The Strcuture Control Of G-C₃N₄ For Photocatalytic Hydrogen Evolution

Graphitic carbon nitride（g-C₃N₄）has attracted persistent attention in the field of photocatalysis due to its non-metallic and non-polluting properties.The disadvantages of bulk g-C₃N₄ such as low surface area,wide bandgap,high composition rate of photocarriers and low catalytic efficiency limit its further development in the field of energy and enviro nment.To solve those problems,we prepared nanosheet g-C₃N₄ with cavity defects by using the template-free and hard template methods.Carbon self-doping g-C₃N₄was also prepared using glucose as carbon source to demonstrate the change of bond-structure of g-C₃N₄.Samples were analyzed and characterized by X-ray diffraction（XRD）,transmission electron microscope（TEM）,X-ray photoelectron spectroscopy（XPS）,uv-vis diffuse reflection spectroscopy（UV-vis）,photoluminescence spectroscopy（PL）,photocurrent（i-t）,Brunauer-Emmett-Teller（BET）and photocatalytic hydrogen evolution（PHE）.The specific contents are as follows:1.Urea used as precursor was heated at 550℃and the increase of pyrolysis time changed not only the g-C₃N₄ morphology,also its atomic componention,resulting in the increase of specific surface area from 40.22 to 117.27 m²g^–1.Bulk g-C₃N₄was peeled with inner hole on the surface and the pore diameterwas changed from 3.99 to 2.77 nm during the pyrolysis process.Continuing increase of heating treatment time causedthe destruction of g-C₃N₄,promoting the thermal decomposition reaction at the same time.When heating treatment time arrives 9hours,the highest photocatalytic hydrogen evolution was achieved in both visible and ultraviolet light radiation.Comparing with the sample of pyrolysis time 3 hours,the catalytic performance of 9 hourssample was increased by 1.77 times and 1.99 times respectively.2.With glucose as the carbon source,C self-doping g-C₃N₄（Gg-C₃N₄）was achieved,causing the change of bond structure and the frame structure of Gg-C₃N₄.XPS analysis showed that doping increased the pyridine nitrogen and decreased the graphite nitrogen.The electrons were more lively and easy to inspire for the present of delocalizedπ-bond.UV-vis showed that the introduction of carbon changed the bond-structure,decreased the width of bandgap,broadened the absorption edge,suppressed the combination of eletron-hole pairs,especially enhanced the photocatalytic hydrogen evolution performance.When the amount of doping reaching 3mg,photocatalytic hydrogen evolution reached 2800μmolg^-1h^-1.Comparing with pure g-C₃N_4,the performance increased 3.4 times.3.Using hydrochloric acid treatment of kaolin as a hard template and urea as precursor,g-C₃N₄ with cavity defects was achieved.we report that promoting interfacial oxidation ability of graphitic carbon nitride（g-C₃N₄）by introducing cavity defects can effectively improve photocatalytic hydrogen evolution（PHE）activity.The g-C₃N₄ with cavity defects was fabricated by constraining growth of g-C₃N₄ on porous kaolinite-derived template.These cavity interfaces exhibited higher electrocatalytic activity for oxidation process in comparison with reduction process.This feature benefits electron-transfer reaction to quench photo-excited holes during photocatalysis and promote photoelectrons reaction.The results showed that PHE rate reaches1917μmolg^-1h^-1,2.37 times of non-cavity g-C₃N₄.