Morphology Control And Photocatalytic Performance Of Carbon Nitride Polymer Semiconductors

The photocatalytic water splitting by utilizing solar energy is regarded as a promising strategy to deal with the energy problem,but an obstacle is to develop a kind of suitable and high-effective photocatalyst.Graphitic carbon nitride?g-C3N4?has attracted researchers'interest because of its capability to harvest visible light to split water into hydrogen and oxygen.However,the photocatalytic capacity of traditional bulk g-C3N4 can be restrained by small specific surface area and high recombination ratio of photo-generated current carriers.Therefore,to develop a simple method to regulate the structure of g-C3N4 in order to improve its photocatalytic properties has become an important task.In this work,we focus on the morphology of g-C₃N₄ material for prompting its hydrogen evolution performance under visible light.The main research contents are shown as follows:1.Melamine has three equivalent amino groups in the structure.The existence of three amidogens makes melamine be easy to construct hydrogen bonds with many oxygen-containing groups to obtain a regular structure.During the formation of hydrogen bonding,the heteroatoms in the oxygen-containing group may be introduced into the whole structure,not only to obtain better morphology,but also to achieve the introduction of heteroatoms.Therefore,we choose melamine as the raw material,add different amounts of H₂SO₄ to control pH value of reaction system,hydrogen-bonded precursor was obtained through the hydrothermal process,and then S-doped g-C₃N₄ material with regular tubular structure was produced through the thermal polymerization process.The g-C3N4 material obtained by this method has a higher photoinduced electron-hole separation rate,which also improve its photocatalytic hydrogen production performance under visible light.2.Hydrogen-bonded organic frameworks?HOFs?as a kind of novel material with unique structures are generally used for gas separations.Herein,melamine can react with inorganic acid?such as H₂SO₄,HNO₃ and HCl?to form HOF-liked precursors with various morphologies.The framework structure can maintain main features and convert into porous nitrogen rich carbon nitride after proper calcination process.Besides,the“N-rich effect”is also investigated under the influence of different acid radical.The whole reaction procedure could enrich the nitrogen content in all final carbon nitride products compared with bulk CN,which can be ascribed to the formation tendency of high N ratio triazine rather than heptazine in general.This result indicates that the carbon nitrides from HOF contain more active sites?N-C3?and tune the band gap by decreasing energy level of conduction band.Moreover,heterogeneous sulfur doping derived from H₂SO₄ is another key factor to tune energy level structure.This method provides a feasible way to prepare the graphite carbon nitride materials with preeminent photocatalytic activity.3.The melamine solution was reacted with cysteine/cysteine hydrochloride to synthesis a rod-like prepolymer with needle-like hierarchical structure by hydrothermal process.And the modified carbon nitride can be obtained by calcining the prepolymer.According to SEM images,the final product has the similar structure with prepolymer,except the rod-like shape turns into tube with needle-like hierarchical structure.In addition,the element analysis and XPS test improved that sulfur was introduced into the structure of the final product in which S replaces the position of a part of N in the original structure to form S-C structure.The special morphology and heterogeneous elements doping promote the photo-generated electron-hole separation.The adjustment of carbon nitride material not only improves the performance of the material in the hydrogen evolution of visible light,but also enables the material to have good photocatalytic decomposition performance in the absence of sacrificial agent.