Chemiluminescence Of Nitrogen-Sulfur Co-Doped Graphene Quantum Dots And Its Analytical Application

Chemiluminescence?CL?-based analytical technique exhibits several characteristics including high sensitivity,simple operation,no interference from background scattering light and wide linear range,which has become one of important methods for the determination of trace analytes.However,due to the low reaction efficiency and quantum yield,signal of some CL systems is weak,which limits its analytical application.As a new type of carbon nanomaterials,graphene quantum dots?GQD?have the advantage of strong fluorescence activity,chemical inertia and excellent light stability.The introduction of graphene quantum dots?GQD?can improve the CL intensity of weak system and expand the analytical application of CL.In this work,nitrogen-sulfur co-doped graphene quantum dots?NSGQD?was synthesized by pyrolysis route using citric acid as carbon source and L-cysteine as nitrogen and sulfur source,and its optical properties,chemical structure and morphology were characterized.The effects of NSGQD on three different CL systems was investigated,the specific contents are as follows:1.Establishment of NSGQD-Ce?IV?CL system and its application for I^–and Hg²⁺detection.The CL of the redox reactions between NSGQD and some oxidants were investigated.It was found that the introduction of Ce?IV?into NSGQD resulted in CL with highest intensity in acidic medium.So NSGQD-Ce?IV?system was selected as further study,and the CL mechanism was investigated.Further results indicate that I^-markedly quenched the CL intensity of the NSGQD-Ce?IV?system.When Hg²⁺was added,the inhibited CL signal was restored.Thus we designed a“turn off-on”CL analysis method based on the NSGQD-Ce?IV?system for simultaneous determination of I^-and Hg²⁺.Under the optimum condition,the linear range was 0.04–3.0?M with a detection limit of 4.23 nM for I^-,and the linear range was 0.3–7.0?M with a detection limit of 20.0 nM for Hg²⁺.The proposed method has been applied to the determination of I^-in kelp and tea,and Hg²⁺in water samples,respectively with satisfactory result.2.Establishment of NSGQD-NaHSO₃-oxidant CL system and its application for folic acid.The effect of NSGQD on the CL system of NaHSO₃-oxidant was studied.It was found that NSGQD could enhance the weak CL of the NaClO-NaHSO₃ system,the H₂O₂-NaHSO₃system,and the KMnO₄-NaHSO₃ system.The mechanism research indicated that the reaction of NaHSO₃ and NaClO/H₂O₂/KMnO₄ produce excited state sulfur dioxide?SO₂*?.Then the energy from the SO₂*could transfer to NSGQD to generate the excited NSGQD?NSGQD*?.Folic acid?FA?,as a water-soluble B vitamin,had a certain inhibition on the CL intensity of the above system.The percentage inhibition of FA on CL intensity of NSGQD-NaHSO₃-NaClO system was greatest,so a fast and low-cost method was developed to analyze FA in spinach and kiwifruit samples.The the linear rangewass 0.5–70.0?M and the detection limit was 78.0 nM.3.The construction of NSGQD-IO₄^–-H₂O₂ CL system and the application for L-tryptophan?Try?and Hg²⁺detection.The effect of NSGQD on the weak CL system induced by H₂O₂ was studied.It was found that NSGQD could greatly enhance the CL intensity of H₂O₂-IO₄^–system in acidic medium.Therefore,the NSGQD-IO₄^–-H₂O₂ system was established,and its mechanism was discussed.Further studies showed Try dramatically suppressed the CL intensity of the NSGQD-IO₄^–-H₂O₂ system.The Inhibited CL intensity was found to be linear with the concentration of Try in the range from 0.6–20.0?M,and the detection limit was 0.058?M.The method was successfully applied to detect Try in milk and human plasma samples.Unlike Try,Hg²⁺could amplify the CL signal of NSGQD-IO₄^–-H₂O₂system,so a new method for detecting Hg²⁺has been established,the linear range was 0.1–9.0?M,the detection limit was 0.064?M.And the method was applied to the determination of Hg²⁺in drinking water.