Synthesis And Properties Of Carbon Quantum Dots And Application In Analysis

Carbon quantum dots(C-dots,CQDs or CDs),a new class of zero dimensional semiconductor nanomaterials,which have attracted tremendous attention in recent year because of their fascinating properties such as small particle size,low molecular weight,stable photoluminescence(PL),low cytotoxicity and excellent biocompatibility,broad and continuous light excitation and emission light can be tuned.Compared with conventional fluorescent material,carbon quantum dots have more excellent performance,so carbon quantum dots showed important application value in biological imaging,optoelectronic devices,catalysis,fluorescence probe biological detection,drug diagnosis,metal cation and anion detection.However,many carbon quantum dots synthesized by different materials have weak fluorescence,which led to its application value greatly reduced.Therefore,this study used different carbon sources to prepared carbon quantum dots and doped different element to improve the fluorescence properties of CDs.The specific research contents are as follows:In this chapter,the green synthesis of fluorescent carbon dots(CDs)via one-step hydrothermal treatment of cornstalk was investigated.The synthesized CDs were characterized by TEM,XPS and FTIR.The obtained CDs with an average diameter of 5.2 nm possess many excellent properties such as emitting green fluorescence under UV light(365 nm),high monodispersity,good stability,excellent water dispersibility,and absolute quantum yield of 7.6%.When H2U2 and Fe2+ were simultaneous added into the CDs aqueous solution,the fluorescence of CDs could be quenched.Based on this principle,these CDs were used as sensing probes for the detection of Fe2+ and H2O2 with detection limits as low as 0.18 ?M and 0.21 ?M,respectively.This sensing platform shows advantages such as high selectivity,good precision,and rapid operation.Graphene quantum dots(GQDs)was synthesized by nitric acid oxidation and hydrothermal assisted methods using Taixi Coals as carbon source.The optical performance and structural properties of GQDs were studied based on two kinds of synthetic methods by TEM,XPS and FTIR.The synthesis of GQDs with particle size about 4.5 nm.It was further demonstrated that such GQDs can serve as effective fluorescent sensing platform for Fe3+,in the PBS buffer solution(0.02 M,pH 3.02),the concentration of Fe3+ and fluorescence intensity of GQDs shows a good linear relationship in the range of 0-21?M,and the detection limit was 0.67 nM.It was successfully applied to determination of Fe3+ in samples.Here a facile and economical one-pot hydrothermal approach for preparing stable and highly luminescent magnesium and nitrogen co-droped carbon quantum dots(Mg,N-CDs)which using alginic acid as a carbon source,Mg(OH)2 and triethanolamine as modified reagent has been well established.The fluorescence of the as-prepared Mg,N-CDs is linearly quenched by Hg2+ and the fluorescence of the CDs-Hg2+ system is completely recovered with the addition L-cysteine.Therefore,the CDs-Hg2+system can serve as "turn on" sensor for highly selective and sensitive detection of L-Cys.The results show that in pH=7 phosphate buffer solution,the fluorescence intensity of Mg,N-CDs has a good linear relationship with the concentration of Hg2+ in the range of 0-45 ?M,the detection limit is 0.17?M.The detection range of L-cysteine is 0-55 ?M and detection limit of 0.09 ?M.Fluorescent Mg,N-CDs was synthesized via one-step hydrothermal treatment with alginic acid.Mg,N-CDs was used as a fluorescent probe for sensitivite and selectivitive detection of organophosphorus pesticides.When the Mg,N-CDs aqueous solution was added pralidoxime(PAM)and organophosphorus(OPs),respectively,it was found that the fluorescence intensity of Mg,N-CDs changed inconspicuously.In contrast,when PAM and OPs were simultaneous added into the Mg,N-CDs aqueous solution,the fluorescence intensity quenched obviously.This work also optimized the detection conditions such as:pH,reaction time,PAM concentration on the detection of organic phosphorus.Under the optimal detection conditions,the detection range of organic phosphorus was 0.05-45 ?M and the detection limit was 0.87?M.