Preparation Of Nitrogen-doped Carbon Quantum Dots And Their Applications In Fe³⁺ And Cn^-’s Detection

At present,there are still some challenges to realize the instant and sensitive detection of cations or anions on a single platform.In recent years,carbon nanomaterials have received extensive attention due to their simple preparation process and unique advantages in integrating and improving platform performance.Carbon quantum dots（CQDs）are an emerging and promising fluorescent carbon-based nanomaterial.Due to their large specific surface volume,small particle size and high surface functionalization,CQDs have high activity and can easily interact with a variety of chemical substances,resulting in a variety of properties,especially optical properties have great changes.In addition,compared with traditional fluorescent organic dyes and semiconductor quantum dots,CQDs are widely used due to their chemical stability,inertness,formation of stable colloidal solutions,and high resistance to photobleaching.The main contents of this article are:1.Using p-aminosalicylic acid（PAS）and glycine（Gly）as carbon and nitrogen sources,respectively,a simple one-step hydrothermal treatment was used to synthesize nitrogen（N）-doped carbon quantum dots（N_A-CQDs）with strong blue fluorescence.The rate（QY）is about 6.8%.The N_A-CQDs exhibited excitation wavelength-dependent photoluminescence properties with a maximum excitation wavelength of 355 nm and a maximum emission wavelength of 426 nm.By changing the molar ratio of reactants,reaction temperature and reaction time,the conditions for synthesizing N_A-CQDs with the best performance were determined as follows:the molar ratio of PAS and Gly was 1:1,the reaction temperature was 180°C,and the reaction time was 4 h.The morphology and chemical composition of the N_A-CQDs were characterized by transmission electron microscopy（TEM）,X-ray powder diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）.N_A-CQDs mainly contain C,N,O,and H elements,are approximately spherical,disperse well in water,and are in the linear range of 1×10^-5 mol·L^-1～1.2×10^-4mol·L^-1,showed high selectivity and sensitivity to Fe³⁺with the detection limit of4.9×10^-6 mol·L^-1.2.Nitrogen（N）-doped carbon quantum dots（N_B-CQDs）with green fluorescence were prepared by a one-step hydrothermal method using p-aminosalicylic acid（PAS）and tartaric acid（TA）as raw materials,and the quantum yield（QY）was 5.0%.The N_B-CQDs exhibited excitation wavelength-dependent photoluminescence properties with a maximum excitation wavelength of 495 nm and a maximum emission wavelength of 514 nm.By changing the molar ratio of reactants,reaction temperature and reaction time,the conditions for synthesizing N_B-CQDs with the best performance were determined as follows:the molar ratio of PAS and TA was 1:4,the reaction temperature was 180°C,and the reaction time was 6 h.The morphology and chemical composition of the N_B-CQDs were characterized by transmission electron microscopy（TEM）,X-ray powder diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）.N_B-CQDs mainly contain C,N,O and H elements,are approximately spherical,and disperse well in water,within the linear range of 1×10^-5 mol·L^-1～5.2×10^-4 mol·L^-1,exhibited high selectivity and sensitivity towards CN^-,with the detection limit of 14.5×10^-6 mol·L^-1.