Synthesis Of Carbon Nitride-based Nano-fluorescent Materials And Their Use In The Detection Of Chlorine-containing Environmental Substances

As a nano-semiconductor material,carbon nitride is often used in the field of fluorescence detection due to its unique photoluminescence characteristics.Usually,carbon nitride is a bulk material formed by heat treatment,with a small specific surface area,insufficient surface-active groups,and poor selective adsorption capacity,resulting in its unsatisfactory detection ability.In addition,carbon nitride powder samples or suspension samples are generally used in detection research,which is difficult to achieve rapid recovery,and due to problems in preparation technology and detection methods,it is difficult to achieve miniaturization and portable detection.In response to these problems,this thesis chooses the sol-gel method to prepare carbon nitride film as the sensor unit,improves the detection ability of chlorine-containing substances through optimization and modification methods,and explores the fluorescence detection mechanism.At the same time,a fluorescence-fiber transmission sensing system was built in combination with optical fiber transmission,and the study of fluorescence detection of chlorine-containing substances in environmental water was completed.The specific research contents are as follows:First,the porous carbon nitride nanosheets were synthesized by the cyanuric acid-controlled melamine method.Using optical glass as the substrate,the Si O₂ sol-gel method was used to successfully prepare carbon nitride films with good fluorescence properties and stability.Analyze the influence of concentration,temperature and p H factors on its optical performance,and determine the best parameters of the optical properties of the film and the best conditions for detection.In order to improve the detection ability and broaden the detection range,Ag is used to modify the surface of the carbon nitride film,which effectively promotes the electron transfer in the process of quenching the fluorescence of the film by chlorine-containing substances,the film's ability to detect inorganic and organic chlorine-containing environmental substances—chloride ion(Cl^-)and p-chlorophenol(4-CP)was explored,respectively.Through surface photovoltaic technology,time-resolved fluorescence technology and other means,the fluorescence sensing mechanism of the film is deeply revealed,and the reason why the Ag modified film has better detection ability is analyzed.Second,combining traditional fluorescence spectroscopy technology and optical fiber transmission technology to construct a small,light-weight and portable fluorescence-fiber transmission sensing system for the concentration detection of two chlorine-containing substances.The Ag-modified carbon nitride film is used as the fluorescence sensing unit,and the appropriate excitation light source,filter device,fiber optic spectrometer and other optical devices are selected to optimize the fluorescence collection efficiency of the carbon nitride film,and the best index parameters are confirmed.The fluorescence-fiber transmission system is used to detect the concentration of Cl^-in the range of 5 mmol/L?0.07 mol/L,and the detection concentration of 4-CP is in the range of 100 mg/L?500 mg/L.