Dimolecular Interaction And Adsorption Process Between Graphitic Carbon Nitride Nanosheets And Phenols

Graphitic carbon nitride （g-C₃N₄） is a popular semiconductor material with non-metallic composition, which has simple preparation methods, abundant raw materials, active structure and special properties. The addition of environmental friendliness and biocompatibility allow g-C₃N₄ to directly use in sustainable chemistry. Recently, researchers have developed preparation and the modification methods of g-C₃N₄ which make it play more excellent performances in energy, environment, medicine etc. In these applications, g-C₃N₄, as support, carrier or electron donor can interact with water, heavy metal cations, electron-deficient organic matters to participate reactions. Intermolecular interactions exist widely in molecular reactions in nature which is one of the driving forces of the molecular reaction and stabilizing force of special structures. Molecular interaction is an important scientific concept in supramolecular chemistry which is much weaker than chemical bond, but non-negligible especially when they cooperate with each other. Many indirect techniques have been used to research intermolecular interaction, such as spectroscopy method, electrochemistry to get the informations such as binding constant, and interaction site, force types. Phenolic compounds are important chemical materials but pollutants if were misapplied and here were chosen as guest molecules. It is useful to study the detection and degradation of phenols. The benzene ring, hydroxyl and different substituent may be the potential active groups of interaction.This dissertation provided new aspects of scientific interest in g-C₃N₄ and provided an example to understand the mechanism and process of the dimolecular interaction of g-C₃N₄ with other guest molecules which was helpful for other researchers in this field. The kinetic and thermodynamic datas attained by fluorescence spectroscopy, UV-vis absorption spectroscopy and molecular simulation helped reveal the interaction process and mechanism between g-C₃N₄ and phenols. Also, adsorption degradation of picric acid by two dimensional g-C₃N₄ nanosheets was studied. Finally, the natural reasons for these behaviors were explained from the molecular structure and electronic property of g-C₃N₄.1. Dimolecular interaction between graphitic carbon nitride nanosheets and phenols:A mechanism studyGraphitic carbon nitride （g-C₃N₄） has been applied extensively in many fields, where there often shows synergistic intermolecular interaction to promote reaction process. In chapter 2, the dimolecular interactions between g-CaN4 and phenols （picric acid （PA）, pentachlorophenol （PCP）, phenol （PhOH）） were examined by photoluminescence quenching of g-C₃N₄. The spectroscopy analysis, thermomechanical analysis combined with theoretical simulation helped to reveal mechanism. UV-vis absorption spectroscopy indicated that the interaction mechanism was charge-transfer. The fluorescence quenching constants calculated from Stern-Volmer equation showed weak binding complexes between g-C₃N₄ and phenols were formed. The interaction affinity decreased in the order of PA> PCP> PhOH. The enthalpy change （AH） and entropy change （AS） calculated from Van’t Hoff equation showed that electrostatic interaction was the essential force in stabilizing g-C₃N₄-PA, while hydrogen bond was the essential force in stabilizing g-C₃N₄-PCP and g-C₃N₄-PhOH. Theoretical simulation showed that the-N-residue or the cavity of g-C₃N₄ was the preferential active sites. It is the auto-doped N atom in g-C₃N₄ nanosheets that lead to region charge polarization and introduce active sites for adsorption of molecules.2. Adsorption thermodynamics and dynamics of PA onto g-C₃N₄ nanosheetsThe g-C₃N₄ has no secondary pollution to environment and has the potential to adsorb electron-defient organic pollutant as a kind of Lewis base. Ultrasonic exfoliation made the surface area of g-C₃N₄ nanosheets increased from 22 m2/g to 70 m2/g. The adsorption thermodynamics, dynamics, model and mechanism of PA onto nanosheets were sdudied in this chapter. Experimental adsorption showed that g-C₃N₄ can selectively remove PA and dinitrophenol from aqueous solution.The maximum adsorption capacity of PA was 224 mmol/kg （50 mg/g）. Physical and chemical interaction played roles in the whole adsorption. Acidic conditions and heating promoted the adsorption.The dynamic experiment showed that the pseudo-sencond order kinetic model can well describe the PA asdsoption onto g-C₃N₄ nanosheets. The adsorption rate constant increased with increasing tempreture and calculative Ea was 39.26 kJ/mol. The thermodynamic experiment showed that the PA asdsoption was spontaneous, endothermic and entropy driven. Both Langmuir （R2=0.98） and Freundlich （R2=0.95） model can well describe the asdsoption process. According to the actual situation, Freundlich model was better and the adsorption-resolution constant increased with the rising temperature which further indicanted that there was chemisorption.The more electron-defient nitrocompound had a larger adsorbing capacity by g-C₃N₄ nanosheets.Weber-Morris diffusion model indicated that the adsorption of PA onto g-C₃N₄ was affected by film diffusion in 1 h and intrapatical diffusion after 1 h.