Removal of Methylene Blue Dye Using Metal-Free g-C<sub>3</sub>N<sub>4</sub> Photocatalyst over Natural Sunlight Irradiation

Abstract

This work presented the high activity of metal-free g-C3N4 photocatalyst for methylene blue (MB) removing over natural sunlight irradiation. These g-C3N4 photocatalysts materials were synthesized by a conventional thermal condensation method using melamine as a precursor under treated at the various annealing temperatures (450 °C, 500 °C, 550 °C, 600 °C and 650 °C). All as-synthesized samples were characterized and confirmed by a several techniques, such as, X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectrometer (DRS), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) specific surface area. XRD and FTIR results confirmed that the as-synthesized g-C3N4 samples were completely synthesized at annealing temperature of 500 °C. SEM images showed the morphologies of the g-C3N4 samples had more flake-like structures upon the increasing of annealing temperatures. While DRS results indicated that the absorption edges of as-synthesized g-C3N4 samples were shifted to visible-light region, except the sample as-synthesized at 650 °C (g-C3N4-650 °C). Moreover, the photocatalytic properties of metal-free g-C3N4 photocatalyst materials were evaluated by degrading of MB dye solution under natural sunlight irradiation for 100 min. The results revealed that the highest photocatalytic activity was exhibited by the sample synthesized at 600 °C, which the apparent rate constant (kapp.) was 0.0291 min-1. The orders of activities as: g-C3N4-600 °C > g-C3N4-650 °C > g-C3N4-550 °C > g-C3N4-500 °C > g-C3N4-450 °C. Hence, the metal-free g-C3N4 photocatalyst appears to be an attractive-material for water or wastewater purification applications over activated by sunlight irradiation.