Electrochemiluminescence Behavior Of Graphitic Carbon Nitride

ECL features the advantages of superior sensitivity of CL methods,on-line and controllability of electrochemistry method.As an ECL emitter,graphite carbon nitride（CN）has drawn much attention in analytical chemistry and the development of biosensors.Owing to its appealing properties such as simple preparation,cheap raw materials,physical chemical and thermal stability,facile functionalization,modulable band gap and unique photoelectrochemical features,CN is considered to probably replace the traditional ECL emitter Ru（bpy）₃²⁺.However,pristine CN suffer from poor dispersibility,relative weak and unstable signals,which hinder the further development of CN in ECL field.Unfortunately,CN-based nanocomposites have complicated preparation process with low reproducibility and unsatisfied ECL amplification.This problems encountered by CN inspires us to explore some effective and simple strategies to improve ECL performances of CN and further expand its applications in ECL.In this work,we adopted the regulation of CN molecular structure and the adjustment of Au oxidation state to improve the ECL signals and stability,as well as tunable ECL wavelength,which providing a theoretical basis for the construction of ECL high-performance CN nanomaterials and the design of CN-based sensors..In addition,the characterization method of oxygen vacancy in layered double hydroxides（LDHs）was developed based on as-prepared high-performance CN.1.Nitrogen vacancy engineering in graphitic carbon nitride for strong,stable,and wavelength tunable electrochemiluminescence emissions.In this work,a simple nitrogen vacancy（NV）engineering strategy has been developed for the improvement of ECL performances.CNs with tunable nitrogen vacancy（NV）contents（CN-NVs）were fabricated by thermal treatment of pristine CN at different temperatures in a N₂atmosphere.In comparison to pristine CN,the ECL intensity and stability were obviously improved in CN-NVs.Especially for CN-NV-550 sample,ca.60 times amplification in ECL intensity,more stable ECL emission（RSD=0.53%for 10 continuous scan）and 70 times enhancement in ECL efficiency were obtained.The NVs on CN-NVs can not only facilitate electron transfer,speed up the electro-reduction of CN and S₂O₈^2-,but also serve as the electron trap to buffer excess electron.Compared with the PL spectra of CN-NVs samples,the ECL wavelength were red-shifted,indicating the formation of new surface state originated from the introduction of NV.More interestingly,a series of CN-NVs exhibited a different ECL wavelength range from 470 to 516 nm dependent on NV contents.This work may open up a new way for improving the ECL performances of CN,and also create new possibilities for the construction of color tunable ECL light-emitting devices and simultaneous detection of multiple targets.2.Investigations on the improvement of CN ECL properties by Au oxidation state regulation.The different d-band structure of metal single-atom will produce different oxidation states,which may change the adsorption of reaction intermediates to the catalyst and affect its catalytic activity.Therefore,the oxidation states of Au were modulated by the different electronic metal-support interaction（EMSI）between Au single-atoms,Au nanoparticles（Au NPs）and CN,and the effect of Au oxidation states on CN ECL performances were investigated.In comparison with pristine CN and CN nanosheets supported Au nanoparticles（Au NPs/CN）,stronger and more stable ECL intensity of CN nanosheets supported Au single-atoms（Au^S/CN）was obtained.The ECL signal of Au^S/CN was about 32.2 times that of the original CN,and 2.8 times that of Au NPs/CN in the same Au loading content（0.8%）.Detailed mechanism revealed that Au^S/CN with higher Au oxidation state has better conductivity and stronger catalytic activity,which promotes the electric reduction of CN and S₂O₈^2-.The synergistic effect of Au single atom and CN can increase the lifetime of the excited state CN*,and significantly improve the ECL performance of CN.In this work as-obtained Au^S/CN nanocomposite has a simple preparation process and high atomic efficiency,providing a promising ECL emitter for high sensitivity analysis of ECL.The essence of EMSI for the improvement of CN ECL performances was the increased of oxidation state of Au and the synergistic effect of Au and CN.In addition,this work provides a detailed understanding of the essence of EMSI for the ECL intensity amplification,and established a feasible method for the improvement of ECL capacities of nanocomposites.3.Electrochemiluminescence identification of oxygen vacancies in layered double hydroxides.The ECL properties of nanomaterial are closely related to their surface defects,such as surface vacancies,surface charges and surface ligands.This feature of nanomaterial ECL makes it has an application potential in the rapid detection of surface defects in nanomaterials.Here,we developed a novel ECL platform to screen oxygen vacancies in layered double hydroxides（LDHs）.Based on NV-riched CN/Mg Al-LDH（CN/LDH）nanocomposites,the ECL mechanism of CN/LDH nanocomposites and the effect of oxygen vacancies were investigated.Oxygen vacancy in LDHs can promote charge injection and transfer process in CN/LDH nanocomposites ECL reaction,improve the electrochemical activity of LDHs,and promote the synergy effect of free radicals.In the range of 29.8～40.3%,the ECL intensities of CN/LDH nanocomposites were proportional to the content of oxygen vacancies in LDHs.Therefore,an ECL platform was established to detect the oxygen vacancy content of LDHs.The ECL platform has promising applications in the rational design and performance optimization of LDHs.In addition,due to the simple and rapid preparation method of the nanocomposites probe,the ECL platform can not only characterizate oxygen vacancies in LDHs,but also has a potential application for the rapid identification of vacancies in other two-dimensional nanomaterials.