Constructing of 3D graphene aerogel-g-C3N4 metal-free heterojunctions with superior purification efficiency for organic dyes

Abstract

Porous semiconductor-based materials are promising for purifying wastewaters caused by organic dyes because of their superior adsorption capacity and photocatalytic activity. Herein, graphitic carbon nitride (g-C3N4) thin sheets are prepared by the thermal polymerization method by using ammonium chloride (NH4Cl). The NH4Cl dosage is optimized based on the corresponding photocatalytic efficiency for methylene blue (MB) purification and the optimal g-C3N4 is further construct with graphene aerogel (GA) by a hydrothermal strategy, resulting in the formation of a serious of porous GA-g-C3N4 heterojunctions. Among them, GA-g-C3N4(30%) possesses a hierarchical porous structure with much higher specific surface area (SBET = 161.0 m2 g−1) in comparison with the pristine g-C3N4 (SBET = 26.1 m2 g−1). The purification efficiency of GA-g-C3N4(30%) (5.0 mg) for MB solution (20.0 mg L−1, 25.0 mL) reaches 83.0% within 3 h under visible light irradiation. The combination of GA enhances the adsorption capacity for dye molecules and the separation efficiency of the photo-induced electron-hole pairs, thus promoting the photocatalytic efficiency of GA-g-C3N4(30%). Recycle experiments reveal that GA-g-C3N4(30%) still retains 94.3% of the initial purification efficiency after 3 cycles. In addition, GA-g-C3N4(30%) exhibits obvious removal efficiency for other organic dyes, such as rhodamine B (RhB), methyl violet (MV) and crystal violet (CV). A possible photocatalytic mechanism is offered based on the radical trapping experiments. This work provides an effective way to construct porous heterojunctions for the purification of organic wastewaters.