Dear Weaam Hakami, numerous documents are available via google. If you need specific thing please don't hesitate to tell. My Regards

doi:10.3762/bjoc.14.153

https://www.researchgate.net/publication/216491213_Simple_Pyrolysis_of_Urea_into_Graphitic_Carbon_Nitride_with_Recyclable_Adsorption_and_Photocatalytic_Activity

https://doi.org/10.1021/acs.iecr.6b00041

https://doi.org/10.1021/acssuschemeng.5b01139

g-C3N4 samples were synthesized by heating 10 g of urea in air at a ramp rate of 2.3 K min−1 to a given temperature (773–923 K), keeping that temperature for 4 h, then cooling without temperature control.

Dear Weaam Hakami, I used the same method described by Elsayed T. Helmy, but at 450 oC. By changing the holding time you can tune the size of the g-C3N4 platelets. The main thing that should be mentioned - that the reaction should be performed in a closed vessel - in the air, but the crucible should be covered with some plate or a special cover. The reaction is specific - it supports the self-propagating atmosphere, and as a result, it is not necessary to use inert one. But avoid to open the reaction vessel and the furnace until the end of the reaction - the product may just burn out.

Kind regards.