS and its composite materials,and then used for fluorescent sensors and electrochemical sensor.The main contents are as follows:（1）A novel approach for preparation of CNNS from stripping graphitic carbon nitride（g-C₃N₄）by strong acid and ultrasonic technology was demonstrated in this study the first time.Transmission electron microscopy was employed to characterize the surface morphology.Atomic force microscope was carried out to characterize the thickness of nanosheets.X-ray diffraction was performed to estimate the lattice structure.X-ray photoelectron spectroscopy was carried out to characterize the surface composition and element analysis.Fourier transform infrared spectroscopy was allowed to identify the functional groups.The as-synthesized CNNS exhibited excellent emission property as well as excitation-independent emission behavior,and fluorescence quantum yields can reach approximately 12.53%.Mercury ion(Hg²⁺)can make a result of quenching the significant intensity of fluorescence of CNNS by formation of a covalent bond between empty orbital of Hg²⁺and theπelectrons of N（turn-off）.And the addition of the L-cysteine（L-Cys）can enhance the intensity of fluorescence of CNNS-Hg²⁺system through the thiol group of L-Cys anchored with Hg²⁺and dragged it from the surface of CNNS（turn-on）.The CNNS was consequently functioned as fluorescence probe towards“off-on”detection of Hg²⁺and L-Cys with high sensitivity and selectivity.Moreover,the fluorescent probe was applied to detect tap water and well water with satisfactory results.（2）CNNS with a graphite-like structure have strong covalent bonds between carbon and nitride atoms,and nitrogen atoms in the carbon architecture can accelerate the electron transfer and enhance electrical properties effectually.The graphitic carbon nitride nanosheets-graphene oxide（CNNS-GO）composite was synthesized.And the electrochemical performance of the composite was investigated by cyclic voltammetry and differential pulse voltammetry ulteriorly.Due to the synergistic effects of layer-by-layer structures byπ-πstacking or charge-transfer interactions,CNNS-GO composite can improved conductivity,electro-catalytic and selective oxidation performance.The proposed CNNS-GO composite modified electrode was employed for simultaneous determination of ascorbic acid,dopamine and uric acid in their mixture solution,it exhibited distinguished sensitivity,wide linear range and low detection limit.Moreover,the modified electrode was applied to detect urine and dopamine injection sample,and then the samples were spiked with certain concentration of three substances with satisfactory recovery results.（3）Inthispaper,three-dimensional（3D）graphiticcarbonnitride nanosheets-carbonnanotube（CNNS-CNT）compositewassynthesizedvia hydrothermal reaction of 2D CNNS and 1D CNT-COOH byπ-πstacking and electrostatic interactions.This CNNS-CNT composite was characterized by transmission electron microscope,scanning electron microscope,x-ray diffraction and Fourier-transform infrared.In addition,the CNNS-CNT composite displayed excellent conductivity comparing with CNNS and CNT-COOH monomer.This composite was applied for simultaneous electrochemical sensor catechol（CC）and hydroquinone（HQ）with good sensitivity,wide linear range and low detection limit.In addition,this CNNS-CNT composite modified electrode was also applied to detect practical samples with satisfactory results.