Studies On Synthesis And Photocatalytic Properties Of Carbon-nitrogen Material

Semiconductor photocatalysis technology has attracted much attention in the field of environmental purification because of its advantages of energy-saving,clean and non-toxic to the environment.Carbon-nitrogen materials,only consists of C and N elements,which are abundant in the earth’s reserves,have attracted much attention because of their unique semiconductor properties.At present,nitrogen-doped carbon materials mainly have the problem of low nitrogen content,which affect their catalytic efficiency,and among the carbon-nitrogen materials,the typical g-C₃N₄materials have the problems of high photogenerated carrier recombination and narrow visible light response range,so the low catalytic quantum efficiency greatly limits the application of carbon-nitrogen materials.These problems limit the large-scale application of carbon-nitrogen materials.To solve these problems,the nitrogen-doped carbon materials with high nitrogen content were synthesized by direct pyrolysis of nitrogen-rich heterocyclic compounds.Meanwhile,lamellar porous g-C₃N₄ material were synthesized by molecular self-assembly mechanism.The characterization of morphology,crystal structure and photocatalytic degradation of methylene blue dye（MB）show that the nitrogen-doped carbon materials and lamellar porous g-C₃N₄materials possess high photocatalytic activity.The main achievements of this paper are as follows:（1）For the first time,benzotriazole,a nitrogen-rich heterocyclic compound,was selected as the precursor to synthesize nitrogen-doped carbon materials with high nitrogen content by direct pyrolysis,and this synthesis method has the advantages of novel precursor selection,simple operation,short time-consuming and low cost.The results show that at higher pyrolysis temperature,the nitrogen element in the precursor has stronger impact on the material when it escapes in the form of nitrogen,which promotes the morphology of the materials to change from bulk to fragment.The fragment morphology of the materials provides a large number of active sites for the photocatalytic degradation reaction.Meanwhile,high nitrogen content can provides a large number of oxygen reduction active sites for the materials,resulting in a large number of hydroxyl radical（·OH）active substances with strong oxidation.Under the synergistic effect of these factors,nitrogen-doped carbon materials synthetized at 550℃pyrolysis temperature possess high photocatalytic degradation activity.（2）Lamellar porous g-C₃N₄ with high visible light photocatalytic activity were designed and fabricated by NaOH solution-assisted supramolecular self-assembly method.The results show that,comparing to bulk g-C₃N₄,the synthesized lamellar porous g-C₃N₄ possess smaller interlayer spacing and band gap.Meanwhile,the adsorption performance of methylene blue dye molecules was improved obviously because of the larger pore capacity of the synthesized porous g-C₃N₄.The nitrogen defect and cyanogen group introduced in the synthesis process not only broaden the optical absorption range of the lamellar porous g-C₃N₄ materials,but also promote the rapid separation of photogenerated carriers.The unique lamellar porous structure also provides large number of active sites for the photocatalytic degradation reaction.Under the synergistic effect of these factors,the materials exhibit excellent visible photocatalytic degradation performance,moreover,the cyclic degradation experiment shows the good stability of lamellar porous g-C₃N₄ materials.