A novel graphene oxide decorated with halloysite nanotubes (HNTs/GO) composite used for the removal of levofloxacin and ciprofloxacin in a wide pH range

Abstract

Halloysite nanotubes have been recognized as an effective and environmentally friendly adsorbent for organic compounds. A novel adsorbent was synthesized by immobilizing graphene oxide with halloysite nanotubes (HNTs/GO). HNTs/GO was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscope, and X-ray photoelectron spectroscopy, and was used to remove levofloxacin (LEV) and ciprofloxacin (CIP) from solution. Several factors affecting the adsorption of LEV and CIP were investigated, such as pH, the amount of HNTs/GO, the shaking time, temperature and initial concentration. HNTs/GO could be used for the adsorption of LEV (pH 1–9) and CIP (pH 2–10) in a wide pH range. Pseudo-second-order kinetics, intraparticle diffusion model and the Langmuir model fitted the adsorption process well. The maximum adsorption capacity of LEV and CIP on HNTs/GO reached 264 and 215 mg g⁻¹, respectively. The adsorption process was spontaneous, endothermic, and increasingly disordered. The effect of increasing temperature on the adsorption process was not obvious (ΔH < 5 kJ mol⁻¹). The main mechanism of LEV and CIP onto HNTs/GO included electrostatic interactions and physical binding. Therefore, the environmental behavior of LEV and CIP could be affected by HNTs/GO.