Effect of porous modification on the synthesis and photocatalytic activity of graphitic carbon nitride/carbon quantum dot nanocomposite

Abstract

Metal-free graphitic carbon nitride (g-C3N4) and carbon quantum dots (CQDs) have a promising attention as to their superior photocatalytic activities and physicochemical properties. In the article, g-C3N4 and CQDs were connected effectively through porous modification of g-C3N4 by directly heating melamine hydrochlorid, which benefits to the enhancement of the composites’ photocatalytic activity. The structures and morphologies of the photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption–desorption, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectrum and photoluminescence spectroscopy. Meanwhile, the porous g-C3N4 and CQDs composite (pg-C3N4/CQDs) exhibited the improved photocatalytic activity for the degradation of RhB under visible light irradiation, which may be contributed three reasons: (1) pg-C3N4 has much higher surface area (~ 20 times) and more stronger photocatalytic oxidation capacity than that of g-C3N4; (2) as the electron-sinks, CQDs can improve the photogenerated electron–hole pair’s separation; (3) CQDs can upconvert the light with wavelengths longer than 650 nm into the shorter wavelengths to increase light harvesting, while pg-C3N4 utilizes the light to degrade pollutants. In addition, the possible photocatalytic degraded mechanism was investigated in detail. This work will be useful for designing other CQDs-based photocatalysts and providing a promising approach to environmental purification.