Study On The Structure And Photoluminescence Properties Of Graphitic Carbon Nitride

In this thesis,we prepared graphitic carbon nitride(g-CN)materials through a two-step thermalcondensation process,and characterized their degree of polycondensation(DP),structure,chemical bonding properties and morphologies,revealing the correlation between the DP and structure of the synthesized g-CN and the experimental conditions.We further investigated the photoluminescence(PL)properties of the g-CN samples and the corresponding mechanism of PL emission,illustrated the effect of structure evolution of g-CN on its PL properties.We chose heptazine as the basic unit,calculated the relationship between the condensate's composition and its DP based on the linear and planar condensation pathways,respectively.The results showed that,for linear condensation the N/C molar ratio of the condensate tended to be 1.5 and its H content tended to be 16.67 at.%.While the planar condensation ultimately formed g-C3N4,its N/C molar ratio tended to be 4/3 with the H content dropping to 0.As far as the linear condensation to be concerned,the condensate's composition started to be nearly stable when DP is higher than 50.Under different heating temperatures,we prepared a series of g-CN samples through long-time thermalcondensation,and characterized their compositions,structures and chemical bonding properties.The experiment results suggested the average DP of the samples was gradually improved as the heating temperature rose.Under lower heating temperatures,the products contained mixed multiple primary condesates with a poor structural order.When the pyrolysis temperature reached 600 ?,the as-prepared sample had a high average DP,linear and planar condensates were found to be coexisted,leading to the minimum value of N/C molar ratio.When the heating temperature rose further,the g-CN sample was mainly composed of linear condensates,the molecule chains were paralelly arranged and tightly linked by hydrogen bonds to form a stable layer structure;finally an orthorhombic crystal structure was obtained through the ABAB stacking.We discussed the PL spectrum of a typical g-CN sample,explained the corresponding PL emission mechanism and further investigated the effect of the product's structure on its PL emission properties.The results revealed that,for short-time thermalcondensation,the PL emission of g-CN samples showed a red shift as increasing the pyrolysis temperature.Similar red shit of the PL emission was also observed when prolonging the heating time under lower pyrolysis temperatures.When heating temperature was high and the thermalcondenation time was long enough,however,the PL emission of the obtained g-CN samples showed a blue shift.The mechanisms responsible for the observed red and blue shifts of the PL emission were clearly explained.