Synthesis of Porous g-C₃N₄ and Its Application as Photocatalyst for Methylene Blue Degradation

Graphitic carbon nitride (g-C₃N₄) is a photocatalyst possessing a unique layered structure, remarkable thermal and chemical stability, and tunable bandgap. However, the bulk g-C₃N₄ has limited active sites and fast electron-holes recombination. In this work, we prepared porous g-C₃N₄ with an enhanced photoactivity toward methylene blue (MB) degradation. The porous g-C₃N₄ were prepared from melamine with addition of various amount of citric acid as a pore-forming agent (0.0 mmole, 0.1 mmole, 0.2 mmole, and 0.3 mmole; assigned as g-C₃N₄-0, g-C₃N₄-1, g-C₃N₄-2, and g-C₃N₄-3, respectively). The structural and morphological properties of the samples were analyzed using XRD, SEM, FTIR, and N₂ sorption. The optical property was analyzed using UV-vis diffuse reflectance and photoluminesence spectroscopy. Meanwhile the electronic conductivity was analyzed using Mott-Schottky analysis and electron impedance spectroscopy (EIS). The photocatalytic test revealed that g-C₃N₄-2 exhibited the highest MB degradation rate (k= 0.00904 min^-1), while the bulk g-C₃N₄-0 showed the lowest rate (k= 0.00689 min^-1). The g-C₃N₄-2 possesed relatively smaller crystallite size (~43.5 nm) and a larger surface area (13.975 m² g^-1) compared to the bulk g-C₃N₄-0 (crystallite size: 46.9 nm; surface area: 9.163 m² g^-1). The optical property and charge carrier transfer analysis also revealed that the g-C₃N₄-2 possessed more efficient charge carrier transfer, which suppress the charge recombination. The combination between a larger surface area and more efficient charge carrier transfer contributes to the enhanced photocatalytic activity of porous g-C₃N₄ toward MB degradation.