Synthesis of an efficient hydroxyapatite–chitosan–montmorillonite thin film for the adsorption of anionic and cationic dyes: adsorption isotherm, kinetic and thermodynamic study

Adsorption of indigo carmine (IC), methyl orange (MO) and methylene blue (MB) onto hydroxyapatite–chitosan–montmorillonite (HAP–CTS–Mt) film was studied. The influence of contact time, solution pH, initial dyes concentration, amount of HAP–CTS–Mt film and solution temperature were scrutinized. Characteristic bands and structure of HAP–CTS–Mt film were determined using Fourier infrared spectroscopy and X-ray diffraction. The optimal concentrations of IC, MO, and MB were 20 mg/L, 50 mg/L, and 20 mg/L, respectively. Optimal dose of HAP–CTS–Mt was 0.2 g/L for IC and MB and 0.5 g/L for MO. The adsorption process of IC, MO, and MB using HAP–CTS–Mt film was verified by Langmuir isotherm model with maximum adsorption capacities of 243.18 mg/g, 137.5 mg/g and 168.52 mg/g for IC, MO, and MB, respectively. The adsorption kinetics of IC, MO, and MB onto HAP–CTS–Mt film were well fitted by the pseudo-second-order model. The HAP–CTS–Mt thin film can be employed as an efficient adsorbent for removal of IC, MO, and MB dyes from aqueous solutions.