Synthesis strategies to prepare ideal g-C3N4 have been summarized in 2008 [36]. PVD, CVD, solvothermal method, solid state reaction and thermal nitridation have been employed in the previous reports. However, strict conditions were required in the above protocols. Thermal condensation, a facile new method among the above strategies, is employed for preparation. The precursors of the reaction normally adopt nitrogen-rich species, especially melamine [37], [38], [39], [40] and [41], which will undergo self-condensation with deammonation process via thermal reaction. Thermogravimetric-differential scanning calorimetry analysis (TG-DSC) done by Yan et al. (shown in Fig. 2[13]) demonstrated that melamine sublimates and condenses at 297–390 °C, the following deammonation process and decomposition of material will occur at higher temperature about 545–630 °C. Intermediate products including melam 8, melem 4e, and melon 9 will generate during the thermal condesation. A postulated thermal condensation of melamine 1a is shown in Fig. 3[37]. Though melam form during the deammonation process of melamine, it is just as one intermediate products and will finally transform into melem which have superior thermodynamic stability to exist in higher
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