Synthesis of Carbon Nitride Polymorphs by Sacrificial Template Method: Correlation between Physicochemical Properties and Photocatalytic Performance

Carbon nitride compounds (CNCs) in the form of graphitic carbon nitride (g-C₃N₄) and poly(heptazine imide) were synthesized using different metal chloride salts (MCl_x), i. e., NaCl, KCl and CaCl₂, as sacrificial templates and by varying the MCl_x to melamine molar ratios. A systematic study of their photocatalytic activity for H₂ production in relation to the physicochemical, morphological, and optical properties was carried out. Each sample was tested achieving the highest hydrogen evolution rates of about 7660 μmol g^-1 h^-1, 5380 μmol g^-1 h^-1 and 3140 μmol g^-1 h^-1 using CaCl₂, KCl, and NaCl, respectively. This work demonstrates how the synthesis of CNCs with different MCl_x leads to the production of high-performance photocatalysts due to a combination of factors as the formation of vacancies or cyano groups, a shift in the optical threshold and tuning of micro(nano)structure. The results demonstrate that, when CaCl₂ is used as a sacrificial template, porous and exfoliated g-C₃N₄ nanosheets are formed leading to hydrogen productions which outperform most of the previously reported g-C₃N₄ prepared using a single synthetic step.