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

Abstract

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 morphologycal 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. While 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=0.0090 min-1), while the bulk g-C3N4-0 showed the lowest rate (k=0.0068 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.