Preparation Of Benzoxazine-based Fluorescent Carbon Nanoparticles For Ion Detection

Fluorescent carbon nanoparticles have developed rapidly and have been applied in many fileds,such as bioimaging,catalysis,optoelectronic devices and chemical sensing due to its excellent optical properties,good chemical stability and low toxicity in the past decade.However,there are still some problems for fluorescent carbon nanoparticles in the field of chemical sensing.For example,the prepared fluorescent carbon nanoparticles mostly emit short-wavelength light(blue),and they can only perform detection under relatively mild pH conditions and the pH environment used for detection is relatively simple.In view of the above problems,this paper synthesized green fluorescent carbon nanoparticles by using benzoxazine monomer as a carbon source,which could be applied in the detection of different ions.It mainly includes the following two aspects:(1)Benzoxazine(BZ)monomers were synthesized by Mannich reaction using melamine,formaldehyde and phenol as raw materials.Green fluorescent-carbon nanoparticles(G-CNPs)were synthesized by a one-step hydrothermal method using the synthesized BZ monomer as a carbon source.The average particle size of G-CNPs was about 150 nm by scanning electron microscopy and transmission electron microscopy.X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy showed that the surface of G-CNPs contained a large number of carboxyl functional groups.UV-vis spectrometer and fluorescence spectrometer were used to characterize the optical properties of G-CNPs.The results showed that G-CNPs had good fluorescenceemitting properties under excitation dependence.G-CNPs could detect Cr(?)with a high selectivity and sensitivity by the Inner filter effect(IFE)in a strongly alkaline(pH=14)environment with the detection range of 1-300 ?M and the limit of detection of 0.58 ?M.G-CNPs were also applied to evaluate the Cr(?)content in actual samples(lake water).(2)Green fluorescent-carbon dots(G-CDs)were synthesized by one-step hydrothermal method using BZ monomer as a carbon source,and the average particle size of G-CDs was about 5 nm by transmission electron microscopy and atomic force microscopy.X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy showed that the G-CDs contained carboxyl and amide functional groups.The results of UV-Vis and fluorescence spectra indicated that G-CDs had strong fluorescence efficiency(18%).It was found that the fluorescence intensity of G-CDs changed with different pH,the fluorescence intensity was low under neutral conditions(pH=7.0)and could be specifically enhanced by Zn(?),so a fluorescence turn-on probe with the detection range of 1-100 ?M and the limit of detection of 0.32 ?M was constructed to detect Zn(?).It was also successfully applied for the determination of Zn(?)in serum.When under alkaline conditions(pH=10.0),the fluorescence intensity of G-CDs was high,and it could be specifically quenched with Cr(?),so a turn-off probe with a Cr(?)detection range of 1-50 ?M and a detection limit of 0.99 ?M was constructed.The probe was also applied for the detection of Cr(?)in real samples(lake water).