Study On Fluorescence Probes And Their Performances For Environmental Pollutants Based On Carbon Quantum Dots

Carbon quantum dots（CQDs）have attracted extensive attention as fluorescence probes in analysis field for heavy metal ions and pesticide residues detection,due to their good fluorescent stability,low toxicity and color-tunable performances.Considering of the toxicity of hazardous heavy metal ions,the highly-selective detection at low concentration presents great research significance.For low-toxicity pesticides such as carbendazim（CBZ）and dinotefuran（DNF）,highly-selective determination at high concentration is required due to their large scale applications and massive usage.Therefore,improving the selectivity of CQDs probe in heavy metal ion and pesticides detection presents great research value and significance,especially for the determination of hazardous metal ions at low concentration and the detection of widely used pesticides at high concentration.In this work,doped carbon quantum dots probe were synthesized by hydrothermal method and applied to detect Hg²⁺and Fe³⁺.Ratiometric fluorescence probes were established for CBZ and DNF ratiomatric fluorescent detection by simply combining the doped CQDs with gold nanoclusters（AuNCs）and copper nanoclusters（CuNCs）,respectively.The detection mechanism was also discussed and the analytical results showed that the as-synthesized fluorescent probe presented good detection performance on heavy metal ions(Hg²⁺,Fe³⁺),CBZ and DNF.The major results are as follows:1.Ethylenediamine,rhodamine B,sodium sulfide and thioacetamide were selected as nitrogen and sulfur source to prepare nitrogen-doped CQDs（N-CQDs）,sulfur-doped CQDs（S-CQDs）and nitrogen,sulfur co-doped CQDs（N,S-CQDs）by hydrothermal method.The fluorescent properties and structural information of as-synthesized doped CQDs were also investigated.First principle simulation indicated that the band gap of CQDs could be effectively adjusted by the surface oxygen-containing groups and the doping of N atoms.The simulation for the interaction between doped CQDs and heavy metal Hg²⁺,Fe³⁺ions suggested that the adsorption process of Fe³⁺could be promoted by the presence of doped N atoms in CQDs.Furthermore,the good affinity between Hg²⁺and carboxyl on the surface of CQDs was the basis of effective fluorescence quenching.Theoretical and experimental investigations showed that the fluorescence quenching of as-synthesized CQDs by Hg²⁺and Fe³⁺was related to the dynamic quenching process,which attributed to the charge transfer between CQDs and heavy metal ions.From this,the trace detection of Hg²⁺and Fe³⁺was carried out by the fluorescent quenching effect of doped CQDs.Experimental analysis indicated that the presence of rhodamine B could significantly enhance the selectivity of CQDs on Hg²⁺.Rh B-CQDs present good analytical performance in the ranges of 1-10 n M and 50-1000n M,with low detection limits as 0.16 n M and 40.87 n M.The thiol groups introduced by S doping could improve the selectivity of as-synthesized N,S-CQDs on Hg²⁺,while the surface amino groups and doped N atoms also contributed to the adsorption of Fe³⁺on N,S-CQDs.Hence,the as-synthesized N,S-CQDs have applied as a fluorescence probe for the trace detection of Hg²⁺and Fe³⁺,and the detection limits as low as 0.27 n M and2.88 n M,respectively.2.Carbendazim ratiometric fluorescence probe was established by the combination of N-CQDs and AuNCs.The photoluminescence intensity of N-CQDs could be deactivated by AuNCs with the consequence of fluorescence resonance energy transfer（FRET）.The fluorescence of N-CQDs was gradually recovered by the addition of CBZ due to the aggregation of AuNCs reduced the FRET process,which resulted in the enhancement of Second-order Rayleigh scattering（SRS）signals of N-CQDs/AuNCs.The ratiometric detection of CBZ was achieved by recording the fluorescence and SRS signal of N-CQDs/AuNCs system.Experimental results showed that the as-established N-CQDS/AuNCs present good selectivity to CBZ in the concentration ranges of 1-100μM and 150-1000μM,with low detection limits as 0.83μM and 37.25μM,respectively.The fluorescence signal of S-CQDs in S-CQDs/CuNCs ratiometric fluorescence probe was quenched by CuNCs via inner filter effect（IFE）and then recovered after the addition of DNF.While the fluorescence signals of CuNCs presented aggregation-related quenching performance.The ratiometric performance of as-established sensing probe for DNF was carried out by the fluorescent changes of S-CQDs/CuNCs with various concentrations of DNF.The as-established S-CQDs/CuNCs sensing probe presented good selectivity to DNF in the dynamic response range from 10 to 500μM,the corresponding detection limit was calculated as7.04μM.The as-established sensing probes were applied to determine pesticides with simple operation procedure and cost-effective performance,which presented a feasible analytical method for environmental pollutants determination.