Removal of methylene blue by a bones fish-based adsorbent: Synthesis, characterization, experiments and mechanism investigation

This research focuses on the use a new biosorbent material prepared from the waste of fish (swordfish bones: MSF) in removing Methylene Blue (MB, as a model toxic, basic dye) from aqueous solutions. The MSF biosorbent was prepared following a simple method; the process involved washing, drying and bone freeze-drying, followed by crushing and then activation using only diluted NaOH at a low temperature (60 degrees C). The biosorbent was characterized via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) techniques, Brunauer-Emmett-Teller method (BET), and determined pHpzc\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${pH}_{pzc}$$\end{document}. The study revealed that the composition of MSF consisted mainly of hydroxyapatite, and SEM images demonstrated the existence of numerous irregular and heterogeneous pores of varying sizes and geometry with a value of the point of zero-charge pHpzc=7.2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${pH}_{pzc}=7.2$$\end{document}. Batch equilibrium experiments were conducted to investigate the effects of contact time, initial MB concentration, pH, temperature, and the adsorbent dose on the adsorption of MB onto the MSF biosorbent. The biosorbent study selected for the removal of MB gave a maximum experimental biosorption capacity of 100.15 mg/g. Among three isotherm models, the Langmuir model displayed the most accurate fit for the experimental data. The thermodynamic parameters indicate spontaneous and exothermic physisorption. Finally, the findings demonstrated that the waste fish (MSF) can be used as an adsorbent for the removal of cationic dye from aqueous solutions.