Modification Of Carbon Nitride And Its Optical Sensing Application

Optical sensors,which use visual signals to detect targets,have become an indispensable detection method due to their high sensitivity,low detection limit,simple operation,and fast signal reading.As the basis of optical sensing,the development of optical sensing materials has always been the focus of research.Carbon nitride is considered as a promising new luminescent material due to its suitable electronic band structure and unique photoelectric properties.It shows excellent application prospects in optical sensing fields,such as photoluminescence（PL）and electrochemiluminescence（ECL）.However,the further application of PL sensing is limited by the poor dispersion of carbon nitride.In addition,the low photocharge separation efficiency of carbon nitride is inconducive to the development of new optical sensing mechanisms.This dissertation focuses on improving the optical properties and exploring the new optical sensing mechanisms of carbon nitride by developing two modification methods,i.e.,non-covalent interaction and alkali metal doping.Accordingly,a high sensitivity PAHs paper-based PL sensor,oxygen（O₂）colorimetric sensor with adaptive sensitivity/detection range and photoelectron driven highly sensitive catalase（CAT）luminescence sensor based on electron storage mechanism are explored.The details are listed as follows:1.CNNS were uniformly dispersed in solid polymer matrix by incorporating CNNS in hierarchical polymethyl acrylic acid（PMAA,a biocompatible polymer）matrix,which not only effectively solved the problem of poor long-term stability and dispersion of CNNS,but also addressed the limitation of CNNS agglomeration on the application of photoluminescence（PL）sensor.To facilitate the detection,a paper-based fluorescence sensor was prepared by depositing the composite material on filter papers.The CNNS in the resulting nanocomposite not only kept the perpetual dispersity and had sufficient free channels for mass transfer but also well retained the pristine PL properties.Based on the above advantages,further usingβ-CD as the molecule recognition unit,the resultant nanohybrid was applied to construct an economical,highly selective,and sensitive paper-based PL sensor via an inner filter effect for detecting polycyclic aromatic hydrocarbons（PAHs）,a large class of toxic and carcinogenic compounds.2.Colorimetric sensors have been widely used for centuries across diverse fields,thanks to easy operation and uncompromisingly high sensitivity with no need for electricity.However,it is still a great challenge for a conventional chromogenic system to perform multiple measurements meanwhile maintaining high robustness.Since the traditional metal oxides only show blue color after photoelectron storage,the modified CN with different alkali metal doping shows the blue and brown colors under the same condition.Mechanism studies revealed that cyano and carbonyl groups in CN crucially elongated the centroids distance of electron/hole,which stabilized the specific excited states with different light absorption;meanwhile,the counter cations strengthened these processes.Accordingly,a highly sensitive colorimetric sensing mechanism based on the newly discovered principle was developed by using carbon nitrides（CN）with photoelectron storage capability as the chromogenic unit.As a result,O₂ was quantitatively detected by the CN-derived colorimetric sensor,showing high reversibility in hundreds of cycles and adaptable sensitivity/detection range,outperforming most reported and commercial oxygen sensors.3.In addition to the construction of colorimetric sensors,new optical sensors also can be develpoed based on the electron storage mechanism of modified carbon nitride.Different from the electrode system of electrochemiluminescence（ECL）,a new luminescent mechanism driven by photoelectrons was developed based on the electrons-storing properties of the modified carbon nitride（CN-K）by replacing electricity with light.In order to facilitate the detection of targets and realize the recycling of CN-K,a CN-K film sensor was prepared by electrophoretic deposition.On the basis of luminescent quenching of the CN-K sensor by the oxygen produced by catalase（CAT）catalyzing the decomposition of hydrogen peroxide（H₂O₂）,a CN-K-based CAT luminescent sensor was constructed using CN-K film as the luminescent compound.Further combined with microfluidic technology for CAT analysis,the sensor shows good performance with high sensitivity,wide detection range,and recyclability,revealing great potential in luminescent sensing.