Preparation Of N,Cl-doped Lignin-carbon Quantum Dots And Their Detection And Separation Of PS Microplastics

The problem of how to quickly,easily and efficiently identify microplastics in water environment is urgent to be solved.At present,accurate identification still requires a variety of instruments to analyze.Using fluorescent materials to identify microplastics is an important step in the detection of microplastics.Fluorescence method has the advantages of fast recognition and simple method.At present,traditional fluorescent dyes are still used in the detection and recognition of microplastics.As a new type of fluorescent material,carbon quantum dots are more and more widely used in environmental detection due to their strong selectivity,high sensitivity,strong luminescence ability,stable fluorescence effect and less susceptible to photobleaching.The detection of microplastics in water environment using carbon quantum dots is more advantageous than traditional fluorescent dyes,the detection effect is more stable,and the selectivity to a microplastic is stronger.(1)According to the characteristics of polystyrene in the environment,N,Cl co-doped biomass carbon quantum dots with blue fluorescence were synthesized by one-step hydrothermal method using dealkali lignin,polyethyleneimine and sodium hypochlorite as raw materials.The synthesized carbon quantum dots have amino and chlorine atoms on the surface,which can improve the selectivity of carbon quantum dots to polystyrene.At the same time,the synthesis conditions of carbon quantum dots were optimized,and the hydrothermal temperature of 180 °C was selected for 10 hours to make the luminescence performance of carbon quantum dots stronger and the preparation process more environmentally friendly.It can maintain good stability under ultraviolet light irradiation for 8 hours.(2)The prepared carbon quantum dots were used as the detection reagent,and the polystyrene microplastics were used as the research object.The polystyrene microplastics of millimeter level,micron level and nanometer level 0.001-0.01 g/L were characterized by fluorescence detection,and the rules were analyzed and summarized.The fluorescence intensity showed a nonlinear relationship when carbon quantum dots were added to polystyrene microplastics with different concentrations.The detection mechanism at different p H was analyzed.The 8-hour UV irradiation shows that the carbon quantum dots have excellent light stability during the detection process.It provides a new method and idea for microplastic detection.(3)Micro-nanoplastics with small particle size are widely present in the environment and the separation cost is high.Bentonite,as a natural and pollution-free inorganic material,has a wide range of applications in removing pollutants in the water environment.The separation of microplastics by compounding bentonite with other materials can reduce the separation cost,and the adsorption capacity and adsorption speed of the composite bentonite for microplastics are greatly enhanced.In this paper,lignin-based carbon quantum dots were compounded with bentonite.The specific surface area of the composite material increased by 23.8 %,and the pore volume increased by 51 %.The surface wrinkles are more abundant and the adsorption performance is stronger.The adsorption equilibrium of microplastics can be reached within 1hour,which greatly shortens the adsorption time.Compared with unmodified bentonite,the effective separation of microplastics can be achieved.