Carbon Dot-based Fluorescent Material For Detection Of Quinoline In Coking Wastewater

Quinoline and other nitrogen heterocyclic compounds in coking wastewater are highly toxic and difficult to degrade,which has caused long-term and serious harm to the ecological environment and human health.Therefore,it is urgent and critical to strictly control the discharge of quinoline and other organics and find a highly sensitive and selective detection method.To overcome the difficulties of the existing quinoline detection technologies,such as complicated operation and poor selectivity,in this thesis,carbon dot-based（CD-based）fluorescence detection technology with high sensitivity,simple operation,environmental protection,and low toxicity is combined with molecular imprinting technology with high selectivity and specific recognition to design CD-based fluorescence detection materials.The morphology and structure of the materials are characterized,the optical properties are analyzed,and the the detection behavior of quinoline in aqueous solution is investigated.This work provides a theoretical and technical basis for the sensitive detection of quinoline in coking wastewater.The detailed research contents and results are as follows:（1）Preparation and detection property of CD fluorescent materialWith citric acid as carbon source,and N-（β-aminoethyl）-γ-aminopropyl trimethoxysilane（KH792）as coupling agent,fluorescent CDs were prepared by one-step microwave-assisted hydrothermal method for fluorescent detection of quinoline in coking wastewater.The morphology,structure,and thermal stability of CDs were characterized and analyzed.Besides,the detection behavior and detection mechanism of CDs towards quinoine were investigated.The results show that the particle size of CDs is about 5 nm and their carbon core is formed in the dehydration,condensation,and carbonization process of citric acid and KH792.The prepared CDs exhibit excellent optical property and fluorescence stability.The detection limit of CDs towards quinoline in aqueous solution is as low as 13.2 mg L^-1 and the detection concentration is between 20?200 mg L^-1 with good detection sensitivity.There are abundant amino and amide groups on the surface of CDs,which can interact with quinoline by hydrogen bonding.Thus,CDs can recognize and capture quinoline,and then output fluorescence signal.Fluorescent detection of CDs is a fluorescence quenching process,mainly based on the charge transfer between–CONH on the surface of CDs and N atoms in quinoline molecules.（2）Preparation and specific detection property of CD-based quinoline molecularly imprinted fluorescent materialTo realize selective and specific detection of quinoline in coking wastewater and material（CD-MIP）was prepared by the introduction of molecular imprinting technology.The CD-MIP used the above-mentioned CDs as the fluorescence signal source and seed,quinoline as template molecule,KH792 as functional monomer,and tetraethyl silicate as crosslinking agent.The morphology,structure,and thermal stability of CD-MIP were characterized and analyzed.The detection properties including detection time,selectivity,and reproducibility were investigated.The experimental results show that CD-MIP has a regular morphology,and can maintain excellent fluorescence performance with good fluorescence stability.With optimized detection conditions,the fluorescence intensity of CD-MIP has a good linear relationship with the quinoline concentration in aqueous solution in the range of 20?200 mg L^-1,the detection limit is 16.4 mg L^-1,and the detection time is as low as 90 s.Owing to the imprinted cavities highly matching with quinoline,CD-MIP shows a high imprinting factor of3.46.It has higher affinity for quinoline than for other structural analogues,and has excellent anti-interference ability.After six elution-recombination cycles,the fluorescence intensity and detection ability are not significantly reduced,indicating the excellent regeneration performance.In addition,the quenching rate of quinoline by CD-MIP reaches the highest when the p H value is around 8,indicating that CD-MIP is suitable for the detection of quinoline in weak alkaline coking wastewater.For real coking wastewater samples,the detection recovery is between 98.45%and 104.14%,and the relative standard deviation RSD is between 2.8%and 3.9%.CD-MIP shows excellent photoluminescence performance,good stability,high detection sensitivity,excellent selection performance,outstanding anti-interference ability,short detection time,and good reproducibility.Therefore,it has great potential to be applied to the quinoline trace analysis in actual coking wastewater.