Facile fabrication of Bi₂WO₆/BiOCl hierarchical structure as adsorbents for methylene blue dye removal

Bi₂WO₆/BiOCl hierarchical structure was synthesized via a facile one-step hydrothermal method. The prepared samples were characterized by x-ray diffraction (XRD), Scanning electron microscopy (SEM), x-ray Energy dispersive Spectroscopy (EDS), Brunauer-Emmett-Teller (BET) and Fourier transform infrared spectra (FT-IR). The results of SEM revealed that Bi₂WO₆ agglomerates consist of nano-particles gradually transformed into a Bi₂WO₆/BiOCl hierarchical structure composed of nano-sheets by adding NaCl solution. Bi₂WO₆/BiOCl composites were used as adsorbents to remove methylene blue (MB) from aqueous solution. Some effects were used to investigated the removal efficiency of MB dye, including the amount of NaCl added, initial pH, adsorbent dose, contact time and MB initial concentration. The results revealed that the optimum saturated adsorption capacity of Bi₂WO₆/BiOCl composites to MB dye reached to 56.7 mg.g⁻¹. In addition, the fitting results of adsorption kinetic and adsorption equilibrium models were matched with pseud-second-order model and Langmuir isotherm, respectively. Also, the intraparticle diffusion results indicated adsorption process was not the sole rate limiting mechanism. Furthermore, the thermodynamic results indicated that adsorption process was more favorable to low temperature and this process is mainly physical adsorption process. (paper)