Efficient adsorption of methylene blue by xanthan gum derivative modified hydroxyapatite

In this work, hydroxyapatite modified by xanthan gum (XG) derivative material (XMH) was prepared and applied to remove methylene blue (MB) from water. The physicochemical properties of XMH were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-Ray spectroscopy and thermogravimetric analysis. Results showed the operating variables (pH, ionic strength and adsorbent dosage) were related to the MB removal efficiency. Adsorption kinetic and adsorption isotherm were well fitted by the pseudo-second-order model and the Langmuir isotherm model, respectively. It indicated that the adsorption process was a monolayer layer adsorption and chemisorption process. Besides, the result of intra-particle diffusion model demonstrated that the intra-particle diffusion was not the only rate determining step. The maximum adsorption capability on MB was 769 mg/g. Thermodynamic parameters (ΔG⁰, ΔH⁰, and ΔS⁰) showed that the adsorption was a spontaneous and endothermic process. Adsorption mechanisms of MB on XMH might be governed by electrostatic attraction and hydrogen-bonding. Furthermore, XMH could be regenerated well and retained MB removal efficiency of 81% after five cycles of adsorption and desorption. Therefore, XMH is a promising adsorbent for the efficient removal of MB from aqueous solution due to its low cost, good thermal stability and excellent adsorption performance.