Construction Of Carbon Dots Fluorescent Composite Based On Bean Dregs For Optical Detection Of P-nitrophenol In Water

As a common organic pollutant in wastewater from agriculture,dyestuff and chemical industry,p-nitrophenol is difficult to biodegrade and its toxic effect lasts for a long time.It has been detected many times in the environment,which has seriously affected the ecological environment and even endangered human health.The routine detection methods of pnitrophenol have complicated procedures,long time consumption and high cost.Fluorescence analysis based on quantum dots is widely used to detect various environmental pollutants because of its simple,rapid and sensitive response.As a new carbon nano-material,carbon dots have gradually replaced the traditional semiconductor quantum dots because of its outstanding stability and excellent biocompatibility.Carbon dots are rich in resources and can be obtained from various biomass as raw materials.However,at present,the research on biomass carbon point mostly focuses on plant sources with high lignin and cellulose content,and requires complex pretreatment,complicated process operation and low carbon conversion rate.Therefore,it is still necessary to screen out carbon sources with low cost,simple preparation process and high utilization rate.Based on this,we selected bean dregs as the representative of biomass with low lignin,low cellulose and high water content,and developed a green and simple synthesis route to make bean dregs into fluorescent carbon dots with high added value.After that,we synthesized bean dregs-based composite materials by different methods and developed them into fluorescent sensors to realize the quantitative detection of trace pnitrophenol in the environment.The specific research contents are as follows:(1)First,using waste bean dregs as carbon source precursor and only water as solvent,nitrogen was doped in the hydrothermal process to prepare blue carbon dots(N-CDs).The fluorescence quantum yield of N-CDs was 10.64%,and it emitted bright blue fluorescence at the optimal excitation wavelength of 340 nm,with the strongest emission peak around 415 nm.The physical and chemical properties of N-CDs were analyzed and tested.N-CDs were spherical particles with a particle size of about 4.8 nm,which had excellent oxidation resistance,ion interference resistance and photobleaching resistance.In the concentration range of 0.4～40μM,the concentration of p-nitrophenol and the fluorescence quenching degree of N-CDs aqueous solution conformed to the Stern-Volmer equation.Experiments showed that the quenching of N-CDs fluorescence was based on internal filtration effect.The N-CDs sensor was successfully applied to the quantitative detection of PNP in actual water samples,which provided a new idea for the reuse of waste biomass and showed potential environmental and economic benefits.(2)Using food waste bean dregs as carbon source and deep eutectic solvents as modifying solvent.Deep eutectic solvents,with its outstanding dissolving ability,dissolved and dispersed insoluble small molecular substances in bean dregs,and provided nitrogen and chlorine doping while promoting the carbon conversion of bean dregs in the hydrothermal process,thus improving the conversion rate of carbon dots and the fluorescence quantum yield.The synthesized carbon dots(N,Cl-CDs)were uniform in size,with a particle size of 5.0～7.0 nm and a fluorescence quantum yield of about 26.74%.Study on the optical properties of N,ClCDs showed that the obtained N,Cl-CDs could still maintain high fluorescence intensity in harsh environments such as peracid,high ionic strength and long-term illumination.The constructed N,Cl-CDs fluorescent probe could accurately detect PNP in the concentration range of 0.1～60μM,and the detection limit was as low as 30 n M.The quenching of PNP by N,Cl-CDs sensor was based on internal filtering effect.The fluorescence detection of PNP in environmental samples by N,Cl-CDs was successfully realized through the recovery experiment of actual water samples.(3)In order to improve the selective recognition effect of N,Cl-CDs on PNP,a carbon dots molecularly imprinted fluorescence sensor based on bean dregs(MIP@CDs)was prepared by sol-gel method.The morphology,structure and optical properties of MIP@CDs were explored by various characterization methods.The effects of concentration,p H and response time of MIP@CDs on the detection results were studied by fluorescence spectrophotometer.Under the best detection conditions,the detection linear range of MIP@CDs for PNP concentration was 0.6～50 μM,the detection limit was 200 n M,and the imprinting factor was2.72.The results of selective experiments showed that MIP@CDs was better than NIP@CDs in detecting PNP,because MIP@CDs polymer had a binding site that specifically recognized PNP,and could quickly lock the target,which leaded to the quenching of the fluorescence of quantum dots.The recovery rate of MIP@CDs was between 93.8% and 103.3% when it was used to detect PNP in environmental water samples,which provided a reliable method for rapid identification of PNP.