Novel design of porous hollow hydroxyapatite microspheres decorated by reduced graphene oxides with superior photocatalytic performance for tetracycline removal

Photocatalysis is a well-established and green technology with cost-effective, high-performance and environment benign for tetracycline (TC) removal in wastewater. Recently, HAp-based materials have been proved to be cheap and green photocatalysts for wastewater pollutant treatment. However, the photocatalytic removal efficiency of these existing HAp-based materials is still not desirable. Herein, a series of new porous hollow hydroxyapatite microspheres decorated with small amounts of reduced graphene oxides (0.5, 1.5 and 3 wt%) were firstly and successfully fabricated by a facile hydrothermal method. The as-prepared RGO/HAp composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), Brunauer Emmett-Teller (BET) and photoelectrochemical measurements. Furthermore, their photocatalytic applications were investigated by using TC as a model contaminant. It turned out that the as-prepared RGO (1.5 wt%)/HAp composite exhibits an outstanding photocatalytic activity for TC degradation (60 mg/L) under a 300 W xenon lamp with full spectrum irradiation (92.1%, 30 min). Note that its adsorption efficiency for TC in dark period was only 7.9% after 30 min. Thus, the total removal efficiency for TC was nearly 100%. Furthermore, the as-prepared RGO (1.5 wt%)/HAp exhibited remarkable stability and repeatability, demonstrating its promising potential as an efficient photocatalyst. A plausible photocatalytic reaction mechanism was proposed on the basis of electron spin resonance (ESR) and trapping experiments. This fundamental research will provide a promising strategy for developing highly efficient and compatible photocatalysts with wide applications.