Optimization Of Preparation Conditions Of Graphitic Carbon Nitride And Establishment Of Efficient Coupled Photocatalytic System

Development and environment applications of graphite carbon nitride (g-C3N4) photocatalyst research were briefly summarized in this thesis. After that preparation conditions of g-C3N4photocatalysts were optimized in this research. The effects of preparation conditions on the photocatalytic activities and physico-chemical properties of g-C3N4were characterized systematically. The specific mechanisms of preparation conditions influencing photocatalytic activities of g-C3N4were investigated. A coupled light Fenton system consisted of g-C3N4and persulfate activated by Fe(III) for phenol degradation was proposed in this paper. The effects of different photocatalytic systems and external reaction environments on the photocatalytic degradation efficiency were evaluated systematically in order to investigate the mechanism of pollutants degradation. The main contents and conclusions of this research are as follows:1.12groups of g-C3N4samples were prepared under different calcination temperatures (450℃,500℃,550℃and600℃) and retention times (2h,4h and8h) by using melamine (C3H6N6) as the precursor. Preparation conditions of g-C3N4were optimized through the photocatalytic dye degradation experiments and the characterization of physico-chemical properties. The elemental composition, crystal structure, chemical structure, and band structure of g-C3N4were observed to vary slightly compared with non-optimized g-C3N4, while obvious changes in the surface morphology and texture properties of g-C3N4were found. Specifically, the morphology of g-C3N4was more ordered and tended to the accumulation of lamellar structure; the specific surface area (SSA) of g-C3N4increased from12.7m2/g to34.4m2/g. The photocatalytic activity of g-C3N4after optimization of preparation conditions in the degradation of rhB under visible light was more than100times of non-optimized g-C3N4, which was attributed to the increased SSA of the material and also the increased migration velocity of photogenerated electron-hole pairs.2. The phenol photocatalytic degradation ratio and the apparent kinetic constant of g-C3N4/Fe(III)/Persulfate system were16.5-and240-fold higher than those of individual g-C3N4system, meanwhile2.3-and2.7-fold higher than those of Fe(III)/Persulfate system, respectively. The results indicated the existence of the synergistic interaction between g-C3N4, Fe(III) and Persulfate, thus significantly enhancing the photocatalytic activity of the system. The enhanced phenol photocatalytic degradation process of g-C3N4/Fe(Ⅲ)/Persulfate system can be described by two promotions:production of active species (SO4-) by persulfate activation and establishment of light Fenton system by Fe(Ⅱ)/H2O2reaction. The study also found that g-C3N4/Fe(Ⅲ)/Persulfate system was scarcely influenced by external reaction environments (pH, ion concentration, and ultrasonic treatment), which broadens its applicability.