Studies On Synthesis, Characterization And Photocatalytic Properties Of Graphitic Carbon Nitride

Semiconductor photocatalytic technology could convert solar energy to chemical energyunder mild reaction condition, and degrade many organics completely, consequently, it has greatapplied potential in solar energy conversion and environmental pollution control. However,traditional TiO2-based inorganic semiconductor photocatalysts have some defects, such as poorsolar energy utilization, low quantum efficiency and easily deactivation. These seriously limit thelarge-scale application of photocatalytic technology. Therefore, to develop new photocatalystswith high efficiency and to broaden photoresponse range of the photocatalysts have becomechallenging topics in the environmental photocatalytic field.Graphitic carbon nitride （g-C₃N₄） has good chemical inertness, thermal stability andbio-compatibility, which are promising candidates to complement carbon in materialsapplications. The graphitic carbon nitride polymer is an organic semiconductor material,exhibiting a band gap of2.7eV, with an appropriate conduction band and valence band position,thus, it has great applied potential in photocatalytic field. In the present research, g-C₃N₄wasmodified by many ways to enhance its photocatalytic performance without destroying the basicchemical structures, including:（1） Bulk g-C₃N₄was firstly prepared by thermal polymerization,and then post-annealed in air and nitrogen atmosphere. The effect of annealing in the structure,optical properties and photocatalytic performance of g-C₃N₄was studies. The results show thatpost-annealing can effectively improve the photocatalytic activity for hydrogen evolution;（2）Ordered mesoporous structure of g-C₃N₄was prepared by using hard template. It was found thatits photoelectric property and photocatalytic efficiency for H2evolution was much better thanthat of the bulk sample;（3） Metal ions were introduced into g-C₃N₄structure and the applicationof metal containing carbon nitride in photocatalytic organic synthesis were studied. The resultsshow that the modification of g-C₃N₄by metal irons not only improves the electronic structureand optical properties of carbon nitride, but also achieves the activation of hydrogen peroxideand molecular oxygen under mild conditions by simulating bio-oxidation enzyme via the groupsand catalytic functional. The modified samples show high catalytic activity and selectivity inboth direct oxidation of benzene to phenol and styrene epoxidation;（4） Metal containing carbonnitride was loaded on the SBA-15by the impregnation-chemical modification method andnanostructured materials with large surface area were obtained. The photocatalytic/catalyticactivities were evaluated by oxidation of benzene to phenol. The results show that the well-dispersed Fe-modified nanomaterials exhibited excellent catalytic activity in the oxidationof benzene,2.7times higher than that of bulk materials;（5） Mesoporous g-C₃N₄was prepared byhard template method, and then coupled with inorganic semiconductor CdS by solvethermalprocess. It was found that the CdS/mpg-C₃N₄composites exhibited excellent photocatalyticactivity in both decomposition of organic pollution and water splitting for H2.The original results of this study are as follows:（1） Bulk g-C₃N₄was firstly treated bypostcalcination, and the photocatalytic activity of g-C₃N₄was enhanced from the optimization ofthe preparation procedure;（2） Ordered mesoporous g-C₃N₄was successfully prepared by hardtemplate method with SBA-15as template. The photoelectric property and photocatalyticactivity for H2evolution of the mesoporous g-C₃N₄were fully studied;（3） Metal ions weresuccessfully introduced into g-C₃N₄matrix by a simple soft-chemical method. The novel metalcontaining carbon nitride materials were firstly applied in photocatalytic organic systhesis;（4）Metal containing carbon nitride compounds were firstly loaded on the SBA-15, andwell-dispersed M-g-C₃N₄/SBA-15composites were obtained. It was found that theFe-g-C₃N₄/SBA-15nanomaterials exhibited higher catalytic activity for the oxidation of benzenethan bulk materials;（5） The mesoprous g-C₃N₄were coupled with CdS with solvothermaltreatment, the photocatalytic performance in decomposition of organic pollution and watersplitting for H2of g-C₃N₄were enhanced from optimization of texture structure and adjustmentof band structure.