Preparation Of Graphite-Phase Carbon Nitride-Based Materials And Their Enhanced Catalytic Performance For HCHO Oxidation

Formaldehyde（HCHO）is regarded to be a major toxic indoor polltutant,which directly impacts on the human henlth.Thus,the removal of HCHO from indoor air is important for human health.Graphitic carbon nitride（g-C₃N₄）has been widely used in catalytic degradation of poisonous pollutans,H₂O splitting,and CO₂or heavy metal ions reduction.As for the disavantages of g-C₃N₄such as the low specific surface arer,high recombination of photo-generated carriers and low catalytic performance,some strategies were used to promote the catalytic performance of g-C₃N₄by adjusting microstructure,dopping metal element and constructing heterojunction structures.In this work,g-C₃N₄-based materials such as the water-solubility g-C₃N₄,strong base g-C₃N₄and g-C₃N₄@CeO₂,showing an enhanced catalytic oxidation performance for HCHO assisted by fluorescent lamp irradiation,were prepared via template method,low temperature polymerization menthod and electrostaltic self-assembly method,respectively.The microstructure,optical properties and catalytic performance of WCN-NS,Na/K-CN-NS and g-C₃N₄@CeO₂at room temperature were studied and the possible mechanism of HCHO decomposition over the g-C₃N₄-based materials were preliminarily explored.The main research contents and results of this work are as follows:（1）Preparation of water-solubility graphite-phase carbon nitride（WCN-NS）and its catalytic oxidation performance of HCHO at room temperatureUsing sodium chloride and potassium chloride as modifiers and dicyandiamide as precursors,the water-soluble g-C₃N₄（WCN-NS）was prepared via calcination-ultrasonic and removal of template process.The effect of the presence of the template on the catalytic oxidation performance of graphite-phase carbon nitride（g-C₃N₄）at room tempareture was investigated.The results showed that the catalytic degradation performance of formaldehyde over graphite-phase carbon nitride（g-C₃N₄）was significantly improved by fluorescent lamp irradaition after the catalyst was synthesized via the process of soft template calcination,liquid phase ultrasonic stripping and water washing to remove template.（2）Preparation of strong based graphite-phase carbon nitride（K/Na-CN-NS）and the catalytic oxidation performance of HCHO at room temperatureUsing sodium nitrate and potassium nitrate as strong base additives and dicyandiamide asprecursors,respectively,K/Na co-doped g-C₃N₄（K/Na-CN-NS）regarded as strong based graphite-phase carbon nitride were prepared by low thermal polymerization and liquid phase ultrasonic stripping method.Exfoliation results showed that graphite-phase carbon nitride with the molar ratio of 8:1:1 of strong base additives and asprecursors and thermal polymerization temperature at 400℃showed the best catalytic oxidation performance of HCHO at room temperature under fluorescent lamp irradiation.The effects of alkali metal doping on g-C₃N₄structure,morphology,specific surface area,physical and chemical properties of material surface and photocatalytic properties were also investigated.The results showed that the formation of Na-C,K-C and K-N bonds further improved theπconjugate structure of the g-C₃N₄and increased the basicity of the surface.The optimized structure and separation and rapid transfer of photogenerated electrons/holes improves the catalytic activity of g-C₃N₄towards HCHO removal.（3）The Construction of g-C₃N₄@CeO₂ heterojunction and its catalytic oxidation performance of HCHOThe g-C₃N₄@CeO₂ composites were prepared by electrostatic self-assembly.XRS、XPS、TEM、FTIR and UV-vis DRS were used to characterize the catalyst.The effects of precursors and g-C₃N₄content on the catalytic performance of the composites were investigated.The results showed that the heterojunction structure was formed on the interface of CeO₂and g-C₃N₄,which significantly improved its catalytic degradation of HCHO.The as-prepared composite with the mass ratio of 4:1 for CeO₂@g-C₃N₄exhibited the best catalytic performance.Moreover,the fluorescent lamp irradiation could boost the catalytic oxidation performance of HCHO at ambient temperature mainly attributed to the fast separation of the photocarriers over the heterogeneous structure between CeO₂and g-C₃N₄.