Photocatalytic activity under visible light illumination of organic dyes over g-C<inf>3</inf>N<inf>4</inf>/MgAl<inf>2</inf>O<inf>4</inf> nanocomposite

Abstract

Using a grinding method, nanocomposites of graphitic carbon nitride (g-C3N4) and magnesium aluminate (MgAl2O4) spinel were successfully synthesized for the photocatalytic degradation of methylene blue (MB) and methyl orange (MO). Variously formulated g-C3N4/MgAl2O4 nanocomposites were characterized by thermal gravimetric analysis (TGA), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy equipped with energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM) and surface area and micropore analysis (BET surface area). The g-C3N4 powder exhibited a nanosheet structure whereas the MgAl2O4 spinel comprised agglomerated nanoparticles. The optical properties of the g-C3N4/MgAl2O4 nanocomposites were investigated by diffuse reflectance spectroscopy (DRS). As the g-C3N4 loading content increased from 0 to 30%, the optical band gap energy of the nanocomposite decreased from 3.84 to 2.86 eV, the specific surface area decreased from 153.78 to 114.45 m2/g, and the porosity decreased from 0.447 to 0.347 cm3/g. A 20%g-C3N4/MgAl2O4 nanocomposite proved to be the most effective photocatalyst and degraded MB faster and more completely than MO. The degradation rates of both MO (0.0107 min−1) and MB (0.0386 min−1) in a mixed MO-MB system were greater than the degradation rates in their single systems. The key factor that improved the photocatalytic degradation of MO was the synergistic effect whereas the synergistic effect and photosensitization were the key factors that enhanced the photocatalytic degradation of MB. The g-C3N4/MgAl2O4 nanocomposite is suitable for the photocatalytic degradation of mixed dyes because its point of zero charge is neutral and it is stable and recyclable.